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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. 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.

  3. 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.

  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. Magma mingling in the panozero sanukitoid intrusion, baltic shield

    NASA Astrophysics Data System (ADS)

    Rollinson, H.

    2003-04-01

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

  6. 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.

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

    NASA Astrophysics Data System (ADS)

    Galland, Olivier

    2012-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Galland, O.

    2012-04-01

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

  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

    2016-01-01

    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

  10. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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.

  12. Relationships between volcano gravitational spreading and magma intrusion

    NASA Astrophysics Data System (ADS)

    Delcamp, Audray; van Wyk de Vries, Benjamin; James, Mike R.; Gailler, L. S.; Lebas, E.

    2012-04-01

    Volcano spreading, with its characteristic sector grabens, is caused by outward flow of weak substrata due to gravitational loading. This process is now known to affect many present-day edifices. A volcano intrusive complex can form an important component of an edifice and may induce deformation while it develops. Such intrusions are clearly observed in ancient eroded volcanoes, like the Scottish Palaeocene centres, or in geophysical studies such as in La Réunion, or inferred from large calderas, such as in Hawaii, the Canaries or Galapagos volcanoes. Volcano gravitational spreading and intrusive complex emplacement may act simultaneously within an edifice. We explore the coupling and interactions between these two processes. We use scaled analogue models, where an intrusive complex made of Golden syrup is emplaced within a granular model volcano based on a substratum of a ductile silicone layer overlain by a brittle granular layer. We model specifically the large intrusive complex growth and do not model small-scale and short-lived events, such as dyke intrusion, that develop above the intrusive complex. The models show that the intrusive complex develops in continual competition between upward bulging and lateral gravity spreading. The brittle substratum strongly controls the deformation style, the intrusion shape and also controls the balance between intrusive complex spreading and ductile layer-related gravitational spreading. In the models, intrusive complex emplacement and spreading produce similar structures to those formed during volcano gravitational spreading alone (i.e. grabens, folds, en échelon fractures). Therefore, simple analysis of fault geometry and fault kinetic indicators is not sufficient to distinguish gravitational from intrusive complex spreading, except when the intrusive complex is eccentric from the volcano centre. However, the displacement fields obtained for (1) a solely gravitational spreading volcano and for (2) a gravitational

  13. Mushy magma processes in the Tuolumne intrusive complex, Sierra Nevada, California

    NASA Astrophysics Data System (ADS)

    Memeti, V.; Paterson, S. R.

    2012-12-01

    Debates continue on the nature of volcanic-plutonic connections and the mechanisms of derivation of large volcanic eruptions, which require large volumes of magma to be readily available within a short period of time. Our focus to understand these magma plumbing systems has been to study the nature of their mid-to upper crustal sections, such as the 1,000 km2, 95-85 Ma old Tuolumne intrusive complex in the Sierra Nevada, California, USA. The Tuolumne intrusive complex is a great example where the magma mush model nicely explains observations derived from several datasets. These data suggest that a magma mush body was present and may have been quite extensive especially at times when the Tuolumne intrusive complex was undergoing waxing periods of magmatism (increased magma input), which alternated with waning periods of magmatism (decreased magma addition) and thus a smaller mush body, essentially mimicking in style periodic flare-ups and lulls at the arc scale. During waxing stages, magma erosion and mixing were the dominant processes, whereas waning stages allowed mush domains to continue to undergo fractional crystallization creating additional compositional variations. Over time, the imprint left behind by previous waxing and waning stages was partly overprinted, but individual crystals successfully recorded the compositions of these earlier magmas. Waxing periods in the Tuolumne intrusive complex during which large magma mush bodies formed are supported by the following evidence: 1) Hybrid units and gradational contacts are commonly present between major Tuolumne units. 2) CA-TIMS U/Pb zircon geochronology data demonstrate that antecrystic zircon recycling took place unidirectional from the oldest, marginal unit toward the younger, interior parts of the intrusion, where increasing zircon age spread encompasses the entire age range of the Tuolumne. 3) The younger, interior units also show an increasing scatter and complexity in geochemical element and isotope

  14. Sequence of magma emplacement and sulfide saturation in the Gaojiacun-Lengshuiqing intrusive complex (SW China)

    NASA Astrophysics Data System (ADS)

    Munteanu, Marian; Wilson, Allan H.; Yao, Yong; Chunnett, Gordon; Luo, Yaonan

    2010-08-01

    The Lengshuiqing area contains several small intrusions made up of peridotite ± quartz diorite ± granite spatially associated with the Gaojiacun pluton (gabbroids + peridotite + diorite). Ni-Cu sulfide ore occur at Lengshuiqing, hosted in peridotite. SHRIMP U-Pb zircon dating produced the ages of 803 ± 4.2 Ma (peridotite), 807 ± 2.6 Ma (oikocrystic hornblende gabbro), 809 ± 4.3 Ma (hornblende gabbronorites) for the Gaojiacun pluton and 807 ± 3.8 Ma (diorite, intrusion I), 817 ± 6.3 Ma (quartz diorite, intrusion II) and 817 ± 5 Ma (peridotite, intrusion 101) for Lengshuiqing. These ages suggest the emplacement of the Gaojiacun pluton later than the intrusions from Lengshuiqing. The olivine from Lengshuiqing does not contain sulfide inclusions and is relatively Ni-rich (1,150-1,550 ppm Ni), suggesting its crystallisation before the sulfide saturation that generated the Ni-Cu deposits. The olivine of the gabbros in the Gaojiacun pluton is Ni-poor (250-800 ppm), which indicates crystallisation from a severely metal-depleted magma after a sulfide saturation event. The olivine in the peridotites from the Gaojiacun pluton has 800-1,150 ppm Ni and contains sulfide inclusions. Moreover, geological evidence suggests the genesis of the peridotites from Gaojiacun in conduits that were ascending through the gabbroids. A sequence of at least three stages of magma emplacement is proposed: (1) Lengshuiqing; (2) gabbroids from Gaojiacun; (3) peridotites from Gaojiacun. Given the age differences, the intrusions at Lengshuiqing and the Gaojiacun pluton might have been produced by different magmatic events.

  15. 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.

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

    NASA Astrophysics Data System (ADS)

    Annen, C.

    2007-12-01

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

  17. 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

  18. Dykes, cups, saucers and sills: Analogue experiments on magma intrusion into brittle rocks

    NASA Astrophysics Data System (ADS)

    Mathieu, L.; van Wyk de Vries, B.; Holohan, Eoghan P.; Troll, Valentin R.

    2008-07-01

    Magma is transported in the crust by blade-like intrusions such as dykes, sills, saucers, and also collects in thicker laccoliths, lopoliths and plutons. Recently, the importance and great number of shallow (< 5 km) saucer-shaped intrusions has been recognized. Lopoliths and cup-shaped intrusions have also been reported in many geological contexts. Our field observations indicate that many intrusions, especially those emplaced into breccias or fractured rocks, have bulging, lobate margins and have shear faults at their bulbous terminations. Such features suggest that magma can propagate along a self-induced shear fault rather than a hydraulic tension-fracture. To investigate this we use analogue models to explore intrusion propagation in a brittle country rock. The models consist of the injection of analogue magma (honey or Golden syrup) in a granular material (sand or sieved ignimbrite) that is a good analogue for brittle or brecciated rocks. These models have the advantage (over other models that use gelatin) to well represent the properties of brittle materials by allowing both shear-faults and tension fractures to be produced at suitable stresses. In our experiments we mainly obtain vertical dykes and inverted-cone like structures that we call cup-shaped intrusions. Dykes bifurcate into cup-shaped intrusions at depths depending on their viscosity. All cup-shaped intrusions uplift a central block. By injecting against a vertical glass plate we obtain detailed observations of the intrusion propagation style. We observe that dykes commonly split and produce cup-shaped intrusions near the surface and that shear zone-related intrusions develop at the dyke tip. We conclude that many dykes propagate as a viscous indenter resulting from shear failure of host rock rather than tensional hydraulic fracturing of host rocks. The shear propagation model provides an explanation for the shape and formation of cup-shaped intrusions, saucer-sills and lopoliths.

  19. Lateral magma flow in sill-complexes: towards a paradigm shift in volcanology

    NASA Astrophysics Data System (ADS)

    Magee, C.; Muirhead, J.; Karvelas, A.; Holford, S. P.; Jackson, C. A. L.; Bastow, I. D.; Schofield, N.; Stevenson, C.; McLean, C.; McCarthy, W.; Shtukert, O.

    2015-12-01

    The structure of magma plumbing systems controls the distribution of volcanism, thereby influencing continental break-up and passive margin evolution. However, delimiting the structure of entire plumbing systems is difficult because: (1) intrusion networks cannot be directly accessed at active volcanoes; (2) field outcrops are limited by exposure; and (3) the resolution of geophysical data imaging the sub-surface is restricted. As a result, models involving the vertical transfer of magma in dikes, which extend from a melt source to overlying reservoirs and eruption sites, dominate the volcanic literature. Whilst there is evidence supporting the existence of vertically stacked plumbing systems, we compile a series of field- and seismic reflection-based case studies documenting the importance of extensive lateral magma transport (up to 4100 km) within sill-complexes. Most of these sill-complexes are emplaced into sediment-filled rift basins (e.g., Rockall Basin, NE Atlantic; Ceduna Sub-basin, offshore southern Australia; Karoo Basin, South Africa). There is also evidence that some sill-complexes occur within crystalline, continental crust (e.g., in the Yilgarn Craton, Australia). The case studies presented demonstrate that sill-complex emplacement is largely controlled by host rock lithology and structure. Sill intrusion is accommodated through roof uplift or, alternatively, via non-brittle processes (e.g., porosity reduction induced by host rock fluidization) that may not deform the overburden. The full or partial accommodation of magma by space-making mechanisms other than roof uplift means that intruding magma volumes may be underestimated by or completely hidden from ground deformation analyses. We show that plumbing systems need not be vertically stacked. Magma can instead be transported within laterally extensive (up to 3 × 106 km2) sill-complexes, promoting the development of volcanoes that do not overlie the melt source.

  20. 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

  1. 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.

  2. 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.

  3. Segment linkage in Afar via magma intrusion: the birth of a transform fault?

    NASA Astrophysics Data System (ADS)

    Aronovitz, A. C.; Ebinger, C. J.; Campbell, E.; Keir, D. B.; Ayele, A.; Mitra, G.

    2007-12-01

    Both continental and oceanic rifts are segmented along their length, but the relation between transfer faults and transform faults linking segments remains unclear. How and when do transform faults initiate to link rift segments? Does magma intrusion achieve some of the strain transfer between segments? A temporary seismic array in the volcanically and seismically active Afar rift of Ethiopia provides insights into these two fundamental questions. We analyze the spatial and temporal patterns of earthquakes, and compare these to patterns in high-resolution satellite imagery and space geodetic data from the ongoing seismo-volcanic episode that began in 2005. We integrate these results to understand how stresses are transferred between ridge segments and how this possibly relates to the initiation of transform faults. Earthquake swarms from October 2005 to March 2006 form narrow bands coinciding with NW-SE striking fault zones linking the active Erta' Ale and Tat `Ale magmatic rift segments, and the Dabbahu and Alayta magmatic segments. Step over distances are ~15 km and ~20 km respectively. The time and spatial distribution of these seismic events as well as the correlation of events with magmatic centers suggests that earthquakes are triggered by magma intrusion. These patterns offer insight to magma accommodation along faults and between rift segments, suggesting magma intrusion facilitates transform fault initiation. We compare and contrast active structures during the 2005- 2006 episode with segment linkage patterns preserved in the rock record to understand transform evolution.

  4. Remobilization of silicic intrusion by mafic magmas during the 2010 Eyjafjallajökull eruption

    NASA Astrophysics Data System (ADS)

    Sigmarsson, O.; Vlastelic, I.; Andreasen, R.; Bindeman, I.; Devidal, J.-L.; Moune, S.; Keiding, J. K.; Larsen, G.; Höskuldsson, A.; Thordarson, Th.

    2011-12-01

    Injection of basaltic magmas into silicic crustal holding chambers and subsequent magma mingling or mixing is a process that has been recognised since the late seventies as resulting in explosive eruptions. Detailed reconstruction and assessment of the mixing process caused by such intrusion is now possible because of the exceptional time-sequence sample suite available from the tephra fallout of the 2010 summit eruption at Eyjafjallajökull volcano in South Iceland. Fallout from 14 to 19 April contains three glass types of basaltic, intermediate, and silicic compositions recording rapid magma mingling without homogenisation, involving evolved FeTi-basalt and silicic melt with composition identical to that produced by the 1821-1823 AD Eyjafjallajökull summit eruption. The time-dependent change in the magma composition suggests a binary mixing process with changing end-member compositions and proportions. Beginning of May, a new injection of primitive basalt was recorded by deep seismicity, appearance of Mg-rich olivine phenocrysts together with high sulphur dioxide output and presence of sulphide crystals. Thus, the composition of the basaltic injection became more magnesian and hotter with time provoking changes in the silicic mixing end-member from pre-existing melt to the solid carapace of the magma chamber. Finally, decreasing proportions of the mafic end-member with time in the erupted mixed-magma demonstrate that injections of Mg-rich basalt was the motor of the 2010 Eyjafjallajökull explosive eruption, and that its decreasing inflow terminated the eruption. Significant quantity of silicic magma is thus still present in the interior of the volcano. Our results show that detailed sampling during the entire eruption was essential for deciphering the complex magmatic processes at play, i.e. the dynamics of the magma mingling and mixing. Finally, the rapid compositional changes in the eruptive products suggest that magma mingling occurs on a timescale of a few

  5. 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

  6. Origin of postcollisional intrusions in NW Anatolia, Turkey: Implications for magma chamber processes

    NASA Astrophysics Data System (ADS)

    Aysal, Namık

    2013-04-01

    Post-collisional magmatic activities of NW Anatolia are represented by a series of granitic intrusions and volcanic successions in the Biga Peninsula, NW Turkey. These plutonic rocks have distinct textures, chemical compositions and Sr-Nd isotope characteristics. They consist of coarse grained, equigranular and/or hypidiomorphic textured granite, gronodiorite, monzogranite, quartz-monzonite, pyroxene-monzonite and leucocratic alkali feldspar granites. These intrusions are composed of quartz, K-feldspar, plagioclase, hornblende, pyroxene and biotite. However, leucocratic facies rocks contain tourmaline with minor amount of mafic minerals. Accessory phases are represented by zircon, apatite, monozite, magnetite, sphene and rarely allanite. ASI values of the plutonic rocks vary between 0.7 and 1.24. These intrusive rocks are therefore classified as metaluminous-peraluminous with I-type affinity. K2O contents show that the intrusive rock samples show calc-alkaline, high K-calc-alkaline and shoshonitic character. Initial 87Sr/86Sr(t) (0.69980-0.70835), 143Nd/144Nd(t) (0.51238-0.51247) isotope ratios and negative ɛNd(t) (-4.4 - -2.6) values imply that these intrusive rocks could have been derived from enriched mantle sources. N-MORB normalized spidergrams of NW Anatolian plutonic rocks display enrichments in large ion lithophile elements (LILE), light rare earth elements (LREE) and depletion in high field strength elements (HFSE) indicating hydrous melting of a mantle wedge in a subduction zone and/or enrichment of the mantle source with an inherited subduction component from an ancient arc magmatism. Chondrite-normalized Rare Earth Element spidergrams are indicative of the importance of plagioclase and amphibole fractionation. On tectonic discrimination diagrams, all granite samples fall into the volcanic arc granite, syn and post-collisional granite fields. The geochemical data also indicate that a number of magma chamber processes involving magma mixing, fractional

  7. Diabasic intrusion and lavas, segregation veins, and magma differentiation at Kahoolawe volcano, Hawaii

    NASA Astrophysics Data System (ADS)

    Fodor, R. V.; Bauer, G. R.

    2014-04-01

    A mafic sill-like intrusion, ~5 × 30 m, exposed along the eastern shoreline of Kahoolawe Island, Hawaii, represents tholeiitic magma emplaced as diabase among caldera-filling lavas. It differentiated from ~7.8 wt.% MgO to yield low-MgO (2.9 wt.%) vesicular segregation veins. We examined the intrusion for whole-rock and mineral compositions for comparison to Kahoolawe caldera-fill lavas (some also diabasic), to the Uwekahuna laccolith (Kilauea), and to gabbros, diabases, and segregations and oozes of other tholeiitic shield volcanoes (e.g., Mauna Loa and Kilauea lava lakes). We also evaluate this extreme differentiation in terms of MELTS modeling, using parameters appropriate for Hawaiian crystallization environments. Kahoolawe intrusion diabase samples have major and trace element abundances and plagioclase, pyroxene, and olivine compositions in agreement with those in gabbros and diabases of other volcanoes. However, the intrusion samples are at the low-MgO end of the large MgO range formed by the collective comparative samples, as many of those have between 8 and 20 wt.% MgO. The intrusion's segregation vein has SiO2 53.4 wt.%, TiO2 3.2 wt.%, FeO 13.5 wt.%, Zr 350 ppm, and La 16 ppm. It plots in compositional fields formed by other Hawaiian segregations and oozes that have MgO <5 wt.%—fields that show large variances, such as factor of ~2 differences for incompatible element abundances accompanying SiO2 from ~49 to 59 wt.%. Our MELTS modeling assesses the Kahoolawe intrusion as differentiating from ~8 wt.% MgO parent magma beginning along oxygen buffers equivalent to FMQ and FMQ-2, having magmatic H2O of 0.15 and 0.7 wt.% (plus traces of CO2 and S), and under 100 and 500 bars pressure. Within these parameters, MELTS calculates that <3 wt.% MgO occurs at ~1,086 to 1,060 °C after ~48 to 63 % crystallization, whereby the lesser crystallization percentages and lower temperatures equate to higher magmatic H2O, leading to high SiO2, ~56-58 wt.%. To contrast

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

    NASA Astrophysics Data System (ADS)

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

    1996-12-01

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

  9. 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.

  10. The magmatic plumbing of the submarine Hachijo NW volcanic chain, Hachijojima, Japan: long distance lateral magma transport?

    NASA Astrophysics Data System (ADS)

    Ishizuka, O.; Geshi, N.; Itoh, J.; Kawanabe, Y.; Tsujino, T.

    2005-12-01

    Recent geophysical observations on basaltic composite volcanoes in Izu-Bonin arc reveal the process of long distance lateral magma transport within the shallow middle crust. Such intrusion events sometimes caused flank fissure eruption and also triggered a formation of collapsed caldera (Miyakejima 2000). To clarify a long-distance magma transport system of the basaltic composite volcano in volcanic arc from geological and petrological aspects, we investigated a submarine volcanic chain (Hachijo NW chain) nested Hachijo Nishiyama volcano, a frontal composite volcano in the northern Izu arc. The volcanic chain extends 15 km from Hachijo-Nishiyama volcano and is composed of ridges and many small cones with basal diameters generally less than 2km. Dredge sampling recovered basaltic lavas and spatters. A diving survey using a ROV (Hyper Dolphin) revealed pillow lava flows on steep slopes and accumulation of spatters and agglutinates near the eruption center. Basalts from the Hachijo NW chain generally have more primitive composition (up to nearly 7% of MgO) compared to the basaltic rocks from the Nishiyama. The bulk magma composition of Hachijo NW chain is controlled by fractionation of clinopyroxene, olivine and plagioclase while plagioclase accumulation was indicated by aluminum-rich character of the Nishiyama volcano and its subaerial satellite cones. Trace element ratios unaffected by melting or crystal fractionation (e.g., Nb/Zr) are not significantly different between the Nishiyama and the Hachijo NW chain. This implies that the sources of magma for these volcanic systems are basically identical. However, ratios affected by melting process are significantly different between the two. Hachijo NW chain shows lower LREE/HREE and Zr/Y, implying difference in degree of partial melting of the source. Other possible processes for producing these differences in trace element characteristics include crustal assimilation. These results obtained so far appear to

  11. 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

  12. 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. PMID:16902133

  13. Magma storage and plumbing of adakite-type post-ophiolite intrusions in the Sabzevar ophiolitic zone, NE Iran

    NASA Astrophysics Data System (ADS)

    Jamshidi, K.; Ghasemi, H.; Troll, V. R.; Sadeghian, M.; Dahren, B.

    2014-08-01

    Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous-Paleocene Sabzevar ophiolite zone, NE Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium models, including amphibole thermobarometry, plagioclase-melt thermobarometry and clinopyroxene-melt barometry. Based on the results of these thermobarometric models, plagioclase crystallized dominantly at pressures of ~ 350 (468-130) MPa, while amphiboles record both low pressures (~ 300 MPa) and very high pressures (> 700 MPa) of crystallization. The latter is supported by the calculated pressures for clinopyroxene crystallization (550 to 730 MPa). The association of amphibole with clinopyroxene and no plagioclase in the most primitive samples (Mg-andesites) is consistent with amphibole fractionation from very hydrous magmas at deep crustal levels of the plumbing system, which may have been a key process to intensify adakite-type affinities in this rock suite. Barometry, combined with frequent disequilibrium features, such as oscillatory-zoned and sieve-textured plagioclase crystals with An-rich overgrowths in more evolved samples, imply final magma differentiation occurred in an open upper crustal magma system that developed progressively stronger compositional modifications during high-level magma storage.

  14. Magma storage and plumbing of adakite-type post-ophiolite intrusions in the Sabzevar ophiolitic zone, northeast Iran

    NASA Astrophysics Data System (ADS)

    Jamshidi, K.; Ghasemi, H.; Troll, V. R.; Sadeghian, M.; Dahren, B.

    2015-01-01

    Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous-Paleocene Sabzevar ophiolite zone, northeast Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium models, including amphibole thermobarometry, plagioclase-melt thermobarometry and clinopyroxene-melt barometry. Based on the results of these thermobarometric models, plagioclase crystallized dominantly at pressures of ~350 (130 to 468) MPa, while amphiboles record both low pressures (~300 MPa) and very high pressures (>700 MPa) of crystallization. The latter is supported by the calculated pressures for clinopyroxene crystallization (550 to 730 MPa). The association of amphibole with clinopyroxene and no plagioclase in the most primitive samples (Mg-andesites) is consistent with amphibole fractionation from very hydrous magmas at deep crustal levels of the plumbing system, which may have been a key process in intensifying adakite-type affinities in this rock suite. Barometry, combined with frequent disequilibrium features such as oscillatory-zoned and sieve-textured plagioclase crystals with An-rich overgrowths in more evolved samples, implies that final magma differentiation occurred in an open upper crustal magma system that developed progressively stronger compositional modifications during high-level magma storage.

  15. 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.

  16. Melilitolite intrusion and pelite digestion by high temperature kamafugitic magma at Colle Fabbri, Spoleto, Italy

    NASA Astrophysics Data System (ADS)

    Stoppa, Francesco; Sharygin, Victor V.

    2009-10-01

    A subvolcanic body in Colle Fabbri (Umbria, Central Italy) intrudes sedimentary rocks and the overlaying extrusive breccia. The intrusive rock is melilitolite with essential leucite, kalsilite, and wollastonite plus accessory Ti-garnet, Ti-Al-Fe 3+-clinopyroxene, magnetite, perovskite, rankinite, Si-bearing apatite, Fe-Ni sulphides, and carbonate/zeolite. Bulk chemistry of melilitolite indicates a strong SiO 2-undersaturation, extremely high CaO composition, and strong initial potassic character. Sr and Nd isotopic ratios support a link with the source of kamafugites and carbonatites found in the same region. The igneous contact rock contains variable amounts of quenched clinopyroxene, anorthite, sanidine ± wollastonite, plus spinel and glass. Extremely high temperature melilitolite magma digested pelite country-rock, thus leading to a unique mineral composition. The homogenisation temperatures of mineral inclusions in contact rock demonstrate that crystallisation occurred well above 1230 °C. A large thermal aureole formed in a local clinker-like breccia, characterised by the association of felsic glass + indialite + tridymite ± Ti-magnetite, confirms high-temperature emplacement. Metasomatic/thermometamorphic phenomena favoured zone-specific mineralisation of hydrated Ca-silicates, hydrated complex sulphates and zeolites in breccias and encasing rocks.

  17. 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

  18. Seismic Evidences of Magma Intrusion At Intermediate Depth Before The July-august 2001 Mt. Etna (italy) Eruption

    NASA Astrophysics Data System (ADS)

    Privitera, E.; Alparone, S.; D'Amico, S.; Gambino, S.; Maiolino, V.; Spampinato, S.; Zuccarello, L.

    Several authors investigated the seismic behavior before Mt. Etna eruptions and some models were proposed in order to explain peculiar features of seismicity preceding flank eruptions. In particular, stress and strain fields seemed to modify their orienta- tion due to the action of magma overpressure. Recently, about 40 additional seismic stations boosted the Mt. Etna permanent network and enabled us to study in great de- tail the seismicity that occurred before the July-August 2001 eruption. More than 2600 earthquakes occurred over about 8 months prior to the seismic swarm that heralded the lateral eruption and they pointed out a change in the dynamic condition acting on the volcano starting from November 5, 2000. Seismicity in the November 2000 - June 2001 period was characterised by the occurrence of several relevant seismic swarms. The epicentres of events were spread over a wide area covering mostly the southern and eastern parts of the volcano and delineated two main alignments. A NNW-SSE epicentres alignment built up gradually and was composed of earthquakes occurred both clustered and sparsely in time. A clear NE-SW alignment was also defined mainly by the occurrence of a 4 days swarm. A peculiar feature of the earthquakes' spatial pattern was the depth distribution. Under the eastern part of the volcano seismicity was confined in the depth range 1 - 6 km b.s.l., in the western part hypocentres were distributed in two volumes under 5 km and upper 2 km b.s.l., respectively. This pat- tern defined two volumes affected by few earthquakes. These volumes correspond to crust portions where magma reservoirs were located by previous studies. On the basis of a fault plane solutions analysis, we observed relevant rotation of maximum compressive axis at very short distance, indicating a local stress source elongated in NNW-SSE direction at about 5 - 6 km depth under the summit craters. Analyses on the space distribution of b value outlined that the NNW-SSE epicentres

  19. 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

  20. Sheared sheet intrusions as mechanism for lateral flank displacement on basaltic volcanoes: Applications to Réunion Island volcanoes

    NASA Astrophysics Data System (ADS)

    Cayol, V.; Catry, T.; Michon, L.; Chaput, M.; Famin, V.; Bodart, O.; Froger, J.-L.; Romagnoli, C.

    2014-10-01

    Field work carried out on the Piton des Neiges volcano (Réunion Island) suggests that the injection of magma along detachments could trigger flank failure by conjugate opening and shear displacement. We use 3-D numerical models to compare the ability of purely opened sheet intrusions, sheared sheet intrusions, and normal faults to induce flank displacement on basaltic volcanoes. We assume that shear stress change on fractures results from stress anisotropy of the host rock under gravity. Exploring a large range of stress anisotropies, fracture dips, and fracture depth over length ratios, we determine that the amount of shear displacement is independent of the proximity to the ground surface. Sheared sheet intrusions are the most efficient slip medium on volcanoes. Consequently, the largest flank displacement is induced by the longest, deepest sheared intrusion dipping closest to 45° in a host rock with the highest stress anisotropy. Using our model in a forward way, we provide shear and normal displacements for buried fractures. Applying the model to a pile of sills at the Piton des Neiges volcano, we determine that the mean shear displacement caused by each intrusion was 3.7 m, leading to a total of a 180-260 m of lateral displacement for the 50 m high pile of sills. Using our model in an inverse way, we formulate a decision tree to determine some fracture characteristics and the host rock stress anisotropy from ratios of maximum surface displacements. This procedure provides a priori models, which can be used to bound the parameter space before it is explored through a formal inversion. Applying the decision tree to the 1.4 m coeruptive flank displacement recorded at Piton de la Fournaise in 2007, we find that it probably originated from a shallow eastward dipping subhorizontal normal fault.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  2. 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

  3. Sheared sheet intrusions as a mechanism for lateral flank displacement on basaltic volcanoes: Applications to Réunion Island volcanoes

    NASA Astrophysics Data System (ADS)

    Cayol, V.; Catry, T.; Michon, L.; Chaput, M.; Famin, V.; Bodart, O.; Froger, J. L.; Romagnoli, C.

    2014-12-01

    Field work carried out on the Piton des Neiges volcano (Réunion Island) suggests that the injection of magma along detachments could trigger flank failure by conjugate opening and shear displacement [Famin and Michon, 2010]. We use 3D numerical models to compare the ability of purely opened sheet intrusions, sheared sheet intrusions, and normal faults to induce flank displacement on basaltic volcanoes (Figure). We assume that shear stress change on fractures which are not normal to a principal stress results from stress anisotropy of the host rock under gravity. Exploring a large range of stress anisotropies, fracture dips, and fracture depth over length ratios, we determine that the amount of shear displacement is independent of the proximity to the ground surface. Sheared sheet intrusions are the most efficient slip medium on volcanoes. Using our model in a forward way, we provide shear and normal displacements for buried fractures. Applying the model to a pile of sills at the Piton des Neiges volcano, we determine that the mean shear displacement caused by each intrusion was 3.7 m, leading to a total of a 180-260 m of lateral displacement for the 50 m high pile of sills. Using our model in an inverse way, we formulate a decision tree to determine some fracture characteristics and the host rock stress anisotropy from ratios of maximum surface displacements. This procedure provides a priori models, thus limits to the parameter space which can be further explored through a formal inversion. Applying this procedure to the 1.4 m co-eruptive flank displacement recorded at Piton de la Fournaise in 2007, we find that it probably originated from a shallow eastward-dipping sub-horizontal normal fault.

  4. 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).

  5. 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.

  6. 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

  7. Multiple magma evolution and ore-forming processes of the Hongge layered intrusion, SW China: Insights from Sr-Nd isotopes, trace elements and platinum-group elements

    NASA Astrophysics Data System (ADS)

    Liao, Mingyang; Tao, Yan; Song, Xieyan; Li, Yubang; Xiong, Feng

    2015-12-01

    The Hongge layered intrusion (259 Ma), which is located in the inner zone of the Emeishan large igneous province (ELIP), is one of the most typical Fe-Ti-V ore deposits in the Pan-Xi area. Mafic-ultramafic layered intrusions of the ELIP have attracted a lot of attention lately because these intrusions host world class Fe-Ti-V oxide deposits plus interesting Cu-Ni-(PGE) mineralization which may have economic potential. This paper, reports new whole-rock major and trace element compositions, PGE abundances and Sr-Nd isotopic data for selected cumulate rocks and basalts. We use these data to investigate the nature of parental magmas and the controls on its evolution from the source mantle en route to the surface involving the Hongge ore-bearing intrusion. Two abrupt changes in Mt/Ilm and trace element ratios such as Ba/Th with depths in the Hongge layered intrusion indicate that this intrusion formed by at least two pluses of relatively primitive magma. The whole rock Sr-Nd isotopic data of basaltic and intrusive rocks plot in the region of Emeishan low-Ti basalts and the compositions of residual liquid (at ∼1260 °C and 1155 °C) calculated by MELTS are similar to our actual high-Ti (BFQ-2) and low-Ti (BC-1) basltic samples, indicate they are co-magmatic rather than derivation from a distinct source. Total PGE abundances in the Hongge samples are extremely low, ranging from 0.5 to 10 ppb. Sulfide-bearing rocks in the Hongge intrusion and the nearby coeval Banfangqing and Baicao basalts have similar mantle-like Pd/Pt ratios (2-6) and extremely high Cu/Pd ratios (3 × 104 to 4 × 105), indicating that sulfide segregation took place at depth prior to emplacement at Hongge and eruption in this region. Sulfide saturation in the Hongge magma may have resulted from such crustal contamination event. Crystallization of silicate minerals under the anhydrous magma, magma hydration plus Fe-Ti enrichments in the parental magma are three critical factors for the formation of Fe

  8. 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. PMID:27418515

  9. 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.

  10. 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

  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. Time-space focused intrusion of genetically unrelated arc magmas in the early Paleozoic Ross-Delamerian Orogen (Morozumi Range, Antarctica)

    NASA Astrophysics Data System (ADS)

    Rocchi, S.; Di Vincenzo, G.; Dini, A.; Petrelli, M.; Vezzoni, S.

    2015-09-01

    The growth of continental crust in accretionary orogenic belts takes place through repeated cycles of subduction-accretion of rock units from continental and oceanic magmatic arcs, supra-subduction zone backarcs and forearcs loaded with continent-derived materials. An ancient example relevant to magmatic arc accretion models is represented by the remnants of the Cambrian-Ordovician Ross Orogen in the Morozumi Range, Victoria Land (Antarctica). There, late Neoproterozoic phyllites host an intrusive complex which preserves a remarkably uncommon record of genetically unrelated magma pulses emplaced under a variable stress regime in a short time span: (1) a dominant K-feldspar-phyric granite, (2) fine-grained dioritic stocks and dykes, (3) a peraluminous granite; and (4) a tonalitic-granodioritic dyke swarm. Laserprobe U-Pb zircon dates cluster at late Cambrian times for all these units, yet they carry differential cargoes of relict cores. Unique geochemical-isotopic signatures for both the less evolved magmas (diorite and dyke tonalite) and the most acidic ones (granite and peraluminous granite) indicate that each one of them originated from distinct sources at depth. Additionally, field relationships and chemical evolutionary trends testify for a variety of shallow level open-system processes, such as magma mingling/mixing between diorite and main granite magmas, as well as progressive incorporation of the host schists by the dyke tonalite magma. In summary, crustal growth in the Morozumi intrusive complex was contributed by fresh mantle magma issuing from the metasomatised mantle wedge, while the production of other melts did recycle different crustal portions/layers: the main granite derived from Grenville-age granulitic lower crust; the peraluminous granite from late Proterozoic upper crust, and the tonalite magmas derived from subduction erosion-enriched subarc mantle and evolved by ingestion of local metasedimentary rocks. Overall, the Morozumi intrusive complex

  14. Development of a 3D numerical model to evaluate the Stromboli NW flank instability in relation to magma intrusion

    NASA Astrophysics Data System (ADS)

    Apuani, T.; Merri, A.

    2009-04-01

    A stress-strain analysis of the Stromboli volcano was performed using a three-dimensional explicit finite difference numerical code (FLAC 3D, ITASCA, 2005), to evaluate the effects associated to the presence of magma pressure in magmatic conduit and to foresee the evolution of the magmatic feeding complex. The simulations considered both the ordinary state for the Stromboli, characterized by a partial fill of the active dyke with regular emission of gas and lava fountains and the paroxysmal conditions observed during the March 2007's eruptive crisis, with the magma level in the active dyke reaching the topographic surface along the Sciara del Fuoco depression. The modeling contributes to identify the most probable directions of propagation of new dikes, and the effects of their propagation on the stability of the volcano edifice. The numerical model extends 6 x 6 x 2.6 km3, with a mesh resolution of 100 m, adjusting the grid to fit the shape of the object to be modeled. An elasto-plastic constitutive law was adopted and an homogeneous Mohr-Coulomb strength criterion was chosen for the volcanic cone, assuming one lithotechnical unit (alternation of lava and breccia layers "lava-breccia unit"- Apuani et al 2005). The dykes are represented as discontinuities of the grid, and are modeled by means of interfaces. The magmatic pressure is imposed to the model as normal pressure applied on both sides of the interfaces. The magmastatic pressure was calculated as Pm=d•h, where d is the magma unit weight assumed equal to 25 KN/m3, and h (m) is the height of the magma column. Values of overpressure between 0 and 1 MPa were added to simulate the paroxysmal eruption. The simulation was implemented in successive stages, assuming the results of the previous stages as condition for the next one. A progressive propagation of the dike was simulated, in accordance with the stress conditions identified step by step, and in accordance with the evidences detected by in situ survey, and

  15. 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

  16. 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.

  17. 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

  18. 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

  19. Sedimentation in Magma Chambers: Evidence From the Geochemistry, Microstructure and Crystallography of Troctolite and Gabbro Cumulates, Rum Layered Intrusion, Scotland.

    NASA Astrophysics Data System (ADS)

    Lo Ré, F. C.; Cheadle, M. J.; Swapp, S. M.; Coogan, L. A.

    2003-12-01

    The formation of igneous cumulates remains poorly understood. In particular, petrologists disagree about the relative importance of crystal accumulation by sedimentation or in-situ growth, partly because post-cumulus processes often overprint evidence for the primary mechanism. We address this problem with a detailed geochemical, microstructural and crystallographic study of gabbros and troctolites from the Eastern Layered Series of the Rum Layered Intrusion, NW Scotland. We collected samples, approximately every 50cm, through the complete 11m sequence of foliated gabbros and troctolites from Unit 9. The samples were quantitatively analyzed for crystal shape and size, shape preferred orientation (SPO), crystallographic preferred orientation (CPO), modal mineralogy, and whole rock and mineral chemistry. We present the following results: Within cumulate layers just cm's apart, olivine crystal shape can vary from sub-equant to tabular, and crystal diameter can vary from 1-8mm. This suggests at least one olivine population was derived elsewhere in the magma chamber. Complex anorthite zoning is also consistent with an extended history of plagioclase crystal transport. A one-crystal thick olivine layer between feldspathic layers of differing grain size is interpreted to be a lag deposit. Two possible examples of cross bedding also exist. Taken together, these observations suggest sedimentation was the primary method of crystal accumulation. The data also provide constraints on post-cumulus processes. Complex plagioclase zoning suggests that processes of viscous compaction and/or recrystallization were not extensive. The preservation of magmatic and deformation twins and absence of a polygonal fabric support this conclusion. In addition, the CPO and SPO are the same. Lacking evidence for compaction and recrystallization lead us to believe similar CPO and SPO are the preserved artifact of a sedimentary foliation. Therefore, we conclude the gabbros and troctolites of Unit 9

  20. Petrogenetic connections between volcanic rocks and intrusive suites in the California arc - toward an integrated model for upper-crustal magma system evolution

    NASA Astrophysics Data System (ADS)

    Barth, A. P.; Riggs, N.; Walker, J. D.; Andrew, J.; Jacobson, C. E.; Miller, D. M.; Robert, J.

    2014-12-01

    Volcanic and clastic sedimentary rocks in deeply eroded, predominantly plutonic arcs provide records of arc development and the links between volcanic and plutonic processes. We are analyzing existing and new geochronologic and petrologic data from volcanic breccias, ignimbrites and intrusive suites in the Sierra Nevada and Mojave Desert sectors of the Mesozoic California arc, in an effort to construct an integrated volcano-plutonic model for silicic magmatism in arc upper crust. SIMS and TIMS U-Pb zircon ages, immobile element abundances in whole rocks, and trace element abundances in zircons allow us to interpret the magmatic heritage of ignimbrites and components of underlying granodioritic to granitic intrusive suites. Preliminary results suggest several conclusions: (1) first-order magma production was episodic, with plutonic, forearc and retro-arc detrital zircons defining three magmatic pulses of ~40-60 m.y. duration that are largely mimicked by the more limited record of zircons in ignimbrites; (2) in the Triassic and Jurassic, second-order pulses on 2-10 m.y. time scales are recorded in both the intrusive and ignimbrite records, suggesting that eruption of ignimbrites was synchronous at the shortest resolvable time scales with assembly of underlying incrementally emplaced intrusive suites; (3) ignimbrites range from dacite to rhyolite in bulk composition, and are petrographically similar to modern "monotonous intermediate" dacite or phenocryst-poor low-silica rhyolite; (4) these tuffs are as fractionated as intrusive rocks, and commonly, though not always, contain zircons with similarly complex, multi-stage growth histories. Thus ignimbrites and felsic granodiorites in this arc are complementary elements recording lengthy and episodic evolutionary histories in cool and hydrous upper-crustal arc magma systems.

  1. 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

  2. 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. PMID:26057584

  3. Interaction between felsic and mafic magmas in the Salmas intrusive complex, Northwestern Iran: Constraints from petrography and geochemistry

    NASA Astrophysics Data System (ADS)

    Ghaffari, Mitra; Rashidnejad-Omran, Nematollah; Dabiri, Rahim; Santos, José Francisco; Mata, João; Buchs, David; McDonald, Iain; Appel, Peter; Garbe-Schönberg, Dieter

    2015-11-01

    The Salmas plutonic complex, in the northernmost part of Sanandaj-Sirjan Zone of Iran, provides evidence for magma interaction processes. The complex contains mafic-intermediate, hybrid and felsic rocks which intruded into the Paleozoic metamorphic complex. They show typical relationships described in many mafic-felsic mingling and mixing zones worldwide, such as mafic microgranular enclaves (in felsic and hybrid rocks), mafic sheets, and hybrid rocks. The mafic microgranular enclaves (MMEs) are characterized by fine-grained, equigranular and hypidiomorphic texture and some special types of microscopic textures, e.g., quartz xenocrysts, oscillatory-zoned plagioclase, small lath-shaped plagioclase in large plagioclase, spike zones in plagioclase and spongy-cellular plagioclase textures, rounded plagioclase megacrysts blade-shaped biotite, acicular apatite. The mafic sheets and MMEs in granites (MME-Gr), which indicated magma mingling structures, show ISr values and εNd(i) similar to diorites. The hybrid rocks and their mafic enclaves (MME-H) show isotope signatures similar to each other. Granites have isotope signatures [higher 87Sr/86Sr(i) (0.70788-0.71075) and lower εNd(i) (-2.4 to -4.2)] distinct to those of the all rock types and MMEs. Major, trace and REE modeling show that hybrid rocks are generated via 40-60% mixing of mafic (dioritic) and felsic (granitic) end-members. All the geochemical data suggest that underplating of dioritic magma, which has been produced by fractional crystallization of gabbros, under the lower crust caused its melting to make felsic (granitic) magma. Injection of dioritic magma into the base of the felsic magma chamber and a limited mixing of two end-members, the lower crust-derived magma and mantle-derived melts, formed hybrid magma and their enclaves. Injections of new mafic magma pulses into hybrid magma generated mafic enclaves into them. The injections of denser dioritic magma pulses into a felsic magma chamber and spreading

  4. 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

    2001-01-01

    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. PMID:11343114

  5. The Cretaceous Duimiangou adakite-like intrusion from the Chifeng region, northern North China Craton: Crustal contamination of basaltic magma in an intracontinental extensional environment

    NASA Astrophysics Data System (ADS)

    Fu, Lebing; Wei, Junhao; Kusky, Timothy M.; Chen, Huayong; Tan, Jun; Li, Yanjun; Shi, Wenjie; Chen, Chong; Zhao, Shaoqing

    2012-03-01

    Zircon U-Pb ages, major and trace element and Sr, Nd and Pb isotope compositions of the Duimiangou (DMG) quartz monzonite from the Chifeng region on the northern North China Craton (NCC) were studied to investigate its derivation, evolution and geodynamic significance. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating yields an emplacement age of 128 ± 1 Ma for this intrusion, with numerous Mesozoic inherited zircons clustering at 219 ± 12 Ma and 161 ± 3 Ma, along with some ancient zircons with ages of 2.5 Ga, 1.77 Ga and 324 Ma. Bulk-rock analyses show that this intrusion is characterized by variable SiO2 (63.4-69.4 wt.%), Al2O3 (14.5-16.3 wt.%), Na2O + K2O (8.01-8.95 wt.%), and Mg# (41.3-48.0). They are enriched in large ion lithophile elements and light rare earth elements without significant Eu anomalies (mostly between 0.89-1.10), and depleted in heavy rare earth elements and high field strength elements, with high Sr/Y (63.7-101.7) and (La/Yb)N (20.5-31.0) ratios. The DMG intrusion formed in an intracontinental extensional setting contemporaneous with the formation of pull-apart basins, metamorphic core complexes and intense magmatism, rather than in a convergent margin. It has homogeneous Sr ((87Sr/86Sr)i = 0.7059-0.7066), Nd (εNd(t) = - 6.2 to - 7.2) and Pb ((206Pb/204Pb)i = 17.289-17.375, (207Pb/204Pb)i = 15.359-15.463, (208Pb/204Pb)i = 37.130-37.472) isotope compositions. Sr-Nd isotope modeling results, plus relatively young Nd model ages (1522-1618 Ma) and the presence of relict zircons, suggest that this intrusion could have originated from crustal contamination of newly formed basaltic melts derived from asthenospheric mantle, accompanied by fractional crystallization of K-feldspar, biotite, apatite, Fe-Ti oxides and minor hornblende and plagioclase. Thus, the DMG adakite-like intrusion may record the magmatic event associated with underplating of asthenospheric magma in an intracontinental extensional

  6. Crustal melting and magma mixing in a continental arc setting: Evidence from the Yaloman intrusive complex in the Gorny Altai terrane, Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Chen, Ming; Sun, Min; Buslov, Mikhail M.; Cai, Keda; Zhao, Guochun; Kulikova, Anna V.; Rubanova, Elena S.

    2016-05-01

    Granitoids and their hosted mafic enclaves may retain important information on crust-mantle interaction, and thus are significant for study of crustal growth and differentiation. An integrated petrological, geochronological and geochemical study on the granitoid plutons of the Yaloman intrusive complex from the Gorny Altai terrane, northwestern Central Asian Orogenic Belt, was conducted to determine their source nature, petrogenesis and geodynamics. Mafic enclaves are common in the plutons, and a zircon U-Pb age (389 Ma ± 4 Ma) indicates that they are coeval with their granitoid hosts (ca. 393-387 Ma). Petrographic observations reveal that these mafic enclaves probably represent magmatic globules commingled with their host magmas. The relatively low SiO2 contents (46.0-60.7 wt.%) and high Mg# (38.9-56.5) further suggest that mantle-derived mafic melts served as a crucial component in the formation of these mafic enclaves. The granitoid hosts, including quartz diorites and granodiorites, are I-type in origin, possessing higher SiO2 contents (60.2-69.9 wt.%) and lower Mg# (32.0-44.2). Their zircon Hf and whole-rock Nd isotopic compositions indicate that the magmas were dominated by remelting of Neoproterozoic (0.79-1.07 Ga) crustal materials. Meanwhile, the geochemical modeling, together with the common occurrence of igneous mafic enclaves and the observation of reversely zoned plagioclases, suggests that magma mixing possibly contributed significantly to the geochemical variation of the granitoid hosts. Our results imply that mafic magmas from the mantle not only provided substantial heat to melt the lower crust, but also mixed with the crust-derived melts to form the diverse granitoids. The oxidizing and water-enriched properties inferred from the mineral assemblages and compositions imply that the granitoid plutons of the Yaloman intrusive complex were possibly formed in a continental arc-related setting, which is also supported by their geochemistry. The

  7. 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

  8. A Chill Sequence to the Bushveld Complex - Insight into the First Stages of Emplacement and the Parental Magmas to the World's Largest Layered Intrusion

    NASA Astrophysics Data System (ADS)

    Wilson, A.

    2012-04-01

    Evidence of the initial stages of magma emplacement in large mafic chambers is commonly lacking because of resorption of early-formed chills and complicated by the fact that the first magmas that entered the chamber were usually more evolved than the true parental magma. Deep drilling has revealed a rare occurrence of a chill sequence from the eastern Bushveld Complex at the base of a previously unrecognized thick succession of ultramafic rocks that forms part of the Lower Zone. The chill sequence (1.8 m thick) includes a true chill against quartzite floor rock, crystalline quench textured and orthopyroxene spinifex textured rocks. Importantly the chill composition represents a relatively evolved magma formed by the separation of high-Mg olivines prior to its emplacement, probably in a conduit or a pre-chamber. An overlying pyroxene dunite represents the extract that gave rise to the chill and was emplaced either as a crystal slurry derived from the feeder conduit or as the crystallization product from a slightly later influx of primitive magma of komatiitic composition. This highly-Mg rich pyroxene dunite most likely acted as a barrier to the thermal erosion of the chill sequence as the chamber filled. The olivine in the pyroxene dunite layer is the most primitive yet recorded for the Bushveld Complex at Mg# 0.915, and the cores of associated orthopyroxene are Mg# 0.93. Compositions of the orthopyroxene in the quench and spinifex textured units range from Mg# 0.91 to 0.72 and preserve cores close to the original liquidus as well as tracking the complete in-situ solidification process. Olivine contains abundant dendritic exsolution structures of Cr-spinel and Al-rich clinopyroxene indicating that they formed at high temperature from incorporation of Ca, Al and Cr into olivine, with little time to equilibrate before emplacement. Chromite in the section is the most primitive yet recorded for the Bushveld Complex. The komatiite magma that was initially emplaced into

  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. Dynamic model of intrusion of magma and/or magmatic fluids in the large-scale deformation source of the Campi Flegrei caldera (Italy).

    NASA Astrophysics Data System (ADS)

    Crescentini, Luca; Amoruso, Antonella; Luongo, Annamaria

    2015-04-01

    The Campi Flegrei (CF) caldera is located in a densely populated area close to Naples (Southern Italy). It is renowned as a site of continual slow vertical movements. After the last eruption in 1538, the caldera generally subsided until 1969 when minor uplift occurred. In the early 1970s this uplift became significant (~1.5 m max). A further large uplift episode occurred from 1982 to 1984 (~1.8 m max), and subsequently smaller uplift episodes have occurred since then. Amoruso et al. (2014a,b) have recently shown that the CF surface deformation field from 1980 to 2013 can be decomposed into two stationary parts. Large-scale deformation can be explained by a quasi-horizontal source, oriented NW to SE and mathematically represented by a pressurized finite triaxial ellipsoid (PTE) ~4 km deep, possibly related to the injection of magma and/or magmatic fluids from a deeper magma chamber into a sill, or pressurization of interconnected (micro)cavities. Residual deformation not accounted for by PTE is confined to the Solfatara fumarolic area and can be mathematically explained by a small (point) pressurized oblate spheroid (PS) ~2 km below the Solfatara fumarolic field, that has been equated with a poroelastic response of the substratum to pore pressure increases near the injection point of hot magmatic fluids into the hydrothermal system. A satisfying feature of this double source model is that the geometric source parameters of each are constant over the period 1980-2013 with the exception of volume changes (potencies). Several papers have ascribed CF deformation to the injection of magmatic fluids at the base of the hydrothermal system. All models predict complex spatial and temporal evolution of the deformation pattern and consequently contrast with the observed deformation pattern stationarity. Also recently proposed dynamic models of sill intrusion in a shallow volcanic environment do not satisfy the observed CF deformation pattern stationarity. We have developed an

  11. 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.

  12. 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.

  13. Lateral variation of H2O/K2O ratios in Quaternary Magma of the Northeastern Japan arc

    NASA Astrophysics Data System (ADS)

    Miyagi, I.

    2012-12-01

    Water plays a fundamental role in the magma genesis beneath subduction zones. In order to estimate a spatial distribution of the density of water flux in the wedge mantle of the Northeastern Japan arc, this study examines a lateral variation of pre-eruptive bulk rock H2O/K2O contents among volcanoes located both in the frontal and in back arc settings. The analytical targets are the frontal volcanoes Nigorikawa (N42.12 E140.45), Zenikame (N41.74 E140.85), Adachi (N38.22 E140.65), and Nanashigure (N40.07 E141.11), and the back arc ones Hijiori (N38.61 E140.17) and Kanpu (N39.93 E139.88). The bulk magmatic H2O content (TH2O) is calculated from a mass balance of hydrogen isotopic ratios among three phases in a batch of magma; dissolved water in melt, excess H2O vapor, and hydrous phenocrysts such as amphiboles (Miyagi and Matsubaya, 2003). Since the amount of H2O in hydrous phenocryst is negligible, the bulk magmatic H2O content can be written as TH2O = (30 XD CD) / (15 - dT + dMW), where dMW is the measured hydrogen isotopic ratio of hydrous phenocrysts, XD is a melt fraction of magma, CD is a water concentration of the melt, and dT is hydrogen isotopic ratios of a bulk magma (assumed to be -50 per-mil). Both XD and CD are estimated from bulk rock chemistry of the sample using the MELTS program (Ghiorso and Sack, 1995). Hydrogen isotopic fractionation factors are assumed to be -15 and -30 per-mil for vapor and hydrous mineral, and vapor and silicate melt, respectively. There observed a clear difference among the H2O/K2O ratios of bulk magmas from the frontal and back arc volcanoes. For instance higher H2O/K2O wt ratios was observed in the frontal volcanoes (Nigorikawa 5.3, Zenikame 11-12, Adachi 8-10, and Nanashigure 4-18), while lower H2O/K2O wt ratios was observed in the back arc ones (Kanpu 0-2.5 and Hijiori 1.4). The lateral variation of H2O/K2O ratios infer the higher water flux through the frontal side of wedge mantle, which can be a potential cause of the

  14. Granite intrusion by externally induced growth and deformation of the magma reservoir, the example of the Plasenzuela pluton, Spain

    NASA Astrophysics Data System (ADS)

    Castro, Antonio; Fernández, Carlos

    1998-09-01

    The Plasenzuela pluton in the Central Extremadura batholith in the southern Iberian Massif, is an example of permissive emplacement in relation to the tectonic development of extensional fractures in the upper continental crust. Paradoxically, this pluton has a concordant structural pattern which is classically attributed to diapirism or ballooning. This pattern consists of the following elements: (a) nearly elliptical shape in the horizontal section; (b) conformity of the pre-existing aureole structures to the shape of the pluton contacts; and (c) development of a crenulation cleavage, parallel to the contacts, in the vicinity of the pluton walls. All these features have been interpreted in many plutons as resulting from the pushing-aside of the country rock structures due to the expansion of the pluton. However, the detailed structural relationships in the aureole do not favour a forceful emplacement mechanism. By contrast, these relationships constitute prime evidence of permissive intrusion in extensional fractures. According to this interpretation, the concordant shape of the pluton was acquired by syn-plutonic opening of a mixed tensional-shear fracture, parallel to the main foliation in the host rocks, and by folding of the fracture walls together with the previous anisotropy of the country rocks. This is a growth-deformation process that can operate at local conditions in the upper continental crust giving rise to concordant syn-tectonic plutons.

  15. Construction of an Upper Crustal Reservoir by Lateral Magma Propagation: New insights from Geochronological Data of La Gloria Pluton, Central Chile

    NASA Astrophysics Data System (ADS)

    Gutiérrez, F. J.; Guillong, M.; Payacán, I. J.; Aravena, A.; Bachmann, O.; Parada, M. A.

    2014-12-01

    La Gloria Pluton (LGP) is a 10 Ma shallow elongated NNW reservoir of 17 km length and 4-6 km width as part of a NS trend of Miocene plutons in Central Chile. New LA-ICPMS U-Pb ages in zircons of La Gloria Pluton indicate that crystallization occurs mostly within an interval between 11.2 to 10 Ma, with southeastward decreasing ages. Zircon crystallization ages are consistently older at the boundaries of the pluton than at the center for a given cross-section. At regional scale the ages of LGP follows a plutonic trend of southward decreasing age: Estero Yerba Loca (10 Ma) and San Francisco Batholith (SFB), in the north; and Cerro Mesón Alto (12.5 Ma) and San Gabriel (SG; 13 Ma), in the south. Both regional and local (within-LGP) age trends suggest: 1) a progressive northward migration of the main deep magmatic source during the Miocene; and 2) a southeastward lateral propagation of the magma during the reservoir construction. The lateral propagation of the magma is also supported by subhorizontal mineral and magnetic lineations with a preferred NNW orientation within LGP. The within-pluton age distribution and internal configuration suggest incremental construction with horizontal propagation of magma within channels. Because the lateral migration of the magma play an important role on the thermal structure of the cooling pluton we perform numerical simulations that account for reheating caused by refilling along the axial core of the pluton . We speculate that pre-existing shallow crustal structures (faults and folds) would allow lateral magma canalization, particularly between the lower highly deformed volcanic Abanico Fm. and the less deformed overlaying volcanic Farellones Fm. The pluton distribution and internal organization in and around LGP suggest incremental construction with vertical and horizontal migration of magma within channels and reservoirs, yielding plutonic complexes with protracted ages and elongated geometries.

  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. Quantification of the Intrusion Process at Kïlauea Volcano, Hawai'I

    NASA Astrophysics Data System (ADS)

    Wright, T. L.; Marsh, B. D.

    2014-12-01

    Knowing the time between initial intrusion and later eruption of a given volume of differentiated magma is key to evaluating the connections among magma transport and emplacement, solidification and differentiation, and melt extraction and eruption. Cooling rates for two Kïlauea lava lakes as well as known parent composition and residence times for intrusions that resulted in fractionated lavas later erupted on the East Rift Zone in 1955 (34 years) and 1977 (22 years) allow intrusion dimensions to be calculated. We model intrusions beneath Kïlauea's East Rift Zone near their point of separation from the magma transport path at ~ 5 km depth using Jaeger's (1957) method calibrated against Alae and Makaopuhi lava lakes with wallrock temperatures above the curie point at 450-550°C. Minimum thicknesses of 50-70 meters are found for intrusions that fed the two fractionated lavas, as well as for long-lived magma bodies identified from geodetic monitoring during many East Rift eruptions. These intrusions began as dikes, but probably became sills or laccolithic bodies that remained near the transport path. Short-lived intrusions also arrested near the magma transport path, but that retain a dike geometry, are hypothesized to serve as a trigger for the small but discrete increments of seaward movement on Kïlauea's south flank that characterize slow-slip earthquakes. Two additional thoughts arise from the quantitative modeling of magma cooling. First, long-term heating of the wallrock surrounding the horizontal East Rift Zone transport path slows the rate of cooling within the conduit, possibly contributing to the longevity of the East Rift eruption that began in 1983. Second, the combined effects of heating of the wall rock and ever-increasing magma supply rate from the mantle may have forced breakdown and widening of the vertical transport conduit, which could explain the 5-15-km deep long-period earthquake swarms beneath Kīlauea's summit between 1987 and 1992.

  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, 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.

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

    NASA Astrophysics Data System (ADS)

    Sigmarsson, Olgeir

    2015-04-01

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

  20. 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

  1. Late Triassic intrusive complex in the Jidong region, Jiamusi-Khanka Block, NE China: Geochemistry, zircon U-Pb ages, Lu-Hf isotopes, and implications for magma mingling and mixing

    NASA Astrophysics Data System (ADS)

    Yang, Hao; Ge, Wen-chun; Zhao, Guo-chun; Dong, Yu; Xu, Wen-liang; Ji, Zheng; Yu, Jie-jiang

    2015-05-01

    Whole-rock major and trace element geochemistry together with zircon U-Pb ages and Lu-Hf isotope compositions are reported for a Late Triassic intrusive complex in the Jidong region, Jiamusi-Khanka Block, NE China. Zircon U-Pb dating yields ages between 211 and 208 Ma for enclaves of microgranular diorite and quartz diorite, and between 211 and 209 Ma for the host granitoids. These ages correlate with a previously established intensive Late Triassic magmatic event along the eastern Asian margin. Field observations, together with petrographic features, geochemistry, and zircon Hf isotope data, preclude simple crystal fractionation or restite unmixing as a genetic link for the various rock types within the intrusive complex. The syenogranite suite has high SiO2 (75.5-76.3 wt.%) and low MgO (0.15-0.19 wt.%), and yields enriched LILE and LREE patterns. Most of the zircons in the syenogranites have two-stage model ages of 766 and 1461 Ma, together with positive εHf(t) values of + 0.6 to + 9.1. These results indicate that the granitoid magmas were generated by partial melting of Meso- to Neoproterozoic lower crust. The gabbro suite has a restricted range of SiO2 (46.1-51.9 wt.%) together with high Mg# values (49-70) and high concentrations of Ni, Co, and Cr. Zircons from two diorite samples have single-stage Hf model ages of 557-787 Ma and εHf(t) values of + 1.9 to + 8.3 that are consistent with the coeval gabbros previously studied in the Jidong region. These features, together with the observation that all the gabbros are enriched in LREE and LILE, suggest that the mafic magmas were derived from melting of depleted Neoproterozoic lithospheric mantle that had been metasomatized by slab-derived fluids. It is concluded that the dominant igneous suites within the Late Triassic intrusive complex formed by mingling/mixing of felsic and mafic magmas. The geochemical data, combined with regional geological investigations, indicate that the Late Triassic intrusive complex

  2. 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

  3. 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

  4. 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.

  5. 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

  6. 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.

  7. Magma mixing in the genesis of the Kalatongke dioritic intrusion: Implications for the tectonic switch from subduction to post-collision, Chinese Altay, NW China

    NASA Astrophysics Data System (ADS)

    Gao, Jian-Feng; Zhou, Mei-Fu

    2013-03-01

    The Kalatongke complex, located in south Chinese Altay of the Central Asian Orogenic Belt (CAOB), consists of the ~ 308 Ma dioritic suite intruded by the 287 Ma noritic suite. The noritic suite is composed of olivine norite and hornblende norite and hosts sulfide mineralization. The dioritic suite is composed of ferrodiorite, diorite and quartz diorite. Ferrodiorites have 43.6 to 51.8 wt.% SiO2, 8.2 to 12.1 wt.% Fe2O3T, 2.87 to 4.86 wt.% MgO, with Mg# ranging from 42 to 53. They have highly variable Al2O3 (17.4-20.7 wt.%), Na2O (2.78-4.50%), K2O (0.58-3.70%), Sr (280-1300 ppm) and Ba (219-3100 ppm). Diorites and quartz diorites have 15.2-19.6 wt.% Al2O3, 239-890 ppm Sr and170-1100 ppm Ba, 11.2-25.5 ppm Y and1.2-2.2 ppm Yb. All rocks have LREE enriched REE patterns and do not display Eu anomalies. They have primitive mantle-normalized trace element patterns enriched in large ion lithosphile elements (LILE) (e.g. Ba and Sr) and depleted in Ti, Nb and Ta. Both ferrodiorites and diorites have relatively constant initial 87Sr/86Sr ratios of 0.7037 to 0.7040 but highly variable ɛNd(t) values of + 4.5 to + 11.6, whereas quartz diorites have higher initial 87Sr/86Sr ratios (0.7056) and lower ɛNd(t) values (+ 0.5). Plagioclase from ferrodiorites, diorites and quartz diorites has similar initial 87Sr/86Sr ratios of 0.7015 to 0.7055. The dioritic suite formed from a mixed magma of an evolved mantle-derived basaltic magma by partial melting of subduction-modified mantle source in response to slab breakoff and a crustal-derived granitic magma at ~ 308 Ma. Before mixing with granitic magmas, basaltic magmas underwent fractional crystallization of olivine to form ferrodiorite. The mixed magma also formed diorite and quartz diorite combining fractionation clinopyroxene, amphibole and plagioclase. The noritic suite formed from a mantle-derived high-Mg magma in a post-collisional environment. Both the dioritic and noritic suites in Kalatongke suggest the switch from subduction to

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  9. 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., Jr.

    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.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

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

    NASA Astrophysics Data System (ADS)

    Gardine, Matt; West, Michael; Werner, Cynthia; Doukas, Michael

    2011-03-01

    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 SO 2 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 5 km depth beneath Fourpeaked, which remained active over several months as this magma equilibrated into the crust. By early 2007 declining seismicity and SO 2 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.

  16. Experimental modelling of thin-skinned shortening around magmatic intrusions

    NASA Astrophysics Data System (ADS)

    Merle, Olivier; Vendeville, Bruno

    1995-03-01

    Magmatic intrusions can trigger thin-skinned compression of the adjacent sedimentary cover by three processes: (a) gravity gliding away from the topographic dome resulting from the ascending magma; (b) fluid push from the rear resulting from forceful intrusion then lateral spreading of the magma; and (c) increased loading by volcanic accumulation. The applicability of the first two mechanisms, gravity gliding and fluid push, was tested using dynamically scaled experiments. Model results help to elucidate the kinematics and structural evolution of thrusts and folds formed by such processes and determine which geological parameters control the deformation style. The results show that the presence of a weak layer within the sedimentary overburden is essential to form thrust and fold belts around the intrusion. Experiments suggest that although gravity gliding can dominate the early stages of deformation, most of the deformation is caused by lateral spreading of the fluid magma pushing the adjacent sedimentary rocks. Models also suggest that true laccoliths can form only if the sedimentary section comprises a basal low-viscosity stratum. Comparison with natural examples allows the evaluation of the applicability of experimental results.

  17. Post-Emplacement Behaviour of Magma Reservoirs

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  18. 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.

  19. 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.

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

    PubMed

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

    2016-01-01

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

  1. 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

  2. Source mechanism of a very-long-period event at Mt Ontake, central Japan: Response of a hydrothermal system to magma intrusion beneath the summit

    NASA Astrophysics Data System (ADS)

    Nakamichi, Haruhisa; Kumagai, Hiroyuki; Nakano, Masaru; Okubo, Makoto; Kimata, Fumiaki; Ito, Yoshihiro; Obara, Kazushige

    2009-11-01

    A very-long-period (VLP) volcanic event, which occurred on 25 January 2007 beneath Mt Ontake, central Japan, was recorded by nearby broadband seismometers as well as the Japanese nationwide Hi-net and F-net seismic networks. The VLP waveforms show a pulse-like shape with a duration of approximately 1 min. The VLP event was accompanied by a burst sequence of long-period (LP) events. We carried out waveform inversion to determine the source mechanism and location of the VLP event. Our analysis indicates volumetric changes in an inclined crack (seismic moment of 10 14 Nm) at the VLP source, which is located at 0.6 km above sea level beneath the summit of Mt Ontake and above dikes determined from GPS data. The source-time functions of the VLP event showed a pulse-like triangular shape, indicating inflation followed by deflation of the crack at the source. We interpreted the result of the waveform inversion as follows. Gases released from the intruded magma heated an aquifer system beneath the summit of Mt Ontake. A break of unstable superheated water in a hydrothermal crack in the system caused vaporization of water and associated crack inflation, which was followed by discharge of steam from the crack resulting in its collapse. These processes caused the VLP event, which may have been a precursor of a small phreatic eruption that occurred in late March 2007.

  3. Differentiation and magma mixing on Kilauea's east rift zone: A further look at the eruptions of 1955 and 1960. Part II. The 1960 lavas

    USGS Publications Warehouse

    Wright, T.L.; Helz, R.T.

    1996-01-01

    New and detailed petrographic observations, mineral compositional data, and whole-rock vs glass compositional trends document magma mixing in lavas erupted from Kilauea's lower east rift zone in 1960. Evidence includes the occurrence of heterogeneous phenocryst assemblages, including resorbed and reversely zoned minerals in the lavas inferred to be hybrids. Calculations suggest that this mixing, which is shown to have taken place within magma reservoirs recharged at the end of the 1955 eruption, involved introduction of four different magmas. These magmas originated beneath Kilauea's summit and moved into the rift reservoirs beginning 10 days after the eruption began. We used microprobe analyses of glass to calculate temperatures of liquids erupted in 1955 and 1960. We then used the calculated proportions of stored and recharge components to estimate the temperature of the recharge components, and found those temperatures to be consistent with the temperature of the same magmas as they appeared at Kilauea's summit. Our studies reinforce conclusions reached in previous studies of Kilauea's magmatic plumbing. We infer that magma enters shallow storage beneath Kilauea's summit and also moves laterally into the fluid core of the East rift zone. During this process, if magmas of distinctive chemistry are present, they retain their chemical identity and the amount of cooling is comparable for magma transported either upward or laterally to eruption sites. Intrusions within a few kilometers of the surface cool and crystallize to produce fractionated magma. Magma mixing occurs both within bodies of previously fractionated magma and when new magma intersects a preexisting reservoir. Magma is otherwise prevented from mixing, either by wall-rock septa or by differing thermal and density characteristics of the successive magma batches.

  4. Evidence for a new shallow magma intrusion at La Soufrière of Guadeloupe (Lesser Antilles). Insights from long-term geochemical monitoring of halogen-rich hydrothermal fluids

    NASA Astrophysics Data System (ADS)

    Villemant, B.; Komorowski, J. C.; Dessert, C.; Michel, A.; Crispi, O.; Hammouya, G.; Beauducel, F.; De Chabalier, J. B.

    2014-09-01

    -1977 crisis. The contrasting behaviours of S- and Cl-bearing species in fumarolic gas and in thermal springs suggest that the current activity is the result of a new magma intrusion which was progressively emplaced at shallow depth since ~ 1992. Although it might still be evolving, the characteristics of this new intrusion indicate that it has already reached a magnitude similar to the intrusion that was emplaced during the 1976-1977 eruptive crisis. The assessment of potential hazards associated with evolution of the current unrest must consider the implications of recurrent intrusion and further pressurisation of the hydrothermal system on the likelihood of renewed phreatic explosive activity. Moreover, the role of hydrothermal pressurisation on the basal friction along low-strength layers within the upper part of the edifice must be evaluated with regards to partial flank collapse. At this stage enhanced monitoring, research, and data analysis are required to quantify the uncertainties related to future scenarios of renewed eruptive activity and magmatic evolution.

  5. Shallow intrusive directions of sheeted dikes in the Troodos ophiolite: Anisotropy of magnetic susceptibility and structural data

    SciTech Connect

    Staudigel, H.; Gee, J.; Tauxe, L. ); Varga, R.J. )

    1992-09-01

    Sheeted dikes play a central role in the formation of oceanic crust. It is commonly assumed that sheeted dikes intrude vertically upward, from elongated mid-ocean ridge (MOR) magma chambers, but there are no direct observational data bearing on this hypothesis. This assumption contrasts with the intrusive behavior of subaerial volcanoes where magmas rise into shallow central magma chambers that laterally feed vertically oriented dikes. The authors have studied intrusive directions of sheeted dikes in a structural analogue to oceanic crust, the Troodos ophiolite. Structural and magnetic fabric data of 65 dikes provide consistent results and suggest a broad distribution of shallow (< 20[degree]) to nearly vertical, upward magma-transport directions. These data suggest that horizontal emplacement has to be considered for sheeted dikes at MORs, implying more centralized MOR plumbing systems than previously thought. Such plumbing systems provide ample opportunity for complex mixing, fractionation, and contamination of MOR lavas in magma chambers and tabular magma-storage volumes. Whether the MOR magma supply is linear or centralized also has a fundamental effect on crustal accretion processes and the geometry of hydrothermal convection systems.

  6. Magma energy

    SciTech Connect

    Dunn, J.C.

    1987-01-01

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

  7. Magma Fragmentation

    NASA Astrophysics Data System (ADS)

    Gonnermann, Helge M.

    2015-05-01

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

  8. Mixing of rhyolite, trachyte and basalt magma erupted from a vertically and laterally zoned reservoir, composite flow P1, Gran Canaria

    NASA Astrophysics Data System (ADS)

    Freundt, Armin; Schmincke, Hans-Ulrich

    1992-10-01

    The 14.1 Ma composite welded ignimbrite P1 (45 km3 DRE) on Gran Canaria is compositionally zoned from a felsic lower part to a basaltic top. It is composed of four component magmas mixed in vertically varying proportions: (1) Na-rhyolite (10 km3) zoned from crystal-poor to highly phyric; (2) a continuously zoned, evolved trachyte to sodic trachyandesite magma group (6 km3); (3) a minor fraction of Na-poor trachyandesite (<1 km3); and (4) nearly aphyric basalt (26 km3) zoned from 4.3 to 5.2 wt% MgO. We distinguish three sites and phases of mixing: (a) Mutual mineral inclusions show that mixing between trachytic and rhyolitic magmas occurred during early stages of their intratelluric crystallization, providing evidence for long-term residence in a common reservoir prior to eruption. This first phase of mixing was retarded by increasing viscosity of the rhyolite magma upon massive anorthoclase precipitation and accumulation. (b) All component magmas probably erupted through a ring-fissure from a common upper-crustal reservoir into which the basalt intruded during eruption. The second phase of mixing occurred during simultaneous withdrawal of magmas from the chamber and ascent through the conduit. The overall withdrawal and mixing pattern evolved in response to pre-eruptive chamber zonation and density and viscosity relationships among the magmas. Minor sectorial variations around the caldera reflect both varying configurations at the conduit entrance and unsteady discharge. (c) During each eruptive pulse, fragmentation and particulate transport in the vent and as pyroclastic flows caused additional mixing by reducing the length scale of heterogeneities. Based on considerations of magma density changes during crystallization, magma temperature constraints, and the pattern of withdrawal during eruption, we propose that eruption tapped the P1 magma chamber during a transient state of concentric zonation, which had resulted from destruction of a formerly layered zonation

  9. Magma energy

    SciTech Connect

    Hardee, H.C.

    1985-01-01

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

  10. Variations in magma supply and magma partitioning: the role of tectonic settings

    NASA Astrophysics Data System (ADS)

    Takada, Akira

    1999-11-01

    Magma supply rates for 200 years at Krafla and Lakagigar, Iceland, and those for 150 years at Kilauea and Mauna Loa, Hawaii, are estimated roughly, based on their geophysical and geological observations. A diagram that relates erupted volumes to eruption intervals at volcanoes under various tectonic settings is represented. These results lead to a new model that a large volume (1-10 km 3) of magma is supplied intermittently at a long interval (10 2-10 4 years) beneath volcanoes in rift zones, while magma is supplied continuously with oscillations or fluctuations beneath intraplate volcanoes. Chemical data such as the MgO wt.% of lava may be one indicator in evaluating the magma supply rates of Hawaiian volcanoes. Systematic variation with time in magma partitioning within a volcano or to the surface is obtained in comparisons between among migration patterns of eruption sites, cumulative supplied volumes, and the volume ratios of erupted to supplied magma at Krafla and Kilauea. The variations suggest that a magma plumbing system may act under self-control (regulating) system through stress as one system. In response to a change in magma supply rate, the system partitions magma horizontally into dikes or vertically toward the surface. A large magma supply rate promotes the vertical extent of a crack to result in an eruption with a large volume ratio of erupted to supplied magma. This tendency is supported by field observations of flood basalts. The partitioned magma as dike intrusions suppresses magma supply partially in the shallow crust. Using analog experiments on liquid-filled cracks in gelatin, this paper demonstrates fundamental processes for magma partitioning on the effect of magma supply and stress change by the partitioned magma. A dynamical system of two differential equations on magma supply rate and stress around a magma plumbing system is proposed, to understand the qualitative variations in magma supply rate imposed by tectonic settings.

  11. 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

  12. Use of a Resin-Bonded Bridge to Replace a Congenitally Missing Lateral Incisor: Treatment of "Intrusion" of Teeth.

    PubMed

    Rosen, Paul S; Bahat, Oded; Froum, Stuart J; Daftary, Fereidoun; Rosenthal, Howard; Feldman, Sylvan

    2016-07-01

    Craniofacial growth is an important factor to consider when providing dental implant treatment for adolescents to replace missing teeth. Ongoing longitudinal observation has demonstrated that such tooth replacements may appear intruded over time, because there may be ongoing downward and anterior movement of both the alveolus and the teeth at a rate exceeding that of the dental implant, which acts like an ankylosed unit. This case reports on a 23.5-year-old female patient who, at age 16, had orthodontics completed and was left with a space where the maxillary right lateral incisor was congenitally missing with the hope of future restoration with a dental implant. A resin-bonded bridge had been placed to fill the space in the interim. After approximately 7.5 years, the bridge loosened and the patient sought an implant option as its replacement. Clinical images revealed that the bridge, which contained two bonded wings, may have limited physiologic growth, causing both the maxillary right central incisor and canine to appear intruded compared with the left central incisor and canine. This case illustrates, at the very least, that growth and development may not be complete in females aged 16 years and that the way in which a missing tooth is replaced must be carefully considered given the impact that ongoing growth and development may have on restorative care. Moreover, further growth and development may also impact adults. PMID:27548400

  13. 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.

  14. 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

  15. 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

  16. 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

  17. 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.

  18. Magma chambers

    NASA Technical Reports Server (NTRS)

    Marsh, Bruce D.

    1989-01-01

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

  19. 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.

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

    PubMed

    Richardson, Stephen H; Shirey, Steven B

    2008-06-12

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

  1. Zircon SHRIMP U Pb ages and in-situ Hf isotopic analysis for the Mesozoic intrusions in South Taihang, North China craton: Evidence for hybridization between mantle-derived magmas and crustal components

    NASA Astrophysics Data System (ADS)

    Chen, B.; Tian, W.; Jahn, B. M.; Chen, Z. C.

    2008-04-01

    The North China craton (NCC) was stabilized in Paleo-Proterozoic times, and the eastern part of it was remobilized in the Mesozoic, as is indicated by the presence of voluminous Mesozoic magmas in eastern NCC. In particular, the lithospheric mantle beneath eastern NCC was significantly thinned during the intense Mesozoic tectono-magmatic activity, which makes the NCC different from most other ancient cratons. The Mesozoic magmas may thus provide crucial evidence regarding the processes that transformed the NCC from craton to a tectonically active region. The South Taihang magmatic complex lies in the western part of the Mesozoic magmatic zone in the NCC. The complex falls into three main plutonic rocks: the Hongshan syenite, the Xishu gabbroic diorite-monzonite and the Wu'an monzonitic rocks. Zircon U-Pb dating reveals that the three plutonic rocks were emplaced contemporaneously at ˜ 132 Ma. In-situ Hf isotopic analyses for the dated zircons indicate that the Hongshan syenites show homogeneous ɛHf( t) values (- 10 to - 13) which are slightly lower than those (- 9.0) for the enriched subcontinental lithospheric mantle (SCLM), as revealed by zircons from mafic rocks that originated from melting of SCLM. This suggests that the parental magma to the syenites was likely derived from melting of the enriched SCLM and contaminated slightly by old lower continental crustal material during ascent. The Xishu and Wu'an gabbroic diorites to monzonitic rocks, however, show significantly varied Hf isotopic compositions, with ɛHf( t) = - 9.2 to - 16 and - 15.5 to - 24, respectively. The wide range of ɛHf( t) values for a single sample suggests that the Xishu and Wu'an plutons formed through a process of hybridization between enriched mantle-derived mafic magma and crustal components in variable proportions. This is supported by the textural and compositional disequilibrium of plagioclase phenocrysts from the two plutons. The Wu'an monzonitic rocks show lower ɛHf( t) values

  2. 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.

  3. Emplacement of magma in sedimentary basins

    NASA Astrophysics Data System (ADS)

    Malthe-Sorenssen, A.; Planke, S.

    2002-12-01

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

  4. 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.

  5. 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

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

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

    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

  7. Volcanic Eruption and Intrusion Processes on 4 Vesta: A Reappraisal

    NASA Astrophysics Data System (ADS)

    Keil, K.; Wilson, L.

    2012-03-01

    A new analysis supports our earlier predictions of sizes of lava flows and pyroclast deposits on Vesta, but argues against a magma ocean, instead suggesting eruptions were fed by magma from large sill-like intrusions at the base of the lithosphere.

  8. Magmatic intrusions in the lunar crust

    NASA Astrophysics Data System (ADS)

    Michaut, C.; Thorey, C.

    2015-10-01

    The lunar highlands are very old, with ages covering a timespan between 4.5 to 4.2 Gyr, and probably formed by flotation of light plagioclase minerals on top of the lunar magma ocean. The lunar crust provides thus an invaluable evidence of the geological and magmatic processes occurring in the first times of the terrestrial planets history. According to the last estimates from the GRAIL mission, the lunar primary crust is particularly light and relatively thick [1] This low-density crust acted as a barrier for the dense primary mantle melts. This is particularly evident in the fact that subsequent mare basalts erupted primarily within large impact basin: at least part of the crust must have been removed for the magma to reach the surface. However, the trajectory of the magma from the mantle to the surface is unknown. Using a model of magma emplacement below an elastic overlying layer with a flexural wavelength Λ, we characterize the surface deformations induced by the presence of shallow magmatic intrusions. We demonstrate that, depending on its size, the intrusion can show two different shapes: a bell shape when its radius is smaller than 4 times Λ or a flat top with small bended edges if its radius is larger than 4 times Λ[2]. These characteristic shapes for the intrusion result in characteristic deformations at the surface that also depend on the topography of the layer overlying the intrusion [3].Using this model we provide evidence of the presence of intrusions within the crust of the Moon as surface deformations in the form of low-slope lunar domes and floor-fractured craters. All these geological features have morphologies consistent with models of magma spreading at depth and deforming an overlying elastic layer. Further more,at floor-fractured craters, the deformation is contained within the crater interior, suggesting that the overpressure at the origin of magma ascent and intrusion was less than the pressure due to the weight of the crust removed by

  9. 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.

  10. Taxonomy Of Magma Mixing I: Magma Mixing Metrics And The Thermochemistry Of Magma Hybridization Illuminated With A Toy Model

    NASA Astrophysics Data System (ADS)

    Spera, F. J.; Bohrson, W. A.; Schmidt, J.

    2013-12-01

    The rock record preserves abundant evidence of magma mixing in the form of mafic enclaves and mixed pumice in volcanic eruptions, syn-plutonic mafic or silicic dikes and intrusive complexes, replenishment events recorded in cumulates from layered intrusions, and crystal scale heterogeneity in phenocrysts and cumulate minerals. These evidently show that magma mixing in conjunction with crystallization (perfect fractional or incremental batch) is a first-order petrogenetic process. Magma mixing (sensu lato) occurs across a spectrum of mixed states from magma mingling to complete blending. The degree of mixing is quantified (Oldenburg et al, 1989) using two measures: the statistics of the segregation length scales (scale of segregation, L*) and the spatial contrast in composition (C) relative to the mean C (intensity of segregation, I). Mingling of dissimilar magmas produces a heterogeneous mixture containing discrete regions of end member melts and populations of crystals with L* = finite and I > 0. When L*→∞ and I→0 , the mixing magmas become hybridized and can be studied thermodynamically. Such hybrid magma is a multiphase equilibrium mixture of homogeneous melt, unzoned crystals and possible bubbles of a supercritical fluid. Here, we use a toy model to elucidate the principles of magma hybridization in a binary system (components A and B with pure crystals of α or β phase) with simple thermodynamics to build an outcome taxonomy. This binary system is not unlike the system Anorthite-Diopside, the classic low-pressure model basalt system. In the toy model, there are seven parameters describing the phase equilibria (eutectic T and X, specific heat, melting T and fusion enthalpies of α and β crystals) and five variables describing the magma mixing conditions: end member bulk compositions, temperatures and fraction of resident magma (M) that blends with recharge (R) magma to form a single equilibrium hybrid magma. There are 24 possible initial states when M

  11. Magma Plumbing and Emplacement Mechanisms within Sedimentary Basins

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  12. The differentiation of the Skaergaard Intrusion

    NASA Astrophysics Data System (ADS)

    Hunter, R. H.; Sparks, R. S. J.

    1987-04-01

    Previous interpretations of the Skaergaard Intrusion suggested that differentiation involved extreme iron-enrichment but no silica-enrichment until a very late stage. This model is difficult to reconcile with petrological and geochemical evidence, with the behaviour of tholeiitic volcanic suites and with phase equilibria. We propose that the Skaergaard magma evolved on a trend of pronounced silica-enrichment after cumulus magnetite appeared at the top of the Lower Zone. At that stage, the magma was of ferrobasaltic composition with close to 50% SiO2. The Middle and Upper Zones of the intrusion dominantly represent crystal accumulation during differentiation from ferrobasalt through iron-rich basaltic andesite and icelandite to rhyolite, a fractionation sequence common in tholeiitic volcanic provinces. This interpretation requires re-appraisal of the physical processes responsible for the differentiation. In particular, residual liquids became lower in density with fractionation and would have caused the Skaergaard magma chamber to have become compositionally zoned.

  13. 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.

  14. Impact of Melt Segregation on Genesis of Intermediate and Silicic Magmas in Deep Crustal Hot Zones

    NASA Astrophysics Data System (ADS)

    Solano, J.; Jackson, M.; Sparks, R. S.; Blundy, J.

    2009-12-01

    The evolution of a system in which hot magmatic sills are repeatedly intruded into cool country rock at depth in the crust is modelled in one dimension. The model couples that of Annen et al. (2002), describing heat transfer and phase change during repeated sill intrusions, with that of Jackson et al. (2003), describing heat transfer, phase change and associated buoyancy driven melt segregation and compaction of the solid matrix following a single sill intrusion. The aim of the work is to investigate the impact of melt segregation on melt fraction and composition during repeated sill intrusions in deep crustal hot zones. The model developed uses an enthalpy based method whilst solving for temperature. This allows complex melting behaviour, including isothermal and non-linear relations, to be parameterised and included. The emplacement of hot, mantle-derived basaltic sills causes the pre-existing country rock to warm, which allows later sills to remain partially molten over timescales which are long enough to facilitate melt segregation processes. At fast emplacement rates, a large partially molten zone is generated above the intrusions into which melt can percolate, leading to the generation of high porosity melt lenses which can mobilise and form magmas. At slower emplacement rates, the hot zone evolves differently depending upon whether the intruded sills accumulate by over- or under-accretion. Under-accretion of sills does not produce a large partially molten zone in the overlying country rock, so the melt is contained within the intrusion zone. Over-accretion continues to melt the overlying country rock for all emplacement rates. Two types of melt are present in the system, crustal melt formed via partial melting, and residual melt formed from the crystallisation of the intruded basalt. The mobilised magmas comprise varying degrees of crustal and residual melts which, alongside with temperature and depth of melting, will determine their composition. The process

  15. 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

  16. Comparative Magma Oceanography

    NASA Technical Reports Server (NTRS)

    Jones, J. H.

    1999-01-01

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

  17. 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].

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

    NASA Astrophysics Data System (ADS)

    Geshi, Nobuo

    2000-05-01

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

  19. 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.

  20. Igneous Structures, Magma Transport, and Crystallization in Simple and Complex Plumbing Systems of the Central Atlantic Magmatic Province, Pennsylvania and New Jersey, USA

    NASA Astrophysics Data System (ADS)

    Srogi, L.; Martinson, P.; Willis, K. V.; Kulp, R.; Pollock, M.; Lutz, T. M.

    2014-12-01

    Recent studies showing the importance of sills and sheets in crustal magmatic plumbing at rifted continental margins prompt re-examination of the Mesozoic Central Atlantic Magmatic Province, eastern North America. The Newark-Gettysburg Basins in New Jersey, Pennsylvania, Maryland, contain Jurassic diabase (dolerite) intrusions and lava flows. Most intrusions are considered a single sheet or saucer sill. However, at the W end of the Newark Basin the Jacksonwald Syncline (JS) includes small plutons, sills, dikes, and a lava flow; and the Morgantown Pluton (MP) is a connected network of sills and inclined sheets with the 250-m-wide Birdsboro Dike forming the E side. After crystallization most intrusions were tilted or folded and dip/plunge toward the NW border faults. In the SE part of the MP, small magmatic pipes (originally vertical) and modal layering were tilted 20 degrees NNW, similar to plunge of the JS. If tilting was due to movement along the border faults then the basins expose cross-sections of a few kms from shallower (N/NW) to deeper (S/SE) crustal levels. There is a difference of 3.5-6 km in paleo-depth between basal S/SE units and upper N/NW units within JS, MP, and York Haven Sheet, consistent with estimated thicknesses of Triassic sedimentary rocks. Basal cumulus and upper Fe-rich and granophyric zones occur in most Newark-Gettysburg Basin intrusions implying similar magma transport and crystallization processes regardless of plumbing geometry. MELTS modeling of early orthopyroxene crystallization at high P suggests that opx-rich diabase marks magma feeder locations; at least 2 feeders at different emplacement levels occur in the MP. Modally-layered opx cumulus in the MP basal sill accumulated from dozens of m-scale magma pulses with lateral migration of most liquid. Distributions of distinctive phenocrysts provide insights into magma transport and crystal sorting. MP and JS chilled margins and lava flows have almost identical REE and other

  1. Evidence for magma convection to shallow depths during quiescent degassing of Mt. Etna

    NASA Astrophysics Data System (ADS)

    La Spina, Alessandro; Mike, Burton; Giovanni, Salerno Giuseppe

    2015-04-01

    degassing relative to HCl indicates a process of deep intrusion, in which magma rather than ascending to the shallow (~3 km depth) conduit is stored at depth where it may later erupt. On the contrary, reduced HCl degassing indicates a reduction in magma supply to the uppermost 500m of the magmatic system, which may occur during a shallow intrusion. Over the investigated period we observed both these processes, but overall the system remained very close to bulk degassing, suggesting that such intrusions are temporary deviations from a system which can efficiently degas essentially all the magma that enters the uppermost 4-5km of the feeding system.

  2. 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.

  3. Reconstructing magma reservoir dynamics from field evidence

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. A conduit-related genesis of the Lengshuiqing intrusive assemblage (Sichuan, SW China)

    NASA Astrophysics Data System (ADS)

    Munteanu, Marian; Wilson, Allan H.; Yao, Yong; Jiang, Shao-Yong; Chunnett, Gordon; Luo, Yaonan; Mafurutu, Leonard; Phadagi, Rofhiwa

    2010-01-01

    Lengshuiqing is part of the late Proterozoic igneous province from the western margin of the Yangtze craton. The Lengshuiqing area comprises five ultramafic-mafic intrusions, emplaced in the late Proterozoic Yanbian Group. The intrusions from Lengshuiqing contain cumulate ultramafic zones (peridotite + olivine pyroxenite), with cumulus olivine and Cr-spinel, and intercumulus pyroxenes, hornblende, phlogopite and plagioclase. Ni-Cu ore (pyrrhotite + pentlandite + chalcopyrite) is hosted in the ultramafic zones. Olivine-free diorite-quartz diorite ± gabbro and granite zones commonly occur above the ultramafic rocks. The genesis of the intrusions (conduit-related accumulation or differentiation from stagnant magma) was investigated. The amount of sulphides in the intrusions from Lengshuiqing is one order of magnitude bigger than the sulphides that can be dissolved by a volume of mafic magma similar with the volume of the intrusions. Most intrusions from Lengshuiqing have bulk composition (peridotite ± diorite ± granite) more magnesian (MgO = 21-22%; Mg# > 78) than the deduced composition of their parental magma (MgO = 9-11%; Mg# = 64-67). This indicates the accumulation of sulphide and mafic silicates from a volume of magma much bigger than the volume of the intrusions, which can be explained by the fractionation from magma ascending through the intrusions to shallower depths. A continuous supply and vent of magma is consistent with the lack of chilled margins, the melting of the wall rocks and the generation of high-temperature mineral assemblages (K-feldspar, diopside, and sillimanite) in the Yanbian Group. The intrusions from Lengshuiqing are seen as microchambers on conduits draining olivine-, Cr-spinel-, and sulphide-bearing mafic magma from a larger staging chamber.

  12. 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.

  13. Magma energy extraction

    SciTech Connect

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

    1987-01-01

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

  14. 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.

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

    NASA Technical Reports Server (NTRS)

    Wilson, L.; Head, James W.

    1991-01-01

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

  16. 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

  17. 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

  18. 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.

  19. 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

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

    PubMed

    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

  1. 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

  2. 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.

  3. Magmatic Cu-Ni sulfide mineralization of the Huangshannan mafic-untramafic intrusion, Eastern Tianshan, China

    NASA Astrophysics Data System (ADS)

    Zhao, Yun; Xue, Chunji; Zhao, Xiaobo; Yang, YongQiang; Ke, Junjun

    2015-06-01

    The Huangshannan Ni-Cu (-PGE) sulfide deposit, a new discovery from geological prospecting in Eastern Tianshan, is in a belt of magmatic Ni-Cu (-PGE) sulfide deposits along the southern margin of the Central Asian Orogenic Belt. The host intrusion of the Huangshannan deposit is composed of a layered ultramafic sequence and a massive gabbro-diorite unit. The major sulfide orebodies occur mainly within websterite and lherzolite in the layered ultramafic sequence. In-situ zircon U-Pb dating analyses yielded a crystallization age of 282.5 ± 1.4 Ma, similar to the ages of the Permian Tarim mantle plume. Samples from the Huangshannan intrusion are characterized by nearly flat rare earth elements patterns, negative Zr, Ti and Nb anomalies, arc-like Th/Yb and Nb/Yb ratios, and significantly lower rare earth element and immobile trace element contents than the Tarim basalts. These characteristics suggest that the Huangshannan intrusion was not generated from the Tarim mantle plume. The primary magma for the Huangshannan intrusion and its associated sulfide mineralization were formed from different pulses of picritic magma with different degrees of crustal contamination. The first pulse underwent an initial removal of 0.016% sulfide in the deep magma chamber. The evolved magma reached sulfide saturation again in the shallow magma chamber and formed sulfide ores in lherzolite. The second pulse of magma reached a level of 0.022% sulfide segregation at staging chamber before ascending up to the shallow magma chamber. In the shallow conduit system, this sulfide-unsaturated magma mixed with the first pulse of magma and with contamination from the country rocks, leading to the formation of sulfide ores in websterite. The third magma pulse from the deep chamber formed the unmineralized massive gabbro-diorite unit of the Huangshannan intrusion.

  4. 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.

  5. Mesoscale pervasive felsic magma migration: alternatives to dyking

    NASA Astrophysics Data System (ADS)

    Weinberg, Roberto F.

    1999-03-01

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

  6. Effects of an extensional tectonic stress on magmatic reservoir failure and magma propagation within the Venusian lithosphere

    NASA Astrophysics Data System (ADS)

    Le Corvec, N.; McGovern, P. J., Jr.; Grosfils, E. B.; Goldman, R. T.; Albright, J. A.

    2015-12-01

    Failure of magmatic reservoirs and propagation of magmas is controlled in part by the state of stress within the lithosphere. Such stresses are induced by a range of loadings (e.g., gravitational and magmatic). Additional stresses can be introduced by flexural deformation of the lithosphere due to a large volcanic edifice or mantle plume loading, or as a consequence of the regional tectonic environment. Rifting environments, for instance are the results of extensional stresses at the surface of planets (e.g., Devana Chasma on Venus). The resulting stress field may influence the failure of a magmatic reservoir and the propagation of magmas. To explore this scenario, we created 3D elastic models of the Venusian lithosphere using COMSOL Multiphysics, in which an extensional stress was applied. The stress state was implemented through horizontal deformation created by orthogonal contraction and extension on the outer boundaries of the quarter symmetry model. A spherical reservoir is embedded within the lithosphere to represent a magma chamber. In these models, we analyzed magma reservoir stability at different depths, the amount of overpressure needed to reach failure, and the type of resulting intrusions within the 3D model for three distinct environments: 1- lithostatic; 2- upward flexure due to a rising mantle plume; and 3- downward flexure due to a basaltic shield volcano. Preliminary results show that as the extensional stress increases: magmatic reservoirs become unstable at shallow depth and the amount of overpressure needed to reach failure decreases. In addition, the failure location along the reservoir flank rotates to parallel the horizontal contraction, which favors the formation of lateral dikes along the magma reservoir flanks over vertical dikes at the summit.

  7. Magma transport and storage at Kilauea volcano, HI

    NASA Astrophysics Data System (ADS)

    Wright, T. L.

    2010-12-01

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

  8. The characteristics of magma reservoir failure beneath a volcanic edifice

    NASA Astrophysics Data System (ADS)

    Hurwitz, Debra M.; Long, Sylvan M.; Grosfils, Eric B.

    2009-12-01

    Eruptions fed from subsurface reservoirs commonly construct volcanic edifices at the surface, and the growth of an edifice will in turn modify the subsurface stress state that dictates the conditions under which subsequent rupture of the inflating reservoir can occur. We re-examine this problem using axisymmetric finite element models of ellipsoidal reservoirs beneath conical edifices, explicitly incorporating factors (e.g., full gravitational loading conditions, an elastic edifice instead of a surface load, reservoir pressures sufficient to induce tensile rupture) that compromise previous solutions to illustrate why variations in rupture behavior can occur. Relative to half-space model results, the presence of an edifice generally rotates rupture toward the crest of a spherical reservoir, with increasing flank slope (for an edifice of constant volume) and larger edifices (or greater reservoir scaled depths) normally serving to enhance this trend. When non-spherical reservoirs are considered, the presence of an edifice amplifies previously identified half-space failure characteristics, shifting rupture to the crest more rapidly for prolate reservoirs while forcing rupture closer to the midpoint of oblate reservoirs. Rupture is always observed to occur in the σt orientation, and depending on where initial failure occurs rupture favors the initial emplacement of either lateral sills, circumferential intrusions or vertically ascending dikes. Ultimately, integration of our numerical model results with other information, for instance the sequence of intrusion/eruption events observed at a given volcano, can provide useful new insight into how a volcano's subsurface magma plumbing system evolved. We demonstrate this process through application of our model to Summer Coon, a well-studied stratocone on Earth, and Ilithyia Mons, a large conical shield volcano on Venus.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2015-10-01

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

  11. 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

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

    PubMed

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2015-01-01

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

  13. 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.

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

    PubMed

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

    2006-03-01

    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. PMID:16511491

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

    USGS Publications Warehouse

    Wicks, C.W.; Thatcher, W.; Dzurisin, D.; Svarc, J.

    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 material. 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 ago. Since the last eruption, Yellowstone has remained restless, with high seismicity, continuing uplift/subsidence episodes with movements of ???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. ?? 2006 Nature Publishing Group.

  16. 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.

  17. 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.

  18. 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

  19. 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

  20. 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.

  1. Magma accumulation rates and thermal histories of plutons of the Sierra Nevada batholith, CA

    NASA Astrophysics Data System (ADS)

    Davis, Jesse W.; Coleman, Drew S.; Gracely, John T.; Gaschnig, Richard; Stearns, Michael

    2012-03-01

    Zircon U-Pb geochronology results indicate that the John Muir Intrusive Suite of the central Sierra Nevada batholith, California, was assembled over a period of at least 12 Ma between 96 and 84 Ma. Bulk mineral thermochronology (U-Pb zircon and titanite, 40Ar/39Ar hornblende and biotite) of rocks from multiple plutons comprising the Muir suite indicates rapid cooling through titanite and hornblende closure following intrusion and subsequent slow cooling through biotite closure. Assembly of intrusive suites in the Sierra Nevada and elsewhere over millions of years favors growth by incremental intrusion. Estimated long-term pluton assembly rates for the John Muir Intrusive Suite are on the order of 0.001 km3 a-1 which is inconsistent with the rapid magma fluxes that are necessary to form large-volume magma chambers capable of producing caldera-forming eruptions. If large shallow crustal magma chambers do not typically develop during assembly of large zoned intrusive suites, it is doubtful that the intrusive suites represent cumulates left behind following caldera-forming eruptions.

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

    NASA Astrophysics Data System (ADS)

    Wilson, M.; Wheeler, W.

    2002-12-01

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

  3. 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

  4. 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.

  5. 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.

  6. Dynamically-induced structures formation in congested magma

    NASA Astrophysics Data System (ADS)

    Petford, N.

    2008-12-01

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

  7. 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. PMID:23891994

  8. 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...

  9. Watching magma from space

    USGS Publications Warehouse

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

    2000-01-01

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

  10. 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.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

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

  13. 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

  14. 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

  15. 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

  16. Triggering of microearthquakes in Iceland by volatiles released from a dyke intrusion

    NASA Astrophysics Data System (ADS)

    Martens, Hilary R.; White, Robert S.

    2013-09-01

    We suggest that carbon dioxide exsolved from a mid-crustal basaltic dyke intrusion in Iceland migrated upwards and triggered shallow seismicity by allowing failure on pre-existing fractures under the relatively low elastic stresses (100-200 kPa; 1-2 bar) generated by the dyke inflation. Intense swarms of microseismicity accompanied magmatic intrusion into a dyke at depths of 13-19 km in the crust of Iceland's Northern Volcanic Rift Zone during 2007-2008. Contemporaneously, a series of small normal earthquakes, probably triggered by elastic stresses imposed by the dyke intrusion, occurred in the uppermost 4 km of crust: fault plane solutions from these are consistent with failure along the extensional fabric and surface fissure directions mapped in the area, suggesting that the faults failed along existing rift zone fabric even though the mid-crustal dyke is highly oblique to it. Several months after the melt froze in the mid-crust and seismicity associated with the intrusion had ceased, an upsurge in shallow microseismicity began in the updip projection of the dyke near the brittle-ductile transition at 6-7 km depth below sea level. This seismicity is caused by failure on right-lateral strike-slip faults, with fault planes orientated 23 ± 3°, which are identical with the 24 ± 2° orientation in this area of surface fractures and fissures caused by plate spreading and extension of the volcanic rift zone. However, these earthquakes have T-axes approximately aligned with the opening direction of the dyke, and the right-lateral sense of failure is opposite that of regional strike-slip faults. We suggest that the fractures occurred along pre-existing weaknesses generated by the pervasive fabric of the rift zone, but that the dyke opening in the mid-crust beneath it caused right-lateral failure. The seismicity commenced after a temporal delay of several months and has persisted for over 3 yr. We propose that fluids exsolved from the magma in the dyke, primarily carbon

  17. 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.

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Kazahaya, Ryunosuke; Aoki, Yosuke; Shinohara, Hiroshi

    2015-05-01

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

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. Carbon dioxide in magmas and implications for hydrothermal systems

    USGS Publications Warehouse

    Lowenstern, J. B.

    2001-01-01

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

  6. 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

  7. Influence of substrate tectonic heritage on the evolution of composite volcanoes: Predicting sites of flank eruption, lateral collapse, and erosion

    NASA Astrophysics Data System (ADS)

    Tibaldi, Alessandro; Corazzato, Claudia; Kozhurin, Andrey; Lagmay, Alfredo F. M.; Pasquarè, Federico A.; Ponomareva, Vera V.; Rust, Derek; Tormey, Daniel; Vezzoli, Luigina

    2008-04-01

    This paper aims to aid understanding of the complicated interplay between construction and destruction of volcanoes, with an emphasis on the role of substrate tectonic heritage in controlling magma conduit geometry, lateral collapse, landslides, and preferential erosion pathways. The influence of basement structure on the development of six composite volcanoes located in different geodynamic/geological environments is described: Stromboli (Italy), in an island arc extensional tectonic setting, Ollagüe (Bolivia-Chile) in a cordilleran extensional setting, Kizimen (Russia) in a transtensional setting, Pinatubo (Philippines) in a transcurrent setting, Planchon (Chile) in a compressional cordilleran setting, and Mt. Etna (Italy) in a complex tectonic boundary setting. Analogue and numerical modelling results are used to enhance understanding of processes exemplified by these volcanic centres. We provide a comprehensive overview of this topic by considering a great deal of relevant, recently published studies and combine these with the presentation of new results, in order to contribute to the discussion on substrate tectonics and its control on volcano evolution. The results show that magma conduits in volcanic rift zones can be geometrically controlled by the regional tectonic stress field. Rift zones produce a lateral magma push that controls the direction of lateral collapse and can also trigger collapse. Once lateral collapse occurs, the resulting debuttressing produces a reorganization of the shallow-level magma migration pathways towards the collapse depression. Subsequent landslides and erosion tend to localize along rift zones. If a zone of weakness underlies a volcano, long-term creep can occur, deforming a large sector of the cone. This deformation can trigger landslides that propagate along the destabilized flank axis. In the absence of a rift zone, normal and transcurrent faults propagating from the substrate through the volcano can induce flank

  8. 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

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-10-01

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

  11. Detecting deep crustal magma movement: Exploring linkages between increased gas emission, deep seismicity, and deformation (Invited)

    NASA Astrophysics Data System (ADS)

    Werner, C. A.; Poland, M. P.; Power, J. A.; Sutton, A. J.; Elias, T.; Grapenthin, R.; Thelen, W. A.

    2013-12-01

    Typically in the weeks to days before a volcanic eruption there are indisputable signals of unrest that can be identified in geophysical and geochemical data. Detection of signals of volcanic unrest months to years prior to an eruption, however, relies on our ability to recognize and link more subtle changes. Deep long-period earthquakes, typically 10-45 km beneath volcanoes, are thought to represent magma movement and may indicate near future unrest. Carbon dioxide (CO2 ) exsolves from most magmas at similar depths and increases in CO2 discharge may also provide a months-to-years precursor as it emits at the surface in advance of the magma from which it exsolved. Without the use of sensitive monitoring equipment and routine measurements, changes in CO2 can easily go undetected. Finally, inflation of the surface, through use of InSAR or GPS stations (especially at sites tens of km from the volcano) can also indicate accumulation of magma in the deep crust. Here we present three recent examples, from Redoubt, Kilauea, and Mammoth Mountain volcanoes, where increases in CO2 emission, deep long-period earthquakes, and surface deformation data indicate either the intrusion of magma into the deep crust in the months to years preceding volcanic eruptions or a change in ongoing volcanic unrest. At Redoubt volcano, Alaska, elevated CO2 emission (~ 1200 t/d, or roughly 20 times the background emission) was measured in October, 2008, over 5 months prior to the first magmatic eruption in March, 2009. In addition to CO2 release, deep long-period earthquakes were first recorded in December, 2008, and a deep deformation signal was detected starting in May 2008, albeit retrospectively. At Kilauea, Hawaii, increases in CO2 emissions from the summit (up to nearly 25 kt/d, over three times the background emission) were measured mid-2004, roughly coincident with a change in deformation behavior from deflation to inflation. Nearly 3 years later, a change in eruptive activity occurred

  12. Draining mafic magma from conduits during Strombolian eruption

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  13. Successive episodes of reactive liquid flow through a layered intrusion (Unit 9, Rum Eastern Layered Intrusion, Scotland)

    NASA Astrophysics Data System (ADS)

    Leuthold, J.; Blundy, J. D.; Holness, M. B.; Sides, R.

    2014-07-01

    laterally through the remobilized cumulate pile and precipitating clinopyroxene en route. This process, called reactive liquid flow, is potentially important in open magma chambers.

  14. 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.

  15. Comparative Magma Oceanography

    NASA Technical Reports Server (NTRS)

    Jones, John H.

    1999-01-01

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

  16. 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

  17. 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

  18. The Surtsey Magma Series.

    PubMed

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

    2015-01-01

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

  19. 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

  20. 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.

  1. 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

  2. Rift initiation with volatiles and magma

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  3. 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. PMID:17510364

  4. 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)

  5. Bro Intrusion Detection System

    SciTech Connect

    Paxson, Vern; Campbell, Scott; leres, Craig; Lee, Jason

    2006-01-25

    Bro is a Unix-based Network Intrusion Detection System (IDS). Bro monitors network traffic and detects intrusion attempts based on the traffic characteristics and content. Bro detects intrusions by comparing network traffic against rules describing events that are deemed troublesome. These rules might describe activities (e.g., certain hosts connecting to certain services), what activities are worth alerting (e.g., attempts to a given number of different hosts constitutes a "scan"), or signatures describing known attacks or access to known vulnerabilities. If Bro detects something of interest, it can be instructed to either issue a log entry or initiate the execution of an operating system command. Bro targets high-speed (Gbps), high-volume intrusion detection. By judiciously leveraging packet filtering techniques, Bro is able to achieve the performance necessary to do so while running on commercially available PC hardware, and thus can serve as a cost effective means of monitoring a site’s Internet connection.

  6. 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.

  7. Forecasting the path of a laterally propagating dike

    NASA Astrophysics Data System (ADS)

    Heimisson, Elías Rafn; Hooper, Andrew; Sigmundsson, Freysteinn

    2015-12-01

    An important aspect of eruption forecasting is predicting the path of propagating dikes. We show how lateral dike propagation can be forecast using the minimum potential energy principle. We compare theory to observed propagation paths of dikes originating at the Bárðarbunga volcano, Iceland, in 2014 and 1996, by developing a probability distribution for the most likely propagation path. The observed propagation paths agree well with the model prediction. We find that topography is very important for the model, and our preferred forecasting model considers its influence on the potential energy change of the crust and magma. We tested the influence of topography by running the model assuming no topography and found that the path of the 2014 dike could not be hindcasted. The results suggest that lateral dike propagation is governed not only by deviatoric stresses but also by pressure gradients and gravitational potential energy. Furthermore, the model predicts the formation of curved dikes around cone-shaped structures without the assumption of a local deviatoric stress field. We suggest that a likely eruption site for a laterally propagating dike is in topographic lows. The method presented here is simple and computationally feasible. Our results indicate that this kind of a model can be applied to mitigate volcanic hazards in regions where the tectonic setting promotes formation of laterally propagating vertical intrusive sheets.

  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. [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. PMID:24409751

  10. Igneous intrusion models for floor fracturing in lunar craters

    NASA Technical Reports Server (NTRS)

    Wichman, R. W.; Schultz, P. H.

    1991-01-01

    Lunar floor-fractured craters are primarily located near the maria and frequently contain ponded mare units and dark mantling deposits. Fracturing is confined to the crater interior, often producing a moat-like feature near the floor edge, and crater depth is commonly reduced by uplift of the crater floor. Although viscous relaxation of crater topography can produce such uplift, the close association of modification with surface volcanism supports a model linking floor fracture to crater-centered igneous intrusions. The consequences of two intrusion models for the lunar interior are quantitatively explored. The first model is based on terrestrial laccoliths and describes a shallow intrusion beneath the crater. The second model is based on cone sheet complexes where surface deformation results from a deeper magma chamber. Both models, their fit to observed crater modifications and possible implications for local volcanism are described.

  11. 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

  12. 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.

  13. 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

  14. Deformation Structures associated with the emplacement of high level intrusions: A study of Trachyte Mesa Intrusion, Henry Mountains, Utah

    NASA Astrophysics Data System (ADS)

    Wilson, P. I. R.; McCaffrey, K. J. W.; Jarvis, I.; Murphy, P.; Davidson, J. P.

    2012-04-01

    Most studies of sill and laccolith complexes have focused on the internal architecture and thermal effects of these intrusions, while few have looked in detail at host rock deformation structures associated with their emplacement. Various sill and laccolith emplacement mechanisms have been proposed (e.g. radial growth/ bulldozing, and two-stage growth), each with their own distinct deformation style. Compressional structures likely dominate during radial growth (bulldozing) emplacement, while extensional structures are more likely to form during two-stage growth emplacement. In this study we focus on deformation structures (faults, deformation bands and joints) associated with emplacement of Tertiary sills and laccolith intrusions in the Henry Mountains, Utah. Trachyte Mesa, the most distal satellite intrusion to the Mt. Hilliers intrusive centre, is an elongate (NE-SW) laccolith concordant with the Entrada sandstone it intrudes. The intrusion is comprised of multiple, stacked intrusive sheets. Two structural transects across the northwest lateral margin have identified distinct structural domains within the host rock that reflect both temporal and kinematic variations in deformation. Three deformation phases are identified, interpreted to be pre-, syn- and late-emplacement structures. A background set of deformation bands (phase 1), trending oblique to the intrusion margin, is apparent across the entire area. A second set of deformation bands (phase 2) overprint the early phase. These are characterised by conjugate deformation bands that parallel the intrusion margin, and increase in intensity and spacing towards the intrusion. Within this same zone a series of calcite filled normal faults, striking parallel and perpendicular to the intrusion margin, are apparent. Due to their spatial, kinematic and overprinting relationships we interpret these to be linked to the emplacement of the intrusive body. Overprinting all other structures, are two sets of tensile joints

  15. 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

  16. Geology, petrology and geochemistry of the "Americano do Brasil" layered intrusion, central Brazil, and its Ni-Cu sulfide deposits

    NASA Astrophysics Data System (ADS)

    E Silva, Jonas Mota; Ferreira Filho, Cesar Fonseca; Bühn, Bernhard; Dantas, Elton Luiz

    2011-01-01

    The "Americano do Brasil" Complex (ABC) is part of a cluster of coeval synorogenic mafic-ultramafic intrusions emplaced during the Brasiliano/Pan-African Orogenic Cycle in Brazil. The medium-sized ABC consists of interlayered dunite, peridotite, websterite, and gabbronorite. High Fo values of olivine (up to Fo88) and the crystallization sequence of the ABC (Ol + Chr ≥ Ol + Opx + Chr ≥ Cpx + Opx ≥ Opx + Pl + Cpx ≥ Opx + Pl + Cpx + Ilm + Mag) suggest crystallization from tholeiitic high-MgO parental magmas. Light rare earth element (REE)-enriched mantle-normalized REE profiles and ɛNd(T) values of +2.4 for cumulate rocks from the ABC suggest a depleted mantle source for the parental magma. The ABC Ni-Cu sulfide deposit (3.1 Mt at 1.12 wt.% Ni and 1.02 wt.% Cu) consists of three distinctively different orebodies (S1, S2, and G2). The S2 orebody, an unusual occurrence of stratiform massive sulfide hosted by dunite and peridotite in the interior of a layered intrusion, results from sulfides accumulated at the transient base of the magma chamber following a new influx of parental magma. The G2 orebody has an irregular and roughly cylindrical shape, consisting mainly of net-textured sulfides. The G2 orebody is hosted by peridotite and pyroxenite and located stratigraphically below the S1 orebody. S2 and G2 orebodies are characterized by low Cu/Cu + Ni ratios (mainly below 0.4). The S1 orebody, hosted by websterite and gabbronorite in the more fractionated sequence of the ABC, is a cluster of several irregular discontinuous orebodies of Ni-Cu disseminated sulfides. The sulfides of the S1 orebody have high Cu/Cu + Ni ratios (mainly between 0.5 and 0.8) and are highly depleted in PGE. The S1 orebody is interpreted to result from a later event of sulfide segregation in the magma chamber, possibly following the event that originated the G2 orebody. The bulk of δ34S values for sulfides of the ABC orebodies and their host rocks fall in the range of 0 ± 2‰. Higher

  17. Fracture mode analysis and related surface deformation during dyke intrusion: Results from 2D experimental modelling

    NASA Astrophysics Data System (ADS)

    Abdelmalak, M.; Mourgues, R.; Bureau, D.

    2012-04-01

    The analysis of surface deformation in response to approaching intrusion is important for assessing volcanic hazards. In this paper, we present results from 2D scaled models of magma intrusion, in which we discuss the propagation mode and related surface deformation during dyke growth. Our experiments consist in the injection of analogue magma (Golden syrup) into cohesive fine-grained silica powder, simulating the brittle upper crust. Using an optical image correlation technique (Particle Imaging Velocimetry), we were able to follow the surface deformation, the displacements within the country rock and to calculate strains induced by the magma emplacement. We identified two kinds of intrusion morphologies resulting from different interactions between the dyke and plastic deformations occurring in the country rock near the surface. In both morphologies, the dyke is vertical at depth. Our analysis demonstrates that both hydraulic tensile opening and shear-related propagation operate during this first stage of vertical growth. At the same time, the surface lifted up and formed a smooth symmetrical dome. Both types of morphologies differ in the upper part. During a second stage of evolution, the first type of intrusion inclined at a dip between 45 to 65°. This inclination is not caused by shear deformations and is attributed to stress rotation near the tip. Closer to the surface, the growth of the inclined sheet creates shear bands which conduct the fluid toward the surface. The surface uplift becomes asymmetric. The second type of intrusion does not rotate at depth and continues its vertical propagation by catching vertical tensile cracks. The intrusion of magma in these cracks creates horizontal stresses which are responsible for the closure of fractures and the formation of reverse faults. At the surface the dome remains symmetrical. For both intrusions, the surface uplift accelerates during the second stage and it is strongly influenced by the presence or the

  18. 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.

  19. Late Neoproterozoic post-collisional mafic magmatism in the Arabian-Nubian Shield: A case study from Wadi El-Mahash gabbroic intrusion in southeast Sinai, Egypt

    NASA Astrophysics Data System (ADS)

    Khalil, A. E. S.; Obeid, M. A.; Azer, M. K.

    2015-05-01

    Late Neoproterozoic gabbroic intrusion of Wadi El-Mahash lays in the northwestern sector of the Arabian-Nubian Shield (ANS) which is exposed in the Sinai Peninsula, Egypt. It occurs as small undeformed mafic body intruding metamorphic rocks and truncated by alkali granites. Field relations, mineralogical characteristics and chemical data indicate that Wadi El-Mahash mafic intrusion is unmetamorphosed. The intrusion consists of medium- to coarse-grained gabbroic rocks. The medium-grained one (hornblende gabbro) formed nearly simultaneous with, or slightly later than, the coarse-grained rock (pyroxene-hornblende gabbro). Geochemically, the gabbroic samples are characterized by enrichment in LILE relative to HFSE and LREE relative to HREE [(La/Yb)n = 4.52-6.35]. They show geochemical signature similar to other post-collisional gabbroic intrusions of south Sinai. The subduction-related geochemical characteristic of the gabbroic intrusion of Wadi El-Mahash can be explained by partial melting of a relatively enriched lithospheric mantle source following a previous subduction process in the ANS. The gabbroic rocks crystallized at pressures between 6.2 and 6.5 kbar (∼15-20 km depth) with crystallization temperature ranging from 750 to 970 °C. Lithospheric delamination model is suggested for the mafic magma of Wadi El-Mahash since delamination of lithospheric mantle allowed asthenosphere to rise rapidly causing partial melting and generating gabbroic melts. The produced melts then infiltrated the base of the crust to induce the post-collisional magmatism in south Sinai.

  20. 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

  1. 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

  2. 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.

  3. Simulation of Layered Magma Chambers.

    ERIC Educational Resources Information Center

    Cawthorn, Richard Grant

    1991-01-01

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

  4. 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.

  5. 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

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

    NASA Astrophysics Data System (ADS)

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

    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.

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

    PubMed

    Passarelli, L; Rivalta, E; Shuler, A

    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

  8. Superheat in magma oceans

    NASA Technical Reports Server (NTRS)

    Jakes, Petr

    1992-01-01

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

  9. Mineralogical, petrological, and geochemical studies of the Limahe mafic-ultramatic intrusion and associated Ni-Cu sulfide ores, SW China

    NASA Astrophysics Data System (ADS)

    Tao, Yan; Li, Chusi; Song, Xie-Yan; Ripley, Edward M.

    2008-11-01

    The Limahe Ni-Cu sulfide deposit is hosted by a small mafic-ultramafic intrusion (800 × 200 × 300 m) that is temporally associated with the voluminous Permian flood basalts in SW China. The objective of this study is to better understand the origin of the deposit in the context of regional magmatism which is important for the ongoing mineral exploration in the region. The Limahe intrusion is a multiphase intrusion with an ultramafic unit at the base and a mafic unit at the top. The two rock units have intrusive contacts and exhibit similar mantle-normalized trace element patterns and Sr-Nd isotopic compositions but significantly different cumulus mineralogy and major element compositions. The similarities suggest that they are related to a common parental liquid, whereas the differences point to magma differentiation by olivine crystallization at depth. Sulfide mineralization is restricted to the ultramafic unit. The abundances of sulfides in the ultramafic unit generally increase towards the basal contacts with sedimentary footwall. The δ 34S values of sulfide minerals from the Limahe deposit are elevated, ranging from +2.4 to +5.4‰. These values suggest the involvement of external S with elevated δ 34S values. The mantle-normalized platinum-group element (PGE) patterns of bulk sulfide ores are similar to those of picrites associated with flood basalts in the region. The abundances of PGE in the sulfide ores, however, are significantly lower than that of sulfide liquid expected to segregate from undepleted picrite magma. Cr-spinel and olivine are present in the Limahe ultramafic rocks as well as in the picrites. Mantle-normalized trace element patterns of the Limahe intrusion generally resemble those of the picrites. However, negative Nb-Ta anomalies, common features of contamination with the lower or middle crust, are present in the intrusion but absent in the picrites. Sr-Nd isotopes suggest that the Limahe intrusion experienced higher degrees of

  10. Evolution of a magma-driven earthquake swarm and triggering of the nearby Oldoinyo Lengai eruption, as resolved by InSAR, ground observations and elastic modeling, East African Rift, 2007

    NASA Astrophysics Data System (ADS)

    Baer, G.; Hamiel, Y.; Shamir, G.; Nof, R.

    2008-07-01

    An earthquake swarm struck the North Tanzania Divergence, East African Rift over a 2 month period between July and September 2007. It produced approximately 70 M > 4 earthquakes (peak magnitude Mw 5.9), and extensive surface deformation, concurrent with eruptions at the nearby Oldoinyo Lengai volcano. The spatial and temporal evolution of the entire deformation event was resolved by Interferometric Synthetic Aperture Radar (InSAR) observations, owing to a particularly favorable acquisition programming of the Envisat and ALOS satellites, and was verified by detailed ground observations. Elastic modeling based on the InSAR measurements clearly distinguishes between normal faulting, which dominated during the first week of the event, and intermittent episodes of dike propagation, oblique dike opening and dike-induced faulting during the following month. A gradual decline in the intensity of deformation occurred over the final weeks. Our observations and modeling suggest that the sequence of events was initiated by pressurization of a deep-seated magma chamber below Oldoinyo Lengai which opened the way to lateral dike injection, and dike-induced faulting and seismicity. As dike intrusion terminated, silicate magma ascended the volcano conduit, reacted with the carbonatitic magma, and set off a major episode of explosive ash eruptions producing mixed silicate-carbonatitic ejecta. The rise of the silicate magma within the volcano conduit is attributed to bubble growth and buoyancy increase in the magma chamber either due to a temporary pressure drop after the termination of the diking event, or due to the dynamic effects of seismic wave passage from the earthquake swarm. Similar temporal associations between earthquake swarms and major explosive ash eruptions were observed at Oldoinyo Lengai over the past half century.