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Sample records for lateral magma intrusion

  1. Deep intrusions, lateral magma transport and related uplift at ocean island volcanoes

    NASA Astrophysics Data System (ADS)

    Klügel, Andreas; Longpré, Marc-Antoine; García-Cañada, Laura; Stix, John

    2015-12-01

    Oceanic intraplate volcanoes grow by accumulation of erupted material as well as by coeval or discrete magmatic intrusions. Dykes and other intrusive bodies within volcanic edifices are comparatively well studied, but intrusive processes deep beneath the volcanoes remain elusive. Although there is geological evidence for deep magmatic intrusions contributing to volcano growth through uplift, this has rarely been demonstrated by real-time monitoring. Here we use geophysical and petrological data from El Hierro, Canary Islands, to show that intrusions from the mantle and subhorizontal transport of magma within the oceanic crust result in rapid endogenous island growth. Seismicity and ground deformation associated with a submarine eruption in 2011-2012 reveal deep subhorizontal intrusive sheets (sills), which have caused island-scale uplift of tens of centimetres. The pre-eruptive intrusions migrated 15-20 km laterally within the lower oceanic crust, opening pathways that were subsequently used by the erupted magmas to ascend from the mantle to the surface. During six post-eruptive episodes between 2012 and 2014, further sill intrusions into the lower crust and upper mantle have caused magma to migrate up to 20 km laterally, resulting in magma accumulation exceeding that of the pre-eruptive phase. A comparison of geobarometric data for the 2011-2012 El Hierro eruption with data for other Atlantic intraplate volcanoes shows similar bimodal pressure distributions, suggesting that eruptive phases are commonly accompanied by deep intrusions of sills and lateral magma transport. These processes add significant material to the oceanic crust, cause uplift, and are thus fundamentally important for the growth and evolution of volcanic islands. We suggest that the development of such a magma accumulation zone in the lower oceanic crust begins early during volcano evolution, and is a consequence of increasing size and complexity of the mantle reservoir system, and potentially

  2. 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

    transmitted into the inclusions during magma flow. We suggest that this represents a modification of the magma dynamics from Newtonian-like to Bingham-like behaviour. Furthermore, the spatial restriction of inclusions within the sheet intrusions suggest that subtle variations in magma rheology may partition apparently continuous intrusions, perhaps affecting lateral mixing and the longevity of discrete sheet segments. Detailed fabric analysis of other inclusion-free intrusions in the Ardnamurchan Central Complex supports this interpretation. Our results highlight that the crystalline cargo of a magma can result in temporal and spatial variations in magma rheology. This can partition coalesced magma bodies into ';zones' characterised by different magma properties, potentially affecting the location of magma flow pathways or even eruption sites.

  3. Space-geodetic evidence for multiple magma reservoirs and subvolcanic lateral intrusions at Fernandina Volcano, Galápagos Islands

    NASA Astrophysics Data System (ADS)

    Bagnardi, Marco; Amelung, Falk

    2012-10-01

    Using Interferometric Synthetic Aperture Radar (InSAR) measurements of the surface deformation at Fernandina Volcano, Galápagos (Ecuador), acquired between January 2003 and September 2010, we study the structure and the dynamics of the shallow magmatic system of the volcano. Through the analysis of spatial and temporal variations of the measured line-of-sight displacement we identify multiple sources of deformation beneath the summit and the southern flank. At least two sources are considered to represent permanent zones of magma storage given their persistent or recurrent activity. Elastic deformation models indicate the presence of a flat-topped magma reservoir at ˜1.1 km below sea level and an oblate-spheroid cavity at ˜4.9 km b.s.l. The two reservoirs are hydraulically connected. This inferred structure of the shallow storage system is in agreement with previous geodetic studies and previous petrological analysis of both subaerial and submarine lavas. The almost eight-year-long observation interval provides for the first time geodetic evidence for two subvolcanic lateral intrusions from the central storage system (in December 2006 and August 2007). Subvolcanic lateral intrusions could provide the explanation for enigmatic volcanic events at Fernandina such as the rapid uplift at Punta Espinoza in 1927 and the 1968 caldera collapse without significant eruption.

  4. 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.

  5. Numerical modeling of shallow magma intrusions with finite element method

    NASA Astrophysics Data System (ADS)

    Chen, Tielin; Cheng, Shaozhen; Fang, Qian; Zhou, Cheng

    2017-03-01

    A numerical approach for simulation of magma intrusion process, considering the couplings of the stress distribution, the viscous fluid flow of magma, and the fracturing of host rock, has been developed to investigate the mechanisms of fracture initiation and propagation in host rock during magma intrusion without pre-placing a set of fractures. The study focused on the dike intrusions filled with injected viscous magma in shallow sediments. A series of numerical modellings were carried out to simulate the process of magma intrusion in host rocks, with particular attention on the magma propagation processes and the formation of intrusion shapes. The model materials were Mohr-Coulomb materials with tension failure and shear failure. The scenarios of both stochastically heterogeneous host rocks and layered host rocks were analyzed. The injected magma formed intrusions shapes of (a) dyke, (b) sill, (c) cup-shaped intrusion, (d) saucer-shaped intrusion. The numerical results were in agreement with the experimental and field observed results, which confirmed the adequacy and the power of the numerical approach.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  7. 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.

  8. Magma transport in sheet intrusions of the Alnö carbonatite complex, central Sweden

    PubMed Central

    Andersson, Magnus; Almqvist, Bjarne S. G.; Burchardt, Steffi; Troll, Valentin R.; Malehmir, Alireza; Snowball, Ian; Kübler, Lutz

    2016-01-01

    Magma transport through the Earth’s crust occurs dominantly via sheet intrusions, such as dykes and cone-sheets, and is fundamental to crustal evolution, volcanic eruptions and geochemical element cycling. However, reliable methods to reconstruct flow direction in solidified sheet intrusions have proved elusive. Anisotropy of magnetic susceptibility (AMS) in magmatic sheets is often interpreted as primary magma flow, but magnetic fabrics can be modified by post-emplacement processes, making interpretation of AMS data ambiguous. Here we present AMS data from cone-sheets in the Alnö carbonatite complex, central Sweden. We discuss six scenarios of syn- and post-emplacement processes that can modify AMS fabrics and offer a conceptual framework for systematic interpretation of magma movements in sheet intrusions. The AMS fabrics in the Alnö cone-sheets are dominantly oblate with magnetic foliations parallel to sheet orientations. These fabrics may result from primary lateral flow or from sheet closure at the terminal stage of magma transport. As the cone-sheets are discontinuous along their strike direction, sheet closure is the most probable process to explain the observed AMS fabrics. We argue that these fabrics may be common to cone-sheets and an integrated geology, petrology and AMS approach can be used to distinguish them from primary flow fabrics. PMID:27282420

  9. Magma transport in sheet intrusions of the Alnö carbonatite complex, central Sweden.

    PubMed

    Andersson, Magnus; Almqvist, Bjarne S G; Burchardt, Steffi; Troll, Valentin R; Malehmir, Alireza; Snowball, Ian; Kübler, Lutz

    2016-06-10

    Magma transport through the Earth's crust occurs dominantly via sheet intrusions, such as dykes and cone-sheets, and is fundamental to crustal evolution, volcanic eruptions and geochemical element cycling. However, reliable methods to reconstruct flow direction in solidified sheet intrusions have proved elusive. Anisotropy of magnetic susceptibility (AMS) in magmatic sheets is often interpreted as primary magma flow, but magnetic fabrics can be modified by post-emplacement processes, making interpretation of AMS data ambiguous. Here we present AMS data from cone-sheets in the Alnö carbonatite complex, central Sweden. We discuss six scenarios of syn- and post-emplacement processes that can modify AMS fabrics and offer a conceptual framework for systematic interpretation of magma movements in sheet intrusions. The AMS fabrics in the Alnö cone-sheets are dominantly oblate with magnetic foliations parallel to sheet orientations. These fabrics may result from primary lateral flow or from sheet closure at the terminal stage of magma transport. As the cone-sheets are discontinuous along their strike direction, sheet closure is the most probable process to explain the observed AMS fabrics. We argue that these fabrics may be common to cone-sheets and an integrated geology, petrology and AMS approach can be used to distinguish them from primary flow fabrics.

  10. Eddy flow and associated particle dynamics during magma intrusion: the Basement Sill, Antarctica

    NASA Astrophysics Data System (ADS)

    Petford, Nick; Mirhadizadeh, Seyed

    2014-05-01

    The McMurdo Dry Valleys magmatic system Antarctica forms part of the Ferrar dolerite Large Igneous Province. The intrusions comprise a vertical stack of four interconnected sills linked to surface flows of the Kirkpatrick flood basalts. Together the complex provides a world-class example of pervasive lateral flow of magma on a continental scale. In addition the Basement Sill offers unprecedented two and three dimensional sections through the now frozen particle macrostructure of a congested magma slurry. Using image-based numerical modelling (the intrusion geometry defines its unique finite element mesh) it is possible to simulate aspects of the flow regime and rheology that have bearing on the formation of mesostructures including compositional layering. A distinction between structures formed during flow, where the shearing regime dominates, and post-emplacement features due to local crystal-melt segregation constrained by thermal modeling, is made. In the former regime we describe a potentially novel crystal-liquid segregation that may have been overlooked because it is so simple. The critical boundary condition is an undulating base or roof in the intrusion where magma eddies can develop during low Reynolds Number flow. Numerical particle tracing is used to show that wall eddies can either trap (and ultimately freeze) crystals in-situ or retain and eject them back into the flow at a later time according to their mass density. The mechanism has potential to develop local variations in magma chemistry and structure that would not otherwise arise where the contact between magma and country rock is linear. We refer to this local fluid dynamical effect as 'slingshot' fractionation and are not aware of any previous quantitative description of this effect in igneous rocks.

  11. 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

    elevated incompatible element concentrations and primitive mantle normalised spectra characteristic for the Canary Island basanites (e.g. La is of 100 times higher concentration than primitive mantle with important LREE enrichments). In contrast, the trace element composition of the alkali rhyolite shows surprisingly low concentrations for all elements except the most incompatible ones (such as Rb, Ba, K and Th). All other measured incompatible LILE, HFSE and REE have significantly lower concentration than the basanitic counterpart. This differences increase with the atomic number of the REE reaching maximum for the MREE and thus forming an intriguing U-shaped rhyolite spectra. Furthermore, unusual U-depletion is observed in the rhyolite. Other negative spikes, such as those for Sr and P, are readily accounted for by the removal of plagioclase and apatite during magma evolution from a basanite to a more evolved melt. The results obtained so far suggest an intrusion of gas-rich basanitic melt at the base of an evolved intrusion remobilising a stagnant phonolitic melt present as late differentiate in the crust. Interaction with old oceanic crust and the volcanic edifice can be quantified and shown to have modified the phonolite melt composition and produced the alkali rhyolitic composition of the white floating pumice. Extensive gas exsolution shortly before the melt-glass transition explains the foam texture and the low volatile concentrations in the quenched alkali rhyolite.

  12. Seismogenic ';trapdoors' during magma intrusion at Eyjafjallajökull volcano, Iceland

    NASA Astrophysics Data System (ADS)

    White, R. S.; Tarasewicz, J.; Brandsdottir, B.; Schonnman, C.

    2013-12-01

    Relocated earthquake hypocentres for >1000 microearthquakes that occurred prior to and during the 2010 fissure and summit eruptions of Eyjafjallajökull volcano in Iceland map out magma conduits from the upper mantle (30 km depth) to the surface. During the two weeks prior to the first, flank eruption, hypocentre locations lie predominantly in horizontally separated clusters at 3-4 km below sea level. They represent the filling with magma of an inflating sill beneath the eastern flank of the volcano, from which feeder dykes propagated laterally and vertically toward the flank eruption site three days prior to the eruption onset. The majority of events within some clusters of up to >100 earthquakes exhibit similar waveforms and identical patterns of P-wave first-motion polarities recorded across the monitoring network. In the clearest example, 104 out of 105 events in a single cluster appear to have the same source mechanism based on P-wave first-motion polarities and waveform similarity. These observations suggest that the clusters of similar events may comprise many earthquakes generated by source processes that have the same orientation of failure, perhaps even on the same rupture plane, in fixed locations that are repeatedly active. The epicentral clustering and similarity of source mechanisms suggest that much of the seismicity was generated at approximately static constrictions to magma flow in an inflating sill. These constrictions may act as a form of pressure valve or ';trapdoor' in the country rock, which ruptures when the melt pressure exceeds a critical level, then reseals after a pulse of melt has passed through. We infer that the magmatic intrusion causing the seismicity was likely to be a laterally inflating sill at 3-4 km depth, with seismogenic pinch-points occurring between aseismic compartments of the sill, or between adjacent magma lobes as they inflate. A second eruption followed from the summit, 8 km west of the first eruption site. During the

  13. Zircon Saturation and the Viability of Magma Bodies During Intrusion of the Tuolumne Intrusive Series, Sierra Nevada Batholith, California

    NASA Astrophysics Data System (ADS)

    Miller, J.; Burgess, S.; Miller, C.; Miller, R.; Bergantz, G.

    2005-05-01

    The Tuolumne Intrusive Series (TIS) is a prime example of a zoned arc intrusion, and is one of a belt of large (>1000 km2) consanguineous, Cretaceous, zoned intrusions within the Sierra Nevada batholith. Past work linked the differentiation of the TIS with field petrology and modification of magma in situ in large reservoirs. New single-zircon geochronology and field studies show that the TIS was assembled from numerous magma inputs from 94-85 Ma, casting doubt on the existence of a large body of mobile magma during growth and emplacement [1], and calling into question where the bulk of the chemical differentiation occurred (exposure level or deep source). Zircon saturation temperatures (Tzrc; [2]) for the TIS are useful for understanding its assembly, particularly in combination with high precision, single zircon ages. The two largest units of the TIS (Half Dome and Cathedral Peak granodiorites) have low calculated Tzrc (Half Dome: 710-765°C, mean=740°C; Cathedral Peak: 715-780°C, mean=760°C), which implies complexities in how zircon ages are used to interpret the construction of the TIS: (1) at T's appropriate for anatexis, transport, and initial emplacement of granitoid magmas, source-derived zircons would be dissolved; zircons in TIS thus crystallized during post-emplacement conductive cooling upon reaching Tzrc, or were inherited late; (2) because Tzrc is not far above the solidus, appreciable age differences (several 105 yr?) might be produced by slow cooling of a large magma body that was open to heat input; heat added need only have been sufficient to maintain near-eutectic conditions, perhaps as persistent mush, but with net cooling (qout > qin), such that ages track the migration of the Tzrc isotherm during solidification; (3) reheating of any mush, or melting of intrusions associated with earlier inputs to T's >> Tzrc would dissolve older zircons on time scales of 104-105 years (e.g. [3]); this time scale sets a limit on the longevity of melt

  14. Evidence for the mixing of granitic and basaltic magmas in the Pleasant Bay layered intrusion, coastal Maine

    SciTech Connect

    Powers, P.M. . Geology Dept.)

    1993-03-01

    The Pleasant Bay layered intrusion has the shape of a shallow basin about 200 km[sup 2] in area and crops out along the coast of Maine between Bar Harbor and Machias. This intrusion evolved as repeated replenishments of basaltic magma were emplaced into a silicic magma chamber (Wiebe, in press). These replenishments surged into the chamber through fractures, spreading laterally on a floor of silicic cumulates and beneath silicic magma. This produced a sequence of layers (up to 100 m thick) that grade from chilled basalt at the base to gabbroic, dioritic, or granitic emulates at the top. This study focuses on two layers, each of which grades from chilled gabbro at the base to quartz syenite at the top. Petrography and geochemistry suggest that mechanical mixing and other interactions between two stably stratified magmas were responsible for much of this variation. Plagioclase grains typically have corroded calcic cores (An[sub 52--56]) that decrease in size upward and sodic rims (An[sub 32--36]) that thicken upward. Larger plagioclase grains at higher levels often have K-spar cores. Scarce large zircon, apatite, and biotite crystals in the lower parts of the layers are often corroded. The apatites have dark pleochroic halos, suggesting they crystallized from a liquid enriched in U and Th. The silicic melt was likely the source of K and H[sub 2]O needed to crystallize hornblende and biotite. The large corroded zircon, apatite, and biotite crystals, as well as much of the hornblende, probably grew at an interface between separately convecting silicic and basaltic magmas.

  15. 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.

  16. Titanium in plagioclase as a monitor of magma differentiation in the Skaergaard Intrusion

    NASA Astrophysics Data System (ADS)

    Salmonsen, L.; Tegner, C.; Humphreys, M.

    2011-12-01

    There is a general consensus that the Skaergaard Intrusion formed by inwards crystallization from the margins. Furthermore, it is agreed that the magma evolved largely due to crystal fractionation. However, the resulting liquid line of descent has been debated and it remains unclear which processes govern the required mass transport, and whether magma zonation developed. In recent studies, the influence of diffusion, crystal mush compaction, compositional convection and segregation of immiscible liquids are under dispute. The liquid line of descent is commonly approached by simple mass balance calculations, which hinge on assumptions regarding the composition of the parent magma and the shape of the intrusion. Moreover, this approach only provides information on the average composition of the main magma and thus, does not address whether the magma was zoned or homogenous. As an alternative, we here invoke an analytical approach; microprobe analyses of unzoned plagioclase cores from a new suite of samples from the Upper Border Series are compared to those in the Layered Series. We find (1) that the Ti concentrations at given anorthite contents in the two series are identical and (2) Ti increases gradually from 0.07 wt% in the most primitive plagioclase analysed (An70) and peaks at 0.13 wt% (An52). It then decreases continuously toward 0.02 wt% in plagioclase from the Sandwich Horizon (An23). Based on experimentally determined distribution coefficients, we calculate a parent magma containing 2.0 wt% Ti. During the early stages of differentiation it gradually increases to 4.3 wt% and subsequently decreases towards 2.3 wt% in the most evolved liquid. As expected, the onset of Ti depletion occurs where the calculated magma crosses the theoretical solubility curve. Consistently, this coincides with appearance of cumulus FeTi oxides in the cumulates at the floor and roof of the intrusion, as indicated by a sudden peak in whole rock Ti and V. Key implications of this study

  17. Remanent and induced magnetic anomalies over a layered intrusion: Effects from crystal fractionation and magma recharge

    NASA Astrophysics Data System (ADS)

    McEnroe, Suzanne A.; Brown, Laurie L.; Robinson, Peter

    2009-12-01

    The Bjerkreim-Sokndal (BKS) norite - quartz mangerite layered intrusion is part of the early Neoproterozoic Rogaland Anorthosite Province intruded into the Fennoscandian shield in south Norway at ~ 930 Ma. The BKS is exposed over an area of 230 km 2 with a thickness of ~ 7000 m and is of economic interest for ilmenite, magnetite and apatite deposits. From the point of view of magnetic minerals, in the course of fractional crystallization and magma evolution, the ilmenite becomes less Fe 3+-rich reflected by a change from ilmenite with hematite exsolution to nearly pure ilmenite. Magnetite starts to crystallize relatively late in the intrusive history, but its crystallization is interrupted by influxes of more primitive magma. The variations in aeromagnetic and ground-magnetic anomalies measured over the BKS can be explained in terms of the measured magnetic properties of NRM, susceptibility, and hysteresis presented here, and in terms of mineralogy. Early layers in the intrusion contain hemo-ilmenite. As the magma evolved and magnetite started to crystallize, this caused a distinct change over the layering from remanence-controlled negative anomalies to induced positive anomalies. When new, more primitive magma was injected into the system, hemo-ilmenite returned as the major oxide and the resulting magnetic anomalies are again negative. The most dramatic change in the magnetic signature is in the upper part of the intrusion in MCU IVe, where magnetite became a well established cumulate phase as indicated by susceptibility, but its induced magnetization is overcome by large NRMs associated either with hemo-ilmenite, or with hemo-ilmenite and magnetite exsolved from pyroxenes. The average natural remanent magnetizations change from ~ 3 A/m in MCU IVd, to 15 A/m in MCU IVe, and back to 2 A/m in the overlying MCU IVf, producing a strong negative remanent anomaly that has been followed along strike for at least 20 km by ground-magnetic measurements. The highly varied

  18. Magma intrusion beneath Long Valley caldera confirmed by temporal changes in gravity

    USGS Publications Warehouse

    Battaglia, Maurizio; Roberts, C.; Segall, P.

    1999-01-01

    Precise relative gravity measurements conducted in Long Valley (California) in 1982 and 1998 reveal a decrease in gravity of as much as -107 ?? 6 microgals (1 microgal = 10-8 meters per square second) centered on the uplifting resurgent dome. A positive residual gravity change of up to 64 ?? 15 microgals was found after correcting for the effects of uplift and water table fluctuations. Assuming a point source of intrusion, the density of the intruding material is 2.7 x 103 to 4.1 x 103 kilograms per cubic meter at 95 percent confidence. The gravity results require intrusion of silicate magma and exclude in situ thermal expansion or pressurization of the hydrothermal system as the cause of uplift and seismicity.

  19. The Record of Magma Accumulation Processes and Magma-Crust Interactions in Arcs from Ultramafic Intrusions with Ni-Cu-PGE Mineralization

    NASA Astrophysics Data System (ADS)

    Scoates, J. S.; Manor, M. J.; Jackson-Brown, S.; Nixon, G. T.; Ames, D. E.

    2015-12-01

    Ultramafic arc plutons, key tracers of subduction zone magmatism, are present as Alaskan-type intrusions (no orthopyroxene) and a wide range of mineralogically diverse (ol-opx-cpx-hbl) intrusions. Turnagain (Alaskan-type) and Giant Mascot (opx-rich) are two Mesozoic mid-crustal ultramafic bodies in the Cordillera of British Columbia. They preserve lithologic, trace element, and isotopic records of magmatic evolution and crustal assimilation during the earliest stages of fractionation from mantle wedge-derived magmas. These processes are highlighted by sulfide saturation mechanisms in their respective oxidized parent magmas and the formation of significant magmatic Ni-Cu-PGE mineralization at Turnagain (1841.8 Mt at 0.21% Ni) and Giant Mascot (4.2 Mt at 0.77% Ni and 0.34% Cu). The intrusions represent mid-crustal magma conduits through which magmas laden with Mg-rich olivine and pyroxene ascended, stalled, fractionated, locally assimilated fusible pyrite- and graphite-bearing metasedimentary rocks, and ultimately left their crystal cargos as cumulates. Their extrusive components are picritic to ankaramitic basalts. The combined effects of fractional crystallization, sulfide melt segregation, and re-equilibration with sulfide melt are recorded by notable Ni-in-olivine variations. At Turnagain, there is a direct correlation between the presence of sulfide and partially digested phyllite blocks, which is reflected in a broad range of relatively light S isotope ratios. This contrasts with restricted near-mantle S isotope values from the steeply plunging Ni-sulfide pipes at Giant Mascot where sulfide saturation occurred in response to assimilation of host granitoids and schists. Many other similar Paleozoic to Mesozoic ultramafic intrusions in the North American Cordillera, extending from Alaska to Baja, also represent former magma pathways that potentially capture the record of arc growth through magmatic and mineralization processes from primitive arc magmas.

  20. An origin of marginal reversal of the Fongen-Hyllingen layered intrusion by prolonged magma emplacement

    NASA Astrophysics Data System (ADS)

    Egorova, V.; Latypov, R.

    2012-04-01

    The ~100 m thick marginal zone of the Fongen-Hyllingen Intrusion (FHI) consists of nonlayered, highly iron-enriched ferrodiorites that are overlain by a ~6 km thick layered sequence of gabbroic to dioritic rocks of the Layered Series. From the base upwards the marginal zone become more primitive as exemplified by a significant increase in whole-rock MgO, Mg-number, and normative An. The reverse trends are also evident from an upward increase in An-content of plagioclase (from ~30 to ~43 at.%) and Mg-number of amphibole (from ~9 to ~23 at.%) and clinopyroxene (from ~23 to ~37 at.%). The marginal zone is abruptly terminated at the contact with the overlying Layered Series as is evident from a step-like increase in Mg-number of mafic minerals and An-content of plagioclase, as well as a sharp increase in whole-rock MgO and Mg-number in overlying olivine gabbronorites of the Layered Series. Based on these features the marginal zone of the FHI can be interpreted as an aborted marginal reversal. Reverse trends in whole-rock and mineral compositions, as well as a sharp break in these parameters are indicative of its formation in an open system with the involvement of the prolonged emplacement of magma that became increasingly more primitive. Such development of the marginal reversal was interrupted by the emplacement of a major influx of more primitive magma that produced the Layered Series. The open system evolution of a basaltic magma chamber may represent a general mechanism for the origin of marginal reversals in mafic sills and layered intrusions.

  1. Crustal Strain Patterns in Magmatic and Amagmatic Early Stage Rifts: Border Faults, Magma Intrusion, and Volatiles

    NASA Astrophysics Data System (ADS)

    Ebinger, C. J.; Keir, D.; Roecker, S. W.; Tiberi, C.; Aman, M.; Weinstein, A.; Lambert, C.; Drooff, C.; Oliva, S. J. C.; Peterson, K.; Bourke, J. R.; Rodzianko, A.; Gallacher, R. J.; Lavayssiere, A.; Shillington, D. J.; Khalfan, M.; Mulibo, G. D.; Ferdinand-Wambura, R.; Palardy, A.; Albaric, J.; Gautier, S.; Muirhead, J.; Lee, H.

    2015-12-01

    Rift initiation in thick, strong continental lithosphere challenges current models of continental lithospheric deformation, in part owing to gaps in our knowledge of strain patterns in the lower crust. New geophysical, geochemical, and structural data sets from youthful magmatic (Magadi-Natron, Kivu), weakly magmatic (Malawi, Manyara), and amagmatic (Tanganyika) sectors of the cratonic East African rift system provide new insights into the distribution of brittle strain, magma intrusion and storage, and time-averaged deformation. We compare and contrast time-space relations, seismogenic layer thickness variations, and fault kinematics using earthquakes recorded on local arrays and teleseisms in sectors of the Western and Eastern rifts, including the Natron-Manyara basins that developed in Archaean lithosphere. Lower crustal seismicity occurs in both the Western and Eastern rifts, including sectors on and off craton, and those with and without central rift volcanoes. In amagmatic sectors, lower crustal strain is accommodated by slip along relatively steep border faults, with oblique-slip faults linking opposing border faults that penetrate to different crustal levels. In magmatic sectors, seismicity spans surface to lower crust beneath both border faults and eruptive centers, with earthquake swarms around magma bodies. Our focal mechanisms and Global CMTs from a 2007 fault-dike episode show a local rotation from ~E-W extension to NE-SE extension in this linkage zone, consistent with time-averaged strain recorded in vent and eruptive chain alignments. These patterns suggest that strain localization via widespread magma intrusion can occur during the first 5 My of rifting in originally thick lithosphere. Lower crustal seismicity in magmatic sectors may be caused by high gas pressures and volatile migration from active metasomatism and magma degassing, consistent with high CO2 flux along fault zones, and widespread metasomatism of xenoliths. Volatile release and

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  3. Time-resolved seismic tomography detects magma intrusions at Mount Etna.

    PubMed

    Patanè, D; Barberi, G; Cocina, O; De Gori, P; Chiarabba, C

    2006-08-11

    The continuous volcanic and seismic activity at Mount Etna makes this volcano an important laboratory for seismological and geophysical studies. We used repeated three-dimensional tomography to detect variations in elastic parameters during different volcanic cycles, before and during the October 2002-January 2003 flank eruption. Well-defined anomalous low P- to S-wave velocity ratio volumes were revealed. Absent during the pre-eruptive period, the anomalies trace the intrusion of volatile-rich (>/=4 weight percent) basaltic magma, most of which rose up only a few months before the onset of eruption. The observed time changes of velocity anomalies suggest that four-dimensional tomography provides a basis for more efficient volcano monitoring and short- and midterm eruption forecasting of explosive activity.

  4. Uplift and magma intrusion at Long Valley caldera from InSAR and gravity measurements

    USGS Publications Warehouse

    Tizzani, Pietro; Battaglia, Maurizio; Zeni, Giovanni; Atzori, Simone; Berardino, Paolo; Lanari, Riccardo

    2009-01-01

    The Long Valley caldera (California) formed ~760,000 yr ago following the massive eruption of the Bishop Tuff. Postcaldera volcanism in the Long Valley volcanic field includes lava domes as young as 650 yr. The recent geological unrest is characterized by uplift of the resurgent dome in the central section of the caldera (75 cm in the past 33 yr) and earthquake activity followed by periods of relative quiescence. Since the spring of 1998, the caldera has been in a state of low activity. The cause of unrest is still debated, and hypotheses range from hybrid sources (e.g., magma with a high percentage of volatiles) to hydrothermal fluid intrusion. Here, we present observations of surface deformation in the Long Valley region based on differential synthetic aperture radar interferometry (InSAR), leveling, global positioning system (GPS), two-color electronic distance meter (EDM), and microgravity data. Thanks to the joint application of InSAR and microgravity data, we are able to unambiguously determine that magma is the cause of unrest.

  5. Compaction and Crystallisation in Magma Chambers: Towards a Model of the Skaergaard Intrusion

    NASA Astrophysics Data System (ADS)

    McKenzie, D. P.

    2010-12-01

    The equations governing the conservation of mass, momentum and energy are first simplified by using the extended Boussinesq approximation, and then solved numerically to study the time dependent behaviour of a compacting solidifying layer at the base of a magma chamber when variations in the horizontal plane can be neglected. The most important result is that the concept of a trapped liquid fraction, which has been widely used to model the bulk composition of layered intrusions, is a useful concept to describe the steady state behaviour of compacting layers. The result is at first sight surprising, because there is relative movement between the melt and crystals during compaction, and the system is therefore open. The reason why it is correct is because both the melt and the crystals are moving downwards in a frame fixed to the upper surface of the compacting layer. Since the mass of all elements must be conserved, what goes into the top of the layer as melt and solid must come out of its bottom as a solid when the behaviour is not time dependent. However, when time dependent behaviour occurs the concept of a trapped liquid fraction ceases to be useful. The governing equations are then used to model the concentration of phosphorous in the lower part of the Skaergaard intrusion, where it behaves incompatibly. The observed behaviour requires the viscosity of the solid part of the compacting layer to have a viscosity of about 10^18 Pa s.

  6. Elastic models for the magma intrusion associated with the 2000 eruption of Usu Volcano, Hokkaido, Japan

    NASA Astrophysics Data System (ADS)

    Jousset, Philippe; Mori, Hitoshi; Okada, Hiromu

    2003-07-01

    After 23 years of dormancy, Usu Volcano (Hokkaido, Japan) erupted on March 31, 2000. Many observations (seismicity, deformation rates, gravity data, groundwater level monitoring) show that the period of intense activity was short, starting abruptly, and continuing for ca. 5 months with a decreasing rate. Uplift was observed at two successive and separate locations at the time of the eruption. We obtained GPS and microgravity data at Usu Volcano for two intervals, the first from August 1996 to July 1998, once every 2-4 months, and the second in November 2000, 2 months after the end of the eruption. Between July 1998 and November 2000, the displacements and gravity variations are among the largest ever recorded on an active volcano in association with an eruption. We review three different elastic models commonly used in volcano-geodesy (sphere, fault system, fissure zone) and invert the high-quality data using each of these models. The combined inversion of GPS and microgravity data leads to the best solution in the least-squares sense. It is compatible with the intrusion of approximately 5×10 11 kg of new magma into the western part of Usu Volcano. This appears to have occurred in a subvertical fracture zone (about 2.4 km length, 0.1 km width) aligned in the east-west direction. The fracture zone is between 0.4 and 3.3 km depth with an extension of about 30 m. The fractures are likely to be filled with material having a density slightly higher than the density of old products of Mount Usu, i.e. about 2400 kg m -3. This model is consistent with the locations and magnitudes of the earthquakes recorded during the period of intense seismic activity in April and May 2000. These earthquakes correspond to the boundaries of the intruded magma body. The model suggests that the two locations of uplift are not independent.

  7. Elastic modelling of magma intrusions: example of the 2000 eruption of Usu Volcano, Japan.

    NASA Astrophysics Data System (ADS)

    Jousset, P.; Mori, H.; Okada, H.

    2003-04-01

    After 23 years of dormancy, Usu Volcano (Hokkaido, Japan) erupted on 31st of March, 2000. Many observations (seismicity, deformation rates, gravity observations, groundwater level monitoring) show that the period of intense activity was short, starting abruptly, and continuing for ca. 5 months with a decreasing rate. Uplift was observed at two successive and separate locations at the time of the eruption. We obtained GPS and microgravity data at Usu Volcano for two intervals, first from August 1996 to July 1998, once every 2 to 4 months, and second in November 2000, 2 months after the end of the eruption. Between July 1998 and November 2000, the displacements and gravity variations are among the largest ever recorded on an active volcano in association with an eruption. We review three different elastic models commonly used in volcano-geodesy (sphere, fault system, fissure zone) and invert the high quality data using each of these models. The combined inversion of GPS and microgravity data leads to the best solution in the least-squares sense. It is compatible with the intrusion of approximately 5× 1011 kg of new magma into the western part of Usu Volcano. This appears to have occurred in a subvertical fracture zone (about 2.4 km length, 0.1 km width) aligned in the East-West direction. The fracture zone is between 0.4 and 3.3 km depth with an extension of about 30 m. The fractures are likely to be filled with material having a density slightly higher than the density of old products of Mount Usu, i.e., about 2400 kg m-3. This model is consistent with the locations and magnitudes of the earthquakes recorded during the period of the intense seismic activity in April and May 2000. These earthquakes correspond to the boundaries of the intruded magma body. The model suggests that the two locations of uplift are not independent.

  8. Rate of lateral magma transport in the Earth's crust beneath submarine volcanic arcs derived from earthquake swarm analysis

    NASA Astrophysics Data System (ADS)

    Spicak, A.; Vanek, J.

    2015-12-01

    This contribution deals with subduction-related submarine magmatism. We are offering a tool to contribute to delimitation of domains of current magma unrest at convergent plate margins and to understand better the behavior of magma in the lithospheric wedge above the subducting slab: a detailed analysis of teleseismic earthquake occurrence. A specific seismicity pattern has been observed beneath submarine portions of several volcanic arcs at convergent plate margins (Andaman Sea region, southern Ryukyu area). We have found three arguments that allowed us to interpret such a seismicity pattern as a magma-driven process: (i) clustering of medium-size earthquakes (M~5) in space and time in shallow earthquake swarms; (ii) rapid migration of seismic activity during the swarms (comparison of epicentral maps of individual stages of the swarm development showed consistently that earthquake epicenters migrate laterally at a rate of several hundred meters per hour); (iii) correlation of epicentral zones of the swarms with distinct seamounts and submarine ridges (current seismically active intrusions probably propagate along plumbing systems that served as conduits of magma to the surface in the past). The repeated occurrence of relatively strong, teleseismically recorded earthquake swarms thus probably reflects fluid and/or magma ascent through the plumbing system of the volcanic arc, points to brittle character of the lithospheric wedge at respective depths and favors the studied areas - the Andaman Sea region and the southern Ryukyu area - to be potential sites of submarine volcanic activity.. The study documents high accuracy of hypocenter parameter determinations published by data centers such as ISC and NEIC USGS, and the usefulness of the EHB relocation procedure.

  9. Development of a deep-crustal shear zone in response to syntectonic intrusion of mafic magma into the lower crust, Ivrea-Verbano zone, Italy

    USGS Publications Warehouse

    Snoke, A.W.; Kalakay, T.J.; Quick, J.E.; Sinigoi, S.

    1999-01-01

    A 1 to 1.5 km-thick, high-temperature shear zone is localized in wall rocks subparallel to the eastern intrusive contact of the Permian Mafic Complex of the Ivrea-Verbano zone (IVZ), Italy. The shear zone is characterized by concentrated ductile deformation manifested by a penetrative foliation subparallel to the intrusive contact and a northeast-plunging sillimanite lineation. Evidence of noncoaxial strain and transposition is widespread in the shear zone including such features as rootless isoclinal folds, dismemberment of competent layers, and scattered kinematic indicators. The metasedimentary rocks in the shear zone are migmatitic, and the accumulation of leucosome is variable within the shear zone. Near the intrusive contact with the Mafic Complex leucosome forms ~20 vol% of the wall rock, whereas leucosome concentrations may locally reach ~60 vol% of the wall rock near the outer limits of the shear zone. This variation in vol% leucosome suggests melt/magma migration from the inferred site of anatexis along the intrusive contact to lower-strain regions within and near the margins of the shear zone. The leucosome accumulations chiefly occur as layer-parallel concentrations, but are also folded and boudined, and locally are associated with tension gashes and fracture arrays. Networks of granitic dikes and small plutons in the eastern IVZ suggest that some magmas migrated out of the high-temperature shear zone. Some magma apparently migrated laterally along the strike of the shear zone and concentrated in areas of lower strain where the intrusive contact takes a major westward bend. The high-temperature shear zone is interpreted as a 'stretching fault' (or stretching shear zone) after Means [W.D. Means, Stretching faults, Geology 17 (1989) 893-896], whereupon the metasedimentary wall rocks and associated leucosome deformed synchronously with the multistage emplacement and deformation flow of the Mafic Complex. The recognition of a high-temperature shear zone

  10. The Role of Magma Replenishment in the Construction of the Lower 500m of the Layered Mafic Dufek Intrusion, Antarctica

    NASA Astrophysics Data System (ADS)

    Grimes, C. B.; Cheadle, M. J.; Gee, J. S.; Meurer, W. P.; Swapp, S.; Lusk, M.

    2008-12-01

    The Jurassic age Dufek Intrusion is arguably one of the largest layered mafic intrusions on Earth, yet it remains relatively little studied due to the remoteness of its location. During the austral summer of 2006/07, we conducted detailed sampling and logging of exposures in the lower ~500m of the Dufek Massif section of the intrusion. We collected 630 oriented cores over this interval from the Walker Anorthosite and portions of the overlying Aughenbaugh Gabbro along two vertical transects 5 km apart - a spur of Neuburg Peak and at Walker Peak. Cryptic mineral chemistry variations have been determined by electron microprobe analysis of both the cores and the rims of cumulus and intercumulus plagioclase, orthopyroxene (inverted pigeonite), and clinopyroxene from ~50 thin sections, with an average sample spacing of 10 m over the lower 500m of the Dufek Massif. The mineral composition data reveal a dramatic change of 74 to 56 in orthopyroxene Mg# and An83 to An61 in plagioclase anorthite content with increasing stratigraphic height. The change of 22 An# occurs over an interval of 500m compared to thicknesses of 3-4 km required for a similar change in the Bushveld and Stillwater intrusions. This rapid change is consistent with these lower cumulates forming from a relatively thin magma body. Field observations and trends in the mineral chemistry are interpreted to indicate three units within the lower 500m of the intrusion. The change from three phase to two-phase cumulates and the change in the slope of plagioclase An#, FeO and K2O content, and orthopyroxene Mg# with height across the boundary between the Walker Anorthosite and the overlying Aughenbaugh Gabbro suggests crystallization from two batches of magma with different compositions. Also, the occurrence of the sharp-bottomed, several meter- thick Neuburg Pyroxenite at ~210 m above the Walker-Aughenbaugh contact together with changes in plagioclase, orthopyroxene and clinopyroxene composition and an influx of meta

  11. Remanent and Induced Magnetic Anomalies over the Bjerkreim-Sokndal Layered Intrusion: Effects from Crystal Fractionation and Magma Recharge

    NASA Astrophysics Data System (ADS)

    McEnroe, S. A.; Brown, L. L.; Robinson, P.

    2013-12-01

    The Bjerkreim-Sokndal (BKS) norite-quartz mangerite layered intrusion is part of the early Neoproterozoic Rogaland Anorthosite Province intruded into the Fennoscandian shield in south Norway at ~930 Ma. The BKS is exposed over an area of 230 km2 with a thickness of ~7000m and is of economic interest for hemo-ilmenite, magnetite and apatite deposits. From the point of view of magnetic minerals, in the course of fractional crystallization and magma evolution, the ilmenite becomes less Fe3+-rich reflected by a change from ilmenite with hematite exsolution to nearly pure ilmenite. Magnetite starts to crystallize relatively late in the intrusive history, but its crystallization is interrupted by influxes of more primitive magma containing hemo-ilmenite. The variations in aeromagnetic and ground-magnetic anomalies measured over the BKS can be explained in terms of the magnetic properties of NRM, susceptibility, and hysteresis. Magnetic properties are correlated with the oxide mineralogy and mineral chemistry. Early layers in the intrusion contain hemo-ilmenite. As the magma evolved and magnetite started to crystallize, this caused a distinct change over the layering from remanence-controlled negative anomalies to induced positive anomalies. When new, more primitive magma was injected into the system, hemo-ilmenite returned as the major oxide and the resulting magnetic anomalies are again negative. The most dramatic change in the magnetic signature is in the upper part of the intrusion in MCU IVe, where magnetite became a well established cumulate phase as indicated by susceptibility, but its induced magnetization is overcome by large NRM's associated either with hemo-ilmenite or with hemo-ilmenite and magnetite exsolved from pyroxenes. The average natural remanent magnetizations change from ~3 A/m in MCU IVd, to 15 A/m in MCU IVe, and back to 2 A/m in the overlying MCU IVf, producing a strong negative remanent anomaly that has been followed along strike for at least 20

  12. Assimilation of preexisting Pleistocene intrusions at Long Valley by periodic magma recharge accelerates rhyolite generation: rethinking the remelting model

    NASA Astrophysics Data System (ADS)

    Simon, Justin I.; Weis, Dominique; DePaolo, Donald J.; Renne, Paul R.; Mundil, Roland; Schmitt, Axel K.

    2014-01-01

    had long crustal magma residence times and high crustal affinity, (2) the caldera-related Bishop Tuff and early postcaldera rhyolites have lower crustal affinity and short magma residence times, and (3) later postcaldera rhyolites again have stronger crustal signatures and longer magma residence times.

  13. Evidence for multiple pulses of crystal-bearing magma during emplacement of the Doros layered intrusion, Namibia

    NASA Astrophysics Data System (ADS)

    Owen-Smith, T. M.; Ashwal, L. D.

    2015-12-01

    The Doros Complex is a relatively small (maximum 3.5 km × 7.5 km) shallow-level, lopolithic, layered mafic intrusion in the early Cretaceous Paraná-Etendeka Large Igneous Province. The stratigraphy broadly comprises a minor, fine-grained gabbroic sill and a sequence of primitive olivine-cumulate melagabbros, with a basal chilled margin, an intermediate plagioclase-cumulate olivine gabbro, and a sequence of mineralogically and texturally variable, intermediate, strongly foliated, plagioclase-, olivine- or magnetite-cumulate gabbros. An evolved syenitic (bostonite) phase occurs as cross-cutting dykes or as enclaves within the foliated gabbros. Major element modelling of the liquid line of descent shows that the spectrum of rock types, including the bostonite, is consistent with the fractionation of a basaltic parental magma that crystallised olivine, clinopyroxene, plagioclase, magnetite, K-feldspar and apatite. However, the stratigraphic succession does not correspond to a simple progressive differentiation trend but instead shows a series of punctuated trends, each defined by a compositional reversal or hiatus. Incompatible trace element concentrations do not increase upwards though the body of the intrusion. The major units show similar, mildly enriched rare earth element patterns, with minimal Eu anomalies. Back-calculation of the rare earth element concentrations of these cumulate rocks produces relatively evolved original liquid compositions, indicating fractionation of this liquid from a more primitive precursor. Based on combined field, petrographic, geochemical and geophysical evidence, we propose an origin for the Doros Complex by a minimum of seven closely spaced influxes of crystal-bearing magmas, each with phenocryst contents between 5% and 55%. These findings represent a departure from the traditional single-pulse liquid model for the formation of layered mafic intrusions and suggest the presence of an underlying magmatic mush column, i.e., a large

  14. Generation, ascent and eruption of magma on the Moon: New insights into source depths, magma supply, intrusions and effusive/explosive eruptions (Part 1: Theory)

    NASA Astrophysics Data System (ADS)

    Wilson, Lionel; Head, James W.

    2017-02-01

    zones deeper within the mantle. Thus magma accumulations at the base of the crust would have been able to intrude dikes part-way through the crust, but not able to feed eruptions to the surface; in order to be erupted, magma must have been extracted from deeper mantle sources, consistent with petrologic evidence. Buoyant dikes growing upward from deep mantle sources of partial melt can disconnect from their source regions and travel through the mantle as isolated bodies of melt that encounter and penetrate the crust-mantle density boundary. They adjust their lengths and internal pressure excesses so that the stress intensity at the lower tip is zero. The potential total vertical extent of the resulting melt body depends on the vertical extent of the source region from which it grew. For small source extents, the upper tip of the resulting dike crossing the crust-mantle boundary cannot reach the surface anywhere on the Moon and therefore can only form a dike intrusion; for larger source extents, the dike can reach the surface and erupt on the nearside but still cannot reach the surface on the farside; for even larger source extents, eruptions could occur on both the nearside and the farside. The paucity of farside eruptions therefore implies a restricted range of vertical extents of partial melt source region sizes, between ∼16 and ∼36 km. When eruptions can occur, the available pressure in excess of what is needed to support a static magma column to the surface gives the pressure gradient driving magma flow. The resulting typical turbulent magma rise speeds are ∼10 to a few tens of m s-1, dike widths are of order 100 m, and eruption rates from 1 to 10 km long fissure vents are of order 105 to 106 m3 s-1. Volume fluxes in lunar eruptions derived from lava flow thicknesses and surface slopes or rille lengths and depths are found to be of order 105 to 106 m3 s-1 for volume-limited lava flows and >104 to 105 m3 s-1 for sinuous rilles, with dikes widths of ∼50 m. The

  15. High Temperature Metamorphism In The Conductive Boundary Layer Of An Intrusion Of Rhyolite Magma In The Krafla Geothermal System, Iceland

    NASA Astrophysics Data System (ADS)

    Schiffman, P.; Zierenberg, R. A.; Fridleifsson, G. O.; Elders, W. A.; Mortensen, A. K.

    2011-12-01

    A rhyolite magma body within the Krafla geothermal system- encountered at a depth of 2.1 km during drilling of the Iceland Deep Drilling Project's IDDP-1 borehole - is producing high temperature metamorphism within adjacent country rocks. Cuttings recovered during drilling within a few meters of the intrusive contact are undergoing recrystallization into granoblastic, pyroxene hornfelses. In mafic rocks, clinopyroxene-orthopyroxene-plagioclase-magnetite-ilmenite assemblages record temperatures in the range of 800-950°C. Silicic lithologies - mainly older felsitic intrusions -contain pockets of rhyolite melt, quenched to glass during drilling, amongst alkali feldspar, plagioclase, quartz, clinopyroxene, and magnetite. Curiously, no lower grade metamorphic assemblages have been identified in the drill cuttings, and country rocks at distances beyond 30 m of the contact are essentially unaltered. These findings suggest that the intruding rhyolite magma body has created a thin conductive boundary layer above it, but that a contact metamorphic aureole has not as yet developed beyond this. The heat flow across the boundary layer is calculated to be a minimum of 23 W m-2. This flux is capable of supplying steam to a geothermal power plant that can produce approximately 40 MW of electrical generation from a single well that has a measured well-head temperature of up to 415°C.

  16. Generation, ascent and eruption of magma on the Moon: New insights into source depths, magma supply, intrusions and effusive/explosive eruptions (Part 2: Predicted emplacement processes and observations)

    NASA Astrophysics Data System (ADS)

    Head, James W.; Wilson, Lionel

    2017-02-01

    We utilize a theoretical analysis of the generation, ascent, intrusion and eruption of basaltic magma on the Moon to develop new insights into magma source depths, supply processes, transport and emplacement mechanisms via dike intrusions, and effusive and explosive eruptions. We make predictions about the intrusion and eruption processes and compare these with the range of observed styles of mare volcanism, and related features and deposits. Density contrasts between the bulk mantle and regions with a greater abundance of heat sources will cause larger heated regions to rise as buoyant melt-rich diapirs that generate partial melts that can undergo collection into magma source regions; diapirs rise to the base of the anorthositic crustal density trap (when the crust is thicker than the elastic lithosphere) or, later in history, to the base of the lithospheric rheological trap (when the thickening lithosphere exceeds the thickness of the crust). Residual diapiric buoyancy, and continued production and arrival of diapiric material, enhances melt volume and overpressurizes the source regions, producing sufficient stress to cause brittle deformation of the elastic part of the overlying lithosphere; a magma-filled crack initiates and propagates toward the surface as a convex upward, blade-shaped dike. The volume of magma released in a single event is likely to lie in the range 102 km3 to 103 km3, corresponding to dikes with widths of 40-100 m and both vertical and horizontal extents of 60-100 km, favoring eruption on the lunar nearside. Shallower magma sources produce dikes that are continuous from the source region to the surface, but deeper sources will propagate dikes that detach from the source region and ascend as discrete penny-shaped structures. As the Moon cools with time, the lithosphere thickens, source regions become less abundant, and rheological traps become increasingly deep; the state of stress in the lithosphere becomes increasingly contractional

  17. Formation of low-δ18O magmas of the Kangerlussuaq Intrusion by addition of water derived from dehydration of foundered basaltic roof rocks

    NASA Astrophysics Data System (ADS)

    Riishuus, Morten S.; Harris, Chris; Peate, David W.; Tegner, Christian; Wilson, J. Richard; Brooks, C. Kent

    2015-05-01

    The Kangerlussuaq Intrusion in East Greenland is concentrically zoned from quartz nordmarkite (quartz syenite) at the margin, through pulaskite, to foyaite (nepheline syenite) in the centre, with no apparent intrusive contacts. The δ18O values of coexisting minerals are consistent with oxygen isotope equilibrium at magmatic temperatures. Most of the intrusion formed from low-δ18O magma; magma δ18O values generally increased upwards from about 3.3 ‰ in the quartz nordmarkites to 5.6 ‰ in the foyaites. The lowest magma δ18O value of about -1.0 ‰ is from the upper part of the nordmarkites, where there is a high concentration of foundered basaltic xenoliths (stoped from the roof of the intrusion). The amphiboles in the syenites have δD values that range from those typical of hydrous mantle-derived minerals to much lower values (-86 to -157 ‰), as do whole-rock samples of xenolith and country rock (-125 to -148 ‰). The low magma δ18O and δD values are consistent with continuous incorporation, exchange and upward escape of low-δ18O and δD fluids released from stoped basaltic roof material. Mass balance suggests that the integrated amount of water involved was 7 wt% of the volume of the magma, but locally reached 30 wt% water. The requirement for large amounts of water with low δ18O value is satisfied only if the foundered basalt contained most of its water in cavities as opposed to hydrous minerals. Even with this requirement, the volume of stoped basalt would have been equal to the volume of the magma. Repeated recharge of the residual magma with progressively less contaminated silica undersaturated melt resulted in a gradual shift across the low-pressure thermal divide. Crystallisation was suppressed by the depression of the liquidus due to water saturation of the residual magma (pH2O ~1 kbar).

  18. Oligo-Miocene mafic intrusions of the San Juan Volcanic Field, southwestern Colorado, and their relationship to voluminous, caldera-forming magmas

    NASA Astrophysics Data System (ADS)

    Lake, Ethan T.; Farmer, G. Lang

    2015-05-01

    The trigger(s) of ignimbrite flare-ups in continental environments and their connection to "high power" mantle-melting events are the subject of ongoing debate, often hampered by the relative scarcity of mantle-derived basalts compared to voluminous amounts of intermediate and silicic lavas, intrusions, and welded-tuffs. This study focused on locating and analyzing mafic magmas in the San Juan Mountains of Colorado, the largest erosional remnant of the Oligocene Southern Rocky Mountain ignimbrite flare-up. The "flare-up in" the San Juan Volcanic Field (SJVF) has several potential explanations including: crustal anatexis or MASH processes from either an asthenospheric "high power" melting event triggered by rifting and/or lithospheric delamination or a lithospheric mantle "high power" event caused by exposure of Farallon metasomatism to the underlying asthenosphere. The required volumes of crustal melt (a column 34-45 km tall over an area of 10,000 km2) and crustal heterogeneity disqualify anatexis as a source of the SJVF. Basalt and basaltic andesite magmas of the SJVF have εNd (-6 to -8) and 87Sr/86Sr (0.705-0.706), high Ba concentrations (750-1500 ppm) with low Rb/Zr (0.25-0.5) compatible with a lithospheric basalt MASH model. An OIB-like basalt source would require nearly twice the crustal assimilation (50%+) and MASH zone thickness (∼17 km) to produce the isotopic ratios of intermediate to silicic SJVF rocks and could not produce their elevated Ba concentrations. The location of the SJVF may be controlled by its maximum distance of magma capture and lateral transport or by the underlying lithospheric mantle.

  19. Rapid intrusion of magma into wet rock: groundwater flow due to pore pressure increases.

    USGS Publications Warehouse

    Delaney, P.T.

    1982-01-01

    Analytical and numerical solutions are developed to simulate the pressurization, expansion, and flow of groundwater contained within saturated, intact host rocks subject to sudden heating from the planar surface of an igneous intrusion. For most rocks, water diffuses more rapidly than heat, assuring that groundwater is not heated along a constant-volume pressure path and that thermal expansion and pressurization adjacent to the intrusion drives a flow that extends well beyond the heated region. -from Author

  20. Lateral Reactive Infiltration in a Vertical Gabbroic Crystal Mush, Skaergaard Intrusion, East Greenland

    NASA Astrophysics Data System (ADS)

    Namur, O.; Humphreys, M.; Holness, M. B.

    2012-12-01

    The Marginal Border Series of the Skaergaard intrusion (East Greenland) is comprised of rocks having crystallized in situ along the vertical walls of the magma chambers. It is subdivided into an outer Unbanded Division and an inner Banded Division. The Banded Division contains abundant cm- to dm-thick bands dominated by fine-grained mafic minerals, with a morphology evolving from almost planar to deeply scalloped and fingered with increasing distance from the intrusion margin. The morphology of these bands is reminiscent of the reaction fronts described in sedimentary basins infiltrated by reactive fluid. We propose that the banding in the Skaergaard Marginal Border Series is produced by chemical disequilibrium into the crystal mush resulting from the suction of primitive liquid from the main magma body into the crystal mush. Shrinkage of the mush during solidification is the driving force for liquid migration. Liquid porous flow produces partial dissolution of evolved pre-existing mafic minerals in the mush, which changes the new mush liquid composition to one capable of crystallizing mafic rocks with a very minor plagioclase component. Abrupt solidification of this liquid, which results in the formation of the actual colloform bands, is explained by supersaturation of some mafic mineral components (e.g. olivine, clinopyroxene, Fe-Ti oxides) in the infiltrating melt. The morphological evolution of the colloform bands, from almost planar to deeply scalloped and fingered with increasing distance from the intrusion margin, is thought to result from increasing crystal mush thickness with progressive differentiation.

  1. Coronae as a result of giant magma intrusions in the lithosphere of Venus: insights from laboratory experiments

    NASA Astrophysics Data System (ADS)

    Galland, Olivier; Polteau, Stephane; Werner, Stephanie C.

    2013-04-01

    Coronae on the surface of Venus are unique volcano-tectonic structures in the solar systems. Their circular morphology is associated with various topographic signatures, from bell-shape domes, flat-topped plateaus, to uplifted rings surrounding a subsided centre similar to caldera. Their extensive size and associated lava flows erupting from their periphery, indicate that they result from deep processes in the Venus mantle. Understanding their origin is thus essential for unraveling the dynamics of Venus through time. There are several scenarios explaining the formation of coronae, the most popular being the interaction between an upwelling mantle plume and the lithosphere, creating dynamic topography. In this contribution, we propose that coronae can result from the emplacement of giant magma intrusions below the Venus' lithosphere, on the basis of laboratory experiments. The experimental apparatus consists of a square box filled with compacted fine-grained silica flour (model crust), in which a low viscosity vegetable oil (model magma) is injected at constant flow rate. The initial conditions are such that magma initially flows horizontally, forming a sill-like body, to simulate magmatic underplating. During the experiments, oil injection triggers deformation of the model surface, which is monitored periodically using a moiré projection device, producing time series topographic maps of the model surface. Our results show that the surface evolution of the models follows three stages: (1) initial bell-shaped doming occurs above the injection inlet, producing radial open fractures at the model surfaces; (2) the bell-shape dome evolves to a flat-topped plateau, at the rim of which the oil erupts; (3) after the injection stops, the centre of the plateau subsides, and a positive topographic ring surrounding a depression, like a caldera, remains. The collapse of the plateau also generates concentric extensional fractures at the rims of the caldera. After the dynamic

  2. Experimental effects of pressure and fluorine on apatite saturation in mafic magmas, with reference to layered intrusions and massif anorthosites

    NASA Astrophysics Data System (ADS)

    Tollari, N.; Baker, D. R.; Barnes, S.-J.

    2008-08-01

    Apatite is a cumulate phase in the upper parts of some mafic layered intrusions and anorthositic complexes. We investigated the effect of pressure and fluorine on apatite saturation in mafic magmas to better understand under which conditions this mineral crystallizes. Apatite saturation gives information about the formation of silicate rocks, and is of interest in explaining the formation of apatite-oxide-rich rocks (e.g. nelsonites comprising approximately, one-third apatite and two-third Fe-Ti oxide). Two models of formation are proposed for this rock type: crystal fractionation followed by accumulation of apatite and Fe-Ti oxides and liquid immiscibility. New experiments carried out with mafic compositions at 500 MPa confirm that the most important variables on phosphate saturation are SiO2 and CaO. Fluorine addition leads to apatite saturation at lower SiO2 and higher CaO concentrations. Comparison of our results with those of previous experimental studies on liquid-liquid immiscibility at upper-to-mid-crustal conditions allows us to investigate the relative importance of apatite saturation versus liquid-liquid immiscibility in the petrogenesis of nelsonites and similar rocks. The liquid line of descent of three natural examples studied (the Sept-Îles intrusive suite, the anorthositic Complex of the Lac-St-Jean and the Skaergaard layered intrusion) do not cross the liquid-liquid immiscibility field before they reach apatite saturation. Thus, the apatite-oxide-rich rock associated with these three intrusive suites are best explained by crystal fractionation followed by accumulation of apatite and Fe-Ti oxides.

  3. Melt inclusions in the olivine from the Nantianwan intrusion: Implications for the parental magma of Ni-Cu-(PGE) sulfide-bearing mafic-ultramafic intrusions of the ∼260 Ma Emeishan large igneous province (SW China)

    NASA Astrophysics Data System (ADS)

    Zhang, Le; Ren, Zhong-Yuan; Wang, Christina Yan

    2017-02-01

    Olivine-hosted melt inclusions provide an archive of the parental magma and early magma history that is unavailable from bulk-rock analyses of cumulates. For those olivine-bearing mafic-ultramafic intrusions, a combined in situ analysis of major elements and Pb isotopic compositions for the melt inclusions and host olivine crystals may provide an effective way to understand the nature of the parental magma of the intrusions. In this study, we take the Nantianwan intrusion in the Emeishan large igneous province (SW China) as an example to analyze the melt inclusions and the host olivine. The Nantianwan intrusion is mainly composed of gabbronorite, with minor olivine gabbro. The olivine crystals in the olivine gabbro have Fo contents varying from 81.1 to 89.2 and Ni from 0.05 to 0.30 wt.%. The melt inclusion hosted in the most Mg-rich olivine has 50.9 wt.% SiO2, 1.0 wt.% TiO2, 15.1 wt.% MgO and 2.9 wt.% Na2O + K2O, indicating that the parental magma of the intrusion was of high-Mg basaltic composition. The melt inclusions overall have 208Pb/206Pb ratios of 2.0567-2.1032 and 207Pb/206Pb of 0.8287-0.8481, similar to the Pb isotopic compositions of the Emeishan flood basalts and consistent with insignificant crustal contamination. Given that the Nantianwan intrusion contains the most Mg-rich olivine among the Ni-Cu-(PGE) sulfide-bearing mafic-ultramafic intrusions in the Emeishan LIP, we infer that the composition of the melt inclusion in the most Mg-rich olivine from the Nantianwan intrusion may represent the least evolved parental magma of the Ni-Cu-(PGE) sulfide-bearing mafic-ultramafic intrusions in the Emeishan LIP. This can be further used to constrain the magma process related to Ni-Cu-(PGE) sulfide mineralization.

  4. Wall Rock Assimilation and Magma Migration in the Sierra Nevada Batholith: A Study of the Courtright Intrusive Zone, Central California

    NASA Astrophysics Data System (ADS)

    Torrez, G.; Putirka, K. D.

    2010-12-01

    The Sierra Nevada Batholith is composed of various plutons that interact with each other, and with pre- and syn-batholith metamorphic rocks. In the central part of the Sierra Nevada Batholith, at Courtright Reservoir in California, the younger Mt. Givens Pluton (87-93 Ma; McNulty et al., 2000) intrudes the Dinkey pluton (103 Ma; Bateman et al., 1964), and metasediments (a metamorphic screen) that, in places, separate the two plutons. This Courtright Reservoir Intrusive zone, as termed by Bateman et al. (1964), provides an ideal setting to examine the dynamics of intrusion and assimilation. Whole rock major and trace element compositions of the plutons, their mafic enclaves, and the metasediments, show that all such samples, from both plutons, fall on a single mixing trend. We thus infer that magmas parental to both plutons were roughly similar in composition, and assimilated significant amounts of the same, or very similar metasedimentary wall rocks. We also examined changes in whole rock compositions within the Mt. Givens pluton, as a function of distance from the two rock units with which it is now in contact (the metasediments, and the Dinkey Creek). In the vicinity of the contact between are an abundance of enclaves that are rounded, and appear to have been transported in vertical pipes. Whole rock analysis of the host granitoid material that surrounds these enclaves is clearly more mafic than the granitoid magmas from interior parts of the pluton. These whole rock compositions indicate that the pluton becomes more homogenous moving away from the contact, with a compositional decay occurring over a span of about 50-100 m. There are at least two possible interpretations. The compositional decay may represent a diffusive exchange of mass between an early crystallizing marginal phase of the pluton and the pluton interior. Another (not mutually incompatible) possibility is that the mafic margins represent pipes or tubes (Paterson, 2010), related to some convective

  5. Parental magma of the Skaergaard intrusion: constraints from melt inclusions in primitive troctolite blocks and FG-1 dykes

    NASA Astrophysics Data System (ADS)

    Jakobsen, Jakob K.; Tegner, Christian; Brooks, C. Kent; Kent, Adam J. R.; Lesher, Charles E.; Nielsen, Troels F. D.; Wiedenbeck, Michael

    2010-01-01

    Troctolite blocks with compositions akin to the Hidden Zone are exposed in a tholeiitic dyke cutting across the Skaergaard intrusion, East Greenland. Plagioclase in these blocks contains finely crystallised melt inclusions that we have homogenised to constrain the parental magma to 47.4-49.0 wt.% SiO2, 13.4-14.9 wt.% Al2O3 and 10.7-14.1 wt.% FeOT. These compositions are lower in FeOT and higher in SiO2 than previous estimates and have distinct La/SmN and Dy/YbN ratios that link them to the lowermost volcanic succession (Milne Land Formation) of the regional East Greenland flood basalt province. New major- and trace element compositions for the FG-1 dyke swarm, previously taken to represent Skaergaard magmas, overlap with the entire range of the regional flood basalt succession and do not form a coherent suite of Skaergaard like melts. These dykes are therefore re-interpreted as feeder dykes throughout the main phase of flood basalt volcanism.

  6. Gradual caldera collapse at Bárdarbunga volcano, Iceland, regulated by lateral magma outflow.

    PubMed

    Gudmundsson, Magnús T; Jónsdóttir, Kristín; Hooper, Andrew; Holohan, Eoghan P; Halldórsson, Sæmundur A; Ófeigsson, Benedikt G; Cesca, Simone; Vogfjörd, Kristín S; Sigmundsson, Freysteinn; Högnadóttir, Thórdís; Einarsson, Páll; Sigmarsson, Olgeir; Jarosch, Alexander H; Jónasson, Kristján; Magnússon, Eyjólfur; Hreinsdóttir, Sigrún; Bagnardi, Marco; Parks, Michelle M; Hjörleifsdóttir, Vala; Pálsson, Finnur; Walter, Thomas R; Schöpfer, Martin P J; Heimann, Sebastian; Reynolds, Hannah I; Dumont, Stéphanie; Bali, Eniko; Gudfinnsson, Gudmundur H; Dahm, Torsten; Roberts, Matthew J; Hensch, Martin; Belart, Joaquín M C; Spaans, Karsten; Jakobsson, Sigurdur; Gudmundsson, Gunnar B; Fridriksdóttir, Hildur M; Drouin, Vincent; Dürig, Tobias; Aðalgeirsdóttir, Guðfinna; Riishuus, Morten S; Pedersen, Gro B M; van Boeckel, Tayo; Oddsson, Björn; Pfeffer, Melissa A; Barsotti, Sara; Bergsson, Baldur; Donovan, Amy; Burton, Mike R; Aiuppa, Alessandro

    2016-07-15

    Large volcanic eruptions on Earth commonly occur with a collapse of the roof of a crustal magma reservoir, forming a caldera. Only a few such collapses occur per century, and the lack of detailed observations has obscured insight into the mechanical interplay between collapse and eruption. We use multiparameter geophysical and geochemical data to show that the 110-square-kilometer and 65-meter-deep collapse of Bárdarbunga caldera in 2014-2015 was initiated through withdrawal of magma, and lateral migration through a 48-kilometers-long dike, from a 12-kilometers deep reservoir. Interaction between the pressure exerted by the subsiding reservoir roof and the physical properties of the subsurface flow path explain the gradual, near-exponential decline of both collapse rate and the intensity of the 180-day-long eruption.

  7. FEM-based Surface Displacement Modeling of Magma Intrusions at Kilauea Volcano

    NASA Astrophysics Data System (ADS)

    Charco, M.; González, P. J.; Galán del Sastre, P.; Negredo, A. M.

    2015-12-01

    Volcanic deformation is the surface expression of the internal dynamics of an inherently complex system resulting from the interaction of magma with the surrounding rocks. Geodetic techniques, as Global Positioning System (GPS) and/or Interferometric Synthetic Aperture Radar (InSAR), are being extensively used to monitor such ground deformation. Nevertheless, it is impossible to directly observe the processes at depth that cause the observed ground deformation. The interpretation of geodetic data requires both, mathematical modeling to simulate the observed signals and inversion approaches to estimate the deformation source parameters. In this study we provide a numerical tool for interpreting geodetic data by solving in an efficient and accurate way the inverse problem to estimate the optimal parameters for magmatic sources (spherical magma chambers and tensile dislocations). In doing so, we propose a Finite Element Method (FEM) for the calculation of Green functions in an heterogeneous medium. The key aspect of the methodology lies in how to incorporate the source into the model and in applying the reciprocity relationship between the station and the source. In our approach, deformation sources are independent of the simulation mesh. The search for the best fit point source(s) is conducted for an array of 3-D locations extending below a predefined volume region. The total number of Green functions is reduced to the number of the observation points by using the reciprocity relationship. We apply this methodology to the recent inflation observed at Kilauea's Southwest Rift Zone in May 2015, observed with the new Sentinel-1 radar interferometry satellite mission, to report the magma transport along the zone.

  8. Theoretical prediction of gold vein location in deposits originated by a wall magma intrusion

    NASA Astrophysics Data System (ADS)

    Martin, Pablo; Maass-Artigas, Fernando; Cortés-Vega, Luis

    2016-05-01

    The isotherm time-evolution resulting from the intrusion of a hot dike in a cold rock is analized considering the general case of nonvertical walls. This is applied to the theoretical prediction of the gold veins location due to isothermal evolution. As in previous treatments earth surface effects are considered and the gold veins are determined by the envelope of the isotherms. The locations of the gold veins in the Callao mines of Venezuela are now well predicted. The new treatment is now more elaborated and complex that in the case of vertical walls, performed in previous papers, but it is more adequated to the real cases as the one in El Callao, where the wall is not vertical.

  9. Nonexplosive and explosive magma/wet-sediment interaction during emplacement of Eocene intrusions into Cretaceous to Eocene strata, Trans-Pecos igneous province, West Texas

    USGS Publications Warehouse

    Befus, K.S.; Hanson, R.E.; Miggins, D.P.; Breyer, J.A.; Busbey, A.B.

    2009-01-01

    Eocene intrusion of alkaline basaltic to trachyandesitic magmas into unlithified, Upper Cretaceous (Maastrichtian) to Eocene fluvial strata in part of the Trans-Pecos igneous province in West Texas produced an array of features recording both nonexplosive and explosive magma/wet-sediment interaction. Intrusive complexes with 40Ar/39Ar dates of ~ 47-46??Ma consist of coherent basalt, peperite, and disrupted sediment. Two of the complexes cutting Cretaceous strata contain masses of conglomerate derived from Eocene fluvial deposits that, at the onset of intrusive activity, would have been > 400-500??m above the present level of exposure. These intrusive complexes are inferred to be remnants of diatremes that fed maar volcanoes during an early stage of magmatism in this part of the Trans-Pecos province. Disrupted Cretaceous strata along diatreme margins record collapse of conduit walls during and after subsurface phreatomagmatic explosions. Eocene conglomerate slumped downward from higher levels during vent excavation. Coherent to pillowed basaltic intrusions emplaced at the close of explosive activity formed peperite within the conglomerate, within disrupted Cretaceous strata in the conduit walls, and within inferred remnants of the phreatomagmatic slurry that filled the vents during explosive volcanism. A younger series of intrusions with 40Ar/39Ar dates of ~ 42??Ma underwent nonexplosive interaction with Upper Cretaceous to Paleocene mud and sand. Dikes and sills show fluidal, billowed, quenched margins against the host strata, recording development of surface instabilities between magma and groundwater-rich sediment. Accentuation of billowed margins resulted in propagation of intrusive pillows into the adjacent sediment. More intense disruption and mingling of quenched magma with sediment locally produced fluidal and blocky peperite, but sufficient volumes of pore fluid were not heated rapidly enough to generate phreatomagmatic explosions. This work suggests that

  10. San Jacinto Intrusive Complex: 1. Geology and mineral chemistry, and a model for intermittent recharge of tonalitic magma chambers

    NASA Astrophysics Data System (ADS)

    Hill, R. I.

    1988-09-01

    Geological mapping within the San Jacinto Mountains of southern California has delineated three major and numerous minor plutons of the Cretaceous Peninsular Ranges batholith. Early minor intrusives emplaced into quartz-rich metasedimentary sequences span the compositional range olivine gabbro to granite. The three large (to 250 km2) plutons span a limited compositional range between mafic tonalite (color index (CI) > 15) and K-feldspar-poor granodiorite (CI ≃ 10). All units are composed of plagioclase (An30-40) (50-55%), quartz (20-30%), K-feldspar (1-8%), biotite (10-15%), hornblende (0-5%), titanite (0-2%), and accessory zircon, apatite, allanite, and ilmenite. Variations in mineral abundances are geographically systematic only within the youngest major mass (unit III), which grades from marginal mafic tonalite to central K-feldsparpoor granodiorite. Mineral foliations and banding, schlieren, and inclusion orientation within each unit usually parallel the nearest contact. Alignment of foliations and apparent flow-sorting and scour features are interpreted as reflecting flow patterns within each chamber. Mafic synplutonic dykes (of quartz diorite and tonalite) intruded the tonalites and were broken up to form extensive inclusion trains. Dyke-tonalite relations are interpreted as showing that (1) magma adjacent to the pluton wall had considerable yield strength, (2) magmatic flow adjacent to pluton walls was capable of moving material some distance (up to kilometers) to form the inclusion trains, and (3) the dykes represent conduits through which a considerable amount of liquid was added to the inflating magma chambers. Mineral compositions throughout the major plutons are relatively uniform. Mean plagioclase composition ranges from An40 in the most mafic tonalites to An30 in the most felsic granodiorites; the total microprobe-observed range is An44 to An25 (and to An47 in a mafic inclusion). Mg/(Mg + Fe + Mn) of biotite and hornblende drop similarly from 0

  11. Imaging of magma intrusions beneath Harrat Al-Madinah in Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Abdelwahed, Mohamed F.; El-Masry, Nabil; Moufti, Mohamed Rashad; Kenedi, Catherine Lewis; Zhao, Dapeng; Zahran, Hani; Shawali, Jamal

    2016-04-01

    High-resolution tomographic images of the crust and upper mantle beneath Harrat Al-Madinah, Saudi Arabia, are obtained by inverting high-quality arrival-time data of local earthquakes and teleseismic events recorded by newly installed borehole seismic stations to investigate the AD 1256 volcanic eruption and the 1999 seismic swarm in the study region. Our tomographic images show the existence of strong heterogeneities marked with low-velocity zones extending beneath the AD 1256 volcanic center and the 1999 seismic swarm area. The low-velocity zone coinciding with the hypocenters of the 1999 seismic swarm suggests the presence of a shallow magma reservoir that is apparently originated from a deeper source (60-100 km depths) and is possibly connected with another reservoir located further north underneath the NNW-aligned scoria cones of the AD 1256 eruption. We suggest that the 1999 seismic swarm may represent an aborted volcanic eruption and that the magmatism along the western margin of Arabia is largely attributed to the uplifting and thinning of its lithosphere by the Red Sea rifting.

  12. Zircon trace element, and O and Hf isotopic records of magma sources and pluton assembly in the Sierra Crest intrusions (Sierra Nevada batholith, USA)

    NASA Astrophysics Data System (ADS)

    Miller, J. S.; Lackey, J. S.; Davies, G. R.; Sendek, C.

    2014-12-01

    The Sierra Crest Intrusions of the Sierra Nevada Batholith are the last major magmatic pulse associated with the Cretaceous flare-up. They are characterized by long assembly times (several 106 years), and are normally zoned from marginal, horblende-biotite granodiorites to more felsic, K-feldspar megacrystic, biotite granodiorites. Combined trace element and O and Hf isotopes on zircon are presented from the major Sierra Crest Intrusions. Zircon saturation temperatures (TZrc,sat) are similar and low (ca. 700°C) for most of the individual units, but Ti-in-zircon temperatures (TZrn,Ti) and trace element ratios contrast strongly between outer marginal units and inner megacrystic units (low TZrn,Ti ≈ TZrc,sat, high Yb/Gd, low Th/U, high and similar Hf, and high Eu/Eu*). Zircon O and Hf isotopes vary markedly across the suite (ΔɛHf = 15; Δδ18O = 2.5‰). Individual intrusive suites (gabbro to high-silica granite) record variable O-Hf variations; no correlation (John Muir), subtle binary or ternary arrays (e.g., Whitney, Sonora), or bimodal distribution of values (Tuolumne). In some cases single hand samples (small-volume mafic or felsic units), may record the entire variability within a suite. Inner megacrystic units generally have lower ɛHf than outer marginal units. Whole rock geochemical data for the intrusive suites also show an increase in the "garnet signature" with time (higher Sr/Y and Dy/Yb). The isotopic data are consistent with variable mantle sources and progressively cooler, more water-rich magmatism with a simultaneous shift to greater crustal involvement, and deepening of the magma sources. Magmatic underplating and intraplating of mafic arc magmas produced increasing crustal assimilation but under PT conditions that allowed production of more felsic, zircon-saturated, magmas. The isotopic variability requires that plutons are amalgams of many magmas mixed at varying scales before final solidification.

  13. Stress barriers controlling lateral migration of magma revealed by seismic tomography

    PubMed Central

    Martí, J.; Villaseñor, A.; Geyer, A.; López, C.; Tryggvason, A.

    2017-01-01

    Understanding how monogenetic volcanic systems work requires full comprehension of the local and regional stresses that govern magma migration inside them and why/how they seem to change from one eruption to another. During the 2011–2012 El Hierro eruption (Canary Islands) the characteristics of unrest, including a continuous change in the location of seismicity, made the location of the future vent unpredictable, so short term hazard assessment was highly imprecise. A 3D P-wave velocity model is obtained using arrival times of the earthquakes occurred during that pre-eruptive unrest and several latter post-eruptive seismic crises not related to further eruptions. This model reveals the rheological and structural complexity of the interior of El Hierro volcanic island. It shows a number of stress barriers corresponding to regional tectonic structures and blocked pathways from previous eruptions, which controlled ascent and lateral migration of magma and, together with the existence of N-S regional compression, reduced its options to find a suitable path to reach the surface and erupt. PMID:28084436

  14. Stress barriers controlling lateral migration of magma revealed by seismic tomography

    NASA Astrophysics Data System (ADS)

    Martí, J.; Villaseñor, A.; Geyer, A.; López, C.; Tryggvason, A.

    2017-01-01

    Understanding how monogenetic volcanic systems work requires full comprehension of the local and regional stresses that govern magma migration inside them and why/how they seem to change from one eruption to another. During the 2011–2012 El Hierro eruption (Canary Islands) the characteristics of unrest, including a continuous change in the location of seismicity, made the location of the future vent unpredictable, so short term hazard assessment was highly imprecise. A 3D P-wave velocity model is obtained using arrival times of the earthquakes occurred during that pre-eruptive unrest and several latter post-eruptive seismic crises not related to further eruptions. This model reveals the rheological and structural complexity of the interior of El Hierro volcanic island. It shows a number of stress barriers corresponding to regional tectonic structures and blocked pathways from previous eruptions, which controlled ascent and lateral migration of magma and, together with the existence of N-S regional compression, reduced its options to find a suitable path to reach the surface and erupt.

  15. Oxygen isotope evidence for crustal assimilation and magma mixing in the Granite Harbour Intrusives, Northern Victoria Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Dallai, L.; Ghezzo, C.; Sharp, Z. D.

    2003-03-01

    The stable isotope composition (O,H) of whole-rock and mineral separates of Cambrian-Ordovician gabbros, diorites, granodiorites and granites forming the Mt. Abbott composite intrusions (Northern Victoria Land, Antarctica) was measured to constrain the origin and evolution of the magmas postdating the Ross Orogen. The δ18O values of olivine gabbros plot in the field of slightly evolved mantle-derived melts ( δ18O WR=6.8-7.4‰). The O-isotope character of the mantle source inferred from the δ18O values of cumulous olivine in gabbros (5.7-6.8‰) is enriched in 18O compared to modern arc-related magmas. Geochemical data and concurrent high δ18O values, and initial strontium ( 87Sr/ 86Sr=0.7060) and neodymium ( 143Nd/ 144Nd=0.5122) isotope ratios indicate that the olivine gabbros formed by crustal contamination of a primary calc-alkaline basaltic melt. The diorites have high δ18O values, among the highest ever measured for dioritic rocks (8.7-10.3‰), and Sr-isotope ratios that partially overlap with the adjacent and mingled felsic lithologies (0.708-0.710). The diorites have pyroxene with high, nearly constant δ18O values (8.2-8.6‰) that are independent from the silica content of the rocks; thus, they did not increase in response of the chemical evolution of the rocks. The diorites originated from the same primary calc-alkaline basalt experiencing different amounts of crustal contamination, and underwent different degrees of mixing with the adjacent granites, producing granodioritic facies and quartz/feldspar xenocrystic diorites. The δ18O, 87Sr/ 86Sr and 143Nd/ 144Nd compositions of the granites and granodiorites overlap (10.8-12.1‰, 0.7096-0.7108, 0.5119-0.5120). They are distinct from the values of the mafic rocks and indicate that gabbros and granites were not cogenetic. The granites are a separate melt component likely derived from nonmodal partial melting of fertile meta-igneous protoliths.

  16. Iron in plagioclase in the Bushveld and Skaergaard intrusions: implications for iron contents in evolving basic magmas

    NASA Astrophysics Data System (ADS)

    Tegner, Christian; Cawthorn, R. Grant

    2010-05-01

    The evolved, iron-rich rocks of the tholeiitic Bushveld and Skaergaard intrusions are similar in containing cumulus magnetite, ilmenite, plagioclase, clinopyroxene, apatite and olivine, and also orthopyroxenes/pigeonite in Bushveld. Here, we evaluate their liquid evolution trends using the total iron content in plagioclase determined by electron microprobe analyses. To aid this analysis a revised mass balance model for the liquid evolution of Skaergaard is presented. For plagioclase in the Upper Zone of Skaergaard it was previously demonstrated that total FeO increases from ~0.25 to ~0.45 wt% with differentiation and correlates inversely with An% [100 × Ca/(Na + Ca)]. The reverse trend is observed in two recently published datasets for Bushveld, showing that total FeO in plagioclase decreases upward through the magnetite-bearing Upper Zone from ~0.30 to ~0.15% and from ~0.40 to ~0.25% in the western and northern limbs, respectively, and correlates positively with An%. The partition coefficient of total iron between plagioclase and magma increases with oxidation and polymerisation in the liquid. Although Bushveld formed under slightly more oxidizing conditions than Skaergaard, differences in the partition coefficients cannot explain the two observed trends. We therefore conclude that the differentiation trends of the liquids subsequent to magnetite saturation were fundamentally different. The inferred liquid composition for Bushveld contained about 15 wt% total FeO at the level of magnetite-in, which is slightly less than the total FeO content of the subsequent cumulates. In contrast, the Skaergaard liquid contained more total FeO than the ensuing cumulates. As a result, in Bushveld residual liquids total FeO decreased after magnetite saturation, whereas in Skaergaard the residual liquids continued to become enriched in iron. This conclusion is corroborated by simple mass balance calculations between modelled residual liquids and extracted cumulate rocks. Despite

  17. Multi-element variations in olivine as geochemical signatures of Ni-Cu sulfide mineralization in mafic magma systems—examples from Voisey's Bay and Pants Lake intrusions, Labrador, Canada

    NASA Astrophysics Data System (ADS)

    Bulle, Florian; Layne, Graham D.

    2016-01-01

    gabbro (BG) and upper gabbro (UG) of the Pants Lake intrusion is fairly homogeneous (˜Fo60, ˜4300 ppm Mn, ˜460 ppm Zn, ˜340 ppm Ni, ˜50 ppm Cr), with a more evolved composition (˜2100 ppm Ca, ˜20 ppm Sc, ˜300 ppm Ti, ˜4 ppm Y) than the average olivine of the Voisey's Bay intrusion (˜570 ppm Ca, ˜6 ppm Sc, ˜65 ppm Ti, ˜0.3 ppm Y). Pants Lake olivine also commonly lacks the mutually Mn-Zn-rich signature of olivine from the basal breccia at Voisey's Bay that is characteristic of contamination of the parent magma by country rock gneiss, and there reflects a close proximity to massive sulfides. In conjunction with petrographic observation and the stratigraphic context, a multiple-element (V-Cr-Mn-Fe-Co-Ni-Zn) regression can be applied to calculate a lateral proximity of olivine to massive sulfide mineralization in the Eastern Deeps part of the Voisey's Bay intrusion, over a distance exceeding 150 m. The compositional variations in olivine from the economic Voisey's Bay intrusion (bimodal and primitive) and the mainly barren Pants Lake intrusion (homogeneous and evolved) provide potential as a regional-scale mineralogical fertility indicator for mafic intrusions with comparable types of sulfide mineralization.

  18. Estimation of Contaminant Subslab Concentration in Vapor Intrusion Including Lateral Source-Building Separation.

    PubMed

    Yao, Yijun; Shen, Rui; Pennell, Kelly G; Suuberg, Eric M

    2013-08-01

    Most current vapor-intrusion screening models employ the assumption of a subsurface homogenous source distribution, and groundwater data obtained from nearby monitoring wells are usually taken to reflect the source concentration for several nearby buildings. This practice makes it necessary to consider the possible influence of lateral source-building separation. In this study, a new way to estimate subslab (nonbiodegradable) contaminant concentration is introduced that includes the influence of source offset with the help of a conformal transform technique. Results from this method are compared with those from a three-dimensional numerical model. Based on this newly developed method, a possible explanation is provided here for the great variation in the attenuation factors of the soil vapor concentrations of groundwater-to-subslab contaminants found in the EPA vapor-intrusion database.

  19. Estimation of Contaminant Subslab Concentration in Vapor Intrusion Including Lateral Source–Building Separation

    PubMed Central

    Yao, Yijun; Shen, Rui; Pennell, Kelly G.; Suuberg, Eric M.

    2014-01-01

    Most current vapor-intrusion screening models employ the assumption of a subsurface homogenous source distribution, and groundwater data obtained from nearby monitoring wells are usually taken to reflect the source concentration for several nearby buildings. This practice makes it necessary to consider the possible influence of lateral source–building separation. In this study, a new way to estimate subslab (nonbiodegradable) contaminant concentration is introduced that includes the influence of source offset with the help of a conformal transform technique. Results from this method are compared with those from a three-dimensional numerical model. Based on this newly developed method, a possible explanation is provided here for the great variation in the attenuation factors of the soil vapor concentrations of groundwater-to-subslab contaminants found in the EPA vapor-intrusion database. PMID:24795543

  20. Role of the source to building lateral separation distance in petroleum vapor intrusion.

    PubMed

    Verginelli, Iason; Capobianco, Oriana; Baciocchi, Renato

    2016-06-01

    The adoption of source to building separation distances to screen sites that need further field investigation is becoming a common practice for the evaluation of the vapor intrusion pathway at sites contaminated by petroleum hydrocarbons. Namely, for the source to building vertical distance, the screening criteria for petroleum vapor intrusion have been deeply investigated in the recent literature and fully addressed in the recent guidelines issued by ITRC and U.S.EPA. Conversely, due to the lack of field and modeling studies, the source to building lateral distance received relatively low attention. To address this issue, in this work we present a steady-state vapor intrusion analytical model incorporating a piecewise first-order aerobic biodegradation limited by oxygen availability that accounts for lateral source to building separation. The developed model can be used to evaluate the role and relevance of lateral vapor attenuation as well as to provide a site-specific assessment of the lateral screening distances needed to attenuate vapor concentrations to risk-based values. The simulation outcomes showed to be consistent with field data and 3-D numerical modeling results reported in previous studies and, for shallow sources, with the screening criteria recommended by U.S.EPA for the vertical separation distance. Indeed, although petroleum vapors can cover maximum lateral distances up to 25-30m, as highlighted by the comparison of model outputs with field evidences of vapor migration in the subsurface, simulation results by this new model indicated that, regardless of the source concentration and depth, 6m and 7m lateral distances are sufficient to attenuate petroleum vapors below risk-based values for groundwater and soil sources, respectively. However, for deep sources (>5m) and for low to moderate source concentrations (benzene concentrations lower than 5mg/L in groundwater and 0.5mg/kg in soil) the above criteria were found extremely conservative as the

  1. Role of the source to building lateral separation distance in petroleum vapor intrusion

    NASA Astrophysics Data System (ADS)

    Verginelli, Iason; Capobianco, Oriana; Baciocchi, Renato

    2016-06-01

    The adoption of source to building separation distances to screen sites that need further field investigation is becoming a common practice for the evaluation of the vapor intrusion pathway at sites contaminated by petroleum hydrocarbons. Namely, for the source to building vertical distance, the screening criteria for petroleum vapor intrusion have been deeply investigated in the recent literature and fully addressed in the recent guidelines issued by ITRC and U.S.EPA. Conversely, due to the lack of field and modeling studies, the source to building lateral distance received relatively low attention. To address this issue, in this work we present a steady-state vapor intrusion analytical model incorporating a piecewise first-order aerobic biodegradation limited by oxygen availability that accounts for lateral source to building separation. The developed model can be used to evaluate the role and relevance of lateral vapor attenuation as well as to provide a site-specific assessment of the lateral screening distances needed to attenuate vapor concentrations to risk-based values. The simulation outcomes showed to be consistent with field data and 3-D numerical modeling results reported in previous studies and, for shallow sources, with the screening criteria recommended by U.S.EPA for the vertical separation distance. Indeed, although petroleum vapors can cover maximum lateral distances up to 25-30 m, as highlighted by the comparison of model outputs with field evidences of vapor migration in the subsurface, simulation results by this new model indicated that, regardless of the source concentration and depth, 6 m and 7 m lateral distances are sufficient to attenuate petroleum vapors below risk-based values for groundwater and soil sources, respectively. However, for deep sources (> 5 m) and for low to moderate source concentrations (benzene concentrations lower than 5 mg/L in groundwater and 0.5 mg/kg in soil) the above criteria were found extremely conservative as

  2. Petrogenesis of postcollisional magmatism at Scheelite Dome, Yukon, Canada: Evidence for a lithospheric mantle source for magmas associated with intrusion-related gold systems

    USGS Publications Warehouse

    Mair, John L.; Farmer, G. Lang; Groves, David I.; Hart, Craig J.R.; Goldfarb, Richard J.

    2011-01-01

    The type examples for the class of deposits termed intrusion-related gold systems occur in the Tombstone-Tungsten belt of Alaska and Yukon, on the eastern side of the Tintina gold province. In this part of the northern Cordillera, extensive mid-Cretaceous postcollisional plutonism took place following the accretion of exotic terranes to the continental margin. The most cratonward of the resulting plutonic belts comprises small isolated intrusive centers, with compositionally diverse, dominantly potassic rocks, as exemplified at Scheelite Dome, located in central Yukon. Similar to other spatially and temporally related intrusive centers, the Scheelite Dome intrusions are genetically associated with intrusion-related gold deposits. Intrusions have exceptional variability, ranging from volumetrically dominant clinopyroxene-bearing monzogranites, to calc-alkaline minettes and spessartites, with an intervening range of intermediate to felsic stocks and dikes, including leucominettes, quartz monzonites, quartz monzodiorites, and granodiorites. All rock types are potassic, are strongly enriched in LILEs and LREEs, and feature high LILE/HFSE ratios. Clinopyroxene is common to all rock types and ranges from salite in felsic rocks to high Mg augite and Cr-rich diopside in lamprophyres. Less common, calcic amphibole ranges from actinolitic hornblende to pargasite. The rocks have strongly radiogenic Sr (initial 87Sr/86Sr from 0.711-0.714) and Pb isotope ratios (206Pb/204Pb from 19.2-19.7), and negative initial εNd values (-8.06 to -11.26). Whole-rock major and trace element, radiogenic isotope, and mineralogical data suggest that the felsic to intermediate rocks were derived from mafic potassic magmas sourced from the lithospheric mantle via fractional crystallization and minor assimilation of metasedimentary crust. Mainly unmodified minettes and spessartites represent the most primitive and final phases emplaced. Metasomatic enrichments in the underlying lithospheric mantle

  3. Crystallization sequence of the Upper Border Series of the Skaergaard Intrusion: revised subdivision and implications for chamber-scale magma homogeneity

    NASA Astrophysics Data System (ADS)

    Salmonsen, Lars Peter; Tegner, Christian

    2013-06-01

    Although it is one of the best-studied layered mafic intrusions in the world, the crystallization sequence of the Skaergaard Intrusion, east Greenland, remains in debate. In particular, it has been argued that the crystallization sequence in the Upper Border Series, which crystallized downwards from the roof of the magma chamber, differs from that in the Layered Series formed at the floor. The proposed deviation would require chemical stratification of the magma, and a reexamination of the crystallization sequence therefore has important implications for understanding the dynamics of the system. Here, we examine a new sample set from the Upper Border Series, combining field observations, petrography and anorthite contents of plagioclase with bulk rock Ti, V, P, Cu and Mn concentrations. We demonstrate that the first phases on the liquidus were plagioclase and olivine followed by augite, then ilmenite and magnetite (simultaneously), sulfides, apatite and finally ferrobustamite (now inverted to hedenbergite). This crystallization sequence represents extreme differentiation along the tholeiitic trend, and it mirrors those at the floor (Layered Series) and walls (Marginal Border Series). We therefore propose a revised subdivision of the Upper Border Series into equivalents of the subzones in the Layered Series denoted by apostrophes (LZa', LZb', etc.). Moreover, the first appearance of each of the cumulus phases occurs at similar plagioclase core anorthite contents. The mirror images of the crystallization sequences and the anorthite contents of plagioclase cores in the three series imply that the Skaergaard magma chamber solidified by in situ crystallization along the floor, walls and roof from one, largely homogenous, convecting magma body.

  4. Evaluation of site-specific lateral inclusion zone for vapor intrusion based on an analytical approach

    PubMed Central

    Yao, Yijun; Wu, Yun; Tang, Mengling; Wang, Yue; Wang, Jianjin; Suuberg, Eric M.; Jiang, Lin; Liu, Jing

    2016-01-01

    In 2002, U.S. EPA proposed a general buffer zone of approximately 100 feet (30 m) laterally to determine which buildings to include in vapor intrusion (VI) investigations. However, this screening distance can be threatened by factors such as extensive surface pavements. Under such circumstances, EPA recommended investigating soil vapor migration distance on a site-specific basis. To serve this purpose, we present an analytical model (AAMLPH) as an alternative to estimate lateral VI screening distances at chlorinated compound-contaminated sites. Based on a previously introduced model (AAML), AAMLPH is developed by considering the effects of impervious surface cover and soil geology heterogeneities, providing predictions consistent with the three-dimensional (3-D) numerical simulated results. By employing risk-based and contribution-based screening levels of subslab concentrations (50 and 500 µg/m3, respectively) and source-to-subslab attenuation factor (0.001 and 0.01, respectively), AAMLPH suggests that buildings greater than 30 m from a plume “boundary” can still be affected by VI in the presence of any two of the three factors, which are high source vapor concentration, shallow source and significant surface cover. This finding justifies the concern that EPA has expressed about the application of the 30 m lateral separation distance in the presence of physical barriers (e.g., asphalt covers or ice) at the ground surface. PMID:26057584

  5. Evaluation of site-specific lateral inclusion zone for vapor intrusion based on an analytical approach.

    PubMed

    Yao, Yijun; Wu, Yun; Tang, Mengling; Wang, Yue; Wang, Jianjin; Suuberg, Eric M; Jiang, Lin; Liu, Jing

    2015-11-15

    In 2002, U.S. EPA proposed a general buffer zone of approximately 100 feet (30 m) laterally to determine which buildings to include in vapor intrusion (VI) investigations. However, this screening distance can be threatened by factors such as extensive surface pavements. Under such circumstances, EPA recommended investigating soil vapor migration distance on a site-specific basis. To serve this purpose, we present an analytical model (AAMLPH) as an alternative to estimate lateral VI screening distances at chlorinated compound-contaminated sites. Based on a previously introduced model (AAML), AAMLPH is developed by considering the effects of impervious surface cover and soil geology heterogeneities, providing predictions consistent with the three-dimensional (3-D) numerical simulated results. By employing risk-based and contribution-based screening levels of subslab concentrations (50 and 500 μg/m(3), respectively) and source-to-subslab attenuation factor (0.001 and 0.01, respectively), AAMLPH suggests that buildings greater than 30 m from a plume boundary can still be affected by VI in the presence of any two of the three factors, which are high source vapor concentration, shallow source and significant surface cover. This finding justifies the concern that EPA has expressed about the application of the 30 m lateral separation distance in the presence of physical barriers (e.g., asphalt covers or ice) at the ground surface.

  6. Evidence from gabbro of the Troodos ophiolite for lateral magma transport along a slow-spreading mid-ocean ridge.

    PubMed

    Abelson, M; Baer, G; Agnon, A

    2001-01-04

    The lateral flow of magma and ductile deformation of the lower crust along oceanic spreading axes has been thought to play a significant role in suppressing both mid-ocean ridge segmentation and variations in crustal thickness. Direct investigation of such flow patterns is hampered by the kilometres of water that cover the oceanic crust, but such studies can be made on ophiolites (fragments of oceanic crust accreted to a continent). In the Oman ophiolite, small-scale radial patterns of flow have been mapped along what is thought to be the relict of a fast-spreading mid-ocean ridge. Here we present evidence for broad-scale along-axis flow that has been frozen into the gabbro of the Troodos ophiolite in Cyprus (thought to be representative of a slow-spreading ridge axis). The gabbro suite of Troodos spans nearly 20 km of a segment of a fossil spreading axis, near a ridge-transform intersection. We mapped the pattern of magma flow by analysing the rocks' magnetic fabric at 20 sites widely distributed in the gabbro suite, and by examining the petrographic fabric at 9 sites. We infer an along-axis magma flow for much of the gabbro suite, which indicates that redistribution of melt occurred towards the segment edge in a large depth range of the oceanic crust. Our results support the magma plumbing structure that has been inferred indirectly from a seismic tomography experiment on the slow-spreading Mid-Atlantic Ridge.

  7. Analytical model of surface uplift above axisymmetric flat-lying magma intrusions: Implications for sill emplacement and geodesy

    NASA Astrophysics Data System (ADS)

    Galland, O.; Scheibert, J.

    2013-03-01

    In this paper, we develop a new axisymmetric analytic model of surface uplift upon sills and laccoliths, based on the formulation of a thin bending plate lying on an elastic foundation. In contrast to most former models also based on thin bending plate formulation, our model accounts for (i) axi-symmetrical uplift, (ii) both upon and outside the intrusion. The model accounts for shallow intrusions, i.e. the ratio a/h > 5 where a and h are the radius and depth of the intrusion, respectively. The main parameter of the model is the elastic length l, which is a function of the elastic properties of the bending plate and of the elastic foundation. The model exhibits two regimes depending on the ratio a/l. When a/l < 5, the uplift spreads over a substantial domain compared to that of the intrusion. In contrast, when a/l > 5, the uplift is mostly restricted upon the intrusion. When the elastic foundation is very stiff, our model converges towards that of a clamped plate. We provide, as supplementary material, a Matlab function that calculates the surface uplift from the set of system and control parameters. We discuss three possible applications of our model: (i) The model can be used to describe sill propagation by introducing a propagation criterion. For realistic values, our model reproduces well the behavior of horizontal intrusions simulated in experiments; (ii) The model can also be used to compute the critical size of saucer-shaped sills. It shows, for instance, that a soft elastic foundation favors the horizontal spreading of sills before they form inclined sheets; (iii) We show that the classical Mogi point source model cannot be used to constrain sill properties from the surface uplift. We thus propose that our model can be used as a valuable alternative to both simple analytical models like Mogi's and more complex numerical models used to analyze ground deformation resulting from sill intrusions in active volcanoes.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  9. CO2-dependent fractional crystallization of alkaline silicate magmas and unmixing of carbonatites within the intrusive complexes of Brava Island (Cape Verde)

    NASA Astrophysics Data System (ADS)

    Weidendorfer, D.; Schmidt, M. W.; Mattsson, H. B.

    2014-12-01

    Intrusive carbonatites often occur in intimate association with SiO2-undersaturated rocks such as melilitites, nephelinites, syenites and phonolites. The occurrence of carbonatites on five of the 10 main islands of the Cape Verde hotspot argues for a CO2-enriched mantle source. Whether alkali-poor carbonatites on the Cape Verdes directly represent small mantle melt fractions or form by extreme fractionation and/or liquid immiscibility from a CO2-rich silicate magma remains a matter of debate. This study focuses on the pyroxenites, nephelinites, ijolites, syenites, phonolites and carbonatites of the intrusive unit of Brava Island. This relative complete series allows for the deduction of a CO2-dependent fractionation pathway from the most primitive basanitic dikes towards phonolitic compositions through an ijolitic series. Major and trace element whole rock and mineral composition trends can be reproduced by fractionating a sequence of olivine, augite, perovskite, biotite, apatite, sodalite and FeTi-oxides, present as phenocrysts in the rocks corresponding to their fractionation interval. To reproduce the observed chemistry of the alkaline silicate rocks a total fractionation of ~87% is required. The melts evolve towards the carbonatite-silicate miscibility gap, an initial CO2 of 0.5 wt% would be sufficient to maintain CO2-saturation in the more evolved compositions. The modelled carbonatite compositions, conjugate to nepheline-syenites to phonolites, correspond well to the observed ones except for an alkali-enrichment with respect to the natural samples. The alkali-depleted nature of the small carbonatite intrusions and dikes on Brava is likely a consequence of fluid-release to the surrounding wall-rocks during crystallization, where fenitization can be observed. The trace element chemistry of primary carbonates and also cpx within both, the carbonatites and the associated silicate rocks, substantiates our fractionation model. Furthermore, carbonatite and silicate

  10. Magma mixing in late-stage granitoids of the Pioneer intrusive complex, south central Idaho and tectonic implications

    SciTech Connect

    Woods, A.J.; Geist, D. . Dept. of Geology)

    1993-04-01

    Eocene granitoids that intrude the Pioneer Mountain core complex, located approximately twenty miles northeast of Sun Valley, Idaho, grad west to east from mafic granodiorite to porphyritic quartz monzonite. The two main phases, porphyritic coarse-grained quartz monzonite and fine-grained granodiorite, exhibit field evidence suggestive of magma mixing as indicated by gradational contacts with swirling textures on scales from centimeters to tens of meters, and both phases are found as inclusion within each other. Generally, granodiorite intrudes quartz monzonite and may represent a late stage injection into the center of the semi-consolidated monzonitic magma. Petrological modeling indicates the hybrids are mixtures of the monzonite and granodiorite. Field and petrographic evidence suggest emplacement of the granitoids occurred before latest faulting, as demonstrated by a lack of contact metamorphic effects on the surrounding Paleozoic sediments. Moreover, the development of gneissic fabric, cataclastic and mylonitic fabrics, development of cross-cutting chlorite, epidote, and quartz veinlets, and brecciated fault contacts within the granitoids provide further support for Eocene emplacement prior to or contemporaneous with faulting. These observations provide additional constraints on the cessation of extensional tectonics in south central Idaho.

  11. Groundwater level changes in a deep well in response to a magma intrusion event on Kilauea Volcano, Hawai'i

    USGS Publications Warehouse

    Hurwitz, S.; Johnston, M.J.S.

    2003-01-01

    On May 21, 2001, an abrupt inflation of Kilauea Volcano's summit induced a rapid and large increase in compressional strain, with a maximum of 2 ??strain recorded by a borehole dilatometer. Water level (pressure) simultaneously dropped by 6 cm. This mode of water level change (drop) is in contrast to that expected for compressional strain from poroelastic theory, and therefore it is proposed that the stress applied by the intrusion has caused opening of fractures or interflows that drained water out of the well. Upon relaxation of the stress recorded by the dilatometer, water levels have recovered at a similar rate. The proposed model has implications for the analysis of ground surface deformation and for mechanisms that trigger phreatomagmatic eruptions.

  12. The effusive-explosive transitions at Rokatenda 2012-2013: unloading by extrusion of degassed magma with lateral gas flow

    NASA Astrophysics Data System (ADS)

    Primulyana, Sofyan; Bani, Philipson; Harris, Andrew

    2017-02-01

    Between October 2012 and August 2013, Rokatenda, one of the most poorly understood volcanoes in Indonesia, entered a phase of intense eruptive activity which involved extrusion of viscous lava, gas discharge and explosive activity. During the 10-month-long eruption, a lava volume of 2-5 × 106 m3 was extruded at mean output rate of 0.3 m3 s-1, with 2 to 3-month-long high extrusion rate phases being terminated by explosive events. Extrusion built a lava dome attaining a maximum height of ˜80 m above the crater rim, with a basal width of about 250 m. The composition of the 2012-2013 lava dome is comparable to that of the 1980 lava dome, both being andesite-trachydacite. Mineralogically, the 2012-2013 lava dome is mainly composed of plagioclase, pyroxene and an undetermined opaque mineral. Halogens released during eruption are consistent with the extrusion being fed, at least in the first eruption phase, by a degassed magma. This resulted in the formation of a dense, viscous plug in the conduit that led to a lateral gas flow, with gasses escaping around the plug to form multiple craters surrounding the dome. During the course of the eruptive activity, degassed magma was progressively forced out of the vent to unload deeper magma and force the system into an explosive phase. Such a scenario has occurred in the past at Rokatenda and is likely to be repeated in the future and creates an activity pattern that may be used to characterize such systems.

  13. Petrological constraints on the recycling of mafic crystal mushes, magma ascent and intrusion of braided sills in the Torres del Paine mafic complex (Patagonia)

    NASA Astrophysics Data System (ADS)

    Leuthold, Julien; Müntener, Othmar; Baumgartner, Lukas; Putlitz, Benita

    2014-05-01

    Cumulate and crystal mush disruption and reactivation are difficult to recognise in coarse grained shallow plutonic rocks. Mafic minerals included in hornblende and zoned plagioclase provide snapshots of early crystallization and cumulate formation, but are difficult to interpret in terms of the dynamics of magma ascent and possible links between silicic and mafic rock emplacement. We will present the field relations, the microtextures and the mineral chemistry of the Miocene mafic sill complex of the Torres del Paine intrusive complex (Patagonia, Chile) and its sub-vertical feeder-zone. The mafic sill complex was built up by a succession of braided sills of shoshonitic and high-K calc-alkaline porphyritic hornblende-gabbro and fine grained monzodioritic sills. The mafic units were over-accreted over 41±11 ka, underplating the overlying granite. Local diapiric structures and felsic magma accumulation between sills indicate limited separation of intercumulus liquid from the mafic sills. Anhedral hornblende cores, with olivine + clinopyroxene ± plagioclase ± apatite inclusions, crystallized at temperatures >900°C and pressures of ~300 to ~500 MPa. The corresponding rims and monzodiorite matrix crystallized at <830°C, ~70 MPa. This abrupt compositional variation suggests stability and instability of hornblende during mafic roots recycling and subsequent decompression. The near lack of intercumulus crystals in the sub-vertical feeder zone layered gabbronorite and pyroxene-hornblende gabbronorite stocks testifies that melt is more efficiently extracted than in sills, resulting in a cumulate signature in the feeding system. The emplacement age of the sill complex topmost granitic unit is identical, within uncertainties, to the feeder zone mafic cumulates. Granitic liquids formed by AFC processes and were extracted at high temperature (T>950°C) from the middle crust reservoir to the emplacement level. We show that hornblende-plagioclase thermobarometry is a useful

  14. A new interpretation of the structure of the Sept Iles Intrusive suite, Canada

    NASA Astrophysics Data System (ADS)

    Higgins, Michael D.

    2005-08-01

    chamber, indicating lateral transport of magma. Chemically distinct syenites in the upper part of the intrusion are part of the Point du Criade intrusion, a large, late composite sill. Diabase and leucogabbro components show a close link with the SIMI and all the acidic magmas may have originally formed by differentiation of the main magma in cupolas towards the centre of the intrusion. A series of late gabbro intrusions that cut the SIMI may represent a rejuvenation of magmatism. The Border zone is a mass of fine-grained rocks that occurs along the border of the SIMI: it may be another magmatic component, or just the lateral border series of the SIMI.

  15. Controls on intrusion of near-trench magmas of the Sanak-Baranof Belt, Alaska, during Paleogene ridge subduction, and consequences for forearc evolution

    USGS Publications Warehouse

    Kusky, Timothy M.; Bradley, Dwight C.; Donely, D. Thomas; Rowley, David; Haeussler, Peter J.

    2003-01-01

    have sheeted margins and appear to have intruded along extensional jogs in margin-parallel strike-slip faults, whereas others form significant angles with the main faults and may have been influenced by minor faults of other orientations. Some of the plutons of the Sanak-Baranof belt have their long axes oriented parallel to faults of an orthorhombic fault set, implying that these faults may have provided a conduit for magma emplacement. This orthorhombic set of late faults is interpreted to have initially formed during the ridge subduction event, and continued to be active for a short time after passage of the triple junction. ENE-striking dextral faults of this orthorhombic fault system exhibit mutually crosscutting relationships with Eocene dikes related to ridge subduction, and mineralized strike-slip and normal faults of this system have yielded 40Ar/39Ar ages identical to near-trench intrusives related to ridge subduction. Movement on the orthorhombic fault system accommodated exhumation of deeper levels of the southern Alaska accretionary wedge, which is interpreted as a critical taper adjustment to subduction of younger oceanic lithosphere during ridge subduction. These faults therefore accommodate both deformation of the wedge and assisted emplacement of near-trench plutons. Structures that crosscut the plutons and aureoles include the orthorhombic fault set and dextral strike-slip faults, reflecting a new kinematic regime established after ridge subduction, during underthrusting of the trailing oceanic plate with new dextral-oblique convergence vectors with the overriding plate. The observation that the orthorhombic fault set both cuts and is cut by Eocene intrusives demonstrates the importance of these faults for magma emplacement in the forearc.A younger, ca. 35 Ma suite of plutons intrudes the Chugach terrane in the Prince William Sound region, and their intrusion geometry was strongly influenced by pre-existing faults developed during ridge subduction

  16. Deformation of host rocks and flow of magma during growth of minette dikes and breccia-bearing intrusions near Ship Rock, New Mexico

    USGS Publications Warehouse

    Delaney, Paul T.; Pollard, David D.

    1981-01-01

    We have studied a small group of minette dikes and plugs that crop out within a flat-lying sequence of siltstone and shale near Ship Rock, a prominent volcanic throat of tuff breccia in northwestern New Mexico. Seven dikes form a radial pattern about Ship Rock we describe in detail the northeastern dike, which has an outcrop length of about 2,900 m, an average thickness of 2.3 m, and a maximum thickness of 7.2 m. The dike is composed of 35 discrete segments arranged in echelon; orientation. of dike segments ranges systematically from N. 52? E. to N. 66? E. A prominent joint set strikes parallel to the segments and is localized within several tens of meters of the dike. Regional joint patterns display no obvious relation to dike orientation. Small offsets of segment contacts, as well as wedge-shaped bodies of crumpled host rock within segments mark the sites of coalescence of smaller segments during dike growth. Bulges in the dike contact, which represent a nondilational component of growth, indicate that wall rocks were brecciated and eroded during the flow of magma. Breccias make up about 9 percent of the 7,176-m 2 area of the dike, are concentrated in its southwest half, and are commonly associated with its thickest parts. We also describe three subcircular plugs; each plug is smaller than 30 m in diameter, is laterally associated with a dike, and contains abundant breccias. Field evidence indicates that these plugs grew from the dikes by brecciation and erosion of wallrocks and that the bulges in the contact of the northeastern dike represent an initial stage of this process. From continuum-mechanical models of host-rock deformation, we conclude that dike propagation was the dominant mechanism for creating conduits for magma ascent where the host rock was brittle and elastic. At a given driving pressure, dikes dilate to accept greater volumes of magma than plugs, and for a given dilation, less work is done on the host rocks. In addition, the pressure required

  17. Important role of magma mixing in generating the Mesozoic monzodioritic-granodioritic intrusions related to Cu mineralization, Tongling, East China: Evidence from petrological and in situ Sr-Hf isotopic data

    NASA Astrophysics Data System (ADS)

    Chen, C. J.; Chen, B.; Li, Z.; Wang, Z. Q.

    2016-04-01

    The Mesozoic ore-bearing high-Mg monzodioritic-granodioritic rocks in the Tongling mining district (East China) have been described as having adakitic affinities, and their origin has been attributed to partial melting of delaminated eclogite at depth in the mantle, followed by interaction of the resultant granitic magma with mantle peridotite. Here we present petrological data and in situ Sr isotopic data for zoned plagioclase that are inconsistent with the eclogite-derived model and instead propose a model that involves magma mixing of siliceous crustal melts and basaltic magma that was derived from metasomatized mantle in a back-arc extensional regime. The principal geochemical signatures of these Mesozoic rocks include a high-K calc-alkaline affinity, high values of Mg#, high Sr-Ba abundances, high Sr/Y and La/Yb ratios, εNd(t) = - 13.1 to - 9.0, and ISr = 0.70707-0.70824. The magma mixing model is supported by (1) the common existence of mafic microgranular enclaves (MMEs) and the disequilibrium textures of plagioclase and amphibole, (2) the 87Sr/86Sr ratios of embayed high-Ca cores of plagioclase that are distinctly lower than in the euhedral low-Ca overgrowth rims, (3) the negative correlations between whole-rock Nd and Sr isotopic ratios, and (4) the significant differences in the values of εHf(t) (- 9.5 to - 26) within different zircons from the same intrusion.

  18. Important role of magma mixing in generating the Mesozoic monzodioritic-granodioritic intrusions related to Cu mineralization, Tongling, East China: evidence from petrological and in situ Sr-Hf isotopic data

    NASA Astrophysics Data System (ADS)

    Chen, Bin; Chen, ChangJian

    2016-04-01

    The Mesozoic ore-bearing high-Mg monzodioritic-granodioritic rocks in the Tongling mining district (East China) have been described as having adakitic affinities, and their origin has been attributed to partial melting of delaminated eclogite at depth in the mantle, followed by interaction of the resultant granitic magma with mantle peridotite. Here we present petrological data and in situ Sr isotopic data for zoned plagioclase that are inconsistent with the eclogite-derived model, and instead propose a model that involves magma mixing of siliceous crustal melts and basaltic magma that was derived from metasomatized mantle by subduction zone fluids in an extensional regime. The principal geochemical signatures of these Mesozoic rocks include a hydrous and high-K calc-alkaline affinity, high values of Mg#, high Sr abundances, high Sr/Y and La/Yb ratios, ɛNd(t)=-13.1 to -9.0, and ISr=0.70707-0.70824. The magma mixing model is supported by (1) the common existence of mafic microgranular enclaves (MMEs) and the disequilibrium textures of plagioclase and hornblende, (2) the increase in Ti and Al(IV) from hornblende cores to rims, and the overgrowths of high-Ca pyroxene around hornblende grains as well, indicative of episode of heating and rejuvenation of the magma chamber as a result of recharge of mafic magma, (3) the 87Sr/86Sr ratios of embayed high-Ca cores of plagioclase that are distinctly lower than in the euhedral low-Ca overgrowth rims, (4) negative correlations between whole-rock Nd and Sr isotopic ratios, and (5) the significant differences in the values of ɛHf(t) (-9.5 to -26) within different zircons from the same intrusion. We propose that underplating of hydrous basaltic magma from the metasomatized lithospheric mantle in the lower crust resulted in partial melting of the lower crustal rocks (Precambrian TTG gneisses and amphibolite/granulite) under water-saturated conditions, during which plagioclase decomposed, leaving hornblende-rich restites and

  19. Underplating of basaltic magmas and crustal growth in a continental arc: Evidence from Late Mesozoic intermediate-felsic intrusive rocks in southern Qiangtang, central Tibet

    NASA Astrophysics Data System (ADS)

    Hao, Lu-Lu; Wang, Qiang; Wyman, Derek A.; Ou, Quan; Dan, Wei; Jiang, Zi-Qi; Wu, Fu-Yuan; Yang, Jin-Hui; Long, Xiao-Ping; Li, Jie

    2016-02-01

    Phanerozoic growth of continental crust has widely been considered as an important geological phenomenon and mainly occurs in an arc setting. However, the crustal growth models (mantle-derived basalt underplating or accretion of island or intra-oceanic arc complexes or oceanic plateau) have been disputed. Here we present new zircon LA-ICPMS U-Pb age, whole-rock major and trace element, Sr-Nd and zircon Hf isotopic data for Late Mesozoic intermediate-felsic intrusive rocks in the Rena Co area in southern Qiangtang, central Tibet. LA-ICP-MS zircon U-Pb dating for two granodiorite and three diorite samples and one granodiorite porphyry sample gives ages of ca. 150 Ma, ca. 112 Ma, respectively, indicating they were generated in the Late Jurassic-Early Cretaceous. All rocks are sub-alkaline in composition and belong to the high-K cal-alkaline series. The ~ 150 Ma diorites (SiO2 = 57.9-61.2 wt.%) exhibit relatively high MgO (3.13-3.88 wt.%) and Cr (52.4-282 ppm) contents and Mg# (47-51) values, similar to magnesian diorites. They are geochemically characterized by uniformly low εNd(t) (- 5.5 to - 5.2), high (87Sr/86Sr)i (0.7071 to 0.7078) and Th/La (0.22-0.32), and variable zircon εHf(t) (- 8.7 to + 4.8) values. They were probably generated by melting of oceanic sediment diapirs, followed by interaction with the surrounding mantle during the northward subduction of Bangong-Nujiang Oceanic lithosphere. The ~ 150 Ma granodiorites and ~ 112 Ma granodiorite porphyries are characterized by low MgO (< 3 wt.%) contents and Mg# (< 45) values, high Al2O3 (> 15% wt.%) and Sr (> 400 ppm) and low Y (< 18 ppm) and Yb (< 1.9 ppm) contents, and high Sr/Y and La/Yb ratios, which are similar to those of typical adakites. The granodiorites have low εNd(t) (- 7.6 to - 3.7) and zircon εHf(t) (- 9.8 to + 0.2) and high (87Sr/86Sr)i (0.7069 to 0.7086) values, and were likely produced by partial melting of a thickened and heterogeneous ancient lower continental crust. The relatively

  20. Evidence for multiple mechanisms of crustal contamination of magma from compositionally zoned plutons and associated ultramafic intrusions of the Alaska Range

    USGS Publications Warehouse

    Reiners, P.W.; Nelson, B.K.; Nelson, S.W.

    1996-01-01

    Models of continental crustal magmagenesis commonly invoke the interaction of mafic mantle-derived magma and continental crust to explain geochemical and petrologic characteristics of crustal volcanic and plutonic rocks. This interaction and the specific mechanisms of crustal contamination associated with it are poorly understood. An excellent opportunity to study the progressive effects of crustal contamination is offered by the composite plutons of the Alaska Range, a series of nine early Tertiary, multiply intruded, compositionally zoned (peridotite to granite) plutons. Large initial Sr and Nd isotopic contrasts between the crustal country rock and likely parental magmas allow evaluation of the mechanisms and extents of crustal contamination that accompanied the crystallization of these ultramafic through granitic rocks. Three contamination processes are distinguished in these plutons. The most obvious of these is assimilation of crustal country rock concurrent with magmatic fractional crystallization (AFC), as indicated by a general trend toward crustal-like isotopic signatures with increasing differentiation. Second, many ultramafic and mafic rocks have late-stage phenocryst reaction and orthocumulate textures that suggest interaction with felsic melt. These rocks also have variable and enriched isotopic compositions that suggest that this felsic melt was isotopically enriched and probably derived from crustal country rock. Partial melt from the flysch country rock may have reacted with and contaminated these partly crystalline magmas following the precipitation and accumulation of the cumulus phenocrysts but before complete solidification of the magma. This suggests that in magmatic mush (especially of ultramafic composition) crystallizing in continental crust, a second distinct process of crustal contamination may be super-imposed on AFC or magma mixing involving the main magma body. Finally, nearly all rocks, including mafic and ultramafic rocks, have (87Sr

  1. 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.

  2. Magma-mixing in the genesis of Hercynian calc-alkaline granitoids: an integrated petrographic and geochemical study of the Sázava intrusion, Central Bohemian Pluton, Czech Republic

    NASA Astrophysics Data System (ADS)

    Janoušek, Vojtěch; Braithwaite, Colin J. R.; Bowes, D. R.; Gerdes, Axel

    2004-10-01

    The Devonian-early Carboniferous (354.1±3.5 Ma: conventional zircon U-Pb age) Sázava intrusion (biotite-amphibole quartz diorite, tonalite and granodiorite) of the Central Bohemian Pluton (CBP) associated with bodies of (olivine, pyroxene-) amphibole gabbro, gabbrodiorite, (quartz) diorite and rare hornblendite, gives an opportunity for a comparative study of a rather shallow, calc-alkaline magma-mixing zone at two levels, separated by a vertical difference of approximately 1 km. The deeper section (Příbram) displays the direct evidence for the existence of a long-lived, periodically tapped and replenished, floored magma chamber (MASLI). The contacts between the subhorizontal sheet-like basic bodies and the surrounding, commonly cumulus-rich, Sázava granitoid, are arcuate, and cut by a series of veins and ascending pipes. Shallow-dipping swarms of strongly elongated and flow-aligned mafic microgranular enclaves (MME), concordant with the contacts of the basic bodies, are commonplace. The higher level (Teletín) section shows relatively independent basic intrusions, some of them distinctly hybrid in character and mainly of quartz dioritic composition, surrounded by relatively homogeneous, nearly cumulus-free Sázava tonalite rich in texturally variable MME. Larger quartz microdiorite bodies and the MME, both interpreted as hybrids, contain varying proportions of highly heterogeneous plagioclase megacrysts with complex zoning, particularly well shown by cathodoluminescence (CL). Most often the megacrysts have cores of labradorite-anorthite, partly resorbed and overgrown by andesine rims but some are strongly brecciated and fragments have been annealed by rim growth. Also characteristic are long prisms of apatite, oikocrysts of quartz and K-feldspar and zoned amphibole. The latter has brown pargasite and magnesiohastingsite cores, resorbed and overgrown by magnesiohornblende, compositionally similar to the amphibole in the Sázava tonalite. The brown cores are

  3. Long-term changes in quiescent degassing at Mount Baker Volcano, Washington, USA; Evidence for a stalled intrusion in 1975 and connection to a deep magma source

    USGS Publications Warehouse

    Werner, C.; Evans, William C.; Poland, M.; Tucker, D.S.; Doukas, M.P.

    2009-01-01

    Long-term changes have occurred in the chemistry, isotopic ratios, and emission rates of gas at Mount Baker volcano following a major thermal perturbation in 1975. In mid-1975 a large pulse in sulfur and carbon dioxide output was observed both in emission rates and in fumarole samples. Emission rates of CO2 and H2S were ??? 950 and 112??t/d, respectively, in 1975; these decreased to ??? 150 and < 1??t/d by 2007. During the peak of the activity the C/S ratio was the lowest ever observed in the Cascade Range and similar to magmatic signatures observed at other basaltic-andesite volcanoes worldwide. Increases in the C/S ratio and decreases in the CO2/CH4 ratio since 1975 suggest a long steady trend back toward a more hydrothermal gas signature. The helium isotope ratio is very high (> 7??Rc/RA), but has declined slightly since the mid-1970s, and ??13C-CO2 has decreased by ??? 1??? over time. Both trends are expected from a gradually crystallizing magma. While other scenarios are investigated, we conclude that magma intruded the mid- to shallow-crust beneath Mount Baker during the thermal awakening of 1975. Since that time, evidence for fresh magma has waned, but the continued emission of CO2 and the presence of a long-term hydrothermal system leads us to suspect some continuing connection between the surface and deep convecting magma.

  4. Mafic intrusions triggering eruptions in Iceland

    NASA Astrophysics Data System (ADS)

    Sigmarsson, O.

    2012-04-01

    The last two eruptions in Iceland, Eyjafjallajökull 2010 and Grímsvötn 2011, were both provoked by an intrusion of more mafic magma into pre-existing magmatic system. Injection into the latter volcano, which is located in the main rift-zone of the island, above the presumed centre of the mantle plume and is the most active volcano of Iceland, has been gradual since the last eruption in 2004. In contrast, at Eyjafjallajökull volcano, one of the least active volcano in Iceland and located at the southern part of a propagating rift-zone where extensional tectonics are poorly developed, mafic magma intrusion occurred over less than a year. Beneath Eyjafjallajökull, a silicic intrusion at approximately 6 km depth was recharged with mantle derived alkali basalt that was injected into residual rhyolite from the penultimate eruption in the years 1821-23. The resulting magma mingIing process was highly complex, but careful sampling of tephra during the entire eruption allows the dynamics of the mingling process to be unravelled. Short-lived disequilibria between the gaseous nuclide 210Po and the much less volatile nuclide 210Pb, suggest that basalt accumulated beneath the silicic intrusion over approximately 100 days, or from early January 2010 until the onset of the explosive summit eruption on 14 April. Due to the degassing, crystal fractionation modified the composition of the injected mafic magma producing evolved Fe-and Ti-rich basalt, similar in composition to that of the nearby Katla volcano. This evolved basalt was intruded into the liquid part of the silicic intrusion only a few hours before the onset of the explosive summit eruption. The short time between intrusion and eruption led to the production of very heterogeneous (of basaltic, intermediate and silicic composition) and fine-grained tephra during the first days of explosive eruption. The fine grained tephra resulted from combined effects of magma fragmentation due to degassing of stiff magma rich in

  5. The Sonju Lake layered intrusion, northeast Minnesota: Internal structure and emplacement history inferred from magnetic fabrics

    USGS Publications Warehouse

    Maes, S.M.; Tikoff, B.; Ferre, E.C.; Brown, P.E.; Miller, J.D.

    2007-01-01

    The Sonju Lake intrusion (SLI), in northeastern Minnesota, is a layered mafic complex of Keweenawan age (1096.1 ?? 0.8 Ma) related to the Midcontinent rift. The cumulate paragenesis of the intrusion is recognized as broadly similar to the Skaergaard intrusion, a classic example of closed-system differentiation of a tholeiitic mafic magma. The SLI represents nearly closed-system differentiation through bottom-up fractional crystallization. Geochemical studies have identified the presence of a stratabound, 50-100 m thick zone anomalously enriched in Au + PGE. Similar to the PGE reefs of the Skaergaard intrusion, this PGE-enriched zone is hosted within oxide gabbro cumulates, about two-third of the way up from the base of the intrusion. We present a petrofabric study using the anisotropy of magnetic susceptibility (AMS) to investigate the emplacement and flow patterns within the Sonju Lake intrusion. Petrographic and electron microprobe studies, combined with AMS and hysteresis measurements indicate the primary source of the magnetic signal is pseudo-single domain (PSD) magnetite or titanomagnetite. Low field AMS was measured at 32 sites within the Sonju Lake intrusion, which provided information about primary igneous fabrics. The magnetic fabrics in the layered series of the Sonju Lake intrusion are consistent with sub-horizontal to inclined emplacement of the intrusion and show evidence that the cumulate layers were deposited in a dynamic environment. Well-aligned magnetic lineations, consistently plunging shallowly toward the southwest, indicate the source of the magma is a vertical sill-like feeder, presumably located beneath the Finland granite. The Finland granite acted as a density trap for the Sonju Lake magmas, forcing lateral flow of magma to the northeast. The strongly oblate magnetic shape fabrics indicate the shallowly dipping planar fabrics were enhanced by compaction of the crystal mush. ?? 2007 Elsevier B.V. All rights reserved.

  6. Flow dynamics in mid-Jurassic dikes and sills of the Ferrar large igneous province and implications for long-distance magma transport

    NASA Astrophysics Data System (ADS)

    Airoldi, Giulia M.; Muirhead, James D.; Long, Sylvan M.; Zanella, Elena; White, James D. L.

    2016-06-01

    Magma flow paths in sill-fed dikes of the Ferrar large igneous province (LIP), contrast with those predicted by classic models of dike transport in LIPs and magmatic rift settings. We examine anisotropy of magnetic susceptibility (AMS) flow paths in dike networks at Terra Cotta Mountain and Mt. Gran, which intruded at paleodepths of 2.5 and 1.5 km. These intrusions (up to 30 m thick) exhibit irregular, interconnected dike-sill geometries and adjoin larger sills ( 200-300 m thick) at different stratigraphic levels. Both shallowly dipping and sub-vertical magma flow components are interpreted from AMS measurements across individual intrusions, and often match macroscopic flow indicators and variations in dike attitudes. Flow paths suggest that intrusive patterns and magma flow directions depended on varying stress concentrations and rotations during dike and sill propagation, whereas a regional extensional tectonic control was negligible or absent. Unlike giant dike swarms in LIPs elsewhere (e.g., 1270 Ma MacKenzie LIP), dikes of the Ferrar LIP show no regionally consistent vertical or lateral flow patterns, suggesting these intrusion were not responsible for long-distance transport in the province. In the absence of regionally significant, colinear dike swarms, or observed intrusions at crustal depths ≥ 4 km, we suggest that long distance magma transport occurred in sills within Beacon Supergroup sedimentary rocks. This interpretation is consistent with existing geochemical data and thermal constraints, which support lateral magma flow for 3,500 km across the Gondwana supercontinent before freezing.

  7. 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

  8. A General Model for Shallow Magmatic Intrusions

    NASA Astrophysics Data System (ADS)

    Thorey, C.; Michaut, C.

    2015-12-01

    Shallow magmatic intrusions make room for themselves by upward bending of the elastic overburden. Previous studies have shown that the bending of the overlying layer first controls the dynamics. Then, when the radius reaches a few times the flexural wavelength of the overburden, it transitions to a gravity current regime. This model predicts the appropriate geometry for both terrestrial laccoliths and large mafic sills. However, it underestimates the absolute dimensions of these magmatic intrusions; in particular, it requires abnormally high viscosity to reconcile both observations and predictions. To get some insights into the effective flow viscosity, we develop a model that account for the cooling of such elastic-plated gravity currents. We show that the coupling between the temperature field and the flow itself leads to the formation of a highly viscous region at the tip that slows down the spreading in both regimes. The intrusions are predicted to be thicker and their dimensions, especially in the bending regime, are now consistent with observations. By introducing the potentially complex structure of the overburden, we also show that the topography largely contributes to constrain the final intrusion morphology. For instance, in the case of an intrusion centered below a circular depression, the model predicts that the lithostatic increase at the crater rim prevents the magma from spreading laterally and enhances the thickening of the intrusion. This model has already proven successful in reproducing the deformations observed on potential intrusion centered below lunar impact craters. Caldera complexes often exhibit ground deformations that might be associated to the formation of shallow magmatic intrusions. InSAR imaging and GPS measurements now provide efficient tools to monitor these deformations. We conclude this study by examining the ability of the model to reproduce the deformation observed in several caldera complexes.

  9. Late Eocene-Oligocene post-collisional monzonitic intrusions from the Alborz magmatic belt, NW Iran. An example of monzonite magma generation from a metasomatized mantle source

    NASA Astrophysics Data System (ADS)

    Castro, Antonio; Aghazadeh, Mehraj; Badrzadeh, Zahra; Chichorro, Martim

    2013-11-01

    A potassic magmatic association in the Zagros hinterland of the Tethyan orogen in Iran is identified and characterized for relevant geochronologic and petrologic features. New data, including a combination of field relations, U-Pb zircon geochronology and rock geochemistry, come from seven plutons (Khankandi, Shaivar-Dagh, Yuseflu, Mizan, Saheb-Divan, Roudbar and Abhar) that form the Arasbaran-Taroum batholith (ATB), which forms part of the Alborz magmatic belt (AMB) of NW Iran. Zircon SHRIMP ages range from 38.32 ± 0.17 Ma, 38.94 ± 0.42 Ma and 37.78 ± 0.28 Ma for magma pulses of the Abhar pluton, at the East of the batholith, to 24.51 ± 0.27 Ma and 23.55 ± 0.47 Ma for pulses of the Mizan pluton at the West. Considering these ages and the previously published ones together, emplacement of the batholith took place during Late Eocene and Oligocene, from 38 to 23 Ma, with an age progression from SE to NW at a rate of 2 cm/year. The whole batholith is characterized by potassic rocks with K2O > 2 wt.% in gabbros and diorites (SiO2 < 50 wt.%). Higher contents of K2O, of up to > 6 wt.%, are normally found in rocks with intermediate silica contents of about 60 wt.% SiO2. These intermediate silica rocks are truly monzonites and are the most abundant in each pluton. With regard to trace elements, the monzonitic rocks of the ATB show some of the typical signatures of arc magmatism (depletion in Nb and Ti). Most samples contain moderate contents of Sr (500-800 ppm), close to similar potassic magmas forming Cenozoic complexes in Central Iran. The relatively moderate Sr/Y and La/Yb ratios suggest that ATB magmas retain some adakitic signatures from the source region. Geochemical modeling is performed by using melt compositions and phase relations calculated with MELTS software, combined with experimental data and trace element signatures. We conclude that monzonitic and shoshonitic magmas of some plutons of the ATB (Shaivar-Dagh, Kahnkandi and Yuseflu) have an adakitic

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

    NASA Astrophysics Data System (ADS)

    Rohrman, M.

    2015-12-01

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

  11. Evidence of magma intrusion at Fourpeaked volcano, Alaska in 2006-2007 from a rapid-response seismic network and volcanic gases

    USGS Publications Warehouse

    Gardine, M.; West, M.; Werner, C.; Doukas, M.

    2011-01-01

    On September 17th, 2006, Fourpeaked volcano had a widely-observed phreatic eruption. At the time, Fourpeaked was an unmonitored volcano with no known Holocene activity, based on limited field work. Airborne gas sampling began within days of the eruption and a modest seismic network was installed in stages. Vigorous steaming continued for months; however, there were no further eruptions similar in scale to the September 17 event. This eruption was followed by several months of sustained seismicity punctuated by vigorous swarms, and SO2 emissions exceeding a thousand tons/day. Based on observations during and after the phreatic eruption, and assuming no recent pre-historical eruptive activity at Fourpeaked, we propose that the activity was caused by a minor injection of new magma at or near 5km depth beneath Fourpeaked, which remained active over several months as this magma equilibrated into the crust. By early 2007 declining seismicity and SO2 emission signaled the end of unrest. Because the Fourpeaked seismic network was installed in stages and the seismicity was punctuated by discrete swarms, we use Fourpeaked to illustrate quantitatively the efficacy and shortcomings of rapid response seismic networks for tracking volcanic earthquakes.

  12. When Magma Might but Doesn't Erupt

    NASA Astrophysics Data System (ADS)

    Newhall, C.

    2008-12-01

    whammy. Magma can also enter relatively deformable structures, e.g., rift zones where it can move laterally more easily than it can ascend, or be slowed by layered soft and hard rock (Gudmundsson and Brenner, GRL 2004), increasing the chances of (a) and (b). Opportunities abound for ascending magma to stall; indeed, judging from the number of earthquake swarms and other potential indicators of magma ascent vs actual eruption, the majority of intrusions stall without erupting. Some patterns of unrest suggest that rising magma may abort before reaching the surface but these hints are non-unique. Low initial gas contents and slow rates of ascent increase chances of failure. Nishimura (GRL 2006) inferred that deformation will be constant (rather than accelerate) if magma nearing the surface has already been degassing. The same may hold for seismicity that's directly related to dike intrusion. Interpretation of degassing is tricky. Strong and constant or slowing gas emission that accompanies constant deformation increases the chance that degassing will freeze the magma before it can erupt. In contrast, strong and accelerating degassing that accompanies accelerating deformation may indicate a runaway approach to eruption, as may unusually low gas emission during accelerating deformation if the conduit is still plugged. Accelerated degassing can also occur when a dry chimney develops through water-saturated country rock, with or without deformation. Low (acid) gas emission by itself tells us little, as it can be scrubbed into groundwater. Those interpreting unrest need to consider all possible outcomes, including both total failure to erupt and the possibility that what looks like a failed eruption today may be on hold and may yet occur.

  13. Timing of magmatism following initial convergence at a passive margin, southwestern U.S. Cordillera, and ages of lower crustal magma sources

    USGS Publications Warehouse

    Barth, A.P.; Wooden, J.L.

    2006-01-01

    Initiation of the Cordilleran magmatic arc in the southwestern United States is marked by intrusion of granitic plutons, predominantly composed of alkali-calcic Fe- and Sr-enriched quartz monzodiorite and monzonite, that intruded Paleoproterozoic basement and its Paleozoic cratonal-miogeoclinal cover. Three intrusive suites, recognized on the basis of differences in high field strength element and large ion lithophile element abundances, contain texturally complex but chronologically distinctive zircons. These zircons record heterogeneous but geochemically discrete mafic crustal magma sources, discrete Permo-Triassic intrusion ages, and a prolonged postemplacement thermal history within the long-lived Cordilleran arc, leading to episodic loss of radiogenic Pb. Distinctive lower crustal magma sources reflect lateral heterogeneity within the composite lithosphere of the Proterozoic craton. Limited interaction between derived magmas and middle and upper crustal rocks probably reflects the relatively cool thermal structure of the nascent Cordilleran continental margin magmatic arc. ?? 2006 by The University of Chicago. All rights reserved.

  14. 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

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

    USGS Publications Warehouse

    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.

  16. 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

    2016-08-25

    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.

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

    NASA Astrophysics Data System (ADS)

    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

    2016-08-01

    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.

  18. Quantification of the intrusion process at Kīlauea volcano, Hawai'i

    NASA Astrophysics Data System (ADS)

    Wright, Thomas L.; Marsh, Bruce

    2016-12-01

    The characteristic size of two types of intrusions identified beneath Kīlauea's East Rift zone are uniquely estimated by combining time constraints from fractional crystallization and the rates of magma solidification during cooling. Some intrusions were rapidly emplaced as dikes, but stalled before reaching the surface, and cooled and crystallized to feed later fractionated eruptions. More specifically, using the observed time interval between initial emplacement and eruption of fractionated lava, whose degree of fractionation is estimated from petrologic mixing calculations, the extent of solidification or cooling needed to produce this amount of fractionation can be directly inferred. And from the known erupted volumes the spatial extent or size of this fractionated volume can be analytically related to the full size of the source body itself. Two examples yield dike widths of 82 and 68 m. Other intrusions remain close to the east rift magma transport path and are observed to last for decades or longer as viable magma bodies that may participate in feeding later eruptions. The thickness of semi-permanent reservoirs near the East Rift Zone magma transport path can be estimated by assuming a resupply rate that is sufficiently frequent to restrict cooling to < 10 °C. It is inferred that both types of intrusions likely began as dike offshoots from the East Rift Zone magma transport path, but the frequently resupplied bodies may have later been converted to sills or laccoliths of heights estimated at 43-62 m. Our modeled intrusions contrast with models of rapidly emplaced thinner dikes feeding shallow intrusions, which are accompanied by intense rift earthquake swarms and are often associated with eruptions. These calculations show that long-term heating of the wallrock of the magma transport paths serves to slow conduit cooling, which may be partly responsible for sustaining long East Rift Zone eruptions. Adjacent to the vertical transport path beneath K

  19. Linking magma transport structures at Kīlauea volcano

    NASA Astrophysics Data System (ADS)

    Wech, Aaron G.; Thelen, Weston A.

    2015-09-01

    Identifying magma pathways is important for understanding and interpreting volcanic signals. At Kīlauea volcano, seismicity illuminates subsurface plumbing, but the broad spectrum of seismic phenomena hampers event identification. Discrete, long-period (LP) events dominate the shallow (5-10 km) plumbing, and deep (40+ km) tremor has been observed offshore. However, our inability to routinely identify these events limits their utility in tracking ascending magma. Using envelope cross-correlation, we systematically catalog non-earthquake seismicity between 2008 and 2014. We find that the LPs and deep tremor are spatially distinct, separated by the 15-25 km deep, horizontal mantle fault zone (MFZ). Our search corroborates previous observations, but we find broader band (0.5-20 Hz) tremor comprising collocated earthquakes and reinterpret the deep tremor as earthquake swarms in a volume surrounding and responding to magma intruding from the mantle plume beneath the MFZ. We propose that the overlying MFZ promotes lateral magma transport, linking this deep intrusion with Kīlauea's shallow magma plumbing.

  20. Linking magma transport structures at Kīlauea volcano

    USGS Publications Warehouse

    Wech, Aaron G.; Thelen, Weston A.

    2015-01-01

    Identifying magma pathways is important for understanding and interpreting volcanic signals. At Kīlauea volcano, seismicity illuminates subsurface plumbing, but the broad spectrum of seismic phenomena hampers event identification. Discrete, long-period events (LPs) dominate the shallow (5-10 km) plumbing, and deep (40+ km) tremor has been observed offshore. However, our inability to routinely identify these events limits their utility in tracking ascending magma. Using envelope cross-correlation, we systematically catalog non-earthquake seismicity between 2008-2014. We find the LPs and deep tremor are spatially distinct, separated by the 15-25 km deep, horizontal mantle fault zone (MFZ). Our search corroborates previous observations, but we find broader-band (0.5-20 Hz) tremor comprising collocated earthquakes and reinterpret the deep tremor as earthquake swarms in a volume surrounding and responding to magma intruding from the mantle plume beneath the MFZ. We propose the overlying MFZ promotes lateral magma transport, linking this deep intrusion with Kīlauea’s shallow magma plumbing.

  1. Enhanced anatexis as a consequence of mantle-derived magma intrusion in the middle crust: a case study from the Eastern French Massif Central

    NASA Astrophysics Data System (ADS)

    Couzinié, Simon; Moyen, Jean-François; Villaros, Arnaud; Paquette, Jean-Louis; Scarrow, Jane H.; Marignac, Christian

    2014-05-01

    anatectic melts, as well as the presence of hybrid granitoids including a 'vaugnerite' component. In situ (LA-ICP-MS) U-Pb zircon and monazite dating of vaugnerites or coeval granites in the Southern Velay area yielded ages mostly indistinguishable within analytical uncertainties, spanning from 307.4 ± 1.8 to 303.7 ± 3.1 Ma. Thus, mantle-derived magmas emplaced at ca. 305 Ma which is the very transition from M3 to M4. This striking synchronism between enhanced crustal melting and mantle-derived magmatism suggests that vaugnerites could be the cause of the M3-M4 transition. Depending on the volume involved, the emplacement of hot (ca. 1000 ° C) melts in mid crustal levels would have supplied significant amounts of heat. Vaugnerites could also be the manifestation of a (yet unconstrained) process enhancing the conductive mantle heat flux to the crust. For instance, delamination of a lithospheric mantle root or slab break-off would result in generation of mantle-derived melts as well as increase the heat conduction into the crust. Therefore, the relevant system that must be considered to study late-orogenic periods is not only the crust but the whole lithosphere, taking into account mass/heat transfer from the mantle to the overlying crust.

  2. Granitic magma emplacement and deformation during early-orogenic syn-convergent transtension: The Staré Sedlo complex, Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Tomek, Filip; Žák, Jiří; Chadima, Martin

    2015-07-01

    The Late Devonian Staré Sedlo complex, Bohemian Massif, was emplaced as a subhorizontal sheeted sill pluton into a transtension zone. The transtensional setting is documented by strong constrictional fabric, corroborated by the anisotropy of magnetic susceptibility (AMS), with variably developed subhorizontal magmatic to solid-state foliation suggesting vertical shortening. Intrusive contacts of the granitoids with metapelitic screens and tapered sill tips indicate that magma wedging was the dominant process of sill propagation. The sills exhibit two intrusive styles, ranging from thin lit-par-lit injections to widely spaced meter-thick sills. These two styles are interpreted as reflecting variable viscosities of intruding magma where low-viscosity magma percolated along foliation planes whereas high-viscosity magma produced more localized thicker sills. We propose that the magma/host rock system in transtension must have evolved from initial crack tip propagation and vertical expansion due to new magma additions through conduit flow to ductile thinning after the magma input had ceased. The sill emplacement and their subsequent deformation are then interpreted as recording early-orogenic syn-convergent sinistral transtension along the rear side of an upper-crustal wedge, which was extruded both upward and laterally in response to subduction and continental underthrusting.

  3. Hindered settling and the formation of layered intrusions

    NASA Astrophysics Data System (ADS)

    Bons, Paul D.; Baur, Albrecht; Elburg, Marlina A.; Lindhuber, Matthias J.; Marks, Michael A. W.; Soesoo, Alvar; van Milligen, Boudewijn P.; Walte, Nicolas P.

    2015-04-01

    Layered intrusions are characterized by (often repetitive) layering on a range of scales. Many explanations for the formation of such layering have been proposed over the past decades. We investigated the formation of "mats" by hindered crystal settling, a model that was first suggested by Lauder (1964). The interaction of sinking and rising crystals leads to the amplification of perturbations in crystal density within a magma chamber, a process similar to the formation of traffic jams in dense traffic (Bons et al., 2015). Once these "crystal traffic jams" form they constitute a barrier for further settling of crystals. Between these barriers, the magma evolves in a semi-closed system in which stratification may develop by gravitational sorting. Barriers, and therefore layers, form sequentially during inward cooling of the magma chamber. Barring later equilibration, mineralogical and geochemical trends within the layers are repetitive, but with variations due to the random process of initial perturbation formation. Layers can form in the transition between two end-member regimes: (1) in a fast cooling and/or viscous magma crystals cannot sink or float a significant distance and minerals are distributed homogeneously throughout the chamber; (2) in a slow cooling and/or low-viscosity magma crystals can quickly settle at the top and bottom of the chamber and crystals concentrations are never high enough to form "traffic jams". As a result, heavy and light minerals get fully separated in the chamber. Between these two end members, crystals can sink and float a significant distance, but not the whole height of the magma chamber before entrapment in "traffic jams". We illustrate the development of layers with numerical models and compare the results with the layered nepheline syenites (kakortokites) of the Ilímaussaq intrusion in SW Greenland. References: Bons, P.D., Baur, A., Elburg, M.A., Lindhuber, M.J., Marks, M.A.W., Soesoo, A., van Milligen, B.P., Walte, N.P. 2015

  4. 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

  5. Lunar Intrusive Domes on the Floor of Grimaldi and Near Aristillus

    NASA Astrophysics Data System (ADS)

    Wöhler, C.; Lena, R.; Pau, K. C.

    2010-03-01

    In this contribution we examine two large lunar domes of probably intrusive origin. The morphometric properties of the domes are derived, and geophysical parameters (intrusion depth, magma pressure) are estimated based on modelling.

  6. Crystals in magma chambers

    NASA Astrophysics Data System (ADS)

    Higgins, M.

    2011-12-01

    few crystals, in contrast to lavas from the same volcanoes. Hence, crystallisation must be a high-level process before eruption. Layering in mafic intrusions has many different origins, but some appears to be the result of crystal settling. If such mineralogical layering is present then so must crystals have been present in the magma. However, it is only necessary that crystals are present in local regions, such as along the floor, walls or roof. All this suggests that most mafic or intermediate magmas in chambers do not have substantial quantities of crystals, except at the peripheries. Felsic (sensu lato) rocks present a rather different story: Although there are many examples of low-crystallinity felsic tuffs and lavas, there are also large ignimbrites with high crystal contents, such as the Fish Canyon tuff. Indeed a 'typical' andesite or dacite is loaded with crystals, generally with long and complex histories. The widespread occurrence of megacrysts in felsic plutonic, and some volcanic, rocks also suggests that crystals are present in magma chambers and can exist for extended periods of time. This would suggest that it is possible, and indeed common, for a felsic magma chamber to have crystals throughout. The difficulty here for differentiation is the high viscosity of such magmas.

  7. Rapid laccolith intrusion driven by explosive volcanic eruption

    NASA Astrophysics Data System (ADS)

    Castro, Jonathan M.; Cordonnier, Benoit; Schipper, C. Ian; Tuffen, Hugh; Baumann, Tobias S.; Feisel, Yves

    2016-11-01

    Magmatic intrusions and volcanic eruptions are intimately related phenomena. Shallow magma intrusion builds subsurface reservoirs that are drained by volcanic eruptions. Thus, the long-held view is that intrusions must precede and feed eruptions. Here we show that explosive eruptions can also cause magma intrusion. We provide an account of a rapidly emplaced laccolith during the 2011 rhyolite eruption of Cordón Caulle, Chile. Remote sensing indicates that an intrusion began after eruption onset and caused severe (>200 m) uplift over 1 month. Digital terrain models resolve a laccolith-shaped body ~0.8 km3. Deformation and conduit flow models indicate laccolith depths of only ~20-200 m and overpressures (~1-10 MPa) that likely stemmed from conduit blockage. Our results show that explosive eruptions may rapidly force significant quantities of magma in the crust to build laccoliths. These iconic intrusions can thus be interpreted as eruptive features that pose unique and previously unrecognized volcanic hazards.

  8. Magma flow and thermal contraction fabric in tabular intrusions inferred from AMS analysis. A case study in a late-Variscan folded sill of the Albarracín Massif (southeastern Iberian Chain, Spain)

    NASA Astrophysics Data System (ADS)

    Gil-Imaz, A.; Pocoví, A.; Lago, M.; Galé, C.; Arranz, E.; Rillo, C.; Guerrero, E.

    2006-04-01

    The effects of different petrological processes on the rock fabric of a folded sill from the Albarracin Massif (southeastern Iberian Chain, Spain) were studied by means of the anisotropy of magnetic susceptibility (AMS) technique. The most outstanding feature of the sill at outcrop-scale is a network of joints linked to thermal contraction, which define polygonal columns. The analysis of the magnetic fabric, taking the orientation of sill walls and column axes as a reference and using the 'restored' directional data corresponding to the whole of K3 susceptibility axes, has revealed magnetic fabrics related to two processes: (a) magma flow with a SW-trending flow vector characterized by a curved geometry of the magma foliations and (b) thermal contraction coeval to lava cooling. Early magnetite crystals, grown in a relatively high viscosity calc-alkaline magma, are the main carriers involved in the AMS fabric. Passive rotation of the early magnetic mineralogy within a medium-viscosity magma explains the magnetic fabric linked to both magma flow and near-solidus thermal contraction of the magma. Late-Variscan folding of the sill produced the rigid-body reorientation of the magnetic fabric.

  9. 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

  10. Death Valley bright spot: a midcrustal magma body in the southern Great Basin, California

    SciTech Connect

    de Voogd, B.; Serpa, L.; Brown, L.; Hauser, E.; Kaufman, S.; Oliver, J.; Troxel, B.W.; Willemin, J.; Wright, L.A.

    1986-01-01

    A previously unrecognized midcrustal magma body may have been detected by COCORP deep seismic reflection profiles in the Death Valley region of the southern Great Basin. High-amplitude, relatively broad-band reflections at 6 s (15 km) are attributed to partially molten material within a subhorizontal intrusion. This bright spot extends laterally at least 15 km beneath central Death Valley. A moderately dipping normal fault can be traced from the inferred magma chamber upward to a 690,000-yr-old basaltic cinder cone. The fault zone is inferred to have been a magma conduit during the formation of the cinder cone. Vertical variations in crustal reflection character suggest that the Death Valley magma body may have been emplaced along a zone of decoupling that separates a faulted brittle upper crust from a more ductile and/or intruded lower crust. The Death Valley bright spot is similar to reflections recorded by COCORP in 1977 in the Rio Grande rift, where both geophysical and geodetic evidence support the inference of a tabular magma chamber at 20-km depth.

  11. Drilling investigations of a young magmatic intrusion beneath Inyo domes, Long Valley Caldera, California: The effects of pressure, volatiles, and thermal history on chemical heterogeneity in magma systems: Final report

    SciTech Connect

    Vogel T.A.

    1987-09-28

    Systematic chemical and mineralogical variability occurs in samples from drill holes through Obsidian Dome, the conduit to the dome, and a nearby associated feeder dike. The drill hole samples that occur at the margins of the conduit and most of the lower portion of the dome are high-Ba, low-silica rhyolites, with two populations of phenocrysts, and represent commingled magmas. Whereas samples from the dike and upper portions of the dome are low-Ba, higher silica rhyolites, and do not reflect commingled magmas, samples from the center of the conduit are low-Ba, higher silica rhyolites that are only slightly mixed. A major part of the variability within the drill core samples of the dome and conduit reflects the juxtaposition, and commingling of two distinct magmas during their passage throughout the conduit.

  12. Magma flow pattern in dykes of the Azores revealed by anisotropy of magnetic susceptibility

    NASA Astrophysics Data System (ADS)

    Moreira, M. A.; Geoffroy, L.; Pozzi, J. P.

    2015-02-01

    The localization of magma melting areas at the lithosphere bottom in extensional volcanic domains is poorly understood. Large polygenetic volcanoes of long duration and their associated magma chambers suggest that melting at depth may be focused at specific points within the mantle. To validate the hypothesis that the magma feeding a mafic crust, comes from permanent localized crustal reservoirs, it is necessary to map the fossilized magma flow within the crustal planar intrusions. Using the AMS, we obtain magmatic flow vectors from 34 alkaline basaltic dykes from São Jorge, São Miguel and Santa Maria islands in the Azores Archipelago, a hot-spot related triple junction. The dykes contain titanomagnetite showing a wide spectrum of solid solution ranging from Ti-rich to Ti-poor compositions with vestiges of maghemitization. Most of the dykes exhibit a normal magnetic fabric. The orientation of the magnetic lineation k1 axis is more variable than that of the k3 axis, which is generally well grouped. The dykes of São Jorge and São Miguel show a predominance of subhorizontal magmatic flows. In Santa Maria the deduced flow pattern is less systematic changing from subhorizontal in the southern part of the island to oblique in north. These results suggest that the ascent of magma beneath the islands of Azores is predominantly over localized melting sources and then collected within shallow magma chambers. According to this concept, dykes in the upper levels of the crust propagate laterally away from these magma chambers thus feeding the lava flows observed at the surface.

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

    USGS Publications Warehouse

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

    1980-01-01

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

  14. Hydrogen isotope investigation of amphibole and biotite phenocrysts in silicic magmas erupted at Lassen Volcanic Center, California

    USGS Publications Warehouse

    Underwood, S.J.; Feeley, T.C.; Clynne, M.A.

    2012-01-01

    Hydrogen isotope ratio, water content and Fe3 +/Fe2 + in coexisting amphibole and biotite phenocrysts in volcanic rocks can provide insight into shallow pre- and syn-eruptive magmatic processes such as vesiculation, and lava drainback with mixing into less devolatilized magma that erupts later in a volcanic sequence. We studied four ~ 35 ka and younger eruption sequences (i.e. Kings Creek, Lassen Peak, Chaos Crags, and 1915) at the Lassen Volcanic Center (LVC), California, where intrusion of crystal-rich silicic magma mushes by mafic magmas is inferred from the varying abundances of mafic magmatic inclusions (MMIs) in the silicic volcanic rocks. Types and relative proportions of reacted and unreacted hydrous phenocryst populations are evaluated with accompanying chemical and H isotope changes. Biotite phenocrysts were more susceptible to rehydration in older vesicular glassy volcanic rocks than coexisting amphibole phenocrysts. Biotite and magnesiohornblende phenocrysts toward the core of the Lassen Peak dome are extensively dehydroxylated and reacted from prolonged exposure to high temperature, low pressure, and higher fO2 conditions from post-emplacement cooling. In silicic volcanic rocks not affected by alteration, biotite phenocrysts are often relatively more dehydroxylated than are magnesiohornblende phenocrysts of similar size; this is likely due to the ca 10 times larger overall bulk H diffusion coefficient in biotite. A simplified model of dehydrogenation in hydrous phenocrysts above reaction closure temperature suggests that eruption and quench of magma ascended to the surface in a few hours is too short a time for substantial H loss from amphibole. In contrast, slowly ascended magma can have extremely dehydrogenated and possibly dehydrated biotite, relatively less dehydrogenated magnesiohornblende and reaction rims on both phases. Eruptive products containing the highest proportions of mottled dehydrogenated crystals could indicate that within a few days

  15. Vapor Intrusion

    EPA Pesticide Factsheets

    Vapor intrusion occurs when there is a migration of volatile chemicals from contaminated groundwater or soil into an overlying building. Volatile chemicals can emit vapors that may migrate through subsurface soils and into indoor air spaces.

  16. 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.

  17. Using magma flow indicators to infer flow dynamics in sills

    NASA Astrophysics Data System (ADS)

    Hoyer, Lauren; Watkeys, Michael K.

    2017-03-01

    Fabrics from Anisotropy of Magnetic Susceptibility (AMS) analyses and Shape Preferred Orientation (SPO) of plagioclase are compared with field structures (such as bridge structures, intrusive steps and magma lobes) formed during magma intrusion in Jurassic sills. This is to constrain magma flow directions in the sills of the Karoo Igneous Province along the KwaZulu-Natal North Coast and to show how accurately certain structures predict a magma flow sense, thus improving the understanding of the Karoo sub-volcanic dynamics. The AMS fabrics are derived from magnetite grains and are well constrained, however the SPO results are commonly steeply inclined, poorly constrained and differ to the AMS fabrics. Both techniques resulted in asymmetrical fabrics. Successful relationships were established between the AMS fabric and the long axes of the magma flow indicators, implying adequate magma flow prediction. However, where numerous sill segments merge, either in the form of magma lobes or bridge structures, the coalescence process creates a new fabric between the segments preserving late-stage magma migration between the merged segments, overprinting the initial magma flow direction.

  18. 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.

  19. External Sulfur Addition in the Generation of Sulfide-rich Ni-Cu-PGE Deposits: The Importance of Focused Magma Flow

    NASA Astrophysics Data System (ADS)

    Ripley, E. M.

    2015-12-01

    Sulfide-rich Ni-Cu-PGE orebodies hosted in mafic to ultramafic igneous rocks require focused magma flow and vigorous interaction with country rocks to liberate sulfide, as well as to produce traps for immiscible sulfide liquid. In the 1.1 Ga Midcontinent Rift System (MRS), Ni-rich sulfide deposits occur in conduit systems. Variations in S and Os isotope ratios indicate that magmas which followed different crustal pathways were focused into a central conduit that supplied overlying flows and sills. The 1.3 Ga Voisey's Bay deposit in Labrador represents sulfide liquid collection in a conduit system which includes dike-like bodies and larger sub-horizontal chambers. Variable d34S values again strongly suggest that focused magma flow and turbulence in the conduit resulted in the input of magmatic pulses that had undergone S isotopic homogenization even though pelitic country rocks are characterized by a range in S isotope values from -17 to +18 ‰. A very similar physical setting characterizes the sulfide-bearing Duke Island Complex, a Cretaceous - aged Ural-Alaskan intrusion in an arc setting. Magma pulses of variable sulfur isotopic compositions were focused into a central chamber where sulfide-bearing magma spread laterally. Trapped silicate liquid was efficiently expelled, leaving sulfide-bearing ultramafic cumulates. A less turbulent environment is indicated for sheet-like intrusions that carry disseminated sulfide mineralization in the Duluth Complex within the MRS. However, the potential ore sequences were built from multiple pulses of magma of distinct S isotope values that had interacted with sulfidic country rocks characterized by different S isotope compositions. Hence, the focusing of magmas from different pathways has been essential for the generation of potential sulfide-rich ore bodies in the Duluth Complex as well.

  20. Temporal Evolution of Volcanic and Plutonic Magmas Related to Porphyry Copper Ores Based on Zircon Geochemistry

    NASA Astrophysics Data System (ADS)

    Dilles, J. H.; Lee, R. G.; Wooden, J. L.; Koleszar, A. M.

    2015-12-01

    Porphyry Cu (Mo-Au) and epithermal Au-Ag ores are globally associated with shallow hydrous, strongly oxidized, and sulfur-rich arc intrusions. In many localities, long-lived magmatism includes evolution from early andesitic volcanic (v) and plutonic (p) rocks to later dacitic or rhyolitic compositions dominated by plutons. We compare zircon compositions from three igneous suites with different time spans: Yerington, USA (1 m.y., p>v), El Salvador, Chile (4 m.y., p>v), and Yanacocha, Peru (6 m.y., v>p). At Yerington granite dikes and ores formed in one event, at ES in 2 to 3 events spanning 3 m.y., and at Yanacocha in 6 events spanning 5 m.y. At both ES and Yanacocha, high-Al amphiboles likely crystallized at high temperature in the mid-crust and attest to deep magmas that periodically recharged the shallow chambers. At Yanacocha, these amphiboles contain anhydrite inclusions that require magmas were sulfur-rich and strongly oxidized (~NNO+2). The Ti-in-zircon geothermometer provides estimates of 920º to 620º C for zircon crystallization, and records both core to rim cooling and locally high temperature rim overgrowths. Ore-related silicic porphyries yield near-solidus crystallization temperatures of 750-650°C consistent with low zircon saturation temperatures. The latter zircons have large positive Ce/Ce* and small negative Eu/Eu*≥0.4 anomalies attesting to strongly oxidized conditions (Ballard et al., 2001), which we propose result from crystallization and SO2 loss to the magmatic-hydrothermal ore fluid (Dilles et al., 2015). The Hf, REE, Y, U, and Th contents of zircons are diverse in the magma suites, and Th/U vs Yb/Gd plots suggest a dominant role of crystal fractionation with lesser roles for both crustal contamination and mixing with high temperature deep-sourced mafic magma. Ce/Sm vs Yb/Gd plots suggest that magma REE contents at <900°C are dominated by early crystallization of hornblende and apatite, and late crystallization (~<780°C) of titanite

  1. Modeling sill intrusion in volcanic calderas

    NASA Astrophysics Data System (ADS)

    Macedonio, Giovanni; Giudicepietro, Flora; D'Auria, Luca; Martini, Marcello

    2015-04-01

    We present a numerical model for describing sill intrusion in volcanic calderas. The dynamics of volcanic calderas are often subject to long-term unrests, with remarkable ground deformation, seismicity, and geochemical changes, that do not culminate in an eruption. On the contrary, in some cases, unrests with minor geophysical changes are followed, in few months, by an eruption, as in the case of Rabaul Caldera in 1994 and Sierra Negra (Galapagos) in 2005. The main common features of calderas are the relevant ground deformations with intense uplift episodes, often followed by subsidence. We think that the process of sill intrusion can explain the common features observed on different calderas. In our model, the sill, fed by a deeper magma reservoir, intrudes below a horizontal elastic plate, representing the overlying rocks and expands radially. The model is based on the numerical solution of the equation for the elastic plate, coupled with a Navier-Stokes equation for simulating magma intrusion in the viscous regime. The numerical simulations show that during the feeding process, the ground is subject to uplift. When the feeding stops a subsidence occurs in the central zone. For very low flexural rigidity of the elastic plate, the subsidence can occur even during the intrusion of the sill. The stress field produced by the intrusion is mainly concentrated in a circular zone that follows the sill intrusion front.

  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. 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

  4. Solidification fronts in large magma chambers: insights from the anomalies

    NASA Astrophysics Data System (ADS)

    VanTongeren, J. A.

    2012-12-01

    The emplacement of hot viscous magma into the cold rigid crust causes a thermal disturbance within both the country rock and the magma. With time, heat loss from the molten interior to the walls causes solidification at the floor, roof and margins of the magma chamber. As is observed in both experiment and theory, in the absence of hydrothermal convection, the majority of heat is lost via conduction through the roof of the intrusion. In basaltic sills and layered mafic intrusions (LMIs), this solidification front is manifest in the deposition of mineral assemblages and compositions that become progressively more evolved from the floor of the intrusion upwards (the 'Layered Series'; LS) and from the roof downwards (the UBS) such that the most chemically evolved rocks are found in the interior of the magma body at a 'Sandwich Horizon'. The formation of a UBS, as typified by the Skaergaard Intrusion, is a natural outcome of the progression of the solidification front from the cold roof to the hot center of the magma chamber. There are, however, a few unique LMIs for which little or no UBS exists. Convection of the molten magma, reinjection and mixing of new magma, compaction of cumulates, and porous flow of interstitial liquid, among other processes, can affect the final location and composition of the most differentiated liquids; but ultimately, all are linked to the nature of heat loss from the magma chamber. In this study, I examine the thermal evolution of several classic LMIs as it is recorded in the extent of the preserved upper solidification front (or Upper Border Series; 'UBS'). For those intrusions that have experienced crystallization at the roof, such as the Skaergaard Intrusion, the development of a UBS reduces the temperature gradient at the roof and effectively slows the rate of heat loss from the main magma body. However, for those intrusions that do not have an UBS, such as the Bushveld Complex, the cooling rate is controlled only by the maximum rate

  5. Lateral variation in oxygen fugacity and halogen contents in early Cretaceous magmas in Jiaodong area, East China: Implication for triggers of the destruction of the North China Craton

    NASA Astrophysics Data System (ADS)

    Huang, Xiao-Long; He, Peng-Li; Wang, Xue; Zhong, Jun-Wei; Xu, Yi-Gang

    2016-04-01

    Pacific subduction has been suggested as the trigger of the destruction of the North China Craton, but evidence for it remains ambiguous. To further investigate this issue, we studied Wulian pyroxene monzonite (123 ± 1 Ma) in the west and Rushan gabbro-diorite (115 ± 1 Ma) in the east of the Sulu orogen, East China. The rocks of both locations are characterized by low TiO2 but high SiO2 and K2O, fractionated REE patterns with notable negative Ta-Nb-Ti anomalies, and by high initial 87Sr/86Sr ratios and strongly negative εNd (t) and εHf (t) values. These geochemical and isotopic characteristics can be interpreted to be formed by partial melting of enriched lithosphere mantle refertilized by recycled crustal materials that were associated with the Sulu orogeny. Oxygen fugacities of the Rushan gabbro-diorites, estimated based on magnetite-ilmenite equilibration, are significantly higher than those of Wulian pyroxene monzonite. This lateral difference is mirrored by lower F and F/Cl but higher Cl in biotite in the Rushan gabbro-diorite compared to Wulian pyroxene monzonite. All these data suggest a spatially heterogeneous Cretaceous mantle source in terms of halogens and water contents beneath the Sulu orogen, which was most likely caused by the subduction processes of the Pacific plate. H2O-rich fluid in the mantle beneath the east of the Sulu orogen closer to the mantle wedge was prominently from early dehydration of subducted slab at shallow depth, while F-bearing fluid to further west was released by dehydrated deeper slab or stagnant oceanic slab within the mantle transition zone.

  6. Composite synvolcanic intrusions associated with Precambrian VMS-related hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Galley, Alan G.

    2003-06-01

    Large subvolcanic intrusions are recognized within most Precambrian VMS camps. Of these, 80% are quartz diorite-tonalite-trondhjemite composite intrusions. The VMS camps spatially associated with composite intrusions account for >90% of the aggregate sulfide tonnage of all the Precambrian, intrusion-related VMS camps. These low-alumina, low-K, and high-Na composite intrusions contain early phases of quartz diorite and tonalite, followed by more voluminous trondhjemite. They have a high proportion of high silica (>74% SiO2) trondhjemite which is compositionally similar to the VMS-hosting rhyolites within the volcanic host-rock successions. The quartz-diorite and possibly tonalite phases follow tholeiitic fractionation trends whereas the trondhjemites fall within the composition field for primitive crustal melts. These transitional M-I-type primitive intrusive suites are associated with extensional regimes within oceanic-arc environments. Subvolcanic composite intrusions related to the Archean Sturgeon Lake and Noranda, and Paleoproterozoic Snow Lake VMS camps range in volume from 300 to 1,000 km3. Three have a sill morphology with strike lengths between 15 and 22 km and an average thickness between 1,500 and 2,000 m. The fourth has a gross stock-like shape. The VMS deposits are principally restricted to the volcanic strata above the strike length of the intrusions, as are areally extensive, thin exhalite units. The composite intrusions contain numerous internal phases which are commonly clustered within certain parts of the composite intrusion. These clusters underlie eruptive centers surrounded by areas of hydrothermal alteration and which contain most of the VMS deposits. Early quartz-diorite and tonalite phases appear to have intruded in rapid succession. Evidence includes gradational contacts, magma mixing and disequilibrium textures. They appear to have been emplaced as sill-dike swarms. These early phases are present as pendants and xenoliths within later

  7. Magma paths at Piton de la Fournaise volcano: a synthesis of Hawaiian and Etnean rift zones

    NASA Astrophysics Data System (ADS)

    Michon, Laurent; Ferrazzini, Valérie; Di Muro, Andrea; Chaput, Marie; Famin, Vincent

    2014-05-01

    triggered by shallow sill intrusions below the east flank. We propose that the sub-vertical magma intrusions along the perpendicular summit rift zones, sill intrusions and subsequent magma injections along the outer rift zones are controlled by cycles of stress permutations. Recurrent dyke injections along the summit rift zone in an extensional stress field reduce the deviatoric stress until a switch of the axes of principal stresses and a sill intrusion. The related flank lateral destabilization restores the extensional stress field and initiates a new cycle of stress permutations. To sum up, rift zones of Piton de la Fournaise present strong geometrical and dynamical differences. On the one hand, the lower plumbing system feeds rift zones showing striking similarities to those developed in Hawaii during the alkaline postshield stage. On the other hand, the rift zones connected to upper plumbing system and the related volcano flank movement can be compared to the eruptive and east flank dynamics of Mount Etna.

  8. Granite provenance and intrusion in arcs: Evidence from diverse zircon types in Big Bear Lake Intrusive Suite, USA

    NASA Astrophysics Data System (ADS)

    Barth, A. P.; Wooden, J. L.; Mueller, P. A.; Economos, R. C.

    2016-03-01

    Textural, geochemical and hafnium isotopic data from diverse zircon domains allow discrimination between source and emplacement-level processes in the formation of a large-volume calc-alkalic intrusion. The Big Bear Lake Intrusive Suite is composed of satellite plutons and a main intrusive mass zoned from mafic granodiorites at its margins to central biotite ± muscovite granites, and is estimated to be 7-10 km thick and have a volume of 3500-5100 km3. Zircons in the main intrusive mass and in the satellite plutons are composed of one or more of four domain types: (a) Archean to Proterozoic premagmatic domains and (b) Mesozoic premagmatic domains, both occurring as cores, which are overgrown by (c) luminescent early magmatic domains with low U + Th and relatively high estimated crystallization temperatures and (d) high U + Th main phase magmatic domains. U-Pb zircon geochronology indicates the main intrusive mass was emplaced 78-77 Ma, preceded by satellite plutons intruded 85-81 Ma. Zircon hafnium isotope ratios span 54 epsilon units, recording age and compositional diversity in magma sources and magma batches. We propose a model for assembly of the intrusive suite involving mixing between lithospheric mantle-derived magma and a hybrid lower crustal source, followed by incremental emplacement of magmas in the upper crust at 0.003-0.005 km3 my- 1. This flux rate was sufficiently rapid to generate a large volume of mobile magma that underwent differentiation by limited and imperfect fractional crystallization to form the granodioritic margins and central granites. The estimated flux rate is several times higher than that estimated for other Cretaceous, incrementally emplaced intrusive suites in the California arc, indicating that both source-level and emplacement-level processes played roles in forming these intrusions.

  9. 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.

  10. Episodic Growth and Solidification of the Vinalhaven Intrusive Complex, Maine, USA

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    plutonic rocks consist of cg granite in the west and interlayered granite and mafic sheets associated with large blocks of country rock in the east. In the west, schlieren structures in cg granite indicate crystal accumulation on a chamber floor of transitional rheology. In the east, granitic pipes and other outcrop-scale features indicate that the mafic layers ponded on granitic crystal mush. At higher levels, mafic sheets and country rock blocks gradually become restricted to the eastern third of the complex and are entirely absent in the upper half of the intrusion. Within cg granite the wide occurrence of schlieren related to magma flow and sinking enclaves indicate continued accumulation on a chamber floor. Later injections of basaltic magmas rejuvenated pockets of mostly crystallized granite in the upper levels of homogeneous granite and suggest that crystallization of the granite also proceeded inward from the sides and roof of the chamber. The complex preserves a stratigraphic record of magma chamber evolution and pluton growth by crystal accumulation on magma chamber floors that was interrupted by episodes of replenishment and rejuvenation. This field-based interpretation is corroborated by high-precision U-Pb zircon ages of granitic rocks distributed throughout the complex that indicate the complex was constructed over a nominal time-span of about 0.7 m.y. (Hawkins and Wiebe, this volume).

  11. Petrogenesis of the Pd-rich intrusion at Salt Chuck, Prince of Wales island: an early Paleozoic Alaskan-type ultramafic body

    USGS Publications Warehouse

    Loney, R.A.; Himmelberg, G.R.

    1992-01-01

    The early Paleozoic Salt Chuck intrusion has petrographic and chemical characteristics that are similar to those of Cretaceous Alaskan-type ultramafic-mafic bodies. The intrusion is markedly discordant to the structure of the early Paleozoic Descon Formation, in which it has produced a rather indistinct contact aureole a few meters wide. Mineral assemblages, sequence of crystallization, and mineral chemistry suggest that the intrusion crystallized under low pressures (~2 kbar) with oxidation conditions near those of the NNO buffer, from a hydrous, silica-saturated, orthopyroxene-normative parental magma. The Salt Chuck deposit was probably formed by a two-stage process: 1) a stage of magmatic crystallization in which the sulfides and PGE accumulated in a disseminated manner in cumulus deposits, possibly largely in the gabbro, and 2) a later magmatic-hydrothermal stage during which the sulfides and PGE were remobilized and concentrated in veins and fracture-fillings. In this model, the source of the sulfides and PGE was the magma that produced the Salt Chuck intrusion. -from Authors

  12. Flexural Stresses and Reservoir Stability: Implications for Magma Propagation in the Lithosphere and the Formation of Giant Radial Dike Swarms on Venus

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Giant radial fracture systems on Venus are prominent, widely distributed volcano-tectonic structures that record interactions between the lithosphere and subsurface magmatic processes, specifically the lateral transport of magma at shallow depths. Here we show that the interplay between flexural uplift and magma chamber pressurization can create stress conditions favoring the emplacement of radial dikes. We use elastic, gravitationally-loaded axisymmetric finite element models that incorporate depth-dependent lithostatic stresses and Winkler restoring forces at the base of the elastic lithosphere. To generate uplift, we apply buoyant (upward) loads at the base of a 20 km-thick lithosphere near the model center, with a maximum thickness of 5 km and 200 km in radius, using conical and disk load shapes. An overpressured spherical reservoir, emplaced in each model, is used to simulate magmatic inflation and determine reservoir failure patterns. Stress orientations predicted by our models are helping us understand how laterally spreading sub-lithosphere bodies flex the lithosphere, affect intrusion patterns (radial to circumferential faults/grabens), and influence both magma ascent and eruptive patterns. Loading due to a conical basal load produces a flexural stress state with high differential stresses in the extensional upper and compressional lower lithosphere, separated by a low-stress neutral plane. Principal stress alignments in the upper lithosphere favor the emplacement of laterally extensive radial intrusions. In contrast to this, sill formation is favored in the lower lithosphere. Magma reservoirs emplaced in the upper lithosphere or within the underlying zone of low differential stress fail at the crest, favoring the ascent of magma. Reservoirs emplaced in the lower lithosphere tend to fail near the midsection under conditions that will yield horizontal intrusions. In sharp contrast, disk-shaped or ellipsoidal uplift loads move the flexed part of the

  13. Catastrophic erosion of Hellas basin rim on Mars induced by magmatic intrusion into volatile-rich rocks

    USGS Publications Warehouse

    Tanaka, K.L.; Kargel, J.S.; MacKinnon, D.J.; Hare, T.M.; Hoffman, N.

    2002-01-01

    Malea and Hesperia Plana form large sectors of the rim of Hellas basin that display partly eroded volcanic shields and plains. These regions have topographic profiles that appear to be several hundred meters lower than those of adjacent rim sectors and lack prominent massifs of remnant basement that would be expected to stand above the lava plains. We interpret that before the volcanic edifices were constructed, these regions were denuded by an early stage of voluminous sill intrusion into friable, volatile-rich impact breccia. Magma-volatile interactions may have resulted in catastrophic generation of debris flows deposited into the adjacent basin, particularly if CO2 were involved. Later, lavas covered the eroded terrain; in turn, the lavas were eroded locally by volatile interactions. Across Mars, huge channel systems, erosional features in volcanic terranes, and vast layered deposits may be due to magma-volatile interactions.

  14. Zircon Recycling in Arc Intrusions

    NASA Astrophysics Data System (ADS)

    Miller, J.; Barth, A.; Matzel, J.; Wooden, J.; Burgess, S.

    2008-12-01

    Recycling of zircon has been well established in arc intrusions and arc volcanoes, but a better understanding of where and how zircons are recycled can help illuminate how arc magma systems are constructed. To that end, we are conducting age, trace element (including Ti-in-zircon temperatures; TzrnTi) and isotopic studies of zircons from the Late Cretaceous (95-85 Ma) Tuolumne Intrusive Suite (TIS) in the Sierra Nevada Batholith (CA). Within the TIS zircons inherited from ancient basement sources and/or distinctly older host rocks are uncommon, but recycled zircon antecrysts from earlier periods of TIS-related magmatism are common and conspicuous in the inner and two most voluminous units of the TIS, the Half Dome and Cathedral Peak Granodiorites. All TIS units have low bulk Zr ([Zr]<150 ppm) and thus low calculated zircon saturation temperatures (Tzrnsat). Within the Half Dome and Cathedral Peak, TzrnTi values are predominantly at or below average Tzrnsat, and there is no apparent correlation between age and TzrnTi. At temperatures appropriate for granodiorite/tonalite melt generation (at or above biotite dehydration; >825°C), [Zr] in the TIS is a factor of 2 to 3 lower than saturation values. Low [Zr] in TIS rocks might be attributed to a very limited supply of zircon in the source, by disequilibrium melting and rapid melt extraction [1], by melting reactions involving formation of other phases that can incorporate appreciable Zr [2], or by removal of zircon at an earlier stage of magma evolution. Based on a preliminary compilation of literature data, low [Zr] is common to Late Cretaceous N.A. Cordilleran granodioritic/tonalitic intrusions (typically <200 ppm and frequently 100-150 ppm for individual large intrusions or intrusive suites). We infer from this that [Zr] in anatectic melts is probably not limited by zircon supply and is primarily controlled by melting parameters. Comparison of the data from TIS with one of these intrusions, the smaller but otherwise

  15. The 2001 Mt. Etna eruption: new constraints on the intrusive mechanism from ground deformation data

    NASA Astrophysics Data System (ADS)

    Palano, Mimmo; González, Pablo J.

    2013-04-01

    The occurrence of seismic swarms beneath the SW flank of Mt. Etna, often observed just a few months before an eruption, has been considered as the fragile response to a magma intrusion (Bonanno et al., 2011 and reference therein). These intrusions and/or pressurization of deep magmatic bodies, have been able to significantly affect the seismic pattern within the volcano edifice, leading to a changes in the local stress field. For example, during the months preceding the 1991-1993 Mt. Etna eruption, shallow intense seismic swarms (4-6 km deep) occurring in the SW flank (e.g. Cocina et al., 1998), related to the magma intrusion before the eruption onset, were observed contemporaneously with a rotation of stress field of about 90°. A similar scenario was observed during January 1998, when a magma recharging phases induced a local rotation of stress tensor, forcing a buried fault zone located beneath the SW flank of Mt. Etna to slip as a right-lateral strike-slip fault (Bonanno et al., 2011). This fault system was forced to slip again, during late April 2001 (more than 200 events in less than 5 days; maximum Magnitude = 3.6) by the pressurization of the magmatic bodies feeding the July-August 2001 Mt. Etna eruption. Here we analyzed in detail the July-August 2001 Mt. Etna eruption as well as the dynamics preceding this event, by using a large dataset of geodetic data (GPS and synthetic aperture radar interferometry) collected between July 2000 and August 2001. References Cocina, O., Neri, G., Privitera, E. and Spampinato S., 1998. Seismogenic stress field beneath Mt. Etna South Italy and possible relationships with volcano-tectonic features. J. Volcanol. Geotherm. Res., 83, 335-348. Bonanno A., Palano M., Privitera E., Gresta S., Puglisi G., 2011. Magma intrusion mechanisms and redistribution of seismogenic stress at Mt. Etna volcano (1997-1998). Terra Nova, 23, 339-348, doi: 10.1111/j.1365-3121.2011.01019.x, 2011.

  16. Ultrabasic breccias in layered intrusions - The Rhum complex

    NASA Technical Reports Server (NTRS)

    Donaldson, C. H.

    1975-01-01

    Two breccias in the southwest part of the ultrabasic Rhum complex are considered. Aspects of field relations are discussed along with questions regarding the petrography of the matrix. Attention is given to textures and chemical mineralogy, the mechanism of brecciation, matrix magmas, and the possible implications of the findings. It is concluded that the Harris Bay and Ard Mheall ultrabasic breccias formed by brecciation due to the intrusion of feldspathic peridotite magmas.

  17. Superfund Vapor Intrusion

    EPA Pesticide Factsheets

    In addition to basic information about vapor intrusion, the site contains technical and policy documents, tools and other resources to support vapor intrusion environmental investigations and mitigation activities.

  18. On the formation and lifetime of large silicic magma chambers in the shallow crust

    NASA Astrophysics Data System (ADS)

    Schöpa, A.; Annen, C.

    2012-04-01

    Most large silicic intrusion are believed to have formed by repeated injections of smaller magma pulses that eventually constitute the whole pluton. Geochronology helps to calculate long-term average emplacement rates of intrusions that are in the order of few mm/a. However, numerical simulations showed that these rates are too low to create large magma chambers. The incremental emplacement style limits the size and lifetime of any large magma chamber because the earlier injected magma pulse would cool down below solidus temperature before the next pulse is injected. To better constrain the formation of large-volume magma chambers, we investigate the influence of a changing emplacement rate over the lifetime of a composite plutonic body. That means that the emplacement rate can be temporarily high although the long-term average rate is low and is in agreement with the geochronological data. This is achieved by thermal modelling via an explicit finite difference scheme. The models calculate temperatures in the Earth's crust according to the equation of conductive heat transfer. They also take heat production of radioactive decay and phase changes into account. The conditions necessary to form a magma chamber that is larger than one single magma pulse, in this case a sill intrusion, are investigated and applied to the Tuolumne Intrusive Suite. This granitic intrusion is part of the Mesozoic Sierra Nevada Batholith in California and covers an area of more than 1000 km2. The Tuolumne Intrusive Suite is normally zoned with nested map units getting progressively younger and more evolved towards the centre. Data provided by U-Pb geochronology give an age range from 93.5 Ma for the outermost unit to 85.4 Ma for the core of the intrusive suite. The modelling results show that specific conditions need to be fulfilled to form a magma chamber for the Tuolumne Intrusive Suite. For most models, one sill intrusion cools down before the emplacement of the next sill. Thus, no more

  19. 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.

  20. 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.

  1. Rapid laccolith intrusion driven by explosive volcanic eruption.

    PubMed

    Castro, Jonathan M; Cordonnier, Benoit; Schipper, C Ian; Tuffen, Hugh; Baumann, Tobias S; Feisel, Yves

    2016-11-23

    Magmatic intrusions and volcanic eruptions are intimately related phenomena. Shallow magma intrusion builds subsurface reservoirs that are drained by volcanic eruptions. Thus, the long-held view is that intrusions must precede and feed eruptions. Here we show that explosive eruptions can also cause magma intrusion. We provide an account of a rapidly emplaced laccolith during the 2011 rhyolite eruption of Cordón Caulle, Chile. Remote sensing indicates that an intrusion began after eruption onset and caused severe (>200 m) uplift over 1 month. Digital terrain models resolve a laccolith-shaped body ∼0.8 km(3). Deformation and conduit flow models indicate laccolith depths of only ∼20-200 m and overpressures (∼1-10 MPa) that likely stemmed from conduit blockage. Our results show that explosive eruptions may rapidly force significant quantities of magma in the crust to build laccoliths. These iconic intrusions can thus be interpreted as eruptive features that pose unique and previously unrecognized volcanic hazards.

  2. Rapid laccolith intrusion driven by explosive volcanic eruption

    PubMed Central

    Castro, Jonathan M.; Cordonnier, Benoit; Schipper, C. Ian; Tuffen, Hugh; Baumann, Tobias S.; Feisel, Yves

    2016-01-01

    Magmatic intrusions and volcanic eruptions are intimately related phenomena. Shallow magma intrusion builds subsurface reservoirs that are drained by volcanic eruptions. Thus, the long-held view is that intrusions must precede and feed eruptions. Here we show that explosive eruptions can also cause magma intrusion. We provide an account of a rapidly emplaced laccolith during the 2011 rhyolite eruption of Cordón Caulle, Chile. Remote sensing indicates that an intrusion began after eruption onset and caused severe (>200 m) uplift over 1 month. Digital terrain models resolve a laccolith-shaped body ∼0.8 km3. Deformation and conduit flow models indicate laccolith depths of only ∼20–200 m and overpressures (∼1–10 MPa) that likely stemmed from conduit blockage. Our results show that explosive eruptions may rapidly force significant quantities of magma in the crust to build laccoliths. These iconic intrusions can thus be interpreted as eruptive features that pose unique and previously unrecognized volcanic hazards. PMID:27876800

  3. Magma Mixing: Why Picrites are Not So Hot

    NASA Astrophysics Data System (ADS)

    Natland, J. H.

    2010-12-01

    porosity in regions where crustal-level magma chambers and flanking rift zones do not have a chance to form. Low-magma supply is favored. In the ocean basins, such upper mantle mainlining occurs only at certain fracture zones, deep propagating rifts at microplates, or ultra-slow spreading ridges, but no liquids (glasses) with >10% MgO occur at any of these places. On continents, rift structures through cratons might allow this, but so far no picrite, ferropicrite, or meimichite that has been adequately described from these places lacks evidence for end-member mixing. Low-temperature iron-rich magmas can accumulate in the deep lower crust and later rise to form substantial intrusions (e.g. Skaergaard) or erupt as flood basalts (Columbia River). Some komatiites might represent high-temperature liquids, but many are so altered that original liquid compositions cannot be deduced (e.g., Gorgona). The hottest intraplate volcano is Kilauea, Hawaii, where rare picrite glass with 15% MgO has an estimated eruptive temperature (1) of ~1350C and a potential temperature at 1 GPa of ~1420C. Lavas at all other linear island chains, Iceland and even west Greenland where picrites are abundant, are cooler than this. (1) Beattie, P., 1993. CMP 115: 103-111.

  4. Rift zones and magma plumbing system of Piton de la Fournaise volcano: How do they differ from Hawaii and Etna?

    NASA Astrophysics Data System (ADS)

    Michon, Laurent; Ferrazzini, Valérie; Di Muro, Andrea; Villeneuve, Nicolas; Famin, Vincent

    2015-09-01

    On ocean basaltic volcanoes, magma transfer to the surface proceeds by subvertical ascent from the mantle lithosphere through the oceanic crust and the volcanic edifice, possibly followed by lateral propagation along rift zones. We use a 19-year-long database of volcano-tectonic seismic events together with detailed mapping of the cinder cones and eruptive fissures to determine the geometry and the dynamics of the magma paths intersecting the edifice of Piton de la Fournaise volcano. We show that the overall plumbing system, from about 30 km depth to the surface, is composed of two structural levels that feed distinct types of rift zones. The deep plumbing system is rooted between Piton des Neiges and Piton de la Fournaise volcanoes and has a N30-40 orientation. Above 20 km below sea level (bsl), the main axis switches to a N120 orientation, which permits magma transfer from the lithospheric mantle to the base of the oceanic crust, below the summit of Piton de la Fournaise. The related NW-SE rift zone is 15 km wide, linear, spotted by small to large pyroclastic cones and related lava flows and emits slightly alkaline magmas resulting from high-pressure fractionation of clinopyroxene ± olivine. This rift zone has low magma production rate of ~ 0.5-3.6 × 10- 3 m3s- 1 and an eruption periodicity of around 200 years over the last 30 ka. Seismic data suggest that the long-lasting activity of this rift zone result from regional NNE-SSW extension, which reactivates inherited lithospheric faults by the effect of underplating and/or thermal erosion of the mantle lithosphere. The shallow plumbing system (< 11 km bsl) connects the base of the crust with the Central Cone. It is separated from the deep plumbing system by a relatively large aseismic zone between 8 and 11 km bsl, which may represent a deep storage level of magma. The shallow plumbing system feeds frequent, short-lived summit and flank (NE and SE flanks) eruptions along summit and outer rift zones, respectively

  5. Mapping real time growth of experimental laccoliths: The effect of solidification on the mechanics of magmatic intrusion

    NASA Astrophysics Data System (ADS)

    Currier, Ryan M.; Marsh, Bruce D.

    2015-09-01

    The dynamics of solidification front growth along the margins of magmas have been widely found to be fundamental in controlling magma transport and emplacement. In this vein, the role of solidification fronts in determining the basic growth mechanics of laccoliths are investigated here in a series of scaled experiments using two contrasting magma analogs, water and molten wax that are injected into a visco-elastic gelatin based crustal analog. In non-solidifying, water-style experiments, intrusion is a relatively simple process. In contrast, wax magma emplacement displays a vast palette of compelling behaviors: propagation can slow, stop, and reactivate, and the directionality of lateral growth becomes much more variable. Small flow deviations in water-based intrusions are likely the product of flow instabilities, the result of injecting a viscous fluid along an interface (similar to Hele-Shaw cell experiments). However, the much more complex emplacement style of the wax experiments is attributed to solidification at the leading edge of the crack. The overall effects of solidification during emplacement can be described by a non-dimensional parameter measuring the relative competition between the rates of crack propagation and solidification at the crack leading edge. In this context, laccolith growth mechanics can be separated into three distinctive characteristic stages. Namely, I: A thin pancake style sill initially emanating radially from a central feeder zone, II: As solidification stalls magma propagation at the leading edges, enhanced thickening begins, forming a true, low aspect ratio laccolith, and III: As stresses accumulate, tears and disruptions readily occur in the solidified margin causing fresh breakouts, thus reactivating lateral growth into new lobes. The competitive combination of these latter stages often leads to a characteristic pulsatile growth. The unexpected richness of these results promises to add fundamentally to the basic understanding

  6. Periodicity of Kı¯lauea's Dike Intrusions

    NASA Astrophysics Data System (ADS)

    Montgomery-Brown, E. K.; Miklius, A.

    2015-12-01

    Magmatic intrusions commonly occur in the rift zones of Kı¯lauea Volcano. Individual dike intrusions observed by geodetic methods are usually 5 to 10 km long, and can occur repeatedly in the same region. Five such intrusions in Kı¯lauea's East Rift Zone, with inferred locations downrift of the bend where the NNW trending upper ERZ turns to the ENE trending ERZ, have occurred since the start of the ongoing ERZ eruption in 1983. The intrusions occur on one of two segments that correlate with seismic segments (Wright and Klein, USGS PP1806, 2014): Makaopuhi (1993 and 2007) and Nāpau (1983, 1997, and 2011). During each intrusion, the amount of dike opening was between 2 and 3 meters. Intrusions into the UERZ tend to be much smaller (~10 cm of dike opening) and occur more frequently. The time between ERZ intrusions for same-segment pairs are: 14.07 (1983-1997), 14.09 (1997-2011), and 13.95 (1993-2007) years, with the Nāpau segment becoming active about 3.5 years after the Makaopuhi segment in each case. The amount of modeled dike opening during each of these events roughly corresponds to the amount of seaward south flank motion and deep rift opening accumulated in the time between events, as was noted by Owen et al. (GRL, 2000) for the 1983 and 1997 intrusions. The recurrence interval of ~14 years appears to be unaffected by the magma surge of 2003-2007 (Poland et al., Nature, 2012), suggesting that flank motion, rather than magma supply, could be a controlling factor in the periodicity of intrusions. The long duration of the seismic catalog and the coincidence of repeated dike intrusions with the seismic segments suggest that on the timescale of decades, Kı¯lauea's East Rift Zone segments are persistent rather than ephemeral features related to single intrusion events.

  7. Geochronological and geochemical study of the Pan African intrusive rocks along the Najd Fault system in El Wajh area, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Hassan, Mahmoud; Abu-Alam, Tamer; Hauzenberger, Christoph; Stüwe, Kurt; Tiepolo, Massimo

    2014-05-01

    In the active tectonic regions, shear zones play an important role to re-configure the structure of the lithosphere. One of the largest shear zones on the Earth is the Najd Fault system of the Arabian-Nubian Shield. Literature data record the main active phase of this shear zone during the last stages of the Pan-African Orogeny (ca. 650-550 Ma). Compilation of new geochronological and geochemical data in addition to field relation is used to figure the tectonic history of the Najd Fault system. Different relationships between igneous intrusions and the Najd Fault System are observed. Some igneous bodies predate the activity of the shear zone, others intruded during the shearing process and a later phase intruded after the activity of the Najd Fault system ceased. The intrusive rocks in the study area show a geochemical and compositional diversity. Intrusives with dioritic composition were derived from a metaluminous tholeiitic magma around 700 Ma, and granodiorite-tonalite intrusions have calcalkaline characters and display a metaluminous to peraluminous character (ca. 740 and 660 Ma) then the magmatic activity terminated with peraluminous calcalkaline intrusives which formed granitic rocks with intrusion ages of 605-580 Ma. These magmatic events are identical for the Arabian-Nubian Shield but contamination from the crust or different rates of fractionation are recorded in our samples which are responsible for variations in the geochemical signature of the intrusive rocks. Based on field observations and contact relations, the intrusive rocks within the Ajjaj shear zone were studied in details in order to determine the age and the tectonic history of this shear zone that marks the termination of the Najd System against the eastern margin of the Red Sea. The provided zircon U-Pb dating by LA-ICP-MS and field relationships confine the activation age of the Ajjaj shear zone in limited period between 605 Ma and 580 Ma.

  8. 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

  9. Oblique rift opening revealed by reoccurring magma injection in central Iceland

    PubMed Central

    Ruch, Joël; Wang, Teng; Xu, Wenbin; Hensch, Martin; Jónsson, Sigurjón

    2016-01-01

    Extension deficit builds up over centuries at divergent plate boundaries and is recurrently removed during rifting events, accompanied by magma intrusions and transient metre-scale deformation. However, information on transient near-field deformation has rarely been captured, hindering progress in understanding rifting mechanisms and evolution. Here we show new evidence of oblique rift opening during a rifting event influenced by pre-existing fractures and two centuries of extension deficit accumulation. This event originated from the Bárðarbunga caldera and led to the largest basaltic eruption in Iceland in >200 years. The results show that the opening was initially accompanied by left-lateral shear that ceased with increasing opening. Our results imply that pre-existing fractures play a key role in controlling oblique rift opening at divergent plate boundaries. PMID:27492709

  10. Oblique rift opening revealed by reoccurring magma injection in central Iceland

    NASA Astrophysics Data System (ADS)

    Ruch, Joël; Wang, Teng; Xu, Wenbin; Hensch, Martin; Jónsson, Sigurjón

    2016-08-01

    Extension deficit builds up over centuries at divergent plate boundaries and is recurrently removed during rifting events, accompanied by magma intrusions and transient metre-scale deformation. However, information on transient near-field deformation has rarely been captured, hindering progress in understanding rifting mechanisms and evolution. Here we show new evidence of oblique rift opening during a rifting event influenced by pre-existing fractures and two centuries of extension deficit accumulation. This event originated from the Bárðarbunga caldera and led to the largest basaltic eruption in Iceland in >200 years. The results show that the opening was initially accompanied by left-lateral shear that ceased with increasing opening. Our results imply that pre-existing fractures play a key role in controlling oblique rift opening at divergent plate boundaries.

  11. Unstable flow, magma mixing and magma-rock deformation in a deep-seated conduit: the Gil-Márquez Complex, south-west Spain

    NASA Astrophysics Data System (ADS)

    Castro, A.; la Rosa, J. D. De; Fernández, C.; Moreno-Ventas, I.

    The Gil-Márquez Complex is an exceptional outcrop of plutonic rocks ranging in composition from diorites to granites emplaced into Devonian terrigenous metasediments of the southernmost part of the Hercynian basement of Iberia. A combined study of this complex, including field geology, petrology, structural geology and geochemistry, reveals that it represents an ancient conduit of magma transport through the continental crust. This conduit allowed the intrusion of magmas of contrasted compositions. Two end-members and several hybrids are identified. The first end-member is a biotite granite and the second is a basaltic magma generated by partial melting of a depleted-mantle source. Both magmas rose through a common channel in which favorable conditions for unstable flow and magma mixing occurred. The observed relations in the Gil-Márquez Complex show that mixing in conduits may be an important mechanism for producing homogeneous hybrid magmas.

  12. Unstable flow, magma mixing and magma-rock deformation in a deep-seated conduit: the Gil-Márquez Complex, south-west Spain

    NASA Astrophysics Data System (ADS)

    Castro, A.; de La Rosa, J. D.; Fernández, C.; Moreno-Ventas, I.

    1995-06-01

    The Gil-Marquez Complex is an exceptional outcrop of plutonic rocks ranging in composition from diorites to granites emplaced into Devonian terrigenous metasediments of the southernmost part of the Hercynian basement of Iberia. A combined study of this complex, including field geology, petrology, structural geology and geochemistry, reveals that it represents an ancient conduit of magma transport through the continental crust. This conduit allowed the intrusion of magmas of contrasted compositions. Two end-members and several hybrids are identified. The first end-member is a biotite granite and the second is a basaltic magma generated by partial melting of a depletedmantle source. Both magmas rose through a common channel in which favorable conditions for unstable flow and magma mixing occurred. The observed relations in the Gil-Márquez Complex show that mixing in conduits may be an important mechanism for producing homogeneous hybrid magmas.

  13. The age and origin of felsic intrusions of the Thetford Mines ophiolite, Quebec.

    USGS Publications Warehouse

    Clague, D.A.; Frankel, C.S.; Eaby, J.S.

    1985-01-01

    This ophiolite was obducted in the early Ordovician during the closing of the proto-Atlantic. The tectonized peridotite of the lower unit of the ophiolite is intruded by felsic dykes and pods, including isolated lenses of massive rodingite, small bodies of strongly deformed diorite, and younger, less deformed monzonite. These intrusions are found only near the base of the ophiolite, and are considered to have been emplaced before the ophiolite reached its present position. The young group of intrusions consists of biotite-muscovite quartz monzonite and leuco-quartz monzonite. Analysed samples have high K2O, high (K2O X 100)/Na2O + K2O) ratios, and high initial Sr ratios, indicating that the magma source was continental and that these felsic rocks formed by partial melting of continental sediments. Whole-rock and mineral isochron ages suggest that the felsic intrusions are approx 456 + or - 4 m.y. old and that they were metamorphosed approx 418 + or - 7 m.y. ago. The detachment of the ophiolite occurred approx 491 + or - 3 m.y. ago. The felsic dykes were intruded approx 35 m.y. later, during the Taconic orogeny. The lengthy time between detachment and final nappe emplacement recorded by the felsic dykes may be a requirement for formation of abundant asbestiform chrysotile. Whole-rock analyses (16) and Rb, Sr and 87Sr/86Sr data from the Colline de Granite, King Mts., Vimy Ridge and Black Lake samples are presented.-P.Br.

  14. Magma generation and differentiation in the terrestrial planets - a review of the contributions of Michael J. O'Hara

    NASA Astrophysics Data System (ADS)

    Wilson, M.

    2003-04-01

    During the course of the 20th century Earth Scientists argued, seemingly incessantly, about the processes of magma generation and differentiation within the Earth, Moon and other planetary bodies. Whilst N.L. Bowen's (1928) classic publication "The evolution of the Igneous Rocks " undoubtedly represents a benchmark in our understanding, it was not until the mid 1960s that the complexity of these processes was appreciated fully. The fact that we are still debating many of the key issues, forty years later, reflects the scale of the problem; each new step in our understanding seems to generate more questions! 2003 marks the 70th birthday of Michael J. O'Hara, and the 35th anniversary of the publication of two of his classic papers, which influenced the thinking of a generation of petrologists: (1) "The bearing of phase equilibria studies in synthetic and natural systems on the origin of basic and ultrabasic rocks" [Earth Sci. Rev., 4, 69-133; 1968]; (2) "Are ocean floor basalts primary magmas?" [Nature, 220, 683-686; 1968]. Since 1960, Mike has been the first, sole or joint co-author on over 120 publications, directly or indirectly related to magma generation and differentiation. His contributions have encompassed a diverse range of topics including: high P-T experimental petrology, the CMAS projection, the origin and evolution of basic and ultrabasic magmas, upper mantle petrology and dynamics, geothermometry-geobarometry of mantle rocks, RTF magma chambers and the mechanisms of dyke intrusion. Mike played a leading role in the Lunar Science Programme in the early 1970s and is still "stirring the lunar pot" [3]. (3) "Flood Basalts, Basalt Floods or Topless Bushvelds? Lunar Petrogenesis Revisited" [J.Petrology 41, 1545-1651; 2000].

  15. Rates and Mechanisms of Solidification in Large Magma Bodies: Implications for Melt Extraction in all Tectonic Settings

    NASA Astrophysics Data System (ADS)

    VanTongeren, J. A.

    2013-12-01

    As is observed in both experiment and theory, in the absence of hydrothermal convection, the majority of magma chamber heat loss occurs via conduction through the roof of the intrusion and into the cold country rock above. The formation of an upper solidification front (or Upper Border Series, UBS), recorded in the rocks both geochemically and texturally, is a natural outcome of the progression of the solidification front from the cold roof to the hot center of the magma chamber. There are, however, a few unique layered mafic intrusions for which little or no UBS exists. In this study, I examine the thermal evolution and crystallization rates of several classic layered intrusions as it is recorded in the extent of the preserved UBS. For those intrusions that have experienced crystallization at the roof, such as the Skaergaard Intrusion, the development of a UBS reduces the temperature gradient at the roof and effectively slows the rate of heat loss from the main magma body. However, for those intrusions that do not have an UBS, such as the Bushveld Complex, the cooling rate is controlled only by the maximum rate of conductive heat loss through the overlying roof rocks, which decreases with time. The implications are two-fold: (1) The relative thickness of the UBS in large intrusions may be the key to quantifying their cooling and solidification rates; and (2) The nature of the magma mush zone near the roof of an intrusion may depend principally on the long-term thermal evolution of the magma body. Particularly at the end stages of crystallization, when the liquids are likely to be highly evolved and high viscosities may inhibit convection, intrusions lacking a well-defined UBS may provide important insights into the mechanics of crystal-liquid separation, melt extraction, and compaction in felsic plutons as well as mafic intrusions. These results are important for long-lived (>500 kyr) or repeatedly replenished magma chambers in all tectonic settings.

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

    PubMed

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2015-10-28

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

  17. 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

  18. Facies architecture of a silicic intrusion-dominated volcanic centre at Highway Reward, Queensland, Australia

    NASA Astrophysics Data System (ADS)

    Doyle, M. G.; McPhie, J.

    2000-06-01

    collective volume of 0.5 km 3. Single porphyritic units vary from <10 to 350 m in thickness and some are less than 200 m in diameter. Ten of the porphyritic units studied in the immediate host sequence to the Highway-Reward deposit are entirely intrusive. Two of the units lack features diagnostic of their emplacement mechanism and could be either lavas and intrusions. Direct evidence for eruption at the seafloor is limited to a single partly extrusive cryptodome. However, distinctive units of resedimented autoclastic breccia indicate the presence nearby of additional lavas and domes. The size and shape of the lavas and intrusions reflect a restricted supply of magma during eruption/intrusion, the style of emplacement, and the subaqueous emplacement environment. Due to rapid quenching and mixing with unconsolidated clastic facies, the sills and cryptodomes did not spread far from their conduits. The shape and distribution of the lavas and intrusions were further influenced by the positions of previously or concurrently emplaced units. Magma preferentially invaded the sediment, avoiding the older units or conforming to their margins. Large intrusions and their dewatered envelope may have formed a barrier to the lateral progression and ascent of subsequent batches of magma.

  19. The thick and thin of magma in volcano-tectonics at various scales (Invited)

    NASA Astrophysics Data System (ADS)

    van Wyk de Vries, B.; Delcamp, A.; Mathieu, L.; Lebas, E.; Troll, V.

    2009-12-01

    Magma plays an essential part in the structural development of any volcano. An analysis of eroded volcanoes shows clearly two end member types of intrusion: 1) thin blade-like dykes and 2) thick, bulbous intrusions. Combining several field examples and analogue modelling results we have generated to date, I explore here the role of these different types of intrusion in the deformation of volcanoes on a range of scales. As a smallest scale case study, I use the Lemptègy scoria cone (Chaine de Puys, France; radius = 0.5 km). An intermediate-scale example is the Puy de Sancy stratovolcano (France; radius = c. 8 km).My largest-scale examples are the volcanoes of Mull (Scotland; radius = 20 km) and La Réunion (Indian Ocean; radius = 100k m) , In all examples, the same types of intrusion appear in a characteristic distribution. These include a dense core intrusion and thin central dykes, and an outer set of bulbous or fatter intrusions and cryptodomes. Central conduit areas that were originally fully magma-filled are now preserved as rubble and magma blobs. Analogue experiments indicate that the differences in style of intrusion can be related to different magma viscosities, rates of intrusion, and durations of intrusion. Any model of the role of magma in active volcano-tectonics must take into account the range of possible intrusion types that may occur at the same time. To take a small-scale example, I return to the 1995 Cerro Negro eruption, where activity analogous to Lemptègy must have simultaneously involved thin dykes, bulbous intrusions and an open conduit. For a large-scale example, I take the recent activity at Piton de La Fournaise, where there is a suggestion that dykes and a small central intrusion were involved. I show that the shallow dykes are controlled by primary fracturing due to cooling and deposition. Finally, I suggest a framework for including magmatic intrusions in a generalised model of volcano tectonics, whereby the growth and spreading of

  20. Magma intrusion near Volcan Tancitaro: Evidence from seismic analysis

    SciTech Connect

    Pinzon, Juan I.; Nunez-Cornu, Francisco J.; Rowe, Charlotte Anne

    2016-11-17

    Between May and June 2006, an earthquake swarm occurred near Volcan Tancítaro in Mexico, which was recorded by a temporary seismic deployment known as the MARS network. We located ~1000 events from this seismic swarm. Previous earthquake swarms in the area were reported in the years 1997, 1999 and 2000. We relocate and analyze the evolution and properties of the 2006 earthquake swarm, employing a waveform cross-correlation-based phase repicking technique. Hypocenters from 911 events were located and divided into eighteen families having a correlation coefficient at or above 0.75. 90% of the earthquakes provide at least sixteen phase picks. We used the single-event location code Hypo71 and the P-wave velocity model used by the Jalisco Seismic and Accelerometer Network to improve hypocenters based on the correlation-adjusted phase arrival times. We relocated 121 earthquakes, which show clearly two clusters, between 9–10 km and 3–4 km depth respectively. The average location error estimates are <1 km epicentrally, and <2 km in depth, for the largest event in each cluster. Depths of seismicity migrate upward from 16 to 3.5 km and exhibit a NE-SW trend. The swarm first migrated toward Paricutin Volcano but by mid-June began propagating back toward Volcán Tancítaro. In addition to its persistence, noteworthy aspects of this swarm include a quasi-exponential increase in the rate of activity within the first 15 days; a b-value of 1.47; a jug-shaped hypocenter distribution; a shoaling rate of ~5 km/month within the deeper cluster, and a composite focal mechanism solution indicating largely reverse faulting. As a result, these features of the swarm suggest a magmatic source elevating the crustal strain beneath Volcan Tancítaro.

  1. Uplift, thermal unrest and magma intrusion at Yellowstone caldera

    USGS Publications Warehouse

    Wicks, Charles W.; Thatcher, Wayne; Dzurisin, Daniel; Svarc, Jerry

    2006-01-01

    The Yellowstone caldera, in the western United States, formed 640,000 years ago when an explosive eruption ejected 1,000 km3 of material1. It is the youngest of a series of large calderas that formed during sequential cataclysmic eruptions that began 16 million years ago in eastern Oregon and northern Nevada. The Yellowstone caldera was largely buried by rhyolite lava flows during eruptions that occurred from 150,000 to 70,000 years ago1. Since the last eruption, Yellowstone has remained restless, with high seismicity, continuing uplift/subsidence episodes with movements of 70 cm historically2 to several metres since the Pleistocene epoch3, and intense hydrothermal activity. Here we present observations of a new mode of surface deformation in Yellowstone, based on radar interferometry observations from the European Space Agency ERS-2 satellite. We infer that the observed pattern of uplift and subsidence results from variations in the movement of molten basalt into and out of the Yellowstone volcanic system.

  2. Uplift, thermal unrest and magma intrusion at Yellowstone caldera.

    PubMed

    Wicks, Charles W; Thatcher, Wayne; Dzurisin, Daniel; Svarc, Jerry

    2006-03-02

    The Yellowstone caldera, in the western United States, formed approximately 640,000 years ago when an explosive eruption ejected approximately 1,000 km3 of material. It is the youngest of a series of large calderas that formed during sequential cataclysmic eruptions that began approximately 16 million years ago in eastern Oregon and northern Nevada. The Yellowstone caldera was largely buried by rhyolite lava flows during eruptions that occurred from approximately 150,000 to approximately 70,000 years ago. Since the last eruption, Yellowstone has remained restless, with high seismicity, continuing uplift/subsidence episodes with movements of approximately 70 cm historically to several metres since the Pleistocene epoch, and intense hydrothermal activity. Here we present observations of a new mode of surface deformation in Yellowstone, based on radar interferometry observations from the European Space Agency ERS-2 satellite. We infer that the observed pattern of uplift and subsidence results from variations in the movement of molten basalt into and out of the Yellowstone volcanic system.

  3. Magma intrusion near Volcan Tancitaro: Evidence from seismic analysis

    DOE PAGES

    Pinzon, Juan I.; Nunez-Cornu, Francisco J.; Rowe, Charlotte Anne

    2016-11-17

    Between May and June 2006, an earthquake swarm occurred near Volcan Tancítaro in Mexico, which was recorded by a temporary seismic deployment known as the MARS network. We located ~1000 events from this seismic swarm. Previous earthquake swarms in the area were reported in the years 1997, 1999 and 2000. We relocate and analyze the evolution and properties of the 2006 earthquake swarm, employing a waveform cross-correlation-based phase repicking technique. Hypocenters from 911 events were located and divided into eighteen families having a correlation coefficient at or above 0.75. 90% of the earthquakes provide at least sixteen phase picks. Wemore » used the single-event location code Hypo71 and the P-wave velocity model used by the Jalisco Seismic and Accelerometer Network to improve hypocenters based on the correlation-adjusted phase arrival times. We relocated 121 earthquakes, which show clearly two clusters, between 9–10 km and 3–4 km depth respectively. The average location error estimates are <1 km epicentrally, and <2 km in depth, for the largest event in each cluster. Depths of seismicity migrate upward from 16 to 3.5 km and exhibit a NE-SW trend. The swarm first migrated toward Paricutin Volcano but by mid-June began propagating back toward Volcán Tancítaro. In addition to its persistence, noteworthy aspects of this swarm include a quasi-exponential increase in the rate of activity within the first 15 days; a b-value of 1.47; a jug-shaped hypocenter distribution; a shoaling rate of ~5 km/month within the deeper cluster, and a composite focal mechanism solution indicating largely reverse faulting. As a result, these features of the swarm suggest a magmatic source elevating the crustal strain beneath Volcan Tancítaro.« less

  4. Petroleum Vapor Intrusion

    EPA Pesticide Factsheets

    One type of vapor intrusion is PVI, in which vapors from petroleum hydrocarbons such as gasoline, diesel, or jet fuel enter a building. Intrusion of contaminant vapors into indoor spaces is of concern.

  5. Magma flow-direction indicators in the diabase feeder dike to the first flood basalt in the Mesozoic Hartford basin, Connecticut

    SciTech Connect

    Philpotts, A.R.; Asher, P.M. . Dept. of Geology and Geophysics)

    1993-03-01

    Recent kinematic analysis has indicated that magma may have been emplaced horizontally rather than vertically in some large regional diabase dikes. Such analysis, however, has commonly relied on a single flow indicator, such as anisotropy of magnetic susceptibility, which may reflect only late stage adjustments in a body of crystallizing magma. This study of kinematic indicators in a Mesozoic diabase dike in southern New England indicates that the direction of flow in large dikes may change during emplacement, and that a single flow indicator cannot give a complete picture of the flow history. The 250-km-long Higganum dike fed the first flood basalt in the Hartford basin of Connecticut. The margins of this dike contain 8 independent magma flow indicators, which involve the imbrication and deformation of phenocrysts, the shearing of felsic wisps, and the segregation of residual liquids. The felsic wisps, which were derived by partial melting of the wallrock, preserve the most complete record of flow in the dike. Early felsic liquids exchanged alkalis with the still largely molten diabase magma and consequently are K-poor; ones that entered after the diabase was largely solid are relatively K-rich. Most K-poor felsic wisps were deformed into recumbent folds by back-flowing magma. Later K-rich felsic streaks parallel the axial planes of these folds. The shear of magma past phenocrysts near the dike margins also caused K-rich felsic liquids to segregate in low-pressure zones on the opposing ends of these crystals. All of these flow indicators record a complex history of dike emplacement, with periods of upward intrusion always being followed by periods of back-flow.

  6. Calderas and magma reservoirs

    NASA Astrophysics Data System (ADS)

    Cashman, Katharine V.; Giordano, Guido

    2014-11-01

    Large caldera-forming eruptions have long been a focus of both petrological and volcanological studies; petrologists have used the eruptive products to probe conditions of magma storage (and thus processes that drive magma evolution), while volcanologists have used them to study the conditions under which large volumes of magma are transported to, and emplaced on, the Earth's surface. Traditionally, both groups have worked on the assumption that eruptible magma is stored within a single long-lived melt body. Over the past decade, however, advances in analytical techniques have provided new views of magma storage regions, many of which provide evidence of multiple melt lenses feeding a single eruption, and/or rapid pre-eruptive assembly of large volumes of melt. These new petrological views of magmatic systems have not yet been fully integrated into volcanological perspectives of caldera-forming eruptions. Here we explore the implications of complex magma reservoir configurations for eruption dynamics and caldera formation. We first examine mafic systems, where stacked-sill models have long been invoked but which rarely produce explosive eruptions. An exception is the 2010 eruption of Eyjafjallajökull volcano, Iceland, where seismic and petrologic data show that multiple sills at different depths fed a multi-phase (explosive and effusive) eruption. Extension of this concept to larger mafic caldera-forming systems suggests a mechanism to explain many of their unusual features, including their protracted explosivity, spatially variable compositions and pronounced intra-eruptive pauses. We then review studies of more common intermediate and silicic caldera-forming systems to examine inferred conditions of magma storage, time scales of melt accumulation, eruption triggers, eruption dynamics and caldera collapse. By compiling data from large and small, and crystal-rich and crystal-poor, events, we compare eruptions that are well explained by simple evacuation of a zoned

  7. Modeling the three-dimensional structure of macroscopic magma transport systems: Application to Kilauea volcano, Hawaii

    SciTech Connect

    Ryan, M.P.; Koyanagi, R.Y.; Fiske, R.S.

    1981-08-10

    We report the results of modeling the three-dimensional internal structure of Kilauea's magmatic passageways. The approach uses a clear plexiglass model containing equally-spaced levels upon which well-located seismic hypocenters are plotted. Application of constraining geologic and geophysical criteria to this distributed volume of earthquakes permits the interpretation of seismic structures produced by fracturing in response to locally high fluid pressures. Four magma transport and storage structures produce have been identified within and beneath Kilauea: (1) Primary conduit. The conduit transporting magma into Kilauea's summit storage reservoir rises from the model base (14.6 km) to 6.5 km depth level. It is a zone of intense fracturing and inferred intrusion, whose horizontal sections are elliptical in planform. Over its height, the average major axis of component horizontal section is 3.3 km, with an average minor axis of 1.7 km. This yields an aspect ratio of xi = 0.52. At the 14.6 km level, the strike of the major axis is N67 /sup 0/E. During passage from the upper mantle through the oceanic crust, this axis rotates in a right-handed sense, until the strike is N41 /sup 0/W at the 6.5 km level. (2) Magma chamber complex floor. The interval from 6.5 to 5.7 km, immediately over the primary conduit, is aseismic. This suggests differentially high fluid-to-rock ratios, and relatively weak pathways for further vertical transport into higher levels of the storage complex, as well as lateral leakage eastward into the Mauna Ulu staging area: for later vertical ascent beneath the upper east rift zone. Seismicity within the immediately subjacent rocks that form the top of the primary conduit (at 6.5 km) suggests that this inferred magma-rich horizon forms the effective floor of the summit storage complex. (3) Magma chamber crown. Intense seismicity over the 1.1--1.9 km depth interval defines an elliptical region in plan view.

  8. The lateral extent of volcanic interactions during unrest and eruption

    NASA Astrophysics Data System (ADS)

    Biggs, Juliet; Robertson, Elspeth; Cashman, Katharine

    2016-04-01

    Volcanic eruptions often occur simultaneously or tap multiple magma reservoirs. Such lateral interactions between magmatic systems are attributed to stress changes or hydraulic connections but the precise conditions under which coupled eruptions occur have yet to be quantified. Here we use interferometric synthetic aperture radar satellite data to analyse the surface deformation generated by volcanic unrest in the Kenyan Rift. We identify several magma sources located at depths of 2-5 km importantly, sources that are spaced less than about 10 km apart interact, whereas those spaced more than about 25 km apart do not. However, volcanoes up to 25 km apart have interacted in the geologic past. Thus, volcanic coupling is not simply controlled by the distance between the magma reservoirs. We then consider different tectonic settings globally, including intraplate volcanoes such as Hawaii and Yellowstone, arc volcanism in Alaska and Chile, and other rift settings, such as New Zealand, Iceland and Afar. We find that the most closely spaced magmatic interactions are controlled by the extent of a shallow crystal mush layer, stress changes can couple large eruptions over distances of about 20-40 km, and only large dyke intrusions or subduction earthquakes could generate coupled eruptions over distances of about 50-100 km.

  9. Igneous layering in the peralkaline intrusions ,Kola Peninsula :leading role of gravitational differentiation

    NASA Astrophysics Data System (ADS)

    Kogarko, L. N..

    2012-04-01

    In the center of Kola Peninsula there are two large layered intrusions of agpaitic nepheline syenites - Khibina and Lovozero. . The Khibina alkaline massif (Kola Peninsula,Russia) hosts the world's largest and economically most important apatite deposit. The Khibina massif is a complex multiphase body built up from a number of ring-like and conical intrusions. The apatite bearing intrusion is ring-like and is represented by a layered body of ijolitic composition with a thickness of about 1 - 2 km. The upper zone is represented by different types of apatite ores. These rocks consist of 60-90% euhedral very small (tenths of mm)apatite crystals. The lower zone has mostly ijolitic composition. The lower zone grades into underlying massive urtite consisting of 75-90% large (several mm) euhedral nepheline. Our experimental studies of systems with apatite demonstrated the near-eutectic nature of the apatite-bearing intrusion, resulting in practically simultaneous crystallization of nepheline, apatite and pyroxene. The mathematical model of the formation of the layered apatite-bearing intrusion based on the processes of sedimentation under the conditions of steady state convection taking account of crystal sizes is proposed. Under the conditions of steady-state convection large crystals of nepheline continuously had been settling forming massive underlying urtite whereas smaller crystals of pyroxenes, nepheline and apatite had been stirred in the convecting melt. During the cooling the intensity of convection decreased causing a settling of smaller crystals of nepheline and pyroxene and later very small crystalls of apatite in the upper part of alkaline magma chamber. The Lovozero massif, the largest of the Globe layered peralkaline intrusion, comprises super-large rare-metal (Nb, Ta, REE) deposit. The main ore mineral is loparite (Na, Ce, Ca)2 (Ti, Nb)2O6 which was mined during many years. The composition of cumulus loparite changed systematically upward through the

  10. A tale of two magmas, Fuego, Guatemala

    NASA Astrophysics Data System (ADS)

    Berlo, Kim; Stix, John; Roggensack, Kurt; Ghaleb, Bassam

    2012-03-01

    Fuego volcano in Guatemala erupted in 1974 in a basaltic sub-Plinian event, which has been well documented and studied. In 1999, after a period of quiescence lasting 20 years, Fuego erupted again, this time less violently, but with persistent low-level activity. This study investigates the link between these episodes. Previous melt inclusion studies have shown magma erupted in 1974 to have been a volatile-rich hybrid tapped from a vertically extensive system. By contrast, magma erupted in 1999 and 2003 is similar in composition to that erupted in 1974, but melt inclusions are more evolved. Although melt inclusions from the later period are CO2 rich (up to ˜1,500 ppm), they have low H2O concentration (max 1.5 wt.%, compared to ˜6 wt.% in 1974). These melt inclusions have a modified H2O concentration due to diffusive re-equilibration at shallow pressures. Despite this diffusive exchange, both eruptions show evidence of recent mingling of the same low and higher K melts, one of which was slightly cooler than the other and as a result traversed the amphibole stability field. (210Pb/226Ra) data on selected bulk rock samples from 1974 suggest that whereas the cooler, more evolved end-member may have been degassing since the last major eruption in the 1930s, the warmer end-member intruded at most a decade prior to the 1974 eruption. The two end-members are thus batches of the same magma emplaced shallowly ˜30 years apart during which time the older batch was cooled and differentiated before mixing with the younger influx. The presence of the same two melts in the later eruptions suggests that magma in 1999 and 2003 is partly residual from 1974. The current eruptive activity is clearing the system of this residual magma prior to an expected new magma batch.

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

    NASA Astrophysics Data System (ADS)

    Iyer, H. M.

    1984-04-01

    This paper is a review of seismic, gravity, magnetic and electromagnetic techniques to detect and delineate magma chambers of a few cubic kilometres to several thousand cubic kilometres volume. A dramatic decrease in density and seismic velocity, and an increase in seismic attenuation and electrical conductivity occurs at the onset of partial melting in rocks. The geophysical techniques are based on detecting these differences in physical properties between solid and partially molten rock. Although seismic refraction techniques, with sophisticated instrumentation and analytical procedures, are routinely used for detailed studies of crustal structure in volcanic regions, their application for magma detection has been quite limited. In one study, in Yellowstone National Park, U.S.A., fan-shooting and time-term techniques have been used to detect an upper-crustal magma chamber. Attenuation and velocity changes in seismic waves from explosions and earthquakes diffracted around magma chambers are observed near some volcanoes in Kamchatka. Strong attenuation of shear waves from regional earthquakes, interpreted as a diffraction effect, has been used to model magma chambers in Alaska, Kamchatka, Iceland, and New Zealand. One of the most powerful techniques in modern seismology, the seismic reflection technique with vibrators, was used to confirm the existence of a strong reflector in the crust near Socorro, New Mexico, in the Rio Grande Rift. This reflector, discovered earlier from data from local earthquakes, is interpreted as a sill-like magma body. In the Kilauea volcano, Hawaii, mapping seismicity patterns in the upper crust has enabled the modelling of the complex magma conduits in the crust and upper mantle. On the other hand, in the Usu volcano, Japan, the magma conduits are delineated by zones of seismic quiescence. Three-dimensional modelling of laterally varying structures using teleseismic residuals is proving to be a very promising technique for detecting and

  12. Mechanics of two interacting magma-driven fractures: A numerical study

    NASA Astrophysics Data System (ADS)

    Zhang, Xi; Bunger, Andrew P.; Jeffrey, Robert G.

    2014-11-01

    To understand magma focusing from broad melting zones in the crust, propagation in brittle rocks of two interacting dikes ascending from a single deep source has been modeled using a time-dependent plane strain hydraulic fracturing model. The source is assumed to generate a constant influx rate to feed the dike growth, which is also aided by buoyancy effects. In contrast to uncoupled model results, the simultaneous parallel growth of two dikes to a certain distance is found to occur provided that the two dikes are initially of different heights, which might be produced either by previous magma intrusion or during nucleation. The shorter dike will chase the longer one and they can either progressively merge or continue subparallel growth at a reduced spacing, depending on the deviator stress between the vertical and horizontal stresses and the initial lateral separation, with parameters given in dimensionless forms. Numerical results reveal the mechanics for simultaneous ascents of two subparallel dikes, in that dike interaction can produce a low-stress field, which is just above the tip of the shorter dike, favorable to growth of the shorter dike. The energy analysis indicates that the energy required for two subparallel dikes is less than that for a single dike during the late-time buoyancy-viscosity propagation stage where considerable ascent occurs. This growth behavior might provide the mechanism for simultaneous, instead of sequential, growth of various dikes in a single set.

  13. The relationship between forceful and passive emplacement: The interplay between tectonic strain and magma supply in the Rosses Granitic Complex, NW Ireland

    NASA Astrophysics Data System (ADS)

    Stevenson, Carl

    2009-03-01

    The Rosses Granitic Complex, NW Ireland, part of the late Caledonian (c. 400 Ma) Donegal Batholith, provides the opportunity to study the interplay between relative tectonic strain and magma supply rates in the wall of a major tectonic shear zone. Anisotropy of magnetic susceptibility (AMS) measurements, structural analysis and examination of key intrusive relationships were used to assess the accommodation of magma, associated deformation and magma flow pathways in this complex. In this case the varying emplacement styles, switching from forceful to passive, indicate that relative tectonic strain and magma supply rates were not constant. In the earliest component (a suite of microgranite sheets), AMS reveals subtle fabrics discordant to the sheet margins and is interpreted as post-emplacement deformation fabrics. The concordance of these fabrics to the next component of the complex, the main pluton (G1 and G2 monzogranite), indicates that this deformation was caused by the forceful emplacement of the pluton. AMS fabrics in G1 and G2 reveal a dome shaped foliation with an east-west lineation, indicating an east-west oriented magma transport direction. Outcrops of small stocks or cupolas similar to G2, east of the main pluton, link it to similar lithologies in the Main Donegal Granite further to the east via a partially exposed lateral feeder. This suggests east to west emplacement. The next component, a suite of subvertical porphyritic felsite dykes, is shown (from AMS and visible shearing fabrics) to have been emplaced passively under east-west tension. The final component comprises G3 and G4 of the main pluton, which passively cut all earlier components and contains significant amounts of aplite, pegmatite and greisen. These are interpreted to be cupolas or stocks emanating from an unexposed sheet probably similar in composition and mode of emplacement to G1 and G2. Thus, a general model is put forward where initially forceful subhorizontal sheets extending

  14. Formation of tectonic peperites from alkaline magmas intruded into wet sediments in the Beiya area, western Yunnan, China

    USGS Publications Warehouse

    Xu, X.-W.; Cai, X.-P.; Zhong, J.-Y.; Song, B.-C.; Peters, S.G.

    2007-01-01

    Tertiary (3.78 Ma to 3.65 Ma) biotite-K-feldspar porphyritic bodies intrude Tertiary, poorly consolidated lacustrine sedimentary rocks in the Beiya mineral district in southwestern China. The intrusives are characterized by a microcrystalline and vitreous-cryptocrystalline groundmass, by replacement of some tabular K-feldspar phenocrysts with microcrystalline chlorite and calcite, and by Fe-rich rings surrounding biotite phenocrysts. Peculiar structures, such as contemporary contact faults and slickensides, ductile shear zones and flow folds, foliation and lineations, tension fractures, and banded and boudin peperites, are developed along the contact zones of the intrusives. These features are related to the forceful intrusion of the alkaline magmas into the wet Tertiary sediments. The partially consolidated magmas were deformed and flattened by continued forceful magma intrusion that produced boudinaged and banded peperites. These peperites characterized by containing oriented deformation fabrics are classified as tectonic peperites as a new type of peperite, and formation of these tectonic peperites was related to fracturing of magmas caused by forceful intrusion and shear deformation and to contemporary migration and injection of fluidized sediments along fractures that dismembered the porphyritic magma. Emplacement of the magma into the wet sediments in the Beiya area is interpreted to be related to a large pressure difference rather than to the buoyancy force. ?? 2007 Elsevier Ltd. All rights reserved.

  15. 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.

  16. A cryptic record of magma mixing in diorites revealed by high-precision SIMS oxygen isotope analysis of zircons

    NASA Astrophysics Data System (ADS)

    Appleby, S. K.; Graham, C. M.; Gillespie, M. R.; Hinton, R. W.; Oliver, G. J. H.; EIMF

    2008-05-01

    High-precision in-situ ion microprobe (SIMS) oxygen isotope analysis of zircons from two diorite intrusions associated with the late Caledonian Lochnagar pluton in Scotland has revealed large differences in the degree of heterogeneity in zircon δ18O between the diorites. Zircon crystals from the Cul nan Gad diorite (CnG) show a unimodal distribution of oxygen isotope values ( δ18O = 6.0 ± 0.6‰ (2 σ)) and no or only minor grain-scale variation. Those from the Allt Darrarie diorite (AD1) show a large range in δ18O and an apparent bimodal distribution with modes of 6.6 ± 0.4‰ and 7.3 ± 0.4‰. Variations of up to 1.2‰ occur between and within grains; both an increase and decrease in δ18O with zircon growth has been observed. The δ18O composition of growing zircon can only change if open-system processes affect the magma composition, i.e. if material of contrasting δ18O composition is added to the magma. The variability in AD1 is interpreted to represent a cryptic record of magma mixing. A 'deep crustal hot zone' is a likely site for generation of the dioritic magmas which developed by mixing of residual melts and crustal partial melts or by melting of mafic lower crustal rocks. The overall small number of zircons with mantle-like δ18O values (5.3 ± 0.6‰ (2 σ)) in the Lochnagar diorites is largely the product of crustal differentiation rather than crustal growth. The δ18O of quartz from the CnG and AD1 diorites shows only minor variation (CnG: 10.9 ± 0.5‰ (2 σ), AD1: 11.7 ± 0.6‰ (2 σ)) within single populations, with no evidence of mixing. Quartz-zircon isotopic disequilibrium is consistent with later crystallisation of quartz from late magmatic fluids, and in case of the AD1 diorite after the inferred magma mixing from a homogenised, higher δ18O melt. High-precision SIMS oxygen isotope analysis of zircon provides a new approach to identifying and resolving previously undetected early-stage magma mixing and constraining the compositions

  17. The role of estrogen in intrusive memories.

    PubMed

    Cheung, Jessica; Chervonsky, Liza; Felmingham, Kim L; Bryant, Richard A

    2013-11-01

    Intrusive memories are highly vivid, emotional and involuntary recollections which cause significant distress across psychological disorders including posttraumatic disorder (PTSD). Recent evidence has potentially extended our understanding of the development of intrusive memories by identifying biological factors which significantly impact on memories for emotionally arousing stimuli. This study investigated the role of stress on the development of intrusions for negative and neutral images, and indexed the potential contributions of sex (estrogen and progesterone) and stress (noradrenaline and cortisol) hormones. Whilst viewing the images, half the participants underwent a cold pressor stress (CPS) procedure to induce stress while the control participants immersed their hands in warm water. Saliva samples were collected to index estrogen, progesterone and noradrenergic and cortisol response. Participants (55 university students, 26 men, 29 women) viewed a series of negatively arousing and neutral images. Participants completed recall and intrusions measures 2 days later. Negative images resulted in greater recall and more intrusions than neutral images. In the cold water condition females recalled fewer neutral memories than males. Cortisol increase predicted decreased recall of negative memories in males, and estrogen predicted increased intrusions of negative images in women. These findings are consistent with evidence that circulating levels of ovarian hormones influence memory for emotionally arousing events, and provides the first evidence of the influence of sex hormones on intrusive memories. These results provide one possible explanation for the higher incidence of anxiety disorders in women.

  18. 3D Visualization of "Frozen" Dynamic Magma Chambers in the Duluth Complex, Northeastern Minnesota

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

  19. 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

  20. Watching magma from space

    USGS Publications Warehouse

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

    2000-01-01

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

  1. Earthquake swarms reveal submarine magma unrest induced by distant mega-earthquakes: Andaman Sea region

    NASA Astrophysics Data System (ADS)

    Špičák, Aleš; Vaněk, Jiří

    2016-02-01

    Little is known about earthquake-triggered magma intrusions or eruptions of submarine volcanoes. The analysis of teleseismic earthquake occurrence performed in this study offers a tool to address such enigmatic and inaccessible processes. In the past ten years, the Andaman Sea region repeatedly became a site of shallow earthquake swarms that followed distant mega-earthquakes by days to weeks. The MW 9.1 December 26, 2004 Sumatra-Andaman earthquake was followed by two earthquake swarms about 600 km northward in the Andaman Sea region, delayed by 30 and 35 days, respectively. Earthquakes of one of these seismic episodes, the extensive January 2005 earthquake swarm, migrated laterally at a rate of about 0.25 km per hour during the swarm evolution. The strong Indian Ocean MW 8.6 and 8.2 April 11, 2012 earthquake doublet west of Northern Sumatra was followed by an earthquake swarm approximately 800 km northward in the Andaman Sea region, delayed by 13 days. All the three swarms that followed the 2004 and 2012 mega-earthquakes occurred beneath distinct seamounts and seafloor ridges. Based on the observations of migration of earthquakes during the swarm and swarm occurrence beneath distinct highs at the seafloor, we conclude that these earthquake swarms probably resulted as a consequence of magma unrest induced by static and/or dynamic stress changes following the distant mega-earthquakes. Repeated occurrence of such a phenomenon suggests that the arc magma reservoirs beneath the Andaman Sea have recently reached some form of criticality and are vulnerable to even small stress changes. The Andaman seafloor could thus become a site of submarine volcanic eruptions in near future and deserves close attention of Earth scientists.

  2. Dynamics of magma supply, storage and migration at basaltic volcanoes: Geophysical studies of the Galapagos and Hawaiian volcanoes

    NASA Astrophysics Data System (ADS)

    Bagnardi, Marco

    Basaltic shields forming ocean island volcanoes, in particular those of Hawai'i and of the Galapagos Islands, constitute some of the largest volcanic features on Earth. Understanding subsurface processes such as those controlling magma supply, storage and migration at these volcanoes, is essential to any attempt to anticipate their future behavior. This dissertation presents a series of studies carried out at Hawaiian and Galapagos volcanoes. InSAR measurements acquired between 2003 and 2010 at Fernandina Volcano, Galapagos, are used to study the structure and the dynamics of the shallow magmatic system of the volcano (Chapter 3). Spatial and temporal variations in the measured displacements reveal the presence of two hydraulically connected areas of magma storage, and the modeling of the deformation data provides an estimate of their location and geometry. The same dataset also provides the first geodetic evidence for two subvolcanic sill intrusions (in 2006 and 2007) deep beneath the volcano's flank. The lateral migration of magma from the reservoirs during these intrusions could provide an explanation for enigmatic volcanic events at Fernandina such as the 1968 caldera collapse without significant eruption. Space-geodetic measurements of the surface deformation produced by the most recent eruptions at Fernandina, reveal that all have initiated with the intrusion of subhorizontal sills from the shallow magma reservoir (Chapter 4). A synthetic aperture radar (SAR) image acquired 1-2 h before the start of a radial fissure eruption in 2009 captures one of these sills in the midst of its propagation toward the surface. Galapagos eruptive fissures of all orientations have previously been presumed to be fed by vertical dikes, but these new findings allow a reinterpretation of the internal structure and evolution of Galapagos volcanoes and of similar basaltic shields elsewhere on Earth and on other planets. A joint analysis of InSAR and groud-based microgravity data

  3. Magnetic fabric constraints of the emplacement of igneous intrusions

    NASA Astrophysics Data System (ADS)

    Maes, Stephanie M.

    Fabric analysis is critical to evaluating the history, kinematics, and dynamics of geological deformation. This is particularly true of igneous intrusions, where the development of fabric is used to constrain magmatic flow and emplacement mechanisms. Fabric analysis was applied to three mafic intrusions, with different tectonic and petrogenetic histories, to study emplacement and magma flow: the Insizwa sill (Mesozoic Karoo Large Igneous Province, South Africa), Sonju Lake intrusion (Proterozoic Midcontinent Rift, Minnesota, USA), and Palisades sill (Mesozoic rift basin, New Jersey, USA). Multiple fabric analysis techniques were used to define the fabric in each intrusive body. Using digital image analysis techniques on multiple thin sections, the three-dimensional shape-preferred orientation (SPO) of populations of mineral phases were calculated. Low-field anisotropy of magnetic susceptibility (AMS) measurements were used as a proxy for the mineral fabric of the ferromagnetic phases (e.g., magnetite). In addition, a new technique---high-field AMS---was used to isolate the paramagnetic component of the fabric (e.g., silicate fabric). Each fabric analysis technique was then compared to observable field fabrics as a framework for interpretation. In the Insizwa sill, magnetic properties were used to corroborate vertical petrologic zonation and distinguish sub-units within lithologically defined units. Abrupt variation in magnetic properties provides evidence supporting the formation of the Insizwa sill by separate magma intrusions. Low-field AMS fabrics in the Sonju Lake intrusion exhibit consistent SW-plunging lineations and SW-dipping foliations. These fabric orientations provide evidence that the cumulate layers in the intrusion were deposited in a dynamic environment, and indicate magma flowed from southwest to northeast, parallel to the pre-existing rift structures. In the Palisades sill, the magnetite SPO and low-field AMS lineation have developed orthogonal to

  4. Interior intrusion detection systems

    SciTech Connect

    Rodriguez, J.R.; Matter, J.C. ); Dry, B. )

    1991-10-01

    The purpose of this NUREG is to present technical information that should be useful to NRC licensees in designing interior intrusion detection systems. Interior intrusion sensors are discussed according to their primary application: boundary-penetration detection, volumetric detection, and point protection. Information necessary for implementation of an effective interior intrusion detection system is presented, including principles of operation, performance characteristics and guidelines for design, procurement, installation, testing, and maintenance. A glossary of sensor data terms is included. 36 figs., 6 tabs.

  5. Lunar igneous intrusions.

    PubMed

    El-Baz, F

    1970-01-02

    Photographs taken from Apollo 10 and 11 reveal a number of probable igneous intrusions, including three probable dikes that crosscut the wall and floor of an unnamed 75-kilometer crater on the lunar farside. These intrusions are distinguished by their setting, textures, structures, and brightness relative to the surrounding materials. Recognition of these probable igneous intrusions in the lunar highlands slupports the indications of the heterogeneity of lunar materials and the plausibility of intrusive igneous activity, in addition to extrusive volcanism, on the moon.

  6. Self Sealing Magmas

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  7. Magma energy for power generation

    SciTech Connect

    Dunn, J.C.

    1987-01-01

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

  8. The Role of Spinel Minerals in Lunar Magma Evolution

    NASA Astrophysics Data System (ADS)

    Taylor, L. A.; Head, J. W.; Pieters, C. M.; Sunshine, J. M.; Staid, M.; Isaacson, P.; Petro, N. E.

    2009-12-01

    The Moon Mineralogy Mapper (M3), a NASA guest instrument on Chandrayaan-1, India’s first mission to the Moon, was designed to map the surface mineralogy of the Moon using reflected solar radiation at visible and near-infrared wavelengths, which contain highly diagnostic absorptions due to minerals. The M3 spectrometer has discovered several new and unexpected aspects of the geology and petrology of the Moon, some involving specific oxide phases. Spinel minerals, with the general formula, AB2O4, present clues as to the oxygen fugacity, the nature of magmatic systems, and their evolution, particularly during the early stages of crystallization. On the Moon, with its total lack of Fe3+ and minerals such as magnetite, observed spinels range between spinel, MgAl2O4; hercynite, FeAl2O4; Chromite, FeCr2O4; and ulvöspinel, Fe(FeTi)2O4. They manifest themselves in three distinctly different igneous rock types: highlands rocks of anorthosites/troctolites, gabbro-norites; mare basalts with various TiO2 contents; and basaltic pyroclastic volcanic glasses. Although spinels occur as minor minerals in the Apollo collection, unique rock types dominated by Mg-spinel (with olivine and pyroxene abundances below detection limits, assumed to be ~5%) have been identified by M3 on the Moon. Because the spinel-bearing rocks detected by M3 have no signature of a significant olivine component, they must be dominated by plagioclase and spinel. Pink Mg-spinels typically occur as a minor phase in troctolites (plagioclase + olivine), a highland rock formed after the initial Ferroan Anorthosite (FAN) crust, presumably by serial magmatism deep within the crust, with intrusion upward. FANs were formed by floatation of plagioclase in the lunar magma ocean (LMO), whereas spinels would sink due to their much higher density. Thus, a plagioclase-rich rock type with a strong Mg-spinel spectral signature would have to be part of later highland intrusives. The excess Mg-spinel could be the product of

  9. An Approach for Developing Site-Specific Lateral and Vertical Inclusion Zones within which Structures Should be Evaluated for Petroleum Vapor Intrusion due to Releases of Motor Fuel from Underground Storage Tanks

    EPA Science Inventory

    Buildings may be at risk from Petroleum Vapor Intrusion (PVI) when they overlie petroleum hydrocarbon contamination in the unsaturated zone or dissolved in groundwater. The U.S. EPA Office of Underground Storage Tanks (OUST) is preparing Guidance for Addressing Petroleum Vapor I...

  10. 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

  11. 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.

  12. Episodic intrusion, internal differentiation, and hydrothermal alteration of the miocene tatoosh intrusive suite south of Mount Rainier, Washington

    USGS Publications Warehouse

    du Bray, E.A.; Bacon, C.R.; John, D.A.; Wooden, J.L.; Mazdab, F.K.

    2011-01-01

    The Miocene Tatoosh intrusive suite south of Mount Rainier is composed of three broadly granodioritic plutons that are manifestations of ancestral Cascades arc magmatism. Tatoosh intrusive suite plutons have individually diagnostic characteristics, including texture, mineralogy, and geochemistry, and apparently lack internal contacts. New ion-microprobe U-Pb zircon ages indicate crystallization of the Stevens pluton ca. 19.2 Ma, Reflection-Pyramid pluton ca. 18.5 Ma, and Nisqually pluton ca. 17.5 Ma. The Stevens pluton includes rare, statistically distinct ca. 20.1 Ma zircon antecrysts. Wide-ranging zircon rare earth element (REE), Hf, U, and Th concentrations suggest late crystallization from variably evolved residual liquids. Zircon Eu/Eu*-Hf covariation is distinct for each of the Reflection-Pyramid, Nisqually, and Stevens plutons. Although most Tatoosh intrusive suite rocks have been affected by weak hydrothermal alteration, and sparse mineralized veins cut some of these rocks, significant base or precious metal mineralization is absent. At the time of shallow emplacement, each of these magma bodies was largely homogeneous in bulk composition and petrographic features, but, prior to final solidification, each of the Tatoosh intrusive suite plutons developed internal compositional variation. Geochemical and petrographic trends within each pluton are most consistent with differential loss of residual melt, possibly represented by late aplite dikes or erupted as rhyolite, from crystal-rich magma. Crystal-rich magma that formed each pluton evidently accumulated in reservoirs below the present level of exposure and then intruded to a shallow depth. Assembled by episodic intrusion, the Tatoosh intrusive suite may be representative of midsized composite plutonic complexes beneath arc volcanoes. ?? 2011 Geological Society of America.

  13. Rare earth mineralisation in the Cnoc nan Cuilean intrusion of the Loch Loyal Syenite Complex, northern Scotland

    NASA Astrophysics Data System (ADS)

    Walters, A. S.; Hughes, H. S. R.; Goodenough, K. M.; Gunn, A. G.; Lacinska, A.

    2012-04-01

    Due to growing global concerns about security of rare earth element (REE) supply, there is considerable interest in identifying new deposits and in understanding the processes responsible for their formation. Ongoing studies by BGS on potential indigenous resources have focused on the Caledonian alkaline intrusive complexes of north-west Scotland. The highest values of total rare earth oxide (TREO) have been found in the Cnoc nan Cuilean intrusion of the Loch Loyal Complex in Sutherland. The Loch Loyal Syenite Complex comprises three intrusions: Ben Loyal, Beinn Stumanadh and Cnoc nan Cuilean. The Cnoc nan Cuilean intrusion, which covers an area of about 3 km2, can be subdivided into two zones: a Mixed Syenite Zone (MSZ) and a later Massive Leucosyenite Zone (MLZ). Evidence from field mapping and 3D-modelling suggests that the melasyenites were passively emplaced to form a lopolith concordant with the Moine and Lewisian country rocks. A later episode of leucosyenitic magmatism caused mixing and mingling with the melasyenite forming the MSZ. Continued intrusion of leucosyenite melts then formed the MLZ [1]. The melasyenites are enriched in TREO relative to the leucosyenites with average values of 3800 ppm and 1400 ppm respectively. The highest contents, up to 20 000 ppm TREO, are found in narrow biotite-magnetite-rich veins identified in a single stream section near the eastern margin of the intrusion. All lithologies are light rare earth element (LREE) dominated with high concentrations of Ba and Sr and low levels of Nb and Ta. Various REE-bearing minerals are present but allanite is dominant, being present in all major magmatic lithologies and the biotite-magnetite veins. Three generations of allanite have been identified: a late-magmatic phase rimming apatite; allanite micro veinlets cross-cutting the syenite; and a third phase only observed in the biotite-magnetite veins. TREO concentrations of the different allanite generations are similar, averaging 22%. The

  14. 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

  15. Increased capture of magma in the crust promoted by ice-cap retreat in Iceland

    NASA Astrophysics Data System (ADS)

    Hooper, Andrew; Ófeigsson, Benedikt; Sigmundsson, Freysteinn; Lund, Björn; Einarsson, Páll; Geirsson, Halldór; Sturkell, Erik

    2011-11-01

    Climate warming at the end of the last glaciation caused ice caps on Icelandic volcanoes to retreat. Removal of surface ice load is thought to have decreased pressures in the underlying mantle, triggering decompression melting, enhanced magma generation and increased volcanic activity. Present-day climate change could have the same effect, although there may be a time lag of hundreds of years between magma generation and eruption. However, in addition to increased magma generation, pressure changes associated with ice retreat should also alter the capacity for storing magma within the crust. Here we use a numerical model to evaluate the effect of the current decrease in ice load on magma storage in the crust at the Kverkfjöll volcanic system, located partially beneath Iceland's largest ice cap. We compare the model results with radar and global positioning system measurements of surface displacement and changes in crustal stress between 2007 and 2008, during the intrusion of a deep dyke at Upptyppingar. We find that although the main component of stress recorded during dyke intrusion relates to plate extension, another component of stress is consistent with the stress field caused by the retreating ice cap. We conclude that the retreating ice cap led to enhanced capture of magma within the crust. We suggest that ice-cap retreat can promote magma storage, rather than eruption, at least in the short term.

  16. 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

  17. On the conditions of magma mixing and its bearing on andesite production in the crust.

    PubMed

    Laumonier, Mickael; Scaillet, Bruno; Pichavant, Michel; Champallier, Rémi; Andujar, Joan; Arbaret, Laurent

    2014-12-15

    Mixing between magmas is thought to affect a variety of processes, from the growth of continental crust to the triggering of volcanic eruptions, but its thermophysical viability remains unclear. Here, by using high-pressure mixing experiments and thermal calculations, we show that hybridization during single-intrusive events requires injection of high proportions of the replenishing magma during short periods, producing magmas with 55-58 wt% SiO2 when the mafic end-member is basaltic. High strain rates and gas-rich conditions may produce more felsic hybrids. The incremental growth of crustal reservoirs limits the production of hybrids to the waning stage of pluton assembly and to small portions of it. Large-scale mixing appears to be more efficient at lower crustal conditions, but requires higher proportions of mafic melt, producing more mafic hybrids than in shallow reservoirs. Altogether, our results show that hybrid arc magmas correspond to periods of enhanced magma production at depth.

  18. 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.

  19. Aftershock decay, productivity, and stress rates in Hawaii: Indicators of temperature and stress from magma sources

    USGS Publications Warehouse

    Klein, Fred W.; Wright, Tom; Nakata, Jennifer

    2006-01-01

    We examined dozens of aftershock sequences in Hawaii in terms of Gutenberg-Richter and modified Omori law parameters. We studied p, the rate of aftershock decay; Ap, the aftershock productivity, defined as the observed divided by the expected number of aftershocks; and c, the time delay when aftershock rates begin to fall. We found that for earthquakes shallower than 20 km, p values >1.2 are near active magma centers. We associate this high decay rate with higher temperatures and faster stress relaxation near magma reservoirs. Deep earthquakes near Kilauea's inferred magma transport path show a range of p values, suggesting the absence of a large, deep magma reservoir. Aftershock productivity is >4.0 for flank earthquakes known to be triggered by intrusions but is normal (0.25 to 4.0) for isolated main shocks. We infer that continuing, post-main shock stress from the intrusion adds to the main shock's stress step and causes higher Ap. High Ap in other zones suggests less obvious intrusions and pulsing magma pressure near Kilauea's feeding conduit. We calculate stress rates and stress rate changes from pre-main shock and aftershock rates. Stress rate increased after many intrusions but decreased after large M7–8 earthquakes. Stress rates are highest in the seismically active volcano flanks and lowest in areas far from volcanic centers. We found sequences triggered by intrusions tend to have high Ap, high (>0.10 day) c values, a stress rate increase, and sometimes a peak in aftershock rate hours after the main shock. We interpret these values as indicating continuing intrusive stress after the main shock.

  20. Number of Waste Package Hit by Igneous Intrusion

    SciTech Connect

    M. Wallace

    2004-10-13

    The purpose of this scientific analysis report is to document calculations of the number of waste packages that could be damaged in a potential future igneous event through a repository at Yucca Mountain. The analyses include disruption from an intrusive igneous event and from an extrusive volcanic event. This analysis supports the evaluation of the potential consequences of future igneous activity as part of the total system performance assessment for the license application (TSPA-LA) for the Yucca Mountain Project (YMP). Igneous activity is a disruptive event that is included in the TSPA-LA analyses. Two igneous activity scenarios are considered: (1) The igneous intrusion groundwater release scenario (also called the igneous intrusion scenario) considers the in situ damage to waste packages or failure of waste packages that occurs if they are engulfed or otherwise affected by magma as a result of an igneous intrusion. (2) The volcanic eruption scenario depicts the direct release of radioactive waste due to an intrusion that intersects the repository followed by a volcanic eruption at the surface. An igneous intrusion is defined as the ascent of a basaltic dike or dike system (i.e., a set or swarm of multiple dikes comprising a single intrusive event) to repository level, where it intersects drifts. Magma that does reach the surface from igneous activity is an eruption (or extrusive activity) (Jackson 1997 [DIRS 109119], pp. 224, 333). The objective of this analysis is to develop a probabilistic measure of the number of waste packages that could be affected by each of the two scenarios.

  1. Geochemical constraints on the origin of the Permian Baimazhai mafic-ultramafic intrusion, SW China

    NASA Astrophysics Data System (ADS)

    Wang, Christina Yan; Zhou, Mei-Fu; Keays, Reid R.

    2006-09-01

    The ˜260 Ma Baimazhai mafic-ultramafic intrusion is considered to be part of the Emeishan large igneous province and consists of orthopyroxenite surrounded by websterite and gabbro. The intrusion is variably mineralized with a massive sulfide ore body (˜20 vol.%) in the core of the intrusion. Silicate rocks have Ni/Cu ratios ranging from 0.3 to 46 with majority less than 7 and are rich in LREE relative to HREE and show Nb and Ta anomalies in primitive mantle-normalized trace element patterns, with low Nb/Th (1.0-4.5) and Nb/La (0.3-1.0) ratios. Their ɛ Nd( t) values range from -3.3 to -8.4. Uniform Pd/Pt (0.7-3.5) and Cu/Pd (100,000-400,000) ratios throughout the intrusion indicate that all the sulfides in the rocks were formed in a single sulfide-saturation event. Modeling suggests that the Baimazhai rocks were formed when an Mg-rich magma became crustally contaminated in a deep-seated staging chamber. Crustal contamination (up to ˜35%) drove the magma to S-saturation and forced orthopyroxene (Opx) onto the liquidus. The crystal-bearing magma forced out of the staging chamber was migrated by flow differentiation and consequently, the denser sulfide melt and the Opx crystals became centrally disposed in the flowing magma to form the Baimazhai intrusion.

  2. 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

  3. Time, space, and composition relations among northern Nevada intrusive rocks and their metallogenic implications

    USGS Publications Warehouse

    duBray, E.A.

    2007-01-01

    Importantly, modal composition, age, and geochemical characteristics of intrusions associated with large mineral deposits along the trends, are indistinguishable from non-mineralized intrusions in northern Nevada and thus do not identify intrusions associated with significant deposits. Moreover, intrusion age and composition show little correlation with mineral-deposit type, abundance, and size. Given the lack of diagnostic characteristics for intrusions associated with deposits, it is uncertain whether age, modal composition, and geochemical data can identify intrusions associated with mineral deposits. These findings suggest that associations between northern Nevada intrusions and mineral deposits reflect superimposition of many geologic factors, none of which was solely responsible for mineral-deposit formation. These factors might include intrusion size, efficiency of fluid and metal extraction from magma, prevailing redox and sulfidation conditions, or derivation of metals and ligands from host rocks and groundwater. The abundance and diversity of mineral deposits in northern Nevada may partly reflect geochemical inheritance, for example, along the mineral trends rather than the influence of petrologically unique magma or associated fluids.

  4. Variable H2O content in magmas from the Tongariro Volcanic Centre and its relation to crustal storage and magma ascent

    NASA Astrophysics Data System (ADS)

    Auer, A.; White, J. D. L.; Tobin, M. J.

    2016-10-01

    The water content of crystal-hosted glass inclusions from Mt. Ruapehu has been determined by Fourier transform infrared spectroscopy (FTIR) at the IR beamline of the Australian Synchrotron. The results are compared with those from previous investigations as well as with calculated melt water concentrations in other magmas from the Tongariro Volcannic Center (TgVC). It is shown that low and high water content in different magmas can be related to distinct styles of magma ascent and intermittent crustal storage. The first style is related to frequent small magma batches erupted from the central volcanoes of Mt. Tongariro and Mt. Ruapehu. It produces highly porphyritic two-pyroxene-plagioclase andesites which generally show water contents below 3 wt%. The second style is sourced from mid-crustal intrusions which are characterized by highly differentiated hornblende dacites with dissolved water concentrations of up to 6 wt% H2O.

  5. Igneous Intrusion Impacts on Waste Packages and Waste Forms

    SciTech Connect

    P. Bernot

    2004-08-16

    The purpose of this model report is to assess the potential impacts of igneous intrusion on waste packages and waste forms in the emplacement drifts at the Yucca Mountain Repository. The model is based on conceptual models and includes an assessment of deleterious dynamic, thermal, hydrologic, and chemical impacts. This constitutes the waste package and waste form impacts submodel of the Total System Performance Assessment for the License Application (TSPA-LA) model assessing the impacts of a hypothetical igneous intrusion event on the repository total system performance. This submodel is carried out in accordance with Technical Work Plan for Waste Form Degradation Modeling, Testing, and Analyses in Support of SR and LA (BSC 2003a) and Total System Performance Assessment-License Application Methods and Approaches (BSC 2002a). The technical work plan is governed by the procedures of AP-SIII.10Q, Models. Any deviations from the technical work plan are documented in the TSPA-LA approach to implementing the models for waste package and waste form response during igneous intrusion is based on identification of damage zones. Zone 1 includes all emplacement drifts intruded by the basalt dike, and Zone 2 includes all other emplacement drifts in the repository that are not in Zone 1. This model report will document the following model: (1) Impacts of magma intrusion on the components of engineered barrier system (e.g., drip shields and cladding) of emplacement drifts in Zone 1, and the fate of waste forms. (2) Impacts of conducting magma heat and diffusing magma gases on the drip shields, waste packages, and cladding in the Zone 2 emplacement drifts adjacent to the intruded drifts. (3) Impacts of intrusion on Zone 1 in-drift thermal and geochemical environments, including seepage hydrochemistry. The scope of this model only includes impacts to the components stated above, and does not include impacts to other engineered barrier system (EBS) components such as the invert and

  6. Intrusive Images in Psychological Disorders

    PubMed Central

    Brewin, Chris R.; Gregory, James D.; Lipton, Michelle; Burgess, Neil

    2010-01-01

    Involuntary images and visual memories are prominent in many types of psychopathology. Patients with posttraumatic stress disorder, other anxiety disorders, depression, eating disorders, and psychosis frequently report repeated visual intrusions corresponding to a small number of real or imaginary events, usually extremely vivid, detailed, and with highly distressing content. Both memory and imagery appear to rely on common networks involving medial prefrontal regions, posterior regions in the medial and lateral parietal cortices, the lateral temporal cortex, and the medial temporal lobe. Evidence from cognitive psychology and neuroscience implies distinct neural bases to abstract, flexible, contextualized representations (C-reps) and to inflexible, sensory-bound representations (S-reps). We revise our previous dual representation theory of posttraumatic stress disorder to place it within a neural systems model of healthy memory and imagery. The revised model is used to explain how the different types of distressing visual intrusions associated with clinical disorders arise, in terms of the need for correct interaction between the neural systems supporting S-reps and C-reps via visuospatial working memory. Finally, we discuss the treatment implications of the new model and relate it to existing forms of psychological therapy. PMID:20063969

  7. The oxidation state, and sulfur and Cu contents of arc magmas: implications for metallogeny

    NASA Astrophysics Data System (ADS)

    Richards, Jeremy P.

    2015-09-01

    Global data for measured Fe2O3/FeO ratios and Cu contents in unaltered volcanic and intrusive arc rocks indicate that, on average, they are slightly more oxidized than other magmas derived from depleted upper mantle (such as MORB), but contain similar Cu contents across their compositional ranges. Although Cu scatters to elevated values in some intermediate composition samples, the bulk of the data show a steady but gentle trend to lower concentrations with differentiation, reaching modal values of 50-100 ppm in andesitic rocks. These data suggest that Cu is mildly compatible during partial melting and fractionation processes, likely reflecting minor degrees of sulfide saturation throughout the magmatic cycle. However, the volume of sulfides must be small such that significant proportions of the metal content remain in the magma during fractionation to intermediate compositions. Previous studies have shown that andesitic magmas containing 50 ppm Cu can readily form large porphyry-type Cu deposits upon emplacement in the upper crust. A review of the literature suggests that the elevated oxidation state in the asthenospheric mantle wedge source of arc magmas (ΔFMQ ≈ + 1 ± 1) derives from the subduction of seawater-altered and oxidized oceanic crust, and is transmitted into the mantle wedge via prograde metamorphic dehydration fluids carrying sulfate and other oxidizing components. Progressive hydration and oxidation of the mantle wedge may take up to 10 m.y. to reach a steady state from the onset of subduction, explaining the rarity of porphyry deposits in primitive island arcs, and the late formation of porphyries in continental arc magmatic cycles. Magmas generated from this metasomatized and moderately oxidized mantle source will be hydrous basalts containing high concentrations of sulfur, mainly dissolved as sulfate or sulfite. Some condensed sulfides (melt or minerals) may be present due to the high overall fS2, despite the moderately high oxidation state

  8. 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.

  9. Intrusive LIPs: Deep crustal magmatic processes during the emplacement of Large Igneous Provinces

    NASA Astrophysics Data System (ADS)

    Richards, M. A.; Karlstrom, L.

    2011-12-01

    Large Igneous Provinces (LIPs) are characterized by magmatic activity on two distinct timescales. While these provinces have total active lifetimes of order 10-30 Ma, most of the erupted volume is emplaced within <1 Ma in many cases. The latter timescale is likely controlled by magmatic intrusion/evolution processes within the deep crust. We present seismic evidence for 5-15 km thick Moho-level ultramafic intrusive/cumulate layers underlying Phanerozoic LIPs worldwide [Ridley and Richards, 2010]. These deep crustal bodies are both observed and predicted to have volumes at least as large as the extrusive components of flood volcanism. The evidence for these layers is particularly clear for oceanic LIPs (plateaus). We hypothesize that thermally activated creep of the lower crust due to magma chamber emplacement controls a transition from largely extrusive to largely intrusive magmatism during mantle plume impingement on the lithosphere [Karlstrom and Richards, 2011]. We explore this hypothesis by modeling the thermomechanical evolution of Moho-level magma chambers. Comparing the timescale for viscoelastic relaxation of intrusion-related stresses with the timescale for sill formation and magma differentiation, we find that fracture processes leading to diking from Moho levels may plausibly be shut off on a timescale of ~1 Ma. Continued melt influx therefore results in intrusive magmatism, which may be manifest as plateau growth in oceanic settings. We suggest that maximum intrusion size may be limited by crustal thickness, resulting in smaller volume individual eruptions in oceanic versus continental LIPs.

  10. [The spectrum studies of structure characteristics in magma contact metamorphic coal].

    PubMed

    Wu, Dun; Sun, Ruo-Yu; Liu, Gui-Jian; Yuan, Zi-Jiao

    2013-10-01

    The structural parameters evolution of coal due to the influence of intrusions of hot magma was investigated and analyzed. X-ray diffraction and laser confocal microscope Raman spectroscopy were used to test and analyze 4 coal samples undergoing varying contact-metamorphism by igneous magmas in borehole No. 13-4 of Zhuji coal mine, Huainan coalfield. The result showed that coal XRD spectrum showed higher background intensity, with the 26 degrees and 42 degrees nearby apparent graphite diffraction peak. Two significant vibration peaks of coal Raman spectra were observed in the 1 000-2 000 cm(-1) frequency range: broad "D" peak at 1 328-1 369 cm(-1) and sharp "G" peak at 1 564-1 599 cm(-1). With the influence of magma intrusion, the relationship between coal structural parameters and coal ranks was excellent.

  11. Magma in forearcs: implication for ophiolite generation

    NASA Astrophysics Data System (ADS)

    Jakeŝ, Petr; Miyake, Yasuyuki

    1984-07-01

    Forearc areas ("non-volcanic" arcs) of contemporary island arcs at convergent plate boundaries contain magmatic rocks. Geological evidence, seismic profiles, heat flow data, density considerations and petrological and geochemical arguments suggest that a forearc tholeiitic association (FAT) (containing high-Mg calc-alkaline andesites) is present in "non-volcanic" arcs at some stage of island-arc development. The fractionated, as well as primitive magma, is unable to penetrate low-density sediments and underplates thick piles of unconsolidated accreting rocks. The underplating causes upwelling. The occurrence of magma in forearcs provides an alternative interpretation for the tectonic setting of some ophiolitic masses. Rather than "ocean-ridge formation" and later "obduction" it offers an autochthonous (island-arc bound and geologically-substantiated) interpretation for the ophiolite suite.

  12. 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.

  13. Stress control of deep rift intrusion at Mauna Loa volcano, Hawaii.

    PubMed

    Amelung, Falk; Yun, Sang-Ho; Walter, Thomas R; Segall, Paul; Kim, Sang-Wan

    2007-05-18

    Mauna Loa volcano, Hawaii, deforms by a combination of shallow dike intrusions in the rift zones and earthquakes along the base of the volcano, but it is not known how the spreading is accommodated in the lower part of the volcanic edifice. We present evidence from interferometric synthetic aperture radar data for secular inflation of a dike-like magma body at intermediate depth in the southwest rift zone during 2002 to 2005. Magma accumulation occurred in a section of the rift zone that was unclamped by previous dikes and earthquakes, suggesting that stress transfer plays an important role in controlling subsurface magma accumulation.

  14. Computer Intrusions and Attacks.

    ERIC Educational Resources Information Center

    Falk, Howard

    1999-01-01

    Examines some frequently encountered unsolicited computer intrusions, including computer viruses, worms, Java applications, trojan horses or vandals, e-mail spamming, hoaxes, and cookies. Also discusses virus-protection software, both for networks and for individual users. (LRW)

  15. Detecting Signs of Intrusion.

    DTIC Science & Technology

    1997-08-01

    your systems, you should investigate any warnings they sound. Although monitors are not fool- proof, they can be part of an effective early warning ...Carnegie Mellon University Software Engineering Institute Detecting Signs of Intrusion Robert Firth Gary Ford Barbara Fräser John Kochmar...1997 Detecting Signs of Intrusion Robert Firth Gary Ford Barbara Fräser John Kochmar Suresh Konda John Richael Derek Simmel Networked Systems

  16. A multi-sill magma plumbing system beneath the axis of the East Pacific Rise

    NASA Astrophysics Data System (ADS)

    Marjanović, Milena; Carbotte, Suzanne M.; Carton, Helene; Nedimović, Mladen R.; Mutter, John C.; Canales, Juan Pablo

    2014-11-01

    Upper oceanic crust at fast- to intermediate-spreading mid-ocean ridges is thought to form from the intrusion and eruption of magma accumulated within a mid-crustal reservoir present beneath the ridge axis. However, the mechanisms for formation of the lower crust are debated. Observations from pieces of ancient oceanic crust exposed on land -- ophiolites -- imply that multiple small magma lenses exist throughout the lower crust at mid-ocean ridges and help form the crust, yet seismic data have imaged only a single lens beneath the innermost axial zones of various mid-ocean ridges. Here we use high-fidelity seismic data to image the crust beneath the East Pacific Rise. We identify a series of reflections below the axial magma lens that we interpret as magma lenses in the upper part of the lower crust. These reflections are present between 9° 20' and 9° 57' N and are located up to 1.5 km below the axial magma lens. From the geometry and amplitude of the reflections in a zone beneath a recent volcanic eruption, we infer that magma drained from a lower lens helped replenish the axial magma lens above and, perhaps, contributed to the eruption. Our data indicate that a multi-level complex of magma lenses is present beneath the East Pacific Rise and probably contributes to the formation of both the upper and lower crust.

  17. Crystallization of the magma ocean

    NASA Astrophysics Data System (ADS)

    Caracas, R.; Nomura, R.; Hirose, K.; Ballmer, M. D.

    2015-12-01

    We model the crystallization of the magma ocean using pyrolite as a proxy for its composition. We employ first-principles molecular-dynamics calculations to determine the density of the magmas. We use diamond-anvil cell experiments to trace the chemical evolution of the magmas during cooling and crystallization. We build a grid of pressure and temperature points, following the chemical evolution of the magma during the entire fractional crystallization of perovskite. Then we construct a geodynamical model of the evolving magma fully taking into account the density and chemistry of the melts and crystals. We show that the dynamics of the crystallization of the magma ocean is highly dependent (i) on extrinsic parameters, like pressure at the core-mantle boundary and temperature profile through the magma ocean, and (ii) on intrinsic parameters, like relative density relations between the melt and the crystals and vigor of the stirring. Formation of a solid layer in the middle of the magma ocean is possible, which can lead to the eventual formation of a basal magma ocean.

  18. 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

  19. Isotopic variation in the Tuolumne Intrusive Suite, central Sierra Nevada, California

    USGS Publications Warehouse

    Kistler, R.W.; Chappell, B.W.; Peck, D.L.; Bateman, P.C.

    1986-01-01

    Granitoid rocks of the compositionally zoned Late Cretaceous Toulumne Intrusive Suite in the central Sierra Nevada, California, have initial87Sr/86Sr values (Sri) and143Nd/144Nd values (Ndi) that vary from 0.7057 to 0.7067 and from 0.51239 to 0.51211 respectively. The observed variation of both Sri and Ndi and of chemical composition in rocks of the suite cannot be due to crystal fractionation of magma solely under closed system conditons. The largest variation in chemistry, Ndi, and Sri is present in the outer-most equigranular units of the Tuolumne Intrusive Suite. Sri varies positively with SiO2, Na2O, K2O, and Rb concentrations, and negatively with Ndi, Al2O3, Fe2O3, MgO, FeO, CaO, MnO, P2O5, TiO2, and Sr concentrations. This covariation of Sri, Ndi and chemistry can be modeled by a process of simple mixing of basaltic and granitic magmas having weight percent SiO2 of 48.0 and 73.3 respectively. Isotopic characteristic of the mafic magma are Sri=0.7047, Ndi=0.51269 and ??18O=6.0, and of the felsic magma are Sri=0.7068, Ndi=0.51212 and ??18O=8.9. The rocks sampled contain from 50 to 80% of the felsic component. An aplite in the outer equigranular unit of the Tuolumne Intrusive Suite apparently was derived by fractional crystallization of plagioclase and hornblende from magma with granudiorite composition that was a product of mixing of the magmas described above. Siliceous magmas derived from the lower crust, having a maximum of 15 percent mantle-derived mafic component, are represented by the inner prophyritic units of the Tuolumne Intrusive Suite. ?? 1986 Springer-Verlag.

  20. Decoding low dihedral angles in gabbroic layered intrusions

    NASA Astrophysics Data System (ADS)

    Holness, M. B.; Humphreys, M.; Veksler, I. V.

    2010-12-01

    Texturally equilibrated rocks are granular with a unimodal grain size, smoothly curved grain boundaries, and angles at three-grain junctions of 110-140°. Gabbros are not texturally equilibrated: primocrysts commonly have planar faces whereas later-formed phases fill in the interstitial spaces. Augite-plagioclase-plagioclase dihedral angles (Θcpp) rarely attain the equilibrium value in gabbros and the population of disequilibrium angles preserves otherwise inaccessible information about rock history. The Θcpp population varies significantly between different basaltic bodies. In a rapidly cooled dolerite Θcpp has a low median (60-70°) and a high standard deviation (20-25°). The plagioclase-augite grain boundaries are generally planar. In more slowly cooled gabbros in layered intrusions, the angle populations have a higher median (80-110°) with a low standard deviation (10-15°). The plagioclase-augite grain boundaries are generally planar far from the triple junction, but curve within 10 microns of the junction. This curvature is commonly asymmetric. The angle population in solidified gabbros infiltrated by low-temperature melts is similar to that in dolerites, although the low angles are associated with cuspate interstitial grains. The dihedral angle is a function of both the original solidification process and subsequent high-temperature (melt-absent) grain boundary migration. Infilling of a melt pocket by overgrowth of the bounding solid phases necessitates supersaturation, and this is easier to attain for planar faces, resulting in inhibition of augite growth into pores bounded by planar plagioclase grains and an asymmetry of the initial augite-plag-plag junction. If the solidified gabbro is kept sufficiently hot these initial junction geometries can change during textural equilibration. In the Skaergaard, Rum and Bushveld intrusions, the median Θcpp varies with liquidus assemblage, increasing step-wise on the addition of a new liquidus phase. Locally

  1. 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

  2. Efficiency of differentiation in the Skaergaard magma chamber

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  3. The petrogenesis of late Neoproterozoic mafic dyke-like intrusion in south Sinai, Egypt

    NASA Astrophysics Data System (ADS)

    Azer, M. K.; Abu El-Ela, F. F.; Ren, M.

    2012-08-01

    New field, petrographical and geochemical studies are presented here for the late Neoproterozoic Rimm intrusion (˜15 km long) exposed in the southern Sinai Peninsula, Egypt in the northernmost Arabian-Nubian Shield (ANS). Field relations indicate that the Rimm intrusion is younger than the surrounding metamorphic rocks and calc-alkaline syn-tectonic granodiorite and it was not affected by regional metamorphism. The anorogenic peralkaline granite of Gebel Serbal crosscuts the Rimm intrusion. The Rimm intrusion is made up of several consanguineous rock types with gradational contacts. It is composed chiefly of pyroxene-hornblende gabbro, hornblende gabbro and minor quartz diorite. The chemical composition of the mafic minerals indicated that the studied rocks derived from calc-alkaline mafic magma. Geochemically, the studied rocks are characterized by enrichment in LILE relative to HFSE and LREE relative to HREE [(Ce/Yb)N = 4.50-6.36]. Quartz diorite display slightly concave HREE pattern and slightly negative Eu-anomaly [(Eu/Eu*)n = 0.91] which may be the result of fractionation of amphibole and plagioclase from the source melt, respectively. The Rimm intrusion evolved from mafic mantle magma into different type rocks by fractional crystallization with minor crustal contamination. The initial magma corresponds to pyroxene-hornblende gabbro and the crystallization of hornblende was caused by slight H2O increase in magma after crystallization of near-liquidus clinopyroxene and Ca-rich plagioclase. Amphiboles geobarometer indicate that the gabbroic rocks of the Rimm intrusion crystallized at pressures between 4.8 and 6.4 Kb, while quartz diorite crystallized at 1.3-2.1 Kb. Crystallization temperatures range between 800 and 926 °C for the gabbros and between 667 and 784 °C for the quartz diorite. The Rimm intrusion represents a post-orogenic phase formed during the crustal thinning and extension of the Arabian-Nubian Shield.

  4. Clinical Evaluation of Efficacy of CIA and CNA Intrusion Arches

    PubMed Central

    Vora, Sambhav; Pandey, Vinisha

    2015-01-01

    Background and Objectives Excessive overbite is one of the most common problems that confront the orthodontist. Deep bite can be due to infraocclusion of posterior teeth, supraocclusion of anterior teeth or a combination of the two. Correction of same can be carried out by extrusion of molars, intrusion of incisors or by a combination of both respectively. Various intrusion arches are recommended for correcting deep bite by true intrusion of anterior teeth, Utility arches, Segmental arch, Connecticut Intrusion Arch (CIA) and Connecticut New Arch (CNA). The purpose of this study was to evaluate clinical efficacy of CIA and CNA intrusion arches. Materials and Methods Tracings recorded from pre and post-treatment lateral cephalograms of 25 patients treated by CIA (Group I) and another 25 patients treated by CNA (Group II) intrusion arches in deep bite cases after four months of treatment were analysed and findings were recorded. Statistical Analysis Paired t-test was used to compare pre and post-treatment changes within Groups I and II and unpaired t-test was used to compare treatment changes between Group I and Group II. A P-value of < 0.05 was set for statistical significance. Results Findings of this study demonstrate that an average of 1mm of intrusion takes place with CIA intrusion arch and 1.3mm with CNA intrusion arch in a period of 4 months. Both intrusion arches do not affect the position of molar in vertical or anteroposterior plane. Interpretation & Conclusion Both CIA and CNA intrusion arches are effective in bringing about intrusion of lower incisors. PMID:26501008

  5. Disclosing Multiple Magma Degassing Sources Offers Unique Insights of What's Behind the Campi Flegrei Caldera Unrest

    NASA Astrophysics Data System (ADS)

    Moretti, R.; Civetta, L.; Orsi, G.; Arienzo, I.; D'Antonio, M.; Di Renzo, V.

    2013-12-01

    The definition of the structure and evolution of the magmatic system of Campi Flegrei caldera (CFc), Southern Italy, has been a fundamental tool for the assessment of the short-term volcanic hazard. The ensemble of geophysical and petrologic data show that the CFc magmatic system has been -and still is- characterized by two major reservoirs at different depths. From the deep one (around 8 km), less evolved magmas crystallize and degas, supplying fluids and magmas to the shallow (3-4 km) reservoirs. A thorough reconstruction of processes occurring in magma chamber/s prior and/or during the CFc eruptions has shown that magmas entering shallow reservoirs mixed with resident and crystallized batches. Also the 1982-85 unrest episode has been related to a magma intrusion of 2.1 x 10^7 m^3 at 3-4 km depth, on the basis of geophysical data (ground deformation, gravimetry, seismic imaging) and their interpretation. Thermodynamic evaluation of magma properties, at the time of emplacement, suggests for such an intrusion a bulk density of 2.000 kg/m^3 . Such a value testifies the high amount of exsolved volatiles within the system. The available record of geochemical and isotopic data on surface fumaroles, coupled with melt inclusion data, has already shown that dual (deep and shallow) magma degassing from such two reservoirs, as well as their interaction with the hydrothermal system, allows explaining the relevant fluctuations observed at crater fumaroles after the 1982-85 magma intrusion. An important role was played by the rapid crystallization (around 30 years) of the shallow magma, such that in the recent years gas discharges should be fuelled mostly by the deep magma. Such a process is well recorded in the fumarolic gas composition of the last ~10 years, but has to be reconciled with the unrest dynamics which took place after year 2000, characterized by a slow but continuous ground uplift. All geochemical indicators (major species and noble gases) point to three possible

  6. 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

  7. Petrogenesis of Mount Rainier andesite: magma flux and geologic controls on the contrasting differentiation styles at stratovolcanoes of the southern Washington Cascades

    USGS Publications Warehouse

    Sisson, Thomas W.; Salters, V.J.M.; Larson, P.B.

    2013-01-01

    The dominant cause of magmatic evolution at Mount Rainier, however, is inferred to be a version of in situ crystallization-differentiation and mixing (Langmuir, 1989) wherein small magma batches stall as crustal intrusions and solidify extensively, yielding silicic residual liquids with trace element concentrations influenced by accessory mineral saturation. Subsequent magmas ascending through the intrusive plexus entrain and mix with the residual liquids and low-degree re-melts of those antecedent intrusions, producing hybrid andesites and dacites. Mount St. Helens volcanic rocks have geochemical similarities to those at Mount Rainier, and may also result from in situ differentiation and mixing due to low and intermittent long-term magma supply, accompanied by modest crustal assimilation. Andesites and dacites of Mount Adams isotopically overlap the least contaminated Mount Rainier magmas and derive from similar parental magma types, but have trace element variations more consistent with progressive crystallization-differentiation, probably due to higher magma fluxes leading to slower crystallization of large magma batches, allowing time for progressive separation of minerals from melt. Mount Adams also sits atop the southern projection of a regional anticlinorium, so Eocene sediments are absent, or are at shallow crustal levels, and so are cold and difficult to assimilate. Differences between southwest Washington stratovolcanoes highlight some ways that crustal geology and magma flux are primary factors in andesite generation.

  8. Dissolved volatile concentrations in an ore-forming magma

    USGS Publications Warehouse

    Lowenstern, J. B.

    1994-01-01

    Infrared spectroscopic measurements of glass inclusions within quartz phenocrysts from the Plinian fallout of the 22 Ma tuff of Pine Grove show that the trapped silicate melt contained high concentrations of H2O and CO2. Intrusive porphyries from the Pine Grove system are nearly identical in age, composition, and mineralogy to the tephra, and some contain high-grade Mo mineralization. Assuming that the porphyry magmas originally contained similar abundances of volatile components as the erupted rocks, they would have been saturated with fluid at pressures far greater than those at which the porphyries were emplaced and mineralized. The data are consistent with formation of Climax-type Mo porphyry deposits by prolonged fluid flux from a large volume of relatively Mo-poor (1-5 ppm) magma. -from Author

  9. 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…

  10. 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.

  11. Dike intrusions during rifting episodes obey scaling relationships similar to earthquakes.

    PubMed

    Passarelli, L; Rivalta, E; Shuler, A

    2014-01-28

    As continental rifts evolve towards mid-ocean ridges, strain is accommodated by repeated episodes of faulting and magmatism. Discrete rifting episodes have been observed along two subaerial divergent plate boundaries, the Krafla segment of the Northern Volcanic Rift Zone in Iceland and the Manda-Hararo segment of the Red Sea Rift in Ethiopia. In both cases, the initial and largest dike intrusion was followed by a series of smaller intrusions. By performing a statistical analysis of these rifting episodes, we demonstrate that dike intrusions obey scaling relationships similar to earthquakes. We find that the dimensions of dike intrusions obey a power law analogous to the Gutenberg-Richter relation, and the long-term release of geodetic moment is governed by a relationship consistent with the Omori law. Due to the effects of magma supply, the timing of secondary dike intrusions differs from that of the aftershocks. This work provides evidence of self-similarity in the rifting process.

  12. Dike intrusions during rifting episodes obey scaling relationships similar to earthquakes

    PubMed Central

    L., Passarelli; E., Rivalta; A., Shuler

    2014-01-01

    As continental rifts evolve towards mid-ocean ridges, strain is accommodated by repeated episodes of faulting and magmatism. Discrete rifting episodes have been observed along two subaerial divergent plate boundaries, the Krafla segment of the Northern Volcanic Rift Zone in Iceland and the Manda-Hararo segment of the Red Sea Rift in Ethiopia. In both cases, the initial and largest dike intrusion was followed by a series of smaller intrusions. By performing a statistical analysis of these rifting episodes, we demonstrate that dike intrusions obey scaling relationships similar to earthquakes. We find that the dimensions of dike intrusions obey a power law analogous to the Gutenberg-Richter relation, and the long-term release of geodetic moment is governed by a relationship consistent with the Omori law. Due to the effects of magma supply, the timing of secondary dike intrusions differs from that of the aftershocks. This work provides evidence of self-similarity in the rifting process. PMID:24469260

  13. Tracking dynamics of magma migration in open-conduit systems

    NASA Astrophysics Data System (ADS)

    Valade, Sébastien; Lacanna, Giorgio; Coppola, Diego; Laiolo, Marco; Pistolesi, Marco; Donne, Dario Delle; Genco, Riccardo; Marchetti, Emanuele; Ulivieri, Giacomo; Allocca, Carmine; Cigolini, Corrado; Nishimura, Takeshi; Poggi, Pasquale; Ripepe, Maurizio

    2016-11-01

    Open-conduit volcanic systems are typically characterized by unsealed volcanic conduits feeding permanent or quasi-permanent volcanic activity. This persistent activity limits our ability to read changes in the monitored parameters, making the assessment of possible eruptive crises more difficult. We show how an integrated approach to monitoring can solve this problem, opening a new way to data interpretation. The increasing rate of explosive transients, tremor amplitude, thermal emissions of ejected tephra, and rise of the very-long-period (VLP) seismic source towards the surface are interpreted as indicating an upward migration of the magma column in response to an increased magma input rate. During the 2014 flank eruption of Stromboli, this magma input preceded the effusive eruption by several months. When the new lateral effusive vent opened on the Sciara del Fuoco slope, the effusion was accompanied by a large ground deflation, a deepening of the VLP seismic source, and the cessation of summit explosive activity. Such observations suggest the drainage of a superficial magma reservoir confined between the crater terrace and the effusive vent. We show how this model successfully reproduces the measured rate of effusion, the observed rate of ground deflation, and the deepening of the VLP seismic source. This study also demonstrates the ability of the geophysical network to detect superficial magma recharge within an open-conduit system and to track magma drainage during the effusive crisis, with a great impact on hazard assessment.

  14. Magma Oceans on Exoplanets and Early Earth

    NASA Astrophysics Data System (ADS)

    Elkins-Tanton, Linda

    2009-09-01

    Late, giant accretionary impacts likely form multiple magma oceans of some depth in young rocky planets. Models of magma ocean solidification that incorporate water, carbon, and other incompatible volatile elements in small amounts predict a range of first-order outcomes important to planetary evolution. First, initial planetary bulk composition and size determine the composition of the earliest degassed atmosphere. This early atmosphere appears in a rapid burst at the end of solidification, determined by the ability of nucleating bubbles to reach the surface. Larger planets will have briefer and more catastrophic atmospheric degassing during solidification of any magma ocean. Second, this early atmosphere is sufficiently insulating to keep the planetary surface hot for millions of years. Depending upon the atmospheric composition and temperature structure these hot young planets may be observable from Earth or from satellites. Third, small but significant quantities of volatiles remain in the planet's solid mantle, encouraging convection, plate tectonics, and later atmospheric degassing through volcanism. A critical outcome of magma ocean solidification is the development of a solid mantle density gradient with den-sity increasing with radius, which will flow to gravitational stability. Shallow, dense, damp material will carry its water content as it sinks into the perovskite stability zone and transforms into perovskite. Even in models with very low initial water contents, a large fraction of the sinking upper mantle material will be forced to dewater as it crosses the boundary into the relatively dry lower mantle, leaving its water behind in a rapid flux as it sinks. This water ad-dition could initiate or speed convection in planets in which perovskite is stable, that is, planets larger than Mars.

  15. Pressure waves in a supersaturated bubbly magma

    USGS Publications Warehouse

    Kurzon, I.; Lyakhovsky, V.; Navon, O.; Chouet, B.

    2011-01-01

    We study the interaction of acoustic pressure waves with an expanding bubbly magma. The expansion of magma is the result of bubble growth during or following magma decompression and leads to two competing processes that affect pressure waves. On the one hand, growth in vesicularity leads to increased damping and decreased wave amplitudes, and on the other hand, a decrease in the effective bulk modulus of the bubbly mixture reduces wave velocity, which in turn, reduces damping and may lead to wave amplification. The additional acoustic energy originates from the chemical energy released during bubble growth. We examine this phenomenon analytically to identify conditions under which amplification of pressure waves is possible. These conditions are further examined numerically to shed light on the frequency and phase dependencies in relation to the interaction of waves and growing bubbles. Amplification is possible at low frequencies and when the growth rate of bubbles reaches an optimum value for which the wave velocity decreases sufficiently to overcome the increased damping of the vesicular material. We examine two amplification phase-dependent effects: (1) a tensile-phase effect in which the inserted wave adds to the process of bubble growth, utilizing the energy associated with the gas overpressure in the bubble and therefore converting a large proportion of this energy into additional acoustic energy, and (2) a compressive-phase effect in which the pressure wave works against the growing bubbles and a large amount of its acoustic energy is dissipated during the first cycle, but later enough energy is gained to amplify the second cycle. These two effects provide additional new possible mechanisms for the amplification phase seen in Long-Period (LP) and Very-Long-Period (VLP) seismic signals originating in magma-filled cracks.

  16. Sources and formation conditions of sulfide-silicate magmas in the Noril'sk district

    NASA Astrophysics Data System (ADS)

    Gorbachev, N. S.

    2012-05-01

    Geology, tectonomagmatic reactivation of the Noril'sk district, as well as stratigraphy and geochemistry of the volcanic sequence are considered. Sources and formation mechanism of ore-bearing magma and the scope of ore formation are discussed. The Permian-Triassic flood-basalt magmatism of the Noril'sk district developed in part of the Siberian Platform with Archean-Paleoproterozoic basement broken into blocks and overlapped by a sedimentary cover up to 13 km thick and a volcanic sequence reaching 3.7 km in thickness. The geophysical data show that remnants of the subducted ancient oceanic crust exist in the mantle and fragments of transitional magma chambers and conduits are retained at different levels of the Earth's crust. The cyclic tectonomagmatic evolution of the territory was characterized by alternation of extension with intense volcanic activity and compression accompanied by waning of volcanic eruptions. The early rifting, transitional stage, and late dispersed spreading are distinguished. The associations of volcanic (lavas and tuffs) and intrusive rocks were formed during each stage. The volcanic sequence is subdivided into 11 formations. The intrusions of the Talnakh and Noril'sk ore fields are distinguished by two-level structure with the Upper Noril'sk ore-bearing intrusions above and the Lower Noril'sk barren intrusions below. Two types of primary magmas differ in geochemistry of lavas and intrusions: (1) OIB-type high-Ti magma (iv, sv, gd formations of the first stage from bottom to top) and (2) low-Ti magma (hk, tk, nd formations of the second stage and mr-mk formations of the third stage). The nd formation depleted in ore elements and the ore-bearing cumulus composed of silicate and sulfide melts in combination with early silicate minerals and chromite are products of the fractionation of the primary low-Ti magma. As follows from geochemical parameters, intrusions of the Lower Noril'sk type are comagmatic to the evolved lavas of the nd3

  17. On the Itinerant History of Crystals in Magma Reservoirs

    NASA Astrophysics Data System (ADS)

    Reid, M. R.; Cooper, K. M.; Vazquez, J. A.; Simon, J. I.

    2004-12-01

    -226Ra ages for mineral separates are generally indicative of crystallization on timescales that are an order of magnitude greater than those based on kinetic considerations, while 238U-230Th ages may be even another order of magnitude greater still. These observations can collectively be reconciled if "phenocryst" populations include some older crystals thatare not easily distinguished on petrographic grounds. Accessory phase dating indicates that "old" crystals may be derived from earlier intrusions as well as from country rocks and/or source areas. Eruptions may only evacuate a fraction of a magma reservoir. At the same time, magma reservoirs are rarely close to a steady-state balance between influx and efflux nor are they well-mixed. Thus crystals might carry-over from one eruption to next if they are suspended in the most-mobile liquid portions of the chamber or if they are re-entrained in liquid as the liquid-mush transition zone migrates in response to the thermal effects of recharge and/or eruption. The almost ubiquitous evidence for complex and protracted crystal records is especially notable if nucleation occurs largely in solidification fronts: in this case the crystals most susceptible to recycling would represent only the most-recent intervals of crystal growth. The duration of the radiometric crystal record, in contrast, appears to require more dynamic reservoir processes, involving active crystal suspension, and rapid and large migrations in the mush-liquid transition.

  18. Molar Intrusion in Open-bite Adults Using Zygomatic Miniplates.

    PubMed

    Marzouk, Eiman S; Abdallah, Essam Mohamed; El-Kenany, Walid A

    2015-01-01

    The aim of this study is to evaluate the skeletal, dental and soft tissue changes that arise after intrusion of the maxillary molars using zygomatic miniplates in adult skeletal anterior open bite patients. In addition to measuring the amount and rate of molar intrusion; with special emphasis on changes in the axial inclination of the intruded molars. The study group was composed of 13 anterior open bite patients (mean age 18 years, 8 months ± 2 years, 2 months) with posterior dentoalveolar excess. Mini-plates were placed in the zygomatic buttress bilaterally. The upper arch was segmentally leveled and a double Trans-Palatal Arch (TPA) was bonded. Closed NiTi coil spring was placed bilaterally between the book of the mini-plate just mesial and distal to the first molar buccal tube applying intrusive force of 450 gper side. Lateral and posteroanterior cephalograms were taken before intrusion (T1: post upper segmental leveling) and after intrusion (T2). Comparison between means before and after the intrusion was done using Wilcoxon Signed Ranks test (WSRT). Mandibular autorotation followed the molar intrusion, SNB and SN-Pog angles significantly increased while the ANB, MP-SN angle and N-S-Gn angle significantly decreased. The mean amount of accomplished molar intrusion was 3.1mm ± 0.74mm, with a rate of 0.36mm per month ± 0.08mm per month and a bite closure of 6.55mm ± 1.83mm. There was no significant buccal tip in the right and left molars upon intrusion. Conclusion: Miniplates zygomatic anchorage can be used effectively for skeletal open bite correction through posterior dento-alveolar intrusion. Intrusion of the posterior teeth with skeletal anchorage induced counterclockwise rotation of the mandible and, as a consequence, corrected the anteroposterior intermaxillary relationship with a dramatic improvement in the facial soft tissue convexity.

  19. The role of stress during memory reactivation on intrusive memories.

    PubMed

    Cheung, Jessica; Garber, Benjamin; Bryant, Richard A

    2015-09-01

    Intrusive memories are unwanted recollections that maintain distress in psychological disorders. Increasing evidence suggests that memories that are reactivated through retrieval become temporarily vulnerable to environmental or pharmacological manipulation, including changes in levels of circulating stress hormones. This study investigated the influence of stress during memory reactivation of an emotionally arousing trauma film on subsequent intrusive memories. Three groups of participants (N=63) viewed a trauma film depicting a serious car accident at baseline. Two days later (Time 2), one group received a reactivation induction following a socially evaluated cold pressor test (SECPT; Stress/Reactivation condition), whilst the second group reactivated the memory after a control procedure (Reactivation condition). A third group underwent the SECPT but was not asked to reactivate memory of the trauma film (Stress condition). Two days later (Time 3), all participants received a surprise cued memory recall test and intrusions questionnaire which they completed online. Results showed that those in the Stress/Reactivation group had higher intrusions scores than the other two groups, suggesting that acute stress promotes intrusive memories only when the memory trace is reactivated shortly afterwards. Increased cortisol predicted enhanced intrusive experiences in the Stress/Reactivation condition but not in the other conditions. This pattern of results suggests that acute stress during the reactivation of emotional material impacts on involuntary emotional memories. These findings suggest a possible explanation for the mechanism underlying the maintenance of intrusive memories in clinical disorders.

  20. Volcano-tectonic earthquakes: A new tool for estimating intrusive volumes and forecasting eruptions

    NASA Astrophysics Data System (ADS)

    White, Randall; McCausland, Wendy

    2016-01-01

    We present data on 136 high-frequency earthquakes and swarms, termed volcano-tectonic (VT) seismicity, which preceded 111 eruptions at 83 volcanoes, plus data on VT swarms that preceded intrusions at 21 other volcanoes. We find that VT seismicity is usually the earliest reported seismic precursor for eruptions at volcanoes that have been dormant for decades or more, and precedes eruptions of all magma types from basaltic to rhyolitic and all explosivities from VEI 0 to ultraplinian VEI 6 at such previously long-dormant volcanoes. Because large eruptions occur most commonly during resumption of activity at long-dormant volcanoes, VT seismicity is an important precursor for the Earth's most dangerous eruptions. VT seismicity precedes all explosive eruptions of VEI ≥ 5 and most if not all VEI 4 eruptions in our data set. Surprisingly we find that the VT seismicity originates at distal locations on tectonic fault structures at distances of one or two to tens of kilometers laterally from the site of the eventual eruption, and rarely if ever starts beneath the eruption site itself. The distal VT swarms generally occur at depths almost equal to the horizontal distance of the swarm from the summit out to about 15 km distance, beyond which hypocenter depths level out. We summarize several important characteristics of this distal VT seismicity including: swarm-like nature, onset days to years prior to the beginning of magmatic eruptions, peaking of activity at the time of the initial eruption whether phreatic or magmatic, and large non-double couple component to focal mechanisms. Most importantly we show that the intruded magma volume can be simply estimated from the cumulative seismic moment of the VT seismicity from: Log10 V = 0.77 Log ΣMoment - 5.32, with volume, V, in cubic meters and seismic moment in Newton meters. Because the cumulative seismic moment can be approximated from the size of just the few largest events, and is quite insensitive to precise locations

  1. 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

  2. Intrusive Memories of Distressing Information: An fMRI Study

    PubMed Central

    Battaglini, Eva; Liddell, Belinda; Das, Pritha; Malhi, Gin; Felmingham, Kim

    2016-01-01

    Although intrusive memories are characteristic of many psychological disorders, the neurobiological underpinning of these involuntary recollections are largely unknown. In this study we used functional magentic resonance imaging (fMRI) to identify the neural networks associated with encoding of negative stimuli that are subsequently experienced as intrusive memories. Healthy partipants (N = 42) viewed negative and neutral images during a visual/verbal processing task in an fMRI context. Two days later they were assessed on the Impact of Event Scale for occurrence of intrusive memories of the encoded images. A sub-group of participants who reported significant intrusions (n = 13) demonstrated stronger activation in the amygdala, bilateral ACC and parahippocampal gyrus during verbal encoding relative to a group who reported no intrusions (n = 13). Within-group analyses also revealed that the high intrusion group showed greater activity in the dorsomedial (dmPFC) and dorsolateral prefrontal cortex (dlPFC), inferior frontal gyrus and occipital regions during negative verbal processing compared to neutral verbal processing. These results do not accord with models of intrusions that emphasise visual processing of information at encoding but are consistent with models that highlight the role of inhibitory and suppression processes in the formation of subsequent intrusive memories. PMID:27685784

  3. 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

  4. Estimates of volume and magma input in crustal magmatic systems from zircon geochronology: the effect of modelling assumptions and system variables

    NASA Astrophysics Data System (ADS)

    Caricchi, Luca; Simpson, Guy; Schaltegger, Urs

    2016-04-01

    Magma fluxes in the Earth's crust play an important role in regulating the relationship between the frequency and magnitude of volcanic eruptions, the chemical evolution of magmatic systems and the distribution of geothermal energy and mineral resources on our planet. Therefore, quantifying magma productivity and the rate of magma transfer within the crust can provide valuable insights to characterise the long-term behaviour of volcanic systems and to unveil the link between the physical and chemical evolution of magmatic systems and their potential to generate resources. We performed thermal modelling to compute the temperature evolution of crustal magmatic intrusions with different final volumes assembled over a variety of timescales (i.e., at different magma fluxes). Using these results, we calculated synthetic populations of zircon ages assuming the number of zircons crystallising in a given time period is directly proportional to the volume of magma at temperature within the zircon crystallisation range. The statistical analysis of the calculated populations of zircon ages shows that the mode, median and standard deviation of the populations varies coherently as function of the rate of magma injection and final volume of the crustal intrusions. Therefore, the statistical properties of the population of zircon ages can add useful constraints to quantify the rate of magma injection and the final volume of magmatic intrusions. Here, we explore the effect of different ranges of zircon saturation temperature, intrusion geometry, and wall rock temperature on the calculated distributions of zircon ages. Additionally, we determine the effect of undersampling on the variability of mode, median and standards deviation of calculated populations of zircon ages to estimate the minimum number of zircon analyses necessary to obtain meaningful estimates of magma flux and final intrusion volume.

  5. Controls on magmatic PGE and Au mineralization in the Skaergaard Intrusion

    NASA Astrophysics Data System (ADS)

    Keays, Reid; Tegner, Christian

    2013-04-01

    The Skaergaard Intrusion of East Greenland is the host for significant magmatic PGE and Au mineralization (the Platinova Reefs). It was formed from a single batch of magma that crystallized in its entirety as a closed system. Unlike all other examples of significant magmatic PGE and Ni-Cu-PGE mineralization, the Skaergaard rocks exhibit no evidence of crustal contamination, the major factor responsible for driving magmas to sulphide saturation and ore genesis. Although the Skaergaard rocks and mineralized zones have extremely low S contents, the mineralization is believed to be the product of late stage sulphide saturation of the magma. Three factors drove the magma to sulphide saturation, viz: (1) prolonged build up of S in the residual melt of the fractionating magma; (2) crystallization of magnetite which slowed down the build up of FeO in the fractionating magma; and (3) cooling of the magma against the walls of the intrusion. High quality PGE, Au, Cu, S, Se data and other geochemical data for samples from a detailed stratigraphic section through the Skaergaard intrusion are used to model these elements throughout its crystallization history, estimate their concentrations in the Skaergaard parental magma, and to establish the timing of sulphide saturation and the causes of PGE-Au mineralization. The model indicates that the parental magma contained 4.0 ppb Au, 18.7 ppb Pd, 9.0 ppb Pt, 95 ppb Se and 240 ppm Cu. The high Pd/Pt ratio indicates that the magma had undergone a significant amount of fractionation prior to entry into the Skaergaard magma chamber, consistent with the silicate mineralogy. A sharp increase in PGE contents (but not Cu or incompatible lithophile trace elements) 300m below the Platinova Reefs coincides with the first appearance of cumulus magnetite and marks the stratigraphic position at which tiny amounts of cumulus PGE-rich sulphides segregated from the magma. Although the S contents of all rocks below the Platinova Reefs are below the

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    they also appear to derive from shallow depths (restricted to ~2 kbar). The intermediate batches though, only erupt at Domes 10-12, 14, 24 and 25. Temperatures for these range from 803-1107°C with pressures ranging from 2-10 kbar. Mafic magmas from the Mono Craters proper are even more spatially restricted, having erupted only at Domes 10, 12 and 14, with temperatures ranging from 843-1276°C and pressures ranging from as deep as 17 kbar to as shallow as 2 kbar. These results indicate that the magma plumbing system beneath the Mono Craters segregates into three different levels with contrasting degrees of lateral spatial continuity. We hypothesize that felsic magmas evolve and are stored at shallow depths within a quasi-continuous, or well-linked series of en echelon oriented dikes or chambers, which form as a response to regional transtensional stresses. In contrast, intermediate and mafic magmas are both deeper and spatially more restricted, and apparently do not infiltrate the more shallow brittle-deformed dike system that is so well exploited by felsic magmas. We surmise that this contrast in magma delivery may be controlled by density contrasts between magma and adjacent crust, where intermediate and mafic magmas, due to their greater density, are barred from rising upwards into a low density, brittle uppermost crust in which the en echelon dike-delivery system is mostly, or solely, developed.

  7. Volatile Changes in Magma Related to Magma Evolution: Influences From Magma Mixing, Crustal Assimilation, and Crystallization

    NASA Astrophysics Data System (ADS)

    Sosa-Ceballos, G.; Gardner, J.

    2008-12-01

    The volatile budget of magma is the cumulative product of magma mixing, crustal assimilation, and crystallization, with the concentration of each volatile resulting from how much is added by each process and whether the magma is gas saturate. In order to clarify how volatile budgets fluctuate during magma evolution, we are measuring volatile concentrations in melt inclusions trapped within individual zones of plagioclase crystals from different dacitic Plinian eruptions and a recent small-scale explosion of Popocatépetl Volcano. The plagioclase zones were analyzed for their anorthite (An) composition and their Sr isotopic (87Sr/86Sr) composition in order to investigate the evolutionary processes responsible for crystal growth and their relation to volatile concentrations measured in the melt inclusions. In general, plagioclase from all eruptions display three different correlations between An content and Sr isotopes, with each recording different conditions under which crystals grew. Some crystals have nearly constant 87Sr/86Sr compositions from core to rim with either variable An compositions or a continuous decrease in An, suggesting these crystals were affected only by crystallization and, in some cases, thermal fluctuations. Other crystals display anti-correlations between An and Sr isotopes, which record mass inputs into the system from either magma mixing or crustal assimilation. Single crystals record a variety of processes during their growth, and single pumices contain an extremely heterogeneous population of such crystals, suggesting that the magma system is highly dynamic. Our preliminary results show that water can vary by several weight percent and carbon dioxide by hundreds of ppm between different zones of individual crystals. Interestingly, we find that inclusions related to recharge events by hotter, more primitive magma are more hydrous than those related to assimilation of more radiogenic wall rock. This suggests that the volatile budget of

  8. Linking magnetic fabric and cumulate texture in layered mafic-ultramafic intrusions (Invited)

    NASA Astrophysics Data System (ADS)

    O Driscoll, B.; Stevenson, C.; Magee, C.

    2013-12-01

    Research on the magnetic fabrics of igneous rocks, pioneered by Balsley and Buddington[1] and Khan[2], has greatly contributed to our understanding of magma dynamics in lava flows, sheet intrusions and plutons over the past five decades. However, considerably few magnetic fabric studies have focused on layered mafic-ultramafic intrusions, particularly ';lopolithic' intrusions, despite the fact that such rocks may preserve a large range of small-scale kinematic structures potentially related to important magma chamber processes. This may be partly due to the fact that mafic-ultramafic cumulates commonly exhibit visible planar fabrics (mineral lamination), as well as compositional layering, in contrast to the frequent absence of such features in granite bodies or fine-grained mafic lava flows. Indeed, debates in the 1970s and 1980s on the development of layering and mineral fabrics in mafic-ultramafic intrusions, focused around the crystal settling versus in situ crystallisation paradigms, are classic in the subject of igneous petrology. Central to these debates is the notion that a wide range of magma chamber processes occur in layered mafic-ultramafic intrusions that are not frequently considered to occur in their relatively viscous granitic counterparts; in essence, the latter have historically been viewed as much more likely to ';freeze-in' a primary magma flow fabric whilst mafic-ultramafic intrusions are subjected to a more protracted solidification history. This wide array of potential initial sources for layering and mineral fabrics in layered mafic-ultramafic intrusions, together with the possible modification of textures at the postcumulus stage, demands a cautious application of any fabric analysis and presents a problem well-suited to interrogation by the AMS technique. The purpose of this contribution is to provide specific context on the application of AMS to elucidating the formation of cumulates in layered mafic-ultramafic intrusions. Examples of AMS

  9. Caldera resurgence during magma replenishment and rejuvenation at Valles and Lake City calderas

    NASA Astrophysics Data System (ADS)

    Kennedy, Ben; Wilcock, Jack; Stix, John

    2012-10-01

    A key question in volcanology is the driving mechanisms of resurgence at active, recently active, and ancient calderas. Valles caldera in New Mexico and Lake City caldera in Colorado are well-studied resurgent structures which provide three crucial clues for understanding the resurgence process. (1) Within the limits of 40Ar/39Ar dating techniques, resurgence and hydrothermal alteration at both calderas occurred very quickly after the caldera-forming eruptions (tens of thousands of years or less). (2) Immediately before and during resurgence, dacite magma was intruded and/or erupted into each system; this magma is chemically distinct from rhyolite magma which was resident in each system. (3) At least 1 km of structural uplift occurred along regional and subsidence faults which were closely associated with shallow intrusions or lava domes of dacite magma. These observations demonstrate that resurgence at these two volcanoes is temporally linked to caldera subsidence, with the upward migration of dacite magma as the driver of resurgence. Recharge of dacite magma occurs as a response to loss of lithostatic load during the caldera-forming eruption. Flow of dacite into the shallow magmatic system is facilitated by regional fault systems which provide pathways for magma ascent. Once the dacite enters the system, it is able to heat, remobilize, and mingle with residual crystal-rich rhyolite remaining in the shallow magma chamber. Dacite and remobilized rhyolite rise buoyantly to form laccoliths by lifting the chamber roof and producing surface resurgent uplift. The resurgent deformation caused by magma ascent fractures the chamber roof, increasing its structural permeability and allowing both rhyolite and dacite magmas to intrude and/or erupt together. This sequence of events also promotes the development of magmatic-hydrothermal systems and ore deposits. Injection of dacite magma into the shallow rhyolite magma chamber provides a source of heat and magmatic volatiles

  10. Magma plumbing for the 2014-2015 Holuhraun eruption, Iceland

    NASA Astrophysics Data System (ADS)

    Geiger, Harri; Mattsson, Tobias; Deegan, Frances M.; Troll, Valentin R.; Burchardt, Steffi; Gudmundsson, Ólafur; Tryggvason, Ari; Krumbholz, Michael; Harris, Chris

    2016-08-01

    The 2014-2015 Holuhraun eruption on Iceland was located within the Askja fissure swarm but was accompanied by caldera subsidence in the Bárðarbunga central volcano 45 km to the southwest. Geophysical monitoring of the eruption identified a seismic swarm that migrated from Bárðarbunga to the Holuhraun eruption site over the course of two weeks. In order to better understand this lateral connection between Bárðarbunga and Holuhraun, we present mineral textures and compositions, mineral-melt-equilibrium calculations, whole rock and trace element data, and oxygen isotope ratios for selected Holuhraun samples. The Holuhraun lavas are compositionally similar to recorded historical eruptions from the Bárðarbunga volcanic system but are distinct from the historical eruption products of the nearby Askja system. Thermobarometry calculations indicate a polybaric magma plumbing system for the Holuhraun eruption, wherein clinopyroxene and plagioclase crystallized at average depths of ˜17 km and ˜5 km, respectively. Crystal resorption textures and oxygen isotope variations imply that this multilevel plumbing system facilitated magma mixing and assimilation of low-δ18O Icelandic crust prior to eruption. In conjunction with the existing geophysical evidence for lateral migration, our results support a model of initial vertical magma ascent within the Bárðarbunga plumbing system followed by lateral transport of aggregated magma batches within the upper crust to the Holuhraun eruption site.

  11. 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

  12. 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.

  13. Melt production and magma emplacement: What use are they?

    NASA Astrophysics Data System (ADS)

    Nimmo, F.

    2003-04-01

    I will review the processes of melt production and magma emplacement and address two questions: how do these processes affect planetary evolution?; and what can we learn from observing them, both now and in the future? Melt production is primarily controlled by the temperature of the planetary interior. The extraction of melt from silicate mantles has a number of effects. Firstly, it advects heat (e.g. Io, Venus?). Secondly, it segregates radiogenic materials into the crust, thus cooling the mantle (e.g. Mars, Earth). Thirdly, it removes volatiles from the interior (e.g. Venus, Mars). Recognition that melting is occurring gives us information about likely conditions inside the planet. Models of melt generation by convective upwelling have been used to constrain the interior properties of the Earth, Venus and Mars. Melting during tidal heating (Io) or accretion is less well understood. Magma emplacement is primarily controlled by the density of the magma and the surrounding material. Extrusive activity is likely for high volatile concentrations or low crustal densities. Water is particularly difficult to erupt, since (unlike silicates) the melt is denser than the solid. Different styles of magma emplacement are observed: voluminous surface flows and volcanic edifices of various kinds (ubiquitous); giant radiating dyke swarms (Earth, Venus, Mars); intrusive sills and diapirs (Earth, Venus?, Mars?, Europa?). The extrusive emplacement of magma will cause resurfacing, and is thus easily detected. The release of volatiles during emplacement may have local (e.g. Laki) or global (Venus? Mars?) effects on climate and atmosphere. Intrusive emplacement is harder to detect, but may interact with local volatiles to create unusual landforms (Earth, Mars). The style and volume of emplacement is a useful diagnostic tool. The morphology of lava flows gives information about the rheology and composition of the flow material (e.g. Venus, Miranda). Observations of dykes may be used to

  14. Magma transport and storage at Kilauea volcano, Hawaii II: 1952-2008

    NASA Astrophysics Data System (ADS)

    Klein, F.; Wright, T. L.

    2011-12-01

    We trace the evolution of Kilauea between the Halemaumau eruptions of 1952 and 2008. The magma supply path from the mantle is defined by the distribution of earthquakes deeper than 20 km. We compared the accumulated moment release from deep magma supply, south flank and rift zone earthquakes. We identified every intrusion and eruption in time plots of summit tilt and seismic activity in all regions, and plotted the earthquake distribution for ~ 1 week covering the period prior to, during and following the event. The establishment and continued growth of modern seismic and geodetic networks allow us to define three types of intrusions. 'Normal' intrusions occur with or without eruption and are accompanied by sharp tilt deflation at Kilauea's summit. 'Inflationary' intrusions occur during periods of summit inflation accompanied by rift earthquake swarms in the near-summit parts of both rift zones. 'Slow' intrusions are defined by isolated swarms of south flank earthquakes distributed perpendicular to the rift zones. Magnitudes of inflation and deflation shown by the daily tilt record at Kilauea's summit are converted to volume using a factor determined by previous workers. Magma supply rates are determined by summation of the volumes in cubic kilometers of (1) net summit inflation (2) sharp summit deflation accompanying rift activity and (3) summit and long continuous rift eruptions, divided by the elapsed time in years. Eruption efficiency is calculated by comparing the volumes of rift eruption and summit deflation. In this study we have reached the following conclusions: 1) Magma supply rates have increased from the pre-1952 value of 0.062 km3/yr to 0.1 km3/yr during the Mauna Ulu eruption of 1969-74 to 0.2 km3/yr during much of the eruption that began in 1983. 2) Eruption efficiencies show cyclic increases with increased activity, culminating in an efficiency averaging 100% during episodes of high fountaining in the period 1983-86. 3) Some south flank earthquake

  15. 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.

  16. Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland.

    PubMed

    Sigmundsson, Freysteinn; Hooper, Andrew; Hreinsdóttir, Sigrún; Vogfjörd, Kristín S; Ófeigsson, Benedikt G; Heimisson, Elías Rafn; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Gudmundsson, Gunnar B; Drouin, Vincent; Árnadóttir, Thóra; Jónsdóttir, Kristín; Gudmundsson, Magnús T; Högnadóttir, Thórdís; Fridriksdóttir, Hildur María; Hensch, Martin; Einarsson, Páll; Magnússon, Eyjólfur; Samsonov, Sergey; Brandsdóttir, Bryndís; White, Robert S; Ágústsdóttir, Thorbjörg; Greenfield, Tim; Green, Robert G; Hjartardóttir, Ásta Rut; Pedersen, Rikke; Bennett, Richard A; Geirsson, Halldór; La Femina, Peter C; Björnsson, Helgi; Pálsson, Finnur; Sturkell, Erik; Bean, Christopher J; Möllhoff, Martin; Braiden, Aoife K; Eibl, Eva P S

    2015-01-08

    Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long. Previous models of rifting events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens, or magma flowing vertically into dykes from an underlying source, with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the Bárðarbunga volcanic system grew laterally for more than 45 kilometres at a variable rate, with topography influencing the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred primarily over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning System (GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Bárðarbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with magma source deflation and slow collapse at the Bárðarbunga caldera, accompanied by a series of magnitude M > 5 earthquakes. Dyke growth was slowed down by an effusive fissure eruption near the end of the dyke. Lateral dyke growth with segment barrier breaking by pressure build-up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries.

  17. Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland

    NASA Astrophysics Data System (ADS)

    Sigmundsson, Freysteinn; Hooper, Andrew; Hreinsdóttir, Sigrún; Vogfjörd, Kristín S.; Ófeigsson, Benedikt G.; Heimisson, Elías Rafn; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Gudmundsson, Gunnar B.; Drouin, Vincent; Árnadóttir, Thóra; Jónsdóttir, Kristín; Gudmundsson, Magnús T.; Högnadóttir, Thórdís; Fridriksdóttir, Hildur María; Hensch, Martin; Einarsson, Páll; Magnússon, Eyjólfur; Samsonov, Sergey; Brandsdóttir, Bryndís; White, Robert S.; Ágústsdóttir, Thorbjörg; Greenfield, Tim; Green, Robert G.; Hjartardóttir, Ásta Rut; Pedersen, Rikke; Bennett, Richard A.; Geirsson, Halldór; La Femina, Peter C.; Björnsson, Helgi; Pálsson, Finnur; Sturkell, Erik; Bean, Christopher J.; Möllhoff, Martin; Braiden, Aoife K.; Eibl, Eva P. S.

    2015-01-01

    Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long. Previous models of rifting events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens, or magma flowing vertically into dykes from an underlying source, with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the Bárðarbunga volcanic system grew laterally for more than 45 kilometres at a variable rate, with topography influencing the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred primarily over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning System (GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Bárðarbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with magma source deflation and slow collapse at the Bárðarbunga caldera, accompanied by a series of magnitude M > 5 earthquakes. Dyke growth was slowed down by an effusive fissure eruption near the end of the dyke. Lateral dyke growth with segment barrier breaking by pressure build-up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries.

  18. Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland

    NASA Astrophysics Data System (ADS)

    Sigmundsson, Freysteinn; Hooper, Andrew; Hreinsdóttir, Sigrún; Vogfjörd, Kristín S.; Ófeigsson, Benedikt; Rafn Heimisson, Elías; Dumont, Stéphanie; Parks, Michelle; Spaans, Karsten; Guðmundsson, Gunnar B.; Drouin, Vincent; Árnadóttir, Thóra; Jónsdóttir, Kristín; Gudmundsson, Magnús T.; Samsonov, Sergey; Brandsdóttir, Bryndís; White, Robert; Ágústsdóttir, Thorbjörg; Björnsson, Helgi; Bean, Christopher J.

    2015-04-01

    Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of km long. Previous models of rifting events indicate either a lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens, or magma flowing vertically into dykes from an underlying source, with the role of topography on the evolution of lateral dykes not clear. We show how a recent segmented dyke intrusion in the Bárðarbunga volcanic system, grew laterally for over 45 km at a variable rate, with an influence of topography on the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning System (GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Bárðarbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with a magma source deflation and slow collapse at the Bárðarbunga caldera, accompanied by a series of M>5 earthquakes. The dyke growth was slowed down by an effusive fissure eruption near the end of the dyke. Lateral dyke growth with segment barrier breaking by pressure build-up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries.

  19. Magma supply, storage, and transport at shield-stage Hawaiian volcanoes: Chapter 5 in Characteristics of Hawaiian volcanoes

    USGS Publications Warehouse

    Poland, Michael P.; Miklius, Asta; Montgomery-Brown, Emily K.; Poland, Michael P.; Takahashi, T. Jane; Landowski, Claire M.

    2014-01-01

    Magma supply to Hawaiian volcanoes has varied over millions of years but is presently at a high level. Supply to Kīlauea’s shallow magmatic system averages about 0.1 km3/yr and fluctuates on timescales of months to years due to changes in pressure within the summit reservoir system, as well as in the volume of melt supplied by the source hot spot. Magma plumbing systems beneath Kīlauea and Mauna Loa are complex and are best constrained at Kīlauea. Multiple regions of magma storage characterize Kīlauea’s summit, and two pairs of rift zones, one providing a shallow magma pathway and the other forming a structural boundary within the volcano, radiate from the summit to carry magma to intrusion/eruption sites located nearby or tens of kilometers from the caldera. Whether or not magma is present within the deep rift zone, which extends beneath the structural rift zones at ~3-km depth to the base of the volcano at ~9-km depth, remains an open question, but we suggest that most magma entering Kīlauea must pass through the summit reservoir system before entering the rift zones. Mauna Loa’s summit magma storage system includes at least two interconnected reservoirs, with one centered beneath the south margin of the caldera and the other elongated along the axis of the caldera. Transport of magma within shield-stage Hawaiian volcanoes occurs through dikes that can evolve into long-lived pipe-like pathways. The ratio of eruptive to noneruptive dikes is large in Hawai‘i, compared to other basaltic volcanoes (in Iceland, for example), because Hawaiian dikes tend to be intruded with high driving pressures. Passive dike intrusions also occur, motivated at Kīlauea by rift opening in response to seaward slip of the volcano’s south flank.

  20. IGNEOUS INTRUSION IMPACTS ON WASTE PACKAGES AND WASTE FORMS

    SciTech Connect

    P. Bernot

    2004-04-19

    The purpose of this model report is to assess the potential impacts of igneous intrusion on waste packages and waste forms in the emplacement drifts at the Yucca Mountain Repository. The models are based on conceptual models and includes an assessment of deleterious dynamic, thermal, hydrologic, and chemical impacts. The models described in this report constitute the waste package and waste form impacts submodel of the Total System Performance Assessment for the License Application (TSPA-LA) model assessing the impacts of a hypothetical igneous intrusion event on the repository total system performance. This submodel is carried out in accordance with Technical Work Plan for Waste Form Degradation Modeling, Testing, and Analyses in Support of LA (BSC 2004 [DIRS:167796]) and Total System Performance Assessment-License Application Methods and Approaches (BSC 2003 [DIRS: 166296]). The technical work plan was prepared in accordance with AP-2.27Q, Planning for Science Activities. Any deviations from the technical work plan are documented in the following sections as they occur. The TSPA-LA approach to implementing the models for waste package and waste form response during igneous intrusion is based on identification of damage zones. Zone 1 includes all emplacement drifts intruded by the basalt dike, and Zone 2 includes all other emplacement drifts in the repository that are not in Zone 1. This model report will document the following model assessments: (1) Mechanical and thermal impacts of basalt magma intrusion on the invert, waste packages and waste forms of the intersected emplacement drifts of Zone 1. (2) Temperature and pressure trends of basaltic magma intrusion intersecting Zone 1 and their potential effects on waste packages and waste forms in Zone 2 emplacement drifts. (3) Deleterious volatile gases, exsolving from the intruded basalt magma and their potential effects on waste packages of Zone 2 emplacement drifts. (4) Post-intrusive physical

  1. Constraints on the formation of geochemically variable plagiogranite intrusions in the Troodos Ophiolite, Cyprus

    NASA Astrophysics Data System (ADS)

    Freund, Sarah; Haase, Karsten M.; Keith, Manuel; Beier, Christoph; Garbe-Schönberg, Dieter

    2014-02-01

    The geochemistry and petrology of tonalitic to trondhjemitic samples ( n = 85) from eight different plagiogranite intrusions at the gabbro/sheeted dyke transition of the Troodos Ophiolite were studied in order to determine their petrogenetic relationship to the mafic plutonic section and the lava pile. The plagiogranitic rocks have higher SiO2 contents than the majority of the glasses of the Troodos lava pile, but lie on a continuation of the chemical trends defined by the extrusive rocks, indicating that the shallow intrusions generally represent crystallised magmas. We define three different groups of plagiogranites in the Troodos Ophiolite based on different incompatible element contents and ratios. The first and most common plagiogranite group has geochemical similarities to the tholeiitic lavas forming the lavas and sheeted dyke complex in the Troodos crust, implying that these magmas formed at a spreading axis. The second plagiogranite group occurs in one intrusion that is chemically related to late-stage and off-axis boninitic lavas and dykes. One intrusion next to the Arakapas fault zone consists of incompatible element-enriched plagiogranites which are unrelated to any known mafic crustal rocks. The similarities of incompatible element ratios between plagiogranites, lavas and mafic plutonic rocks, the continuous chemical trends defined by plagiogranites and mafic rocks, as well as incompatible element modelling results, all suggest that shallow fractional crystallisation is the dominant process responsible for formation of the felsic magmas.

  2. Chemical and hydrogen isotope evidence for in situ dehydrogenation of biotite in silicic magma chambers

    NASA Astrophysics Data System (ADS)

    Feeley, T. C.; Sharp, Z. D.

    1996-11-01

    To examine the potential for volatile fluxing of magma chambers by in situ degassing of hydrous minerals, we obtained complete chemical analyses for biotite separates from silicic lavas. The separates exhibit unusually low H2O contents that inversely correlate with host lava temperatures, high Fe3+/Fe2+ ratios that inversely correlate with host lava oxygen fugacities, and the highest δ D values yet reported for biotite from any silicic igneous rock (up to -19‰). These results are direct evidence for selective loss of protium (1H) from biotite during dehydrogenation in magma chambers heated from below by intrusion of mafic magma. The maximum PΔV energy generated from dehydrogenation alone can approach 2 × 103 joules per kilogram of magma. This finding provides support for the concept that injection of mafic magma coupled with sudden degassing of hydrous minerals in a volatile-rich magma chamber can increase pressure, and thus enhance the possibility of initiating a volcanic eruption.

  3. Multiple mafic and felsic magma interaction as exhibited in the Dartmouth Pluton, Avalon zone, southeastern Massachusetts

    SciTech Connect

    Hamidzada, N.A.; Hermes, O.D.; Murray, D.P. . Dept. of Geology)

    1993-03-01

    Dioritic to quartz monzonitic rocks of the Dartmouth Pluton exhibit excellently preserved, diverse features produced by mingling and mixing of mafic and felsic magma during multiple events. The related mafic and hybridized intermediate composition rocks occur both as discrete outcrop-sized masses or as enclaves within quartz monzonite or early-stage mixed rocks. Enclaves are rounded, lack chilled margins, and in some cases exhibit cuspate margins; they range in size from 1m--<1cm. Outcrops dominated by dioritic rock consist of well developed mafic pillows with inter-pillow infillings of hybridized rock that had been subjected to magma mixing during or prior to the final mingling process. Dioritic rocks are fine-grained with sparse plagioclase phenocrysts; they contain small, darker-colored enclaves indicative of preceding magma interaction. Major and trace element variation diagrams for this suite of rocks exhibit general linear trends consistent with mixing processes. Overall, field, petrographic, and geochemical relationships in the Dartmouth Pluton demonstrate: (1) widespread mingling of mafic and felsic magma, (2) variable degrees of mafic and felsic magma mixing, and (3) multiple and repeated episodes of mafic and felsic magma interaction. Significantly, some spatially associated dioritic and granitic rocks, including a 595 Ma alkali feldspar granite formerly considered to be part of the Dartmount Pluton, are geochemically related. Field mapping demonstrates that rocks of the mixed suite are intrusive into these rocks, thus establishing a maximum age, but raising the questions that the suite may be considerably younger.

  4. Magma supply dynamics at Westdahl volcano, Alaska, modeled from satellite radar interferometry

    USGS Publications Warehouse

    Lu, Zhiming; Masterlark, Timothy; Dzurisin, D.; Rykhus, Russ; Wicks, C.

    2003-01-01

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

  5. Magma Plumbing and Transport at Yellowstone--Implications from Geodesy and Geochemistry (Invited)

    NASA Astrophysics Data System (ADS)

    Dzurisin, D.; Wicks, C. W.; Lowenstern, J. B.

    2013-12-01

    Surface deformation, thermal activity, and outgassing at the Yellowstone caldera are manifestations of a vigorous magmatic system that has been active for more than 2 million years. Viable models for Yellowstone's magma plumbing and transport system must account for: (1) high contemporary fluxes of heat and CO2; (2) ground deformation sources beneath each of two resurgent domes, and a third near the intersection of the north caldera rim and Norris-Mammoth corridor; (3) interplay among these sources, as suggested by the timing of major changes in deformation mode; (4) repeated cycles of uplift and subsidence and sudden changes from uplift to subsidence or vice versa; (5) spatial and temporal relationships between changes in deformation mode and earthquake swarms; and (6) lateral dimensions of all three deforming areas that indicate source depths in the range 5-15 km. Seismic tomography studies have imaged a partly molten silicic magma body in the upper crust beneath the caldera and a mantle feeder zone for mafic magma. A model in which surface displacements are caused primarily by variations in the flux of mafic magma into the crust satisfies known thermal, geochemical, and geodetic constraints. In the model, a conduit system centered beneath the northeast part of the caldera supplies basalt from a mantle source to an accumulation zone 5-10 km deep, perhaps at a rheological boundary beneath a crystal-rich rhyolite body remnant from past eruptions. Increases in magma flux favor surface uplift and decreases favor subsidence. A delicate equilibrium exists among the mass and heat flux from basaltic intrusions, heat and volatile loss from the rhyolite, and the overlying hydrothermal system. In the absence of basalt input, steady subsidence should occur as a result of fluid loss from the rhyolite, but if a self-sealing zone in the deep hydrothermal system prevents fluid escape the resulting pressure increase contributes to surface uplift. Such episodes end when the seal

  6. Warm storage for arc magmas

    NASA Astrophysics Data System (ADS)

    Barboni, Mélanie; Boehnke, Patrick; Schmitt, Axel K.; Harrison, T. Mark; Shane, Phil; Bouvier, Anne-Sophie; Baumgartner, Lukas

    2016-12-01

    Felsic magmatic systems represent the vast majority of volcanic activity that poses a threat to human life. The tempo and magnitude of these eruptions depends on the physical conditions under which magmas are retained within the crust. Recently the case has been made that volcanic reservoirs are rarely molten and only capable of eruption for durations as brief as 1,000 years following magma recharge. If the “cold storage” model is generally applicable, then geophysical detection of melt beneath volcanoes is likely a sign of imminent eruption. However, some arc volcanic centers have been active for tens of thousands of years and show evidence for the continual presence of melt. To address this seeming paradox, zircon geochronology and geochemistry from both the frozen lava and the cogenetic enclaves they host from the Soufrière Volcanic Center (SVC), a long-lived volcanic complex in the Lesser Antilles arc, were integrated to track the preeruptive thermal and chemical history of the magma reservoir. Our results show that the SVC reservoir was likely eruptible for periods of several tens of thousands of years or more with punctuated eruptions during these periods. These conclusions are consistent with results from other arc volcanic reservoirs and suggest that arc magmas are generally stored warm. Thus, the presence of intracrustal melt alone is insufficient as an indicator of imminent eruption, but instead represents the normal state of magma storage underneath dormant volcanoes.

  7. Warm storage for arc magmas.

    PubMed

    Barboni, Mélanie; Boehnke, Patrick; Schmitt, Axel K; Harrison, T Mark; Shane, Phil; Bouvier, Anne-Sophie; Baumgartner, Lukas

    2016-12-06

    Felsic magmatic systems represent the vast majority of volcanic activity that poses a threat to human life. The tempo and magnitude of these eruptions depends on the physical conditions under which magmas are retained within the crust. Recently the case has been made that volcanic reservoirs are rarely molten and only capable of eruption for durations as brief as 1,000 years following magma recharge. If the "cold storage" model is generally applicable, then geophysical detection of melt beneath volcanoes is likely a sign of imminent eruption. However, some arc volcanic centers have been active for tens of thousands of years and show evidence for the continual presence of melt. To address this seeming paradox, zircon geochronology and geochemistry from both the frozen lava and the cogenetic enclaves they host from the Soufrière Volcanic Center (SVC), a long-lived volcanic complex in the Lesser Antilles arc, were integrated to track the preeruptive thermal and chemical history of the magma reservoir. Our results show that the SVC reservoir was likely eruptible for periods of several tens of thousands of years or more with punctuated eruptions during these periods. These conclusions are consistent with results from other arc volcanic reservoirs and suggest that arc magmas are generally stored warm. Thus, the presence of intracrustal melt alone is insufficient as an indicator of imminent eruption, but instead represents the normal state of magma storage underneath dormant volcanoes.

  8. The impact of a volcanic edifice on intrusive and eruptive activity

    NASA Astrophysics Data System (ADS)

    Roman, Alberto; Jaupart, Claude

    2014-12-01

    In a volcanic area, the orientation and composition of dikes record the development of the magmatic system that feeds intrusive and eruptive activity. At Spanish Peaks, Colorado, curved dike trajectories issuing from a single focal area have been attributed to horizontal propagation from a pressurized central reservoir in a deviatoric tectonic stress field. These dikes, however, are nowhere in contact with the central intrusion, are younger than it by about 1 My and are not filled with the same magma. They were emplaced at shallow depths (≈ 1 km), where the local stress field is very sensitive to surface loads. Here, we show that their trajectories can be set by the load of a volcanic edifice in a tectonic stress field. The orientation and distribution of the Spanish Peaks dikes have changed in the course of two million years as magmas were evolving chemically. Early dikes that were parallel to each another and filled with primitive melts document ascent in the regional tectonic stress field. They were replaced by curved dikes carrying evolved melts, which record the influence of a sizable volcanic edifice. Beneath this edifice, the induced compression prevented dense primitive magmas from erupting in the focal area and diverted intermediate magmas sideways. The growth of this large volcanic cone was probably responsible for the formation of a magma reservoir. The mechanisms that have shaped the Spanish Peaks dike swarm may control the spatial distribution and migration of eruptive centers in many active volcanic areas.

  9. Lunar floor-fractured craters as magmatic intrusions: Geometry, modes of emplacement, associated tectonic and volcanic features, and implications for gravity anomalies

    NASA Astrophysics Data System (ADS)

    Jozwiak, Lauren M.; Head, James W.; Wilson, Lionel

    2015-03-01

    Lunar floor-fractured craters are a class of 170 lunar craters with anomalously shallow, fractured floors. Two end-member processes have been proposed for the floor formation: viscous relaxation, and subcrater magmatic intrusion and sill formation. Recent morphometric analysis with new Lunar Reconnaissance Orbiter Laser Altimeter (LOLA) and image (LROC) data supports an origin related to shallow magmatic intrusion and uplift. We find that the distribution and characteristics of the FFC population correlates strongly with crustal thickness and the predicted frequency distribution of overpressurization values of magmatic dikes. For a typical nearside lunar crustal thickness, dikes with high overpressurization values favor surface effusive eruptions, medium values favor intrusion and sill formation, and low values favor formation of solidified dikes concentrated lower in the crust. We develop a model for this process, make predictions for the morphologic, morphometric, volcanic, and geophysical consequences of the process and then compare these predictions with the population of observed floor-fractured craters. In our model, the process of magmatic intrusion and sill formation begins when a dike propagates vertically towards the surface; as the dike encounters the underdense brecciated region beneath the crater, the magmatic driving pressure is insufficient to continue vertical propagation, but pressure in the stalled dike exceeds the local lithostatic pressure. The dike then begins to propagate laterally forming a sill which does not propagate past the crater floor region because increased overburden pressure from the crater wall and rim crest pinch off the dike at this boundary; the sill then continues to inflate, further raising and fracturing the brittle crater floor. When the intrusion diameter to intrusion depth ratio is smaller than a critical value, the intrusion assumes a laccolith shape with a domed central region. When the ratio exceeds a critical value

  10. Magma storage of an alkali ultramafic igneous suite from Chamberlindalen, SW Svalbard

    NASA Astrophysics Data System (ADS)

    Gołuchowska, Karolina; Barker, Abigail K.; Czerny, Jerzy; Majka, Jarosław; Manecki, Maciej; Farajewicz, Milena; Dwornik, Maciej

    2016-10-01

    An alkali mafic-ultramafic igneous suite of composite intrusions, lenses and associated greenstones are hosted by Neoproterozoic metasedimentary sequences in Chamberlindalen, Southwest Svalbard. This study focuses on the alkali igneous suite of Chamberlindalen with a view to determining the conditions of magma storage. The rocks from Chamberlindalen display cumulate textures, are highly magnesian and are classified as alkaline by the occurrence of kaersutite. They have textures that indicate cocrystallization of primary magmatic minerals such as diopside, kaersutite-ferrokaersutite and biotite-phlogopite in different proportions. The historic magma plumbing system for the alkaline cumulates has been reconstructed by thermobarometry. Diopside and kaersutite crystallization in the alkaline cumulates show a dominant level of magma storage between 30 and 50 km in the subcontinental lithospheric mantle.

  11. Petrology of mafic and ultramafic intrusions from the Portneuf-Mauricie Domain, Grenville Province, Canada: Implications for plutonic complexes in a Proterozoic island arc

    NASA Astrophysics Data System (ADS)

    Sappin, A.-A.; Constantin, M.; Clark, T.

    2012-12-01

    The Portneuf-Mauricie Domain (PMD), located in the south-central part of the Grenville Province, comprises several mafic and ultramafic intrusions hosting Ni-Cu ± platinum-group element (PGE) prospects and a former small mining operation (Lac Édouard mine). These meter- to kilometer-scale, sulfide-bearing intrusions display diverse forms, such as layered and tabular bodies with no particular internal structure, and zoned plutons. They were injected ~ 1.40 Ga into a mature oceanic arc, before and during accretion of the arc to the Laurentian margin. The pressure-temperature conditions of the magmas at the beginning of their emplacement were 3 kbar and 1319-1200 °C (according to the petrologic modeling results from this study). The PMD mineralized intrusions are interpreted to represent former magma chambers or magma conduits in the roots of the oceanic arc. The parent magmas of the mineralized intrusions resulted mainly from the partial melting of a mantle source composed of spinel-bearing lherzolite. Petrologic modeling and the occurrence of primary amphibole in the plutonic rocks indicate that these parent melts were basaltic and hydrous. In addition, fractional crystallization modeling and Mg/Fe ratios suggest that most of the intrusions may have formed from evolved magmas, with Mg# = 60, resulting from the fractionation of more primitive magmas (primary magmas, with Mg# = 68). Petrologic modeling demonstrates that 30% fractional crystallization resulted in the primitive to evolved characteristics of the studied intrusive rocks (as indicated by the crystallization sequences and mineral chemistry). Exceptions are the Réservoir Blanc, Boivin, and Rochette West parent magmas, which may have undergone more extensive fractional crystallization, since these intrusions contain pyroxenes that are more iron rich and have lower Mg numbers than pyroxenes in the other PMD intrusions. The PMD mafic and ultramafic intrusions were intruded into an island arc located

  12. IRA: Intrusion - Reaction - Appats

    DTIC Science & Technology

    2004-11-01

    méthodes d ’attaques Détection d ’intrusion Cas particulier des Canaux Cachés Notion d ’appât (Honey Pot & Honey Net) Protection entre environnements de...aspects suivants : La notion de « Pot de miel » peut s ’étendre d ’un simple leurre (mot de passe constructeur conservé) à des environnement dédié...d’Attaques Logiques .........................................................................7-10 2.3 Environnement Technique étudié

  13. Acoustic emission intrusion detector

    DOEpatents

    Carver, Donald W.; Whittaker, Jerry W.

    1980-01-01

    An intrusion detector is provided for detecting a forcible entry into a secured structure while minimizing false alarms. The detector uses a piezoelectric crystal transducer to sense acoustic emissions. The transducer output is amplified by a selectable gain amplifier to control the sensitivity. The rectified output of the amplifier is applied to a Schmitt trigger circuit having a preselected threshold level to provide amplitude discrimination. Timing circuitry is provided which is activated by successive pulses from the Schmitt trigger which lie within a selected time frame for frequency discrimination. Detected signals having proper amplitude and frequency trigger an alarm within the first complete cycle time of a detected acoustical disturbance signal.

  14. 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.

  15. Longitudinal Relations of Intrusive Parenting and Effortful Control to Ego-Resiliency during Early Childhood

    ERIC Educational Resources Information Center

    Taylor, Zoe E.; Eisenberg, Nancy; Spinrad, Tracy L.; Widaman, Keith F.

    2013-01-01

    Longitudinal relations among ego-resiliency (ER), effortful control (EC), and observed intrusive parenting were examined at 18, 30, and 42 months of age ("Ns" = 256, 230, and 210) using structural equation modeling. Intrusive parenting at 18 and 30 months negatively predicted EC a year later, over and above earlier levels. EC at…

  16. 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.

  17. Management of a rare combination of avulsion and intrusive luxation: A case report

    PubMed Central

    Dharmani, Umesh; Jadhav, Ganesh Ranganath; Kamal, Charan; Rajput, Akhil; Dua, Ankur

    2014-01-01

    In traumatic dental injury, concomitant occurrence of avulsion and intrusive luxation is exceptional. This is because the vectors of forces responsible for both avulsive and intrusive injuries are in different directions. The present case report reviews the management of a rare combination of avulsion in right maxillary lateral incisor (tooth #12) and intrusive luxation in right maxillary central incisor (tooth #11) in a 22-year-old Asian male. Clinical and radiographic evaluation was done at 12-month follow-up. Various treatment modalities and complications associated with both avulsion and intrusion are also discussed in the paper. PMID:25506151

  18. 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.

  19. Petrogenesis of the Pt-Pd mineralized Jinbaoshan ultramafic intrusion in the Permian Emeishan Large Igneous Province, SW China

    NASA Astrophysics Data System (ADS)

    Tao, Yan; Li, Chusi; Hu, Ruizhong; Ripley, Edward M.; Du, Andao; Zhong, Hong

    2007-03-01

    The Jinbaoshan ultramafic intrusion is a sheet-like body with a thick wehrlite unit in the center and thin pyroxenite units at the margins. PGE are enriched in several disseminated sulfide zones in the intrusion. Olivine from the intrusion has low Fo and depleted Ni contents compared to olivine from coeval Emeishan picrites. Whole rock major and trace element concentrations suggest that the Jinbaoshan wehrlites originally contained <30% trapped liquid. The total amount of sulfide in the rocks exceeds that which could have been dissolved in the trapped liquid. The Jinbaoshan wehrlites are interpreted to represent residual assemblages formed by dissolution of plagioclase by passing magma. No clear evidence of crustal contamination is indicated by S, Nd and Os isotopes. We envision that sulfide saturation occurred at depth due to olivine and chromite crystallization. Immiscible sulfide droplets were transported to the Jinbaoshan conduit where they accumulated and reacted with magma successively passing through the conduit to achieve high PGE concentrations.

  20. Magma differentiation and volatile evolution at Fuego Volcano, Guatemala

    NASA Astrophysics Data System (ADS)

    Berlo, K.; Stix, J.; Roggensack, K.

    2009-12-01

    Fuego is an active stratovolcano in Guatemala that has erupted mainly basaltic magma in recent times. The last large eruption, a subplinian (VEI 4), occurred in 1974 and produced pyroclastic flows and ash fall for 10 days. Many smaller eruptions with pyroclastic, lava and lahars flows have occurred since then and activity is intermittently ongoing. Melt inclusions in olivine phenocrysts from the 1974 eruption testify to the presence of variably crystallized magma over a range of depths. Melt inclusions from 1999 and 2004 overlap and extend the 1974 fractional crystallization trend to lower pressure. Melt inclusions from 1974 record high H2O (~6 wt %) and high CO2 (~2500 ppm) concentrations. In contrast the later eruptions have much lower H2O (maximum observed 1 wt %), but CO2 concentrations up to ~1500 ppm. Whereas melts recorded by the later eruptions could be residual from the magma erupted in 1974, these high CO2 concentrations combined with a somewhat higher alkali concentration point to a more complex process or combination of processes. This contribution will examine the origin and associated implications of these later melts.

  1. Solvents and vapor intrusion pathways.

    PubMed

    Phillips, Scott D; Krieger, Gary R; Palmer, Robert B; Waksman, Javier C

    2004-08-01

    Vapor intrusion must be recognized appropriately as a separate pathway of contamination. Although many issues resemble those of other forms of contamination (particularly its entryway, which is similar to that of radon seepage), vapor intrusion stands apart as a unique risk requiring case-specific action. This article addresses these issues and the current understanding of the most appropriate and successful remedial actions.

  2. Petrogenesis and metallogenesis of the Xinjie layered mafic-ultramafic intrusion, China: Modeling of recharge, assimilation and fractional crystallization

    NASA Astrophysics Data System (ADS)

    Li, Hongbo; Zhang, Zhaochong; Li, Yongsheng; Santosh, M.

    2015-12-01

    The Xinjie layered mafic-ultramafic intrusion in the central Emeishan large igneous province (ELIP), SW China, hosts Fe-Ti-V oxide ore in the upper part and Ni-Cu-platinum-group element (PGE) sulfide deposits in the lower part. In this study, we use published Sr-Nd isotopic data to simulate and evaluate the energy-constrained recharge, assimilation, and fractional crystallization (EC-RAFC) model with a view to track the petrogenesis and mineralization. In contrast to the energy-constrained assimilation fractional crystallization (EC-AFC) model, the EC-RAFC modeling shows that the Xinjie intrusion may represent a shallow crustal magma chamber system, where it experienced the RAFC processes. In the early stage of the magmatic process (Tm = 1460 °C), a pulse of magma was injected into an actively evolving magma chamber. Minor melting (Ma∗ = 0.257) and assimilation of the wallrock (underlying Emeishan basalts) occurred when the temperature of magma (Tm = 1245 °C) decreased close to the equilibration temperature (Teq = 1165 °C). The mass-temperature plots indicate that fractional crystallization was significantly affected by the recharge and assimilation processes, whereas the contaminated magma recharge favored the early crystallization of Fe-Ti oxides as well as the formation of the PGE-bearing immiscible melt in the lower part of the intrusion. In contrast, the formation of the Fe-Ti oxides ores in the upper part occurred probably through fractional crystallization and/or immiscibility of the evolved Fe-Ti-rich magma, resulting in the paragenesis of Fe-Ti-V oxides and Ni-Cu-PGE sulfides in the Xinjie layered intrusion.

  3. Multiple intrusive events in the formation of granite plutons: Evidence from the Lee Vining Diorite, eastern California

    SciTech Connect

    McCarthy, T.C.; Furman, T. . Dept. of Environmental Sciences); Reid, J.B. Jr. . School of Natural Sciences)

    1993-03-01

    The Cretaceous Lee Vining Diorite (eastern Sierra Nevada) preserves important field, petrographic and geochemical evidence for complex intrusive events in a mesozonal magma body. The pluton comprises primarily light grey unfoliated quartz diorite, with color index varying between 10--50. A 1,400 m transect across the pluton yielded samples of (1) mafic diorite from a 300 m thick sill, (2) disaggregated basaltic dikes, (3) rounded mafic inclusions and (4) rounded hornblende-cumulate inclusions in addition to (5) quartz diorite of variable texture and color index. Internal intrusive contacts are observed in several places; the upper contact of the sill is indistinct locally, suggesting a low thermal contrast with host quartz diorite at the time of intrusion. Textural analysis of plagioclase crystals form throughout the pluton indicates a history of pervasive magma mixing. In each thin section, 20--90% of the plagioclase crystals are pitted or corroded, and up to 50% of these crystals are also completely zoned. Disequilibrium plagioclase crystals are not preferentially associated with mafic inclusion, but are distributed randomly within the pluton. Major and trace element analyses of over 40 samples taken along the transect show variations that cannot be explained through simple magma mixing or through progressive crystallization of a single magma body. The pluton is not zoned geochemically, but rather comprises small regions (< 200 m across) of uniform composition that are juxtaposed randomly. Chemical variations across the pluton likely result from both missing of small magma batches and fractional crystallization of mixed magmas. This interpretation is consistent with field and textural requirements for multiple intrusive episodes in the formation of the diorite pluton.

  4. The 1669 eruption at Mount Etna: chronology, petrology and geochemistry, with inferences on the magma sources and ascent mechanisms

    NASA Astrophysics Data System (ADS)

    Corsaro, Rosa Anna; Cristofolini, Renato; Patanè, Loredana

    1996-12-01

    Analysis of the petrochemical characters of the 1669 Etnean lavas shows that they can be grouped into two sets: SET1 lavas were erupted from 11 to 20 March and are more primitive in composition than SET2, erupted later until the end of activity. Both sets may be interpreted as the result of crystallization under different conditions of two primary magmas which are compositionally slightly distinct and which fractionate different volumetric proportions of minerals. To explain why more mafic lavas (SET1) were erupted earlier than more acid ones (SET2), we argue that new deeper magma rose up into a reservoir where residing magma was fractionating. Density calculations demonstrate that new magma is less dense and may originate a plume, rapidly rising through the residing magma which is cooler and more volatile-depleted than the new magma. Calculations of uprise velocity assuming laminar flow are consistent with this hypothesis.

  5. Saltwater intrusion in coastal regions of North America

    NASA Astrophysics Data System (ADS)

    Barlow, Paul M.; Reichard, Eric G.

    2010-02-01

    Saltwater has intruded into many of the coastal aquifers of the United States, Mexico, and Canada, but the extent of saltwater intrusion varies widely among localities and hydrogeologic settings. In many instances, the area contaminated by saltwater is limited to small parts of an aquifer and to specific wells and has had little or no effect on overall groundwater supplies; in other instances, saltwater contamination is of regional extent and has resulted in the closure of many groundwater supply wells. The variability of hydrogeologic settings, three-dimensional distribution of saline water, and history of groundwater withdrawals and freshwater drainage has resulted in a variety of modes of saltwater intrusion into coastal aquifers. These include lateral intrusion from the ocean; upward intrusion from deeper, more saline zones of a groundwater system; and downward intrusion from coastal waters. Saltwater contamination also has occurred along open boreholes and within abandoned, improperly constructed, or corroded wells that provide pathways for vertical migration across interconnected aquifers. Communities within the coastal regions of North America are taking actions to manage and prevent saltwater intrusion to ensure a sustainable source of groundwater for the future. These actions can be grouped broadly into scientific monitoring and assessment, engineering techniques, and regulatory approaches.

  6. How Big is the Dufek Intrusion? Paleomagnetic Constraints on the Cooling History of the Dufek Layered Intrusion (Invited)

    NASA Astrophysics Data System (ADS)

    Gee, J. S.; Cheadle, M. J.; Meurer, W. P.; Grimes, C. B.

    2013-12-01

    may contain five or more magnetization components, including shallow inclinations distinct from the expected Jurassic direction. All of these observations are difficult to reconcile with the slow cooling expected if the Dufek Massif is the lower part of a thicker intrusion that also includes the Forrestal Range. Models of single domain thermoremanence acquisition, contrained by thermal models of the intrusion, reproduce many of the features in the demagnetization data. Although we cannot exclude the possibility that the Dufek Massif cooled more rapidly due to lateral heat loss, the magnetization records from the HP and NW sections can be reconciled most easily if the Dufek Massif was emplaced at shallow depth and represents a separate intrusion from the Forrestal Range.

  7. On the Principles of Building a Layered Intrusion

    NASA Astrophysics Data System (ADS)

    Marsh, B. D.

    2009-12-01

    An accurate and realistic understanding of all magmatic processes involves knowing the combined physical and chemical fundamentals governing the overall process. Magmatic processes involve such a vast array of sub-processes (e.g., heat and mass transfer, crystal growth, slurry transport and sorting, annealing, resorbtion, etc.) that rarely is there any single feature or measurement that can be safely inverted to solve the problem. And each event as in the formation of an intrusion must at some level for heuristic purposes be defined as an isolated event. This is commonly done without much forethought, as is the absolutely critical assumption of the initial conditions defining the beginning of the event. Almost without exception, it is the initial conditions that determine the outcome of the entire process in all physical and biological systems. Automobile factories produce motorized vehicles not water melons or chimpanzees. Nucleosynthesis of H and He always gives the same set of elements. The initial conditions of the magma giving rise to the end product for mafic layered systems are especially difficult to discern and must be bounded by observing simpler, real time magmatic and volcanic processes. Initial conditions come from posing a series of questions: What was the style and duration of filling? What was the rate of influx and final volume of each delivery of magma? What was the compositional variation and phenocryst content of the individual magmatic deliveries? If phenocrysts are present, were they sorted prior to injection during ascension? What was the original and ongoing shape of the magmatic reservoir? A failure to appreciate or answer such basic questions leads to vastly untenable evolutionary scenarios. Unrealistic initial conditions necessarily lead to unrealistic magmatic scenarios. There are certain safe starting points. Eruptive and emplacement fluxes are limited. The larger an intrusion is the longer it took to build and the longer to build the

  8. Volatile budget of Eyjafjallajokull magmas

    NASA Astrophysics Data System (ADS)

    Sigurdsson, H.; Mandeville, C. W.

    2010-12-01

    Volatile elments played a critical role in the style of activity during the 2010 eruptions of the glacier-covered Eyjafjallajokull volcano in Iceland. The alkali basalt flank eruption at Fimmvorduhals was dominated by vigorous fire fountaining that produced dominantly spatter-fed aa lava flows. Production of fine ash during the subsequent summit eruption has been variously attributed to magma fragmentation, either due to water-ice-magma interaction related to the 250 m thick glacier cover over the crater, or juvenile volatile content of the magma. Considering the great impact of the ash dispersal on trans-North Atlantic aviation, knowledge of the fragmentation mechanism and the relative roles of juvenile magmatic gases versus phreatomagmatic fragmentation is of prime significance. To evaluate the potential importance of juvenile components, the concentrations of volatiles in magmas erupted in 2010 from Eyjafjallajokull volcano in Iceland have been measured. Analysis of glass inclusions in olivine Fo 77-85 and plagioclase phenocrysts in the alkali basalt magma erupted at Fimmvorduhals flank eruption contain high total volatiles in the range 0.96 - 2.12 wt.%, and sulfur 0.10 - 0.16 wt.%. These glass inclusions are comparable to major element bulk composition of Fimmvörduháls alkali basalt lavas. In contrast, tephra from the explosive summit crater eruption are trachy-andesitic. This magma contains a rather wide range of olivine and plagioclase phenocrysts of Fo48-79 and An 69-81, with both basaltic and andesitic glass inclusions. This diversity is also reflected in a much wider range of total volatile content from 0.1 - 2.88 wt.% and sulfur 0.1 - 0.24 wt.%. At the basic end, the glass inclusions are comparable to the Fimmvorduhals alkali basalt lava, but some have andesitic composition. The highest volatile content is observed in the andesitic glass inclusions in plagioclase An78. Further analysis of glass inclusions and matrix glass by FTIR and ion probe is in

  9. Magma surge from the mantle: the Father's Day Eruption, Kīlauea Volcano, Hawai'i

    NASA Astrophysics Data System (ADS)

    Salem, L. C.; Edmonds, M.; Maclennan, J.; Houghton, B. F.; Poland, M. P.

    2015-12-01

    The geometry of the shallow plumbing system of Kīlauea Volcano, Hawai'i, is constrained by both geophysical and petrologic studies, yet the loci of lower crustal magma storage and timescales of magma ascent are almost entirely unknown. The petrography and texture of erupted magmas are largely overprinted by processes in the shallow reservoir and conduit. Direct petrological evidence for lower crustal storage and transport is enigmatic but exists in the form of fine-scale crystal zoning in the cores of olivine phenocrysts, in the geochemical heterogeneity of melt inclusions and in fluid inclusion density. The 2007 Father's Day intrusion and eruption occurred at the culmination of a surge in magma supply to the summit reservoir and during a period of heightened CO2 outgassing flux. The erupted lavas provide an opportunity to analyze atypically primitive melts, with > 8.5 wt% MgO in the whole rock, which have undergone relatively little shallow crustal processing. We characterise melt inclusions and their host olivine crystals through a detailed study of olivine morphology, diffusion modelling, and melt and fluid inclusion geochemistry. We show that the melt inclusions preserve primitive geochemical heterogeneity, which we use to reconstruct fractionation, mixing and degassing processes through the crust. We infer timescales and pressures of magma ascent, storage, and CO2 degassing through the crustal plumbing system. These observations are interpreted in the context of the exceptionally detailed set of volcano monitoring data at Kīlauea Volcano.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  11. Magma ascent and the pressurization of Mount Etna's volcanic system.

    PubMed

    Patanè, Domenico; De Gori, Pasquale; Chiarabba, Claudio; Bonaccorso, Alessandro

    2003-03-28

    After a period of deflation during the 1991-1993 flank eruption, Mount Etna underwent a rapid inflation. Seismicity and ground deformation show that since 1994, a huge volume of magma intruded beneath the volcano, producing from 1998 onward a series of eruptions at the summit and on the flank of the volcano. The last of these, started on 27 October 2002, is still in progress and can be considered one of the most explosive eruptions of the volcano in recent times. Here we show how geodetic data and seismic deformation, between 1994 and 2001, indicate a radial compression around an axial intrusion, consistent with a repressurization of Mount Etna's plumbing system at a depth of 6 to 15 kilometers, which triggered most of the seismicity and provoked the dilatation of the volcano and the recent explosive eruptive activity.

  12. Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode.

    PubMed

    Wright, Tim J; Ebinger, Cindy; Biggs, Juliet; Ayele, Atalay; Yirgu, Gezahegn; Keir, Derek; Stork, Anna

    2006-07-20

    Seafloor spreading centres show a regular along-axis segmentation thought to be produced by a segmented magma supply in the passively upwelling mantle. On the other hand, continental rifts are segmented by large offset normal faults, and many lack magmatism. It is unclear how, when and where the ubiquitous segmented melt zones are emplaced during the continental rupture process. Between 14 September and 4 October 2005, 163 earthquakes (magnitudes greater than 3.9) and a volcanic eruption occurred within the approximately 60-km-long Dabbahu magmatic segment of the Afar rift, a nascent seafloor spreading centre in stretched continental lithosphere. Here we present a three-dimensional deformation field for the Dabbahu rifting episode derived from satellite radar data, which shows that the entire segment ruptured, making it the largest to have occurred on land in the era of satellite geodesy. Simple elastic modelling shows that the magmatic segment opened by up to 8 m, yet seismic rupture can account for only 8 per cent of the observed deformation. Magma was injected along a dyke between depths of 2 and 9 km, corresponding to a total intrusion volume of approximately 2.5 km3. Much of the magma appears to have originated from shallow chambers beneath Dabbahu and Gabho volcanoes at the northern end of the segment, where an explosive fissural eruption occurred on 26 September 2005. Although comparable in magnitude to the ten year (1975-84) Krafla events in Iceland, seismic data suggest that most of the Dabbahu dyke intrusion occurred in less than a week. Thus, magma intrusion via dyking, rather than segmented normal faulting, maintains and probably initiated the along-axis segmentation along this sector of the Nubia-Arabia plate boundary.

  13. Melt segregation and assembly of the youngest exposed magma chamber in the world: Takidani Pluton (Japan)

    NASA Astrophysics Data System (ADS)

    Hartung, E.; Caricchi, L.; Floess, D.; Wallis, S.; Harayama, S.

    2014-12-01

    Segregation of residual melt from partially crystallized magmas is a process of paramount importance for the chemical evolution of magmas and the construction of reservoirs of potentially eruptible magma. In this study we investigate the Takidani pluton, one of the youngest exposed plutons on Earth (˜1Ma). This chemically zoned magmatic body is located within the active Norikura Volcanic Chain in the Northern Japan Alps and associated with large dacitic to rhyolitic deposits (Nyukawa Pyroclastic Flow Deposit and Ebisutoge-Fukuda tephra). Our study focuses on the physical processes responsible for the extraction of residual melt from a crystallizing magma and the construction of the subvolcanic reservoirs that fed large silicic eruptions. Detailed structural mapping and sampling along four transects from the base to the top of the pluton were carried out along with a magnetic susceptibility survey. Our preliminary results indicate that the pluton was assembled by multiple intrusions. The pluton can be broadly separated into three distinct lithological units: 1) fine grained granite; 2) equigranular granodiorite that locally grades into either porphyritic granodiorite or granite towards the roof of the intrusion; and 3) mafic granodiorite. Units 1) and 2) form the core of the intrusion and together represent about 70% of the total volume of the pluton. Our results show that the equigranular granodiorite is internally inhomogeneous with felsic lenses of lower magnetic susceptibility. The magnetic susceptibility decreases gradually towards the roof of the pluton reaching its lowest value within leucrocratic porphyritic units. Higher magnetic susceptibility values at the contact with the roof correspond to a slightly more mafic porphyritic unit. Melt segregation and evolution of the Takidani Granodiorite are being further investigated using bulk rock and mineral chemistry (EMPA and LA-ICP-MS) together with anisotropy of magnetic susceptibility.

  14. Deformation structures associated with the Trachyte Mesa intrusion, Henry Mountains, Utah: Implications for sill and laccolith emplacement mechanisms

    NASA Astrophysics Data System (ADS)

    Wilson, Penelope I. R.; McCaffrey, Ken J. W.; Wilson, Robert W.; Jarvis, Ian; Holdsworth, Robert E.

    2016-06-01

    Deformation structures in the wall rocks of igneous intrusions emplaced at shallow crustal depths preserve an important record of how space was created for magma in the host rocks. Trachyte Mesa, a small Oligocene age intrusion in the Henry Mountains, Utah, is composed of a series of stacked tabular, sheet-like intrusions emplaced at 3-3.5 km depth into sandstone-dominated sedimentary sequences of late Palaeozoic-Mesozoic age. New structural analysis of the spatial distribution, geometry, kinematics and relative timings of deformation structures in the host rocks of the intrusion has enabled the recognition of distinct pre-, syn-, and late-stage-emplacement deformation phases. Our observations suggest a two-stage growth mechanism for individual sheets where radial growth of a thin sheet was followed by vertical inflation. Dip-slip faults formed during vertical inflation; they are restricted to the tips of individual sheets due to strain localisation, with magma preferentially exploiting these faults, initiating sill (sheet) climbing. The order in which sheets are stacked impacts on the intrusion geometry and associated deformation of wall rocks. Our results offer new insights into the incremental intrusion geometries of shallow-level magmatic bodies and the potential impact of their emplacement on surrounding host rocks.

  15. Two-stage models for lunar and terrestrial anorthosites: Petrogenesis without a magma ocean

    NASA Astrophysics Data System (ADS)

    Longhi, John; Ashwal, Lewis D.

    1985-02-01

    Two-stage diapiric models for lunar ferroan anorthosites and terrestrial massif anorthosites are examined. The lunar model is developed to explain early lunar differentiation in the absence of a magma ocean. If correct, the terrestrial model serves as an analog for the development of lunar anorthositic diapirs. There is field and textural evidence of transport of mostly crystalline anorthositic material within the terrestrial complexes. This evidence, combined with the absence of anorthositic lavas and phase equilibrium constraints inhibiting the production of hyperaluminous magmas, is consistent with the detachment of plagioclase-rich crystalline mushes from large, uppermost mantle plutons and multiple diapiric intrusion of these mushes into the upper sialic crust with attendant anatexis. Rudimentary dynamical calculations suggest that a simple, single-layer source for the diapirs is improbable: either there were several parental magma chambers or there was a single large chamber that was repeatedly replenished. The lunar model is a development of Wetherill's (1975) suggestion that, following accretion, the outer portion of the moon consisted of a stack of overlapping layered intrusions and that reheating of these intrusions mobilized their anorthositic layers, which intruded upwards to produce the anorthositic lunar crust. Dynamical calculations show that gravitational instabilities in anorthositic layers (≤ 1 km thick) could develop into diapirs on a reasonable time scale (50-100 m.y.) only if the outer portion of the moon was partially remelted. We suggest that partial melting of the interior due to the decay of long-lived radionuclides with the subsequent onset of global convection heated the stack of intrusions from below, thus causing melting and allowing the anorthositic diapirs to grow and ascend fairly rapidly. As the convecting zone thickened, a mass expulsion of anorthositic material out of the lunar interior may have occurred.

  16. 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

  17. Petrogenesis of mixed-magma, high-grade, peralkaline ignimbrite 'TL' (Gran Canaria): diverse styles of mixing in a replenished, zoned magma chamber

    NASA Astrophysics Data System (ADS)

    Sumner, Janet M.; Wolff, John

    2003-08-01

    The Miocene (13.4 Ma) high-grade, peralkaline ignimbrite TL on Gran Canaria comprises two overlapping ignimbrite lobes, an eastern lobe which is high-grade, with rheomorphic lithofacies, and a western lobe which is extremely high-grade with lava-like lithofacies. The two lobes were erupted from different vents tapping the same magma chamber during a single eruption; where they overlap the western lobe overlies the eastern lobe [Sumner and Branney (2002) J. Volcanol. Geotherm. Res., 115, 109-138]. Three magma compositions are present: comendite, trachyte and benmoreite. Fiamme of intermediate composition also occur and magma mingling during withdrawal produced compositionally banded juvenile clasts. Both ignimbrite lobes consist of mixed and mingled comendite and trachyte plus small mafic globules of benmoreite in the western lobe. The ignimbrite lobes have a broad vertical compositional zonation with a basal dominantly comenditic zone, grading up into a mixed zone with subequal amounts of comendite and trachyte, which passes into an overlying trachyte-dominated zone; the magma chamber is inferred to have been zoned upwards from trachyte to comendite. Major and trace element compositional variations and phenocryst-whole rock relations among comendite and trachyte are scattered in a fashion consistent with mingling of, and exchange of phenocrysts between, liquids that lie along the fractionation path from trachyte to comendite. Intrusion of benmoreite magma into the chamber over a period of several months to years before the eruption produced mafic globules that equilibrated to varying degrees with the lower trachyte magma layer. This replenishment ultimately triggered the eruption. Most of the trachyte-comendite mingling probably occurred during withdrawal and eruption; some certainly took place after ignimbrite deposition, during rheomorphic flow. Magmatically heterogeneous high-grade ignimbrites that experience an episode of non-particulate flow show particularly

  18. Magma, Magma, Quite Contaminated, How Does Your Garnet Grow?

    NASA Astrophysics Data System (ADS)

    Lackey, J.; Romero, G. A.; Valley, J. W.

    2010-12-01

    Garnet in granitoid rocks has drawn considerable attention and discussion because of uncertainty surrounding its origins. For example, enrichment of Al, resulting in peraluminous magmas capable of crystallizing garnets, may be controlled by contamination or extreme differentiation; Mn enrichment in aplitic and pegmatitic phases suggests garnet may appear only at relatively low, near solidus temperatures. Peritectic garnet, grown by magma-wallrock reaction, may be confused with magmatic garnet, and xenocrysts of metamorphic garnet, entrained from wallrocks, further complicate interpretation. We address these uncertainties with the SIMS analysis of oxygen isotope variations in single garnet crystals and crystal populations in granitic rocks. Values of δ18O were measured on a CAMECA IMS 1280 using a 10 µm spot size and typical precision of ± 0.3 at 2 standard deviations. Analyses were corrected for instrumental mass fractionation according to the newly solved bias correction protocol for garnet (Page et al. 2010). Samples were collected from the Devonian Togus and Hallowell plutons in the south central Maine. These plutons are an ideal site for this study because they are peraluminous and contain pervasive garnet, they locally intrude pelitic, garnet-bearing wallrocks, and they have field evidence of xenolith entrainment and peritectic reaction of xenoliths and the host magmas. Garnet δ18O values of 7.5-10.5‰ show a large range of crustal input to host magmas. Crystal-to-crystal variation of δ18O in hand-samples varies up to 2‰, confirming that garnet populations have complex origins. Traverses (20-50 spots) of single crystals show that δ18O varies up to 1‰, with rims of crystals (outer 50-100µm) being up to 1‰ higher or lower than interiors. Increases of δ18O are interpreted as late-stage contamination, whereas lower δ18O rims, with correspondence to decreasing Fe/Mg ratio, suggest growth during falling magma temperature (50-100°C). Some garnet

  19. Layered amphibolite sequence in NE Sardinia, Italy: remnant of a pre-Variscan mafic silicic layered intrusion?

    NASA Astrophysics Data System (ADS)

    Franceschelli, Marcello; Puxeddu, Mariano; Cruciani, Gabriele; Dini, Andrea; Loi, Marilisa

    2005-04-01

    analogies with Siberian, Deccan and proto-Atlantic rift tholeiites. Comparisons with Thingmuli, Skaergaard and Kiglapait rocks and with experimental data suggest that the Monte Plebi intrusion was an open-to-oxygen system with fO2 ≥ FMQ. Mafic and ultramafic samples yielded ɛNd(460)=+0.79 /+3.06 and 87Sr/86Sr=0.702934-0.703426, and four silicic samples ɛNd(460)=-0.53/-1.13; 87Sr/86Sr=0.703239-0.703653. Significant differences in Nd isotope ratios between mafic and silicic rocks prove that both groups evolved separately in deeper magma chambers, from different mantle sources, with negligible interaction with crustal material, and were later repeatedly injected within a shallower magma chamber. The spectrum of Sr and Nd isotope data is consistent with a slightly enriched mantle metasomatized during an event earlier than 460 Ma. The metasomatising component was represented by alkali-Th-rich fluids of crustal origin rather than by sedimentary materials, able to modify alkali and Sr-Nd isotope systematics. Monte Plebi layered amphibolites might represent the first example of a strongly metamorphosed fragment of an early Paleozoic mafic silicic layered intrusion emplaced in a thinning continental crust and then tectonically dismembered by Variscan orogeny.

  20. Accelerated uplift and magmatic intrusion of the Yellowstone caldera, 2004 to 2006

    USGS Publications Warehouse

    Chang, W.-L.; Smith, R.B.; Wicks, C.; Farrell, J.M.; Puskas, C.M.

    2007-01-01

    The Yellowstone caldera began a rapid episode of ground uplift in mid-2004, revealed by Global Positioning System and interferometric synthetic aperture radar measurements, at rates up to 7 centimeters per year, which is over three times faster than previously observed inflation rates. Source modeling of the deformation data suggests an expanding volcanic sill of ???1200 square kilometers at a 10-kilometer depth beneath the caldera, coincident with the top of a seismically imaged crustal magma chamber. The modeled rate of source volume increase is 0.1 cubic kilometer per year, similar to the amount of magma intrusion required to supply the observed high heat flow of the caldera. This evidence suggests magma recharge as the main mechanism for the accelerated uplift, although pressurization of magmatic fluids cannot be ruled out.

  1. Accelerated uplift and magmatic intrusion of the Yellowstone caldera, 2004 to 2006.

    PubMed

    Chang, Wu-Lung; Smith, Robert B; Wicks, Charles; Farrell, Jamie M; Puskas, Christine M

    2007-11-09

    The Yellowstone caldera began a rapid episode of ground uplift in mid-2004, revealed by Global Positioning System and interferometric synthetic aperture radar measurements, at rates up to 7 centimeters per year, which is over three times faster than previously observed inflation rates. Source modeling of the deformation data suggests an expanding volcanic sill of approximately 1200 square kilometers at a 10-kilometer depth beneath the caldera, coincident with the top of a seismically imaged crustal magma chamber. The modeled rate of source volume increase is 0.1 cubic kilometer per year, similar to the amount of magma intrusion required to supply the observed high heat flow of the caldera. This evidence suggests magma recharge as the main mechanism for the accelerated uplift, although pressurization of magmatic fluids cannot be ruled out.

  2. The chemical and isotopic differentiation of an epizonal magma body: Organ Needle pluton, New Mexico

    USGS Publications Warehouse

    Verplanck, P.L.; Farmer, G.L.; McCurry, M.; Mertzman, S.A.

    1999-01-01

    Major and trace element, and Nd and Sr isotopic compositions of whole rocks and mineral separates from the Oligocene, alkaline Organ Needle pluton (ONP), southern New Mexico, constrain models for the differentiation of the magma body parental to this compositionally zoned and layered epizonal intrusive body. The data reveal that the pluton is rimmed by lower ??(Nd) (~-5) and higher 87Sr/86Sr (~0.7085) syenitic rocks than those in its interior (??(Nd) ~ 2, 87Sr/86Sr ~0.7060) and that the bulk compositions of the marginal rocks become more felsic with decreasing structural depth. At the deepest exposed levels of the pluton, the ??(Nd)~-5 lithology is a compositionally heterogeneous inequigranular syenite. Modal, compositional and isotopic data from separates of rare earth element (REE)-bearing major and accesory mineral phases (hornblende, titanite, apatite, zircon) demonstrate that this decoupling of trace and major elements in the inequigranular syenite results from accumulation of light REE (LREE)-bearing minerals that were evidently separated from silicic magmas as the latter rose along the sides of the magma chamber. Chemical and isotopic data for microgranular mafic enclaves, as well as for restite xenoliths of Precambrian granite wall rock, indicate that the isotopic distinction between the marginal and interior facies of the ONP probably reflects assimilation of the wall rock by ??(Nd) ~-2 mafic magmas near the base of the magma system. Fractional crystallization and crystal liquid separation of the crystally contaminated magma at the base and along the margins of the chamber generated the highly silicic magmas that ultimately pooled at the chamber top.

  3. Extremely High Magma Emplacement Rates Recorded in the Golden Horn Batholith, WA

    NASA Astrophysics Data System (ADS)

    Eddy, M. P.; Bowring, S. A.; Tepper, J. H.; Miller, R. B.

    2015-12-01

    High SiO2 rhyolites emplaced during 'super-eruptions' demonstrate that large volumes of eruptible magma can exist in the upper crust. However, the timescale over which the magma reservoirs that source these eruptions are built remains controversial. Thermal models suggest that magma emplacement rates need to be > 0.005-0.01 km3/yr in order to accumulate enough eruptible magma to source a 'super-eruption'. Yet, these rates are higher than the time-averaged rates (< 0.001 km3/yr) for nearly all well-studied granitoid plutonic complexes. This disparity contradicts geologic evidence suggesting that the high SiO2 rhyolites emplaced during 'super-eruptions' are extracted from crystal rich magma chambers that should be preserved in the geologic record as granodioritic and granitic plutons. We quantify time-averaged magma emplacement rates for the upper crustal Golden Horn batholith, WA based on new geologic mapping and U-Pb zircon CA-IDTIMS geochronology. The batholith is exposed over 310 km3 and can be separated in the field into five intrusive units. High topography allows the 3D geometry of each phase to be constrained and their volumes range from < 100 km3 to > 400 km3. U-Pb zircon geochronology reveals that four of the five phases were assembled incrementally and distinct zircon populations from samples within these phases suggest that individual magmatic pulses had fully crystallized before the next arrived. However, six nearly identical U-Pb zircon dates from a > 400 km3 rapakivi granite show that this phase was built in ca. 50 kyr and that large portions may have been emplaced nearly simultaneously. The implied emplacement rate for this phase (≥ 0.008 km3/yr) is in agreement with those predicted for assembly of the upper crustal magma chambers that source 'super-eruptions', and it may provide a rare and unprecedented opportunity to study the processes that occur in such chambers.

  4. Three-dimensional numerical analysis of magma transport through a pre-existing fracture in the crust

    NASA Astrophysics Data System (ADS)

    Chen, Zuan; Cheng, Xu; Huang, Xiaoge; Bai, Wuming; Jin, Zhi-He

    2014-05-01

    Magmas are transported through pre-existing fractures in many repeatedly erupting volcanoes. The study of this special process of magma transport is fundamentally important to understand the mechanisms and conditions of volcanic eruptions. In this paper, we numerically simulate the magma propagation process through a pre-existing vertical fracture in the crust by using the combined finite difference method (FDM), finite element method (FEM) and discontinuous deformation analysis (DDA) approach. FDM is used to analyze magma flow in the pre-existing fracture, FEM is used to calculate the opening of the fracture during magma intrusion, and DDA is used to deal with the contact of the closed fracture surfaces. Both two-dimensional (2D) and three-dimensional (3D) examples are presented. Parametric studies are carried out to investigate the influence of various physical and geometric parameters on the magma transport in the pre-existing fracture. We have considered magma chamber depth ranging from 7 km to 10 km under the crust surface, magma viscosity ranging from 2 × 10-2 to 2 × 10-7 MPa s, and the density difference between the magma and host rock ranging from 300 to 700 kg/m3. The numerical results indicate that (1) the fluid pressure p varies gradually along the depth, (2) the shape of the magma body during propagation is like a torch bar and its width ranges from 2 m to 4 m approximately in the 3D case and 10 m to 50 m in the 2D case for the same physical parameters used, (3) the crust surface around the pre-existing fracture begins to increase on both sides of the fracture, forms a trough between them, then gradually uplifts during the transport of the magma, and finally takes the shape of a crater when the magma reaches the surface. We have also examined the influence of physical and geometric parameters on the minimum overpressure for magma transport in the 3D case. The numerical results show that our numerical technique presented in this paper is an effective

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

    SciTech Connect

    John, B.E.

    1988-07-01

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

  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. Characteristics and petrogenesis of Alaskan-type ultramafic-gabbro intrusions, southeastern Alaska

    SciTech Connect

    Loney, R.A. ); Himmelberg, G.R. Univ. of Missouri, Columbia, MO )

    1993-04-01

    Alaskan-type ultramafic-gabbro intrusions occur along a belt that extends from Duke Island to Klukwan in southeastern Alaska and fall into two age groups, 400 to 440 Ma and 100 to 110 Ma. Most of the smaller bodies are magnetite-bearing hornblende clinopyroxenite; the larger ones consist of dunite, wehrlite, olivine clinopyroxenite, with some gabbro, in addition to hornblende clinopyroxenite and hornblendite. Textural, mineralogical, and chemical characteristics of the Alaskan-type ultramafic bodies indicate that they originated by fractional crystallization of a basaltic magma and accumulation in a crustal magma chamber. The Al[sub 2]O[sub 3] content of clinopyroxene shows a marked enrichment with differentiation, suggesting crystallization from progressively more hydrous melts like those characteristics of arc magmas. REE abundance levels and patterns are markedly similar for given rock units in all the bodies studied suggesting that all the bodies were derived by differentiation of closely similar parent magmas under near identical conditions. The exact composition of the primary melt is uncertain but the authors' preferred interpretation is that the parental magma of most Alaskan-type bodies was a subalkaline hydrous basalt. The striking similarity between the REE abundance levels and patterns of the Alaskan-type clinopyroxenites and gabbros, and the clinopyroxenite xenoliths and plutonic gabbros associated with Aleutian Island Arc volcanism, further suggests that the primary magma was probably a hydrous olivine basalt similar to the primary magma proposed for the Aleutian arc lavas. The mineral chemistry and phase equilibria of the ultramafic bodies suggest that they crystallized in magma chambers at depths greater than about 9 km. Except for the Duke Island body, which has sedimentary structures and shows evidence of ubiquitous current activity, most of the other bodies appear to have accumulated under static conditions.

  8. Insights into mare basalt thicknesses on the Moon from intrusive magmatism

    NASA Astrophysics Data System (ADS)

    Michaut, Chloé; Thiriet, Mélanie; Thorey, Clément

    2016-08-01

    Magmatic intrusions preferentially spread along interfaces marked by rigidity and density contrasts. Thus the contact between a lunar mare and its substratum provides a preferential location for subsequent magmatic intrusions. Shallow intrusions that bend the overlying layer develop characteristic shapes that depend on their radius and on the overlying layer flexural wavelength and hence on their emplacement depth. We characterize the topography of seven, previously identified, candidate intrusive domes located within different lunar maria, using data from the Lunar Orbiter Laser Altimeter. Their topographic profiles compare very well with theoretical shapes from a model of magma flow below an elastic layer, supporting their interpretation as intrusive features. This comparison allows us to constrain their intrusion depths and hence the minimum mare thickness at these sites. These new estimates are in the range 400-1900 m and are generally comparable to or thicker than previous estimates, when available. The largest thickness (⩾ 1700 m) is obtained next to the Hortensius and Kepler areas that are proposed to be the relicts of ancient volcanic shields.

  9. Crystallization Pressures of Alkaline Magmas of the Kula Volcanic Province, Western Turkey

    NASA Astrophysics Data System (ADS)

    Solpuker, U.; Kilinc, A. I.

    2013-12-01

    PProducts of Quaternary sodic alkaline volcanism in western Anatolia is mainly observed around Kula region. The Kula Volcanic Province experienced three episodes of alkaline volcanism. We used the MELTS algorithm to model the evolution path of the Kula magmas by imposing fractional crystallization as a constraint and retrieved the initial system pressure using clinopyroxene geobarometer. We showed that the use of clinopyroxene geobarometer and the MELTS algorithm in combination can be used to estimate the initial water content of magma and the oxygen fugacity of the system. Pressure estimates for the most of the clinopyroxenes are between 12 to 7 kbar. The estimated crystallization temperatures decrease from the first episode to the third episode. The first episode magmas crystallized around Moho but the crystallization depths of the later episode magmas can increase up to 15-20 km below Moho. The calculated crystallization temperatures decrease from the first episode to the third episode. Isobaric fractional crystallization modeling using the MELTS algorithm constrained the fractionation conditions of Kula magmas. The initial water content of the magmas decreases from the first episode (4 wt.%) to third episode (2 wt. %). Under hydrous conditions and oxygen fugacity equals to QFM+2, up to 26 wt % fractional crystallization of olivine, clinopyroxene, spinel and apatite is required to generate the compositional diversity of the KVP magmas.

  10. High-resolution insights into episodes of crystallization, hydrothermal alteration and remelting in the Skaergaard intrusive complex

    NASA Astrophysics Data System (ADS)

    Wotzlaw, Jörn-Frederik; Bindeman, Ilya N.; Schaltegger, Urs; Brooks, C. Kent; Naslund, H. Richard

    2012-11-01

    This paper presents a new high-precision zircon U-Pb geochronological view on the crystallization and assembly process of one of the most important and intensely studied intrusive bodies on Earth—the Skaergaard intrusion in East Greenland. With analytical uncertainties of a few tens of thousands of years, we were able to resolve several important events during cooling of this intrusion. Initial cooling of the shallowly intruded ˜300 km3 of tholeiitic basaltic magma from liquidus to zircon saturation at ˜1000 °C is recorded by a precise zircon crystallization age of 55.960±0.018 Ma of an intercumulus gabbroic pegmatite in the lower portion of the intrusion. Based on this zircon crystallization age and a published cooling model we estimate the "true" age of emplacement to be ˜56.02 Ma. The last portions of Skaergaard appear to crystallize completely ˜100 ka after emplacement as recorded by abundant ˜55.91-55.93 Ma zircons in the Sandwich Horizon (SH), where lower and upper solidification fronts met. Intrusion of an isotopically distinct new magma batch, the ˜600 m thick Basistoppen Sill, into the solidified upper portion of Skaergaard, happened at 55.895±0.018 Ma, suggesting close timing between crystallization of evolved rocks around the SH and intrusion of the Basistoppen Sill. The novel result of this work is the demonstration that zircons in the SH, >100 m below the Basistoppen contact, have a bimodal age distribution, with the youngest population of 55.838±0.019 Ma postdating intrusion of the Basistoppen Sill by 57±37 ka. Oxygen isotope analyses reveal that SH zircons are low and heterogeneous with respect to δ18O. These results support the proposed conclusion that the SH crystallized twice: it was fully crystalline, then hydrothermally-altered by low-δ18O surface waters and subsequently partially remelted, triggered by heat of the Basistoppen Sill. The low-degree partial melt generated during remelting partially migrated upward by intergranular

  11. The eruptibility of magmas at Tharsis and Syrtis Major on Mars

    NASA Astrophysics Data System (ADS)

    Black, Benjamin A.; Manga, Michael

    2016-06-01

    Magnetic and geologic data indicate that the ratio of intrusive to extrusive magmatism (the I/E ratio) is higher in the Tharsis and Syrtis Major volcanic provinces on Mars relative to most volcanic centers on Earth. The fraction of magmas that erupt helps to determine the effects of magmatism on crustal structure and the flux of magmatic gases to the atmosphere and also influences estimates of melt production inferred from the history of surface volcanism. We consider several possible controls on the prevalence of intrusive magmatism at Tharsis and Syrtis Major, including melt production rates, lithospheric properties, regional stresses and strain rates, and magmatic volatile budgets. The Curie temperature is the minimum crustal temperature required for thermal demagnetization, implying that if the primary magnetic mineral is magnetite or hematite, the crust was warm during the intrusive magmatism reflected in Tharsis and Syrtis Major I/E ratios. When wall rocks are warm, thermally activated creep relaxes stresses from magma replenishment and regional tectonics, and eruptibility depends on buoyancy overpressure. We develop a new one-dimensional model for the development of buoyancy in a viscous regime that accounts for cooling, crystallization, volatile exsolution, bubble coalescence and rise, fluid egress, and compaction of country rock. Under these conditions, we find that initial water and CO2 contents typically <1.5 wt % can explain the observed range of intrusive/extrusive ratios. Our results support the hypothesis that warm crust and a relatively sparse volatile budget encouraged the development of large intrusive complexes beneath Tharsis and Syrtis Major.

  12. Gas intrusion into SPR caverns

    SciTech Connect

    Hinkebein, T.E.; Bauer, S.J.; Ehgartner, B.L.; Linn, J.K.; Neal, J.T.; Todd, J.L.; Kuhlman, P.S.; Gniady, C.T.; Giles, H.N.

    1995-12-01

    The conditions and occurrence of gas in crude oil stored in Strategic Petroleum Reserve, SPR, caverns is characterized in this report. Many caverns in the SPR show that gas has intruded into the oil from the surrounding salt dome. Historical evidence and the analyses presented here suggest that gas will continue to intrude into many SPR caverns in the future. In considering why only some caverns contain gas, it is concluded that the naturally occurring spatial variability in salt permeability can explain the range of gas content measured in SPR caverns. Further, it is not possible to make a one-to-one correlation between specific geologic phenomena and the occurrence of gas in salt caverns. However, gas is concluded to be petrogenic in origin. Consequently, attempts have been made to associate the occurrence of gas with salt inhomogeneities including anomalies and other structural features. Two scenarios for actual gas intrusion into caverns were investigated for consistency with existing information. These scenarios are gas release during leaching and gas permeation through salt. Of these mechanisms, the greater consistency comes from the belief that gas permeates to caverns through the salt. A review of historical operating data for five Bryan Mound caverns loosely supports the hypothesis that higher operating pressures reduce gas intrusion into caverns. This conclusion supports a permeability intrusion mechanism. Further, it provides justification for operating the caverns near maximum operating pressure to minimize gas intrusion. Historical gas intrusion rates and estimates of future gas intrusion are given for all caverns.

  13. Timing, Formation and Mobility of Melano Granophyric Liquids in the Skaergaard Intrusion

    NASA Astrophysics Data System (ADS)

    Larsen, R. B.; Sorensen, B.; Müller, A.

    2009-12-01

    Melano granophyric rocks are common throughout the cumulus stratigraphy of the Skaergaard intrusion. According to most studies, they comprise the end products of parental Skaergaard melt differentiation. Previous studies suggest that granophyre solidified at 690 to 720 C, long after the main body of the intrusion had solidified at c. 1040 C. However, much uncertainty associates T of formation of the melano granophyric melts. To approach this T we studied the mineralogy of melano granophyric chimney structures in the Middle Zone (MZ), and in gabbroic pegmatites from the Lower Zone, MZ and the Upper Zone (UZa-c). 19 vertical chimney structures perpendicularly intersect the cumulus layering in the upper third of MZ. Each chimney is 1-4 m in diameter and only the upper 2-3 m's are exposed. Melano granophyre also host the uppermost part of gabbroic pegmatite and occur in isolated clots (c. 0.1-0.3 m in diameter) in the cumulus stratigraphy 1-2 m above the pegmatites. Finally, there are several sub conformable bodies in the UZc where large proportions are composed of melano granophyre. The largest body is 50 m thick and can be followed laterally for > 200 m's. Whether in chimney structures, in clots or in gabbroic pegmatite, the melano granophyre feature the same mineral assemblage. Most conspicuously, they carry 5-20 cm black columnar crystals of ferro-hedenbergite with augite rims. In thin sections, the ferro-hedenbergite component form minute platelets much like ferro-hedenbergite in the UZc and, similarly, the texture is taken as evidence for the ferro-bustamite to ferro-hedenbergite inversion that occurs at c. 970 C after ferro-bustamite formed at c. 1040 C. Otherwise the melano granophyres are dominated by euhedral plagioclase, quartz, fayalite, hastingsitic hornblende, apatite and ilmenite and granophyric quartz, alkali feldspar and albite. With 700-2000 ppm, Zr is an important accessory that either form euhedral or skeletal crystals or symplectites. Titanium in

  14. Construction of the Devonian bimodal Gouldsboro pluton via multiple intrusion, coastal Maine, USA

    NASA Astrophysics Data System (ADS)

    Koteas, C.

    2006-12-01

    The Gouldsboro pluton (377 ± 19 ma) (Metzger et al., 1982) of the eastern coastal Maine magmatic province preserves abundant evidence of mechanical interaction between mafic and felsic magmas, as well as the stoping and doming of country rock. Coastal Maine is a unique location where subequal volumes of felsic and mafic material have interacted and are preserved in both plutonic and volcanic complexes. The effects of generation and mobilization of large volumes of magma in the shallow crust are well-preserved. The Gouldsboro pluton provides an excellent perspective from the highest to lowest sections (southwest to northeast) of a hybrid magmatic system. The Gouldsboro magmatic complex is hosted by undated greenstone to the north that is overlain by the 477 ± 18 ma (Metzger, 1977) meta-volcanic/meta-sedimentary Bar Harbor formation. Blocks of both units are discernable as 10 cm to 2 m-diameter blocks within the pluton. The Gouldsboro granite is dominantly a fine to medium grained feldspar- rich leucocratic hornblende granite, although biotite is sometimes present. Miarolitic cavities are common in the highest exposure of the system, especially in the south where the finest grained, most leucocratic granite occurs. Other units include, from lowest to highest in the system, hybrid diorite-gabbro, hybrid granite-granodiorite, granite hosting 30 cm to 3 m-diameter globular basaltic pillows, and a previously unrecognized pyroclastic unit, very similar to the lowermost member of the Cranberry Isle series, a volcanic breccia (Seaman et al., 1999). The pyroclastic unit is intruded by medium grained granite hosting angular fragments of volcanic, mafic plutonic, and country rock. While the contact between gabbro near the base of the pluton and granite in the middle of the pluton is commonly gradational, there are complex intrusive breccias in some areas where fine to coarse, angular diorite to gabbro xenoliths are hosted by granodiorite and granite. Enclave-rich zones

  15. Growth of plutons by incremental emplacement of sheets in crystal-rich host: Evidence from Miocene intrusions of the Colorado River region, Nevada, USA

    USGS Publications Warehouse

    Miller, C.F.; Furbish, D.J.; Walker, B.A.; Claiborne, L.L.; Koteas, G.C.; Bleick, H.A.; Miller, J.S.

    2011-01-01

    Growing evidence supports the notion that plutons are constructed incrementally, commonly over long periods of time, yet field evidence for the multiple injections that seem to be required is commonly sparse or absent. Timescales of up to several million years, among other arguments, indicate that the dominant volume does not remain largely molten, yet if growing plutons are constructed from rapidly solidifying increments it is unlikely that intrusive contacts would escape notice. A model wherein magma increments are emplaced into melt-bearing but crystal-rich host, rather than either solid or crystal-poor material, provides a plausible explanation for this apparent conundrum. A partially solidified intrusion undoubtedly comprises zones with contrasting melt fraction and therefore strength. Depending on whether these zones behave elastically or ductilely in response to dike emplacement, intruding magma may spread to form sheets by either of two mechanisms. If the melt-bearing host is elastic on the relevant timescale, magma spreads rather than continuing to propagate upward, where it encounters a zone of higher rigidity (higher crystal fraction). Similarly, if the dike at first ascends through rigid, melt-poor material and then encounters a zone that is weak enough (poor enough in crystals) to respond ductilely, the ascending material will also spread because the dike tip ceases to propagate as in rigid material. We propose that ascending magma is thus in essence trapped, by either mechanism, within relatively crystal-poor zones. Contacts will commonly be obscure from the start because the contrast between intruding material (crystal-poorer magma) and host (crystal-richer material) is subtle, and they may be obscured even further by subsequent destabilization of the crystal-melt framework. Field evidence and zircon zoning stratigraphy in plutons of the Colorado River region of southern Nevada support the hypothesis that emplacement of magma replenishments into a

  16. 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.

  17. Recent advances in vapor intrusion site investigations.

    PubMed

    McHugh, Thomas; Loll, Per; Eklund, Bart

    2017-02-22

    Our understanding of vapor intrusion has evolved rapidly since the discovery of the first high profile vapor intrusion sites in the late 1990s and early 2000s. Research efforts and field investigations have improved our understanding of vapor intrusion processes including the role of preferential pathways and natural barriers to vapor intrusion. This review paper addresses recent developments in the regulatory framework and conceptual model for vapor intrusion. In addition, a number of innovative investigation methods are discussed.

  18. The mechanics of lower incisor intrusion: experiments in nongrowing baboons.

    PubMed

    Woods, M G

    1988-03-01

    The effects of different combinations of segmented intrusion arch wires and anchorage units on the relative vertical positions of anterior and posterior teeth in the lower arch were demonstrated in four nongrowing baboons. Forces of between 90 and 100 g were delivered by the intrusion arch wires to the four lower incisor teeth in each animal over a period of 5 months. The dental and skeletal changes occurring during that period were assessed from lateral cephalometric radiographs. Lower incisor intrusion, determined by the vertical movement of an internal reference point, was demonstrated in each of the animals. However, the actual effects of the mechanics on the relative anterior and posterior vertical tooth positions, and consequently on the height of the lower face, were found to depend largely on the magnitude of the reactive moments acting on the anchorage units. It was suggested that in general, for a given intrusive force, the further forward the center of resistance is positioned in the anchorage unit, the smaller the reactive moment will be and the more incisor intrusion one might reasonably expect to achieve during arch leveling.

  19. Comparing magnetic and magmatic fabrics to constrain the magma flow record in La Gloria pluton, central Chile

    NASA Astrophysics Data System (ADS)

    Payacán, Italo; Gutiérrez, Francisco; Gelman, Sarah E.; Bachmann, Olivier; Parada, Miguel Ángel

    2014-12-01

    This contribution illustrates a case study of a pluton (La Gloria pluton; LGP) where magnetic and magmatic fabrics are locally decoupled. We compare the magmatic fabric with the available magnetic fabric data to explore their abilities and elucidate the magma flow record of LGP. Results indicate that magnetic (controlled by multi-domain magnetite) and magmatic fabrics are generally consistent throughout LGP. Foliations define an axisymmetric pattern that gradually changes from vertical near lateral margins to less steep in the pluton interior, whereas lineations are subhorizontal following the elongation direction of the pluton. However, samples at the pluton center show marked differences between both fabrics: magnetic fabrics indicate subhorizontal magnetic lineations and foliations, and magmatic fabrics indicate subvertical lineations and foliations. Both magnetic and magmatic fabrics are interpreted to record strain caused by magma flow during thermal convection and lateral magma propagation at the transition between low and high crystallinity stages. We suggest that fabrics acquisition and consistency were determined by shear conditions (pure/simple shear rates ratio) and the orientation of the magma flow direction with respect to a rigid boundary (critical crystalline region) of the pluton. Magmatic fabric differs at the center of the pluton because pure shear is dominant and ascendant flows are orthogonal to the horizontal rigid boundary. LGP represents a whole-scale partly molten magma reservoir, where both thermal convection and lateral propagation of the magma are recorded simultaneously. This study highlights the importance of characterizing both fabrics to properly interpret magma flow recorded in plutons.

  20. Mantle source of the 2.44-2.50-Ga mantle plume-related magmatism in the Fennoscandian Shield: evidence from Os, Nd, and Sr isotope compositions of the Monchepluton and Kemi intrusions

    NASA Astrophysics Data System (ADS)

    Yang, Sheng-Hong; Hanski, Eero; Li, Chao; Maier, Wolfgang D.; Huhma, Hannu; Mokrushin, Artem V.; Latypov, Rais; Lahaye, Yann; O'Brien, Hugh; Qu, Wen-Jun

    2016-12-01

    Significant PGE and Cr mineralization occurs in a number of 2.44-2.50-Ga mafic layered intrusions located across the Karelian and Kola cratons. The intrusions have been interpreted to be related to mantle plume activity. Most of the intrusions have negative ɛNd values of about -1 to -2 and slightly radiogenic initial Sr isotope compositions of about 0.702 to 0.703. One potential explanation is crustal contamination of a magma derived from a mantle plume, but another possibility is that the magma was derived from metasomatized sub-continental lithospheric mantle. Samples from the upper chromitite layers of the Kemi intrusion and most samples from the previously studied Koitelainen and Akanvaara intrusions have supra-chondritic γOs values indicating some crustal contamination, which may have contributed to the formation of chromitites in these intrusions. Chromite separates from the main ore zone of the Kemi and Monchepluton intrusions show nearly chondritic γOs, similar to the coeval Vetreny belt komatiites. We suggest that the Os isotope composition of the primitive magma was not significantly changed by crustal contamination due to a high Os content of the magma and a low Os content of the contaminant. Modeling suggests that the Os and Nd isotope compositions of the Monchepluton and Kemi intrusions cannot be explained by assuming a magma source in the sub-continental lithospheric mantle with sub-chondritic γOs. A better match for the isotope data would be a plume mantle source with chondritic Re/Os and Os isotope composition, followed by crustal contamination.

  1. Strontium Isotopes and Magma Dynamics

    NASA Astrophysics Data System (ADS)

    Wolff, J. A.; Ellis, B. S.; Ramos, F. C.

    2010-12-01

    Over the past decade, it has become clear that volcanic rocks commonly exhibit internal heterogeneity in radiogenic isotopes. In particular, strontium isotopic disequilibrium between co-exisitng phenocrysts, between phenocrysts and matrix, and isotopic zoning within single crystals has been demonstrated in basalts, andesites, dacites, rhyolites and alkaline magmas; in some cases, the range in 87Sr/86Sr among different components in the same rock may equal or exceed the bulk-rock range seen in the entire formation, volcanic center, or province. High-temperature “Snake River type” rhyolites appear to be an exception. Despite the occurrence of Snake River Plain rhyolites in a region of isotopically highly variable crust and mantle, and significant differences from rhyolite unit to rhyolite unit, internally they are near-homogeneous in 87Sr/86Sr. Little or no zoning is found within feldspar phenocrysts, and feldspars within a single unit are tightly grouped. Some units show minor contrasts between phenocrysts and matrix. High temperature rhyolitic magmas possess a unique combination of temperature and melt viscosity. Although they are typically 200°C hotter than common rhyolites, the effect on visocity is offset by lower water contents (~2 wt%), hence their melt viscosities are in the same range as common, water-rich, cool rhyolites (105 - 106 Pa s). Yet magmatic temperatures are in the same range as basaltic andesites and andesites, consequently cation diffusion rates in feldspar are 2 - 3 orders of magnitude greater than in common rhyolites. We hypothesize that this combination of characteristics promotes Sr isotopic homogeneity: high melt viscosities tend to inhibit crystal transfer and mixing of isotopically distinct components on timescales shorter than those required for diffusive homogenization of Sr between phenocrysts and matrix (100 - 1000 years). This is not the case for most magmas, in which either crystal transfer is rapid (<< 100 years) due to low

  2. Petrogenesis of the Ni-Cu-PGE sulfide-bearing Tamarack Intrusive Complex, Midcontinent Rift System, Minnesota

    NASA Astrophysics Data System (ADS)

    Taranovic, Valentina; Ripley, Edward M.; Li, Chusi; Rossell, Dean

    2015-01-01

    The Tamarack Intrusive Complex (TIC, 1105.6 ± 1.2 Ma) in NE Minnesota, was emplaced during the early stages of the development of the Midcontinent Rift System (MRS, "Early Stage": 1110-1106 Ma). Country rocks of the TIC are those of the Paleoproterozoic Thomson Formation, part of the Animikie Group including sulfide-bearing metasedimentary black shale. The magmatic system is composed of at least two principal mafic-ultramafic intrusive sequences: the sulfide-barren Bowl Intrusion in the south and the "dike" area intrusions in the north which host Ni-Cu-Platinum Group Elements (PGE) mineralization with up to 2.33% Ni, 1.24% Cu, 0.34 g/t Pt, 0.23 g/t Pd and 0.18 g/t Au. Two distinct intrusive units in the "dike" area are the CGO (coarse-grained olivine-bearing) Intrusion, a sub-vertical dike-like body, and the overlying sub-horizontal FGO (fine-grained olivine-bearing) Intrusion. Both intrusions comprise peridotite, feldspathic peridotite, feldspathic pyroxenite, melatroctolite and melagabbro. Massive sulfides are volumetrically minor and mainly occur as lenses emplaced into the country rocks associated with both intrusions. Semi-massive (net-textured) sulfides are distributed at the core of the CGO Intrusion, surrounded by a halo of the disseminated sulfides. Disseminated sulfides also occur in lenses along the base of the FGO Intrusion. Olivine compositions in the CGO Intrusion are between Fo89 and Fo82 and in the FGO Intrusion from Fo84 to Fo82. TIC intrusions have more primitive olivine compositions than that of olivine in the sheet-like intrusions in the Duluth Complex (below Fo70), as well as olivine from the smaller, conduit-related, Eagle and East Eagle Intrusions in Northern Michigan (Fo86 to Fo75). The FeO/MgO ratios of the CGO and FGO Intrusion parental magmas, inferred from olivine compositions, are similar to those of picritic basalts erupted during the early stages of the MRS formation. Trace element ratios differ slightly from other intrusions in the

  3. The Ordovician Las Chacritas pluton (Sierra de Humaya, NW Argentina): origin and emplacement triggered by lateral shortening and magmatic stoping at mid-crustal level

    NASA Astrophysics Data System (ADS)

    Larrovere, Mariano A.; Alasino, Pablo H.; de los Hoyos, Camilo R.; Willner, Arne P.

    2015-04-01

    Field relationships and structural studies combined with in situ U-Th-Pb dating of monazite from Las Chacritas pluton (LCP), Sierra de Humaya, provide insight into the emplacement of peraluminous magmas triggered by lateral shortening of the host rock and magmatic stoping at a mid-crustal level of a retro-arc zone in a convergent orogen. Modal and chemical compositions indicate that the LCP is composed of two main igneous units of peraluminous granitoids. The predominant two-mica granitoids were generated by interaction of crustal rocks with mafic or mafic-derived magmas and/or crystal-rich magmas that entrained residual phases, whereas less abundant leucocratic granitoids may have been originated by partial melting of metasedimentary rocks. The calculated crystallization age of 474 ± 4 Ma is consistent with Ordovician ages (477-470 Ma) of the high-grade metamorphic rocks, indicating concomitant magmatism and metamorphism during the Famatinian orogeny. The LCP was emplaced in the middle crust at a maximum depth of ~14.5 km, where attendant fracturing and ductile deformation were active. Field evidence shows strong temporal and spatial relationships between host rock ductile deformation and the emplacement of the pluton such as folding and strike deflection of the host rock layering and folded concordant leucocratic sheets with magmatic fabrics. This suggests that material transfer processes like lateral wall rock displacement (lateral shortening) was a viable mechanism for the emplacement of the LCP. However, cross-sectional restoration and field evidence such as wall rock xenoliths and intrusive truncations of the host rock foliation and fold traces suggest that magmatic stoping was a complementary mechanism to create the necessary space for the emplacement of the LCP. This work supports previous studies showing that participation of multiple material transfer processes are the rule rather than the exception in the emplacement of plutons.

  4. Seismic Characteristics and Evolution of Intrusion in Qiongdongnan Basin: Implications for the Rifting of South China Sea

    NASA Astrophysics Data System (ADS)

    Zhao, Y.; Ren, J.; Yang, L.; Huang, C.

    2014-12-01

    The South China Sea (SCS) formed by magma-poor rifting in the Paleogene. The Qiongdongnan basin (QDNB) located at the north margin was thought to completely lack magma activities. Due to the limited amount of deepwater drills, magmas in deepwater area had been ignored in petroleum exploration, and thus our knowledge of basin analysis is far from complete. Based on a comprehensive study on seismic profiles and P wave velocity data, 12 intrusion-related seismic reflection anomalies in QDNB have been recognized. In the southwest of QDNB, gas chimneys and gas clouds have been found with a low velocity (<3.4 km/s). In the center area, the intensively deformed strata passing towards the diapir flanks suggest the existence of magma diapirs. However, the velocity within diapirs is neither too high nor too low (3.7-4.6 km/s), and there has been no obvious magnetic anomaly or gravity anomaly be found. Previous researches prove that the temperatures of the crustal melt layers at the time that the basalt solidifies are high (900-950 °C) so that the process can produce magmas representing large degrees of partial fusion of the crust. To judge from the evidence, in the center area these could be mixed magmas. Further east, the diapirs possess typical features of basaltic magma intrusions with a high seismic velocity (>6 km/s), a positive magnetic anomaly and a high gravity anomaly. In addition, according to different dips of marginal facies, three phases of diapirism can be identified (32 Ma, 15.5 Ma and 10.5 Ma). Along a narrow area with hyper-extended crust, those intrusions document the opening of SCS at 32 Ma and the volcanic activities afterwards. The results are corresponding to the fact that all of the intrusions in QDNB occurred during the extreme crustal thinning process and after the cessation of seafloor spreading, and thus the intrusion evolved with time would have major implications for post-rift emplacement.

  5. Geochemical signature variation of pre-, syn-, and post-shearing intrusives within the Najd Fault System of western Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Hassan, M.; Abu-Alam, T. S.; Hauzenberger, C.; Stüwe, K.

    2016-10-01

    Late Precambrian intrusive rocks in the Arabian-Nubian Shield emplaced within and around the Najd Fault System of Saudi Arabia feature a great compositional diversity and a variety of degrees of deformation (i.e. pre-shearing deformed, sheared mylonitized, and post-shearing undeformed) that allows placing them into a relative time order. It is shown here that the degree of deformation is related to compositional variations where early, usually pre-shearing deformed rocks are of dioritic, tonalitic to granodioritic, and later, mainly post-shearing undeformed rocks are mostly of granitic composition. Correlation of the geochemical signature and time of emplacement is interpreted in terms of changes in the source region of the produced melts due to the change of the stress regime during the tectonic evolution of the Arabian-Nubian Shield. The magma of the pre-shearing rocks has tholeiitic and calc-alkaline affinity indicating island arc or continental arc affinity. In contrast, the syn- and post-shearing rocks are mainly potassium rich peraluminous granites which are typically associated with post-orogenic uplift and collapse. This variation in geochemical signature is interpreted to reflect the change of the tectonic regime from a compressional volcanic arc nature to extensional within-plate setting of the Arabian-Nubian Shield. Within the context of published geochronological data, this change is likely to have occurred around 605-580 Ma.

  6. Forecasting volcanic eruptions: the narrow margin between eruption and intrusion

    NASA Astrophysics Data System (ADS)

    Steele, Alexander; Kilburn, Christopher; Wall, Richard; Charlton, Danielle

    2016-04-01

    Volcano-tectonic (VT) seismicity is one of the primary geophysical signals for monitoring volcanic unrest. It measures the brittle response of the crust to changes in stress and provides a natural proxy for gauging the stability of a pressurizing body of magma. Here we apply a new model of crustal extension to observations from the 2015 unrest of Cotopaxi, in Ecuador. The model agrees well with field data and is consistent with accelerating unrest during the pressurization and rupture of a vertically-extended magma source within the volcanic edifice. At andesitic-dacitic stratovolcanoes in subduction zones, unrest after long repose is often characterised by increases in VT event rate that change from an exponential to hyperbolic trend with time. This sequence was observed when renewed unrest was detected in April 2015 at Cotopaxi, following at least 73 years of repose. After about 80 days of elevated seismicity at an approximately steady rate, the numbers of VT events increased exponentially with time for c. 80 days, before increasing for c. 15 days along a faster, hyperbolic trend. Both trends were characterised by the same value of 2 for the ratio of maximum applied stress SF to tensile strength of the crust σT, consistent with the pressurization of an approximately vertical, cylindrical magma body. The hyperbolic trend indicated a potential rupture on 25 September. Rupture appears to have occurred on 21-22 September, when the VT rate rapidly decreased. However, no major eruption accompanied the change, suggesting that a near-surface intrusion occurred instead. Although the quantitative VT trends were consistent with the rupture of a magmatic body, they could not on their own distinguish between an eruptive or intrusive outcome. An outstanding goal remains to identify additional precursory characteristics for quantifying the probability that magma will reach the surface after escaping from a ruptured parent body. Data for this analysis were kindly made available

  7. Recycled gabbro signature in Upper Cretaceous Magma within Strandja Massif: NW Turkey

    NASA Astrophysics Data System (ADS)

    Ulusoy, Ezgi; Kagan Kadioglu, Yusuf

    2016-04-01

    Basic magma intrusions within plate interiors upwelling mantle plumes have chemical signatures that are distinct from mid-ocean ridge magmas. When a basic magma interact with continental crust or with the felsic magma, the compositions of both magma changes, but there is no consensus as to how this interaction occurs. Here we analyse the mineral behavior and trace element signature of gabbroic rocks of the samples collected from the Strandja Massif. Srednogorie magmatic arc is a part of Apuseni- Banat-Timok-Srednogorie magmatic belt and formed by subduction and closure of the Tethys Ocean during Upper Cretaceous times. Upper Cretaceous magmatic rocks cutting Strandja Massif in NW Turkey belong to eastern edge of Srednogorie Magmatic arc. Upper Cretacous magmatic rocks divided into four subgroup in Turkey part of Strandja massif: (I) granitic rocks, (II) monzonitic rock, (III) syenitic rocks and (IV) gabbroic rocks. Gabbroic rocks outcropped around study area in phaneritic - equigranular texture. According to mineralogic - petrographic studies gabbros have mainly holocrystalline texture and ophitic to subophitic texture composed of plagioclase, amphibole, pyroxene, and rarely olivine and opaque minerals. Also because of special conditions there have been pegmatitic texture on mafic minerals with euhedral form up to 3 cm in size and orbicular texture which reach 15cm in size and rounded - elliptical form. Confocal Raman Spectroscopy studies reveals that plagioclase are ranging in composition from labradorite to bytownite, the pyroxene are ranging in composition from diopside to augite acting with uralitization processes and the olivine are generally in the composition of forsterite. Petrographic and mineralogical determination reveals some metasomatic magmatic epidote presence. Confocal Raman Spectroscopy studies on anhydrous minerals within gabbroic rocks shows affect of hydrous process because of magma mixing. The gabbroic rocks have tholeiitic and changed towards

  8. Water-rich and volatile-undersaturated magmas at Hekla volcano, Iceland

    NASA Astrophysics Data System (ADS)

    Lucic, Gregor; Berg, Anne-Sophie; Stix, John

    2016-08-01

    Olivine-hosted melt inclusions from four eruptions at Hekla volcano in Iceland were analyzed for their dissolved H2O, CO2, S, and Cl contents. A positive correlation among the repose interval, magmatic evolution, and volatile contents of magmas is revealed. H2O is the dominant volatile species; it behaves as an incompatible component, increasing in concentration over time as a result of fractional crystallization in the magma. The full suite of H2O contents ranges from a low of 0.80 wt % in basaltic andesites to a maximum of 5.67 wt % in rhyolites. Decreasing H2O/K2O at fixed major element compositions suggests that syneruptive degassing reduces H2O contents significantly. Hekla magmas are CO2 poor, with very low concentrations present only in the most evolved compositions (˜20-30 ppm or less). The decrease in S content from basaltic andesite to rhyolite demonstrates that sulfide saturation is attained when the melt composition reaches basaltic andesite, resulting in the precipitation of pyrrhotite. Low CO2/Nb ratios suggest that vapor saturation is most likely reached during an early period of cooling and solidification in the crust. Fresh injections of mafic magma interact with previously solidified intrusives, producing new melts that are volatile undersaturated. Vapor saturation pressures obtained using the most volatile-rich melt inclusions suggest the presence of a magma chamber at a minimum depth of ˜7 km. This is in agreement with geophysical observations from recent small-volume eruptions, but given the possibility of volatile-undersaturated melts, some of the magmas may reside at greater depths.

  9. Chemical heterogeneity of Mt. Etna magmas in the last 15 ka. Inferences on their mantle sources

    NASA Astrophysics Data System (ADS)

    Corsaro, Rosa Anna; Métrich, Nicole

    2016-05-01

    Primitive basaltic magmas are crucial in the study of the geochemical heterogeneity documented in Etna magmas and their inferred mantle sources. We undertook a systematic sampling of the less evolved basalts (Mg# > 50) erupted over the last 15 ka, a time period which corresponds to the activity of the youngest volcanic edifice of Mt. Etna complex, i.e. Mongibello volcano. We focused on lava flows and pyroclastites emplaced during 'deep-dyke fed' (DDF) eruptions which were driven by the rapid ascent of deeply-rooted magma intrusions that bypassed the shallow plumbing system of the volcano. All the samples were analyzed by the same laboratory to avoid analytical bias, to build a comprehensive dataset on their major and trace element compositions and to propose a coherent framework for interpreting the geochemical fingerprints of present-day Etna basalts. Trace element modeling, together with literature data for Sr isotopes, gave insight into long-term magmatic processes related to different melting degrees of the heterogeneous mantle beneath Mt Etna. DDF magma batches provide good snapshots of their mantle source heterogeneities that point to the variable involvement of clinopyroxenitic lithology, Rb-87Sr-Cl-rich fluid component(s) possibly controlled by their source mineralogy, and slab-derived fluids selectively enriched in alkalis (Rb, K). The ongoing alkali (Rb, K) enrichment of the present-day magmas, well manifest since the 1970s, is decoupled from that of Sr and Cl. We propose that this process is linked to mantle source composition and is concomitant with changes in both volcanological and seismotectonic patterns of the volcano. There is no time evolution of DDF magma chemistry.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  11. Relation of Maternal Cognitive Stimulation, Emotional Support, and Intrusive Behavior during Head Start to Children's Kindergarten Cognitive Abilities.

    ERIC Educational Resources Information Center

    Hubbs-Tait, Laura; Culp, Anne McDonald; Culp, Rex E.; Miller, Carrie E.

    2002-01-01

    Examined effect, after 1 year, of parental cognitive stimulation, emotional support, and intrusiveness on verbal and nonverbal abilities of low-income children in Head Start programs. Found that children of parents who provide the highest cognitive stimulation and emotional support coupled with no intrusive behavior fared best in later perceptual…

  12. Convection and mixing in magma chambers

    NASA Astrophysics Data System (ADS)

    Turner, J. S.; Campbell, I. H.

    1986-08-01

    This paper reviews advances made during the last seven years in the application of fluid dynamics to problems of igneous petrology, with emphasis on the laboratory work with which the authors have been particularly involved. Attention is focused on processes in magma chambers which produce diversity in igneous rocks, such as fractional crystallization, assimilation and magma mixing. Chamber geometry, and variations in the density and viscosity of the magma within it, are shown to play a major role in determining the dynamical behaviour and the composition of the erupted or solidified products. Various convective processes are first reviewed, and in particular the phenomenon of double-diffusive convection. Two types of double-diffusive interfaces between layers of different composition and temperature are likely to occur in magma chambers. A diffusive interface forms when a layer of hot dense magma is overlain by cooler less dense magma. Heat is transported between the layers faster than composition, driving convection in both layers and maintaining a sharp interface between them. If a layer of hot slightly less dense magma overlies a layer of cooler, denser but compositionally lighter magma, a finger interface forms between them, and compositional differences are transported downwards faster than heat (when each is expressed in terms of the corresponding density changes). Processes leading to the establishment of density, compositional and thermal gradients or steps during the filling of a magma chamber are considered next. The stratification produced, and the extent of mixing between the inflowing and resident magmas, are shown to depend on the flow rate and on the relation between the densities and viscosities of the two components. Slow dense inputs of magma may mix very little with resident magma of comparable viscosity as they spread across the floor of the chamber. A similar pulse injected with high upward momentum forms a turbulent "fountain", which is a

  13. The transition from diapirism to dike intrusion: Implications for planetary volcanism

    NASA Technical Reports Server (NTRS)

    Rubin, Allan M.

    1994-01-01

    Magma transport processes influence the rate of magma transport and how far the magma travels before it freezes, the degree to which the magma communicates chemically with the host rock, the morphology of volcanic landforms on planetary surfaces, the interplay between magmatism and regional tectonics, and even the direction the magma moves. The primary question motivating this research is: How does magma rheology influence the mechanisms by which it is transported through planetary lithospheres? It is widely recognized that on Earth basaltic intrusions typically take the form of narrow dikes, while granites are typically found in more equidimensional plutons. Several explanations for this observation were offered over the last 50 years. While basalts and rhyolites vary somewhat in temperature and density, the major difference is the 2 to 8 orders of magnitude contrast in viscosity. The significant ductile strains associated with many granitic plutons has led to the statement that the occurrence of granites in diapirs rather than dikes results from the fact that there is insufficient viscosity contrast between the magma and wall rock for the granite to intrude narrow cracks. A second explanation states that granites are so viscous that they cannot propagate far before freezing. Despite the length of time these explanations have been around, there has been relatively little effort to investigate them quantitatively. My goal has been to evaluate these explanations through a series of well-posed numerical models. These models can be tested by the decades of field data collected by structural geologists that have yet to be integrated into any coherent theory, and the results should have important implications for volcanism on the terrestrial planets.

  14. Intrusion triggering of the 2010 Eyjafjallajökull explosive eruption.

    PubMed

    Sigmundsson, Freysteinn; Hreinsdóttir, Sigrún; Hooper, Andrew; Arnadóttir, Thóra; Pedersen, Rikke; Roberts, Matthew J; Oskarsson, Níels; Auriac, Amandine; Decriem, Judicael; Einarsson, Páll; Geirsson, Halldór; Hensch, Martin; Ofeigsson, Benedikt G; Sturkell, Erik; Sveinbjörnsson, Hjörleifur; Feigl, Kurt L

    2010-11-18

    Gradual inflation of magma chambers often precedes eruptions at highly active volcanoes. During such eruptions, rapid deflation occurs as magma flows out and pressure is reduced. Less is known about the deformation style at moderately active volcanoes, such as Eyjafjallajökull, Iceland, where an explosive summit eruption of trachyandesite beginning on 14 April 2010 caused exceptional disruption to air traffic, closing airspace over much of Europe for days. This eruption was preceded by an effusive flank eruption of basalt from 20 March to 12 April 2010. The 2010 eruptions are the culmination of 18 years of intermittent volcanic unrest. Here we show that deformation associated with the eruptions was unusual because it did not relate to pressure changes within a single magma chamber. Deformation was rapid before the first eruption (>5 mm per day after 4 March), but negligible during it. Lack of distinct co-eruptive deflation indicates that the net volume of magma drained from shallow depth during this eruption was small; rather, magma flowed from considerable depth. Before the eruption, a ∼0.05 km(3) magmatic intrusion grew over a period of three months, in a temporally and spatially complex manner, as revealed by GPS (Global Positioning System) geodetic measurements and interferometric analysis of satellite radar images. The second eruption occurred within the ice-capped caldera of the volcano, with explosivity amplified by magma-ice interaction. Gradual contraction of a source, distinct from the pre-eruptive inflation sources, is evident from geodetic data. Eyjafjallajökull's behaviour can be attributed to its off-rift setting with a 'cold' subsurface structure and limited magma at shallow depth, as may be typical for moderately active volcanoes. Clear signs of volcanic unrest signals over years to weeks may indicate reawakening of such volcanoes, whereas immediate short-term eruption precursors may be subtle and difficult to detect.

  15. 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.

  16. Triggers on sulfide saturation in Fe-Ti oxide-bearing, mafic-ultramafic layered intrusions in the Tarim large igneous province, NW China

    NASA Astrophysics Data System (ADS)

    Cao, Jun; Wang, Christina Yan; Xu, Yi-Gang; Xing, Chang-Ming; Ren, Ming-Hao

    2016-08-01

    Three Fe-Ti oxide-bearing layered intrusions (Mazaertag, Wajilitag, and Piqiang) in the Tarim large igneous province (NW China) have been investigated for understanding the relationship of sulfide saturation, Platinum-group element (PGE) enrichment, and Fe-Ti oxide accumulation in layered intrusions. These mafic-ultramafic layered intrusions have low PGE concentrations (<0.4 ppb Os, <0.7 ppb Ir, <1 ppb Ru, <0.2 ppb Rh, <5 ppb Pt, and <8 ppb Pd) and elevated Cu/Pd (2.2 × 104 to 3.3 × 106). The low PGE concentrations of the rocks are mainly attributed to PGE-depleted, parental magma that was produced by low degrees of partial melting of the mantle. The least contaminated rocks of the Mazaertag and Wajilitag intrusions have slightly enriched Os isotopic compositions with γOs(t = 280 Ma) values ranging from +13 to +23, indicating that the primitive magma may have been generated from a convecting mantle, without appreciable input of lithospheric mantle. The Mazaertag and Wajilitag intrusions have near-chondritic γOs(t) values (+13 to +60) against restricted ɛ Nd(t) values (-0.4 to +2.8), indicating insignificant crustal contamination. Rocks of the Piqiang intrusion have relatively low ɛ Nd(t) values of -3.1 to +1.0, consistent with ˜15 to 25 % assimilation of the upper crust. The rocks of the Mazaertag and Wajilitag intrusions have positive correlation of PGE and S, pointing to the control of PGE by sulfide. Poor correlation of PGE and S for the Piqiang intrusion is attributed to the involvement of multiple sulfide-stage liquids with different PGE compositions or sulfide-oxide reequilibration on cooling. These three layered intrusions have little potential of reef-type PGE mineralization. Four criteria are summarized in this study to help discriminate between PGE-mineralized and PGE-unmineralized mafic-ultramafic intrusions.

  17. Transfer of volatiles and metals from mafic to felsic magmas in composite magma chambers: An experimental study

    NASA Astrophysics Data System (ADS)

    Guo, Haihao; Audétat, Andreas

    2017-02-01

    In order to determine the behavior of metals and volatiles during intrusion of mafic magma into the base of silicic, upper crustal magma chambers, fluid-rock partition coefficients (Dfluid/rock) of Li, B, Na, S, Cl, K, Mn, Fe, Rb, Sr, Ba, Ce, Cu, Zn, Ag, Cd, Mo, As, Se, Sb, Te, W, Tl, Pb and Bi were determined experimentally at 2 kbar and 850 °C close to the solidus of mafic magma. In a first step, volatile-bearing mafic glasses were prepared by melting a natural basaltic trachyandesite in the presence of volatile-bearing fluids at 1200 °C/10 kbar in piston cylinder presses. The hydrous glasses were then equilibrated in subsequent experiments at 850 °C/2 kbar in cold-seal pressure vessels, which caused 80-90% of the melt to crystallize. After 0.5-2.0 days of equilibration, the exsolved fluid was trapped by means of in-situ fracturing in the form of synthetic fluid inclusions in quartz. Both the mafic rock residue and the fluid inclusions were subsequently analyzed by laser-ablation ICP-MS for major and trace elements. Reverse experiments were conducted by equilibrating metal-bearing aqueous solutions with rock powder and then trapping the fluid. In two additional experiments, information on relative element mobilities were obtained by reacting fluids that exsolved from crystallizing mafic magma with overlying silicic melts. The combined results suggest that under the studied conditions S, Cl, Cu, Se, Br, Cd and Te are most volatile (Dfluid/rock >10), followed by Li, B, Zn, As, Ag, Sb, Cs, W, Tl, Pb and Bi (Dfluid/rock = 1-10). Less volatile are Na, Mg, K, Ca, Mn, Fe, Rb, Sr, Mo and Rb (Dfluid/rock 0.1-1), and the least fluid-mobile elements are Al, Si, Ti, Zr, Ba and Ce (Dfluid/rock <0.1). This trend is broadly consistent with relative element volatilities determined on natural high-temperature fumarole gases, although some differences exist. Based on the volatility data and measured mineral-melt and sulfide-melt partition coefficients, volatile fluxing in

  18. Petrology of the Upper Border Series of the Skaergaard Intrusion

    NASA Astrophysics Data System (ADS)

    Salmonsen, L.; Tegner, C.; Jakobsen, J. K.

    2009-12-01

    The Upper Border Series crystallized downwards from the roof of the Skaergaard magma chamber. It met with the Layered Series that crystallized upwards from the floor in the Sandwich Horizon that contains the last and most evolved rocks of the intrusion. Previous investigations of the Upper Border Series (Naslund, 1984) have shown that the compositional trends of plagioclase, olivine and pyroxene largely mirror those of the Layered Series. At the same time it was argued that the crystallization sequence in Upper Border Series differed from the Layered Series in that apatite precipitated before magnetite that, in turn, appeared before Ca-rich pyroxene. From the existing data the magma from which the Upper Border Series crystallized was inferred to be enriched in SiO2, K2O, P2O5 and H2O relative to the magma in the lower parts of the intrusion. This has lead to the conception that the Upper Border Series crystallized from a chemically different magma. Here we present new petrography, mineralogy and bulk compositions for samples collected in three profiles through the Upper Border Series (Kilen, Hammerpas and Brødretoppen transects). Although euhedral apatite is present throughout most of the Upper Border Series, we interpret a marked increase in modal apatite late in the crystallization sequence as marking its first appearance on the liquidus at the crystallization front. The plagioclase An% at this level in the Upper Border Series is ˜40 and is identical with plagioclase An% at the level of apatite-in in the Layered Series. Similarly, we find that the plagioclase An% at the onset of FeTi-oxide and sulphide precipitation in the Upper Border Series (52 and 47, respectively) and Layered Series are alike. Finally, we interpret abundant augite in Upper Border Series rocks before magnetite-in as a cumulus phase. We therefore conclude that the crystallization sequences of the two series are identical. The new bulk rock data reveal that the Upper Border Series and the

  19. 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

  20. 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.

  1. Depth of origin of magma in eruptions.

    PubMed

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

    2013-09-26

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

  2. 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.

  3. Degassing and redox effects in the magma chamber of the Guli massif (Polar Siberia)

    NASA Astrophysics Data System (ADS)

    Ryabchikov, I. D.; Kogarko, L. N.; Kuzmin, D. V.

    2012-04-01

    The Guli massif occupies a large area between the Maymecha and Kotui Rivers at the boundary of the Siberian platform with the Khatanga trough. It has a roughly oval shape of 35-45 km, and, including the two-thirds obscured by Quaternary deposits, has an area of 1500-1600 km2. The Guli massif, like many of the other alkaline-ultrabasic intrusions, is a composite, multi-stage pluton. The predominant rocks of the massif are dunites, which occupy about 60% of the total area, and a range of melanocratic alkaline rocks, which extend over about 30%. The other rock types, including melilitolite, ijolite, alkaline syenite and carbonatite, occupy less than 10% of the area. Dunite intrusives were cut by numerous bodies of Ti-Fe ore pyroxenite (kosvite) that are composed mainly of pyroxene and titanomagnetite with accessory apatite and titanite, and form about 10% of the volume of the dunites. Among the volcanics and dyke rocks in the area surrounding the Guli massif olvine-rich meimechites play substantial role. Variations of Mg# of olivines from dunite indicat presence of cryptic layering, whereas evolution of spinels from chromites to titanomagnetites in less magnesian varieties indicate gradual transition from dunites to kosvites. Original layering is obscured by intense folding. Trace-element diagram normalized to pyrolite and Lu shows that interstitial material present between olivines of dunites is identical to meimechites. This implies that primary magma of the Guli intrusion had meimechite composition. Some zoned olivines show regular decrease in Ni and increase in Mn from core to margin, whereas variation of Ca content in the same grains pass through several maxima and minima. This reflects accumulation of both Ca and CO2 in the residual melt with episodic loss of CO2 leading to the increase in the activity of CaO. Eventually this process leads to the formation of melilite-bearing rocks, alkaline magmas and carbonatites. In many samples of kosvites Ni content in

  4. A Long-Lived Porphyry Ore Deposit and Associated Upper Crustal Silicic Magma Body, Bajo de la Alumbrera, Argentina

    NASA Astrophysics Data System (ADS)

    Harris, A. C.; Allen, C. M.; Reiners, P. W.; Dunlap, W. J.; Cooke, D. R.; Campbell, I. H.; White, N. C.

    2004-05-01

    Porphyry Cu deposits form within and adjacent to small porphyritic intrusions that are apophyses to larger silicic magma bodies that reside in the upper parts of the Earth's crusts. Centred on these intrusions are hydrothermal systems of exsolved magmatic fluid with a carapace of convectively circulating meteoric water. We have applied several different dating techniques to assess the longevity of the magmatic-hydrothermal system and to define the cooling history of porphyry intrusions at the Bajo de la Alumbrera porphyry Cu-Au deposit, Argentina. The closure temperatures of these techniques range from 800oC (zircon U-Pb) to ~70oC (apatite (U-Th)/He; Fig. 1). The resulting cooling history indicates that the magmatic-hydrothermal system cooled to ca. 200oC by ~1.5 m.y. after the last porphyry intrusion (i.e., 6.96±0.09 Ma; U-Pb zircon age). Based on (U-Th)/He apatite data (closure temperature ~60-70oC), exposure and cessation of the system occurred before 4 Ma. The longevity of the magmatic-hydrothermal system indicated by these results is inconsistent with accepted mechanisms for porphyry Cu deposit formation. Depending on wallrock permeability, depth and cooling method, a 2 km wide by 3 km high intrusion has been predicted to cool between 0.01 to 0.1 m.y. (marked as the grey interval; Cathles et al., 1997 Economic Geology). We have obtained numerous age determinations younger than the U-Pb zircon age of the last known intrusion at Bajo de la Alumbrera. These imply that simple cooling of the small, mineralized porphyries did not happen. For the magmatic-hydrothermal system to have been sustained for longer than 0.1 m.y., either 1) younger small intrusions have been episodically emplaced below the youngest known intrusions, thus prolonging heat flow, or 2) fluids derived from a deeper and larger parental intrusion have been episodically discharged through the ore deposit long after the porphyry intrusion had lost its available heat. In either case, the longevity of

  5. Magma chamber dynamics and Vesuvius eruption forecasting

    NASA Astrophysics Data System (ADS)

    Dobran, F.

    2003-04-01

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

  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. Gas emissions due to magma-sediment interactions during flood magmatism at the Siberian Traps: Gas dispersion and environmental consequences

    NASA Astrophysics Data System (ADS)

    Iacono-Marziano, Giada; Marecal, Virginie; Pirre, Michel; Gaillard, Fabrice; Arteta, Joaquim; Scaillet, Bruno; Arndt, Nicholas T.

    2012-12-01

    We estimate the fluxes of extremely reduced gas emissions produced during the emplacement of the Siberian Traps large igneous province, due to magma intrusion in the coaliferous sediments of the Tunguska Basin. Using the results of a companion paper (Iacono-Marziano et al., accepted for publication), and a recent work about low temperature interaction between magma and organic matter (Svensen et al., 2009), we calculate CO-CH4-dominated gas emission rates of 7×1015-2×1016 g/yr for a single magmatic/volcanic event. These fluxes are 7-20 times higher than those calculated for purely magmatic gas emissions, in the absence of interaction with organic matter-rich sediments. We investigate, by means of atmospheric modelling employing present geography of Siberia, the short and mid-term dispersion of these gas emissions into the atmosphere. The lateral propagation of CO and CH4 leads to an important perturbation of the atmosphere chemistry, consisting in a strong reduction of the radical OH concentration. As a consequence, both CO and CH4 lifetimes in the lower atmosphere are enhanced by a factor of at least 3, at the continental scale, as a consequence of 30 days of magmatic activity. The short-term effect of the injection of carbon monoxide and methane into the atmosphere is therefore to increase the residence times of these two species and, in turn, their capacity of geographic expansion. The estimated CO and CH4 volume mixing ratios (i.e. the number of molecules of CO or CH4 per cm3, divided by the total number of molecules per cm3) in the low atmosphere are 2-5 ppmv at the continental scale and locally higher than 50 ppmv. The dimension of the area affected by these high volume mixing ratios decreases in the presence of a lava flow accompanying magma intrusion at depth. Complementary calculations for a 10-yr duration of the magmatic activity suggest (i) an increase in the mean CH4 volume mixing ratio of the whole atmosphere up to values 3-15 times higher than the

  8. The Sub-Crustal Magma Chamber Existence and Magma Ascent Rate for Klyuchevskoy Volcano (Kamchatka): Constrains from Ni Zonation in Olivine Phenocrysts

    NASA Astrophysics Data System (ADS)

    Ozerov, A.; Gavrilenko, M.

    2014-12-01

    Klyuchevskoy volcano is the highest active volcano in Europe and Asia (~4800 m). Morphologically it is a classic stratovolcano, but its edifice consists entirely of mafic rocks (up to 55% of SiO2). The absence of andesites and dacites suggests that Klyuchevskoy does not have a crustal magma chamber. This is supported by seismological studies, the results of which have shown that stable crustal structures (magma bodies) are not found. However, [2] petrological barometry, indicates the existence of a magma chamber near the base of the crust beneath Klyuchevskoy at pressures of 5 - 9 kbar, (~ 18-33 km). In later studies, [1] and [4] proposed a model of decompression crystallization during continuous magma ascent in the conduit (from 50-60 km depth to the surface), which explains the genesis of the whole variety of Klyuchevskoy mafic rocks without the magma chamber requirement. The most recent detailed seismological studies combined with petrological barometry [3] suggest the existence of a sub-crustal volume (magma chamber) beneath Klyuchevskoy volcano (25-35 km depths) where processes of magma accumulation most likely occur. In this study we attempt to confirm the presence of a sub-crustal magma chamber using Ni zonation in primitive olivines, which may preserve information about mixing between distinct primitive melts in the magma chamber. Moreover, olivine Ni diffusion rates could help to estimate the rate of magma ascent (from the 35 km depths to the surface) beneath Klyuchevskoy using the approach of [5]. Ni concentration in olivines were measured by the electron microprobe high-precision technique (20kV, 300 nA) developed in [6]. [1] Ariskin et al. (1995) Petrology, 3(5): p.449-472. [2] Kersting & Arculus (1994) J. of Petrology, 35(1): p.1-41. [3] Levin et al. (2014) Geology, (in print). [4] Ozerov et al. (1997) Petrology, 1997. 5(6): p. 550-569. [5] Ruprecht & Plank, (2013) Nature, 500(7460): p.68-72. [6] Sobolev et al. (2007) Science, 316(5823): p.412-417.

  9. The campsite dykes: A window into the early post-solidification history of the Skaergaard Intrusion, East Greenland

    NASA Astrophysics Data System (ADS)

    Holness, Marian B.; Richardson, Chris; Andersen, Jens C. Ø.

    2013-12-01

    The Skaergaard Intrusion of East Greenland is cut by several generations of dykes, the earliest of which is thought to have intruded shortly after solidification of the Skaergaard. Two ~ 6 m wide doleritic dykes from the earliest generation are exposed in the campsite area near Homestead Bay of the Skaergaard Peninsula. One of the dykes (the Campsite Dyke) locally contains abundant xenoliths of troctolitic cumulate. The other (the Plagioclase-phyric Dyke) contains abundant large plagioclase phenocrysts. Cross-cutting relationships between the two dykes are not exposed. The median clinopyroxene-plagioclase-plagioclase dihedral angle, Θcpp, in the Campsite Dyke is 88-89.5°, whereas that of the Plagioclase-phyric Dyke is 79°. Using an empirical relationship between Θcpp and the duration of crystallisation derived from dolerite sills, the observed Θcpp suggests that the Campsite Dyke is the older of the two, intruding the Skaergaard when it had cooled to 920-970 °C. The Plagioclase-phyric Dyke intruded later, once the Skaergaard had cooled below 670 °C. The troctolitic xenoliths divide into two separate groups. Type A xenoliths have microstructures similar to those of the Skaergaard Layered Series although mineral compositions are generally more primitive than those of the exposed cumulates - this type of xenolith is likely to have been derived from either deeper levels in the Skaergaard Intrusion or from a closely-related underlying magma chamber. One Type A xenolith has mineral compositions and Θcpp consistent with an origin in LZb of the Layered Series - this xenolith contains partially inverted pigeonite, suggesting that inversion of low-Ca pyroxene in the lower part of the Layered Series took place after the intrusion had completely solidified. Type B xenoliths are characterized by plagioclase containing large and abundant melt inclusions. Comparison with the microstructures of glassy crystalline nodules from Iceland points to a multi-stage cooling history

  10. 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

  11. Imaging a magma plumbing system from MASH zone to magma reservoir

    NASA Astrophysics Data System (ADS)

    Delph, Jonathan R.; Ward, Kevin M.; Zandt, George; Ducea, Mihai N.; Beck, Susan L.

    2017-01-01

    The Puna Plateau of the Central Andes is a well-suited location to investigate the processes associated with the tectono-magmatic development of a Cordilleran system. These processes include long-lived subduction (including shallow and steep phases), substantial crustal thickening, the emplacement of large volumes of igneous rocks, and probably delamination. To elucidate the processes associated with the development of a Cordilleran system, we pair Common Conversion Point-derived receiver functions with Rayleigh wave dispersion data from Ambient Noise Tomography. The resulting high-resolution shear wave velocity model of the southern Puna Plateau reveals the details of a lithospheric-scale magma plumbing system. Slow velocities near the crust-mantle transition are interpreted as a MASH zone (a partially molten zone where mantle-derived melts interact with the lithosphere and undergo density differentiation) with ∼ 4- 9% melt. After differentiation, less dense and presumably more felsic melts propagate to shallower depths within the crust (∼20 km below surface) and comprise vertically (∼10 km) and laterally (∼75 km) extensive slow velocity bodies that span the frontal arc and plateau interior. These large slow velocity bodies represent a partially molten mid-crust (up to 22%) where magma can further evolve to higher silica concentrations. The periodic influx of melt from the underlying MASH zone into these mid-crustal bodies may serve as a trigger to the eruption of the voluminous ignimbrites observed in the southern Puna Plateau. Many of the active tectonic processes operating along the southern Puna Plateau are thought to be analogous to the processes that formed the North American Cordillera. Thus, these results could provide insight into some of the processes associated with the development of a Cordilleran margin.

  12. 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

  13. Evidence for dynamic withdrawal from a layered magma body: The Topopah Spring Tuff, southwestern Nevada

    SciTech Connect

    Schuraytz, B. C.; Vogel, T. A.; Younker, L. W.

    1989-05-10

    The Topopah Spring Tuff is a classic example of a compositionally zoned ash flow sheet resulting from eruption of a compositionally zoned magma body. Geochemical and petrographic analyses of whole rock tuff samples indicate that the base of the ash flow sheet and the predominant volume of erupted material consist of crystal-poor high-silica rhyolite, with agradational transition into overlying crystal-rich quartz latite. However, major and trace element analyses of glassy pumice lumps and microprobe analyses of their silicate and oxide phenocrysts provide closer approximations of the chemical and thermal gradients within the magma body. The gradients inferred from these data indicate that the transition from high-silica rhyolitic to quartz latitic magma within the chamber was abrupt, rather than gradational, with a distinct liquid-liquid interface separating the contrasting magma layers. Compositionally and texturally distinct pumice lumps are present throughout the ash flow sheet. The degree of heterogeneity within and among pumice lumps increases with stratigraphic height, becoming most pronounced in the uppermost quartz latite, where the chemical variability among pumice lumps is as great as that of the entire ash flow sheet. These observations are consistent with fluid dynamic models in which the velocity field developed near the entrance region of the vent(s) results in simultaneous withdrawal of magma from all points of a continuously expanding lateral and vertical region within the chamber. The abrupt transition to chemically bimodal pumice types near the top of the ash flowsheet, dominated by those of quartz latitic composition, implies that the interface between the magma layers remained relatively stable until drawdown breached the interface and preferentially erupted hotter, more mafic magma along with lesser amounts of remaining high-silica rhyolitic magma.

  14. Amphibole-rich intrusive mafic and ultramafic rocks in arc settings: implications for the H2O budget

    NASA Astrophysics Data System (ADS)

    Tiepolo, M.; Langone, A.; Morishita, T.; Esna-Ashari, A.; Tribuzio, R.

    2011-12-01

    Although amphibole is rarely a phenocryst of arc lavas, many intermediate and silicic magmas in arc settings are considered residual after cryptic amphibole crystallization at mid-low crustal levels (e.g., Davidson et al., 2007). Amphibole-rich mafic and ultramafic intrusive rocks (hornblendites, amphibole-gabbros to amphibole-diorites) are reported worldwide in orogenic settings. These amphibole-rich plutonics could be the "hidden" amphibole reservoir invoked in the arc crust. They usually possess chemical and textural heterogeneities recording the magmatic processes occurring in the mid to low crust (e.g., Tiepolo et al., 2011). Being amphibole-rich, these intrusive rocks are an important source of information on the possible role played by amphibole in arc magma petrogenesis. In particular, for the capability of amphibole to incorporate H2O and elements with a marked affinity for the fluid phase, these rocks are also useful to track the origin and evolution of subduction related fluids. We present here geochemical and geochronologic data on amphibole-rich ultramafic intrusive rocks from different localities worldwide: i) Alpine Orogen (Adamello Batholith and Bregell intrusions); ii) Ross Orogen (Husky Ridge intrusion - Antarctica); iv) Japan Arc (Shikanoshima Island intrusion); v) Sanandaj-Sirjan Zone, Central Iran (Aligoordaz granitoid complex). The coupling of textural information, micro-chemical data and "in situ" zircon geochronology has allowed us to show that these ultramafic intrusive rocks share striking petrologic and geochemical similarities. They are thus the expression of a common magmatic activity that is independent from the age and from the local geological setting and thus related to a specific petrogenetic process. Amphibole-rich mafic and ultramafic intrusive rocks are retained a common feature of collisional-systems worldwide. Amphibole is thus expected to play a major role in the differentiation of arc magmas and in particular in the H2O

  15. Ground surface deformation patterns, magma supply, and magma storage at Okmok volcano, Alaska, from InSAR analysis: 2. Coeruptive deflation, July-August 2008

    USGS Publications Warehouse

    Lu, Zhong; Dzurisin, Daniel

    2010-01-01

    A hydrovolcanic eruption near Cone D on the floor of Okmok caldera, Alaska, began on 12 July 2008 and continued until late August 2008. The eruption was preceded by inflation of a magma reservoir located beneath the center of the caldera and ~3 km below sea level (bsl), which began immediately after Okmok's previous eruption in 1997. In this paper we use data from several radar satellites and advanced interferometric synthetic aperture radar (InSAR) techniques to produce a suite of 2008 coeruption deformation maps. Most of the surface deformation that occurred during the eruption is explained by deflation of a Mogi-type source located beneath the center of the caldera and 2–3 km bsl, i.e., essentially the same source that inflated prior to the eruption. During the eruption the reservoir deflated at a rate that decreased exponentially with time with a 1/e time constant of ~13 days. We envision a sponge-like network of interconnected fractures and melt bodies that in aggregate constitute a complex magma storage zone beneath Okmok caldera. The rate at which the reservoir deflates during an eruption may be controlled by the diminishing pressure difference between the reservoir and surface. A similar mechanism might explain the tendency for reservoir inflation to slow as an eruption approaches until the pressure difference between a deep magma production zone and the reservoir is great enough to drive an intrusion or eruption along the caldera ring-fracture system.

  16. Final OSWER Vapor Intrusion Guidance

    EPA Science Inventory

    EPA is preparing to finalize its guidance on assessing and addressing vapor intrusion, which is defined as migration of volatile constituents from contaminated media in the subsurface (soil or groundwater) into the indoor environment. In November 2002, EPA issued draft guidance o...

  17. Morphology and dynamics of planetary laccoliths: a theoretical model to test for potential planetary intrusions

    NASA Astrophysics Data System (ADS)

    Michaut, C.

    2012-12-01

    Laccoliths are shallow magmatic intrusions which lead to the vertical displacement of the overburden, creating a characteristic dome-like topography. Laccoliths have been proposed to explain various geological features such as low-slope domes or floor-fractured craters at the surface of the Moon, Mars or Mercury. Here I show that planetary dome morphologies should provide indications of their processes of emplacement. Indeed, the dynamics of magma spreading below an elastic crust shows that the first spreading regime of an intrusion is controlled by the elastic response of the crust. In this elastic regime, the intrusion has a bell shape and the flow thickness evolves with flow length to the power 1 or 5/4, depending on the geometry. When the flow length becomes larger than a characteristic length scale, which depends on the flexural wavelength of the crust, the flow edges become steeper and the regime transitions to a gravity current regime. In the gravity current regime, the own flow weight controls the intrusion dynamics and shape, as is the case for surface lava flow, and the flow thickness remains constant or evolves slowly with flow length, depending on the geometry. Hence, co-genetic intrusive domes should exhibit a thickness to length power-law relationship with an exponent equal to 1 or 5/4, when the flow length is less than the elastic length scale, whereas the thickness of extrusive domes should remain constant or slowly evolve with flow length. The scaling law between flow length and thickness in the elastic regime fits observations on laccoliths at Elba Island, Italy. The shape and length scale derived from this model also fits the observed shape and characteristic length of terrestrial laccoliths. The morphologies of candidate intrusive domes at the surface of the Moon and Mars are then tested against this model and correspond to an emplacement at depth. The observed characteristic length of planetary intrusions increases as gravity decreases, as

  18. Geophysical Survey and Detailed Geologic Mapping of an Eroded Stratovolcano's Central Intrusive Complex, Summer Coon, Co.

    NASA Astrophysics Data System (ADS)

    Harp, A.

    2015-12-01

    Eroded volcanoes expose plumbing systems that provide important information on intrusive geometries, magma propagation directions, and the effects of host rock types and heterogeneities. Summer Coon Volcano, CO, is an Oligocene stratovolcano where erosion has removed much of the original edifice, revealing the intrusive stocks of the central intrusive complex (CIC). Surrounding the CIC are hundreds of radial dikes ranging from basaltic to rhyolitic in composition. Published geologic maps indicate most radial dikes do not connect to the intrusive stocks, supporting published theories that most did not emanate from the central intrusions. However, much of the area surrounding the CIC is covered by alluvium, suggesting that the lack of connection might be an artifact of exposure. We completed a ground magnetic survey and detailed geological mapping to determine if the dikes continue beneath the alluvium and into the intrusive stocks. Linear magnetic anomalies indicate four NW-SE trending rhyodacite dikes continue beneath the alluvium for up to 250 m, and mapping indicates that at least two of the rhyodacite dikes do extend into the CIC. Shorter linear anomalies are attributed to seven NW-SE trending basaltic dikes ~100-500-m-long which are sparsely exposed in the alluvium. Mapping shows that three rhyodacite dikes extend into the CIC and to within 200 m of their possible source, an 800-m-wide granodiorite stock. Additionally, three rhyolitic dikes extend to within several meters of a 200×500-m-wide tuff breccia zone of similar composition, likely their source. In summary, magnetic data and detailed mapping indicate that radial dikes do extend into the central intrusive complex in contrast to some model predictions.

  19. Petrological evidence for non-linear increase of magmatic intrusion rates before eruption at open vent mafic volcanoe

    NASA Astrophysics Data System (ADS)

    Ruth, D. C. S.; Costa Rodriguez, F.

    2015-12-01

    The most active volcanoes on earth erupt in a yearly to decadal time scales, typically erupt mafic magmas and are open-vent systems with prominent degassing plumes (e.g. Mayon, Arenal, Llaima, Etna). Here we investigate the plumbing systems, dynamics, and processes that drive eruptions at these systems. These are key questions for improving hazard evaluation, and better understanding the unrest associated with these types of volcanoes. The petrology and geochemistry from six historical eruptions (1947-2006) of Mayon volcano (Philippines) shows that all lavas are basaltic andesite with phenocrysts of plagioclase + orthopyroxene (Opx) + clinopyroxene. Opx crystals show a variety of compositions and zoning patterns (reverse, normal or complex) with Mg# (= 100 *Mg/[Mg+Fe]) varying from 67 to 81. The simplest interpretation is that the low Mg# parts of the crystals resided on an upper crustal and crystal rich reservoir that was intruded by more primitive magmas from which the high Mg# parts of the crystals grew. Modelling Mg-Fe diffusion in Opx shows that times since magma injection and eruption range from a few days up to 3.5 years in all of the investigated eruptions. The longest diffusion times are shorter than the repose times between the eruptions, which implies that crystal recycling between eruptive events is negligible. This is a surprising result that shows that for each eruption a different part of the evolved crystal-rich plumbing system is activated. This can be due to random intrusion location or an irreversibility of the plumbing system that prevents multiple eruptions from the same crystal-rich part. Moreover, we find that the number of intrusions markedly increases before each eruption in a non-linear manner. Such an increased rate of intrusions with time might reflect non-linear rheological properties of the crystal-rich system, of the enclosing rocks, or the non-linear evolution of crystal-melt reaction-dissolution fronts during magma intrusions.

  20. The Fish Canyon magma body, San Juan volcanic field, Colorado: Rejuvenation and eruption of an upper-crustal batholith

    USGS Publications Warehouse

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

    2002-01-01

    More than 5000 km3 of nearly compositionally homogeneous crystalrich dacite (~68 wt % SiO2: ~45% Pl + Kfs + Qtz + Hbl + Bt + Spn + Mag + Ilm + Ap + Zrn + Po) erupted from the Fish Canyon magma body during three phases: (1) the pre-caldera Pagosa Peak Dacite (an unusual poorly fragmented pyroclastic deposit, ~ 200 km3); (2) the syn-collapse Fish Canyon Tuff (one of the largest known ignimbrites, ~ 5000 km3); (3) the post-collapse Nutras Creek Dacite (a volumetrically minor lava). The late evolution of the Fish Canyon magma is characterized by rejuvenation of a near-solidus upper-crustal intrusive body (mainly crystal mush) of batholithic dimensions. The necessary thermal input was supplied by a shallow intrusion of more mafic magma represented at the surface by sparse andesitic enclaves in late-erupted Fish Canyon Tuff and by the post-caldera Huerto Andesite. The solidified margins of this intrusion are represented by holocrystalline xenoliths with Fish Canyon mineralogy and mineral chemistry and widely dispersed partially remelted polymineralic aggregates, but dehydration melting was not an important mechanism in the rejuvenation of the Fish Canyon magma. Underlying mafic magma may have evolved H2O-F-S-Cl-rich fluids that fluxed melting in the overlying crystal mush. Manifestations of the late up-temperature magma evolution are: (1) resorbed quartz, as well as feldspars displaying a wide spectrum of textures indicative of both resorption and growth, including Rapakivi textures and reverse growth zoning (An27-28 to An32-33) at the margins of many plagioclase phenocrysts; (2) high Sr, Ba, and Eu contents in the high-SiO2 rhyolite matrix glass, which are inconsistent with extreme fractional crystallization of feldspar; (3) oscillatory and reverse growth zoning toward the margins of many euhedral hornblende phenocrysts (rimward increases from ~5??5-6 to 7??7-8??5 wt % Al2O3). Homogeneity in magma composition at the chamber-wide scale, contrasting with extreme textural

  1. 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.

  2. Timescale of Petrogenetic Processes Recorded in the Mount Perkins Magma System, Northern Colorado River Extension Corridor, Arizona

    NASA Technical Reports Server (NTRS)

    Danielson, Lisa R.; Metcalf, Rodney V.; Miller, Calvin F.; Rhodes Gregory T.; Wooden, J. L.

    2013-01-01

    The Miocene Mt. Perkins Pluton is a small composite intrusive body emplaced in the shallow crust as four separate phases during the earliest stages of crustal extension. Phase 1 (oldest) consists of isotropic hornblende gabbro and a layered cumulate sequence. Phase 2 consists of quartz monzonite to quartz monzodiorite hosting mafic microgranitoid enclaves. Phase 3 is composed of quartz monzonite and is subdivided into mafic enclave-rich zones and enclave-free zones. Phase 4 consists of aphanitic dikes of mafic, intermediate and felsic compositions hosting mafic enclaves. Phases 2-4 enclaves record significant isotopic disequilibrium with surrounding granitoid host rocks, but collectively enclaves and host rocks form a cogenetic suite exhibiting systematic variations in Nd-Sr-Pb isotopes that correlate with major and trace elements. Phases 2-4 record multiple episodes of magma mingling among cogenetic hybrid magmas that formed via magma mixing and fractional crystallization at a deeper crustal. The mafic end-member was alkali basalt similar to nearby 6-4 Ma basalt with enriched OIB-like trace elements and Nd-Sr-Pb isotopes. The felsic end-member was a subalkaline crustal-derived magma. Phase 1 isotropic gabbro exhibits elemental and isotopic compositional variations at relatively constant SiO2, suggesting generation of isotropic gabbro by an open-system process involving two mafic end-members. One end-member is similar in composition to the OIB-like mafic end-member for phases 2-4; the second is similar to nearby 11-8 Ma tholeiite basalt exhibiting low epsilon (sub Nd), and depleted incompatible trace elements. Phase 1 cumulates record in situ fractional crystallization of an OIB-like mafic magma with isotopic evidence of crustal contamination by partial melts generated in adjacent Proterozoic gneiss. The Mt Perkins pluton records a complex history in a lithospheric scale magma system involving two distinct mantle-derived mafic magmas and felsic magma sourced in the

  3. Workshop on Magmatic Processes of Early Planetary Crusts: Magma Oceans and Stratiform Layered Intrusions

    NASA Technical Reports Server (NTRS)

    Walker, D. (Editor); Mccallum, I. S. (Editor)

    1981-01-01

    The significance of the lunar highland pristine cumulate samples were reevaluated with the aid of the additional insights provided by geologically constrained terrestrial investigations. This exercise involved a review of the state of knowledge about terrestrial and lunar cumulate rocks as well as an enumeration and reevaluation of the processes hypothesized to have been responsible for their formation, both classically and at present.

  4. Magma intrusion near Volcan Tancítaro: Evidence from seismic analysis

    NASA Astrophysics Data System (ADS)

    Pinzón, Juan I.; Núñez-Cornú, Francisco J.; Rowe, Charlotte A.

    2017-01-01

    Between May and June 2006, an earthquake swarm occurred near Volcan Tancítaro in Mexico, which was recorded by a temporary seismic deployment known as the MARS network. We located ∼1000 events from this seismic swarm. Previous earthquake swarms in the area were reported in the years 1997, 1999 and 2000. We relocate and analyze the evolution and properties of the 2006 earthquake swarm, employing a waveform cross-correlation-based phase repicking technique. Hypocenters from 911 events were located and divided into eighteen families having a correlation coefficient at or above 0.75. 90% of the earthquakes provide at least sixteen phase picks. We used the single-event location code Hypo71 and the P-wave velocity model used by the Jalisco Seismic and Accelerometer Network to improve hypocenters based on the correlation-adjusted phase arrival times. We relocated 121 earthquakes, which show clearly two clusters, between 9-10 km and 3-4 km depth respectively. The average location error estimates are <1 km epicentrally, and <2 km in depth, for the largest event in each cluster. Depths of seismicity migrate upward from 16 to 3.5 km and exhibit a NE-SW trend. The swarm first migrated toward Paricutin Volcano but by mid-June began propagating back toward Volcán Tancítaro. In addition to its persistence, noteworthy aspects of this swarm include a quasi-exponential increase in the rate of activity within the first 15 days; a b-value of 1.47; a jug-shaped hypocenter distribution; a shoaling rate of ∼5 km/month within the deeper cluster, and a composite focal mechanism solution indicating largely reverse faulting. These features of the swarm suggest a magmatic source elevating the crustal strain beneath Volcan Tancítaro.

  5. Late Archaean crust-mantle interactions: geochemistry of LREE-enriched mantle derived magmas. Example of the Closepet batholith, southern India

    NASA Astrophysics Data System (ADS)

    Jayananda, M.; Martin, H.; Peucat, J.-J.; Mahabaleswar, B.

    1995-03-01

    The Closepet batholith in South India is generally considered as a typical crustal granite emplaced 2.5 Ga ago and derived through partial melting of the surrounding Peninsular Gneisses (3.3 to 3.0 Ga). In the field, it appears as a composite batholith made up of at least two groups of intrusions. (a) An early SiO2-poor group (clinopyroxene quartz-monzonite and porphyritic phyritic monzogranite) is located in the central part of the batholith. These rocks display a narrow range in both initial 87Sr/86Sr (0.7017 0.7035) and ɛNd(-0.9to -4.1). (b) A later SiO2-rich group (equigranular grey and pink granites) is located along the interface between the SiO2-poor group and the Peninsular Gneisses. They progressively grade into migmatised Peninsular Gneisses, thus indicating their anatectic derivation. Their isotopic characteristics vary over a wide range (87Sr/86Sr ratios=0.7028 0.7336 and ɛNd values from-2.7 to-8.3, at 2.52 Ga). Field and geochronological evidence shows that the two groups are broadly contemporaneous (2.518 2.513 Ga) and mechanically mixed. This observation is supported by the chemical data that display well defined mixing trends in the ɛSr vs ɛNd and elemental variation diagrams. The continuous chemical variation of the two magmatic bodies is interpreted in terms of interaction and mixing of two unrelated end-members derived from different source regions (enriched peridotitic mantle and Peninsular Gneisses). It is proposed that the intrusion of mantle-derived magmas into mid-crustal levels occurred along a transcurrent shear zone; these magmas supplied additional heat and fluids that initiated anatexis of the surrounding crust. During this event, large-scale mixing occurred between mantle and crustal melts, thus generating the composite Closepet batholith. The mantle-derived magmatism is clearly associated with granulite facies metamorphism 2.51±0.01 Ga ago. Both are interpreted as resulting from a major crustal accretion event, possibly related

  6. 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

  7. 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.

  8. Formation of native iron in sediment-contaminated magma: I. A. case study of the Hanekammen Complex on Disko Island, West Greenland

    SciTech Connect

    Ulff-Moller, F. )

    1990-01-01

    For the first time a compositional range of native iron bodies is described in a cogenetic series of sediment-contaminated volcanic rocks from the Tertiary West Greenland Basalt Province. The iron-bearing rocks occur in a high-level composite intrusion, the Hanekammen Complex. Reaction between a tholeiitic parent magma with >11% MgO and carbonaceous Al{sub 2}O{sub 3}-rich shale took place in a reservoir >3 km below the paleosurface and created magmatic layering with basaltic magma overlain by less dense andesitic magma. The contaminated rock series bears a strong imprint of assimilation but very little fractional crystallization, which implies that the two processes were not intimately coupled in the present in basalt and andesite form a general trend, defined by Co versus Ni concentrations, that reflects the degree of assimilation, the amount of immiscible sulfide liquid, and the degree of reduction (in order of decreasing importance). The zoning of single iron grains reflects the dynamics of their growth and, to some extent, subsequent homogenization and reaction with magma. Weakly zoned iron spherules in viscous andesite were formed and remained in situ, whereas iron grains in basalt settled through the layered magma and developed strong zoning. All iron types contain Co-rich domains (<1 mm in diameter); their conservation implies a residence time for the iron at magmatic temperatures on the order of a month or less before the emplacement in the subvolcanic intrusions.

  9. A 550-year-old Plinian eruption at El Chichón Volcano, Chiapas, Mexico: Explosive volcanism linked to reheating of the magma reservoir

    NASA Astrophysics Data System (ADS)

    MacíAs, J. L.; Arce, J. L.; Mora, J. C.; EspíNdola, J. M.; Saucedo, R.; Manetti, P.

    2003-12-01

    Some 550 years ago (1320-1433 A.D.), a powerful Plinian eruption at El Chichón Volcano in southern Mexico produced a widespread pumice fall deposit. We subdivided the deposit into three parts on the basis of structural and textural characteristics, pumice lithology and density, granulometry, and petrologic-geochemical attributes. The deposit covers an area of 1500 km2 within the 1-cm isopach and has a minimum estimated bulk volume of 2.8 km3 (1.1 km3 dense rock equivalent (DRE)); its eruptive column reached an altitude of ˜31 km. Consideration of field evidence, the presence and nature of mafic enclaves, and chemical data strongly suggest that the 550 year B.P. eruption is linked with the intrusion of a high-temperature basaltic magma into preexisting but stagnated trachyandesitic magma beneath El Chichón. Thorough mixing of the two magmas produced a compositionally uniform hybrid trachyandesite magma (average SiO2 55.3 wt %), which subsequently underwent crystal growth and gas exsolution, ultimately overpressurizing the zoned magmatic system to erupt explosively. On the basis of El Chichón's known eruptive history, the intrusion-mixing event occurred sometime after the 900 year B.P. eruption. The hybrid magma had a preeruption temperature of 820-830°C and was water undersaturated (5-6 wt % H2O) at pressures of ˜2-2.5 kbar.

  10. Derivation of S and Pb in phanerozoic intrusion-related metal deposits from neoproterozoic sedimentary pyrite, Great Basin, United States

    USGS Publications Warehouse

    Vikre, P.G.; Poulson, S.R.; Koenig, A.E.

    2011-01-01

    The thick (???8 km), regionally extensive section of Neoproterozoic siliciclastic strata (terrigenous detrital succession, TDS) in the central and eastern Great Basin contains sedimentary pyrite characterized by mostly high d34S values (-11.6 to 40.8%, <70% exceed 10%; 51 analyses) derived from reduction of seawater sulfate, and by markedly radiogenic Pb isotopes ( 207Pb/204Pb <19.2; 15 analyses) acquired from clastic detritus eroded from Precambrian cratonal rocks to the east-southeast. In the overlying Paleozoic section, Pb-Zn-Cu-Ag-Au deposits associated with Jurassic, Cretaceous, and Tertiary granitic intrusions (intrusion-related metal deposits) contain galena and other sulfide minerals with S and Pb isotope compositions similar to those of TDS sedimentary pyrite, consistent with derivation of deposit S and Pb from TDS pyrite. Minor element abundances in TDS pyrite (e.g., Pb, Zn, Cu, Ag, and Au) compared to sedimentary and hydrothermal pyrite elsewhere are not noticeably elevated, implying that enrichment in source minerals is not a precondition for intrusion-related metal deposits. Three mechanisms for transferring components of TDS sedimentary pyrite to intrusion-related metal deposits are qualitatively evaluated. One mechanism involves (1) decomposition of TDS pyrite in thermal aureoles of intruding magmas, and (2) aqueous transport and precipitation in thermal or fluid mixing gradients of isotopically heavy S, radiogenic Pb, and possibly other sedimentary pyrite and detrital mineral components, as sulfide minerals in intrusion-related metal deposits. A second mechanism invokes mixing and S isotope exchange in thermal aureoles of Pb and S exsolved from magma and derived from decomposition of sedimentary pyrite. A third mechanism entails melting of TDS strata or assimilation of TDS strata by crustal or mantle magmas. TDS-derived or assimilated magmas ascend, decompress, and exsolve a mixture of TDS volatiles, including isotopically heavy S and radiogenic Pb

  11. Raman investigation of magma mingling experiments as a tool for tracking the chemical and structural evolution of melt.

    NASA Astrophysics Data System (ADS)

    Di Genova, D.; Morgavi, D.; Hess, K. U.; Pritchard, C. J.; Borovkov, N.; Perugini, D.; Larson, P. B.; Dingwell, D. B.

    2014-12-01

    Magma mixing is a petrologic phenomenon, for which extensive evidence has been documented in rocks young and old, from intrusive and effusive igneous environments. Although magma mixing between mafic and silicic magmas is regarded as a major differentiation process, documentation of the mechanisms acting in melt interaction, both in its physical and chemical aspects, is still incomplete. We present the first Raman spectroscopic investigation of the products of magma-mixing experiments performed using natural basaltic and rhyolitic melts from the Yellowstone Norris-Mammoth Corridor. The mixing process is driven by a recently-developed apparatus that generates chaotic streamlines in the melts, mimicking the development of magma mixing in nature. The chemical variation of major elements is studied in detail by electron microprobe (EMPA) on mixed filaments of 1000 μm diameter. Raman and microprobe measurements have been performed every 10 μm this allow us to investigate the evolution of silicate structure, from the rhyolitic to the basaltic composition. Deconvoluted Raman spectra collected from the mixed experiment yield information about network-forming structural units (Qn species, where n indicates the number of bridging oxygen). By combining Raman spectra and chemical analyses we show, for the first time, how the percent of Qn species evolve with chemical composition in these natural silicate melts. Moreover, our results show how the ratio of network modifiers respect to network former cations, dramatically affects the Raman spectra of the rhyolitic end-member.

  12. Volcanic magma reservoir imaged as a low-density body beneath Aso volcano that terminated the 2016 Kumamoto earthquake rupture

    NASA Astrophysics Data System (ADS)

    Miyakawa, Ayumu; Sumita, Tatsuya; Okubo, Yasukuni; Okuwaki, Ryo; Otsubo, Makoto; Uesawa, Shimpei; Yagi, Yuji

    2016-12-01

    We resolve the density structure of a possible magma reservoir beneath Aso, an active volcano on Kyushu Island, Japan, by inverting gravity data. In the context of the resolved structure, we discuss the relationship between the fault rupture of the 2016 Kumamoto earthquake and Aso volcano. Low-density bodies were resolved beneath central Aso volcano using a three-dimensional inversion with an assumed density contrast of ±0.3 g/cm3. The resultant location of the southern low-density body is consistent with a magma reservoir reported in previous studies. No Kumamoto aftershocks occur in the southern low-density body; this aseismic anomaly may indicate a ductile feature due to high temperatures and/or the presence of partial melt. Comparisons of the location of the southern low-density body with rupture models of the mainshock, obtained from teleseismic waveform and InSAR data, suggest that the rupture terminus overlaps the southern low-density body. The ductile features of a magma reservoir could have terminated rupture propagation. On the other hand, a northern low-density body is resolved in the Asodani area, where evidence of current volcanic activity is scarce and aftershock activity is high. The northern low-density body might, therefore, be derived from a thick caldera fill in the Asodani area, or correspond to mush magma or a high-crystallinity magma reservoir that could be the remnant of an ancient intrusion.[Figure not available: see fulltext.

  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. Magma beneath Yellowstone National Park

    USGS Publications Warehouse

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

    1975-01-01

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

  15. Magma Beneath Yellowstone National park.

    PubMed

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

    1975-05-23

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

  16. Fractional Crystallisation of Archaean Trondhjemite Magma at 12-7 Kbar: Constraints on Rheology of Archaean Continental Crust

    NASA Astrophysics Data System (ADS)

    Sarkar, Saheli; Saha, Lopamudra; Satyanarayan, Manavalan; Pati, Jayanta

    2015-04-01

    Fractional Crystallisation of Archaean Trondhjemite Magma at 12-7 Kbar: Constraints on Rheology of Archaean Continental Crust Sarkar, S.1, Saha, L.1, Satyanarayan, M2. and Pati, J.K.3 1. Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee-247667, Haridwar, India, 2. HR-ICPMS Lab, Geochemistry Group, CSIR-National Geophysical Research Institute, Hyderabad-50007, India. 3. Department of Earth and Planetary Sciences, Nehru Science Centre, University of Allahabad, Allahabad-211002, India. Tonalite-Trondhjemite-Granodiorite (TTGs) group of rocks, that mostly constitute the Archaean continental crusts, evolved through a time period of ~3.8 Ga-2.7 Ga with major episodes of juvenile magma generations at ~3.6 Ga and ~2.7 Ga. Geochemical signatures, especially HREE depletions of most TTGs conform to formation of this type of magma by partial melting of amphibolites or eclogites at 15-20 kbar pressure. While TTGs (mostly sodic in compositions) dominates the Eoarchaean (~3.8-3.6 Ga) to Mesoarchaean (~3.2-3.0 Ga) domains, granitic rocks (with significantly high potassium contents) became more dominant in the Neoarchaean period. The most commonly accepted model proposed for the formation of the potassic granite in the Neoarchaean time is by partial melting of TTGs along subduction zones. However Archaean granite intrusive into the gabbro-ultramafic complex from Scourie, NW Scotland has been interpreted to have formed by fractional crystallization of hornblende and plagioclase from co-existing trondhjemitic gneiss. In this study we have studied fractional crystallization paths from a Mesoarchaean trondhjemite from the central Bundelkhand craton, India using MELTS algorithm. Fractional crystallization modeling has been performed at pressure ranges of 20 kbar to 7 kbar. Calculations have shown crystallization of garnet-clinopyroxene bearing assemblages with progressive cooling of the magma at 20 kbar. At pressure ranges 19-16 kbar, solid phases

  17. Magma storage conditions beneath Dabbahu Volcano (Ethiopia) constrained by petrology, seismicity and satellite geodesy

    NASA Astrophysics Data System (ADS)

    Field, L.; Blundy, J.; Brooker, R. A.; Wright, T.; Yirgu, G.

    2012-07-01

    A variety of methods exist to constrain sub-volcanic storage conditions of magmas. Petrological, seismological and satellite geodetic methods are integrated to determine storage conditions of peralkaline magmas beneath Dabbahu Volcano, Afar, Ethiopia. Secondary ion mass spectrometry (SIMS) analysis of volatile contents in melt inclusions trapped within phenocrysts of alkali feldspar, clinopyroxene and olivine from pantellerite obsidians representing the youngest eruptive phase (<8 ka) show H2O contents ≤5.8 wt.% and CO2 contents generally below 500 ppm, although rarely as high as 1,500 ppm. Volatile saturation pressures (at 679-835°C) are in the range 43-207 MPa, consistent with published experimental data for similar pantellerites, which show that the phenocryst assemblage of alkali feldspar + cpx + aenigmatite ± ilmenite is stable at 100 to 150 MPa. Inferred magma storage depths for these historic eruptions are ~1-5 km below sea-level, consistent with the depths of earthquakes, associated with magma chamber deflation following a dyke intrusion in the period Oct 2005-Apr 2006. Interferometric synthetic aperture radar (InSAR) data for the same period reveal a broad ~20 km diameter area of uplift. Modelling of different geometries reveals that a series of stacked sills over a 1-5 km depth range best matches the InSAR data. The consistency of depth estimates based on petrological study of ancient eruptions and the seismicity, inflation and deflation of Dabbahu observed in relation to the dyking event of 2005, suggest a small but vertically extensive and potentially long-lived magma storage region.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  19. Rapid thermal rejuvenation of high-crystallinity magma linked to porphyry copper deposit formation; evidence from the Koloula Porphyry Prospect, Solomon Islands

    NASA Astrophysics Data System (ADS)

    Tapster, S.; Condon, D. J.; Naden, J.; Noble, S. R.; Petterson, M. G.; Roberts, N. M. W.; Saunders, A. D.; Smith, D. J.

    2016-05-01

    Magmas containing the components needed to form porphyry copper deposits are relatively common within arcs, yet mineralising events are uncommon within the long-lived magmatic systems that host them. Understanding what causes the transition from barren to productive intrusions is critical to the development of conceptual deposit models. We have constrained the tempo of pre- and syn-mineralisation magmatic events in relationship to the thermal evolution of the plutonic body that underlies one of the world's youngest exposed plutonic-porphyry systems, the Inamumu Zoned Pluton, Koloula Porphyry Prospect, Solomon Islands. High precision ID-TIMS U-Pb dates of texturally and chemically characterised zircons indicate pluton emplacement over <150 kyr was superseded after ca. 50 kyr by two discrete episodes of mineralising porphyritic melt emplacement. Their associated hydrothermal systems initiated within ca. 30 kyrs of each other. Zircon populations within evolved intrusions contain resorbed cores that were recycled from the deeper magmatic system, yet their youngest dates are statistically indistinguishable from those yielded by crystals lacking resorption. Comparisons of Ti-in-zircon proxy temperatures, modelled zircon saturation temperatures and temperature-crystallinity relationships suggest that prior to being heated and emplaced within the shallow level pluton, magmas were stored at depth in a high-crystallinity (>50% crystals) state, past the point of rheological lock-up. We estimate that thermal rejuvenation of the deeper high-crystallinity magma and generation of a mobile melt fraction may have occurred ≤10 kyr before its transport and emplacement within the porphyry environment. The underlying pluton likely cooled and returned to high-crystallinity states prior to subsequent remobilisation-emplacement events. Titanium-in-zircon geothermometry and whole-rock geochemistry suggest pre-mineralisation intrusions were remobilised by mixing of a silicic magma with a

  20. Energy extraction from crustal magma bodies

    SciTech Connect

    Dunn, J.C.

    1982-01-01

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

  1. 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.

  2. 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.

  3. Magmatic ore deposits in layered intrusions - Descriptive model for reef-type PGE and contact-type Cu-Ni-PGE deposits

    USGS Publications Warehouse

    Zientek, Michael L.

    2012-01-01

    Layered, ultramafic to mafic intrusions are uncommon in the geologic record, but host magmatic ore deposits containing most of the world's economic concentrations of platinum-group elements (PGE) (figs. 1 and 2). These deposits are mined primarily for their platinum, palladium, and rhodium contents (table 1). Magmatic ore deposits are derived from accumulations of crystals of metallic oxides, or immiscible sulfide, or oxide liquids that formed during the cooling and crystallization of magma, typically with mafic to ultramafic compositions. "PGE reefs" are stratabound PGE-enriched lode mineralization in mafic to ultramafic layered intrusions. The term "reef" is derived from Australian and South African literature for this style of mineralization and used to refer to (1) the rock layer that is mineralized and has distinctive texture or mineralogy (Naldrett, 2004), or (2) the PGE-enriched sulfide mineralization that occurs within the rock layer. For example, Viljoen (1999) broadly defined the Merensky Reef as "a mineralized zone within or closely associated with an unconformity surface in the ultramafic cumulate at the base of the Merensky Cyclic Unit." In this report, we will use the term PGE reef to refer to the PGE-enriched mineralization, not the host rock layer. Within a layered igneous intrusion, reef-type mineralization is laterally persistent along strike, extending for the length of the intrusion, typically tens to hundreds of kilometers. However, the mineralized interval is thin, generally centimeters to meters thick, relative to the stratigraphic thickness of layers in an intrusion that vary from hundreds to thousands of meters. PGE-enriched sulfide mineralization is also found near the contacts or margins of layered mafic to ultramafic intrusions (Iljina and Lee, 2005). This contact-type mineralization consists of disseminated to massive concentrations of iron-copper-nickel-PGE-enriched sulfide mineral concentrations in zones that can be tens to hundreds

  4. 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

  5. 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

  6. Linking enclave formation to magma rheology

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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

  7. Intrusive and extrusive growth of the Mount St Helens lava dome

    NASA Technical Reports Server (NTRS)

    Fink, Jonathan H.; Malin, Michael C.; Anderson, Steven W.

    1990-01-01

    High-resolution, digital topographic maps of the Mount St. Helens dome derived from aerial photographs are used here to make a quantitative assessment of the partitioning of magma into endogenous intrusion and exogenous lobes. The endogenous growth is found to be predictable, which shows that the cooling dome controls its own development independently of such deep-seated factors as magma overpressure and extrusion rate. The observed regular decrease in exogenous growth rate also allows volume prediction. Knowledge of the volume can be used to determine when an ongoing eruptive event should end. Finally, the observed transition from predominantly exogenous to predominantly endogenous growth reflects the increase in crust thickness, which in turn seems to depend on long repose periods rather than some fundamental change in the character of the dome.

  8. Gas slug ascent in a stratified magma: Implications of flow organisation and instability for Strombolian eruption dynamics

    NASA Astrophysics Data System (ADS)

    Capponi, A.; James, M. R.; Lane, S. J.

    2016-02-01

    The canonical Strombolian paradigm of a gas slug ascending and bursting in a homogeneous low-viscosity magma cannot explain the complex details in eruptive dynamics recently revealed by field measurements and textural and geochemical analyses. Evidence points to the existence of high-viscosity magma at the top of the conduit of Strombolian-type volcanoes, acting as a plug. Here, new experiments detail the range of flow configurations that develop during the ascent and burst of a slug through rheologically stratified magma within a conduit. End-member scenarios of a tube fully filled with either high- or low-viscosity liquid bracket three main flow configurations: (1) a plug sufficiently large to fully accommodate an ascending gas slug; (2) A plug that can accommodate the intrusion of low-viscosity liquid driven by the gas expansion, but not all the slug volume, so the slug bursts with the nose in the plug whilst the base is still in the low-viscosity liquid; (3) Gas expansion is sufficient to drive the intrusion of low-viscosity liquid through the plug, with the slug bursting in the low-viscosity layer emplaced dynamically above the plug. We show that the same flow configurations are viable at volcanic-scale through a new experimentally-validated 1D model and 3D computational fluid dynamic simulations. Applied to Stromboli, our results demonstrate that the key parameters controlling the transition between each configuration are gas volume, plug thickness and plug viscosity. The flow processes identified include effective dynamic narrowing and widening of the conduit, instabilities within the falling magma film, transient partial and complete blockage of the conduit, and slug disruption. These complexities influence eruption dynamics and vigour, promoting magma mingling and resulting in pulsatory release of gas.

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

    SciTech Connect

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

    1985-01-01

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

  10. Craters of elevation / forced folds: more examples of shallow magma accumulation and its consequences

    NASA Astrophysics Data System (ADS)

    van Wyk de Vries, Benjamin; Marquez, Alvaro; Craig, Magee; Valdislav, Rapprich; Hetherington, Rachel; Bastow, Ian

    2016-04-01

    Craters of elevation are uplifts with apical depressions that are caused by shallow magma intrusion. Forced folds are dome-like folds caused by magma intrusion that also have apical extensional structures. They are the same feature described from the different viewpoints of the volcanologist and the structural geologist. While working on such features in the Chaîne des Puys (Central France), and Ethiopia we have been searching for other examples in the world. This is our most up to date review of such phenomena taken from a global search in the world of volcanology where some stunning examples are seen in the landscape, and in outcrop. We also show such features from tectonics data and literature, where such features are superbly displayed in seismic data. We take three examples, the Puy de Gouttes, in the Chaîne des Puys, the Montana Encantada in Lanzarote, which we have mapped in the field, and the Diamond Craters National Monument in Oregon to show the different structures and possible evolutionary trends that such features can follow. We use the observations to integrate the possible eruptive, deformational and structural events that can combine in a forced fold to create the surface features observed at such craters of elevation. The hazard implications of the growth and destruction of such features are assessed.

  11. Platinum-group mineralization at the margin of the Skaergaard intrusion, East Greenland

    NASA Astrophysics Data System (ADS)

    Andersen, Jens C. Ø.; Rollinson, Gavyn K.; McDonald, Iain; Tegner, Christian; Lesher, Charles E.

    2017-01-01

    Two occurrences of platinum-group elements (PGEs) along the northern margin of the Skaergaard intrusion include a sulfide-bearing gabbro with slightly less than 1 ppm PGE + Au and a clinopyroxene-actinolite-plagioclase-biotite-ilmenite schist with 16 vol% sulfide and 1.8 ppm PGE + Au. Both have assemblages of pyrrhotite, pentlandite, and chalcopyrite typical for orthomagmatic sulfides. Matching platinum-group mineral assemblages with sperrylite (PtAs2), kotulskite (Pd(Bi,Te)1-2), froodite (PdBi2), michenerite (PdBiTe), and electrum (Au,Ag) suggest a common origin. Petrological and geochemical similarities suggest that the occurrences are related to the Skaergaard intrusion. The Marginal Border Series locally displays Ni depletion consistent with sulfide fractionation, and the PGE fractionation trends of the occurrences are systematically enriched by 10-50 times over the chilled margin. The PGE can be explained by sulfide-silicate immiscibility in the Skaergaard magma with R factors of 110-220. Nickel depletion in olivine suggests that the process occurred within the host cumulate, and the low R factors require little sulfide mobility. The sulfide assemblages are different to the chalcopyrite-bornite-digenite assemblage found in the Skaergaard Layered Series and Platinova Reef. These differences can be explained by the early formation of sulfide melt, while magmatic differentiation or sulfur loss caused the unusual sulfide assemblage within the Layered Series. The PGEs indicate that the sulfides formed from the Skaergaard magma. The sulfides and PGEs could not have formed from the nearby Watkins Fjord wehrlite intrusion, which is nearly barren in sulfide. We suggest that silicate-sulfide immiscibility led to PGE concentration where the Skaergaard magma became contaminated with material from the Archean basement.

  12. 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.

  13. Quasi-horizontal circulation cells in 3D seawater intrusion

    USGS Publications Warehouse

    Abarca, E.; Carrera, J.; Sanchez-Vila, X.; Voss, C.I.

    2007-01-01

    The seawater intrusion process is characterized by the difference in freshwater and seawater density that causes freshwater to float on seawater. Many confined aquifers have a large horizontal extension with respect to thickness. In these cases, while buoyancy acts in the vertical direction, flow is confined between the upper and bottom boundaries and the effect of gravity is controlled by variations of aquifer elevation. Therefore, the effective gravity is controlled by the slope and the shape of the aquifer boundaries. Variability in the topography of the aquifer boundaries is one case where 3D analysis is necessary. In this work, density-dependent flow processes caused by 3D aquifer geometry are studied numerically and specifically, considering a lateral slope of the aquifer boundaries. Sub-horizontal circulation cells are formed in the saltwater entering the aquifer. The penetration of the saltwater can be quantified by a dimensionless buoyancy number that measures the lateral slope of the aquifer relative to freshwater flux. The penetration of the seawater intrusion wedge is controlled more by this slope than by the aquifer thickness and dispersivity. Thus, the slope must be taken into account in order to accurately evaluate seawater intrusion. ?? 2007 Elsevier B.V. All rights reserved.

  14. 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

  15. Bimodal magmatism during the Diego Hernández Formation, Tenerife, Canary Islands: genesis and eruption-triggering of phonolitic magmas during ongoing mafic volcanism

    NASA Astrophysics Data System (ADS)

    Olin, P. H.; Wolff, J. A.; Edgar, C. J.; Cas, R.; Martí, J.

    2008-12-01

    The Diego Hernández Formation (DHF) represents the explosive eruption of nearly 70 cubic km of phonolite over approximately 200 k.y. from the Las Cañadas caldera on Tenerife. Four chemostratigraphic units are distinguished on the basis of trace element contents: DHF bs (represented by the 370 ka Fortaleza and 347 ka Roque Members), DHF I (319 ka Aldea, 309 ka Fasnia, and 268 ka Poris Members), DHF II (Arafo and 223 ka Caleta Members), and DHF III (Cruz Sequence and the 196 ka Abrigo Member); all named units involve plinian and/or ignimbrite components that devastated a significant fraction of the island [1]. These chemostratigraphic units demarcate two dominant compositional trends distinct in incompatible element contents, and in Nb/Ta and REE ratios. DHF bs and DHF III plot along a high-Nb trend, and DHF I and DHF II plot along a low-Nb trend, a feature consistent with divergent fractionation histories involving titanite. Mafic magma was an important component of the DHF magmatic system and flanking mafic volcanism was ongoing during DHF time. Major phonolitic eruptions are conformably bounded by basanitic lavas and scoria deposits. Mafic magmatic components are identifiable in many of the phonolitic pyroclastic deposits as mafic, mingled and banded pumices, or as quenched mafic enclaves. Mafic components in the Abrigo, Caleta, and Poris Members are nearly geochemically identical to the underlying scoria or lava, suggesting that flanking mafic volcanism may in some cases be associated with subcaldera intrusive events that remobilize phonolitic magma to trigger major explosive eruptions. We envisage that the DHF represents a time when the intrusion of mantle-derived mafic magma in the lower crust supplied heat sufficient for the generation of intermediate tephriphonolite and phonotephrite magmas via melting of gabbroic/basaltic crust. Some of these intermediate magmas evolved to phonolite by crystal fractionation, a scenario consistent with DHF III

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

    NASA Astrophysics Data System (ADS)

    Di Muro, Andrea

    2014-05-01

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

  17. Detailed Segmentation and Episodic Propagation of the 2014 Bárðarbunga Dike Intrusion and Seismicity Accompanying the Sustained Holuhraun Eruption, Central Icleand

    NASA Astrophysics Data System (ADS)

    Ágústsdóttir, T.; Woods, J.; Greenfield, T. S.; Green, R. G.; White, R. S.; Brandsdottir, B.

    2015-12-01

    An intense swarm of seismicity on 16 August 2014 marked the intrusion of a large dike from the subglacial Bárðarbunga volcano, central Iceland. Melt propagated laterally from the central volcano at the brittle-ductile boundary at ~6 km b.s.l. and created over 30,000 earthquakes along a 46 km path heading NE from Bárðarbunga. On 31 August a fissure eruption began at Holuhraun and the seismicity rate within the dike dropped instantaneously to a much lower level suggesting that once a pathway to the surface had formed, magma was able to flow freely and largely aseismically. Melt was fed from the subsiding Bárðarbunga volcano to Holuhraun for 6 months, until the eruption ceased on 27 February 2015. We discuss the relationship between bursts of seismicity in the feeder volcano and periods of rapid dike propagation. We use a dense seismic network and relative earthquake relocations to map in detail the segmentation of the dike on all scales. New dike segments were initiated with a rapid advance of the dike tip at typically 1 km/h, separated by pauses of up to 78 h. During the stalled periods the magma pressure built until it was sufficient to fracture a new segment, which then propagated rapidly forward. Large segments became seismically quiet once a new segment had intruded beyond it as extensional stresses had been relieved and melt was able to flow freely. Each rapid propagation phase was accompanied by a drop in the seismicity rate directly behind the dike tip, most likely due to a stress shadow being formed behind the dike tip. Moment tensor solutions show that the dominant failure mechanism is left-lateral strike slip faulting at the leading edge, orientated parallel to the dike, with a combination of right-lateral, left-lateral and normal faulting behind the dike tip, contradicting many widely used models. Much of the seismicity behind the tip may represent fracture of frozen melt as the dike inflated and propagated forward

  18. Asymmetric shock heating and the terrestrial magma ocean origin of the Moon.

    PubMed

    Karato, Shun-ichiro

    2014-01-01

    One of the difficulties of the current giant impact model for the origin of the Moon is to explain the marked similarity in the isotopic compositions and the substantial differences in the major element chemistry. Physics of shock heating is analyzed to show that the degree of heating is asymmetric between the impactor and the target, if the target (the proto-Earth) had a magma-ocean but the impactor did not. The magma ocean is heated much more than the solid impactor and the vapor-rich jets come mainly from the magma-ocean from which the Moon might have been formed. In this scenario, the similarity and differences in the composition between the Moon and Earth would be explained as a natural consequence of a collision in the later stage of planetary formation. Including the asymmetry in shock heating is the first step toward explaining the chemical composition of the Moon.

  19. Magma fracture and hybrid earthquakes in the conduit of Augustine Volcano

    NASA Astrophysics Data System (ADS)

    Buurman, Helena; West, Michael E.

    2013-12-01

    exploit subtle but systematic shifts in seismic waveforms to examine a 2 h cluster of repeating hybrid volcanic earthquakes preceding the first magmatic explosions at Augustine Volcano in January 2006. We extract differential P wave traveltimes of <0.01 s to determine that the source locations migrated downward by approximately 35 m. Waveform characteristics, GPS observations, and visual reports of lava effusion at the summit suggest that the earthquakes were sourced by fracturing magma in the upper conduit. As the lava cooled and degassed at the surface, the conditions in the upper conduit changed causing the zone in which magma fracture could occur to move downward through the magma column. These changes may also have been the first indicators that the conduit was becoming choked, causing a buildup in pressure that resulted in the large magmatic explosions that followed 36 h later.

  20. Layering in the wall rock of Valles Marineris: intrusive and extrusive magmatism

    NASA Astrophysics Data System (ADS)

    Williams, Jean-Pierre; Paige, David A.; Manning, Craig E.

    2003-06-01

    High-resolution images of the walls exposed in Valles Marineris reveal variations in appearance and degree of layering indicating various lithologies comprise the Tharsis plateau. The layered wall rock has been proposed to result from effusive flood basalt volcanism or interbedded sediments and volcanics. We present observations of unlayered rock that indicate layering extends to a greater depth in the western half of Valles Marineris and is confined to the Tharsis plateau, a region of thickened, uplifted crust resulting from prolonged intrusive activity. Consistent with this view, we propose that the observed layering may be a manifestation of intrusive rocks resulting from crystal fractionation of intruded basaltic magmas. Terrestrial layered plutons provide analogs for comparison such as those of the North Atlantic Igneous Province (NAIP) a large igneous province associated with crustal rifting and exposures of thick sequences of layered flood basalts and intruded layered cumulates.

  1. Future Volcanism at Yucca Mountain - Statistical Insights from the Non-Detection of Basalt Intrusions in the Potential Repository

    NASA Astrophysics Data System (ADS)

    Coleman, N.; Abramson, L.

    2004-05-01

    upper-bound probability of 2E-7/yr (95% conf. level) for an igneous intrusion over the next 1E4 yrs. If we assume one undiscovered dike exists, the upper-bound probability would rise to 4E-7/yr. Higher probabilities may be possible if conditions that fostered Plio-Quaternary volcanism became enhanced over time. To the contrary, basalts of the past 11 Ma in Crater Flat have erupted in four episodes that together show a declining trend in erupted magma volume (DOE, TBD13, 2003). Smith et al (GSA Today, 2002) suggest there may be a common magma source for volcanism in Crater Flat and the Lunar Crater volcanic field, and that recurrence rates for YM could be underestimated. Their interpretation is highly speculative given the 130-km (80-mi) distance between these zones. A claim that crustal extension at YM is anomalously large, possibly favoring renewed volcanism (Wernicke et al, Science, 1999), was contradicted by later work (Savage et al, JGR, 2000). Spatial-temporal models that predict future intrusion probabilities of >2E-7/yr may be overly conservative and unrealistic. Along with currently planned site characterization activities, realistic models could be developed by considering the non-detection of basaltic dikes in the potential repository footprint. (The views expressed are the authors' and do not reflect any final judgment or determination by the Advisory Committee on Nuclear Waste or the Nuclear Regulatory Commission regarding the matters addressed or the acceptability of a license application for a geologic repository at Yucca Mt.)

  2. Origins of seawater intrusion in a coastal aquifer - A case study of the Pajaro Valley, California

    USGS Publications Warehouse

    Bond, L.D.; Bredehoeft, J.D.

    1987-01-01

    Seawater may enter and contaminate stratified coastal aquifers through a number of different pathways. These pathways and their relative contribution are examined in the Pajaro Valley, California, a coastal area with extensive groundwater development. This study considers three pathways of possible intrusion of the primary confined aquifer: (1) onshore leakage from brackish sources, the estuary and sloughs, through the confining layer; (2) near-shore leakage from the ocean through the confining layer; and (3) offshore flow from the ocean through the submarine canyon outcrop of the aquifer. Groundwater flow and seawater intrusion are simulated using an areal, two-dimensional solute-transport computer model. This analysis indicates that leakage through confining layers is the principal mechanism of recharge to the aquifer. Although lateral flow through the offshore outcrop contaminates the aquifer, as a whole, at a higher rate, vertical leakage through the sea floor initially is the main pathway of seawater intrusion to the onshore portion of the aquifer. It is likely that leakage generally is the dominant mechanism of recharge and initial cause of seawater intrusion for poorly-confined, stratified coastal aquifers. This analysis suggests that a significant time interval follows the initial observation of seawater intrusion, during which remedial action can be taken to control lateral flow through the offshore outcrop, which ultimately will be the largest component of future intrusion in these aquifers. ?? 1987.

  3. 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.

  4. Petrological mapping of Volcanic Plumbing Systems using amphiboles in mixed intermediate magmas

    NASA Astrophysics Data System (ADS)

    Kiss, Balázs; Harangi, SzZabolcs; Hauzenberger, Christoph; Ntaflos, Theodoros; Mason, Paul R. D.

    2016-04-01

    -felsic) crystal mush column representing a main magma capture zone at upper-mid crustal depths (~7-20km). Zoned amphiboles cored by antecrysts and rimmed by phenocrysts indicate that new intrusions can reactivate these mushes forming the eruptible magma.

  5. The genesis of silicic arc magmas in shallow crustal cold zones

    NASA Astrophysics Data System (ADS)

    Adam, John; Turner, Simon; Rushmer, Tracy

    2016-11-01

    A number of currently popular models for the genesis of evolved arc-magmas (from basaltic andesite to dacite) invoke repeated intrusion, partial-melting and differentiation at the base of the crust. However, several observations suggest that this may be the exception rather than the norm: (1) geobarometry often indicates shallow pressure (0.1-0.3 GPa) evolution; (2) incongruent melting of amphibolite at elevated pressures should yield magmas in equilibrium with high pressure phases like garnet, but rare earth element patterns almost ubiquiously preclude this; (3) compositionally-zoned caldera forming eruptions suggest differentiation at near surface depths; (4) U-series data most commonly indicate differentiation over millennia time-scales. This requires rapid cooling that, in turn, is most easily explained by relatively small magma volumes undergoing crystal fractionation within the shallow (i.e. cool) crust. To further test these ideas, we combined published experimental-data for liquidus equilibria with appropriate silicic arc-magma compositions. On projections of the ternary liquidus system nepheline-silica-olivine, recent data for Tongan silicic lavas plot either on or close to low-pressure (1 atm) cotectics for the rocks' phenocryst phases, suggesting low-pressure differentiation. Using our own and published data from arc volcanoes around the world we find that the majority are consistent with differentiation at shallow depths, regardless of total crustal thickness. Combined with the typical timescales of differentiation, we estimate that the volumes of magma stored during differentiation in shallow crustal zones are usually on the order of only a few km3. There is also a clear role for mixing and recharge that involves magmas that are more deeply-sourced and primitive in character (typically evolved basalts and basaltic andesites). Whether the latter differentiated in the lower-crust or at the crust/mantle boundary has important implications for the

  6. The fate of mafic and ultramafic intrusions in the continental crust

    NASA Astrophysics Data System (ADS)

    Roman, Alberto; Jaupart, Claude

    2016-11-01

    Geochemical and petrological data indicate that the bulk continental crust results from the fractionation of basaltic magmas followed by the foundering of residual mafic cumulates. Structural and geological evidence for foundering has been elusive and it is argued that it lies in the shapes of mafic intrusions that have been preserved in the crust. Numerical calculations of visco-elasto-plastic deformation induced by a dense intrusive body in continental crust have been carried out for a wide range of physical conditions. Three regimes are defined on the basis of the amount of dense material that remains at the original emplacement level as well as on the shape of the residual body. With strong encasing rocks, the intrusion deforms weakly in a sagging regime characterized by downwarping of the floor. At the other extreme, the intrusion sinks through weak surroundings, leaving behind a very small volume of material. In an intermediate regime, the intrusion does not sink wholesale and undergoes a dramatic change of shape. A residual body is preserved with a shape that depends on the aspect ratio of the initial intrusion. For aspect ratios of order one, the residual body is funnel-shaped above a thin and deep vertical extension. For the small aspect ratios that typify large igneous complexes such as the Bushveld, South Africa, the residual body is characterized by thick peripheral lobes with inward-dipping igneous layers and a thinner central area that has lost some of the basal cumulates. The transitions between these regimes depend on the rheology and temperature of encasing rocks.

  7. Longitudinal relations of intrusive parenting and effortful control to ego-resiliency during early childhood.

    PubMed

    Taylor, Zoe E; Eisenberg, Nancy; Spinrad, Tracy L; Widaman, Keith F

    2013-01-01

    Longitudinal relations among ego-resiliency (ER), effortful control (EC), and observed intrusive parenting were examined at 18, 30, and 42 months of age (Ns = 256, 230, and 210) using structural equation modeling. Intrusive parenting at 18 and 30 months negatively predicted EC a year later, over and above earlier levels. EC at 30 months mediated the negative relation between 18-month intrusive parenting and ER at 42 months when controlling for stability of the variables. ER did not predict EC. The findings suggest that intrusive parenting may have a negative effect on children's ego-resiliency through its effects on children's abilities to regulate attention and behavior.

  8. Efficiency of two protocols for maxillary molar intrusion with mini-implants

    PubMed Central

    Paccini, Juliana Volpato Curi; Cotrim-Ferreira, Flávio Augusto; Ferreira, Flávio Vellini; de Freitas, Karina Maria Salvatore; Cançado, Rodrigo Hermont; Valarelli, Fabrício Pinelli

    2016-01-01

    ABSTRACT Objective: The aim of this study was to compare the efficiency of two protocols for maxillary molar intrusion with two or three mini-implants. Methods: Twenty five maxillary first molars extruded for loss of their antagonists in adult subjects were selected. The sample was divided into two groups, according to the intrusion protocol with two or three mini-implants. Group 1 consisted of 15 molars that were intruded by two mini-implants. Group 2 consisted of 10 molars intruded by three mini-implants. Changes with treatment were analyzed in lateral cephalograms at the beginning and at the end of intrusion of maxillary molars. Results: Results showed that there was no difference in efficiency for the two intrusion protocols. It was concluded that extruded maxillary molars can be intruded with two or three mini-implants with similar efficiency. PMID:27409654

  9. Magma crystallisation on a steep side-wall: Physical behaviour of the crystal mush

    NASA Astrophysics Data System (ADS)

    Humphreys, M.; Holness, M. B.

    2009-12-01

    The Marginal Border Series of the Skaergaard Intrusion, East Greenland, crystallised on the steeply dipping side-walls of the magma chamber. The rocks represent a series of mafic cumulates which crystallised inwards during fractional crystallisation of a single pulse of basaltic magma. They show the same progression of mineral assemblage and the same cryptic mineral compositional variation as that of the better known Layered Series, which crystallised on the chamber floor, demonstrating the “onion-skin” style of solidification of this box-shaped magma chamber. The original study of Wager & Deer (1939) divided the Marginal Border Series into the outer Tranquil Zone and an inner Banded Zone, although this field-based division bears no relationship with the progressive fractionation of the gabbros. A key feature of the Tranquil Zone is the “Wavy Pyroxene Rock”, which comprises geometrically aligned, lensoid segregations of very coarse-grained plagioclase and poikilitic augite set within otherwise uniform, unbanded and homogeneous gabbro. These segregations consistently strike parallel to the chamber wall and dip towards the contact. The shape, size, grain-size and mineralogy of the segregations change systematically away from the intrusion wall. They become bigger, chemically more evolved and more irregular in shape with increasing distance from the intrusion’s margins, and thus with stratigraphic position. We suggest that the Wavy Pyroxene Rock represents tearing of the poorly-consolidated crystal mush, during localised sagging of the vertical mush zone. Small, regularly spaced and shaped, tears formed in the thinner, more rapidly chilled, outer parts of the MBS, while larger irregular tears occurred in the inner, highly porous and poorly consolidated regions. Once the tears had formed, interstitial liquid moved into the space, crystallising as relatively evolved coarse-grained segregations. We use mineral chemistry to estimate the porosity when tearing

  10. Rejuvenation of shallow-crustal silicic magma bodies at Augustine and Hayes volcanoes, Alaska

    NASA Astrophysics Data System (ADS)

    Coombs, M. L.; Vazquez, J. A.; Hayden, L. A.; Calvert, A. T.; Lidzbarski, M. I.; Andersen, N. L.; Till, C. B.

    2015-12-01

    Rejuvenation of crystal-rich magma bodies leading to eruption can occur on a variety of scales and in varied tectonic settings. Two examples from the Aleutian arc highlight 1) segregation of silicic melt from an intermediate mush, and 2) "defrosting" of a shallowly emplaced intrusion. Augustine Volcano erupted a late Pleistocene rhyolite pumice fall that we link through zircon geochronology to cumulate dioritic blocks, ripped from Augustine's shallow magmatic plumbing system and ejected during the 2006 eruption. Unpolished zircon rims from the rhyolite yield a U-Th age of ~25 ka, and interiors yield a dominant age population of ~26 ka. Zircons from diorites have interior ages and compositions indistinguishable from those of the rhyolite. The diorites, rhyolite, and early Holocene dacites define whole-rock linear unmixing trends consistent with melt (rhyolite) extraction from a mush (dacites), leaving behind a cumulate residue (diorites). A volatile-rich basalt erupted just prior to the rhyolite likely facilitated melt extraction from the mush. The rhyolitic Hayes River ignimbrite, erupted from Hayes volcano, contains dense porphyry blocks that match pumices in composition and phenocryst content and are samples of a shallow intrusion. Autocrystic monazite accommodated up to several weight % Th and significantly affected the U-Th ratio of the magma during differentiation. An isochron for early melt and low-U monazites yields an age of ~67 ka, whereas one for late melt and high-U monazites yields ~42 ka. This younger age is indistinguishable from the laser single crystal Ar-Ar age for sanidine of 41±2 ka (1 sigma). We interpret the apparent ~25 k.y. crystallization interval to represent the assembly and differentiation timescale associated with the Hayes magma body. Sharp reverse zoning in sanidine from pumice (but not porphyry) records a thermal pulse not seen in the more slowly reacting phases, suggesting that a rejuvenation event occurred just prior to eruption.

  11. Chronological evidence that the Moon is either young or did not have a global magma ocean.

    PubMed

    Borg, Lars E; Connelly, James N; Boyet, Maud; Carlson, Richard W

    2011-08-17

    Chemical evolution of planetary bodies, ranging from asteroids to the large rocky planets, is thought to begin with differentiation through solidification of magma oceans many hundreds of kilometres in depth. The Earth's Moon is the archetypical example of this type of differentiation. Evidence for a lunar magma ocean is derived largely from the widespread distribution, compositional and mineralogical characteristics, and ancient ages inferred for the ferroan anorthosite (FAN) suite of lunar crustal rocks. The FANs are considered to be primary lunar flotation-cumulate crust that crystallized in the latter stages of magma ocean solidification. According to this theory, FANs represent the oldest lunar crustal rock type. Attempts to date this rock suite have yielded ambiguous results, however, because individual isochron measurements are typically incompatible with the geochemical make-up of the samples, and have not been confirmed by additional isotopic systems. By making improvements to the standard isotopic techniques, we report here the age of crystallization of FAN 60025 using the (207)Pb-(206)Pb, (147)Sm-(143)Nd and (146)Sm-(142)Nd isotopic systems to be 4,360 ± 3 million years. This extraordinarily young age requires that either the Moon solidified significantly later than most previous estimates or the long-held assumption that FANs are flotation cumulates of a primordial magma ocean is incorrect. If the latter is correct, then much of the lunar crust may have been produced by non-magma-ocean processes, such as serial magmatism.

  12. Large-scale diabase intrusion in the Durham Triassic Basin of North Carolina: geophysics and geochemistry

    SciTech Connect

    Bolich, R.E.; Bevis, M.G.; Won, I.J.; Fodor, R.V.

    1985-01-01

    Gravity and magnetic data obtained from the Durham Triassic Basin of North Carolina reveal pronounced positive gravity and magnetic anomalies of 10 milligals and 300 gammas, respectively, along the western border of the basin. In the vicinity of these anomalies, diabase outcrops, some with chilled margins and others with flow features, occur sporadically, but have a combined area of about 100 sq. km. Two-dimensional modeling of the gravity data indicates that the diabase body accounts for the gravity anomaly as a semi-continuous subsurface intrusion. The intrusive body is greater than 250 m thick near the western border of the basin, but thins to about 100 m near the center of the basin. Geochemical data for samples recovered from 4 air-drill sites at one diabase outcrop in Butner, North Carolina yield high MgO concentrations, and low FeO, K2O, and TiO2. The geophysical and geochemical data are consistent with an uncontaminated basaltic magma ascending along a major fissure or fissures and into the basin. In the basin, the diabase encountered unlithified sediments, resulting in both intrusive and extrusive forms. Although similar chemical compositions for Mesozoic North American dikes have been reported, this is the first indication of an intrusive body of such a large extent and primitive chemical composition.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  14. From seismic network optimization to real-time diagnosis of magma migration

    NASA Astrophysics Data System (ADS)

    Taisne, B.; Aoki, Y.

    2013-12-01

    Triggering mechanism of a seismic swarm has to be identified with great confidence in real time. Crisis response will not be the same whether magma is involved or not. The method based on the Seismic Amplitude Ratio Analysis enables a rapid and unambiguous diagnosis to detect migrating micro-seismicity. Combined with other measurements, this migrating seismicity could be linked to complex motions of magma within the volcanic edifice. The beauty of this method lies in the fact that the ratio of seismic energy recorded at different stations is independent of the seismic energy radiated at the source. Drastic changes in attenuation are unlikely to occur at the time scale of magma intrusion, therefore temporal evolutions in the measured ratio have to be explained by a change in the source location. Based on a simple assumption this technique can be used to assess the potential of existing monitoring seismic network to detect migrating events in real-time. It can also be used to design monitoring seismic network based on the available number of sensors as well as from field constraints. Network capability also depends on the noise level at each station, therefore this noise is used to define the magnitude threshold that can be detected as a function of the distance.

  15. Magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions

    NASA Astrophysics Data System (ADS)

    Dahren, Börje; Troll, Valentin R.; Andersson, Ulf B.; Chadwick, Jane P.; Gardner, Màiri F.; Jaxybulatov, Kairly; Koulakov, Ivan

    2012-04-01

    Understanding magma plumbing is essential for predicting the behaviour of explosive volcanoes. We investigate magma plumbing at the highly active Anak Krakatau volcano (Indonesia), situated on the rim of the 1883 Krakatau caldera by employing a suite of thermobarometric models. These include clinopyroxene-melt thermobarometry, plagioclase-melt thermobarometry, clinopyroxene composition barometry and olivine-melt thermometry. Petrological studies have previously identified shallow magma storage in the region of 2-8 km beneath Krakatau, while existing seismic evidence points towards mid- to deep-crustal storage zone(s), at 9 and 22 km, respectively. Our results show that clinopyroxene in Anak Krakatau lavas crystallized at a depth of 7-12 km, while plagioclase records both shallow crustal (3-7 km) and sub-Moho (23-28 km) levels of crystallization. These magma storage regions coincide with well-constrained major lithological boundaries in the crust, implying that magma ascent and storage at Anak Krakatau is strongly controlled by crustal properties. A tandem seismic tomography survey independently identified a separate upper crustal (<7 km) and a lower to mid-crustal magma storage region (>7 km). Both petrological and seismic methods are sensitive in detecting magma bodies in the crust, but suffer from various limitations. Combined geophysical and petrological surveys, in turn, offer increased potential for a comprehensive characterization of magma plumbing at active volcanic complexes.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  17. Floor-fractured craters in Mare Smythii and west of Oceanus Procellarum: Implications of Crater Modification by Viscous Relaxation and Igneous Intrusion Models

    NASA Astrophysics Data System (ADS)

    Wichman, R. W.; Schultz, P. H.

    Endogenic modification in lunar floor-fractured craters can constrain spatial variations in early lunar conditions. The nature of these constraints, however, depends on the assumed mechanism of crater modification. For viscous relaxation, the extent of crater modification depends on the surrounding crustal viscosity and thus provides loose constraints on the history of crustal heating within a region. For igneous intrusion models, the extent of crater modification reflects magmatically driven deformation and can be inverted to estimate both local magma pressure and intrusion depth. Both models indicate clear differences between regional conditions at Mare Smythii and in the highlands west of Oceanus Procellarum. The uniformly shallow