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Sample records for active crustal magma

  1. Formation of crustal magma chambers in Iceland

    SciTech Connect

    Gudmundsson, A.

    1986-02-01

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

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

    NASA Technical Reports Server (NTRS)

    Hess, Paul C.; Head, James W.

    1990-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

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

  4. Melt evolution and residence in extending crust: Thermal modeling of the crust and crustal magmas

    NASA Astrophysics Data System (ADS)

    Karakas, Ozge; Dufek, Josef

    2015-09-01

    Tectonic extension and magmatism often act in concert to modify the thermal, mechanical, and chemical structure of the crust. Quantifying the effects of extension and magma flux on melting relationships in the crust is fundamental to determining the rate of crustal melting versus fractionation, magma residence time, and the growth of continental crust in rift environments. In order to understand the coupled control of tectonic extension and magma emplacement on crustal thermal evolution, we develop a numerical model that accounts for extension and thermal-petrographic processes in diverse extensional settings. We show that magma flux exerts the primary control on melt generation and tectonic extension amplifies the volume of melt residing in the crustal column. Diking into an extending crust produces hybrid magmas composed of 1) residual melt remaining after partial crystallization of basalt (mantle-derived melt) and 2) melt from partial melting of the crust (crustal melt). In an extending crust, mantle-derived melts are more prevalent than crustal melts across a range of magma fluxes, tectonic extension rates, and magmatic water contents. In most of the conditions, crustal temperatures do not reach their solidus temperatures to initiate partial melting of these igneous lithologies. Energy balance calculations show that the total enthalpy transported by dikes is primarily used for increasing the sensible heat of the cold surrounding crust with little energy contributing to latent heat of melting the crust (maximum crustal melting efficiency is 6%). In the lower crust, an extensive mush region develops for most of the conditions. Upper crustal crystalline mush is produced by continuous emplacement of magma with geologically reasonable flux and extension rates on timescales of 106 yr. Addition of tectonic effects and non-linear melt fraction relationships demonstrates that the magma flux required to sustain partially molten regions in the upper crust is within the

  5. Electromagnetic Imaging of Crustal Magma Chambers

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

  6. Boron isotope fractionation in magma via crustal carbonate dissolution

    PubMed Central

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

    2016-01-01

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

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

    PubMed

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

    2016-01-01

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

  8. Boron isotope fractionation in magma via crustal carbonate dissolution

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  10. Bulk arc strain, crustal thickening, magma emplacement, and mass balances in the Mesozoic Sierra Nevada arc

    NASA Astrophysics Data System (ADS)

    Cao, Wenrong; Paterson, Scott; Saleeby, Jason; Zalunardo, Sean

    2016-03-01

    Quantifying crustal deformation is important for evaluating mass balance, material transfer, and the interplay between tectonism and magmatism in continental arcs. We present a dataset of >650 finite strain analyses compiled from published works and our own studies with associated structural, geochronologic, and geobarometric information in central and southern Sierra Nevada, California, to quantify the arc crust deformation. Our results show that Mesozoic tectonism results in 65% arc-perpendicular bulk crust shortening under a more or less plane strain condition. Mesozoic arc magmatism replaced ∼80% of this actively deforming arc crust with plutons requiring significantly greater crustal thickening. We suggest that by ∼85 Ma, the arc crust thickness was ∼80 km with a 30-km-thick arc root, resulting in a ∼5 km elevation. Most tectonic shortening and magma emplacement must be accommodated by downward displacements of crustal materials into growing crustal roots at the estimated downward transfer rate of 2-13 km/Myr. The downward transfer of crustal materials must occur in active magma channels, or in "escape channels" in between solidified plutons that decrease in size with time and depth resulting in an increase in the intensity of constrictional strain with depth. We argue that both tectonism and magmatism control the thickness of the crust and surface elevation with slight modification by surface erosion. The downward transported crustal materials initially fertilize the MASH zone thus enhancing to the generation of additional magmas. As the crustal root grows it may potentially pinch out and cool the mantle wedge and thus cause reduction of arc magmatism.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  12. 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.

  13. 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

  14. Crustal thickness control on Sr/Y signatures of recent arc magmas: an Earth scale perspective.

    PubMed

    Chiaradia, Massimo

    2015-01-01

    Arc magmas originate in subduction zones as partial melts of the mantle, induced by aqueous fluids/melts liberated by the subducted slab. Subsequently, they rise through and evolve within the overriding plate crust. Aside from broadly similar features that distinguish them from magmas of other geodynamic settings (e.g., mid-ocean ridges, intraplate), arc magmas display variably high Sr/Y values. Elucidating the debated origin of high Sr/Y signatures in arc magmas, whether due to mantle-source, slab melting or intracrustal processes, is instrumental for models of crustal growth and ore genesis. Here, using a statistical treatment of >23000 whole rock geochemical data, I show that average Sr/Y values and degree of maturation (MgO depletion at peak Sr/Y values) of 19 out of 22 Pliocene-Quaternary arcs correlate positively with arc thickness. This suggests that crustal thickness exerts a first order control on the Sr/Y variability of arc magmas through the stabilization or destabilization of mineral phases that fractionate Sr (plagioclase) and Y (amphibole ± garnet). In fact, the stability of these mineral phases is function of the pressure at which magma evolves, which depends on crustal thickness. The data presented show also that high Sr/Y Pliocene-Quaternary intermediate-felsic arc rocks have a distinct origin from their Archean counterparts. PMID:25631193

  15. Crustal thickness control on Sr/Y signatures of recent arc magmas: an Earth scale perspective

    PubMed Central

    Chiaradia, Massimo

    2015-01-01

    Arc magmas originate in subduction zones as partial melts of the mantle, induced by aqueous fluids/melts liberated by the subducted slab. Subsequently, they rise through and evolve within the overriding plate crust. Aside from broadly similar features that distinguish them from magmas of other geodynamic settings (e.g., mid-ocean ridges, intraplate), arc magmas display variably high Sr/Y values. Elucidating the debated origin of high Sr/Y signatures in arc magmas, whether due to mantle-source, slab melting or intracrustal processes, is instrumental for models of crustal growth and ore genesis. Here, using a statistical treatment of >23000 whole rock geochemical data, I show that average Sr/Y values and degree of maturation (MgO depletion at peak Sr/Y values) of 19 out of 22 Pliocene-Quaternary arcs correlate positively with arc thickness. This suggests that crustal thickness exerts a first order control on the Sr/Y variability of arc magmas through the stabilization or destabilization of mineral phases that fractionate Sr (plagioclase) and Y (amphibole ± garnet). In fact, the stability of these mineral phases is function of the pressure at which magma evolves, which depends on crustal thickness. The data presented show also that high Sr/Y Pliocene-Quaternary intermediate-felsic arc rocks have a distinct origin from their Archean counterparts. PMID:25631193

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

    SciTech Connect

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

    1990-01-01

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

  17. Magma-compensated crustal thinning in continental rift zones.

    PubMed

    Thybo, H; Nielsen, C A

    2009-02-12

    Continental rift zones are long, narrow tectonic depressions in the Earth's surface where the entire lithosphere has been modified in extension. Rifting can eventually lead to rupture of the continental lithosphere and creation of new oceanic lithosphere or, alternatively, lead to formation of wide sedimentary basins around failed rift zones. Conventional models of rift zones include three characteristic features: surface manifestation as an elongated topographic trough, Moho shallowing due to crustal thinning, and reduced seismic velocity in the uppermost mantle due to decompression melting or heating from the Earth's interior. Here we demonstrate that only the surface manifestation is observed at the Baikal rift zone, whereas the crustal and mantle characteristics can be ruled out by a new seismic profile across southern Lake Baikal in Siberia. Instead we observe a localized zone in the lower crust which has exceptionally high seismic velocity and is highly reflective. We suggest that the expected Moho uplift was compensated by magmatic intrusion into the lower crust, producing the observed high-velocity zone. This finding demonstrates a previously unknown role for magmatism in rifting processes with significant implications for estimation of stretching factors and modelling of sedimentary basins around failed rift structures. PMID:19212408

  18. Isotopic disequilibrium and lower crustal contamination in slowly ascending magmas: Insights from Proterozoic anorthosites

    NASA Astrophysics Data System (ADS)

    Bybee, G. M.; Ashwal, L. D.

    2015-10-01

    Many Proterozoic anorthosite massifs show crustal isotopic signatures that have, for decades, fuelled debate regarding the source of these temporally-restricted magmas. Are these signatures indicative of lower crustal melting or of significant assimilation of crustal material into mantle-derived magmas? Traditional whole rock isotopic tracers (Sr, Nd, Pb and Os), like other geochemical, petrological and experimental tools, have failed to identify unambiguously the origins of the crust-like signature and resolve the source controversies for these feldspathic, cumulate intrusives. We make use of high precision Sr, Nd and Pb isotopic compositions of mineral phases (plag, opx, mag) and comagmatic, high-pressure orthopyroxene megacrysts as well as whole rock anorthosites/leuconorites from the Mealy Mountains Intrusive Suite (MMIS) and the Nain Plutonic Suite (NPS) to probe the origin of the crustal isotopic signatures and assess the importance of differentiation at lower crustal depths. This selection of samples represents fragments from various stages of the polybaric ascent of the magmas, while the study of the Mealy Mountains Intrusive Suite and the Nain Plutonic Suite is instructive as each is intruded into crust of significantly different age and isotopic composition. We observe marked differences in the whole-rock isotopic composition of Proterozoic anorthosites and high-pressure megacrysts (e.g. εNd;T = +2 to -10) intruded into crustal terranes of different ages and isotopic compositions. Evidence for varying degrees of internal isotopic disequilibrium (ΔNd, ΔSr, ΔPb) in anorthosites from these different terranes reinforces the notion that crustal contamination, and more importantly, the nature of the crustal assimilant, has a profound influence on the chemical signature of Proterozoic anorthosites. While most samples from the MMIS and NPS show significant and measurable ΔNd and ΔPb disequilibrium, ΔSr compositions cluster around zero. This decoupling in

  19. Seismic signature of crustal magma and fluid from deep seismic sounding data across Tengchong volcanic area

    NASA Astrophysics Data System (ADS)

    Bai, Z. M.; Zhang, Z. Z.; Wang, C. Y.; Klemperer, S. L.

    2012-04-01

    The weakened lithosphere around eastern syntax of Tibet plateau has been revealed by the Average Pn and Sn velocities, the 3D upper mantle velocity variations of P wave and S wave, and the iimaging results of magnetotelluric data. Tengchong volcanic area is neighboring to core of eastern syntax and famous for its springs, volcanic-geothermal activities and remarkable seismicity in mainland China. To probe the deep environment for the Tengchong volcanic-geothermal activity a deep seismic sounding (DSS) project was carried out across the this area in 1999. In this paper the seismic signature of crustal magma and fluid is explored from the DSS data with the seismic attribute fusion (SAF) technique, hence four possible positions for magma generation together with some locations for porous and fractured fluid beneath the Tengchong volcanic area were disclosed from the final fusion image of multi seismic attributes. The adopted attributes include the Vp, Vs and Vp/Vs results derived from a new inversion method based on the No-Ray-Tomography technique, and the migrated instantaneous attributes of central frequency, bandwidth and high frequency energy of pressure wave. Moreover, the back-projected ones which are mainly consisted by the attenuation factor Qp , the delay-time of shear wave splitting, and the amplitude ratio between S wave and P wave + S wave were also considered in this fusion process. Our fusion image indicates such a mechanism for the surface springs: a large amount of heat and the fluid released by the crystallization of magma were transmitted upward into the fluid-filled rock, and the fluid upwells along some pipeline since the high pressure in deep, thus the widespread springs of Tengchong volcanic area were developed. Moreover, the fusion image, regional volcanic and geothermal activities, and the seismicity suggest that the main risk of volcanic eruption was concentrated to the south of Tengchong city, especially around the shot point (SP) Tuantian

  20. Seismic evidence for a crustal magma reservoir beneath the upper east rift zoneof Kilauea volcano, Hawaii

    USGS Publications Warehouse

    Lin, Guoqing; Amelung, Falk; Lavallee, Yan; Okubo, Paul G.

    2014-01-01

    An anomalous body with low Vp (compressional wave velocity), low Vs (shear wave velocity), and high Vp/Vs anomalies is observed at 8–11 km depth beneath the upper east rift zone of Kilauea volcano in Hawaii by simultaneous inversion of seismic velocity structure and earthquake locations. We interpret this body to be a crustal magma reservoir beneath the volcanic pile, similar to those widely recognized beneath mid-ocean ridge volcanoes. Combined seismic velocity and petrophysical models suggest the presence of 10% melt in a cumulate magma mush. This reservoir could have supplied the magma that intruded into the deep section of the east rift zone and caused its rapid expansion following the 1975 M7.2 Kalapana earthquake.

  1. Evidence of ongoing crustal deformation related to magmatic activity near Socorro, New Mexico

    NASA Technical Reports Server (NTRS)

    Larsen, S.; Brown, L.; Reilinger, R.

    1986-01-01

    Leveling measurements conducted in 1980-1981 by the National Geodetic Survey in the Socorro area of the Rio Grande rift are analyzed. Crustal uplift related to magma inflation in the midcrustal magma body is detected; an uplift of 0.18 cm/yr is measured for the time between 1951-1980. The survey data of 1911 and 1959 are compared to the present data and good correlation is observed. The systematic leveling errors including height-dependence and refraction errors are studied. The 30-km-wide subsidence in the area is examined. The spatial correlation between seismic activity, the Socorro magma body, and crustal deformation in Socorro is investigated. The crustal movement from magma reservior activities is modeled using the formulations of Dieterich and Decker (1975). The modeling of the deformation reveals that the movement in the Socorro area is associated with the 19-km deep Socorro magma body.

  2. A multidisciplinary study on the crustal nature of volcanic conduits and magma reservoirs

    NASA Astrophysics Data System (ADS)

    Flinders, Ashton F.

    Volcanic settings vary widely not only in their eruptive style and products, but in the manner magma travels from deep sources to individual eruptive centers. Imaging these pathways, and their associated crustal reservoirs, provides unique and unprecedented views into these environments. Imaging techniques are varied with the strength of the technique often based on data availability. As such, we focus on two methods---gravity and seismic---in two different settings, each with its own unique volcanic environments, crustal structures, and associated data resources. The first, the Hawaiian Islands, are the most geologically studied hot-spot islands in the world, yet the only large-scale compilation of marine and land gravity data is more than 45 years old. We present a new chain-wide gravity compilation allowing us to locate current and former volcanic centers, major rift zones, a previously suggested volcano, and show that volcanoes along the chain are composed of a small proportion of intrusive material (<30% by volume). At the second area, the arc-volcanism of southern Washington, we used ambient seismic noise methods to constrain the crustal pathways of deep-sourced melt to the surface. We image two zones of reduced velocity, one of which correlates with a proposed extensive zone of mid-crustal partial melt which likely supplies evolved magmas to the surrounding volcanoes and vents, including Mounts St. Helens and Adams.

  3. A numerical simulation of magma motion, crustal deformation, and seismic radiation associated with volcanic eruptions

    USGS Publications Warehouse

    Nishimura, T.; Chouet, B.

    2003-01-01

    The finite difference method is used to calculate the magma dynamics, seismic radiation, and crustal deformation associated with a volcanic eruption. The model geometry consists of a cylindrical reservoir and narrow cylindrical conduit embedded in a homogeneous crust. We consider two models of eruption. In the first model, a lid caps the vent and the magma is overpressurized prior to the eruption. The eruption is triggered by the instantaneous removal of the lid, at which point the exit pressure becomes equal to the atmospheric pressure. In the second model, a plug at the reservoir outlet allows pressurization of only the magmatic fluid in the reservoir before the eruption. Magma transfer between the reservoir and conduit is triggered by the instantaneous removal of the plug, and the eruption occurs when the pressure at the conduit orifice exceeds the material strength of the lid capping the vent. In both models, magma dynamics are expressed by the equations of mass and momentum conservation in a compressible fluid, in which fluid expansion associated with depressurization is accounted for by a constitutive law relating pressure and density. Crustal motions are calculated from the equations of elastodynamics. The fluid and solid are dynamically coupled by applying the continuity of wall velocities and normal stresses across the conduit and reservoir boundaries. Free slip is allowed at the fluid-solid boundary. Both models predict the gradual depletion of the magma reservoir, which causes crustal deformation observed as a long-duration dilatational signal. Superimposed on this very-long-period (VLP) signal generated by mass transport are long-period (LP) oscillations of the magma reservoir and conduit excited by the acoustic resonance of the reservoir-conduit system during the eruption. The volume of the reservoir, vent size, and magma properties control the duration of VLP waves and dominant periods of LP oscillations. The second model predicts that when the

  4. Magma oceanography. II - Chemical evolution and crustal formation. [lunar crustal rock fractional crystallization model

    NASA Technical Reports Server (NTRS)

    Longhi, J.

    1977-01-01

    A description is presented of an empirical model of fractional crystallization which predicts that slightly modified versions of certain of the proposed whole moon compositions can reproduce the major-element chemistry and mineralogy of most of the primitive highland rocks through equilibrium and fractional crystallization processes combined with accumulation of crystals and trapping of residual liquids. These compositions contain sufficient Al to form a plagioclase-rich crust 60 km thick on top of a magma ocean that was initially no deeper than about 300 km. Implicit in the model are the assumptions that all cooling and crystallization take place at low pressure and that there are no compositional or thermal gradients in the liquid. Discussions of the cooling and crystallization of the proposed magma ocean show these assumptions to be disturbingly naive when applied to the ocean as a whole. However, the model need not be applied to the whole ocean, but only to layers of cooling liquid near the surface.

  5. An Experimental Perspective on Lower Crustal Processing of (Arc) Magmas (Invited)

    NASA Astrophysics Data System (ADS)

    Muntener, O.; Ulmer, P.

    2013-12-01

    A major question in Earth Sciences is how continental crust forms and how it is modified over geological timescales. While there are a multitude of processes that constantly modify the continental crust (recycling), the initial formation of silicic crust is generally related to two hypotheses. One is melting of mafic or pelitic crust while the alternative is fractionation from primary mantle derived melts. These processes may occur simultaneously since the lower crust is energetically the most favorable place for modification processes of crustal rocks. Volatiles and heat play a key role in determining the respective solidi of lower crustal rocks, with the important difference that volatiles available for partial melting processes are restricted to structural bound volatiles in hydrous phases, while crystallization produces a much larger variability of potential magmatic water contents. Here we present an experimental perspective on both melting and crystallization processes in the lower crust, with an emphasis on experimentally derived liquid lines of descent by fractional and equilibrium crystallization at middle to lower crustal levels for hydrous, calc-alkaline magmas. These results indicate that fractionation can explain some features of plutonic-volcanic systems that are commonly ascribed to partial melting. Experimental simulation of fractional crystallization is particularly suited to understand the major controls on phase relations and compositions of magmas in the lower crust. Experimental data at pressures of 0.4 to 1.5 GPa, simulating thin and thick lower continental crustal settings are compiled and will be presented. The temperature ranged from near-liquidus conditions at 1300 - 1150 °C to near-solidus conditions at 700 °C. We investigate the mutual phase relations of the principal phases olivine, cpx, opx, garnet, amphibole, plagioclase and Fe-Ti-oxides. Crystallization experiments at lower crustal conditions demonstrate that liquids at 0.7 to 1

  6. Crustal-scale degassing due to magma system destabilization and magma-gas decoupling at Soufrière Hills Volcano, Montserrat

    NASA Astrophysics Data System (ADS)

    Christopher, T. E.; Blundy, J.; Cashman, K.; Cole, P.; Edmonds, M.; Smith, P. J.; Sparks, R. S. J.; Stinton, A.

    2015-09-01

    Activity since 1995 at Soufrière Hills Volcano (SHV), Montserrat has alternated between andesite lava extrusion and quiescence, which are well correlated with seismicity and ground deformation cycles. Large variations in SO2 flux do not correlate with these alternations, but high and low HCl/SO2 characterize lava dome extrusion and quiescent periods respectively. Since lava extrusion ceased (February 2010) steady SO2 emissions have continued at an average rate of 374 tonnes/day (± 140 t/d), and incandescent fumaroles (temperatures up to 610oC) on the dome have not changed position or cooled. Occasional short bursts (over several hours) of higher (˜ 10x) SO2 flux have been accompanied by swarms of volcano-tectonic earthquakes. Strain data from these bursts indicate activation of the magma system to depths up to 10 km. SO2 emissions since 1995 greatly exceed the amounts that could be derived from 1.1 km3 of erupted andesite, and indicating extensive partitioning of sulfur into a vapour phase, as well as efficient decoupling and outgassing of sulfur-rich gases from the magma. These observations are consistent with a vertically extensive, crustal magmatic mush beneath SHV. Three states of the magmatic system are postulated to control degassing. During dormant periods (103 to 104 years) magmatic vapour and melts separate as layers from the mush and decouple from each other. In periods of unrest (years) without eruption, melt and fluid layers become unstable, ascend and can amalgamate. Major destabilization of the mush system leads to eruption, characterized by magma mixing and release of volatiles with different ages, compositions and sources.

  7. Imaging the crustal magma sources beneath Mauna Loa and Kilauea volcanoes, Hawaii

    USGS Publications Warehouse

    Okubo, P.G.; Benz, H.M.; Chouet, B.A.

    1997-01-01

    Three-dimensional seismic P-wave traveltime tomography is used to image the magma sources beneath Mauna Loa and Kilauea volcanoes, Hawaii. High-velocity bodies (>6.4 km/s) in the upper 9 km of the crust beneath the summits and rift zones of the volcanoes correlate with zones of high magnetic intensities and are interpreted as solidified gabbro-ultramafic cumulates from which the surface volcanism is derived. The proximity of these high-velocity features to the rift zones is consistent with a ridge-spreading model of the volcanic flank. Southeast of the Hilina fault zone, along the south flank of Kilauea, low-velocity material (<6.0 km/s) is observed extending to depths of 9-11 km, indicating that the Hilina fault may extend possibly as deep as the basal decollement. Along the southeast flank of Mauna Loa, a similar low -velocity zone associated with the Kaoiki fault zone is observed extending to depths of 6-8 km. These two upper crustal low-velocity zones suggest common stages in the evolution of the Hawaiian shield volcanoes in which these fault systems are formed as a result of upper crustal deformation in response to magma injection within the volcanic edifice.

  8. Testing a New Method for Imaging Crustal Magma Bodies: A Pilot Study at Newberry Volcano, Central OR

    NASA Astrophysics Data System (ADS)

    Beachly, M. W.; Hooft, E. E.; Toomey, D. R.; Waite, G. P.; Durant, D. T.

    2010-12-01

    Magmatic systems are often imaged using delay time seismic tomography, though a known limitation is that wavefront healing limits the ability of transmitted waves to detect small, low-velocity regions such as magma chambers. Crustal magma chambers have been successfully identified using secondary arrivals, including both P and S wave reflections and conversions. Such secondary phases are often recorded by marine seismic experiments owing to the density and quality of airgun data, which improves the identification of coherent arrivals. In 2008 we conducted a pilot study at Newberry volcano to test a new method of detecting secondary arrivals in a terrestrial setting. Our experimental geometry used a line of densely spaced (~300 m), three-component seismometers to record a shot-of-opportunity from the High Lave Plains Experiment. An ideal study would record several shots, however, data from this single event proves the concept. As part of our study, we also reanalyze all existing seismic data from Newberry volcano to obtain a tomographic image of the velocity structure to 6 km depth. Newberry is a lone shield volcano in central Oregon, located 40 km east of the Cascade axis. Newberry eruptions are silicic within the central caldera and mafic on its periphery suggesting a central silicic magma storage system, possibly located at upper crustal depths. The system may still be active with a recent eruption ~1300 years ago, and a central drill hole temperature of 256° C at only 932 m depth. A low-velocity anomaly previously imaged at 3-5 km beneath the caldera indicates either a magma body or a fractured pluton. Our tomographic study combines our 2008 seismic data with profile and array data collected in the 1980s by the USGS. In total, the inversion includes 16 active sources and 322 receivers yielding 1007 P-wave first arrivals. Beneath the caldera ring faults we image a high-velocity ring-like anomaly extending to 2 km depth. This anomaly is inferred to be near

  9. 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

  10. Density of alkaline magmas at crustal and upper mantle conditions by X-ray absorption

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    Silicate melts are essential components of igneous processes and are directly involved in differentiation processes and heat transfer within the Earth. Studies of the physical properties of magmas (e.g., density, viscosity, conductivity, etc) are however challenging and experimental data at geologically relevant pressure and temperature conditions remain scarce. For example, there is virtually no data on the density at high pressure of alkaline magmas (e.g., phonolites) typically found in continental rift zone settings. We present in situ density measurements of alkaline magmas at crustal and upper mantle conditions using synchrotron X-ray absorption. Measurements were conducted on ID27 beamline at ESRF using a panoramic Paris-Edinburgh Press (PE Press). The starting material is a synthetic haplo-phonolite glass similar in composition to the Plateau flood phonolites from the Kenya rift [1]. The glass was synthesized at 1673 K and 2.0 GPa in a piston-cylinder apparatus at ETH Zurich and characterized using EPMA, FTIR and density measurements. The sample contains less than 200 ppm water and is free of CO2. Single-crystal diamond cylinders (Øin = 0.5 mm, height = 1 mm) were used as sample containers and placed in an assembly formed by hBN spacers, a graphite heater and a boron epoxy gasket [2]. The density was determined as a function of pressure (1.0 to 3.1 GPa) and temperature (1630-1860 K) from the X-ray absorption contrast at 20 keV between the sample and the diamond capsule. The molten state of the sample during the data collection was confirmed by X-ray diffraction measurements. Pressure and temperature were determined simultaneously from the equation of state of hBN and platinum using the the double isochor method [3].The results are combined with available density data at room conditions to derive the first experimental equation of state (EOS) of phonolitic liquids at crustal and upper mantle conditions. We will compare our results with recent reports of the

  11. Bubbles Accumulation And Their Role On The Eruptability Of Melt-Rich Silicic Lenses In Upper Crustal Magma Reservoirs

    NASA Astrophysics Data System (ADS)

    Parmigiani, A.; Faroughi, S. A.; Huber, C.; Bachmann, O.

    2014-12-01

    A first-order observation in magmatic rocks is that highly evolved rhyolites are relatively abundant in the volcanic realm, but their plutonic counterparts (granites sensu stricto) are rarer, when ratioed to dacitic/granodioritic compositions. As eruptability is a function of the buoyancy of magmas in upper crustal reservoirs, the presence of exsolved gas (bubbles) plays a fundamental role on eruptability by lowering the bulk density of magmas. Then, if exsolved gas content can accumulate in certain areas of magma reservoirs, it follows that such areas might be more prone to erupt. Magma reservoirs in the upper crust likely have relatively stable, sharp transitions in crystallinity between crystal-rich regions and crystal-poor regions. With this framework in mind, in this presentation, by means of theoretical considerations, numerical modelling and laboratory experiments, we suggest that the storage capacity of exsolved gas in magma reservoirs is a function of the relative abundance of melt respect to crystals present; crystal-poor regions (high melt to crystal volume ratio) tend to act as sponges, accumulating bubbles, while crystal-rich regions (mush zones with low melt to crystal ratio) tend to degas efficiently, leading to upward percolation of volatiles. Hence, melt-rich cupolas accumulating in upper parts of crystal-rich upper crustal reservoirs are particularly eruptible and dominate the volume of volcanic deposits in silicic magmatic provinces.

  12. Constraining the Size and Depth of a Shallow Crustal Magma Body at Newberry Volcano Using P-Wave Tomography and Finite-Difference Waveform Modeling

    NASA Astrophysics Data System (ADS)

    Beachly, M. W.; Hooft, E. E.; Toomey, D. R.; Waite, G. P.

    2011-12-01

    Imaging magmatic systems improves our understanding of magma ascent and storage in the crust and contributes to hazard assessment. Seismic tomography reveals crustal magma bodies as regions of low velocity; however the ability of delay-time tomography to detect small, low-velocity bodies is limited by wavefront healing. Alternatively, crustal magma chambers have been identified from secondary phases including P and S wave reflections and conversions. We use a combination of P-wave tomography and finite-difference waveform modeling to characterize a shallow crustal magma body at Newberry Volcano, central Oregon. Newberry's eruptions are silicic within the central caldera and mafic on its periphery suggesting a central silicic magma storage system. The system may still be active with a recent eruption ~1300 years ago and a drill hole temperature of 256° C at only 932 m depth. A low-velocity anomaly previously imaged at 3-5 km beneath the caldera indicates either a magma body or a fractured pluton. With the goal of detecting secondary arrivals from a magma chamber beneath Newberry Volcano, we deployed a line of densely-spaced (~300 m), three-component seismometers that recorded a shot of opportunity from the High Lava Plains Experiment in 2008. The data record a secondary P-wave arrival originating from beneath the caldera. In addition we combine travel-time data from our 2008 experiment with data collected in the 1980's by the USGS for a P-wave tomography inversion to image velocity structure to 6 km depth. The inversion includes 16 active sources, 322 receivers and 1007 P-wave first arrivals. The tomography results reveal a high-velocity, ring-like anomaly beneath the caldera ring faults to 2 km depth that surrounds a shallow low-velocity region. Beneath 2.5 km high-velocity anomalies are concentrated east and west of the caldera. A central low-velocity body lies below 3 km depth. Tomographic inversions of synthetic data suggest that the central low-velocity body

  13. Geophysical Evidence for Mid-crustal Magma Reservoirs in the Lassen Volcanic Region, California

    NASA Astrophysics Data System (ADS)

    Kinman Tavarez, Samantha C.

    Regional-scale complete Bouguer gravity anomalies underlying the Lassen and Shasta -Medicine Lake regions in northern California and southern Oregon are associated with subduction of the Gorda plate beneath North America. These generally negative anomalies reflect where underplating has deepened to form the mantle wedge, and where subduction has given rise to a series of Quaternary volcanoes comprising the southernmost end of the Cascade range. Multiple conductive bodies were identified by Park and Ostos (2013) in their magnetotelluric (MT) study of the broader Lassen volcanic region. Their broadband and long period measurements were conducted along a 250 km profile spanning from the California-Nevada border, to just west of the Great Valley in California. Utilizing their MT conductor geometries as a starting point, a forward gravity model was generated along the same profile, and agrees well with what they interpret to be the locations and depths of mid-crustal magma bodies in the Lassen and surrounding regions. The excess mass and volume of modeled anomaly (a) - most closely attributed to underlying Lassen Peak - were estimated at -2 x 10 14 kg and 7 x 10 11 m 3 , respectively.

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

    SciTech Connect

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

    1994-06-01

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

  15. 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

  16. Crustal contamination and crystal entrapment during polybaric magma evolution at Mt. Somma Vesuvius volcano, Italy: Geochemical and Sr isotope evidence

    NASA Astrophysics Data System (ADS)

    Piochi, Monica; Ayuso, Robert A.; De Vivo, Benedetto; Somma, Renato

    2006-02-01

    New major and trace element analyses and Sr-isotope determinations of rocks from Mt. Somma-Vesuvius volcano produced from 25 ky BP to 1944 AD are part of an extensive database documenting the geochemical evolution of this classic region. Volcanic rocks include silica undersaturated, potassic and ultrapotassic lavas and tephras characterized by variable mineralogy and different crystal abundance, as well as by wide ranges of trace element contents and a wide span of initial Sr-isotopic compositions. Both the degree of undersaturation in silica and the crystal content increase through time, being higher in rocks produced after the eruption at 472 AD (Pollena eruption). Compositional variations have been generally thought to reflect contributions from diverse types of mantle and crust. Magma mixing is commonly invoked as a fundamental process affecting the magmas, in addition to crystal fractionation. Our assessment of geochemical and Sr-isotopic data indicates that compositional variability also reflects the influence of crustal contamination during magma evolution during upward migration to shallow crustal levels and/or by entrapment of crystal mush generated during previous magma storage in the crust. Using a variant of the assimilation fractional crystallization model (Energy Conservation-Assimilation Fractional Crystallization; [Spera and Bohrson, 2001. Energy-constrained open-system magmatic processes I: General model and energy-constrained assimilation and fractional crystallization (EC-AFC) formulation. J. Petrol. 999-1018]; [Bohrson, W.A. and Spera, F.J., 2001. Energy-constrained open-system magmatic process II: application of energy-constrained assimilation-fractional crystallization (EC-AFC) model to magmatic systems. J. Petrol. 1019-1041]) we estimated the contributions from the crust and suggest that contamination by carbonate rocks that underlie the volcano (2 km down to 9-10 km) is a fundamental process controlling magma compositions at Mt. Somma

  17. 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

  18. The oxygen-hafnium isotope paradox in the early post Columbia River Basalt silicic volcanism: Evidence for complex batch assembly of upper crustal, lower crustal and low-δ18O silicic magmas

    NASA Astrophysics Data System (ADS)

    Colon, D.; Bindeman, I. N.; Ellis, B. S.; Schmitt, A. K.; Fisher, C. M.; Vervoort, J. D.

    2013-12-01

    Eruptions of the Columbia River flood basalts were immediately followed by large eruptions of silicic magmas; some may have been coeval, others genetically-linked to the CRB. Among the most voluminous of these eruptions was the Jarbidge Rhyolite, which comprises ~500 km3 of lava erupted from 16.1-15.0 Ma in northern Nevada. Activity at Jarbidge was followed at 15.0 Ma by a series of rhyolitic ignimbrites and lavas in the J-P Desert of Idaho ~50 km NW of the Jarbidge Rhyolite center. To constrain magmatic origins and upper crustal magma storage conditions of these two silicic magmatic systems, we conducted bulk and high spatial resolution analysis of whole rocks and minerals (quartz, feldspar, and zircon). Bulk quartz and plagioclase δ18O values of the J-P Desert units are only moderately lower than mantle values, with δ18O-quartz of 5.0-5.5‰ and plagioclase δ18O of ~3.9-5.8‰, along with slightly unradiogenic Nd and Hf whole rock values (average ɛHf and ɛNd of -13.1 and -10.0, respectively), while quartz from the Jarbidge Rhyolite has normal δ18O (+8.4‰), but very unradiogenic ɛHf-ɛNd (ɛHf = -34.7, ɛNd = -24.0), fingerprinting Archean upper crust. SIMS analysis of J-P Desert zircons reveals considerably diverse δ18O values, ranging from -0.6‰ to +6.5‰ in a single unit. The same zircon spots yielded U-Pb SIMS ages which generally agree with the 40Ar/39Ar eruption ages, with no evidence of inheritance of pre-Miocene zircons. Combined with LA-MC-ICP-MS analysis of Hf isotopes overlapping the earlier SIMS spots, these zircons show a clear near-linear correlation between ɛHf and δ18O values observed in individual zircons. This relationship suggests variable mixing of two distinct silicic magmas prior to eruption of the J-P Desert rhyolites. One of these, characterized by extremely low ɛHf values and normal δ18O values, is likely a mantle magma strongly contaminated with shallow Archean crust, represented by the Jarbidge Rhyolite. The other is

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  20. The generation, segregation, ascent and emplacement of granite magma: the migmatite-to-crustally-derived granite connection in thickened orogens

    NASA Astrophysics Data System (ADS)

    Brown, Michael

    1994-04-01

    Many granites result from anatexis of common crustal rock types and the segregation, aggregation, ascent and emplacement of the resultant magma. What then is the connection between migmatites, rocks which preserve evidence at outcrop-scale for the presence of former melt now frozen as granite, whether in situ or locally displaced with respect to the site of melting, and map-scale bodies of crustally-derived granite, clearly removed from the site of melting? Both water-rich volatile phase-present melting and volatile phase-absent dehydration melting can occur in the middle and lower crust, but dehydration melting that involves the decomposition of mica and amphibole likely is the more important process in the generation of plutonic volumes of magma with sufficient mobility to reach the upper crust. Both volatile phase-present and dehydration melting can occur in each of the two main types of orogenic belt, those that result from thickening before maximum temperatures are achieved (clockwise in P- T space) and those that result from heating prior to or concomitant with thickening (anticlockwise in P- T space). Depending upon the particular tectonic circumstances, the thermal perturbation to provide the heat necessary for crustal anatexis may be caused by internal radiogenic heat production in overthickened crust, intraplating/underplating of mantle-derived magma, an enhanced flux from the mantle, or some combination of these mechanisms. The tectonic environment to a large extent also controls the segregation, ascent and emplacement of granite magma. For example, at the present time a majority of convergent plate margins exhibit an oblique net displacement vector, and it is likely, therefore, that oblique convergence was important in the past. Retreating subduction boundaries will result in regional deformation of the overriding plate by horizontal extension or transtension in contrast to advancing subduction boundaries that will result in regional deformation of the

  1. Mid-Ocean Ridge Magma Supply and Glacial Cycles: Long Time Series Studies of Crustal Thickness and Seafloor Topography

    NASA Astrophysics Data System (ADS)

    Boulahanis, B.; Carbotte, S. M.; Huybers, P. J.; Langmuir, C. H.; Han, S.; Aghaei, O.; Canales, J. P.; Nedimovic, M. R.; Menke, W. H.

    2015-12-01

    Glacial loading has been shown to modulate volcanic melt generation in subaerial systems, and recent studies suggest that eustatic sea level fluctuations induced by glacial cycles may influence mantle-melting regimes at mid-ocean ridges. Models predict temporal variation in crustal thickness, and seafloor topography, linked to sea level change. Recent studies of bathymetry as a proxy for crustal thickness show significant spectral energy at periodicities linked to Milankovitch cycles of 23, 41, and 100ka (Crowley et al., 2015; Tolstoy, M., 2015). In this study we investigate climate driven periodicity in mid-ocean ridge magma supply utilizing basement topography and crustal thickness data. We use multichannel seismic reflection (MCS) data from two prior studies of the flanks of the Juan de Fuca (JdF) ridge, and 3D MCS data from the Northern East Pacific Rise (EPR) 9°37-57'N. The JdF datasets extend to crustal ages up to 8.78 Ma, and EPR data to ~180 ka. By performing spectral analysis on these data along with dO18 climate records from Lisiecki and Raymo (2005) for the last 5.32ma and Zachos et al. (2001) for earlier times we investigate intervals of similar periodicities in order to identify potential links between climate and magma supply to mid-ocean ridges. Further analysis is undertaken to determine whether depth to basement and crustal thickness are correlated within and across datasets, and whether significant spectral peaks occur in basement and crustal thickness data outside of known climate cycles. Initial results show significant spectral energy in basement depth at the 100ky cycle in the 0-1Ma time series, when eccentricity is understood to have the most impact. Long-term temporal variability is apparent in JdF data, with low relief abyssal hills (~70m on average) present 1-3.2Ma and 6-8.78Ma, but higher relief bathymetry (~200m) from 3.2-6Ma. These subsets align well with previously identified climatic subgroups (Zachos et al., 2001), correlating both

  2. Increasing Interaction of Alkaline Magmas with Lower Crustal Gabbroic Cumulates over the Evolution of Mt. Taylor Volcanic Field, New Mexico

    NASA Astrophysics Data System (ADS)

    Schmidt, M. E.; Crumpler, L. S.; Schrader, C.

    2010-12-01

    The Mount Taylor Volcanic Field at the southeastern edge of the Colorado Plateau, New Mexico erupted diverse alkaline magmas from ~3.8 to 1.5 Ma (Crumpler, 1980; Perry et al., 1990). The earliest eruptions include high silica topaz rhyolites of Grants Ridge (plagioclase, quartz, biotite) and Si-under saturated basanites and trachytes at Mt Taylor stratovolcano. Mt. Taylor was later constructed of stacks of thick, trachyandesitic to rhyolitic lava flows that were subsequently eroded into a ~4-km across amphitheatre opening toward the southeast. Early Mt. Taylor rhyolitic lavas exposed within the amphitheatre contain quartz, plagioclase, hornblende, and biotite (± sanidine) phenocrysts. Later cone-building trachydacite to trachyandesite lavas are crystal-rich with plagioclase and augite megacrysts (± hornblende, ± quartz) and record an overall trend of decreasing SiO2 with time. The last eruptions ~1.5 Ma from the stratovolcano (Perry et al. 1990) produced thick (>70 m), viscous lava flows that contain up to 50% zoned plagioclase phenocrysts. While SiO2 decreased among the silicic magmas, the degree of silica saturation increased among peripheral basaltic magmas from basanite to ne-normative hawaiite to hy-normative basalts. Evidence of increasing crustal contamination within the basalts includes zoned plagioclase megacrysts, augite and plagioclase cumulate texture xenoliths with accompanying xenocrysts. These textures within the basalts combined with abundant, complex plagioclase among the cone-building silicic magmas imply interaction and mixing with gabbroic cumulate mush in the lower crust beneath Mt. Taylor Volcano. Contemporaneous basanitic to trachytitc volcanism in the northern part of the volcanic field at Mesa Chivato (Crumpler, 1980) was more widely distributed, smaller volume, and produced mainly aphyric magmas. The lower crustal gabbroic cumulates either do not extend northward beneath Mesa Chivato, or they were not accessed by lower magma flux rate

  3. Evolution of the crustal magma plumbing system during the build-up to the 22-ka caldera-forming eruption of Santorini (Greece)

    NASA Astrophysics Data System (ADS)

    Fabbro, G. N.; Druitt, T. H.; Scaillet, S.

    2013-12-01

    The formation of shallow, caldera-sized reservoirs of crystal-poor silicic magma requires the generation of large volumes of silicic melt, followed by the segregation of that melt and its accumulation in the upper crust. The 21.8 ± 0.4-ka Cape Riva eruption of Santorini discharged >10 km3 of crystal-poor dacitic magma, along with <<1 km3 of hybrid andesite, and collapsed a pre-existing lava shield. We have carried out a field, petrological, chemical, and high-resolution 40Ar/39Ar chronological study of a sequence of lavas discharged prior to the Cape Riva eruption to constrain the crustal residence time of the Cape Riva magma reservoir. The lavas were erupted between 39 and 25 ka, forming a ˜2-km3 complex of dacitic flows, coulées and domes up to 200 m thick (Therasia dome complex). The Therasia dacites show little chemical variation with time, suggesting derivation from one or more thermally buffered reservoirs. Minor pyroclastic layers occur intercalated within the lava succession, particularly near the top. A prominent pumice fall deposit correlates with the 26-ka Y-4 ash layer found in deep-sea sediments SE of Santorini. One of the last Therasia lavas to be discharged was a hybrid andesite formed by the mixing of dacite and basalt. The Cape Riva eruption occurred no more than 2,800 ± 1,400 years after the final Therasia activity. The Cape Riva dacite is similar in major element composition to the Therasia dacites, but is poorer in K and most incompatible trace elements (e.g. Rb, Zr and LREE). The same chemical differences are observed between the Cape Riva and Therasia hybrid andesites, and between the calculated basaltic mixing end-members of each series. The Therasia and Cape Riva dacites are distinct silicic magma batches and are not related by shallow processes of crystal fractionation or assimilation. The Therasia lavas were therefore not simply precursory leaks from the growing Cape Riva magma reservoir. The change 21.8 ky ago from a magma series

  4. 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.

  5. Deep crustal melting in the Peruvian Andes: Felsic magma generation during delamination and uplift

    NASA Astrophysics Data System (ADS)

    Coldwell, B.; Clemens, J.; Petford, N.

    2011-07-01

    The Miocene-aged Yungay and Fortaleza ignimbrites (YFI), 9° S, Cordillera Blanca, Peru, share geochemical affinities typical of Phanerozoic adakite-like rocks and Archaean tonalite-trondhjemite-granodiorite (TTG) suites. In this contribution, we will investigate the melt source region(s) of the adakitic ignimbrites and their relationship to the dynamic tectonic regime in Peru at the time of eruption. The geochemistry of the YFI differs significantly from spatially related lavas in western Peru, which are characterised by classic calc-alkaline arc signatures. The YFI were erupted along crustal-scale normal faults at the culmination of major tectonic changes affecting the western Peruvian margin, where they represent the last volcanic activity recorded in the area. These regional changes included crustal thickening, shallowing of the Nazca Plate from c. 30° to c. 5°, the arrival and subduction of the Nazca Ridge and rapid crustal uplift and exhumation. The previously unstudied adakitic YFI are examined, then a series of high-pressure piston-cylinder experiments are detailed. Synplutonic mafic-intermediate dyke material is used as an analogous source, and direct experiments are performed on ignimbrite samples. These show that the geochemical signature and mineralogy of the YFI can be produced at pressures > 2.2 GPa and temperatures > 1025 °C. These data support an origin for both ignimbrites as partial melts of juvenile, garnet-bearing, hydrous, mafic lower crust (granulite to eclogite), modified by ~ 20% contamination by igneous crust. A slab source is considered highly improbable. Eclogite and granulite at > 2 GPa (> 65 km depth) are absent within the modern lithospheric architecture of the Peruvian margin, requiring removal of this source region syn- or post-eruption. A likely mechanism for removal is crustal delamination in an east-relative motion, associated with shortening caused by progressive shallowing of the Nazca Plate subducting slab. Due to the

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

    NASA Astrophysics Data System (ADS)

    Degruyter, W.; Huber, C.

    2014-10-01

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

  7. 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.

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

    SciTech Connect

    John, B.E.

    1988-07-01

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

  9. Deep crustal anatexis, magma mixing, and the generation of epizonal plutons in the Southern Rocky Mountains, Colorado

    NASA Astrophysics Data System (ADS)

    Jacob, Kristin H.; Farmer, G. Lang; Buchwaldt, Robert; Bowring, Samuel A.

    2015-01-01

    The Never Summer Mountains in north-central Colorado, USA, are cored by two Oligocene, epizonal granitic plutons originally emplaced in the shallow levels of a short-lived (~1 m.y.), small-volume continental magmatic system. The younger Mt. Cumulus stock (28.015 ± 0.012 Ma) is a syenogranite equivalent compositionally to topaz rhyolites. A comparison to the chemical and isotopic composition of crustal xenoliths entrained in nearby Devonian kimberlites demonstrates that the silicic melts parental to the stock were likely derived from anatexis of local Paleoproterozoic, garnet-absent, mafic lower continental crust. In contrast, the older Mt. Richthofen stock is compositionally heterogeneous and ranges from monzodiorite to monzogranite. Major and trace element abundances and Sr, Nd and Pb isotopic ratios in this stock vary regularly with increasing whole rock wt% SiO2. These data suggest that the Mt. Richthofen stock was constructed from mixed mafic and felsic magmas, the former corresponding to lithosphere-derived basaltic magmas similar isotopically to mafic enclaves entrained in the eastern portions of the stock and the latter corresponding to less differentiated versions of the silicic melts parental to the Mt. Cumulus stock. Zircon U-Pb geochronology further reveals that the Mt. Richthofen stock was incrementally emplaced over a time interval from at least 28.975 ± 0.020 to 28.742 ± 0.053 Ma. Magma mixing could have occurred either in situ in the upper crust during basaltic underplating and remelting of an antecedent, incrementally emplaced, silicic intrusive body, or at depth in the lower crust prior to periodic magma ascent and emplacement in the shallow crust. Overall, the two stocks demonstrate that magmatism associated with the Never Summer igneous complex was fundamentally bimodal in composition. Highly silicic anatectic melts of the mafic lower crust and basaltic, mantle-derived magmas were the primary melts in the magma system, with mixing of the two

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

    USGS Publications Warehouse

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

    2002-01-01

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

  11. Contribution of Transverse Structures, Magma, and Crustal Fluids to Continental Rift Evolution: The East African Rift in Southern Kenya

    NASA Astrophysics Data System (ADS)

    Kattenhorn, S. A.; Muirhead, J.; Dindi, E.; Fischer, T. P.; Lee, H.; Ebinger, C. J.

    2013-12-01

    The Magadi rift in southern Kenya formed at ~7 Ma within Proterozoic rocks of the Mozambique orogenic belt, parallel to its contact with the Archean Tanzania craton. The rift is bounded to the west by the ~1600-m-high Nguruman border fault. The rift center is intensely dissected by normal faults, most of which offset ~1.4-0.8 Ma lavas. Current E-W extensional velocities are ~2-4 mm/yr. Published crustal tomography models from the rift center show narrow high velocity zones in the upper crust, interpreted as cooled magma intrusions. Local, surface-wave, and SKS-splitting measurements show a rift-parallel anisotropy interpreted to be the result of aligned melt zones in the lithosphere. Our field observations suggest that recent fault activity is concentrated at the rift center, consistent with the location of the 1998 seismic swarm that was associated with an inferred diking event. Fault zones are pervasively mineralized by calcite, likely from CO2-rich fluids. A system of fault-fed springs provides the sole fluid input for Lake Magadi in the deepest part of the basin. Many of these springs emanate from the Kordjya fault, a 50-km-long, NW-SE striking, transverse structure connecting a portion of the border fault system (the NW-oriented Lengitoto fault) to the current locus of strain and magmatism at the rift center. Sampled springs are warm (44.4°C) and alkaline (pH=10). Dissolved gas data (mainly N2-Ar-He) suggests two-component mixing (mantle and air), possibly indicating that fluids are delivered into the fault zone from deep sources, consistent with a dominant role of magmatism to the focusing of strain at the rift center. The Kordjya fault has developed prominent fault scarps (~150 m high) despite being oblique to the dominant ~N-S fault fabric, and has utilized an en echelon alignment of N-S faults to accommodate its motion. These N-S faults show evidence of sinistral-oblique motion and imply a bookshelf style of faulting to accommodate dextral-oblique motion

  12. Formation of lunar mare domes along crustal fractures: Rheologic conditions, dimensions of feeder dikes, and the role of magma evolution

    NASA Astrophysics Data System (ADS)

    Wöhler, Christian; Lena, Raffaello; Phillips, Jim

    2007-08-01

    In this study we examine a set of lunar mare domes located in the Hortensius/Milichius/T. Mayer region and in northern Mare Tranquillitatis with respect to their formation along crustal fractures, their rheologic properties, the dimensions of their feeder dikes, and the importance of magma evolution processes during dome formation. Many of these domes display elongated summit vents oriented radially with respect to major impact basins, and several dome locations are also aligned in these preferential directions. Analysis of Clementine UV/VIS and Lunar Prospector gamma ray spectrometer data reveals that the examined mare domes formed from low-Si basaltic lavas of high FeO and low to moderate TiO 2 content. Based on their morphometric properties (diameter, height, volume) obtained by photoclinometric and shape from shading analysis of telescopic CCD images, we derive rheologic quantities (lava viscosity during eruption, effusion rate, duration of the effusion process, magma rise speed) and the dimensions of the feeder dikes. We establish three rheologic groups characterised by specific combinations of rheologic properties and dike dimensions, where the most relevant discriminative parameter is the lava viscosity η. The first group is characterised by 10 Pas<η<10 Pas and contains the domes with elongated vents in the Milichius/T. Mayer region and two similar domes in northern Mare Tranquillitatis. The second group with 10 Pas<η<10 Pas comprises the very low aligned domes in northern Mare Tranquillitatis, and the third group with 10 Pas<η<10 Pas the relatively steep domes near Hortensius and in the T. Mayer region. The inferred dike dimensions in comparison to lunar crustal thickness data indicate that the source regions of the feeder dikes are situated within the upper crust for six of the domes in northern Mare Tranquillitatis, while they are likely to be located in the lower crust and in the upper mantle for the other examined domes. By comparing the time scale

  13. Unravelling the complex interaction between mantle and crustal magmas encoded in the lavas of San Vincenzo (Tuscany, Italy). Part I: Petrography and Thermobarometry

    NASA Astrophysics Data System (ADS)

    Ridolfi, Filippo; Braga, Roberto; Cesare, Bernardo; Renzulli, Alberto; Perugini, Diego; Del Moro, Stefano

    2016-02-01

    The San Vincenzo Volcanic Complex was emplaced ~ 4.4 Ma. ago and consists of cordierite-bearing lavas which are the result of a complex interaction between mantle-derived and crustal anatectic magmas. The lavas are mostly characterized by porphyritic, glassy peraluminous rhyolites hosting variable contents of magmatic enclaves (clinopyroxene-bearing latites and amphibole-bearing clinopyroxene crystal mushes), sialic and ultramafic cognates (syenogranites, anorthosites, cordierite-biotite and pyroxenite inclusions), and crustal rocks (sillimanite-cordierite xenoliths, cordierite and biotite xenocrysts) of centimetric-to-millimetric size. Mineral chemistry shows large variations as well. Plagioclase and sanidine are represented respectively by An21-79Or1-13 and An≤ 1Or57-77. Cordierite has a Mg# of 51-78%, while garnet shows almandine compositions with low CaO (≤ 2 wt.%) and variable MnO contents (1-5 wt.%). Clinopyroxene indicates large ranges of Mg# (68-92%) and Al2O3 (0.5-6.3 wt.%), and relatively high CaO contents (up to 24 wt.%); orthopyroxene shows both ferroan enstatite (Mg# = 60-78%) and magnesian ferrosilite (Mg# = 39-44%) compositions; whereas amphibole shows only Mg-rich calcic compositions. On the basis of textural characteristics, as well as Ti and XMg variations, we have identified six different types of biotite associated with oxide minerals such as ilmenite and spinels of both aluminium (Al > 1 in Y site) and iron (Fe > 1 in Y site) subgroups. Compositional/textural relationships indicate crystallization at both equilibrium and disequilibrium conditions. Minerals with euhedral habits and homogeneous compositions usually occur in the same thin sections of partly-equilibrated crustal xenoliths (and xenocrysts) and zones of "active" mixing between mantle-derived and crustal magmas characterized by "needle-like" and skeletal microlites, and subhedral microphenocrysts of amphibole and biotite. These hybrid-mixed features, as well as the occurrence of

  14. Unravelling the complex interaction between mantle and crustal magmas encoded in the lavas of San Vincenzo (Tuscany, Italy). Part I: Petrography and Thermobarometry

    NASA Astrophysics Data System (ADS)

    Ridolfi, Filippo; Braga, Roberto; Cesare, Bernardo; Renzulli, Alberto; Perugini, Diego; Del Moro, Stefano

    2016-02-01

    The San Vincenzo Volcanic Complex was emplaced ~ 4.4 Ma. ago and consists of cordierite-bearing lavas which are the result of a complex interaction between mantle-derived and crustal anatectic magmas. The lavas are mostly characterized by porphyritic, glassy peraluminous rhyolites hosting variable contents of magmatic enclaves (clinopyroxene-bearing latites and amphibole-bearing clinopyroxene crystal mushes), sialic and ultramafic cognates (syenogranites, anorthosites, cordierite-biotite and pyroxenite inclusions), and crustal rocks (sillimanite-cordierite xenoliths, cordierite and biotite xenocrysts) of centimetric-to-millimetric size. Mineral chemistry shows large variations as well. Plagioclase and sanidine are represented respectively by An21-79Or1-13 and An≤ 1Or57-77. Cordierite has a Mg# of 51-78%, while garnet shows almandine compositions with low CaO (≤ 2 wt.%) and variable MnO contents (1-5 wt.%). Clinopyroxene indicates large ranges of Mg# (68-92%) and Al2O3 (0.5-6.3 wt.%), and relatively high CaO contents (up to 24 wt.%); orthopyroxene shows both ferroan enstatite (Mg# = 60-78%) and magnesian ferrosilite (Mg# = 39-44%) compositions; whereas amphibole shows only Mg-rich calcic compositions. On the basis of textural characteristics, as well as Ti and XMg variations, we have identified six different types of biotite associated with oxide minerals such as ilmenite and spinels of both aluminium (Al > 1 in Y site) and iron (Fe > 1 in Y site) subgroups. Compositional/textural relationships indicate crystallization at both equilibrium and disequilibrium conditions. Minerals with euhedral habits and homogeneous compositions usually occur in the same thin sections of partly-equilibrated crustal xenoliths (and xenocrysts) and zones of "active" mixing between mantle-derived and crustal magmas characterized by "needle-like" and skeletal microlites, and subhedral microphenocrysts of amphibole and biotite. These hybrid-mixed features, as well as the occurrence of

  15. Effects of chaotic advection on the timescales of cooling and crystallization of magma bodies at mid crustal levels

    NASA Astrophysics Data System (ADS)

    Petrelli, Maurizio; El Omari, Kamal; Le Guer, Yves; Perugini, Diego

    2016-02-01

    We numerically define the thermochemical evolution of a subduction-related crystal-bearing magmatic mass at mid crustal levels (0.7 GPa, 20-25 km). Two main dynamic mechanisms are considered: (1) a pure buoyancy-driven system where the convective flow is induced by density changes during magma cooling; (2) a buoyancy-driven convective system governed by chaotic advection. The non-Newtonian rheology of natural magmas is taken into account linking the Herschel-Bulkley formulation with the results of fractional crystallization experiments of magmas with the same composition and at the same conditions of temperature and pressure of the studied system. The latent heat of crystallization is also considered in order to address the thermal release in the system induced by the crystallization. Results indicate that the development of chaotic advection generates a complex thermochemical evolution of the system speeding up the crystallization process and the timing required to reach the jamming condition relative to the pure buoyancy-driven convective system (nearly 2 times faster). Our results have important implications for both the rheological history of the magmatic body and the refilling of shallower magmatic systems. In particular, (1) a time-dependent composition ranging from basalt to andesite can be extracted from an initial basaltic magmatic batch; (2) at the attainment of the maximum packing fraction (i.e., just before the jamming condition), homogeneous andesitic melts can be potentially extracted from the system; and (3) the development of chaotic advection within the system allows for the extraction of andesitic melt in shorter times compared to a buoyancy-dominated system.

  16. Constraints on the Upper Crustal Magma Reservoir Beneath Yellowstone Lake Inferred From Lake-Seiche Induced Strain Observations

    NASA Astrophysics Data System (ADS)

    Luttrell, K. M.; Mencin, D.; Francis, O.; Hurwitz, S.; Hodgkinson, K. M.; Kinsey, S.

    2012-12-01

    Periodic seiches with an ~80-minute period and wave heights up to 10 cm are observed in Yellowstone Lake. Though small, these water level variations act as a load on the solid earth that has been observed on highly sensitive borehole strainmeters throughout Yellowstone National Park. In particular, we observe no time delay (five minutes or less) between the appearance of a seiche signal at a close strainmeter (100 m from the lake edge) and a distant strainmeter (20 km away). The amplitude, timing, and spatial distribution of the observed strain response relative to the observed water load can be used to infer the mechanical characteristics of the subsurface. We calculate the strain field induced by the load of Yellowstone Lake seiches using an elastic half-space model that represents the upper few kilometers of solid crust. We determine that the predicted far-field strain response is much smaller (by more than an order of magnitude) than the measured strain at locations that are distant from the lake. This indicates that far-field strain induced by lake seiches may be sensitive to the location and composition of the crustal magma reservoir. To constrain the depth and viscosity of this reservoir, we calculate the strain field induced in a layered viscoelastic half-space using a semi-analytic model. We find that a magma reservoir must be at least 4 km deep with a Maxwell viscosity of less than 1011 Pa s. The best-fitting depth to the top of an idealized magma chamber is 5-6 km. These new strain observations provide independent evidence for the likely presence of a partially molten body at shallow depth. Continuing observations can provide a valuable contribution to the monitoring and improved understanding of the Yellowstone magmatic system.

  17. Crustal composition in southern Norway from active and passive source seismology

    NASA Astrophysics Data System (ADS)

    Stratford, W. R.; Frassetto, A. M.; Thybo, H.

    2010-12-01

    Crustal composition and structure beneath the Fennoscandian shield are highly variable due to the method of crustal accretion and the long history of extensional and compressional tectonics. In southern Norway, the Moho and crust are inferred to be the youngest of the shield, however, it is likely that a large discrepancy between crustal age and Moho age exists beneath the high southern Scandes where the Caledonian orogeny was in effect and beneath the Oslo Graben where 60 million years of rifting and magmatism has altered the crust. Crustal structure in southern Norway was targeted with a multi-disciplinary seismic study (Magnus-Rex - Mantle investigations of Norwegian uplift Structure). Three ~400 km long active source seismic profiles across the southern Norway and a region wide array of broadband seismometers were deployed. P and S-wave arrivals were recorded in the Magnus-Rex project, from which Poisson ratios for the crust in southern Norway are calculated from both active source profiling and receiver functions. Unusually strong S-wave arrivals allow rare insight into crustal Poisson’s ratio structure, within crustal layers, that is not normally available from active source data and are usually determined by earthquake tomography studies where only bulk crustal values are available. An average Poisson’s ratio of 0.25 is calculated for the crust in southern Norway, suggesting it is predominantly of felsic-intermediate composition and lacks any significant mafic lower crust. This differs significantly from the adjacent crust in the Svecofennian domain of the Fennoscandian shield where Moho depths reach ~50 km and an up to 20 km thick mafic lower crust is present. The vast difference in Moho depths in the Fennoscandian shield are, therefore, mostly due to the variation in thickness of the high Vp lower crust. Estimates of crustal composition and the effect of Magma intrusion within the Oslo Graben, and possible delamination of the lowermost crust beneath

  18. Crustal magmatism under a hydrothermal system, and the imprints of assimilation of hydrothermally altered protolith: an investigation of geochemical signatures in rhyolitic magmas at Yellowstone caldera

    NASA Astrophysics Data System (ADS)

    Girard, G.

    2014-12-01

    Yellowstone caldera, Wyoming, hosts one of the largest hydrothermal systems on Earth, fueled by heat and volatiles released from hotspot-derived basalt magmas that stall in the crust. Prolonged hydrothermal activity has pervasively altered the subsurface and such altered material is presumed to have acted as a source for magmas erupted after the two largest caldera eruptions, as evidenced by low-δ18O signatures in these magmas. This study focuses on the youngest Yellowstone volcanic units, the ~ 255 ka to ~ 70 ka large volume (~ 360 km3) Central Plateau Member (CPM) rhyolites. New laser-ablation ICP-MS whole rock, glass and mineral trace element data were obtained in order to refine existing constraints on CPM petrogenesis. Small temporal increases in elements such as As (3.1-4.1 ppm), Rb (170-200 ppm), Cs (3.6-4.3 ppm), Pb (26-31 ppm), Th (23-27 ppm) and U (5.4-6.8 ppm) contrast with increases of ~ 40-50 % in HFSE and REE in the same samples. The highest observed temporal increase is that of Zn, from 65 to 105 ppm. Caesium is highly incompatible with mineral/glass partition coefficients KD < 0.05 measured in all investigated mineral phases. Rubidium is also incompatible but its sanidine/glass KD ~ 0.4 results in a larger bulk distribution coefficient DRb ~ 0.2. For Pb, sanidine/glass KD ~ 0.8 leads to DPb > 0.4. Zinc is observed to be compatible in clinopyroxene, fayalite, zircon, chevkinite (KD ~ 5-12), and Fe-Ti oxides (KD ~ 40), such that DZn may approach 1. Fractional crystallization or partial melting processes alone cannot explain the same small increase rate of elements with diverse degrees of incompatibility (Rb, Cs and Pb), nor a larger increase rate in nearly compatible Zn. Assimilation by the juvenile CPM magmas of a crustal material of distinct composition appears to be required, and hydrothermally altered rhyolites, comprising much of the Yellowstone subsurface represent the most likely assimilant. Lower Rb, Cs, Pb (perhaps also As and U) and higher

  19. Evaluation of crustal recycling during the evolution of Archean-age Matachewan basaltic magmas

    NASA Technical Reports Server (NTRS)

    Nelson, Dennis O.

    1989-01-01

    The simplest model for the Matachewan-Hearst Dike (MHD) magmas is assimilation-fractional crystallization (AFC), presumably occurring at the base of the crust during underplating. Subduction zone enriched mantle sources are not required. Trace elements suggest that the mantle sources for the MHD were depleted, but possessed a degree of heterogeneity. Rates of assimilation were approximately 0.5 (= Ma/Mc); the contaminant mass was less than 20 percent. The contaminant was dominated by tonalites-randodiorites, similar to xenoliths and rocks in the Kapuskasing Structural Zone (KSZ). Assimilation of partial melts of light-rare earth and garnet-bearing basaltic precursors may have produced some the MHD magmas. Apparently, previous underplating-AFC processes had already produced a thick crust. The silicic granitoid assimilant for the MHD magmas was probably produced by earlier processing of underplated mafic crust (4, 5, 10, 21 and 30). Calculations suggest that the derived silicic rocks possess negative Ta and Ti anomalies even though they were not the product of subduction.

  20. Crustal movements due to Iceland's shrinking ice caps mimic magma inflow signal at Katla volcano.

    PubMed

    Spaans, Karsten; Hreinsdóttir, Sigrún; Hooper, Andrew; Ófeigsson, Benedikt Gunnar

    2015-01-01

    Many volcanic systems around the world are located beneath, or in close proximity to, ice caps. Mass change of these ice caps causes surface movements, which are typically neglected when interpreting surface deformation measurements around these volcanoes. These movements can however be significant, and may closely resemble movements due to magma accumulation. Here we show such an example, from Katla volcano, Iceland. Horizontal movements observed by GPS on the flank of Katla have led to the inference of significant inflow of magma into a chamber beneath the caldera, starting in 2000, and continuing over several years. We use satellite radar interferometry and GPS data to show that between 2001 and 2010, the horizontal movements seen on the flank can be explained by the response to the long term shrinking of ice caps, and that erratic movements seen at stations within the caldera are also not likely to signify magma inflow. It is important that interpretations of geodetic measurements at volcanoes in glaciated areas consider the effect of ice mass change, and previous studies should be carefully reevaluated. PMID:25992847

  1. Pressures of Partial Crystallization of Magmas from the Juan de Fuca Ridge: Implications for Crustal Accretion

    NASA Astrophysics Data System (ADS)

    Scott, J. L.; Barton, M.

    2010-12-01

    Plate spreading at the mid-ocean ridges is accompanied by intrusion of dikes and eruption of lava along the ridge axis. It has been suggested that the depth of magma chambers that feed the flows and dikes is related to the rate of spreading. As part of a larger effort to examine this hypothesis, we determined the depths of magma chambers beneath the intermediate spreading Juan de Fuca Ridge (JdF) which extends from the Blanco fracture zone at about 44.5 degrees North to the Triple junction of the JdF, Nootka Fault, and the Socanco fracture zone at 48.7 degrees North. Pressures of partial crystallization were determined by comparing the compositions of natural liquids (glasses) with those of experimental liquids in equilibrium with olivine, plagioclase, and clinopyroxene at different pressures and temperatures using the method described by Kelley and Barton (2008). Chemical analyses mid-ocean ridge basalts glasses sampled from along the JdF were used as liquid compositions. Samples with anomalous chemical compositions and samples that yielded pressures associated with unrealistically large uncertainties were filtered out of the database. The calculated pressures for the remaining 533 samples were used to calculate the depths of partial crystallization and to identify the likely location of magma chambers. Preliminary results indicate that the pressure of partial crystallization decreases from 2 to 1±0.5 kbars from the Blanco fracture zone to the north along the Cleft segment of the ridge. Calculated pressures remain approximately constant at 0.87±0.53 kbars along ridge segments to the north of the Cleft. These low pressures for the remaining segments of the ridge are interpreted to indicate magma chambers at depths of 1.3-4.9 km and agree reasonably well with the depths of seismically imaged tops of axial magma chambers (2-3 km) (Canales et al 2009). The higher pressures obtained for lavas erupted along the Cleft segment of the JdF agree very well with recent

  2. Crustal deformation and volcanism at active plate boundaries

    NASA Astrophysics Data System (ADS)

    Geirsson, Halldor

    Most of Earth's volcanoes are located near active tectonic plate boundaries, where the tectonic plates move relative to each other resulting in deformation. Likewise, subsurface magma movement and pressure changes in magmatic systems can cause measurable deformation of the Earth's surface. The study of the shape of Earth and therefore studies of surface deformation is called geodesy. Modern geodetic techniques allow precise measurements (˜1 mm accuracy) of deformation of tectonic and magmatic systems. Because of the spatial correlation between tectonic boundaries and volcanism, the tectonic and volcanic deformation signals can become intertwined. Thus it is often important to study both tectonic and volcanic deformation processes simultaneously, when one is trying to study one of the systems individually. In this thesis, I present research on crustal deformation and magmatic processes at active plate boundaries. The study areas cover divergent and transform plate boundaries in south Iceland and convergent and transform plate boundaries in Central America, specifically Nicaragua and El Salvador. The study is composed of four main chapters: two of the chapters focus on the magma plumbing system of Hekla volcano, Iceland and the plate boundary in south Iceland; one chapter focuses on shallow controls of explosive volcanism at Telica volcano, Nicaragua; and the fourth chapter focuses on co- and post-seismic deformation from a Mw = 7.3 earthquake which occurred offshore El Salvador in 2012. Hekla volcano is located at the intersection of a transform zone and a rift zone in Iceland and thus is affected by a combination of shear and extensional strains, in addition to co-seismic and co-rifting deformation. The inter-eruptive deformation signal from Hekla is subtle, as observed by a decade (2000-2010) of GPS data in south Iceland. A simultaneous inversion of this data for parameters describing the geometry and source characteristics of the magma chamber at Hekla, and

  3. 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

  4. Rejuvenation of shallow-crustal silicic magma bodies at Augustine and Hayes volcanoes, Alaska

    NASA Astrophysics Data System (ADS)

    Coombs, M. L.; Vazquez, J. A.; Hayden, L. A.; Calvert, A. T.; Lidzbarski, M. I.; Andersen, N. L.; Till, C. B.

    2015-12-01

    Rejuvenation of crystal-rich magma bodies leading to eruption can occur on a variety of scales and in varied tectonic settings. Two examples from the Aleutian arc highlight 1) segregation of silicic melt from an intermediate mush, and 2) "defrosting" of a shallowly emplaced intrusion. Augustine Volcano erupted a late Pleistocene rhyolite pumice fall that we link through zircon geochronology to cumulate dioritic blocks, ripped from Augustine's shallow magmatic plumbing system and ejected during the 2006 eruption. Unpolished zircon rims from the rhyolite yield a U-Th age of ~25 ka, and interiors yield a dominant age population of ~26 ka. Zircons from diorites have interior ages and compositions indistinguishable from those of the rhyolite. The diorites, rhyolite, and early Holocene dacites define whole-rock linear unmixing trends consistent with melt (rhyolite) extraction from a mush (dacites), leaving behind a cumulate residue (diorites). A volatile-rich basalt erupted just prior to the rhyolite likely facilitated melt extraction from the mush. The rhyolitic Hayes River ignimbrite, erupted from Hayes volcano, contains dense porphyry blocks that match pumices in composition and phenocryst content and are samples of a shallow intrusion. Autocrystic monazite accommodated up to several weight % Th and significantly affected the U-Th ratio of the magma during differentiation. An isochron for early melt and low-U monazites yields an age of ~67 ka, whereas one for late melt and high-U monazites yields ~42 ka. This younger age is indistinguishable from the laser single crystal Ar-Ar age for sanidine of 41±2 ka (1 sigma). We interpret the apparent ~25 k.y. crystallization interval to represent the assembly and differentiation timescale associated with the Hayes magma body. Sharp reverse zoning in sanidine from pumice (but not porphyry) records a thermal pulse not seen in the more slowly reacting phases, suggesting that a rejuvenation event occurred just prior to eruption.

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

    NASA Astrophysics Data System (ADS)

    Caricchi, Luca; Simpson, Guy; Schaltegger, Urs

    2016-04-01

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

  6. Coupled interactions between volatile activity and Fe oxidation state during arc crustal processes

    USGS Publications Warehouse

    Humphreys, Madeleine C.S.; Brooker, R; Fraser, D.C.; Burgisser, A; Mangan, Margaret T.; McCammon, C

    2015-01-01

    Arc magmas erupted at the Earth’s surface are commonly more oxidized than those produced at mid-ocean ridges. Possible explanations for this high oxidation state are that the transfer of fluids during the subduction process results in direct oxidation of the sub-arc mantle wedge, or that oxidation is caused by the effect of later crustal processes, including protracted fractionation and degassing of volatile-rich magmas. This study sets out to investigate the effect of disequilibrium crustal processes that may involve coupled changes in H2O content and Fe oxidation state, by examining the degassing and hydration of sulphur-free rhyolites. We show that experimentally hydrated melts record strong increases in Fe3+/∑Fe with increasing H2O concentration as a result of changes in water activity. This is relevant for the passage of H2O-undersaturated melts from the deep crust towards shallow crustal storage regions, and raises the possibility that vertical variations in fO2 might develop within arc crust. Conversely, degassing experiments produce an increase in Fe3+/∑Fe with decreasing H2O concentration. In this case the oxidation is explained by loss of H2 as well as H2O into bubbles during decompression, consistent with thermodynamic modelling, and is relevant for magmas undergoing shallow degassing en route to the surface. We discuss these results in the context of the possible controls on fO2 during the generation, storage and ascent of magmas in arc settings, in particular considering the timescales of equilibration relative to observation as this affects the quality of the petrological record of magmatic fO2.

  7. Using chalcophile elements to constrain crustal contamination and xenolith-magma interaction in Cenozoic basalts of eastern China

    NASA Astrophysics Data System (ADS)

    Zeng, Gang; Huang, Xiao-Wen; Zhou, Mei-Fu; Chen, Li-Hui; Xu, Xi-Sheng

    2016-08-01

    Continental basalts have complicated petrogenetic processes, and their chemical compositions can be affected by multi-staged geological evolution. Compared to lithophile elements, chalcophile elements including Ni, platinum-group elements (PGEs) and Cu are sensitive to sulfide segregation and fractional crystallization during the evolution of mantle-derived magmas and can provide constraints on the genesis of continental basalts. Cenozoic intra-continental alkaline basalts in the Nanjing basaltic field, eastern China, include high-Ca and low-Ca varieties. All these basalts have poor PGE contents with Ir ranging from 0.016 ppb to 0.288 ppb and high Cu/Pd ratios from 0.7 × 105 to 4.7 × 105 (5.7 × 103 for DMM), indicating that they were derived from sulfide-saturated mantle sources with variable amounts of residual sulfide during melting or might undergo an early-sulfide segregation in the mantle. Relatively high Cu/Pd ratios along with high Pd concentrations for the high-Ca alkaline basalts indicate an additional removal of sulfide during magma ascent. Because these basalts have high, variable Pd/Ir ratios (2.8-16.8) with low Ce/Pb (9.9-19.7) ratios and εNd values (+ 3.6-+6.4), crustal contamination is proposed to be a potential process to induce the sulfide saturation and removal. Significantly increased Pd/Ir ratios for few high-Ca basalts can be explained by the fractionation of laurite or Ru-Os-Ir alloys with olivine or chromite. For low-Ca alkaline basalts, their PGE contents are well correlated with the MgO, Sc contents, incompatible element ratios (Lu/Hf, Na/Ti and Ca/Al) and Hf isotopes. Good correlations are also observed between Pd/Ir (or Rh/Ir) and Na/Ti (or Ca/Al) ratios. Variations of these elemental ratios and Hf isotopes is previously documented to be induced by the mixing of peridotite xenolith-released melts during ascent. Therefore, we suggest that such xenolith-magma interaction are also responsible for the variable PGE compositions of low

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  9. Moving Mountains and Deep Crustal Earthquakes: Evidence for Deep Magma Injection Beneath Lake Tahoe, Nevada-California

    NASA Astrophysics Data System (ADS)

    Blewitt, G.; Smith, K. D.; von Seggern, D.

    2004-12-01

    We recently reported [Smith et al., Science 305, 2004] an unusually deep swarm of 1611 earthquakes that occurred in late 2003 at Lake Tahoe, California (depth 29-33 kilometer; Richter Magnitude [ML] < 2.2; sum of the moment magnitude of all events is Mw 3.1). This swarm was coeval with a GPS transient displacement of 6 ± 0.3 mm horizontally outward from the swarm and 7.9 ± 1.0 mm upward measured at the GPS station on Slide Mountain, Nevada (SLID) 18 km to the northeast. Station SLID is a part of the 53-station Basin and Range Geodetic Network (BARGEN) network, continuously operating since 1996 and one of the PBO Nucleus stations. Here we focus on the results of the geodetic analysis for SLID, and other BARGEN stations within 200 km of SLID, starting on 1 January 2000. The SLID transient displacement is 9.8 mm in a direction normal to the planar structure defined by the deep earthquake swarm, spanning the same time period of the swarm. The geodetic displacement here is too large to be explained by the elastic strain from the cumulative seismic moment of the sequence, suggesting an aseismic forcing mechanism. Aspects of the swarm and SLID displacements are consistent with lower-crustal magma injection under Lake Tahoe. During the first 23 days of the swarm, hypocentral depths migrated at a rate of 2.4 millimeters/second up-dip along a 40-km2 structure striking N30° W and dipping 50° to the northeast. Assuming a stress drop of 10 MPa (reasonable for upper crustal earthquakes), this event has an equivalent seismic moment to a magnitude (Mw) 6.0 earthquake with a displacement of ~1 meter at the source. Applying Okada's model for a tensile crack at 28 km depth in the source region, a potency equivalent to a volume of 3.7 × 107 m3, or volumetric moment equivalent of Mw 6.4, fits the SLID observations. As there is no established evidence of recent volcanism (<1 Ma) in the Tahoe region, this discovery suggests the hypothesis that such deep magmatic events in

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

    NASA Astrophysics Data System (ADS)

    Yamasaki, Tadashi

    2016-04-01

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

  11. Crustal contamination and crystal entrapment during polybaric magma evolution at Mt. Somma-Vesuvius volcano, Italy: Geochemical and Sr isotope evidence

    USGS Publications Warehouse

    Piochi, M.; Ayuso, R.A.; de Vivo, B.; Somma, R.

    2006-01-01

    New major and trace element analyses and Sr-isotope determinations of rocks from Mt. Somma-Vesuvius volcano produced from 25 ky BP to 1944 AD are part of an extensive database documenting the geochemical evolution of this classic region. Volcanic rocks include silica undersaturated, potassic and ultrapotassic lavas and tephras characterized by variable mineralogy and different crystal abundance, as well as by wide ranges of trace element contents and a wide span of initial Sr-isotopic compositions. Both the degree of undersaturation in silica and the crystal content increase through time, being higher in rocks produced after the eruption at 472 AD (Pollena eruption). Compositional variations have been generally thought to reflect contributions from diverse types of mantle and crust. Magma mixing is commonly invoked as a fundamental process affecting the magmas, in addition to crystal fractionation. Our assessment of geochemical and Sr-isotopic data indicates that compositional variability also reflects the influence of crustal contamination during magma evolution during upward migration to shallow crustal levels and/or by entrapment of crystal mush generated during previous magma storage in the crust. Using a variant of the assimilation fractional crystallization model (Energy Conservation-Assimilation Fractional Crystallization; [Spera and Bohrson, 2001. Energy-constrained open-system magmatic processes I: General model and energy-constrained assimilation and fractional crystallization (EC-AFC) formulation. J. Petrol. 999-1018]; [Bohrson, W.A. and Spera, F.J., 2001. Energy-constrained open-system magmatic process II: application of energy-constrained assimilation-fractional crystallization (EC-AFC) model to magmatic systems. J. Petrol. 1019-1041]) we estimated the contributions from the crust and suggest that contamination by carbonate rocks that underlie the volcano (2 km down to 9-10 km) is a fundamental process controlling magma compositions at Mt. Somma

  12. The 2010-2011 Microearthquake Swarm in Krýsuvík, SW Iceland: Was it Triggered by Crustal Magma Injection?

    NASA Astrophysics Data System (ADS)

    Liu, J.; Michael, F.; Hager, B. H.

    2013-12-01

    Iceland, the on-land continuation of the Mid-Atlantic Ridge, is the result of the interaction between the Mid-Atlantic Ridge and the North-Atlantic mantle plume. The superposition and relative motion of the spreading plate boundary over the mantle plume are manifested by the volcanism and seismicity in Iceland. The Krýsuvík geothermal field is one of the most active geothermal fields in southwest Iceland. In 2010, Massachusetts Institute of Technology, Reykjanes University, Uppsala University, and the Iceland Geosurvey (ISOR) deployed 38 temporary seismic stations on the Reykjanes Peninsula. Using data from 18 of the temporary seismic stations and from 5 stations of the South Iceland Lowland network around Krýsuvík, we captured an earthquake swarm that occurred between November, 2010 and February, 2011. We applied double difference tomography to relocate the events and determine the velocity structure in the region. Activity is clustered around the center of the Krýsuvík volcano system. Our seismic tomography result indicates a low velocity zone at a depth of about 6 km, right under the earthquake swarm. We consider that this low velocity zone contains some crustal magma that may be the thermal source for the geothermal field. At the same time, our relocated events delineate faults above and around this magma chamber. The system is within the stress field of a combination of left-lateral shear and extension; the majority of the strike-slip faults are right-lateral and most dip-slip faults are normal faults. Published geodetic measurements for the time period between 2009 and 2012 show a few centimeters uplift and extension in the area of the seismic swarm. We modeled the observed deformation using the Coulomb 3.3 software (U.S. Geological Survey). Our result indicates that a Mogi source of about 20×10^6 m^3 at a depth of about 6 km, consistent with the location and size of the tomography result, can explain the main deformation. The normal and the right

  13. Linking Plagioclase Zoning Patterns to Active Magma Processes

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Arnulf, Adrien; Harding, Alistair; Kent, Graham

    2013-04-01

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

  15. Output rate of magma from active central volcanoes

    NASA Technical Reports Server (NTRS)

    Wadge, G.

    1980-01-01

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

  16. 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.

  17. Lead and strontium isotopic evidence for crustal interaction and compositional zonation in the source regions of Pleistocene basaltic and rhyolitic magmas of the Coso volcanic field, California

    USGS Publications Warehouse

    Bacon, C.R.; Kurasawa, H.; Delevaux, M.H.; Kistler, R.W.; Doe, B.R.

    1984-01-01

    The isotopic compositions of Pb and Sr in Pleistocene basalt, high-silica rhyolite, and andesitic inclusions in rhyolite of the Coso volcanic field indicate that these rocks were derived from different levels of compositionally zoned magmatic systems. The 2 earliest rhyolites probably were tapped from short-lived silicic reservoirs, in contrast to the other 36 rhyolite domes and lava flows which the isotopic data suggest may have been leaked from the top of a single, long-lived magmatic system. Most Coso basalts show isotopic, geochemical, and mineralogic evidence of interaction with crustal rocks, but one analyzed flow has isotopic ratios that may represent mantle values (87Sr/86Sr=0.7036,206Pb/204Pb=19.05,207Pb/204Pb=15.62,208Pb/204Pb= 38.63). The (initial) isotopic composition of typical rhyolite (87Sr/86Sr=0.7053,206Pb/204Pb=19.29,207Pb/204Pb= 15.68,208Pb/204Pb=39.00) is representative of the middle or upper crust. Andesitic inclusions in the rhyolites are evidently samples of hybrid magmas from the silicic/mafic interface in vertically zoned magma reservoirs. Silicic end-member compositions inferred for these mixed magmas, however, are not those of erupted rhyolite but reflect the zonation within the silicic part of the magma reservoir. The compositional contrast at the interface between mafic and silicic parts of these systems apparently was greater for the earlier, smaller reservoirs. ?? 1984 Springer-Verlag.

  18. 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.

  19. 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

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

    NASA Astrophysics Data System (ADS)

    Takebe, Yoshinori; Ban, Masao

    2015-10-01

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

  1. Origin of a silica-oversaturated quartz trachyte rhyolite suite through combined crustal melting, magma mixing, and fractional crystallization: the Leyva Canyon volcano, Trans-Pecos Magmatic Province, Texas

    NASA Astrophysics Data System (ADS)

    White, John Charles; Urbanczyk, Kevin M.

    2001-11-01

    The Leyva Canyon Member of the Rawls Formation is a sequence of Oligocene (27.3-27.1 Ma) silicic lava, tuff, and volcaniclastic rock that comprise a trachytic shield volcano in the central Bofecillos Mountains of Big Bend Ranch State Park, Texas. This silicic unit developed within a volcanic field that was otherwise dominated by silica-undersaturated, mafic to intermediate lava. Quartz trachyte to low-silica rhyolite of the Leyva Canyon volcano appears to be the result of magma mixing between mantle-derived, alkalic mafic magmas and peraluminous crustal melt (˜40% crustal input), followed by ˜65% fractional crystallization. The parental mafic component was probably similar to silica-undersaturated, mafic lavas of the Rawls Formation. Peraluminous, A-type high-silica rhyolite represents the earliest-erupted lavas of the Leyva Canyon volcano and is unrelated to quartz trachyte and low-silica rhyolite via fractional crystallization. The high-silica rhyolite provides evidence for an episode of crustal melting beneath the Leyva Canyon volcano. Data from the Rawls Formation suggest that silica-undersaturated, alkalic (ne-normative) mafic magmas may evolve via fractional crystallization alone to silica-undersaturated silicic compositions (ne-trachyte), but require magma mixing with crustal-derived silicic magmas coupled with fractional crystallization to produce silica-oversaturated magmas (quartz trachyte-rhyolite). Mixing with a high-Al 2O 3 crustal component results in silica-oversaturated, mildly peraluminous and metaluminous to mildly peralkalic felsic rocks, rather than the strongly peralkalic rocks more commonly associated with alkalic mafic magmas.

  2. Unravelling the complex interaction between mantle and crustal magmas encoded in the lavas of San Vincenzo (Tuscany, Italy). Part II: Geochemical overview and modelling

    NASA Astrophysics Data System (ADS)

    Ridolfi, Filippo; Renzulli, Alberto; Perugini, Diego; Cesare, Bernardo; Braga, Roberto; Del Moro, Stefano

    2016-02-01

    This work reports a geochemical overview and modelling of the lavas erupted ~ 4.4 Ma ago at San Vincenzo (Tuscan Magmatic Province, TMP). Although these lavas cover a relatively small area (~ 10 km2), they show very large geochemical variations caused by the interaction of mantle-derived and crustal-anatectic magmas. The lavas consist of peraluminous rhyolites (87Sr/86Sr(i) up to 0.726) hosting primarily variably sized magmatic enclaves with shoshonite/latite compositions (87Sr/86Sr(i) down to 0.708). New whole-rock data for a large shoshonite enclave show high concentrations of LREE, LILE, and tetravalent HFSE, coupled with pentavalent HFSE depletions and enrichments in compatible elements such as Cr and Co. The chondrite-normalised REE pattern is strongly fractionated and characterised by a negative Eu anomaly (Eu/Eu* = 0.79). Hybridisation and AFC models suggest that the shoshonite enclave is the result of 12% rhyolite contamination of a mantle-derived magma akin to the potassic trachybasalt/shoshonite lavas of Capraia Island (~ 4.6 Ma; TMP), following an 18.5% assimilation of Late Triassic metasediments (13% evaporite and 5.5% carbonate) and 56% fractionation of clinopyroxene (39%), plagioclase (10%), and biotite (7%). Each rhyolite sample is characterised by mineral-scale isotopic disequilibria (e.g., 87Sr/86Sr(i) = 0.711-0.726), glass inclusions with large K2O/Na2O variations (1.1-3.4) and a poli-thermobarometric history of crustal melt production at eutectic conditions. A multi-parametric approach accounting for K2O/Na2O (1.3-2.2), 87Sr/86Sr(i) (0.713-0.725), Sr (104-311 ppm) and Rb (294-403 ppm) whole-rock variations, allowed us to divide the anatectic (A) rhyolites into five groups (A1, A2.1, A2.2, A2.3, A3). Group A1 shows the highest 87Sr/86Sr(i) ratios and the lowest values of Sr, K2O/Na2O and Rb. It is related to A2.1 and A3 rhyolites by positive K2O/Na2O-Rb and K2O/Na2O-FeO correlations. These three rhyolite groups crop out in the south of San

  3. Geochemical and Tectonic Evidence for the Role of Crustal Thickening and Forearc Subduction Erosion in Miocene to Recent Andean Southern Volcanic Zone Magmas

    NASA Astrophysics Data System (ADS)

    Kay, S. M.; Godoy, E.

    2002-12-01

    Key to understanding temporal and spatial variations in Andean-type margin magmas is identifying their mantle and crustal sources in well constrained tectonic settings. A study of Andean Southern Volcanic Zone (SVZ) Early Miocene to Recent magmas in an west to east transect near 34° S points to a linked role for crustal thickening and forearc subduction erosion. The whole rock and isotopic chemistry of these magmas show a trend from Early Miocene tholeiitic sequences with low pressure pyroxene-bearing residual mineral assemblages and more depleted isotopic signatures (87Sr/^{86}Sr ~ 0.7036; ɛ Nd ~ +6 to +4; 206Pb/^{204}Pb ~ 18.5) to Pliocene/Recent high-K calc-alkaline sequences with high pressure garnet-bearing residual mineral assemblages and enriched isotopic signatures (87Sr/^{86}Sr ~ 0.7042; ɛ Nd ~ +1 to 0; 206Pb/^{204}Pb ~ 18.6). Relatively abrupt breaks in this sequence at ~ 19 to 15 Ma and ~ 7 to 4 Ma coincide with an early Miocene extensional to compressional deformational switch and major Late Miocene out-of-sequence thrusting that accompany eastward shifts of ~ 35 and ~ 50 km of the arc front and peaks in uplift history. These changes are consistent with peaks in forearc subduction erosion that introduce continental crust into subcrustal magma sources and in backarc shortening that enhance MASH processes in a thickening crust. Shifts to higher pressure chemical signatures and isotopic enrichment as frontal arc magmatism wanes in the west and migrates eastward fit with continental crust entering subcrustal magma sources. The projections of extinct arc fronts near 34° S into chemically equivalent units to the south indicate an ~ 35 km shift of the arc front north of 36.5° S at ~ 19 to 15 Ma and another ~ 50 km shift north of 34.5° S between ~ 7 to 4 Ma. These SVZ shifts coincide with major tectonic changes along the Andean margin that are best related to variations in plate convergence parameters.

  4. Deep Crustal Magma Conduits, Diabase Internal Structure, and Coupled Hydrothermal Processes in Mesozoic Basins of Eastern North America

    NASA Astrophysics Data System (ADS)

    Ryan, M. P.; Ingerov, A.; Daniels, D. L.; Carr, P. M.; Elliott, G.; Fox, L.; Pierce, H. A.; Sutphin, D. M.

    2004-05-01

    Integrated geophysical, geological, and hydrological studies of the Culpeper (VA) and Gettysburg (PA) basins have shown fundamental new relationships among the internal structure of their plutonic rocks and have constrained the structural controls on paleo- and contemporary subsurface fluid flow within their ancient rift zone intrusive centers. Deep sub-basin igneous structure and the cross-sectional structure of the Culpeper basin. Magnetotelluric (MT) measurements along two basin-crossing transects have been inverted to reveal the basin cross-sectional structure and the structure of the primary conduit that transported tholeiitic magma through the crust during the Lower Jurassic. In cross-section, the basin deepens abruptly east of the Bull Run and Catoctin mountains, reaching a maximum depth of 2.5 to 2.75 km. The basin then shallows gradually towards the east. Basin rocks span the range 25 to 8,000 Ohm-m and range from fluid-saturated siltstones to unsaturated diabase, respectively. The crustal conduit for the Belmont diabase sheet has been resolved to 20 km depth. At that depth, it is characterized by a vertical region of relatively low resistivity (150 to 4,000 Ohm-m) embedded in relatively resistive (~10,000+ Ohm-m) crystalline Proterozoic rocks. At 4--5 km depth, the conduit width is ~2 km, flaring outward to a mean width of 6 km at 20 km depth. The conduit is inferred to be a laminate-like resistivity ``composite,'' with a central core resistivity of ~150 Ohm-m grading outwards through zones of 103, 2×103, and finally 4×103 Ohm-m near the outer margins. Based on the phase equilibria of ultramafic rocks and the petrology of diabase, the conduit is inferred to be olivine gabbro +/- dunite, and to be compositionally-zoned from core to margin. In general, the resistivity structure of the conduit is bilaterally-symmetric. Intra-basin igneous structure of the Gettysburg basin. The structure and geometry of the diabase sheets, lopoliths, and dikes of the

  5. Mafic magmas from Mount Baker in the northern Cascade arc, Washington: probes into mantle and crustal processes

    NASA Astrophysics Data System (ADS)

    Moore, Nicole E.; Debari, Susan M.

    2012-03-01

    Five mafic lava flows located on the southern flank of Mount Baker are among the most primitive in the volcanic field. A comprehensive dataset of whole rock and mineral chemistry reveals the diversity of these mafic lavas that come from distinct sources and have been variably affected by ascent through the crust. Disequilibrium textures present in all of the lavas indicate that crustal processes have affected the magmas. Despite this evidence, mantle source characteristics have been retained and three primitive endmember lava types are represented. These include (1) modified low-K tholeiitic basalt (LKOT-like), (2) typical calc-alkaline (CA) lavas, and (3) high-Mg basaltic andesite and andesite (HMBA and HMA). The Type 1 endmember, the basalt of Park Butte (49.3-50.3 wt% SiO2, Mg# 64-65), has major element chemistry similar to LKOT found elsewhere in the Cascades. Park Butte also has the lowest overall abundances of trace elements (with the exception of the HREE), indicating it is either derived from the most depleted mantle source or has undergone the largest degree of partial melting. The Type 2 endmember is represented by the basalts of Lake Shannon (50.7-52.6 wt% SiO2, Mg# 58-62) and Sulphur Creek (51.2-54.6 wt% SiO2, Mg# 56-57). These two lavas are comparable to calc-alkaline rocks found in arcs worldwide and have similar trace element patterns; however, they differ from each other in abundances of REE, indicating variation in degree of partial melting or fractionation. The Type 3 endmember is represented by the HMBA of Tarn Plateau (51.8-54.0 wt% SiO2, Mg# 68-70) and the HMA of Glacier Creek (58.3-58.7 wt% SiO2, Mg# 63-64). The strongly depleted HREE nature of these Type 3 units and their decreasing Mg# with increasing SiO2 suggests fractionation from a high-Mg basaltic parent derived from a source with residual garnet. Another basaltic andesite unit, Cathedral Crag (52.2-52.6 wt% SiO2, Mg# 55-58), is an Mg-poor differentiate of the Type 3 endmember. The calc

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  7. Dissolution kinetics of oceanic lower-crustal cumulate-minerals and the potential effect of the melts on ascending magmas

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

    The most primitive Atlantis Bank (SWIR) olivine-gabbros have augite oikocrysts surrounding more evolved plagioclase chadacrysts. In addition, this coarse type of augite commonly shows reverse zoning. The observations motivated an experimental study. We investigated the kinetics of melting of the grain-boundaries between mineral-pairs commonly found in lower ocean-crust, and discovered rapid melting rates and melt-compositions that may explain the phenomenon. In our study, An62 and An54 plagioclase were melted together with Fo73 or Fo82 and with Mg#86 augite. The experiments were distributed over a melting interval of 1240-1330° C and 1180-1300° C respectively. No melting was observed below 1210° C (augite - An54) and 1255° C (Fo82 - An54). Plagioclase is buoyant in the melt, therefore the minerals were melted with the heavier mineral on top, to preserve a short distance between them. The duration of the experiments varied from 30 minutes to 24 hours. The solidus for the plagioclase-clinopyroxene-olivine system was determined to be 1150° C, and the solidus for augite-plagioclase and olivine-plagioclase was inferred to be 5° C and 40degC higher, respectively, on the basis of previous studies. Olivine, the mineral that experiences the fastest internal solid-state diffusion, has very narrow (tens of μ ms) or no observable diffusion gradient along the actively melting surface, indicating that the melting rate is similar to or faster than the diffusion rate for Fe/Mg in olivine. Some recrystallization occurred in the melt close to olivine, away from the most active melt interface. Plagioclase and clinopyroxene grains melted without internal diffusion of major elements in the crystals. Augite starts disintegrating internally at the highest temperatures, but does not show any sign of preferential melting of exsolution lamellae or preferential melting of different crystal faces. Plagioclase show a very narrow (10μ m) jagged reaction zone, but no significant

  8. Crustal structure and active tectonics in the Eastern Alps

    NASA Astrophysics Data System (ADS)

    Brückl, E.; Behm, M.; Decker, K.; Grad, M.; Guterch, A.; Keller, G. R.; Thybo, H.

    2010-04-01

    During the last decade, a series of controlled source seismic experiments brought new insight into the crustal and lithospheric structure of the Eastern Alps and their adjacent tectonic provinces. A fragmentation of the lithosphere into three blocks, Europe (EU), Adria (AD), and the new Pannonian fragment (PA), was interpreted and a triple junction was inferred. The goal of this study has been to relate these deep crustal structures to active tectonics. We used elastic plate modeling to reconsider the Moho fragmentation. We interpret subduction of EU below AD and PA from north to south and underthusting of AD mantle below PA from southwest to northeast. The Moho fragmentation correlates well with major upper crustal structures and is supported by gravity, seismic, and geodetic data. An analysis of crustal thickening suggests that active convergence is associated with continued thrusting and lateral extrusion in the central Eastern Alps and thickening of the Adriatic indenter under the Southern Alps. According to the velocity relations at the triple junction, PA moves relative to EU and AD along ENE and SE striking faults, mainly by strike slip. An eastward directed extensional component is compensated by the lateral extrusion of the central Eastern Alps. The Periadriatic (Insubric) line east of the triple junction and the mid-Hungarian fault zone have relatively recently lost their role as first-order active structures. We favor the idea that the Pannonian fragment and the TISZA block merged to a "soft" microplate surrounded by the Eastern and Southern Alpine, Carpathian, and Dinaric orogens.

  9. Continental crustal formation and recycling: Evidence from oceanic basalts

    NASA Technical Reports Server (NTRS)

    Saunders, A. D.; Tarney, J.; Norry, M. J.

    1988-01-01

    Despite the wealth of geochemical data for subduction-related magma types, and the clear importance of such magmas in the creation of continental crust, there is still no concensus about the relative magnitudes of crustal creation versus crustal destruction (i.e., recycling of crust into the mantle). The role of subducted sediment in the formation of the arc magmas is now well documented; but what proportion of sediment is taken into the deeper mantle? Integrated isotopic and trace element studies of magmas erupted far from presently active subduction zones, in particular basaltic rocks erupted in the ocean basins, are providing important information about the role of crustal recycling. By identifying potential chemical tracers, it is impossible to monitor the effects of crustal recycling, and produce models predicting the mass of material recycled into the mantle throughout long periods of geological time.

  10. Lower crustal mush generation and evolution

    NASA Astrophysics Data System (ADS)

    Karakas, Ozge; Bachmann, Olivier; Dufek, Josef; Wright, Heather; Mangan, Margaret

    2016-04-01

    Recent seismic, field, and petrologic studies on several active and fossil volcanic settings provide important constraints on the time, volume, and melt fraction of their lower crustal magma bodies. However, these studies provide an incomplete picture of the time and length scales involved during their thermal and compositional evolution. What has been lacking is a thermal model that explains the temporal evolution and state of the lower crustal magma bodies during their growth. Here we use a two-dimensional thermal model and quantify the time and length scales involved in the long-term thermal and compositional evolution of the lower crustal mush regions underlying the Salton Sea Geothermal Field (USA), Mt St Helens (USA), and the Ivrea-Verbano Zone (North Italy). Although a number of seismic, tectonic, petrologic, and field studies explained the tectonic and magmatic evolution of these regions, controversy remains on their lower crustal heat sources, melt fraction, and origin of erupted magmas. Our thermal modeling results suggest that given a geologically reasonable range of basalt fluxes (~10^-3 to 10^-4 km3/yr), a long-lived (>105 yr) crystalline mush is formed in the lower crust. The state of the lower crustal mush is strongly influenced by the magma flux, crustal thickness, and water content of intruded basalt, giving an average melt fraction of <0.2 in thin crust with dry injections (Salton Sea Geothermal Field) and up to 0.4-0.5 in thicker crust with wet injections (Mt St Helens and Ivrea Zone). The melt in the lower crustal mush is mainly evolving through fractional crystallization of basalt with minor crustal assimilation in all regions, in agreement with isotopic studies. Quantification of the lower crustal mush regions is key to understanding the mass and heat balance in the crust, evolution of magma plumbing systems, and geothermal energy exploration.

  11. Crustal movements due to Iceland’s shrinking ice caps mimic magma inflow signal at Katla volcano

    PubMed Central

    Spaans, Karsten; Hreinsdóttir, Sigrún; Hooper, Andrew; Ófeigsson, Benedikt Gunnar

    2015-01-01

    Many volcanic systems around the world are located beneath, or in close proximity to, ice caps. Mass change of these ice caps causes surface movements, which are typically neglected when interpreting surface deformation measurements around these volcanoes. These movements can however be significant, and may closely resemble movements due to magma accumulation. Here we show such an example, from Katla volcano, Iceland. Horizontal movements observed by GPS on the flank of Katla have led to the inference of significant inflow of magma into a chamber beneath the caldera, starting in 2000, and continuing over several years. We use satellite radar interferometry and GPS data to show that between 2001 and 2010, the horizontal movements seen on the flank can be explained by the response to the long term shrinking of ice caps, and that erratic movements seen at stations within the caldera are also not likely to signify magma inflow. It is important that interpretations of geodetic measurements at volcanoes in glaciated areas consider the effect of ice mass change, and previous studies should be carefully reevaluated. PMID:25992847

  12. Magma mixing, crustal contamination, contamination before chemical analysis or complex history? The case study from the Wołek Hill, SW Poland

    NASA Astrophysics Data System (ADS)

    Nowak, Monika

    2015-04-01

    Wołek Hill is one of the smallest exposures from ca. 300 occurrences of Cenozoic volcanic rocks from SW Poland. The outcrop is located about 100 km SW from Wrocław and belongs to the Złotoryja Volcanic Field, which is one of the largest volcanic fields in the Polish part of the Central European Volcanic Province (Ladenberger et al. 2006). The volcanic body, which is about 20 m wide, cross-cuts older Permian volcanic rocks (trachyandesites and rhyolites) and is well exposed in an old abandoned quarry. The occurrence was studied in detail because of great amount of mantle and crustal xenoliths brought to the surface by magma. Wołek Hill is one of the two occurrences in SW Poland where amphibole crystals were recognized as results of modal metasomatism in lithospheric mantle (Nowak et al. 2012). The volcanic rock from Wołek Hill represents complex history, difficult to explain by simple model. The rock was classified as basanite (Nowak, 2012). Its texture is porphyritic to glomeroporphyritic, olivine (Ol) and clinopyroxene (Cpx) occurs as phenocrysts, Cpx is also the dominant phase in the groundmass. Wołek Hill basanite differs from other exposures in Złotoryja Volcanic Field by presence of xenocrysts of Ol and Cpx from mantle rocks and also quartz (Qrtz) and feldspars (Feld) xenocrysts from crustal rocks. Those xenocrysts with additional carbonate veins, probably related with post-volcanic processes, were a great difficulty during rock preparation for whole-rock and isotopic analyses. The complex history of Wołek Hill basanite is visible in its chemical content (slight increase of SiO2, positive Pb anomaly, 87Sr/86Sr and 143Nd/144Nd values), but also in its petrography (e.g. by three types of olivine phenocrysts Fo82-91 with differences in zonation patterns reflecting Fo content; the most abundant are phenocrysts with normal zoning, but also crystals with opposite zoning and oscillatory zoning were recognised). According to available data from the basanite

  13. The role of crustal and eruptive processes versus source variations in controlling the oxidation state of iron in Central Andean magmas

    NASA Astrophysics Data System (ADS)

    Grocke, Stephanie B.; Cottrell, Elizabeth; de Silva, Shanaka; Kelley, Katherine A.

    2016-04-01

    The composition of the continental crust is closely tied to subduction zone magmatism. Elevated oxygen fugacity (fO2) plays a central role in fostering crystallization of oxide minerals and thereby aids in generating the calc-alkaline trend of iron depletion that characterizes the continents. Along continental margins, arc magmas erupt through continental crust and often undergo extensive differentiation that may modify magmatic fO2. The importance of the subducting slab and mantle wedge relative to the effects of this differentiation on the fO2 recorded by continental arc magmas remains relatively unconstrained. Here, we focus on the effect of differentiation on magmatic fO2 using a suite of 14 samples from the Central Volcanic Zone (CVZ) of the Andes where the continental crust is atypically thick (60-80 km). The samples range in composition from ∼55 to 74 wt% SiO2 and represent the Neogene history of the arc. Samples are basaltic andesite to rhyolite and span a range of radiogenic isotopic compositions (87Sr/86Sr = ∼0.705-0.712) that represent 30 to 100% crustal assimilation. We use several proxies to estimate the fO2 recorded by lavas, pumice, and scoria: (1) whole rock Fe3+ / Σ Fe ratios, (2) Fe3+ / Σ Fe ratios in quartz-hosted melt inclusions, and (3) Fe-Ti oxide oxygen-barometry. Comparison of the fO2 calculated from bulk Fe3+ / Σ Fe ratios (post-eruptive) with that derived from Fe-Ti oxides or melt inclusion Fe3+ / Σ Fe ratios (pre-eruptive), enables us to quantify the effect of syn- or post-eruptive alteration, and to select rocks for bulk analysis appropriate for the determination of pre-eruptive magmatic fO2 using a strict criterion developed here. Across our sample suite, and in context with samples from the literature, we do not find evidence for systematic oxidation due to crystal fractionation or crustal contamination. Less evolved samples, ranging from 55 to 61 wt% SiO2, record a range of >3 orders of magnitude in fO2, spanning the fO2 range

  14. 3D numerical modeling of mantle flow, crustal dynamics and magma genesis associated with slab roll-back and tearing: The eastern Mediterranean case

    NASA Astrophysics Data System (ADS)

    Menant, Armel; Sternai, Pietro; Jolivet, Laurent; Guillou-Frottier, Laurent; Gerya, Taras

    2016-05-01

    Interactions between subduction dynamics and magma genesis have been intensely investigated, resulting in several conceptual models derived from geological, geochemical and geophysical data. To provide physico-chemical constraints on these conceptual models, self-consistent numerical simulations containing testable thermo-mechanical parameters are required, especially considering the three-dimensional (3D) natural complexity of subduction systems. Here, we use a 3D high-resolution petrological and thermo-mechanical numerical model to quantify the relative contribution of oceanic and continental subduction/collision, slab roll-back and tearing to magma genesis and transport processes. Our modeling results suggest that the space and time distribution and composition of magmas in the overriding plate is controlled by the 3D slab dynamics and related asthenospheric flow. Moreover, the decrease of the bulk lithospheric strength induced by mantle- and crust-derived magmas promotes the propagation of strike-slip and extensional fault zones through the overriding crust as response to slab roll-back and continental collision. Reduction of the lithosphere/asthenosphere rheological contrast by lithospheric weakening also favors the transmission of velocities from the flowing mantle to the crust. Similarities between our modeling results and the late Cenozoic tectonic and magmatic evolution across the eastern Mediterranean region suggest an efficient control of mantle flow on the magmatic activity in this region, which in turn promotes lithospheric deformation by mantle drag via melt-induced weakening effects.

  15. Quaternary volcanism near the Valley of Mexico: implications for subduction zone magmatism and the effects of crustal thickness variations on primitive magma compositions

    NASA Astrophysics Data System (ADS)

    Wallace, Paul J.; Carmichael, Ian S. E.

    The Valley of Mexico and surrounding regions of Mexico and Morelos states in central Mexico contain more than 250 Quaternary eruptive vents in addition to the large, composite volcanoes of Popocatépetl, Iztaccíhuatl, and Nevado de Toluca. The eruptive vents include cinder and lava cones, shield volcanoes, and isolated andesitic and dacitic lava flows, and are most numerous in the Sierra Chichináutzin that forms the southern terminus of the Valley of Mexico. The Chichináutzin volcanic field (CVF) is part of the E-W-trending Mexican Volcanic Belt (MVB), a subduction-related volcanic arc that extends across Mexico. The crustal thickness beneath the CVF ( 50km) is the greatest of any region in the MVB and one of the greatest found in any arc worldwide. Lavas and scoriae erupted from vents in the CVF include alkaline basalts and calc-alkaline basaltic andesites, andesites, and dacites. Both alkaline and calc-alkaline groups contain primitive varieties that have whole rock Mg#, MgO, and Ni contents, and liquidus olivine compositions (<=Fo90) that are close to those expected of partial melts from mantle peridotite. Primitive varieties also show a wide range of incompatible trace element abundances (e.g. Ba 210-1080ppm Ce 25-100ppm Zr 130-280ppm). Data for primitive calc-alkaline rocks from both the CVF and other regions of the MVB to the west are consistent with magma generation in an underlying mantle wedge that is depleted in Ti, Zr, and Nb and enriched in large ion lithophile (K, Ba, Rb) and light rare earth (La, Ce) elements. Extents of partial melting estimated from Ti and Zr data are lower for primitive calc-alkaline magmas in the CVF than for those from the regions of the MVB to the west where the crust is thinner. The distinctive major element compositions (low CaO and Al2O3, high SiO2) of the primitive calc-alkaline magmas in the CVF indicate a more refractory mantle source beneath this region of thick crust. In contrast, primitive alkaline magmas from the

  16. The Sondalo gabbro contact aureole (Campo unit, Eastern Alps): implications for mid-crustal mafic magma emplacement

    NASA Astrophysics Data System (ADS)

    Petri, B.; Mohn, G.; Štípská, P.; Schulmann, K.; Manatschal, G.

    2016-05-01

    Contact aureoles rimming plutonic rocks are the locus of metamorphism and deformations witnessing magma emplacement mechanisms in the crust. In this study, structural and petrological observations are combined to mineral equilibria modelling to unravel the polyphase tectono-metamorphic history of the Permian Sondalo gabbro and its host rock, the Campo unit (Eastern Alps). The Campo unit consists of Grt-St-Ms-Bt-Pl-Qtz ± Sil ± And ± Crd mica schists attesting of a Carboniferous prograde P- T path, reaching 6 kbar/600 °C and subsequently 5.6 kbar/650 °C. This metamorphism is coeval with the formation of a sub-vertical NE-SW trending foliation (S1) and its overprint by a sub-vertical NW-SE trending foliation (S2). The heat brought by the Permian intrusives subsequently caused heating of the Campo unit at around 3-4 kbar/540 °C reflected by regional static crystallization of cordierite and andalusite porphyroblasts. During the intrusion of the Sondalo gabbro, thermal peak conditions are recorded by Grt-Sil-Spl-Crd-Ilm granulitic xenoliths at ~5.5 kbar/930 °C, subsequently exhumed at ~4 kbar during the development of a new foliation (S3). This foliation is localized around the pluton and moderately dips away from the centre of the pluton. In the migmatitic contact aureole, Grt-Sil-Bt-Pl-Qtz-Ilm and Grt-Sil-Crd-Spl-Bt-Kfs-Ilm residual rocks bear the new foliation (S3) and document a decompression from 6 kbar/750 °C to 5 kbar/725 °C and from 5.2 kbar/800 °C to reach 4.8 kbar/770 °C, respectively. The P- T- d paths recorded by the host rock and the xenoliths point to a two-step magma emplacement. First the Sondalo gabbro intruded the Campo unit causing heating of the host rock without deformation at 3-4 kbar. Second, the ductile flow along the pluton margins developed a new foliation (S3) during exhumation of the pluton and its immediate contact aureole from 6 to 4 kbar. Altogether, it indicates a progressive increase in mechanical coupling between the pluton

  17. 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.

  18. The effect of pressure on sulphur speciation in mid- to deep-crustal arc magmas and implications for the formation of porphyry copper deposits

    NASA Astrophysics Data System (ADS)

    Matjuschkin, Vladimir; Blundy, Jon D.; Brooker, Richard A.

    2016-07-01

    Piston cylinder experiments are used to investigate the effect of oxygen fugacity (ƒO2) on sulphur speciation and phase relations in arc magmas at 0.5-1.5 GPa and 840-950 °C. The experimental starting composition is a synthetic trachyandesite containing 6.0 wt% H2O, 2880 ppm S, 1500 ppm Cl and 3800 ppm C. Redox conditions ranging from 1.7 log units below the Ni-NiO buffer (NNO - 1.7) to NNO + 4.7 were imposed by solid-state buffers: Co-CoO, Ni-NiO, Re-ReO2 and haematite-magnetite. All experiments are saturated with a COH fluid. Experiments produced crystal-bearing trachydacitic melts (SiO2 from 60 to 69 wt%) for which major and volatile element concentrations were measured. Experimental results demonstrate a powerful effect of oxidation state on phase relations. For example, plagioclase was stable above NNO, but absent at more reduced conditions. Suppression of plagioclase stability produces higher Al2O3 and CaO melts. The solid sulphur-bearing phases and sulphur speciation in the melt are strong functions of ƒO2, as expected, but also of pressure. At 0.5 GPa, the anhydrite stability field is intersected at NNO ≥ +2, but at 1.0 and 1.5 GPa, experiments at the same ƒO2 produce sulphides and the stability field of sulphate moves towards higher ƒO2 by ~1 log unit at 1.0 GPa and ~1.5 log units at 1.5 GPa. As a result, models that appeal to high oxidation state as an important control on the mobility of Cu (and other chalcophiles) during crustal differentiation must also consider the enhanced stability of sulphide in deep- to mid-crustal cumulates even for relatively oxidized (NNO + 2) magmas. Experimental glasses reproduce the commonly observed minimum in sulphur solubility between the S2- and S6+ stability fields. The solubility minimum is not related to the Fe content (Fe2+/Fe3+ or total) of the melt. Instead, we propose this minimum results from an unidentified, but relatively insoluble, S-species of intermediate oxidation state.

  19. Gold-rich sulfide melt inclusions in xenocrysts from a mid-crustal magma chamber, Mt. Milligan porphyry deposit, British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Hanley, J. J.; Guillong, M.

    2009-05-01

    Very coarse-grained amphibole xenocrysts (potassian magnesiohastingsite) hosted in an early monzonite stock at the Mt Milligan Cu-Au porphyry deposit, British Columbia, Canada contain coeval sulfide and silicate melt inclusions of primary origin. The sulfide melt inclusions have a bulk composition comparable to Cu-rich ISS. Late growth zones in the amphibole are devoid of sulfide inclusions and contain only low salinity, chalcopyrite-bearing fluid inclusions(average 7.4 wt% NaCleq.). Thermobarometry constrains the minimum conditions of sulfide entrapment (amphibole crystallization) to ˜8 kbar and ˜700°C. LA-ICPMS analyses of 22 sulfide melt inclusions show that it was highly enriched in Au (50± 20 ppm, 1σ), Ag (140± 70 ppm, 1σ) and Ni (5000 ± 3000 ppm, 1σ). Ratios of Cu/Au (7500± 2500, 1σ) and Au/Ag (0.45± 0.24, 1σ) are identical to metal ratios in porphyry- stage veins, demonstrating that these metals were not fractionated from one another during suspected volatile exsolution, fluid-melt partitioning, and subsequent transport and precipitation of ore metals. The extremely Au- rich composition of the sulfide melt may reflect fractional crystallization of the sulfide liquid prior to entrapment in the amphibole. Both the xenocrysts and rare, high Mg, alkali basalt xenoliths hosted in the intrusions are depleted in Cr, Co, Ni and Cu, reflecting the sequestering of the base metals into a sulfide liquid in a mid- crustal magma chamber where amphibole and Cr-spinel were cumulus phases. The results of this study show that a Cu-Au-rich sulfide melt coexisted with a amphibole-saturated alkalic basaltic liquid in mid-crustal magma chamber prior to the emplacement of the main intrusions and associated porphyry stage mineralization at Mt. Milligan. This sulfide melt appears to have destabilized with the appearance (exsolution) of a single-phase low salinity aqueous fluid. Identification and analysis of ore metals in sulfide melt inclusions in relatively common

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  1. Magma energy extraction

    SciTech Connect

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

    1987-01-01

    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.

  2. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2004-05-01

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

  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. Active mantle flow and crustal dynamics in southern California

    NASA Astrophysics Data System (ADS)

    Fay, N.; Bennett, R.; Spinler, J.

    2007-12-01

    We present numerical modeling analysis of active upper mantle flow and its role in driving crustal deformation in southern California. The forces driving lithospheric deformation at tectonic plate boundaries can be thought of as the sum from two sources: (1) forces transmitted from the far-field by rigid tectonic plates, and (2) forces created locally at the plate boundary by heterogeneous density distribution. Here we quantify the latter by estimating the stresses acting on the base of the crust caused by density-driven flow of the upper mantle. Anomalous density structure is derived from shear wave velocity models (Yang & Forsyth, 2006) and is used to drive instantaneous incompressible viscous upper mantle flow relative to a fixed crust; this allows isolation of stresses acting on the crust. Comparison of results with the finite element codes Abaqus (commercial) and GALE (community- developed) is good. We find that horizontal tractions range from 0 to ~3 MPa and vertical tractions range between approximately -15 to 15 MPa (negative indicating downward, positive upward); Absolute magnitudes depend on the assumed velocity-density scaling relationship but the overall patterns of flow are more robust. Anomalous density beneath the Transverse Ranges, in particular beneath the San Bernardino Mountains and offshore beneath the Channel Islands, drives convergent horizontal tractions and negative vertical tractions on the base of the crust there. Anomalous buoyancy beneath the southern Walker Lane Belt and anomalous density beneath the southern Great Valley create a small convective cell (the Sierra Nevada "drip"), which promotes extension on the eastern edge of the Sierra Nevada block and subsidence of the Great Valley. Favorable comparison with contemporary crustal thickness, heat flow, and surface strain rate indicates that upper mantle flow plays a very important role in active crustal deformation in southern California and much of the non-ideal behavior of this

  6. Architecture of on- and off-axis magma bodies at EPR 9°37-40‧N and implications for oceanic crustal accretion

    NASA Astrophysics Data System (ADS)

    Han, Shuoshuo; Carbotte, Suzanne M.; Carton, Hélène; Mutter, John C.; Aghaei, Omid; Nedimović, Mladen R.; Canales, J. Pablo

    2014-03-01

    Crustal accretion at fast-spreading mid-ocean ridges is believed to be concentrated in a narrow zone up to a few kilometers wide centered beneath the ridge axis. However, there is increasing evidence for off-axis magmatism occurring beyond this narrow zone. Here, we present 3D multichannel seismic (MCS) images from the East Pacific Rise 9°37-40‧N extending to 11 km on the ridge flanks. In the axial region, two offset axial magma bodies underlie a small ridge-axis discontinuity at ∼9°37‧N, displaying an overlapping geometry similar to that of the seafloor structures above. On the ridge flanks, a series of off-axis magma lenses (OAML) are imaged: they are located 2-10 km from the ridge axis, at 700 to 1520 ms two-way travel time below seafloor (bsf) (∼1.6 to 4.5 km bsf), with variable areas ranging from 0.5 km2 to 5.2 km2. The largest body is centered 4 km east of the ridge axis and is composed of a large, continuous, flat-topped lens and a series of small, discontinuous, westward-dipping bodies along its western edge. The flat crest of the OAML lies at approximately the same depth beneath layer 2A as the axial magma lens and we infer that this OAML has formed by aggregation of ascending melts that accumulate at the base of the sheeted dike section. A cluster of reflections underlying the OAML at 1260-1510 ms bsf are observed that may be deeper lenses feeding melts to the upper lens. This largest OAML is associated with Moho travel time anomalies of 120-260 ms within a zone that extends up to 2 km from the edge of the OAML, suggesting a lower crust that is partially molten with lower crustal velocities reduced by 8-18% and/or thicker than normal by up to 1 km. Local volcanic edifices are found above two of the three OAMLs imaged in our study area and are inferred to be the eruptive products of the OAMLs. From the volume of these edifices and the Moho travel time anomalies we estimate the potential contribution of off-axis magmatism to the total volume of

  7. Evaluating the construction and evolution of upper crustal magma reservoirs with coupled U/Pb zircon geochronology and thermal modeling: A case study from the Mt. Capanne pluton (Elba, Italy)

    NASA Astrophysics Data System (ADS)

    Barboni, Mélanie; Annen, Catherine; Schoene, Blair

    2015-12-01

    Evaluating mechanisms and rates for magma transport and emplacement in the upper crust is important in order to predict the thermal and rheological state of the crust, and understand the relationship between plutonism and volcanism. U-Pb geochronology on zircon is commonly used to constrain magma emplacement and storage time in the crust, but interpreting complex zircon age populations in terms of in-situ crystallization versus crystallization at a deeper level is not trivial. This study focuses on the Mt. Capanne pluton in Elba (Italy), a well-documented example of arc-related laccolith emplaced in the upper continental crust. Previous studies proposed that the Mt. Capanne intrusion was accreted in less than 10 000 yr by distinct and mappable magma pulses. Here, we couple high-precision ID-TIMS U-Pb zircon geochronology with numerical thermal simulations to evaluate emplacement rates, test different emplacement models, inform zircon age interpretations and evaluate the potential for melt storage during construction of the Mt. Capanne pluton. Our results require that the Mt. Capanne intrusion was built in at least 250 000 yr by multiple magma injections. A variety of emplacement scenarios show that melt was preserved for <60 000 yr after each pulse and that the maximum eruptible volumes were approximately equal to the volume of each pulse. Our results also require that the majority of zircon crystallization occurred in zircon saturated reservoirs at deeper crustal levels prior to final magma emplacement and cooling, which has implications for using zircon U-Pb geochronology to infer upper crustal magma residence times.

  8. Magma Energy Overview and Status Report

    SciTech Connect

    Dunn, James C.

    1989-03-21

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

  9. Mechanisms of mafic magma emplacement at a mid-crustal level: insights from AMS, AARM and EBSD analyses on the Sondalo gabbroic complex (Alps, N-Italy)

    NASA Astrophysics Data System (ADS)

    Petri, Benoît; Mohn, Geoffroy; Skrzypek, Etienne; Mateeva, Tsvetomila; Robion, Philippe; Schulmann, Karel; Manatschal, Gianreto; Müntener, Othmar

    2016-04-01

    With the aim of assessing the mechanisms of mafic magma ascent and emplacement in the continental crust, we describe the magmatic and magnetic fabrics of the Sondalo gabbroic complex emplaced at a mid-crustal level (~15 km) during the Permian (Campo unit, Eastern Central Alps, N-Italy). Detailed mapping, field observations and petrological investigations enable to study the general structure of the Sondalo gabbroic complex. The pluton is concentrically zoned and composed of Ol-gabbros in the central zone surrounded by gabbros in the intermediate zone and diorites to granodiorites in a border zone of a variable thickness. We characterize the anisotropy of magnetic susceptibility (AMS) fabric of the intrusions. In order to detect potential abnormal (intermediate) magnetic fabrics with respect to the petrofabric, we refine the magnetic fabric characterization with anisotropy of anhysteretic remnant magnetization (AARM) measurements while the identification of magnetic mineralogy is investigated by coercivity-unblocking temperature spectra of ferromagnetic minerals. In addition, the petrofabric is evaluated by measuring the crystallographic preferred orientation (CPO) in test sites with electron backscatter diffraction (EBSD) measurements. Additional petrological and geochemical observations provide insights on the crystallization sequence of the magmatic rocks and facilitate the interpretation of the magnetic record. The bulk susceptibilities of the rocks range from 448 to 3540*10-6 SI with most of values below 10-3 SI, attesting of a mixed contribution to the AMS signal of paramagnetic and ferromagnetic minerals. Variation of the magnetic susceptibilities can be correlated to both the lithology and the magnetic mineralogy. Measured magnetic foliation orientations are remarkably similar to the observed macroscopic magmatic fabrics defined by the preferred orientation of magmatic plagioclase, pyroxene, hornblende and rarely biotite. In the central zone, the magmatic

  10. 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

  11. Three-dimensional electrical resistivity image of magma beneath an active continental rift, Taupo Volcanic Zone, New Zealand

    NASA Astrophysics Data System (ADS)

    Heise, Wiebke; Caldwell, T. Grant; Bibby, Hugh M.; Bennie, Stewart L.

    2010-05-01

    Magmatic activity in regions of continental extension may result in huge (>400 km3) explosive eruptions of viscous, gas-rich silicic-magma. Geochemical and geological data suggest that the large volumes of magma erupted are produced by extracting interstitial liquid from a long-lived ‘mush zone’ (a mixture of solid crystals and liquid melt) that accumulates in liquid-dominated lenses at the top of a much thicker region of lower melt-fraction mush. Such lenses will be highly electrically conductive compared with normal mid-crustal rocks. Here we use results of 220 magnetotelluric (MT) soundings to construct a 3-D electrical resistivity image of the northern (silicic) part of New Zealand's Taupo Volcanic Zone, a young continental rift associated with very high heat flow and intense silicic volcanism. The electrical resistivity image shows a plume-like structure of high conductivity, interpreted to be a zone of interconnected melt, rising from depths >35 km beneath the axis of extension.

  12. 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.

  13. Geochemical behaviour of trace elements during fractional crystallization and crustal assimilation of the felsic alkaline magmas of the state of Rio de Janeiro, Brazil.

    PubMed

    Motoki, Akihisa; Sichel, Susanna E; Vargas, Thais; Melo, Dean P; Motoki, Kenji F

    2015-01-01

    This paper presents geochemical behaviour of trace elements of the felsic alkaline rocks of the state of Rio de Janeiro, Brazil, with special attention of fractional crystallization and continental crust assimilation. Fractionation of leucite and K-feldspar increases Rb/K and decreases K2O/(K2O+Na2O). Primitive nepheline syenite magmas have low Zr/TiO2, Sr, and Ba. On the Nb/Y vs. Zr/TiO2 diagram, these rocks are projected on the field of alkaline basalt, basanite, and nephelinite, instead of phonolite. Well-fractionated peralkaline nepheline syenite has high Zr/TiO2 but there are no zircon. The diagrams of silica saturation index (SSI) distinguish the trends originated form fractional crystallization and crustal assimilation. In the field of SSI<-200, Zr/TiO2 and Ba/Sr have negative correlations to SSI in consequence of fractional crystallization. In the field of SSI>-200, they show positive correlations due to continental crust assimilation. Total REEs (Rare Earth Elements) is nearly 10 times that of granitic rocks, but LaN/SmN and LaN/YbN are similar. REE trend is linear and Eu anomaly is irrelevant. The pegmatitic liquid generated by country rock partial melting is SiO2-oversaturated and peraluminous with high Ba, Sr, Ba/Sr, Zr/TiO2, and SSI, with high content of fluids. This model justifies the peraluminous and SiO2-oversaturated composition of the rocks with relevant effects of continental crust assimilation. PMID:26628026

  14. 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

    depleted isotope compositions [(87Sr/86Sr)i = 0.7054-0.7065; εNd(t) = - 0.61 to + 0.25; zircon εHf(t) = + 4.7 to + 9.7] of the granodiorite porphyries indicate that they were most probably generated by partial melting of newly underplated and thickened basaltic lower crust. Taking into account ophiolites in the Bangong-Nujiang Suture and Late Mesozoic magmatic rocks in the southern Qiangtang sub-block, we suggest that this area was located in a continental arc setting. Moreover, from the Late Jurassic to Early Cretaceous, the ancient lower crust in the southern Qiangtang sub-block was gradually replaced by mantle-derived juvenile materials. The crustal evolution indicates that, in a continental arc, basaltic magma underplating plays a key role in vertical crustal growth.

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

    PubMed

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

    2006-08-31

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

  16. Earthquake activity and crustal stresses in stable plate interiors

    NASA Astrophysics Data System (ADS)

    Camelbeeck, Thierry; Calais, Eric; Mazzotti, Stéphane; Stein, Seth

    2016-04-01

    Unlike plate-boundary earthquakes that are explained by plate motions and their recurrence interval inferred from the rate at which these motions are released seismically, we have a limited understanding on the triggering causes of earthquakes in stable plate interiors as well as on the mechanisms explaining their apparent episodic, clustered, and migrating nature. An alternative model explaining those characteristics of the seismic activity in those regions where no discernable strain is building up today is that earthquakes result from the release of strain from a long-term pre-stressed lithosphere, triggered by processes weakening fault zones, like fluid circulation, or modifying applied normal stress on well oriented faults, like regional or more local erosion, water or ice loadings. In this talk, we present examples of three complementary approaches that should permit better understanding the mechanisms of this intraplate earthquake activity. They rely on studying their possible triggering factors and regional stresses controlling their mechanism, and also on modelling the possible strain rates of geological domains in relationship to their geological history and their fabrics. Among other things, we question whether the spatial variations of the short wavelengths gravitational potential energy associated to lateral variations of surface topography and crustal density can induce local stress perturbations explaining the complexity of the present-day tectonics in Western Europe and its possible relationship to earthquake activity.

  17. Architecture of Off-Axis Magma Bodies at EPR 9o37-40'N and Implications for Oceanic Crustal Accretion (Invited)

    NASA Astrophysics Data System (ADS)

    Han, S.; Carbotte, S. M.; Carton, H. D.; Mutter, J. C.; Aghaei, O.; Nedimovic, M. R.; Canales, J.

    2013-12-01

    Oceanic crust is formed by decompression melting of upwelling mantle beneath mid-ocean ridges. At fast spreading ridges, although the mantle melting region is several hundred kilometers wide, crustal accretion is believed to be concentrated in a narrow zone a few kilometers wide centered beneath the ridge axis. However, mid-ocean ridge studies over the past two decades have provided increasing evidence that melt focusing may not occur entirely within this narrow zone. Here, we present 3D multichannel seismic (MCS) images from the East Pacific Rise 9o37-40'N extending to 11 km on the ridge flanks. In the axial region, we observe two axial magma bodies underlying the seafloor discontinuity at ~9°37'N at a depth of 1.5-1.6 km, with an overlapping geometry similar to that of the seafloor structures. On the ridge flanks, a series of off-axis melt lenses (OAML) are imaged, located from 2 -10 km from ridge axis, at 700 to 1520 ms twtt below seafloor (bsf) (~1.6 to 4.5 km), and with various sizes from 0.46 km2 to 5.15 km2. The largest body is centered 3.9 km east of the ridge axis and is composed of a series of small discontinuous upward dipping bodies at the western edge of a larger, continuous flat-topped lens. The flat-topped crest of the OAML lies at approximately the same depth beneath layer 2A as the axial magma lens, from which we infer that this OAML has formed by aggregation of smaller melt bodies ascending along the western edge of the main body that accumulate at the base of the sheeted dike section. A cluster of reflectors underlies the OAML at 1260-1510 ms bsf that may be deeper lenses feeding melts to the upper lens. Moho traveltime anomalies associated with this OAML suggest a lower crust that is partially molten with velocities reduced by 8-18% and/or thicker than normal by up to 1 km. The data indicate that melt delivery pathways to the OAML are independent of the axial system. Local volcanic edifices are found above two of the three OAMLs in our study

  18. Near-Solidus Solubility of Albite+Quartz in H2O at 1 GPa: Implications for Crustal Magmas and Fluids

    NASA Astrophysics Data System (ADS)

    Manning, C. E.; Antignano, A.

    2007-12-01

    The solubility and melting of albite (Ab, NaAlSi3O8) ± quartz (Qz, SiO2) in H2O has been used to gain insight into the nature of magmas and metamorphic fluids in the continental crust. For example, the Ab+H2O and Ab+Qz+H2O solidi are widely used as guides to crustal melting. However, some studies suggest that Ab dissolves incongruently in H2O at near-solidus conditions, which implies that these solidi are not likely to be encountered in nature. To address this problem, we carried out experiments on the stability and solubility of the assemblage Ab+Qz in H2O at 1 GPa, 580-640°C. Starting materials were natural Amelia Ab and Brazilian Qz. Ab crystals were placed in a 1.6 mm OD Pt capsule, which was lightly crimped and then loaded with ultrapure H2O and a quartz crystal into a 3.5 mm OD Pt capsule, which was sealed by arc welding. Experiments were conducted for 24 h in a piston-cylinder apparatus using 1" NaCl- graphite furnaces. Quenched run products were evaluated to assess stable assemblages, and solubilities were determined from crystal weight changes. Hydrous melt (L) became stable at 630±10°C. Paragonite (Pg, NaAl3Si3O10(OH)2) was present in all run products, indicating that Ab+Qz and L+Qz dissolve incongruently in H2O, and that Ab+Qz+L+H2O is metastable at 1 GPa. The bulk solubility of the assemblage Ab+Pg+Qz in H2O doubles from 4.0 to 8.0 wt% as the solidus is approached (580- 630°C), with corresponding increases Si, Al, and Na molalities. Over the same T range, Na/Al and Na/Si (molar) respectively decrease (2.1 to 1.5) and increase (0.153 to 0.175), indicating that fluids are Na- and Si-rich peralkaline solutions far from Ab stoichiometry. At 580°C, measured Al solubility agrees well with that predicted from extrapolation of thermodynamic data for Al and Na-Al species; however, measured Al solubility at the solidus is much greater than predicted. Similar observations hold for Na and Si. This implies that there is a strong, pre-melting increase in the

  19. PGE abundance and Re-Os isotope Systematics of Native-Fe-Bearing Basaltic Rocks and Their Carbonaceous Crustal Contaminants: Insights into magma plumbing-system dynamics in LIPs

    NASA Astrophysics Data System (ADS)

    Howarth, G. H.; Day, J. M.; Goodrich, C. A.; Pernet-Fisher, J.; Pearson, D. G.; Taylor, L. A.

    2014-12-01

    Native-Fe grains form in basaltic melts at highly reducing conditions (magmas. Only three known terrestrial occurrences exist: 1) ~60 Ma basalts at Disko Island, Greenland; 2) ~20 Ma Bühl basalts, Germany, and 3) intrusions of the ~250 Ma Siberian Large Igneous Province (LIP). The reducing conditions recorded are the direct result of assimilation of carbonaceous crustal material during emplacement of the basaltic magmas at or near the surface. Native Fe-bearing basalts are useful natural analogues for studying PGE pre-concentration mechanisms, and the potential for PGE additions to magmas from crustal sources. Here, we present PGE LA-ICP-MS data for Fe-alloy, cohenite, and sulfide for a suite of Siberian and Disko Island native-Fe basalts, in combination with whole-rock PGE data for all known occurrences. The Siberian native-Fe alloys are characterized by highly variable PGE concentrations (1-30 ppm total PGEs), distinct low Os abundances, and PGE profiles similar to those of the nearby Noril'sk sulfide ores. In contrast, the Disko Island alloys are characterized by total PGE concentrations of 1-10 ppm and distinct positive Os and Re anomalies in extended PGE profiles. The Bühl basalts contain low PGE concentrations (~20 ppb). In order to understand contamination contributions, Os-isotopes analyses have been performed. Preliminary whole-rock 187Os/188Os data for high metal content samples from Siberia (0.33606 ± 37) and Disko (0.15402 ± 15) indicate high-time integrated Re/Os. The Re anomalies observed in extended PGE profiles of the Disko Island samples may reflect a potential crustal contribution to the overall PGE budget, through the addition of carbonaceous material. Whereas the Siberian samples contain abundant carbonaceous xenoliths, there is no apparent PGE contribution from crustal materials. Therefore, the role of crustal contamination is important in forming the native-Fe alloys, but the interaction

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

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

    PubMed Central

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

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

    PubMed

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

    2015-01-01

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

  5. Changing source regions of magmas and crustal growth in the Trans-Himalayas: evidence from the Chalt volcanics and Kohistan batholith, Kohistan, northern Pakistan

    NASA Astrophysics Data System (ADS)

    Petterson, M. G.; Windley, B. F.

    1991-03-01

    The Kohistan batholith and Chalt volcanics form a major part of the Kohistan island arc terrane in northern Pakistan. They record some 70-80 Ma of magmatism within the northwestern Himalayan orogen; the Chalt volcanics are Albian-Aptian (mid-Cretaceous), and currently available Rb sbnd Sr age data for the batholith indicate an intrusive age span of 102 to 30 Ma. The volcanics are composed of medium-K, calc-alkaline andesites and low-K, high-Mg, tholeiites, some of which have boninitic and basaltic komatiitic chemistry. Three intrusive stages are recognised in the batholith: (1) (110-90 Ma) comprises low-K trondhjemites and medium-high-K calc-alkaline gabbro-diorites with associated hornblendite cumulates; (2) (85-40 Ma) comprises low-high-K, calc-alkaline gabbro-diorites (with hornblendite cumulates, granodiorites and granites; and (3) (circa 30 Ma) comprises biotite ± muscovite ± garnet leucogranites. 87Sr/ 86Sr 0 for the batholith range between 0.7039 and 0.7052. Four magmatic source regions (Sce 1-Sce 4) have been identified. Sce 1 is a variably metasomatised mantle wedge situated above an active subduction zone during stages 1 and 2. Sce 2 is a harzburgite depleted with respect to major elements and incompatibles, whilst retaining "subduction-related" trace element ratios. Sce 2 melted during stage 1 within a fore-arc position during the subduction of young, hot oceanic crust to provide the necessary extra thermal input for harzburgite anatexis. Melts from Sce 2 produced the high-Mg tholeiitic volcanics. Sce 3 melted during stage 1 to produce the low-K trondhjemites, and it is envisaged as incompatible element-depleted primitive arc crust with a similar composition to the depleted Chalt volcanics. Sce 4 melted at 30 Ma during stage 3 as India underthrust Eurasia: frictional heating and dehydration of the Indian plate caused crustal anatexis within the deep Kohistan arc and these melts formed the stage 3 leucogranites. The low 87Sr/ 86Sr initial ratios for the

  6. Polymagmatic activity and complex magma evolution at the monogenetic Mt Gambier Volcanic Complex in the Newer Volcanics Province, SE Australia

    NASA Astrophysics Data System (ADS)

    van Otterloo, Jozua; Raveggi, Massimo; Cas, Ray; Maas, Roland

    2015-04-01

    Monogenetic volcanism can produce eruptive suites showing considerable complexity in compositional features and pre-eruptive magma evolution. The ~5 ka Mt Gambier Volcanic Complex (MGVC), a monogenetic volcanic centre in the Newer Volcanics Province (NVP), SE Australia, is a good example. It displays a complex stratigraphy of interbedded deposits related to different eruption styles from a multi-vent system. Formation of the MGVC proceeded through simultaneous eruption of two alkali basaltic magma batches: a more alkaline and light rare earth element enriched basanite batch (Mg# 58-62) in the west and a trachybasalt batch (Mg# 58-64) enriched in SiO2 and CaO in the east. Trace element modelling suggests an origin of both magma batches from a single parental melt formed by 4-5% partial melting of a metasomatised lherzolite source in the asthenospheric mantle (2.2 GPa; ~80 km). At the base of the lithosphere, part of this parental melt interacted with a deep-seated pyroxenite contaminant to form the trachybasaltic suite. Further modification of either magma batch at crustal levels appears to have been negligible. Isotope and trace element signatures are consistent with the inferred asthenospheric magma source; Pb isotopes in particular suggest a source with mixed Indian mid-ocean ridge basalt (MORB)-Enriched Mantle 2 (EM2) affinities, the latter perhaps related to metasomatic overprinting. It is argued that Cainozoic NVP volcanism in SE Australia is not necessarily related to a mantle plume but can be explained by other models involving asthenospheric upwelling. Fast magma ascent rates in the lithosphere evidenced by the presence of mantle xenoliths may reflect reactivation of lithospheric structures that provide magma pathways to the surface.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  8. The ˜AD 1250 effusive eruption of El Metate shield volcano (Michoacán, Mexico): magma source, crustal storage, eruptive dynamics, and lava rheology

    NASA Astrophysics Data System (ADS)

    Chevrel, Magdalena Oryaëlle; Guilbaud, Marie-Noëlle; Siebe, Claus

    2016-04-01

    Medium-sized volcanoes, also known as Mexican shields due to their andesitic composition and slightly higher slope angles in comparison to Icelandic shields, occur across the Trans-Mexican Volcanic Belt and represent nearly one third of all volcanic edifices in the Michoacán-Guanajuato Volcanic Field (MGVF). Many questions about their origin and eruptive dynamics remain unanswered. Here, we focus on El Metate, the youngest (˜AD 1250) monogenetic shield volcano of the MGVF and the most voluminous (˜9.2 km3 dense rock equivalent) Holocene eruption in Mexico. Its eruptive history was reconstructed through detailed mapping, geochemical analysis (major and trace elements, Sr-Nd-Pb isotopic data), and rheological study of its thick andesitic flows. Early and late flow units have distinct morphologies, chemical and mineralogical compositions, and isotopic signatures which show that these lavas were fed by two separate magma batches that originated from a heterogeneous mantle source and followed distinct differentiation paths during their ascent. Thermobarometry calculations constraining the conditions of crystallization indicate a temporary storage of the last erupted magma batch at a depth of ˜7-10 km. Lava rheology was estimated using petrographic characteristics, geochemical data, and flow dimensions. The magma viscosity increased from 102-103 Pa s prior to eruption through 106-108 Pa s during ascent, to 109-1011 Pa s during lava emplacement. Though magma viscosity was quite high, the eruption was purely effusive. The explosive eruption of such a large magma volume was probably avoided due to efficient open system degassing (outgassing) of the magma as it ascended through the uppermost crust and erupted at the surface.

  9. Deep to shallow crustal differentiation of within-plate alkaline magmatism at Mt. Bambouto volcano, Cameroon Line

    NASA Astrophysics Data System (ADS)

    Marzoli, Andrea; Aka, Festus T.; Merle, Renaud; Callegaro, Sara; N'ni, Jean

    2015-04-01

    At Mt. Bambouto, a continental stratovolcano of the Cameroon Line, magmatic activity lasted for over 20 Ma and was characterized by at least two caldera formation events. Here we present detailed mineral and whole-rock compositions of Mt. Bambouto basanites, hawaiites, trachytes and phonolites, with emphasis on caldera related volcanic rocks. These data show that differentiation took place within a complex magma plumbing system, with magma chambers occurring at different depths within the crust. Though differentiation was chiefly dominated by fractional crystallization, chemical mineral zoning of olivines, clinopyroxenes, and feldspars is also indicative of open-system processes such as magma mixing and magma chamber recharge. Chemical zoning is evident mainly in the outer 100 microns of the analyzed crystals, suggesting that magma mixing occurred shortly before eruption. The last caldera collapse at about 15 Ma also marked a clear change in the magma plumbing system. Before caldera collapse, Mt. Bambouto was characterized by a dominant production of peralkaline quartz trachytic magmas in shallow magma chambers. During this phase, evolved basic magmas (hawaiites) and strongly evolved alkaline magmas were formed in middle and upper crustal magma chambers, respectively. After emptying of the shallow quartz trachytic magma chamber and caldera collapse, magmas from the deep magmatic plumbing system were mobilized and partially mixed. This triggered eruptions of magmas on the caldera rims.

  10. Microbial life in cold, hydrologically active oceanic crustal fluids

    NASA Astrophysics Data System (ADS)

    Meyer, J. L.; Jaekel, U.; Girguis, P. R.; Glazer, B. T.; Huber, J. A.

    2012-12-01

    It is estimated that at least half of Earth's microbial biomass is found in the deep subsurface, yet very little is known about the diversity and functional roles of these microbial communities due to the limited accessibility of subseafloor samples. Ocean crustal fluids, which may have a profound impact on global nutrient cycles given the large volumes of water moving through the crustal aquifer, are particularly difficult to sample. Access to uncontaminated ocean crustal fluids is possible with CORK (Circulation Obviation Retrofit Kit) observatories, installed through the Integrated Ocean Drilling Program (IODP). Here we present the first microbiological characterization of the formation fluids from cold, oxygenated igneous crust at North Pond on the western flank of the Mid Atlantic Ridge. Fluids were collected from two CORKs installed at IODP boreholes 1382A and 1383C and include fluids from three different depth horizons within oceanic crust. Collection of borehole fluids was monitored in situ using an oxygen optode and solid-state voltammetric electrodes. In addition, discrete samples were analyzed on deck using a comparable lab-based system as well as a membrane-inlet mass spectrometer to quantify all dissolved volatiles up to 200 daltons. The instruments were operated in parallel and both in situ and shipboard geochemical measurements point to a highly oxidized fluid, revealing an apparent slight depletion of oxygen in subsurface fluids (~215μM) relative to bottom seawater (~245μM). We were unable to detect reduced hydrocarbons, e.g. methane. Cell counts indicated the presence of roughly 2 x 10^4 cells per ml in all fluid samples, and DNA was extracted and amplified for the identification of both bacterial and archaeal community members. The utilization of ammonia, nitrate, dissolved inorganic carbon, and acetate was measured using stable isotopes, and oxygen consumption was monitored to provide an estimate of the rate of respiration per cell per day

  11. CO2 contents of basaltic arc magmas from the southern Cascades: Corrections for shrinkage bubble effects and implications for crustal storage

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Volatiles such as H2O and CO2 play an important role in a variety of magmatic processes from magma generation to eruption, and melt inclusions (MI) - small volumes of melt trapped inside phenocrysts - have been used to measure their pre-eruptive concentrations. In particular, the volatile contents of MI from basaltic arc magmas have been used to track the role of dehydrating subducted oceanic lithosphere in magma formation in subduction zones. However, recent studies have shown that MI are imperfect storage containers and can lose H by diffusion through the mineral host and CO2 due to formation of a vapor bubble in the inclusion. Such results suggest that even the least degassed melt inclusions from a volcano may have volatile concentrations that underestimate the initial volatile contents of the magma. Thus, recognizing pre- and post-entrapment processes that influence MIs is important for interpreting magmatic processes at depth. Recent studies have developed methods that can be used to distinguish and correct for H diffusive loss (Bucholz et al., 2013) and CO2 loss to vapor bubbles (Wallace et al., 2015). Here, we focus on MI from eight cinder cones that erupted primitive basaltic magmas in the Lassen region of the Cascade arc, where H2O and Cl concentrations have been shown to relate to the amount of a subduction component added to the mantle wedge (Walowski et al., 2015). Using methods of Aster (2015), we correct for the loss of CO2 to a vapor bubble formed within a melt inclusion as the result of post-entrapment crystallization and thermal contraction. The results of the CO2 restoration calculations suggest that ~25-75% of the initial dissolved CO2 in the melt inclusions at the time of trapping was lost to a vapor bubble after entrapment. Trapping pressures for the restored CO2 and maximum H2O contents calculated using methods of Iacono-Marziano et al. (2012) range from ~2-5 kbar, equivalent to entrapment depths of ~7-18 km below the surface. The results

  12. Melt zones beneath five volcanic complexes in California: an assessment of shallow magma occurrences

    SciTech Connect

    Goldstein, N.E.; Flexser, S.

    1984-12-01

    Recent geological and geophysical data for five magma-hydrothermal systems were studied for the purpose of developing estimates for the depth, volume and location of magma beneath each area. The areas studied were: (1) Salton Trough, (2) The Geysers-Clear Lake, (3) Long Valley caldera, (4) Coso volcanic field, and (5) Medicine Lake volcano, all located in California and all selected on the basis of recent volcanic activity and published indications of crustal melt zones. 23 figs.

  13. Magma Feeding System of the Past ca. 30-ky Activities of the Zao Volcano, NE Japan

    NASA Astrophysics Data System (ADS)

    Ban, M.; Kotaro, M.; Takebe, Y.; Sato, H.; Sagawa, H.

    2006-12-01

    In the youngest stage (30 ka to present) of the Zao volcano, three active periods (ca. 31 to 29 ka, 7.5 to 4.1 ka, and 2.0 to present) can be observed. Piles of pyroclastic rocks by numerous small to medium sized eruptions are main products of the activities. In this study we examined the magma feeding system in the three periods, based on the petrologic features of the products. Rocks erupted in the three periods are olivine± pyroxene basaltic andesite to andesite, and these were formed by mixing of two end-member magmas, judged from the petrographic and mineralogic features. The estimated felsic end-members are similar among the periods, andesite (ca.60% in silica content) with orthopyroxene (Mg#=ca.64), clinopyroxene (Mg#=ca.68), plagioclase (An=ca.65) phenocrysts. The estimated mafic end-members are basalt with olivine (Fo=ca.80) and plagioclase (An=ca.90) phenocrysts in all periods, however, the bulk MgO, Cr and Ni contents of the erupted rocks are higher in the second period than in the other two periods. During the second and third periods, silica contents of the rocks decreased temporally from 58 to 55-56 % and recovered up to 58 %, and these variations can be explained by the different percentages of the basaltic magma involved in the mixing. Those features are suggesting that the mafic end-member magmas are distinct among periods, and may have been stored in the deeper part of the crust for ca.3.5 to 2.0 ky. Looking at the chemical compositions of rocks in the past ca.0.8-ky eruptions closely, gradual decrease in Zr (and increase in Cr) contents toward upper part can be seen at least twice, which may correspond to the progressive injection of the basaltic magma to the shallower andesitic magma chamber, and it is estimated that the duration of each injection is less than 0.2 ky.

  14. 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.

  15. Recent Eruptive Activity at Etna Volcano Inferred by Borehole Strainmeters : Source Modeling and Magma Volume Balance

    NASA Astrophysics Data System (ADS)

    Bonaccorso, Alessandro; Calvari, Sonia; Currenti, Gilda; Linde, Alan; Sacks, Selwyn

    2015-04-01

    After the end of the last effusive flank 2008-2009 eruption, in January 2011 the eruptive activity resumed at Etna producing a new phase with 44 lava fountain episodes through December 2013. Almost all the lava fountains had similar characteristics. The intensity of the initial strombolian explosions increased rapidly and the activity soon shifted to lava fountains. The paroxysmal phase was accompanied by increasing tephra emission with lava fountain reaching up to ~0.5-0.8 km above the crater and an eruption column rising several kilometers above the volcano summit before being dispersed by wind to the distal volcano flanks and by lava flow output. The paroxysmal episodes lasted a few hours and fed lava flows that expanded in the Valle del Bove depression with maximum lengths of 4-6 km. These eruptive episodes emitted much more magma than in the phases occurred in the previous decades. In November 2011, the first two borehole strainmeters, dilatometers type with nominal precision of ~ 10^10 - 10^11, were installed at Etna at ~180 m depth below the ground surface with distances from the summit central crater of 6 (DEGI) and 10 km (DRUV), respectively. During the paroxysmal events these high precision instruments detected negative strain changes indicating medium expansion at both sites. For each fountain episode the amplitude of the stain changes were almost similar with ~0.2 and ~1 μstrain at DRUV and DEGI, respectively. A Finite Element Model was set up to estimate accurately the tilt and volumetric strain, taking into account the real profile of the volcano and the elastic medium heterogeneity. The numerical computations indicated an elongated depressurizing source located at 0 km b.s.l., which underwent a volume change of ~2 × 106 m3 which is the most of the magma volume erupted, while a smaller remaining part (~0.5 × 106 m^3) is accommodated by the magma compressibility. This allowed to infer a representative average erupted volume of ~2.5 × 106 m3 for

  16. Crustal differentiation due to partial melting of granitic rocks in an active continental margin, the Ryoke Belt, Southwest Japan

    NASA Astrophysics Data System (ADS)

    Akasaki, Eri; Owada, Masaaki; Kamei, Atsushi

    2015-08-01

    The continental margin of Pacific Asia is dominated by the voluminous Cretaceous to Paleogene granitic rocks. The Ryoke granitoids that occur in the Ryoke Belt in the Southwest Japan Arc are divided into the older and younger granites. The high-K Kibe Granite represents the younger granitic intrusion and is exposed in the Yanai area in the western part of Ryoke Belt. The Kibe Granite is associated with the coeval Himurodake Quartz Diorite and their intrusive age is 91 Ma. However, the Gamano-Obatake Granodiorite, the older granite, intruded the host Ryoke gneisses at 95 Ma. The Gamano-Obatake Granodiorite is characterized by the localized development of migmatitic structure attributed to the intrusion of the Himurodake Quartz Diorite into the granodiorite. Leucocratic pools and patches occur in the granodiorite in the vicinity of the quartz diorite. The Sr and Nd isotopic compositions of the Gamano-Obatake Granodiorite corrected to 91 Ma are plotted within those of the Kibe Granite. Geochemical modeling suggests that partial melting took place in the Gamano-Obatake Granodiorite and resulted in the formation of the Kibe Granite magma. The Himurodake Quartz Diorite is believed to be a heat source for this event. This can be considered as an essential process for the formation of the evolved younger Ryoke granite and for the crustal differentiation in the active continental margin.

  17. Locating Active Plate Boundaries by Earthquake Data. Crustal Evaluation Education Project. Teacher's Guide [and] Student Investigation.

    ERIC Educational Resources Information Center

    Stoever, Edward C., Jr.

    Crustal Evolution Education Project (CEEP) modules were designed to: (1) provide students with the methods and results of continuing investigations into the composition, history, and processes of the earth's crust and the application of this knowledge to man's activities and (2) to be used by teachers with little or no previous background in the…

  18. Geochemical heterogeneities and dynamics of magmas inside the plumbing system of a persistently active volcano: evidences from Stromboli

    NASA Astrophysics Data System (ADS)

    Pompilio, Massimo; Bertagnini, Antonella; Métrich, Nicole; Belhadj, Oulfa

    2010-05-01

    Shallow processes such as degassing, crystallization and magma drain-back commonly operate in the upper parts of the plumbing systems of open-conduit basaltic volcanoes, often hindering the identification of potentially important geochemical changes in the volcano systems. Stromboli, known for its long-lived persistent activity over the last 18 centuries, is a suitable subject of study for addressing this issue, since basaltic magmas presently erupting at in this volcano record both deep and shallow processes. We report petrological and geochemical data on magmas erupted by Stromboli since the beginning of the persistent activity, in order to find a correlation between magma composition and the dynamics of magma in the plumbing system. Geochemical data on deep-derived magmas erupted as pumice during paroxysmal eruptions allowed us to identify two distinct parental melts (1944- and 2003-Type). These magmas, in which geochemical differences are linked to source processes rather than crystal fractionation, have alternately fed the deep reservoir in the last two millennia several times. The chemical heterogeneities recorded in lava flows and the products of Strombolian activity testify to the extent of homogenization after magma recharges at shallow depths. Persistent heterogeneities in the shallow plumbing system have important implications for magma residence times calculated on the basis of time-series analysis. These models are based on the assumptions that the reservoir is well stirred and chemically homogeneous and that the time for the re-homogenization after recharge (or mixing) is shorter than the residence time. We argue that these models do not apply to present-day activity at Stromboli and may not apply to other open-conduit, persistently degassing basaltic volcanoes. Thus compositional variations within the shallow magma bodies provide only a biased signal of ongoing changes within the plumbing system. We conclude that source changes responsible for

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

  20. 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

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

  2. Earthquake relocations, crustal rheology, and active deformation in the central-eastern Alps (N Italy)

    NASA Astrophysics Data System (ADS)

    Viganò, Alfio; Scafidi, Davide; Ranalli, Giorgio; Martin, Silvana; Della Vedova, Bruno; Spallarossa, Daniele

    2015-10-01

    A revised seismic catalogue (1994-2007) for the central-eastern Alps (N Italy) is presented. 396 earthquake relocations, for local magnitudes in the 1.2-5.3 range, are performed using a 3D crustal velocity structure and probabilistic locations. The location procedure is validated by computing a set of 41 quarry shot solutions and all the results, both about shots and seismic events, are compared with those obtained using the routine location procedure. Results are shown for five contiguous seismotectonic domains, as supported by geological and geophysical evidence (e.g., fault systems, crustal tomography, focal mechanisms types). Earthquake hypocentres are mostly located in the upper crust (0-15 km of depth), in good agreement with thermo-rheological models about the brittle-ductile transitions (8-9 km of depth) and total crustal strengths (1.0-2.0 TN m- 1). Epicentres are clustered and/or aligned along present-day active geological structures. The proposed seismotectonic model shows dominant compression along the Giudicarie and Belluno-Bassano-Montello thrusts, with strain partitioning along the dominant right-lateral strike-slip faults of the Schio-Vicenza domain. The present-day deformation of the Southern Alps and the internal Alpine chain is compatible with Adria indentation and the related crustal stress distribution.

  3. Os and S isotope studies of ultramafic rocks in the Duke Island Complex, Alaska: variable degrees of crustal contamination of magmas in an arc setting and implications for Ni-Cu-PGE sulfide mineralization

    NASA Astrophysics Data System (ADS)

    Stifter, Eric C.; Ripley, Edward M.; Li, Chusi

    2016-03-01

    The Duke Island Complex is one of the several "Ural-Alaskan" intrusions of Cretaceous age that occur along the coast of SE Alaska. Significant quantities of magmatic Ni-Cu-PGE sulfide mineralization are locally found in the complex, primarily within olivine clinopyroxenites. Sulfide mineralization is Ni-poor, consistent with petrologic evidence which indicates that sulfide saturation was reached after extensive olivine crystallization. Olivine clinopyroxenites were intruded by magmas that produced sulfide-poor, adcumulate dunites. As part of a study to investigate the potential for Ni-rich sulfide mineralization in association with the dunites, a Re-Os and S isotope study of the dunites, as well as sulfide mineralization in the olivine clinopyroxenites, was initiated. Importantly, recent drilling in the complex identified the presence of sulfidic and carbonaceous country rocks that may have been involved in the contamination of magmas and generation of sulfide mineralization. γOs (110 Ma) values of two sulfidic country rocks are 1022 and 2011. δ34S values of the country rocks range from -2.6 to -16.1 ‰. 187Os/188Os ratios of sulfide minerals in the mineralization hosted by olivine clinopyroxenites are variable and high, with γOs (110 Ma) values between 151 and 2059. Extensive interaction with Re-rich sedimentary country rocks is indicated. In contrast, γOs (110 Ma) values of the dunites are significantly lower, ranging between 2 and 16. 187Os/188Os ratios increase with decreasing Os concentration. This inverse relation is similar to that shown by ultramafic rocks from several arc settings, as well as altered abyssal dunites and peridotites. The relation may be indicative of magma derivation from a sub-arc mantle that had experienced metasomatism via slab-derived fluids. Alternatively, the relation may be indicative of minor contamination of magma by crustal rocks with low Os concentrations but high 187Os/188Os ratios. A third alternative is that the low Os

  4. Deep-crustal magma reservoirs beneath the Nicaraguan volcanic arc, revealed by 2-D and semi 3-D inversion of magnetotelluric data

    NASA Astrophysics Data System (ADS)

    Brasse, Heinrich; Schäfer, Anja; Díaz, Daniel; Alvarado, Guillermo E.; Muñoz, Angélica; Mütschard, Lutz

    2015-11-01

    A long-period magnetotelluric (MT) experiment was conducted in early 2009 in western Nicaragua to study the electrical resistivity and thus fluid/melt distribution at the Central American continental margin where the Cocos plate subducts beneath the Caribbean plate. Strike analysis yields a preference direction perpendicular to the profile, with moderate deviation from two-dimensionality, however. Two-dimensional modeling maps the sediments of the Nicaraguan Depression and a high-conductivity zone in the mid-crust, slightly offset from the arc. Further conductors are modeled in the backarc. However, these features are probably artifacts when a 2-D program is applied to data which show moderate 3-D characteristics. 3-D inversion clarifies the situation, and the major remaining conductive structure is now quasi directly beneath the volcanic chain and interpreted as a deep-seated magma deposit. Conductivity in the backarc is also relatively high and may either be caused by still existing partial melts beneath the Paleocene to Miocene volcanic arcs or by related metallic deposits in the aureoles of hydrothermal alteration.

  5. Heat flux and crustal radio-activity near the Sudbury neutrino observatory, Ontario, Canada

    NASA Astrophysics Data System (ADS)

    Mareschal, J.; Perry, C.; Jaupart, C.

    2009-05-01

    During its next phase, the Sudbury neutrino observatory (SNO) will detect geoneutrinos, antineutrinos produced by the decay of U and Th in the Earth. These observations will provide direct constraints on the contribution of radiogenic heat production in the crust and mantle to the energy budget of the Earth. The geoneutrino flux at SNO depends on the local level of crustal radio-activity. Surface heat flux data record average crustal radio-activity unaffected by small scale heterogeneities. We review all available heat flux data measurements in the Sudbury structure as well as measurements of U, Th, and K concentrations in the main geological units of the area. With all available data, the average heat flux in the Sudbury basin is ~53mW m-2, higher than the mean value of 42mW m-2 for the entire Canadian Shield. The elevated heat flux is due to high heat production in the shallow crust. We estimate that the average heat production of the upper crust near Sudbury is >1.5μ W m-3 compared to an average of 0.95μ W m-3 for the Superior Province. The high crustal radio-activity near Sudbury results in an about 50% increase of the local crustal component of the geoneutrino flux. Crustal radio-activity is highest in the southern part of the structure, near the Creighton mine where SNO is located. High heat flux and heat production values are also found in the Southern Province, on the margin of the Superior Province. An azimuthal variation in the geoneutrino flux with a higher flux from the south than from the north is expected on the basis on the present information. However, we shall need better estimates of the contribution of the rocks in the Superior Province to the North to assess the extent of azimuthal effects. The many available exploration drill holes and core samples provide an opportunity to determine the spatial variations in crustal radioactivity near SNO and improve the interpretation of future measurements of the geoneutrino flux.

  6. Central Compact Objects in Kes 79 and RCW 103 as `Hidden' Magnetars with Crustal Activity

    NASA Astrophysics Data System (ADS)

    Popov, S. B.; Kaurov, A. A.; Kaminker, A. D.

    2015-05-01

    We propose that observations of `hidden' magnetars in central compact objects can be used to probe crustal activity of neutron stars with large internal magnetic fields. Estimates based on calculations by Perna & Pons, Pons & Rea and Kaminker et al. suggest that central compact objects, which are proposed to be `hidden' magnetars, must demonstrate flux variations on the time scale of months-years. However, the most prominent candidate for the `hidden' magnetars - CXO J1852.6+0040 in Kes 79 - shows constant (within error bars) flux. This can be interpreted by lower variable crustal activity than in typical magnetars. Alternatively, CXO J1852.6+0040 can be in a high state of variable activity during the whole period of observations. Then we consider the source 1E161348 - 5055 in RCW103 as another candidate. Employing a simple 2D-modelling we argue that properties of the source can be explained by the crustal activity of the magnetar type. Thus, this object may be supplemented for the three known candidates for the `hidden' magnetars among central compact objects discussed in literature.

  7. Temporal change of the mode of eruptive activity and the magma plumbing system of Sakurajima Volcano since 20th century : Implications for forecast future eruptive activity

    NASA Astrophysics Data System (ADS)

    Nakagawa, M.; Matsumoto, A.; Amma-Miyasaka, M.; Togashi, Y.; Iguchi, M.

    2011-12-01

    Sakurajima volcano is a post-caldera volcano of Aira caldera and has repeated large plinian eruptions with dormant periods in AD 1471, AD 1779 and AD 1914. After AD 1914 eruption, medium scale of lava effusion occurred in AD 1946. Since AD 1955, frequent vulcanian eruptions have repeated until now. Thus, mode of eruptive activity of the volcano has changed since 20th century. Based on temporal change of petrological features of these eruptive materials, We discuss the relationship between the mode of eruptive activity and magma system to forecast the future eruptive activity. The rocks of AD 1471 and AD 1779 eruptions are CPX-OPX dacite, in which normally and reversely zoned pyroxene and plagioclase phenocrysts coexist. In addition, compositional distribution of plagioclase phenocrysts is bi-modal. These suggest that these rocks are mixing products between dacitic and andesitic magmas. This is consistent with compositional variations of whole-rock chemistry for these rocks. On the other hand, the rocks of AD 1914 and AD 1946 eruption often contain olivine phenocrysts. Plagioclase and pyroxenes phenocrysts in these rocks show similar features to those of AD 1471 and AD 1779 eruptions, suggesting that these rocks are also mixing products of two end-member magmas, dacitic and andesitic ones. However, olivine phenocrysts are much magnesian compared with pyroxenes phenocrysts, indicating that these olivine phencorysts are derived from another basaltic magma. Thus, the basaltic magma injected into the mixed magma between dacitic and andesitic ones. Mixing among three magmas has been recognized since 20th century. The rocks from frequent eruptions since AD 1955 also contain minor amount of olivine phenocrysts, suggesting the injection of basaltic magma has continued. In 1970's and AD 1987 periods, relatively larger scale of vulcanian eruptions had occurred. The rocks from these periods contain considerable amount of olivine phenocrysts, indicating mixing ratio of the

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  9. Crustal Deformation around Zhangjiakou-Bohai Seismically Active Belt

    NASA Astrophysics Data System (ADS)

    Jin, H.; Fu, G.; Kato, T.

    2011-12-01

    Zhangjiakou-Bohai belt is a seismically active belt located in Northern China around Beijing, the capital of China. Near such a belt many great earthquakes occurred in the past centuries (e.g. the 1976 Tanshan Ms7.8 earthquake, the 1998 Zhangbei Ms6.2 earthquake, etc). Chinese Government established dense permanent and regional Global Positioning System (GPS) stations in and near the area. We collected and analyzed all the GPS observation data between 1999 and 2009 around Zhangjiakou-Bohai seismic belt, and obtained velocities at 143 stations. At the same time we investigated Zhangjiakou-Bohai belt slip rate for three profiles from northwest to southeast, and constructed a regional strain field on the Zhangjiakou-Bohai seismic belt region by least-square collocation. Based on the study we found that: 1) Nowadays the Zhangjiakou-Bohai seismic belt is creeping with left-lateral slip rate of 2.0mm~2.4mm/a, with coupling depth of 35~50km; 2) In total, the slip and coupling depth of the northwestern seismic belt is less than the one of southeast side; 3) The maximum shear strain is about 3×10-8 at Beijing-Tianjin-Tangshan area.

  10. 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.

  11. The Ratio Between Magma Supply and Lithospheric Stretching Rates Controls the Architecture of Continental and Oceanic Rifts

    NASA Astrophysics Data System (ADS)

    Bourgeois, O.; Dauteuil, O.

    2010-12-01

    Magma-poor rifts (e.g. Rhine Graben, North Sea), non-volcanic passive continental margins (e.g. Galicia) and slow-spreading oceanic ridges (e.g. Mid-Atlantic Ridge), are composed of faulted crustal blocks that dip generally away from the rift axis. By contrast, magma-rich rifts (e.g. Afars), volcanic passive margins (e.g. Norway, Greenland, Namibia) and hotspot-influenced slow-spreading oceanic ridges (e.g. Iceland), are composed of faulted crustal blocks that dip generally towards the rift axis. On the basis of a detailed structural study of Iceland (Bourgeois et al. 2005, Geodinamica Acta 18:59-80), we demonstrate that, in magma-rich rifts, lithospheric stretching is accomodated in a long-term deformation strip, n x 100 km wide, by the development of successive roll-over structures controlled by growth-faults and underlain by shallow magma chambers. As a given roll-over structure progressively develops and tilts in response to lithospheric stretching, it is continuously covered by lavas erupted from the associated magma chamber and reaching the surface through dike swarms dominantly located along the growth fault. After a lifetime of a few My, this roll-over structure dies at the expense of the activation of a new, laterally offset, one. Correspondingly, such roll-over structures form successively at different places within a diffuse plate boundary n x 100 km wide. After several roll-over structures have developed and died, the overall structure of the long-term deformation strip is composed of faulted crustal blocks that generally dip towards the rift axis. This architecture differs from that of magma-poor rifts, where lithospheric strectching is accomodated in a fixed and narrow (n x 10 km) strip, by the developpement of outward-tilted blocks. Physical laboratory experiments conducted with analogue materials demonstrate that this difference in rift architectures is controlled by the ratio between the rate of lithospheric stretching and the rate of magma supply

  12. Formation of a zoned magma chamber and its temporal evolution during the historic eruptive activity of Tarumai Volcano, Japan: Petrological implications for a long-term forecast of eruptive activity of an active volcano

    NASA Astrophysics Data System (ADS)

    Nakagawa, Mitsuhiro; Hiraga, Naoto; Furukawa, Ryuta

    2011-08-01

    Tarumai Volcano started a series of historic eruptive activity in AD 1667 after a dormancy of approximately 2000 years. The historic juvenile ejecta are mainly silicic andesite pumice associated with scoria, banded pumice and dome lava (SiO 2 = 55-63%), and are mixing products of two or three end-member magmas. In the initial largest plinian eruptions (AD 1667 period), simple mixing between two end-member magmas, silicic andesite (SA) and basalt, occurred. Large plinian eruptions (AD 1739 period) and the latest intermittent eruptions (AD 1804-AD 1909: latest period) also produced mixed magmas including both the SA, intermediate-SiO 2 andesite (IA), and basalt. Magmatic temperatures of the SA and IA magmas are 900-950 °C and approximately 1000 °C, respectively. The rocks of each period form linear trends in oxide-oxide diagrams, suggesting that mixing of two end-member magmas occurred in each period. Thus, it can be estimated that the IA magma was formed by mixing between the basaltic and SA magmas. These relations suggest that the injection of the basaltic magma into the SA magma occurred before the AD 1667 period, resulting in the formation of a zoned magma chamber. These two magmas were then withdrawn to mingle, during the AD 1667 period. After the period, the zoned chamber was composed of an upper SA magma and a lower mixed IA magma. Chemical compositions of the basaltic magma have been slightly different in each period since AD 1667. In addition, the phenocrystic minerals of the IA magma also have changed as a consequence of re-equilibration with the more mafic IA bulk magma compositions present from AD 1739 to AD 1909. Thus, distinct basaltic magma has repeatedly injected into the zoned chamber before each eruption. Although the scale of eruptions became much smaller after the plinian eruptions of AD 1739, the ratio of IA magma in the latest eruptive materials is much larger than that in AD 1739, suggesting that a larger amount of the lower part (IA magma

  13. Activities and source mechanisms of volcanic deep low-frequency earthquakes and its implication for deep crustal process in magmatic arc (Invited)

    NASA Astrophysics Data System (ADS)

    Nakamichi, H.

    2013-12-01

    Rocks under upper mantle and lower crustal temperatures and pressures typically deform in a ductile manner, therefore it is difficult to accumulate enough deviatoric stress in rocks to generate brittle failure under this condition. However earthquakes occur at upper mantle and lower crust beneath active volcanoes, and are recognized as volcanic deep low-frequency earthquakes (VDLFs). VDLFs are characterized by mostly low-frequency energy (<5 Hz), emergent arrivals and long-duration codas. VDLF activity observed at depths of 10-50 km in Japan, the Philippines, Alaska and the Western US (Power et al., 2004; Ukawa, 2005; Nichols et al. 20011), has generally been attributed to magma transport in the mid-to-lower crustal and uppermost mantle regions. However because VDLF seismicity is infrequent, with relatively weak and emergent signals, the relationship between deep magma transport and seismic radiation remains poorly understood. Borehole dense seismic observation systems, such as the high-sensitivity seismograph network 'Hi-net' in Japan (Obara et al. 2005), are effective for detecting not only non-VDLFs (Obara, 2002) but also VDLFs. Since 1997 the Japan Meteorological Agency has routinely detected and located DLFs using the Hi-net dataset, and have identified DLFs in and around most quaternary volcanoes in Japan (Takahashi and Miyamura, 2009). Several studies have attempted to estimate source mechanisms of VDLFs in Japan. The first attempt by Ukawa and Ohtake (1987), obtained a single force as the source mechanism of a VDLF beneath Izu-Ohshima by using particle motions of S-waves. Following that work strike-slip type and non-double-couple source mechanisms were obtained using waveform inversions for VDLFs in Northeast Japan (Nishidomi and Takeo 1996; Okada and Hasegawa, 2000). Nakamichi et al. (2003; 2004) estimated the source mechanisms of Mts. Iwate and Fuji through the moment tensor inversion of spectral ratios of body waves from using data from a dense seismic

  14. Geochemical constraints on the origin of mafic and silicic magmas at Cordón El Guadal, Tatara-San Pedro Complex, central Chile

    NASA Astrophysics Data System (ADS)

    Feeley, T. C.; Dungan, M. A.; Frey, F. A.

    The aim of this study is to quantify the crustal differentiation processes and sources responsible for the origin of basaltic to dacitic volcanic rocks present on Cordón El Guadal in the Tatara-San Pedro Complex (TSPC). This suite is important for understanding the origin of evolved magmas in the southern Andes because it exhibits the widest compositional range of any unconformity-bound sequence of lavas in the TSPC. Major element, trace element, and Sr-isotopic data for the Guadal volcanic rocks provide evidence for complex crustal magmatic histories involving up to six differentiation mechanisms. The petrogenetic processes for andesitic and dacitic lavas containing undercooled inclusions of basaltic andesitic and andesitic magma include: (1) assimilation of garnet-bearing, possibly mafic lower continental crust by primary mantle-derived basaltic magmas; (2) fractionation of olivine + clinopyroxene + Ca-rich plagioclase + Fe-oxides in present non-modal proportions from basaltic magmas at 4-8kbar to produce high-Al basalt and basaltic andesitic magmas; (3) vapor-undersaturated (i.e., PH2Ocrustal rocks at 3-7kbar to produce dacitic magmas; (4) crystallization of plagioclase-rich phenocryst assemblages from dacitic magmas in shallow reservoirs; (5) intrusion of basaltic andesitic magmas into shallow reservoirs containing crystal-rich dacitic magmas and subsequent mixing to produce hybrid basaltic andesitic and andesitic magmas; and (6) formation and disaggregation of undercooled basaltic andesitic and andesitic inclusions during eruption from shallow chambers to form commingled, mafic inclusion-bearing andesitic and dacitic lavas flows. Collectively, the geochemical and petrographic features of the Guadal volcanic rocks are interpreted to reflect the development of shallow silicic reservoirs within a region characterized by high crustal temperatures due to focused basaltic activity and high magma supply rates. On the periphery of

  15. 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)

  16. Io: Loki Patera as a Magma Sea

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  18. Quantifying crustal response to deep active intrusions with geodesy-based finite element modeling

    NASA Astrophysics Data System (ADS)

    Henderson, S. T.; Pritchard, M. E.; Elliott, J.

    2013-12-01

    The Altiplano-Puna Volcanic Complex (APVC, 21-24 S, 66-69 W) is a first order feature of the Central Andes Volcanic Arc. The APVC consists of over 10,000 km^3 of dacitic ignimbrites deposited in the late Miocene, making it one of the largest concentrations of silicic volcanism in the world. The persistent and intense magmatic flux in this region has likely contributed to the thickened crust (50-70 km), elevated geotherm (>50 C/km) and extensive partial melt (<20 %) inferred under the APVC in modern times. Furthermore, satellite geodetic measurements show surface deformation centered on Uturuncu Volcano (22.27 S, 67.22 W) that is consistent with an ongoing magmatic intrusion in the middle to lower crust. The unique geologic setting and availability of multiple geophysical datasets provide an exceptional opportunity to locate fluid accumulation depths and model the resulting crustal mechanical response. InSAR data between 05/1992 and 01/2011 show that the deformation anomaly is characterized by axis-symmetric constant vertical uplift of 1-10 mm/yr over a radius of 35 km, which is surrounded by 1-4 mm/yr subsidence out to 75 km. One possible explanation for such a signal is diapiric rise of melt from the middle crust. We seek to determine if observed deformation can be alternatively explained by vertical ascent of magma from the lower (~70 km) to middle crust (~20 km). Such a model would be consistent with the short duration of deformation from geomorphic studies (less than 2200 years) and the potential abrupt cessation of uplift seen in a single continuous GPS station starting in 04/2010 near the center of deformation. We therefore test multiple finite element models that match spatial and temporal surface deformation, achieve mass balance between source and sink reservoirs, and require physically realistic rheological parameters of the crust. Modeling is performed with Pylith finite element software on a cylindrical three dimensional domain with a radius of 300 km

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

    NASA Astrophysics Data System (ADS)

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

    1999-04-01

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

  20. Bubble plumes generated during recharge of basaltic magma reservoirs

    NASA Astrophysics Data System (ADS)

    Phillips, Jeremy C.; Woods, Andrew W.

    2001-03-01

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

  1. Southeast Papuan crustal tectonics: Imaging extension and buoyancy of an active rift

    NASA Astrophysics Data System (ADS)

    Abers, G. A.; Eilon, Z.; Gaherty, J. B.; Jin, G.; Kim, YH.; Obrebski, M.; Dieck, C.

    2016-02-01

    Southeast Papua hosts the world's youngest ultra-high-pressure (UHP) metamorphic rocks. These rocks are found in an extensional setting in metamorphic core complexes. Competing theories of extensional shear zones or diapiric upwelling have been suggested as driving their exhumation. To test these theories, we analyze the CDPAPUA temporary array of 31 land and 8 seafloor broadband seismographs. Seismicity shows that deformation is being actively accommodated on the core complex bounding faults, offset by transfer structures in a manner consistent with overall north-south extension rather than radial deformation. Rayleigh wave dispersion curves are jointly inverted with receiver functions for crustal velocity structure. They show crustal thinning beneath the core complexes of 30-50% and very low shear velocities at all depths beneath the core complexes. On the rift flanks velocities resemble those of normal continents and increase steadily with depth. There is no evidence for velocity inversions that would indicate that a major density inversion exists to drive crustal diapirs. Also, low-density melt seems minor within the crust. Together with the extension patterns apparent in seismicity, these data favor an extensional origin for the core complexes and limit the role of diapirism as a secondary exhumation mechanism, although deeper mantle diapirs may be undetected. A small number of intermediate-depth earthquakes, up to 120 km deep, are identified for the first time just northeast of the D'Entrecasteaux Islands. They occur at depths similar to those recorded by UHP rocks and similar temperatures, indicating that the modern seismicity occurs at the setting that generates UHP metamorphism.

  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. Long-Span Continuous Self-Potential Measurements Around Earthquake Swarms for Monitoring Crustal Activity

    NASA Astrophysics Data System (ADS)

    Yoshimura, R.; Oshiman, N.; Yamazaki, K.; Uyeshima, M.; Ogawa, T.

    2008-12-01

    Earthquake swarm activity has been continuously observed around the southeastern flank of Ontake stratovolcano since 1976. A large earthquake with the depth about 2 km and a magnitude of 6.8 occurred in 1984 in the southeastern flank of the volcano. Recently, Kimata et al. (2004) revealed uplift ground deformation above the earthquake swarm area by using repeated leveling. Furthermore, MagnetoTelluric (MT) soundings estimated a low resistivity region with the depth about 2km beneath the uplift area (Kasaya et al., 2002). In order to investigate a relationship between tectonic movements and subsurface low resistivity zone, Yoshimura et al. (2007) carried out self-potential (SP) measurements from 2003 to 2005 around the earthquake swarm areas. As the result of SP measurements, a torus-shape positive SP anomaly has been detected at the eastern part of the survey profile. This anomaly is located between recent active clusters of earthquakes and near the ground uplift detected by Kimata et al. (2004). Given that the obtained anomaly delineates the subsurface fluid"fs motion due to thermal or crustal activities, it could be expected that the anomaly varies in association with fluctuation of crustal activities. In February 2007, we established a continuous SP observation network with the aim of monitoring the crustal/hydrothermal activity by reference to the obtained SP distribution. This network consists of 8 Pb- PbCl2 electrodes and uses metallic telephone lines as insulated cables for measuring SP. Voltage differences between electrodes are measured at an interval of 1 sec. This observation technique, called "Network-MT", has been developed to determine large-scale electrical conductivity structure and the spatial distribution of the telluric potentials (Uyeshima, 2007). As a preliminary result of longitudinal data analysis, night time daily median values showed remarkable stepwise SP time variations with relaxation time about 15 days in August 2007. Additionally

  4. Crustal-scale active deformation along the Ecuadorian Andes using Persistent Scatterers SAR Interferometry

    NASA Astrophysics Data System (ADS)

    Champenois, J.; Baize, S.; Audin, L.; Pinel, V.; Alvarado, A.; Jomard, H.; Yepes, H. A.

    2013-12-01

    Located in the Northern Andes along the active subduction zone of the Nazca plate beneath the South American continent, Ecuador is highly exposed to seismic hazard. For the last ten years, numerous multidisciplinary studies focused on major seismicity related to the subduction, whereas few investigations concentrated on M>7 crustal seismicity in the upper plate (like 1797 Riobamba earthquake, ML 8.3, 12.000 deaths). The active faults producing these earthquakes are poorly known in term of slip rate and for some cases are even not identified yet. Additionnally, Ecuador is one of the most active volcanic areas of the northern Andean volcanic zone. Three among the nine active volcanoes are actually erupting (Reventador, Tungurahua, and Sangay). For the last 5 years, geodetic networks have been deployed in Ecuador to enhance crustal deformation monitoring, but these point-wise techniques cannot provide spatially dense maps of ground deformation and are quite expensive methods. To address this issue, we applied the Persistent Scatterers SAR Interferometry technique (StaMPS/MTI freeware developed by A. Hooper) to ENVISAT SAR data between 2003 and 2009. Using these cost-effective techniques, we are able to investigate both tectonic and volcanic surface deformations with an unprecedented spatial density of measurements. This study presents new PS-InSAR results along the Ecuadorian Andes, close to the area of Riobamba. We generated average velocity maps and consistent time-series of displacements measured along the radar line of sight. These results evidence large scale deformation localized on the Pallatanga fault system (locked fault) compatible with a model of locked strike slip fault. Moreover, these results show an important growth of the Tungurahua volcanic complex (maximum rate about 9 mm/yr) with a rapid uplift prior and post 2006 explosive eruption. We investigate the time-series of displacement for 22 images. Our results permitted to propose two crustal source

  5. Tracing the evolution of crustal-scale, transient permeability in a tectonically active, mid-crustal, low-permeability environment by means of quartz veins

    NASA Astrophysics Data System (ADS)

    Sintubin, M.

    2013-12-01

    In mid-crustal, low-permeability environments pervasive fluid flow is primarily driven by the production of internally-derived metamorphic fluids, causing a near permanent state of near-lithostatic fluid-pressure conditions. In a tectonically active crust, these overpressured fluids will generate intermittently an enhanced permeability that will facilitate fluid flow through the crust. The High-Ardenne slate belt (Belgium, France, Germany) can be considered as a fossil (late Palaeozoic) analogue of such mid-crustal, low-permeability environment at the brittle-plastic transition (depth range from 7 to 15 km). Low-grade metamorphic (250°C-350°C), predominantly fine-grained, siliciclastic metasediments were affected by a contraction-dominated deformation, materialized by a pervasive slaty cleavage. Quartz veins, abundantly present in the slate belt, are used as a proxy for the enhanced permeability. Detailed structural, petrographical, mineralogical and geochemical studies of different quartz-vein occurrences has enabled to reconstruct the evolution of the crustal-scale permeability , as well as to constrain the coupled fluid-pressure and stress-state evolution throughout the orogenic history. Extensive veining on a regional scale seems confined to periods of tectonic stress inversion, both at the onset (compressional stress inversion) and in the final stages (extensional stress inversion) of orogeny. Firstly, compressional stress inversion is expressed by pre-orogenic bedding-normal extension veins, consistently arranged in parallel arrays, followed by early orogenic bedding-parallel hybrid veins. Fluid-inclusion studies demonstrate near-lithostatic to supralithostatic fluid pressures, respectively. Secondly, discordant veins, transecting the pre-existing cleavage fabric, are interpreted to be initiated shortly after the extensional stress inversion, reflecting the late-orogenic extensional destabilisation of the slate belt. Veining again occurred at high fluid

  6. Degassing system from the magma reservoir of Miyakejima volcano revealed by GPS observations

    NASA Astrophysics Data System (ADS)

    Oikawa, J.; Nakao, S.; Matsushima, T.

    2013-12-01

    Miyake-jima is a volcanic island located approximately 180 km south of Tokyo. The island is an active basaltic volcano that was dormant for a 17-year period between an eruption in 1983 and June 26, 2000, when it again became active. The volcanic activity that occurred in 2000 is divided into the following four stages: the magma intrusion stage, summit subsidence stage, summit eruptive stage, and degassing stage (Nakada et al., 2001). Earthquake swarm activity began on June 26, 2000, accompanied by large-scale crustal deformation. This led to a summit eruption on July 8, 2000. Based on the pattern of hypocenter migration and the nature of crustal deformation, it was estimated that magma migrated from beneath the summit of Miyake-jima to the northwest during the magma intrusion stage. The rapid collapse of the summit took place between July 8 and the beginning of August 2000 (summit subsidence stage). Large-scale eruptions took place on August 10, 18, and 29, 2000 (explosion stage). The eruptions largely ceased after August 29, followed by the release of large amounts of gas from the summit crater (degassing stage). In this study, we examined the location of the magma reservoir during the degassing stage based on crustal deformation observed by GPS. By comparing the amounts of degassing and volume change of the magma reservoir, as determined from crustal deformation, we determined the mechanism of degassing and the nature of the magma reservoir-vent system. According to observations by the Japan Meteorological Agency, a large amount of volcanic gas began to be released from Miyake-jima in September 2000 (Kazahaya et al., 2003). Approximately 42,000 tons/day of SO2 was released during the period between September 2000 and January 2001. Analysis of GPS data during the period [Figure 1] indicates a source of crustal deformation on the south side of the summit crater wall at a depth of 5.2 km. The rate of volume change was -3.8 x 106 m3/month [Figure 2]. As the volume is

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  8. Investigation of the deep crustal structure and magmatic activity at the NW Hellenic Volcanic Arc with 3-D aeromagnetic inversion and seimotectonic analysis.

    NASA Astrophysics Data System (ADS)

    Efstathiou, Angeliki; Tzanis, Andreas; Chailas, Stylianos; Stamatakis, Michael

    2013-04-01

    structures of relatively high magnetic susceptibility (>0.035), which all dip to the NNE and do not exceed the depth of 2km; these have all been identified with outcropping ophiolitic bodies. With particular reference to the Argolid, the results also indicate the existence of extensive and massive deep magnetized domains at depths > 4km, with susceptibilities of the order of 0.02. The latter include a rather conspicuous volume beneath the Methana volcanic complex, at depths between 4 and 8km. Because the modeled susceptibility values are generally consistent with the values expected for hot (200°C - 500°C) calc-alcaline igneous rocks, this feature was interpreted to comprise a magma chamber. By analogy to the Methana chamber, all such massive structures were attributed to recent magmatic intrusions (plutons). The pervasive presence of the intrusive igneous rocks beneath the Argolid indicates a rather extensive complex of magmatic activity associated with the western volcano group of the HVA. Particular attention is due to one such elongate and deep reaching "pluton", which develops in a NNW direction (approx. 330°) along the axis of the Argolic Gulf, to the south of the Argolid peninsula; this is situated almost directly above the local inflection (steepening) of the subducting slab and is almost exactly aligned with to it. The sub-crustal stress field due to the subducting slab has been determined by Rondogianni et al (2011) and has been re-appraised in the frame of the present analysis using the method of Michael (1984, 1987). It turns out to be extensional and NE-SW oriented, with the azimuth/dip of the maximum principal axis (compression) being approx. 230°/57° and the same for thee minimum principal axis (extension) being 59°/33°. With such a field, deformation is expected to associate with steeply dipping dislocation surfaces parallel to approx. 325° and to be primarily extensional, with a non-trivial left-lateral heave. An analogous analysis was conducted for

  9. Crustal root beneath the Rif Cordillera as imaged from both active seismic data and teleseismic receiver functions.

    NASA Astrophysics Data System (ADS)

    Diaz, Jordi; Gil, Alba; Gallart, Josep; Carbonell, Ramon; Harnafi, Mimoun; Levander, Alan

    2015-04-01

    The Rif cordillera forms, together with the Betic ranges, one of the tightest orogenic arcs on Earth. This continental boundary zone is dominated now by the slow convergence between Nubia and Eurasia, but with clear evidences of extensional tectonics. One of the missing elements to constrain the complex geodynamics of the Gibraltar Arc System is the knowledge of the crustal architecture beneath northern Morocco. In the last decade a major effort has been done in this sense, from active and passive seismics. We compile here the recent results available from the Rif domains. Two 330 km long wide angle DSS profiles were recorded end of 2011 across the Rif in NS and EW transects within the Rifsis project, complemented by onshore recordings of the Gassis-WestMed marine profiles. At the same period, BB seismic arrays were deployed in the area within Topo-Iberia and Picasso projects, allowing receiver function analyses of crustal depths. The ray-tracing modeling of the Rifsis profiles reveal a large Moho step and an area of crustal thickening both in EW and NS directions, grossly coincident with the Bouguer gravity anomalies. The deployment logistics allowed that all the stations recorded all the shots, thus providing useful offline data. We will use here all available in-line and offline data to provide a map of the crustal thickness in northern Morocco. We combined two approaches: i) a hyperbolic time reduction applied to the seismic data, resulting in low-fold stacks in which the reflections from the Moho should appear as subhorizontal lines; ii) the arrival times of the observed PmP phases allow, assuming a mean crustal velocity, to assign a midpoint crustal thickness to each lecture. Although some uncertainties may be inherent to those approaches, a large crustal root, reaching more than 50 km, is well documented in the central part of the Rif Cordillera, close to the zone where the Alboran slab may still be attached to the lithosphere. We also compared these results

  10. Seismic hydraulic fracture migration originated by successive deep magma pulses: The 2011-2013 seismic series associated to the volcanic activity of El Hierro Island

    NASA Astrophysics Data System (ADS)

    Díaz-Moreno, A.; Ibáñez, J. M.; De Angelis, S.; García-Yeguas, A.; Prudencio, J.; Morales, J.; Tuvè, T.; García, L.

    2015-11-01

    In this manuscript we present a new interpretation of the seismic series that accompanied eruptive activity off the coast of El Hierro, Canary Islands, during 2011-2013. We estimated temporal variations of the Gutenberg-Richter b value throughout the period of analysis, and performed high-precision relocations of the preeruptive and syneruptive seismicity using a realistic 3-D velocity model. Our results suggest that eruptive activity and the accompanying seismicity were caused by repeated injections of magma from the mantle into the lower crust. These magma pulses occurred within a small and well-defined volume resulting in the emplacement of fresh magma along the crust-mantle boundary underneath El Hierro. We analyzed the distribution of earthquake hypocenters in time and space in order to assess seismic diffusivity in the lower crust. Our results suggest that very high earthquake rates underneath El Hierro represent the response of a stable lower crust to stress perturbations with pulsatory character, linked to the injection of magma from the mantle. Magma input from depth caused large stress perturbations to propagate into the lower crust generating energetic seismic swarms. The absence of any preferential alignment in the spatial pattern of seismicity reinforces our hypothesis that stress perturbation and related seismicity, had diffusive character. We conclude that the temporal and spatial evolution of seismicity was neither tracking the path of magma migration nor it defines the boundaries of magma storage volumes such as a midcrustal sill. Our conceptual model considers pulsatory magma injection from the upper mantle and its propagation along the Moho. We suggest, within this framework, that the spatial and temporal distributions of earthquake hypocenters reflect hydraulic fracturing processes associated with stress propagation due to magma movement.

  11. Relationship between the regional tectonic activity and crustal structure in the eastern Tibetan plateau discovered by gravity anomaly

    NASA Astrophysics Data System (ADS)

    Xu, Xiao; Gao, Rui; Guo, Xiaoyu

    2016-04-01

    The eastern Tibetan plateau has been getting more and more attention because it combines active faults, uplifting, and large earthquakes together in a high-population region. Based on the previous researches, the most of Cenozoic tectonic activities were related to the regional structure of the local blocks within the crustal scale. Thus, a better understanding of the crustal structure of the regional tectonic blocks is an important topic for further study. In this paper, we combined the simple Bouguer gravity anomaly with the Moho depths from previous studies to investigate the crustal structure in this area. To highlight the crustal structures, the gravity anomaly caused by the Moho relief has been reduced by forward modeling calculations. A total horizontal derivative (THD) had been applied on the gravity residuals. The results indicated that the crustal gravity residual is compatible with the topography and the geological settings of the regional blocks, including the Sichuan basin, the Chuxiong basin, the Xiaojiang fault, and the Jinhe fault, as well as the Longmenshan fault zone. The THD emphasized the west margin of Yangtze block, i.e., the Longriba fault zone and the Xiaojiang fault cut through the Yangtze block. The checkboard pattern of the gravity residual in the Songpan-Garze fold belt and Chuandian fragment shows that the crust is undergoing a southward and SE-directed extrusion, which is coincident with the flowing direction indicated from the GPS measurements. By integrating the interpretations, the stepwise extensional mechanism of the eastern Tibetan plateau is supported by the southeastward crustal deformation, and the extrusion of Chuandian fragment is achieved by Xianshuihe fault.

  12. The three-dimensional pattern of crustal deformation associated with active normal fault systems observed using continuous GPS geodesy

    NASA Astrophysics Data System (ADS)

    Bennett, R. A.; Hreinsdottir, S.

    2009-12-01

    Geological examples of shallow dipping normal faults with large displacements are exposed at numerous locations throughout the world and it is widely recognized that extensional deformation at brittle crustal levels is most efficiently accomplished by slip across such structures. It has previously been shown that lower dip angles reduce the regional stresses required to drive large horizontal displacements. Nevertheless, the traditional theory of fault mechanics—based on Anderson’s classification of stress regimes, the Coulomb failure criterion, and Byerlee’s friction law—precludes such faults from slipping at low angle. Observational support for this traditional theory includes the absence of large unequivocally low-angle normal fault earthquakes in the global catalog; all well-determined normal fault earthquakes appear to have occurred on moderate to steeply dipping planes. However, precise measurements of 3D crustal motions based on continuous GPS in central Italy and Utah reveal deformation patterns across active normal fault systems that are inconsistent with active slip across steeply dipping planes. Instead, the combination of observed horizontal and vertical surface motions are consistent with slip across low angle surfaces independently imaged in the subsurface by seismic reflection and other geophysical data. For the Alto Tiberina fault in central Italy, active aseismic creep occurs at shallow crustal levels, most likely within the brittle-frictional regime at which Andersonian-Byerlee fault mechanics should be applicable. The actively creeping portion of the fault inferred using GPS geodesy correlates well with the observed pattern of micro-seismicity, which concentrates along the inferred subsurface fault plane. GPS measurements across the greater Wasatch fault zone in the vicinity of Salt Lake City, Utah, reveal crustal motions consistent with aseismic displacement across a shallow dipping fault or sub-horizontal shear zone at mid-crustal

  13. Active Crustal Faults in the Forearc Region, Guerrero Sector of the Mexican Subduction Zone

    NASA Astrophysics Data System (ADS)

    Gaidzik, Krzysztof; Ramírez-Herrera, Maria Teresa; Kostoglodov, Vladimir

    2016-01-01

    This work explores the characteristics and the seismogenic potential of crustal faults on the overriding plate in an area of high seismic hazard associated with the occurrence of subduction earthquakes and shallow earthquakes of the overriding plate. We present the results of geomorphic, structural, and fault kinematic analyses conducted on the convergent margin between the Cocos plate and the forearc region of the overriding North American plate, within the Guerrero sector of the Mexican subduction zone. We aim to determine the active tectonic processes in the forearc region of the subduction zone, using the river network pattern, topography, and structural data. We suggest that in the studied forearc region, both strike-slip and normal crustal faults sub-parallel to the subduction zone show evidence of activity. The left-lateral offsets of the main stream courses of the largest river basins, GPS measurements, and obliquity of plate convergence along the Cocos subduction zone in the Guerrero sector suggest the activity of sub-latitudinal left-lateral strike-slip faults. Notably, the regional left-lateral strike-slip fault that offsets the Papagayo River near the town of La Venta named "La Venta Fault" shows evidence of recent activity, corroborated also by GPS measurements (4-5 mm/year of sinistral motion). Assuming that during a probable earthquake the whole mapped length of this fault would rupture, it would produce an event of maximum moment magnitude Mw = 7.7. Even though only a few focal mechanism solutions indicate a stress regime relevant for reactivation of these strike-slip structures, we hypothesize that these faults are active and suggest two probable explanations: (1) these faults are characterized by long recurrence period, i.e., beyond the instrumental record, or (2) they experience slow slip events and/or associated fault creep. The analysis of focal mechanism solutions of small magnitude earthquakes in the upper plate, for the period between 1995

  14. A magma-hydrothermal system beneath Hakone volcano, central Japan, revealed by highly resolved velocity structures

    NASA Astrophysics Data System (ADS)

    Yukutake, Yohei; Honda, Ryou; Harada, Masatake; Arai, Ryuta; Matsubara, Makoto

    2015-05-01

    High-resolution images of subsurface structures are necessary to understand the transport processes of crustal fluids from deep magma sources and their relationship to earthquake swarms in active volcanic regions. Based on a seismic tomography approach, we have developed a new model for the magma-hydrothermal system beneath Hakone volcano, central Japan, where shallow earthquake swarms and crustal deformation associated with inflation of an open-crack source are often observed. By applying travel-time data for local earthquakes to a tomographic inversion, we obtained highly resolved seismic velocity structures that show a region of low P-wave velocity (Vp), low S-wave velocity (Vs), and high Vp/Vs ratios at depths of 10-20 km beneath the volcano, corresponding to the location of the open-crack source. We suggest that the high Vp/Vs ratios represent a deep magma chamber with a high concentration of melt and/or fluids. Deep low-frequency earthquakes, located just beneath this high Vp/Vs zone, may indicate that magmatic fluids are supplied from below. Above the high Vp/Vs zone, a region of low Vp, low Vs, and low Vp/Vs ratios exists at depths of 3-10 km, suggesting the presence of crack-filled water or CO2 supplied from the inferred deep magma chamber. Many earthquake swarms occur in this low Vp/Vs zone, indicating that crustal fluids play an important role in generating the swarms. Similar relationships between magma reservoirs, overlying hydrothermal systems, and swarm activity have been reported from other volcanic areas and thus may be a ubiquitous feature beneath active volcanoes.

  15. Three-Dimensional Numerical Modeling of Crustal Growth at Active Continental Margins

    NASA Astrophysics Data System (ADS)

    Zhu, G.; Gerya, T.; Tackley, P. J.

    2011-12-01

    Active margins are important sites of new continental crust formation by magmatic processes related to the subduction of oceanic plates. We investigate these phenomena using a three-dimensional coupled petrological-geochemical-thermomechanical numerical model, which combines a finite-difference flow solver with a non-diffusive marker-in-cell technique for advection (I3ELVIS code, Gerya and Yuen, PEPI,2007). The model includes mantle flow associated with the subducting plate, water release from the slab, fluid propagation that triggers partial melting at the slab surface, melt extraction and the resulting volcanic crustal growth at the surface. The model also accounts for variations in physical properties (mainly density and viscosity) of both fluids and rocks as a function of local conditions in temperature, pressure, deformation, nature of the rocks, and chemical exchanges. Our results show different patterns of crustal growth and surface topography, which are comparable to nature, during subduction at active continental margins. Often, two trench-parallel lines of magmatic activity, which reflect two maxima of melt production atop the slab, are formed on the surface. The melt extraction rate controls the patterns of new crust at different ages. Moving free water reflects the path of fluids, and the velocity of free water shows the trend of two parallel lines of magmatic activity. The formation of new crust in particular time intervals is distributed in finger-like shapes, corresponding to finger-like and ridge-like cold plumes developed atop the subducting slabs (Zhu et al., G-cubed,2009; PEPI,2011). Most of the new crust is basaltic, formed from peridotitic mantle. Granitic crust extracted from melted sediment and upper crust forms in a line closer to the trench, and its distribution reflects the finger-like cold plumes. Dacitic crust extracted from the melted lower crust forms in a line farther away from the trench, and its distribution is anticorrelated with

  16. Recent progress in magma energy extraction

    SciTech Connect

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

    1987-01-01

    Ongoing research in the area of Magma Energy Extraction is directed at developing a fundamental understanding of the establishment and long term operation of an open, direct-contact heat exchanger in a crustal magma body. The energy extraction rate has a direct influence on the economic viability of the concept. An open heat exchanger, in which fluid is circulated through the interconnecting fissures and fractures in the solidified region around drilling tubing, offers the promise of very high rates of heat transfer. This paper discusses recent research in five areas: (1) fundamental mechanisms of solidifying and thermally fracturing magma; (2) convective heat transfer in the internally fractured solidified magma; (3) convective flow in the molten magma and heat transfer from the magma to the cooled heat exchanger protruding into it; (4) numerical simulation of the overall energy extraction process; and (5) the thermodynamics of energy conversion in a magma power plant at the surface. The studies show that an open heat exchanger can be formed by solidifying magma around a cooled borehole and that the resulting mass will be extensively fractured by thermally-induced stresses. Numerical models indicate that high quality thermal energy can be delivered at the wellhead at nominal rates from 25 to 30 MW electric. It is shown that optimum well circulation rates can be found that depend on the heat transfer characteristics of the magma heat exchanger and the thermodynamic power conversion efficiencies of the surface plant.

  17. Recent activity of Anatahan volcano, Northern Marina Islands, and its magma plumbing system

    NASA Astrophysics Data System (ADS)

    Nakada, S.; Morita, Y.; Matsushima, T.; Tabei, T.; Watanabe, A.; Maeno, F.; Camacho, J. T.

    2009-12-01

    . The GPS observation detected the westward displacement of 2cm and subsidence of 2-3cm in the west part of the island during 6 months of 2008. The deformation can be explained by a deflation source at depth of 5km, 2km west offshore, plus a shallow, inflation source in the shape of EW open crack (40cm wide) in the western part. The deflation source has the volume of 10**7 m3, much larger than the volume of inflation source, suggesting that the open crack was accompanied by a small activity in the 2008 summer. The distribution of seismic hypocenters and the deformation sources support the magmatic path rising from the deep part of the west part of the island, as proposed by Watanabe et al. (2005). Interaction of magma with seawater likely became the trigger of phreatic explosions in the waning stage.

  18. Crustal recycling and the aleutian arc

    SciTech Connect

    Kay, R.W.; Kay, S.M. )

    1988-06-01

    Two types of crustal recycling transfer continental crust back into its mantle source. The first of these, upper crustal recycling, involves elements that have been fractionated by the hydrosphere-sediment system, and are subducted as a part of the oceanic crust. The subduction process (S-process) then fractionates these elements, and those not removed at shallow tectonic levels and as excess components of arc magmas are returned to the mantle. Newly determined trace element composition of Pacific oceanic sedimants are variable and mixing is necessary during the S-process, if sediment is to provide excess element in the ratios observed in Aleutian arc magmas. Only a small fraction of the total sediment subducted at the Aleutian trench is required to furnish the excess elements in Aleutian arc magmas. Ba and {sub 10}Be data indicate that this small fraction includes a contribution from the youngest subducted sediment. The second type of recycling, lower crustal recycling, involves crystal cumulates of both arc and oceanic crustal origin, and residues from crustal melting within arc crust. Unlike the silicic sediments, recycled lower crust is mafic to ultramafic in composition. Trace element analyses of xenoliths representing Aleutian arc lower crust are presented. Recycling by delamination of lower crust and attached mantle lithosphere may occur following basalt eclogite phase transformations that are facilitated by terrane suturing events that weld oceanic island arcs to the continents. The relative importance of upper and lower crustal recycling exerts a primary control on continental crustal composition.

  19. CHARACTERISTICS OF THE CRUSTAL MAGMA BODY IN THE 2005-2006 ERUPTION AREA AT 9°50'N ON THE EAST PACIFIC RISE FROM 3D MULTI-CHANNEL SEISMIC DATA

    NASA Astrophysics Data System (ADS)

    Carton, H. D.; Carbotte, S. M.; Mutter, J. C.; Canales, J.; Nedimovic, M. R.; Marjanovic, M.; Aghaei, O.; Xu, M.; Han, S.; Stowe, L.

    2009-12-01

    In the summer of 2008 a large 3D multi-channel seismic dataset (expedition MGL0812) was collected over the 9°50’N Integrated Study Site at the East Pacific Rise, providing insight into the architecture of the magmatic system and its relationship with hydrothermal activity and volcanic/dyking events associated with the 2005-06 eruption. The main area of 3D coverage is located between 9°42’N and 9°57’N, spanning ~28km along-axis, and was acquired along 94 (1 partial) prime lines shot across-axis and each ~24km-long. Pre-processing of the data acquired in this area is now well under way, with significant efforts targeted at amplitude spike removal. Current work focuses on setting up the 3D processing sequence up to the stack stage for a small group of inlines (axis-perpendicular grid lines spaced 37.5m apart) located over the “bull’s eye” site at 9°50’N, a sequence that will subsequently be applied to the whole dataset. At the meeting we will present stacked and migrated sections - inlines, crosslines, time slices - obtained through 3D processing. We will discuss results focusing on the characteristics of the axial magma body, whose detailed structure and along-axis segmentation will be resolved by the 3D data.

  20. Seismic activity, inferred crustal stresses and seismotectonics in the Rana region, Northern Norway

    NASA Astrophysics Data System (ADS)

    Hicks, Erik C.; Bungum, Hilmar; Lindholm, Conrad D.

    2000-10-01

    The seismotectonic significance of the Rana region is known both from the fact that this was the location of the largest known earthquake in Fennoscandia in recent times, the MS 5.8-6.2 earthquake of August 31, 1819, and from its relatively high, constant seismic activity also in the 20th century. In order to study this region in more detail, a local seismic network has been in operation there since July 1997, as part of the NEONOR (Neotectonics in Norway) project. The network was primarily designed to detect possible activity on the Båsmoen fault which runs ˜50 km subparallel to the Rana fjord, and which shows signs of likely post glacial activity. The results have revealed a quite complex spatio-temporal distribution of seismic activity, and has also shown no activity on the Båsmoen fault itself. During the first 18 months of operation (July 1997-January 1999), the network has detected 373 locatable seismic events, of which 267 were local earthquakes. Most of these earthquakes occurred in five groups in the western parts of the network. All five groups had similar NNW-ESW trends in epicenter locations, and all have shallow foci (2-12 km), similar to what has also been found earlier for other concentrated earthquake zones in Northern Norway, and the magnitude range is between ML 0.1 and 2.8. Earthquake focal mechanism solutions within the network reveal a predominance for normal faulting with the tensional stress axis perpendicular do the coastline (implying an unusual coast-parallel orientation of the principal horizontal compressive stress). The earthquakes occur in a region of maximum post-glacial uplift gradients, which supports deglaciation flexure as a viable explanation for these earthquakes. A certain influence from more local factors, however, tied in general to crustal in homogeneities, cannot be ruled out.

  1. Magma Plumbing System of Baru Volcano From Deep to Shallow Crust

    NASA Astrophysics Data System (ADS)

    Hidalgo, P. J.; Rooney, T. O.

    2009-12-01

    Linking shallow and deep crustal processes at volcanic arcs has been an important component in evaluating the growth and evolution of the continental crust. Commonly, deep crustal processes and the nature of sub-arc lithosphere are studied long after the volcanism has ceased in locations such as obducted arc terranes. In active arcs, studies of deep crustal processes focus on rare cumulates or restites derived from lower crustal levels. Although uncommon in the erupted magmas, these cumulates are required by crustal differentiation models of arc magmatism. Quaternary magmas at Baru volcano in Panama contain ubiquitous amphibole bearing cumulates that provide an opportunity to probe the magma plumbing system of an active arc volcano. These cumulates are present in andesitic-dacitic lavas and pyroclastic flows of adakitic character and are not related to their host magmas by crystal fractionation processes. Two cumulate groups can be readily identified. The first group typically consists of 2-5 cm nodules of large amphiboles (3-6 mm) with minor (<2%) interstitial glass and small plagioclase phenocrysts (~0.5 mm). Amphiboles from this group are mostly tschermakites or magnesiohornblendes and are typically zoned with increasing MgO and decreasing AlT in core to rim transects. The second group forms larger nodules (5-10 cm) that are composed of variable amounts of amphibole and plagioclase microlites along with minor glass. Amphiboles from this group are all magnesiohornblendes and are typically unzoned. Pressure and temperature estimates for both groups of cumulates and the host amphiboles are consistent with sampling of mush/magma zones from the lower to upper crust within the plumbing system of Baru volcano. The first cumulate group may be derived from deep hot zones were magmatic differentiation of water-saturated arc magmas takes place by crystallization of amphibole-rich cumulates. The second group is consistent with derivation from shallow levels where

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

    SciTech Connect

    Peppin, W.A.

    1986-02-10

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

  3. Comparative Magma Oceanography

    NASA Technical Reports Server (NTRS)

    Jones, J. H.

    1999-01-01

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

  4. Crustal Structure Across the Okavango Rift Zone, Botswana: Initial Results From the PRIDE-SEISORZ Active-Source Seismic Profile

    NASA Astrophysics Data System (ADS)

    Canales, J. P.; Moffat, L.; Lizarralde, D.; Laletsang, K.; Harder, S. H.; Kaip, G.; Modisi, M.

    2015-12-01

    The PRIDE project aims to understand the processes of continental rift initiation and evolution by analyzing along-axis trends in the southern portion of the East Africa Rift System, from Botswana through Zambia and Malawi. The SEISORZ active-source seismic component of PRIDE focused on the Okavango Rift Zone (ORZ) in northwestern Botswana, with the main goal of imaging the crustal structure across the ORZ. This will allow us to estimate total crustal extension, determine the pattern and amount of thinning, assess the possible presence of melt within the rift zone, and assess the contrasts in crustal blocks across the rift, which closely follows the trend of a fold belt. In November 2014 we conducted a crustal-scale, 450-km-long seismic refraction/wide-angle reflection profile consisting of 19 sources (shots in 30-m-deep boreholes) spaced ~25 km apart from each other, and 900 receivers (IRIS/PASSCAL "Texan" dataloggers and 4.5Hz geophones) with ~500 m spacing. From NW to SE, the profile crosses several tectonic domains: the Congo craton, the Damara metamorphic belt and the Ghanzi-Chobe fold belt where the axis of the ORZ is located, and continues into the Kalahari craton. The record sections display clear crustal refraction (Pg) and wide-angle Moho reflection (PmP) phases for all 17 of the good-quality shots, and a mantle refraction arrival (Pn), with the Pg-PmP-Pn triplication appearing at 175 km offset. There are distinct changes in the traveltime and amplitude of these phases along the transect, and on either side of the axis, that seem to correlate with sharp transitions across tectonic terrains. Initial modeling suggests: (1) the presence of a sedimentary half-graben structure at the rift axis beneath the Okavango delta, bounded to the SE by the Kunyere-Thamalakane fault system; (2) faster crustal Vp in the domains to the NW of the ORZ; and (3) thicker crust (45-50 km) at both ends of the profile within the Congo and Kalahari craton domains than at the ORZ and

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

    NASA Astrophysics Data System (ADS)

    Di Muro, Andrea

    2014-05-01

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

  6. A reduced crustal magnetization zone near the first observed active hydrothermal vent field on the Southwest Indian Ridge

    NASA Astrophysics Data System (ADS)

    Zhu, Jian; Lin, Jian; Chen, Yongshun J.; Tao, Chunhui; German, Christopher R.; Yoerger, Dana R.; Tivey, Maurice A.

    2010-09-01

    Inversion of near-bottom magnetic data reveals a well-defined low crustal magnetization zone (LMZ) near a local topographic high (37°47‧S, 49°39‧E) on the ultraslow-spreading Southwest Indian Ridge (SWIR). The magnetic data were collected by the autonomous underwater vehicle ABE on board R/V DaYangYiHao in February-March 2007. The first active hydrothermal vent field observed on the SWIR is located in Area A within and adjacent to the LMZ at the local topographic high, implying that this LMZ may be the result of hydrothermal alteration of magnetic minerals. The maximum reduction in crustal magnetization is 3 A/M. The spatial extent of the LMZ is estimated to be at least 6.7 × 104 m2, which is larger than that of the LMZs at the TAG vent field on the Mid-Atlantic Ridge (MAR), as well as the Relict Field, Bastille, Dante-Grotto, and New Field vent-sites on the Juan de Fuca Ridge (JdF). The calculated magnetic moment, i.e., the product of the spatial extent and amplitude of crustal magnetization reduction is at least -3 × 107 Am2 for the LMZ on the SWIR, while that for the TAG field on the MAR is -8 × 107 Am2 and that for the four individual vent fields on the JdF range from -5 × 107 to -3 × 107 Am2. Together these results indicate that crustal demagnetization is a common feature of basalt-hosted hydrothermal vent fields at mid-ocean ridges of all spreading rates. Furthermore, the crustal demagnetization of the Area A on the ultraslow-spreading SWIR is comparable in strength to that of the TAG area on the slow-spreading MAR.

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

    PubMed

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

    2008-10-10

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

  8. Nanocalorimetric Characterization of Microbial Activity in Deep Subsurface Oceanic Crustal Fluids

    PubMed Central

    Robador, Alberto; LaRowe, Douglas E.; Jungbluth, Sean P.; Lin, Huei-Ting; Rappé, Michael S.; Nealson, Kenneth H.; Amend, Jan P.

    2016-01-01

    Although fluids within the upper oceanic basaltic crust harbor a substantial fraction of the total prokaryotic cells on Earth, the energy needs of this microbial population are unknown. In this study, a nanocalorimeter (sensitivity down to 1.2 nW ml-1) was used to measure the enthalpy of microbially catalyzed reactions as a function of temperature in samples from two distinct crustal fluid aquifers. Microorganisms in unamended, warm (63°C) and geochemically altered anoxic fluids taken from 292 meters sub-basement (msb) near the Juan de Fuca Ridge produced 267.3 mJ of heat over the course of 97 h during a step-wise isothermal scan from 35.5 to 85.0°C. Most of this heat signal likely stems from the germination of thermophilic endospores (6.66 × 104 cells ml-1FLUID) and their subsequent metabolic activity at temperatures greater than 50°C. The average cellular energy consumption (5.68 pW cell-1) reveals the high metabolic potential of a dormant community transported by fluids circulating through the ocean crust. By contrast, samples taken from 293 msb from cooler (3.8°C), relatively unaltered oxic fluids, produced 12.8 mJ of heat over the course of 14 h as temperature ramped from 34.8 to 43.0°C. Corresponding cell-specific energy turnover rates (0.18 pW cell-1) were converted to oxygen uptake rates of 24.5 nmol O2 ml-1FLUID d-1, validating previous model predictions of microbial activity in this environment. Given that the investigated fluids are characteristic of expansive areas of the upper oceanic crust, the measured metabolic heat rates can be used to constrain boundaries of habitability and microbial activity in the oceanic crust. PMID:27092118

  9. Nanocalorimetric Characterization of Microbial Activity in Deep Subsurface Oceanic Crustal Fluids.

    PubMed

    Robador, Alberto; LaRowe, Douglas E; Jungbluth, Sean P; Lin, Huei-Ting; Rappé, Michael S; Nealson, Kenneth H; Amend, Jan P

    2016-01-01

    Although fluids within the upper oceanic basaltic crust harbor a substantial fraction of the total prokaryotic cells on Earth, the energy needs of this microbial population are unknown. In this study, a nanocalorimeter (sensitivity down to 1.2 nW ml(-1)) was used to measure the enthalpy of microbially catalyzed reactions as a function of temperature in samples from two distinct crustal fluid aquifers. Microorganisms in unamended, warm (63°C) and geochemically altered anoxic fluids taken from 292 meters sub-basement (msb) near the Juan de Fuca Ridge produced 267.3 mJ of heat over the course of 97 h during a step-wise isothermal scan from 35.5 to 85.0°C. Most of this heat signal likely stems from the germination of thermophilic endospores (6.66 × 10(4) cells ml(-1) FLUID) and their subsequent metabolic activity at temperatures greater than 50°C. The average cellular energy consumption (5.68 pW cell(-1)) reveals the high metabolic potential of a dormant community transported by fluids circulating through the ocean crust. By contrast, samples taken from 293 msb from cooler (3.8°C), relatively unaltered oxic fluids, produced 12.8 mJ of heat over the course of 14 h as temperature ramped from 34.8 to 43.0°C. Corresponding cell-specific energy turnover rates (0.18 pW cell(-1)) were converted to oxygen uptake rates of 24.5 nmol O2 ml(-1) FLUID d(-1), validating previous model predictions of microbial activity in this environment. Given that the investigated fluids are characteristic of expansive areas of the upper oceanic crust, the measured metabolic heat rates can be used to constrain boundaries of habitability and microbial activity in the oceanic crust. PMID:27092118

  10. Magma Beneath Yellowstone National park.

    PubMed

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

    1975-05-23

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

  11. Rapid transition to long-lived deep crustal magmatic maturation and the formation of giant porphyry-related mineralization (Yanacocha, Peru)

    NASA Astrophysics Data System (ADS)

    Chiaradia, Massimo; Merino, Daniel; Spikings, Richard

    2009-11-01

    The Yanacocha magmatic field (northern Peru) hosts the largest high sulfidation gold deposit on Earth. Mineralization is associated with porphyritic intrusions distributed along a NE-trending magmatic structural corridor. Eight of these intrusions investigated in this study range in age from 12.4 to 8.4 Ma and show systematic chemical and isotopic changes through time. They are interpreted to derive from hydrous mafic magmas evolving through amphibole-clinopyroxene ± garnet fractionation and lower crust melting (leaving a garnet residue) at deeper levels, which led to variably strong adakite-like signatures, and through plagioclase-amphibole fractionation at shallower levels, both accompanied by crustal assimilation and recharge (recharge assimilation fractional crystallization, RAFC, processes). Systematic geochemical and isotopic changes with intrusion ages, coupled with plagioclase zoning and amphibole geobarometry, suggest that the evolution of the magmatic system occurred through interaction of mantle-derived melts with an increasing length of the crustal column and propagation from deep towards shallower crustal levels through time. This was probably the result of a steadily increasing compression that has progressively slowed down magma ascent forcing magmas to evolve at a series of intermediate level chambers between the lower and upper crust. Increased compression might have been related to the onset of subduction of the buoyant Inca oceanic plateau, estimated to occur at ˜ 12 Ma, i.e., the same time of the onset of the rapid transition from "normal" to adakite-like signatures. The giant Yanacocha ore system developed in coincidence with the ˜ 3.6-4.0 Ma-long intrusion of the adakite-like magmas (12.4/12.0-8.4 Ma) formed by the above processes into a small upper crustal volume and peaked during the last ˜ 2.4 Ma (10.8-8.4 Ma) of magmatic activity after a ˜ 1.4 Ma long (12.4-11.0 Ma) maturation of magmas at deep crustal levels. Further investigation is

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  13. Spectral damping scaling factors for shallow crustal earthquakes in active tectonic regions

    USGS Publications Warehouse

    Rezaeian, Sanaz; Bozorgnia, Yousef; Idriss, I.M.; Campbell, Kenneth; Abrahamson, Norman; Silva, Walter

    2012-01-01

    Ground motion prediction equations (GMPEs) for elastic response spectra, including the Next Generation Attenuation (NGA) models, are typically developed at a 5% viscous damping ratio. In reality, however, structural and non-structural systems can have damping ratios other than 5%, depending on various factors such as structural types, construction materials, level of ground motion excitations, among others. This report provides the findings of a comprehensive study to develop a new model for a Damping Scaling Factor (DSF) that can be used to adjust the 5% damped spectral ordinates predicted by a GMPE to spectral ordinates with damping ratios between 0.5 to 30%. Using the updated, 2011 version of the NGA database of ground motions recorded in worldwide shallow crustal earthquakes in active tectonic regions (i.e., the NGA-West2 database), dependencies of the DSF on variables including damping ratio, spectral period, moment magnitude, source-to-site distance, duration, and local site conditions are examined. The strong influence of duration is captured by inclusion of both magnitude and distance in the DSF model. Site conditions are found to have less significant influence on DSF and are not included in the model. The proposed model for DSF provides functional forms for the median value and the logarithmic standard deviation of DSF. This model is heteroscedastic, where the variance is a function of the damping ratio. Damping Scaling Factor models are developed for the “average” horizontal ground motion components, i.e., RotD50 and GMRotI50, as well as the vertical component of ground motion.

  14. Crustal Structure in the Imperial Valley Region of California From Active-Source Seismic Investigations

    NASA Astrophysics Data System (ADS)

    Fuis, G. S.; Mooney, W. D.

    2008-12-01

    shallow as 12 km beneath the Imperial Valley. Modeling of gravity data requires that this layer deepen and/or pinch out beneath the bordering mesas and mountain ranges. This pinch-out is imaged in the 1992 data beneath the Chocolate Mountains. Based on its high velocity and the presence of intrusive basaltic rocks in the sedimentary section in the Imperial Valley, the subbasement is thought to be a mafic intrusive complex similar to oceanic middle crust. (4) Crustal thickness and upper-mantle velocity are 21-22 km and 7.6-7.7 km/s, respectively, beneath the Imperial Valley but increase to 27 km and 8.0 km/s, respectively, beneath the Chocolate Mountains. Our results from the Salton Trough may be contrasted with active-source seismic results from the northern Gulf of California (Guaymas basin; Lizarralde et al., 2007). These results show the crust to thin to 10-14 km within the Gulf. Below 3-4 km of sediment, the crust has a velocity of 6.8 km/s, interpreted to be new igneous (gabbroic) crust. Thus, the rifting process appears to have produced negligible metasedimentary basement and a crustal thickness as little as half that beneath the Salton Trough.

  15. The Mineralogy, Geochemistry, and Redox State of Multivalent Cations During the Crystallization of Primitive Shergottitic Liquids at Various (f)O2. Insights into the (f)O2 Fugacity of the Martian Mantle and Crustal Influences on Redox Conditions of Martian Magmas.

    NASA Technical Reports Server (NTRS)

    Shearer, C. K.; Bell, A. S.; Burger, P. V.; Papike, J. J.; Jones, J.; Le, L.; Muttik, N.

    2016-01-01

    The (f)O2 [oxygen fugacity] of crystallization for martian basalts has been estimated in various studies to range from IW-1 to QFM+4 [1-3]. A striking geochemical feature of the shergottites is the large range in initial Sr isotopic ratios and initial epsilon(sup Nd) values. Studies by observed that within the shergottite group the (f)O2 [oxygen fugacity] of crystallization is highly correlated with these chemical and isotopic characteristics with depleted shergottites generally crystallizing at reduced conditions and enriched shergottites crystallizing under more oxidizing conditions. More recent work has shown that (f)O2 [oxygen fugacity] changed during the crystallization of these magmas from one order of magnitude in Y980459 (Y98) to several orders of magnitude in Larkman Nunatak 06319. These real or apparent variations within single shergottitic magmas have been attributed to mixing of a xenocrystic olivine component, volatile loss-water disassociation, auto-oxidation during crystallization of mafic phases, and assimilation of an oxidizing crustal component (e.g. sulfate). In contrast to the shergottites, augite basalts such as NWA 8159 are highly depleted yet appear to be highly oxidized (e.g. QFM+4). As a first step in attempting to unravel petrologic complexities that influence (f)O2 [oxygen fugacity] in martian magmas, this study explores the effect of (f)O2 [oxygen fugacity] on the liquid line of descent (LLD) for a primitive shergottite liquid composition (Y98). The results of this study will provide a fundamental basis for reconstructing the record of (f)O2 [oxygen fugacity] in shergottites and other martian basalts, its effect on both mineral chemistries and valence state partitioning, and a means for examining the role of crystallization (and other more complex processes) on the petrologic linkages between olivine-phyric and pyroxene-plagioclase shergottites.

  16. Characteristics of the crustal magma body in the 2005-06 eruption area at 9°50'N on the East Pacific Rise from a 3D multi-channel seismic investigation

    NASA Astrophysics Data System (ADS)

    Carton, H.; Carbotte, S. M.; Mutter, J. C.; Canales, J. P.; Nedimovic, M. R.; Newman, K. R.; Marjanovic, M.; Xu, M.; Aghaei, O.; Stowe, L.

    2008-12-01

    In July-August 2008 the first 3D academic multi-streamer seismic survey was carried out aboard R/V Langseth, focusing on the 9°50'N Integrated Study Site (ISS) at the East Pacific Rise. Preliminary results from 2D processing of along-axis and across-axis grid lines provide insight into the architecture of the magmatic system at the ISS and its relationship with hydrothermal activity and volcanic/dyking events associated with the 2005-06 eruption. Segmentation at length scales of about 5-10km of the axial magmatic system of the 9°50'N area can be mapped based on variations in two-way travel time, reflection strength and along-axis dip of the axial magma chamber (AMC) reflector on the stack sections, as well as the presence of edge diffractions. The main hydrothermal vents around 9°50'N are located over the region of shallowest AMC, which can be divided into two sub-regions, between 9°45.2'N - 9°48.7'N and 9°48.7'N - 9°51.9'N, respectively, separated by a discontinuity that has been interpreted as a potential hydrothermal downflow zone based on microseismicity studies. The northern lens event is rather flat-lying, while the southern one is more complex, dips south and shows pronounced edge diffractions. Both of these shallow lenses display distinctly weaker amplitudes than AMC reflections located immediately to the north and south. Lava flows from the most recent eruption overlie these two 'dim' lenses, and also extend over part of the north-dipping, brighter AMC to the north. Though detailed quantification is required, such along-axis variations in reflection strength are suggestive of a lower present-day melt percentage between 9°45.2'N - 9°51.9'N, an observation consistent with melt being drained by the 1991 and 2005-06 eruptions.

  17. Patterns in Long-Lived Continental Magmatism; Crustal Modulation of Mantle-Derived Input

    NASA Astrophysics Data System (ADS)

    Grunder, A. R.; de Silva, S. L.

    2007-12-01

    Patterns in volumetric eruption rate of continental intermediate to silicic magmatic systems have implications for how heat is delivered and processed in the crust, and reveal the evolution of crustal scale magmatic systems. Drawing on the Neogene volcanic rocks of the Altiplano Puna Volcanic Complex (APVC) and the Aucanquilcha Volcanic Cluster (AVC) of the Central Andes, we compare their histories to other long-lived crustal magmatic complexes. Erupted volumes of such systems vary from a few tens of km3 to tens of thousands of km3 of magma with associated plutonic volumes several times that. Despite differences in volume, these complexes share a general family resemblance. They have lifespans of about 10 million years. Where resolution allows, the record of activity may reveal distinct pulses, lasting a few hundred thousand to ~1 to 2 m.y., demonstrating the composite nature of the magmatic systems. These complexes bear isotopic and compositional evidence of crustal and mantle involvement in the origin of the magmas and mineralogic evidence for subsequent equilibration at shallow crustal levels. Many, but not all, have abundant ignimbrites. Most strikingly they all have a three stage evolutionary history that is scale independent. An early waxing stage characterized by low volume, low flux volcanism that is compositionally diverse and may be dispersed; a climactic stage of dramatically higher flux, that is compositionally more focused and may be spatially more focused; and a final waning stage of small eruptions. We interpret these patterns to be the result of long-lived thermal pulses delivered from the mantle in the form of basaltic magma. A fundamental question is to what extent does the surface pattern reflect the mantle input. We suggest that the thermal signal is modulated by interaction and thermal incubation in the crust that leads to development of a large crustal magma reservoir that in turn modulates the composition of erupted magma. The interplay

  18. 3D crustal-scale heat-flow regimes at a developing active margin (Taranaki Basin, New Zealand)

    NASA Astrophysics Data System (ADS)

    Kroeger, K. F.; Funnell, R. H.; Nicol, A.; Fohrmann, M.; Bland, K. J.; King, P. R.

    2013-04-01

    The Taranaki Basin in the west of New Zealand's North Island has evolved from a rifted Mesozoic Gondwana margin to a basin straddling the Neogene convergent Australian-Pacific plate margin. However, given its proximity to the modern subduction front, Taranaki Basin is surprisingly cold when compared to other convergent margins. To investigate the effects of active margin evolution on the thermal regime of the Taranaki Basin we developed a 3D crustal-scale forward model using the petroleum industry-standard basin-modelling software Petromod™. The crustal structure inherited from Mesozoic Gondwana margin breakup and processes related to modern Hikurangi convergent margin initiation are identified to be the main controls on the thermal regime of the Taranaki Basin. Present-day surface heat flow across Taranaki on average is 59 mW/m2, but varies by as much as 30 mW/m2 due to the difference in crustal heat generation between mafic and felsic basement terranes alone. In addition, changes in mantle heat advection, tectonic subsidence, crustal thickening and basin inversion, together with related sedimentary processes result in variability of up to 10 mW/m2. Modelling suggests that increased heating of the upper crust due to additional mantle heat advection following the onset of subduction is an ongoing process and heating has only recently begun to reach the surface, explaining the relatively low surface heat flow. We propose that the depth of the subducted slab and related mantle convection processes control the thermal and structural regimes in the Taranaki Basin. The thermal effects of the subduction initiation process are modified and overprinted by the thickness, structure and composition of the lithosphere.

  19. Incipient Crustal Stretching across AN Active Collision Belt: the Case of the Siculo-Calabrian Rift Zone (central Mediterranean)

    NASA Astrophysics Data System (ADS)

    Catalano, S.; Tortorici, G.; Romagnoli, G.; Pavano, F.

    2012-12-01

    In the Central Mediterranean, the differential roll-back of the subducting Nubia Plate caused the Neogene-Quaternary extrusion of the Calabrian arc onto the oceanic Ionian slab, and the opening of the oceanic Tyrrhenian Basin, in the overriding Eurasia Plate. The differential motion at the edges of the arc was largely accommodated along transform faults that propagated across the orogenic belt. Since the Late Quaternary, the southern edge of the arc has been replaced by the roughly N-S oriented Siculo-Calabrian Rift Zone (SCRZ) that formed as the NNW-directed normal faults of NE Sicily, crossing the orogenic belt, have linked the NNE-oriented Tyrrhenian margin of southern Calabria with the NNW-trending Africa-Ionian boundary of southeastern Sicily. Our study focused on the Sicily shoulder of the SCRZ, where the transition zone between the extensional belt and the still active Nubia-Eurasia convergent margin is characterized by two distinct mobile crustal wedges, both lying on an upwarped Mantle, where a re-orientations of the σ1 is combined with volcanism (e.g. Etna, Aeolian islands) and a huge tectonic uplift. In southeastern Sicily, the Hyblean-Etnean region evolved, since about 0.85 Ma, as an indipendent crustal wedge, moving towards the NNW and pointing to the active Mt. Etna volcano. A local ENE crustal stretching accompanied the traslation of the block and pre-dated the ESE-oriented extension governing the propagation of the southernmost branch of the SCR, which started at about 330 ka B.P.. Similarly, the Peloritani-Aeolian region, flanked by the 125 ka-old NE-Sicily branch of the rift zone, represents a mostly submerged crustal wedge that migrates towards the NE, diverging from the rest of the Sicily collision zone and pointing to the Stromboli volcano. The Peloritani-Aeolian block is characterized by the occurrence of a wide central NE-oriented collapsed basin contoured by an actively uplifting region, whose tectonic boundaries are evidenced by a sharp

  20. Magma accumulation, migration and structure of spreading segments in Iceland - inferences from geophysical data and FEM models

    NASA Astrophysics Data System (ADS)

    Pedersen, R.; Sigmundsson, F.; de Zeeuw-van Dalfsen, E.; Masterlark, T.

    2011-12-01

    Iceland is the only sub-aerial exposure of the mid-Atlantic ridge on Earth, and is an ideal place to study the mechanics and dynamics of magma ascent related to plate spreading processes. We focus on the Northern Volcanic Zone (NVZ) - an extensional rift segment bounded to the south by the Icelandic mantle plume, currently beneath the Vatnajökull ice cap, and to the north by the Tjörnes Fracture zone, a transform zone connecting the offset on-shore rift segment to the sub-aqueous mid-Atlantic ridge. Based on geologic and tectonic mapping, the NVZ is divided into five partly overlapping en-echelon fissure swarms, each with a central main volcanic production area. Two of these, Askja and Krafla, have been active in historic time. Both are known to have shallow crustal magma chambers, and are the only segments with associated caldera collapse structures, reflecting on the maturity of the systems. InSAR images from several SAR satellites span the 1993-2010 period. The data reveal a complex interplay of crustal deformation in the NVZ originating from a number of tectonic and magmatic processes. Episodic uplift due to magma migration and accumulation at depths considerably greater than the elastic upper layer has been observed at several locations within the NVZ. Individual injection points with magma accumulation in the lower and mid crust appear to dominate the deformation signals. If, and then how, these magma accumulations connect to the two well-established upper crustal magma chambers is unknown. The inferences from deformation data have been complimented since 2005 by seismic data recorded at an increasingly sensitive network of portable seismometers. While magma is being injected into the mid crustal layers at several locations in the NVZ, subsidence is observed near both of the known upper crustal magma chambers. At the Askja caldera, continuous subsidence has been observed for almost three decades. Micro seismicity at lower crustal levels suggest that melts

  1. Crustal features of the northeastern South China Sea: insights from seismic and magnetic interpretations

    NASA Astrophysics Data System (ADS)

    Yeh, Yi-Ching; Hsu, Shu-Kun; Doo, Wen-Bin; Sibuet, Jean-Claude; Liu, Char-Shine; Lee, Chao-Shing

    2012-12-01

    We interpret seven two-dimensional deep-penetration and long-offset multi-channel seismic profiles in the northernmost South China Sea area, which were collected by R/V Marcus G. Langseth during the TAIwan GEodynamics Research (TAIGER) project in 2009. To constrain the crustal characteristics, magnetic inversion and forward magnetic modeling were also performed. The seismic results clearly show tilted faulting blocks in the upper crust and most of the fault plane connects downward to a quasi-horizontal detachment as its bottom in the south of the Luzon-Ryukyu transform plate boundary. North of the plate boundary, a small-scale failed rifted basin (minimum 5 km in crustal thickness) with negative magnetization probably indicates an extended continental origin. Significant lower crustal material (LCM) was imaged under a crustal fracture area which indicated a continent and ocean transition origin. The thickest LCM (up to 6.5 km) is located at magnetic isochron C15 that is probably caused by the magma supply composite of a Miocene syn-rift volcanic event and Pliocene Dongsha volcanic activity for submarine volcanoes and sills in the surrounding area. The LCM also caused Miocene crustal blocks to be uplifted reversely as 17 km crustal thickness especially in the area of magnetic isochron C15 and C16. In addition, the wide fault blocks and LCM co-existed on the magnetic striped area (i.e. C15-C17) in the south of the Luzon-Ryukyu transform plate boundary. Magnetic forward modeling suggests that the whole thick crustal thickness (>12 km thick) needs to be magnetized in striped way as oceanic crust. However, the result also shows that the misfit between observed and synthetic magnetic anomaly is about 40 nT, north of isochron C16. The interval velocity derived from pre-stack time migration suggests that the crust is composed of basaltic intrusive upper crust and lower crustal material. The crustal nature should refer to a transition between continent and ocean. Thus, the

  2. Active fault kinematics and crustal stresses along the Ionian margin of southeastern Sicily

    NASA Astrophysics Data System (ADS)

    Adam, J.; Reuther, C.-D.; Grasso, M.; Torelli, L.

    2000-11-01

    Since the late Cretaceous onset of plate convergence between Africa and Europe, the Malta Escarpment has been converted from a Mesozoic passive margin into a mega-hinge fault system with an additional sinistral strike-slip component. The modern tectonic stress regime with NW-SE-directed maximum horizontal stresses has been established since Late Messinian times. Since the Pleistocene, sinistral strike-slip deformation and contemporaneous normal faulting along the Malta Escarpment have induced the opening of oblique trending onshore grabens at the eastern margin of the Hyblean Plateau. In this study, we focus on the kinematics, the controlling state of stress, and the temporal variation of the neotectonic to active strike-slip and normal fault structures. The stress-tensor calculations reveals that the widespread map-scaled to meso-scaled normal fault structures are governed by the long-term extensional state of stress during the Quaternary. This long-term stress tensor is predominantly controlled by gravitational induced stresses due to vertical load ( σ1= SV) and lateral extension due to the topographic gradient of the Malta Escarpment ( σ3= Sh=NE-SW). In this case, the average tectonic stresses ( σ2= SH=NW-SE) transmitted by the regional to plate-tectonic stress field are significantly smaller than the gravitational induced stresses. In contrast, the clear localization of conjugate sets of meso-scaled strike-slip fault structures and shear zones without accompanying normal fault structures give strong indications for episodic seismotectonic strike-slip faulting under critical stress conditions. In this state, tectonically induced maximum horizontal stresses are successively increased by ongoing plate convergence from low-level stress magnitudes ( σ1= SV, σ2= SH=NW-SE) up to critical stress magnitudes ( σ1= SH=NW-SE, σ2= SV), which are significantly larger than gravitational stresses. At the critical state, seismotectonic stress release occurs by active

  3. Volatile concentrations in variably vesicular pyroclasts from the Rotongaio ash (181 AD Taupo eruption): did shallow magma degassing trigger exceptionally violent phreatomagmatic activity?

    NASA Astrophysics Data System (ADS)

    Tuffen, Hugh; Houghton, Bruce F.; Dingwellp, Donald B.; Pinkerton, Harry

    2010-05-01

    Measurement of dissolved volatile concentrations in pyroclasts has formed the basis of our understanding of the links between magma degassing and the explosivity of silicic eruptions[1]. To date these studies have focussed exclusively on the densest pyroclastic obsidians, which comprise on a tiny proportion of the erupted products, in order to bypass the difficulty of analysing vesicular material. As a consequence, crucial information is missing about how degassing in the densest clasts relates to the behaviour of the bulk of the magma volume. To overcome this shortcoming, the volatile content of variably vesicular pyroclasts from the Rotongaio ash has been analysed using both micro-analytical (SIMS, synchrotron FTIR) and bulk techniques (TGA-MS). The Rotongaio ash was an exceptionally violent phase of phreatomagmatic activity during the 181 AD rhyolitic eruption of Taupo (New Zealand), the most powerful worldwide in the last 5000 years. The Rotongaio phase involved opening of new vents beneath Lake Taupo and the ash is characterised by a wide range of clast vesicularities (<10 to ~80 % by volume). Volatile measurement was challenging due to the high bubble number densities and small clast sizes. The mismatch between the water content of matrix glasses measured using bulk and micro-analytical techniques reflects pervasive post-eruption hydration of vesicle walls, which is most problematic at high vesicularities. Micron-scale maps of water concentration variations around vesicles in 30-50 vol % vesicular samples were acquired using SIMS. They indicate strong hydration within ~5 microns of vesicle walls, with pockets of unhydrated glass remaining in the thickest septa. Analysis of these unhydrated domains allowed robust measurement of water contents in pyroclasts ranging from ~1 to >50 vol % vesicles. Matrix glasses had largely degassed (0.19-0.49 wt % H2O, compared with an initial concentration in melt inclusions of ~3.6 wt %). The water contents measured using SIMS

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

    model is consistent with a geophysical model that explains whole crustal deformation as being due to a single source located 7-8 km northwest of the Shinmoe-dake summit. However, even the shallowest estimated source of this deformation (7.5-6.2 km) is deeper than the SA reservoir, which thus requires a contribution of deeper BA magmas to the observed deformation. Remobilization of mush-like SA magma occurred in two stages before the early sub-Plinian event. Firstly, precursor mixing with BA magma and associated heating occurred (925-871 °C; stage-1 of ≥ 350 h), followed by final mixing with BA magma (stage-2). MgO profiles of magnetite phenocrysts define timescales of 0.7-15.2 h from this final mixing to eruption. The mixed and heated magmas, and stagnant mush that existed in the SA reservoir in the precursor stage, were finally erupted together. Magnetite phenocrysts in the Feb 18 ash reveal the occurrence of continuous erosion of the stagnant mush during the course of the 2011 eruptive activity.

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

    SciTech Connect

    Asmerom, Y.

    1988-01-01

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

  6. 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

  7. Magma ascent pathways associated with large mountains on Io

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  8. Deep Magma Transport beneath Soufriere Hills Volcano, Montserrat, WI: 1995-2007

    NASA Astrophysics Data System (ADS)

    Elsworth, D.; Mattioli, G.; Taron, J.; Voight, B.; Herd, R.; Foroozan, R.

    2009-04-01

    Magma melting and transport produces a complex architecture of connected magmatic systems present beneath many arc volcanoes. Although melt supplied by subduction may be considered constant over very long timescales (>Ma), rates of magma transport and eruptive episodes are episodic at timescales encompassing millennia and centuries to hours. A variety of mechanisms act at these various timescales; in general longer periodicities imply controlling processes rooted at greater depth and involving reservoirs of increasing volumes. Here we use histories of magma efflux and surface deformation to quantitatively constrain magma transfer into and within the deep (>12 km) crustal plumbing of the Soufrière Hills volcano over a 12-year eruptive cycle of active effusion punctuated by discrete pauses. For three cycles of effusion followed by pause, with a periodicity of 4-6 years, deep supply to the system is continuous and never drops below ~0.5-1 m3/s; this minimum supply is similar in magnitude to both the mean measured eruptive efflux (including pauses) (~0.7 m3/s) and the mass accumulation due to crustal convergence (~0.6 m3/s). Deep fluxes rise synchronously from this background magnitude in times of active eruption (~1-5 m3/s), are augmented by deflation (~1-2 m3/s) of a reservoir centered at ~12 km, and pass through an upper magmatic reservoir. An eruptive pause is marked by a decrease in supply from the deep crust, fully accommodated as the deep reservoir switches to reinflate, and with no resulting supply to the shallow crust. For a two-reservoir model, these observations implicate the deep system in controlling short-term (~3-5 yr) eruptive periodicity. They are consistent with a model involving the continuous supply of magma from the deep crust/mantle into a voluminous and compliant deep reservoir, episodically-valved below the shallow reservoir.

  9. Extensive, water-rich magma reservoir beneath southern Montserrat

    NASA Astrophysics Data System (ADS)

    Edmonds, M.; Kohn, S. C.; Hauri, E. H.; Humphreys, M. C. S.; Cassidy, M.

    2016-05-01

    South Soufrière Hills and Soufrière Hills volcanoes are 2 km apart at the southern end of the island of Montserrat, West Indies. Their magmas are distinct geochemically, despite these volcanoes having been active contemporaneously at 131-129 ka. We use the water content of pyroxenes and melt inclusion data to reconstruct the bulk water contents of magmas and their depth of storage prior to eruption. Pyroxenes contain up to 281 ppm H2O, with significant variability between crystals and from core to rim in individual crystals. The Al content of the enstatites from Soufrière Hills Volcano (SHV) is used to constrain melt-pyroxene partitioning for H2O. The SHV enstatite cores record melt water contents of 6-9 wt%. Pyroxene and melt inclusion water concentration pairs from South Soufriere Hills basalts independently constrain pyroxene-melt partitioning of water and produces a comparable range in melt water concentrations. Melt inclusions recorded in plagioclase and in pyroxene contain up to 6.3 wt% H2O. When combined with realistic melt CO2 contents, the depth of magma storage for both volcanoes ranges from 5 to 16 km. The data are consistent with a vertically protracted crystal mush in the upper crust beneath the southern part of Montserrat which contains heterogeneous bodies of eruptible magma. The high water contents of the magmas suggest that they contain a high proportion of exsolved fluids, which has implications for the rheology of the mush and timescales for mush reorganisation prior to eruption. A depletion in water in the outer 50-100 μm of a subset of pyroxenes from pumices from a Vulcanian explosion at Soufrière Hills in 2003 is consistent with diffusive loss of hydrogen during magma ascent over 5-13 h. These timescales are similar to the mean time periods between explosions in 1997 and in 2003, raising the possibility that the driving force for this repetitive explosive behaviour lies not in the shallow system, but in the deeper parts of a vertically

  10. Crustal thickening drives arc front migration

    NASA Astrophysics Data System (ADS)

    Karlstrom, Leif; Lee, Cin-Ty; Manga, Michael

    2014-05-01

    The location of volcanic arcs, relative to the trench evolves over time. Arc front migration has been observed in relic (Sierra Nevada, Andes) as well as active (Cascades) arcs, sometimes with cycles of retreat and return of the front towards the trench over millions of years. Other arcs, particularly where back-arc extension dominates, migrate more slowly, if at all. Coupled with arc migration there are systematic changes in the geochemistry of magmas such as the ratio of trace elements La/Yb and 87Sr/86Sr isotopes (e.g., Haschke et al., 2002). The position of active volcanic arcs relative to the trench is controlled by the location where melt is generated in the mantle wedge, in turn controlled by the geometry of subduction, and the processes that focus rising melt. Arc front migration is commonly attributed to variation in dip angle of the downgoing slab, delamination of overthickened crust, or to subduction erosion. Here we present an alternative hypothesis. Assuming mantle wedge melting is a largely temperature-dependant process, the maximum isotherm in the wedge sets arc front location. Isotherm location depends on slab angle, subduction velocity and wedge thermal diffusivity (England and Katz, 2010). It also depends on crustal thickness, which evolves as melt is transferred from the wedge to the crust. Arc front migration can thus occur purely through magmatic thickening of crust and lithosphere. Thickening rate is determined by the mantle melt flux into the crust, modulated by tectonics and surface erosion. It is not steady in time, as crustal thickening progressively truncates the mantle melt column and eventually shuts it off. Thus slab angle need not change, and in the absence of other contribution processes front location and crustal thickness have long-time steady state values. We develop a quantitative model for arc front migration that is consistent with published arc front data, and explains why arc fronts do not move when there is extension, such

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  12. Geochemical monitoring of volcano unrest and multi-step magma propagation: the example of the 2007-2011 Piton de la Fournaise activity.

    NASA Astrophysics Data System (ADS)

    Di Muro, Andrea; Métrich, Nicole; Deloule, Etienne; Civetta, Lucia

    2014-05-01

    The 2007 eruption represents a major event in the recent history of Piton de la Fournaise volcano because it produced: i) the most voluminous lava field (at least 0.21 km3), ii) the most intense lava fountaining activity (>200 m high), iii) the largest SO2 plume (>230 kt), iv) the largest summit collapse (1 km wide x 0.34 km deep) and v) the main flank slip event (up to 1.4 m eastwards) ever documented at PdF. The bulk magma volume extruded during the 2007 eruption is similar to that emitted during the entire 1998-2006 period. As a whole, the volume of lavas emitted during the whole 1998-2007 cycle is remarkably close to that estimated (~0.35 km3) for the shallow plumbing system of Piton de la Fournaise. The 2007 eruptive sequence consisted of three successive phases (February, March and April). The main phase in April ended a 9 years long period (1998-2007) of continuous edifice inflation and frequent eruptive activity (3 eruptions per year on average). On the contrary, the 2008-2011 activity is associated with a trend of continuous deflation and consists of small-volume summit eruptions of moderate/low MgO magmas and frequent shallow magma intrusions. Bulk rocks, minerals, melt inclusions, matrices and very fast cooled ejecta (Pele's hairs and tears) are studied in order to assess the link between volcano unrest processes, structure of the magma plumbing system, ascent dynamics and summit caldera collapse. Melt heterogeneity demonstrate that the shallow part of PdF edifice (upper 3 km) host low-MgO (MgO: 6.2 wt%) melts with variable normative An/Di ratios and olivine content, at variable steps of evolution towards a common ternary eutectic minimum. Repeated summit collapses favor the formation of discontinuities for shallow temporary magma storage. Extrusion of shallow evolved melts is triggered by ascent of small volumes of deeper, hotter magnesian melts (MgO: up to 8.7 wt%), previously stored in the depth range 2-4 km below sea level. Finally, the good match

  13. Parsing Aleutian Arc Magma Compositions

    NASA Astrophysics Data System (ADS)

    Nye, C. J.

    2011-12-01

    -andesites through dacites are essentially unfractionated; or that low-RITE compositions are dominated by processes other than crystal fractionation, including remobilization of cumulate sludges and addition of silicic partial melts of crustal-level rocks. Low-RITE magmas are usually crystal-rich, while high-RITE magmas are usually crystal-poor - although existing modal data do not permit quantitative investigation of this relationship. There is a high degree of correlation among these chemical characteristics, resulting in two major endmember groups: Type-O suites typically have, as a function of SiO2, low Ca# (are Peacock calc-alkalic), low Mg# (are Miyashiro tholeiitic), high-RITE, are generally sparsely phyric, and are often relatively mafic on average. Type-A magma suites typically have high Ca# (Peacock calcic), high Mg# (Miyashiro calcalkaline), low-RITE, are generally very porphyritic, and usually andesitic on average. Type-O magma suites are found in the central arc - where the arc-crest appears to be under moderate extension. Type-A suites dominate the eastern arc - where the arc-crest is under compression, and are scattered among the type-O volcanoes of the central arc. The western arc is more diverse, although A-type magmas dominate.

  14. Crustal structures under the active volcanic areas of central and eastern Mediterranean (M-44)

    NASA Technical Reports Server (NTRS)

    Gasparini, P. (Principal Investigator); Mantovani, M. S. M.; Monaco, F.; Pierattini, D.; Fedi, M.

    1981-01-01

    Programs are being adapted to the UNIVAC 1000 computer and others are being developed for immediate utilization in processing MAGSAT data. stability intermediate for lower continental crust and to upper manele conditions. Attempts to residuate crustal anomalies from one selected profile passing through western mediterranean using procedures commonly used at NASA yielded dubious results because of uncertainties in the adoption of coefficients in the expression accounting for the effect of equatorial ring currents and the empirical approach used for other corrections. Instead, filtering techniques are to be applied to each profile once investigator B tapes relative to the whole planet are received.

  15. Magma chamber paradox: decompression upon replenishment

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  16. Magma rheology variation in sheet intrusions (Invited)

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  17. Geochemical and Isotopic Data from Micron to Across-Arc Scales in the Andean Central Volcanic Zone: Applications for Resolving Crustal Magmatic Differentiation and Modification Processes

    NASA Astrophysics Data System (ADS)

    Michelfelder, G.; Wilder, A.; Feeley, T.

    2014-12-01

    Plagioclase crystals from silicic (andesitic to dacitic) lavas and domes at Volcán Uturuncu, a potentially active volcano in the back-arc of the Andean CVZ (22.3°S, 67.2°W), exhibit large variations in An contents, textures, and core to rim 87Sr/86Sr ratios. Many of the isotopic variations can not have existed at magmatic temperatures for more than a few thousand years. The crystals likely derived from different locations in the crustal magmatic system and mixed just prior to eruption. Uturuncu magmas initially assimilated crustal rocks with high 87Sr/86Sr ratios. The magmas were subsequently modified by frequent recharge of more mafic magmas with lower 87Sr/86Sr ratios. A typical Uturuncu silicic magma therefore only attains its final composition just prior to or during eruption. In the Lazufre region of active surface uplift (~25˚14'S; Volcán Lastarria and Cordon del Azufre) closed system differentiation processes are not the only factors influencing silicic magma compositions. 87Sr/86Sr (0.70651-0.70715) and 206Pb/204Pb ratios (18.83-18.88) are highly elevated and143Nd/144Nd ratios (0.512364 -0.512493) are low relative to similar composition rocks from the "southern Cordillera domain." These data, along with major and trace element trends, reflect a multitude of differentiation processes and magma sources including crystallization-differentiation of more mafic magmas, melting and assimilation of older crustal rocks, and magma mixing and mingling. On an arc-wide scale silicic lavas erupted from three well-characterized composite volcanoes between 21oS and 22oS (Aucanquilcha, Ollagüe, and Uturuncu) display systematically higher K2O, LILE, REE and HFSE contents and 87Sr/86Sr ratios with increasing distance from the arc-front. In contrast, the lavas have systematically lower Na2O, Sr, and Ba contents; LILE/HFSE ratios; 143Nd/144Nd ratios; and more negative Eu anomalies. Silicic magmas along the arc-front apparently reflect melting of relatively young, mafic

  18. 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

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

    NASA Astrophysics Data System (ADS)

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

    2003-04-01

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

  20. Pliocene-Quaternary crustal melting in central and northern Tibet and insights into crustal flow

    NASA Astrophysics Data System (ADS)

    Wang, Qiang; Hawkesworth, Chris J.; Wyman, Derek; Chung, Sun-Lin; Wu, Fu-Yuan; Li, Xian-Hua; Li, Zheng-Xiang; Gou, Guo-Ning; Zhang, Xiu-Zheng; Tang, Gong-Jian; Dan, Wei; Ma, Lin; Dong, Yan-Hui

    2016-06-01

    There is considerable controversy over the nature of geophysically recognized low-velocity-high-conductivity zones (LV-HCZs) within the Tibetan crust, and their role in models for the development of the Tibetan Plateau. Here we report petrological and geochemical data on magmas erupted 4.7-0.3 Myr ago in central and northern Tibet, demonstrating that they were generated by partial melting of crustal rocks at temperatures of 700-1,050 °C and pressures of 0.5-1.5 GPa. Thus Pliocene-Quaternary melting of crustal rocks occurred at depths of 15-50 km in areas where the LV-HCZs have been recognized. This provides new petrological evidence that the LV-HCZs are sources of partial melt. It is inferred that crustal melting played a key role in triggering crustal weakening and outward crustal flow in the expansion of the Tibetan Plateau.

  1. Pliocene-Quaternary crustal melting in central and northern Tibet and insights into crustal flow.

    PubMed

    Wang, Qiang; Hawkesworth, Chris J; Wyman, Derek; Chung, Sun-Lin; Wu, Fu-Yuan; Li, Xian-Hua; Li, Zheng-Xiang; Gou, Guo-Ning; Zhang, Xiu-Zheng; Tang, Gong-Jian; Dan, Wei; Ma, Lin; Dong, Yan-Hui

    2016-01-01

    There is considerable controversy over the nature of geophysically recognized low-velocity-high-conductivity zones (LV-HCZs) within the Tibetan crust, and their role in models for the development of the Tibetan Plateau. Here we report petrological and geochemical data on magmas erupted 4.7-0.3 Myr ago in central and northern Tibet, demonstrating that they were generated by partial melting of crustal rocks at temperatures of 700-1,050 °C and pressures of 0.5-1.5 GPa. Thus Pliocene-Quaternary melting of crustal rocks occurred at depths of 15-50 km in areas where the LV-HCZs have been recognized. This provides new petrological evidence that the LV-HCZs are sources of partial melt. It is inferred that crustal melting played a key role in triggering crustal weakening and outward crustal flow in the expansion of the Tibetan Plateau. PMID:27307135

  2. Petrology and Physics of Magma Ocean Crystallization

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  3. Origins of felsic magmas in Japanese subduction zone: Geochemical characterizations of tephra from caldera-forming eruptions <5 Ma

    NASA Astrophysics Data System (ADS)

    Kimura, Jun-Ichi; Nagahashi, Yoshitaka; Satoguchi, Yasufumi; Chang, Qing

    2015-07-01

    Dacitic to rhyolitic glass shards from 80 widespread tephras erupted during the past 5 Mys from calderas in Kyushu, and SW, central, and NE Japan were analyzed. Laser ablation inductively coupled plasma mass spectrometry was used to determine 10 major and 33 trace elements and 207Pb/206Pb-208Pb/206Pb isotope ratios. The tephras were classified into three major geochemical types and their source rocks were identified as plutonic, sedimentary, and intermediate amphibolite rocks in the upper crust. A few tephras from SW Japan were identified as adakite and alkali rhyolite and were regarded to have originated from slab melt and mantle melt, respectively. The Pb isotope ratios of the tephras are comparable to those of the intermediate lavas in the source areas but are different from the basalts in these areas. The crustal assimilants for the intermediate lavas were largely from crustal melts and are represented by the rhyolitic tephras. A large heat source is required for forming large volumes of felsic crustal melts and is usually supplied by the mantle via basalt. Hydrous arc basalt formed by cold slab subduction is voluminous, and its heat transfer with high water content may have melted crustal rocks leading to effective felsic magma production. Coincidence of basalt and felsic magma activities shown by this study suggests caldera-forming eruptions are ultimately the effect of a mantle-driven cause.

  4. Linkage between crustal structure, mantle temperature and axial morphology: A study of the intermediate spreading Southeast Indian Ridge

    NASA Astrophysics Data System (ADS)

    Baran, Janet Maureen

    There is a systematic variation in axial morphology and axial depth along the Southeast Indian ridge (SEIR) with distance away from the Australian Antarctic Discordance, an area of cold uppermost mantle. Since spreading rate (72-76 mm/yr) and mantle geochemistry appear constant along this portion of the SEIR, the observed variations in axial morphology and axial depth are attributed to a gradient in mantle temperature. In this study, we report results from a multichannel seismic investigation of on-axis and off-axis crustal structure along this portion of SEIR. Axial highs have a shallow magma lens and a thin layer 2A along the ridge crest that doubles in thickness off-axis. Rifted axial highs have a deeper magma lens and thicker layer 2A on-axis that thickens by 50% off-axis. Beneath shallow axial valleys, no magma lens is imaged, and layer 2A is thick with no pattern of thickening off-axis. Near the ridge axis hydrothermal circulation has a large role in the observed seismic layer 2A velocity increase and thickening off-axis. Near-axis, in the vicinity of a magma lens, active hydrothermal circulation occurs, infilling pore spaces, as well as resulting downward cracking. Where there is no magma lens imaged, little active hydrothermal circulation occurs, thus resulting in a small velocity increase. With an observed magma lens, eruption of less viscous, far-traveling lobate laves can extend far off-axis, whereas in areas with no observed magma lens, lava may be emplaced through eruption of cooler more viscous lavas that form constructional pillows. The velocity of layer 2B increases through cooling and healing of fractures through infilling due to hydrothermal circulation. We conclude that a small change in melt production can cause a large change in axial morphology and shallow crustal structure. This implies a threshold type behavior where a small change in melt production results in a transition between two very different modes of crustal generation, resulting in

  5. Temporal Variations of Gamma-Ray for Detecting Crustal Activity Changes in the Longitudinal Valley, Eastern Taiwan

    NASA Astrophysics Data System (ADS)

    Fu, C. C.; Wang, P. G.; Lee, L. C.; Lin, C. H.; Giuliani, G.; Ouzounov, D.

    2014-12-01

    A gamma-ray station was established along the Longitudinal Valley Fault, which is an extremely active high-angle thrust with NNE-striking on the boundary between Eurasia plate and Philippine Sea plate. Stresses arise in the crust in accordance with crustal deformations due to plate motions and geodynamic processes. Gamma-ray emission associated with the radioactive decay of radon is continuously recorded in the station, considered to be discharged into surface from deep source area. Fluctuations of gamma-ray data are found to show a clear inverse correction with atmospheric temperature. Based on the linear regression method, possible temperature effects can be removed and the corrected data can be obtained. Variations exceeding the normal trend can be used to identify events associated with geodynamic processes such as earthquake. These anomalies usually appeare as procursors a few days before the local earthquakes, which occur in eastern Taiwan. It is noted that there are two significant increases in the gamma-ray counting rate during the period of 20th to 25th March and the period of 22nd April to 1st May. These increases are observed one week before the earthquake swarm. Furthermore, a progressive anomalies were recorded two weeks before the Fanglin earthquake (ML = 5.9, May 21, 2014) located in the Longitudinal Valley area. A continuous monitoring on the multiple parameters can improve our understanding of the relationship between the observed gamma-ray variations and the regional crustal stress/strain in the area.

  6. The RAMESSES experiment-V. Crustal accretion at axial volcanic ridge segments-a gravity study at 57°45'N on the slow spreading Reykjanes Ridge

    NASA Astrophysics Data System (ADS)

    Peirce, Christine; Navin, Debbie A.

    2002-04-01

    Presented in this paper are the results of a two-stage analysis of gravity data acquired during a multidisciplinary geophysical survey of a magmatically active axial volcanic ridge (AVR) segment located at 57°45'N on the Reykjanes Ridge, part of the slow spreading Mid-Atlantic Ridge south of Iceland. Modelling of the free-air anomaly in 2-D shows that, across-axis, the observed anomaly results largely from density and layer thickness variation in the mid-lower crust. Although seismic control on crustal thickness along-axis is limited, modelling also suggests that both crustal density and thickness also vary towards AVR tips. Using the 2-D modelling results as crustal reference, the residual mantle Bouguer anomaly (RMBA) is calculated to assess whether magma-related density anomalies are present in the mantle and to investigate the structure of, and relationship between, adjacent AVRs along-axis. RMBA lows are associated with both an along-ridge trend encompassing a number of adjacent AVRs and with individual, more topographically robust AVRs. Modelling of the RMBA low associated with the 57°45'N AVR further suggests that along-axis density variation is confined to the central region of this AVR and that the anomaly can largely be accounted for by density variation within Layer 3 and a degree of crustal thinning towards AVR tips. The nature of the along-axis variation in crustal density further suggests that it may result from repeated phases of magma supply to the crustal system from the mantle. Within the resolution of the RMBA, modelling does not confirm or preclude the presence of a subcrustal density anomaly associated with retention of a small percentage of melt in the mantle. However, a melt-free model for at least the top 40 km of the mantle is preferred as this is consistent with the results of modelling a coincident magnetotelluric data set. The ridge-trend characteristics of the RMBA also suggest that magma delivery may take place along this trend, and

  7. Seismic images of multiple magma sills beneath the East Pacific Rise

    NASA Astrophysics Data System (ADS)

    Marjanovic, M.; Carbotte, S. M.; Carton, H. D.; Mutter, J. C.; Nedimovic, M. R.; Canales, J.

    2013-12-01

    Along fast and intermediate spreading centers, thin and narrow axial magma lenses (AMLs) are detected beneath much of the ridge axis, and the notion that the AML is the primary melt reservoir for dike intrusions and volcanic eruptions that build the upper crust is commonly accepted. However the role of the AML in construction of the lower crust is still actively debated. Some models based on geochemistry and structural observations from ophiolites suggest that formation of the lower crustal gabbro section takes place in situ, from multiple small magma sills, with the AML being the shallowest of these. Here, we present new observations from multichannel seismic data collected in 2008 along the East Pacific Rise (EPR) for seismic reflectors below the AML or sub-axial magma lens (SAML). The most prominent SAML events are found between latitudes 9°20' and 9°56'N, where they appear as moderately bright, discontinuous reflectors, at ~ 50 to 300 ms (~ 200-600 m) below the AML. From an analysis of the characteristics of these events, we rule out possible 'artifact' origins for the SAML including, seafloor side scattering, out-of-plane imaging of the AML or other crustal horizons, internal multiples, and the presence of a P-to-S converted phase (PAMLS). We interpret these deep melt lenses to have a low crystalline component (i.e. they are mostly molten). Disruptions in the SAML reflector, represented by relatively abrupt steps in two-way travel time are collocated with small-scale discontinuities in the AML and further support the notion of crustal accretion through small magmatic units. In addition, within the area of documented volcanic eruptions in 1991-1992 and 2005-2006, two prominent gaps centered at 9°46' and 9°50.5' N in the SAML reflectors are identified. We hypothesize that magma from these deeper lenses have also contributed to the eruption, implying hydraulic connectivity between the AML and SAMLs during eruption events. We suggest that the SAMLs play an

  8. El Hierro's floating stones as messengers of crust-magma interaction at depth

    NASA Astrophysics Data System (ADS)

    Burchardt, S.; Troll, V. R.; Schmeling, H.; Koyi, H.; Blythe, L. S.; Longpré, M. A.; Deegan, F. M.

    2012-04-01

    and vesiculate. The "floating stones" from El Hierro thus represent the products of crust-magma interaction beneath the Canary Islands, but is probably relevant in most volcanic areas and tectonic settings. In addition, xenolith devolatilisation has important general implications for the mechanics of crustal recycling, magma emplacement into the upper crust and volatile release from active volcanic systems.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    USGS Publications Warehouse

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

    2004-01-01

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

  11. Persistent multitiered magma plumbing beneath Katla volcano, Iceland

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

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

    USGS Publications Warehouse

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

    1988-01-01

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

  15. Numerical modelling of Triple Junction Tectonics at Karlıova, Eastern Turkey: implications for the mechanism of magma transport

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    Few places on Earth are as tectonically active as the Karlıova region of eastern Turkey. In this region, complex interactions between the Arabian, Eurasian and Anatolian plates occur at the Karlıova Triple Junction (KTJ). Suitably stressed crustal materials of the extruded block on the Karlıova-type triple junctions are potential regions for magma ascent. The relationship between tectonics and magma propagation in triple junction tectonic settings is, however, poorly understood. This study discusses the mechanism of magma propagation in the Karlıova Triple Junction (KTJ) tectonic regime. We aim to demonstrate how the geometry and mechanical properties of faults and rock units affect magma propagation under a variety of tectonic boundary loads. We discuss the geologic setting of the KTJ and the manifestations of shallow and deeper magma chambers within the crustal segment. Our numerical modelling study aims to quantify the crustal response of various tectonic regimes in Eastern Turkey. The region is characterised by lithological heterogeneity which is considered in our models. We present a series of two-dimensional and three-dimensional numerical models to help constrain evolving ideas regarding inversion and transtensional tectonics in an east-west direction along the KTJ. We also consider a north to south striking profile which is subjected to regional compression and local extensional tectonic phases which likely operated in the region ~3 My. A three-dimensional model is presented to investigate the effect of regional differential stresses. Our numerical models demonstrate that the regional tectonic stresses that are capable of encouraging magma-chamber failure and dyke propagation. Turnadaǧ volcanism at the western part of this triple junction has been fed by a shallow magma chamber located at 8-10 km depth during E-W extension. The Varto caldera is also fed by a shallow magma chamber at 8-10 km depth. Numerical results show that if the region were to be

  16. Evaluating the construction and evolution of upper crustal reservoirs with coupled U/Pb zircon geochronology and thermal modeling: A case study from the Mt. Capanne pluton (Elba, Italy)

    NASA Astrophysics Data System (ADS)

    Barboni, M.; Annen, C.; Schoene, B.

    2015-12-01

    Understanding timescales and mechanisms of magma emplacement and storage in the upper crust is fundamental for evaluating the controls on melt mobility and the tempo and magnitude of volcanic eruptions. U-Pb dating on zircons is commonly used to estimate these processes in upper crustal reservoirs, but increasing precision in zircon ages has lead to increasing difficulty interpreting them in terms of melt emplacement and storage. We present >150 ID-TIMS U/Pb dates on zircon coupled to numerical thermal simulations that 1) constrain the emplacement history and thermal evolution of upper-crustal reservoirs with analytical precision of thousands of years, 2) aid interpretation of complex age spectra and identification of zircon inherited from deeper crustal levels, and 3) provide insight into time-integrated rates of magma recharge and duration of potential eruption windows in active system. Our study of the Late Miocene Mt. Capanne intrusion (Elba, Italy) - a well-documented example of arc-related laccolith emplaced in the upper-continental crust - shows that this reservoir was incrementally built in minimum 300'000 years by accretion of numerous batches of magma. A variety of numerically simulated emplacement scenarios show that maximum volumes that can be erupted correspond to the volume of each pulse injected. Our results also require that the majority of zircon crystallization occurred in zircon-saturated reservoirs at deeper crustal levels prior to final magma emplacement and cooling, which has implications for using zircon U-Pb geochronology to infer upper crustal magma residence times and for accurate interpretation of volcanic ashbed geochronologic data.

  17. Io's theothermal (sulfur) - Lithosphere cycle inferred from sulfur solubility modeling of Pele's magma supply

    NASA Astrophysics Data System (ADS)

    Battaglia, Steven M.; Stewart, Michael A.; Kieffer, Susan W.

    2014-06-01

    Surface deposits of volatile compounds such as water (Earth) or sulfur (Io) on volcanically active bodies suggest that a magmatic distillation process works to concentrate volatiles in surface reservoirs. On Earth, this is the combined hydrologic and tectonic cycle. On Io, sulfurous compounds are transferred from the interior to the surface reservoirs through a combination of a mantle-sourced magmatic system, vertical cycling of the lithosphere, and a sulfur-dominated crustal thermal system that we here call the "theothermal" system. We present a geochemical analysis of this process using previously inferred temperature and oxygen fugacity constraints of Pele's basaltic magma to determine the behavior of sulfur in the ionian magmas. Sulfate to sulfide ratios of Pele's magma are -4.084 ± 0.6 and -6.442 ± 0.7 log10 units, comparable to or lower than those of mid-ocean ridge basalts. This reflects the similarity of Io's oxidation state with Earth's depleted mantle as previously suggested by Zolotov and Fegley (Zolotov, M.Y., Fegley, B. [2000]. Geophys. Res. Lett. 27, 2789-2792). Our calculated limits of sulfur solubility in melts from Pele's patera (˜1100-1140 ppm) are also comparable to terrestrial mid-ocean ridge basalts, reflecting a compositional similarity of mantle sources. We propose that the excess sulfur obvious on Io's surface comes from two sources: (1) an insoluble sulfide liquid phase in the magma and (2) theothermal near-surface recycling.

  18. Magma-assisted rifting in Ethiopia.

    PubMed

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

    2005-01-13

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

  19. Investigation of the deep crustal structure and magmatic activity at the NW Hellenic Volcanic Arc with 3-D aeromagnetic inversion and seimotectonic analysis.

    NASA Astrophysics Data System (ADS)

    Efstathiou, Angeliki; Tzanis, Andreas; Chailas, Stylianos; Stamatakis, Michael

    2013-04-01

    structures of relatively high magnetic susceptibility (>0.035), which all dip to the NNE and do not exceed the depth of 2km; these have all been identified with outcropping ophiolitic bodies. With particular reference to the Argolid, the results also indicate the existence of extensive and massive deep magnetized domains at depths > 4km, with susceptibilities of the order of 0.02. The latter include a rather conspicuous volume beneath the Methana volcanic complex, at depths between 4 and 8km. Because the modeled susceptibility values are generally consistent with the values expected for hot (200°C - 500°C) calc-alcaline igneous rocks, this feature was interpreted to comprise a magma chamber. By analogy to the Methana chamber, all such massive structures were attributed to recent magmatic intrusions (plutons). The pervasive presence of the intrusive igneous rocks beneath the Argolid indicates a rather extensive complex of magmatic activity associated with the western volcano group of the HVA. Particular attention is due to one such elongate and deep reaching "pluton", which develops in a NNW direction (approx. 330°) along the axis of the Argolic Gulf, to the south of the Argolid peninsula; this is situated almost directly above the local inflection (steepening) of the subducting slab and is almost exactly aligned with to it. The sub-crustal stress field due to the subducting slab has been determined by Rondogianni et al (2011) and has been re-appraised in the frame of the present analysis using the method of Michael (1984, 1987). It turns out to be extensional and NE-SW oriented, with the azimuth/dip of the maximum principal axis (compression) being approx. 230°/57° and the same for thee minimum principal axis (extension) being 59°/33°. With such a field, deformation is expected to associate with steeply dipping dislocation surfaces parallel to approx. 325° and to be primarily extensional, with a non-trivial left-lateral heave. An analogous analysis was conducted for

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

    PubMed

    Caricchi, Luca; Simpson, Guy; Schaltegger, Urs

    2014-07-24

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

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

  2. Depth of origin of magma in eruptions.

    PubMed

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

    2013-01-01

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

  3. Depth of origin of magma in eruptions

    PubMed Central

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

    2013-01-01

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

  4. The Modulation of Crustal Magmatic Systems by Tectonic Forcing

    NASA Astrophysics Data System (ADS)

    Karakas, O.; Dufek, J.

    2010-12-01

    The amount, location and residence time of melt in the crust significantly impacts crustal structure and influences the composition, frequency, and volume of eruptive products. In this study, we develop a two dimensional model that simulates the response of the crust to prolonged mantle-derived intrusions in arc environments. The domain includes the entire crustal section and upper mantle and focuses on the evolving thermal structure due to intrusions and external tectonic forcing. Magmatic intrusion into the crust can be accommodated by extension or thickening of the crust or some combination of both mechanisms. Additionally, external tectonic forcing can generate thicker crustal sections, while tectonic extension can significantly thin the crust. We monitor the thermal response, melt fraction and surface heat flux for different tectonic conditions and melt flux from the mantle. The amount of crustal melt versus fractionated primary mantle melts present in the crustal column helps determine crustal structure and growth through time. We express the amount of crustal melting in terms of an efficiency; we define the melting efficiency as the ratio of the melted volume of crustal material to the volume of melt expected from a strict enthalpy balance as explained by Dufek and Bergantz (2005). Melting efficiencies are less than 1 in real systems because heat diffuses to sections of the crust that never melt. In general, thick crust and crust experiencing extended compressional regimes results in an increased melting efficiency; and thin crust and crust with high extension rates have lower efficiency. In most settings, maximum efficiencies are less than 0.05-0.10. We also observe that with a geophysically estimated flux, the mantle-derived magma bodies build up isolated magma pods that are distributed in the crust. One of the aspects of this work is to monitor the location and size of these magma chambers in the crustal column. We further investigate the rheological

  5. Crustal structure during active rifting in the central Salton Trough, California, constrained by the Salton Seismic Imaging Project (SSIP)

    NASA Astrophysics Data System (ADS)

    Han, L.; Hole, J. A.; Stock, J. M.; Fuis, G. S.; Driscoll, N. W.; Kell, A. M.; Kent, G.; Harding, A. J.; Gonzalez-Fernandez, A.; Lazaro-Mancilla, O.

    2013-12-01

    Seismic refraction and reflection travel times from the Salton Seismic Imaging Project (SSIP) were used to constrain crustal structure during active continental rifting in the central Salton Trough, California. SSIP, funded by NSF and USGS, acquired seismic data in and across the Salton Trough in 2011 to investigate rifting processes at the northern end of the Gulf of California extensional province and earthquake hazards at the southern end of the San Andreas Fault system. Seven lines of refraction and low-fold reflection data were acquired onshore, two lines and a grid of airgun and OBS data were acquired in the Salton Sea, and onshore-offshore data were recorded. North American lithosphere in the central Salton Trough appears to have been rifted apart and replaced by new crust added by magmatism from below and sedimentation from above. Ongoing active rifting of this new crust is manifested by shallow (<10km depth) seismicity in the oblique Brawley Seismic Zone (connecting the Imperial and San Andreas transform faults), the small Salton Buttes volcanoes, and very high heat flow that enables geothermal energy production. Analyses of the onshore-offshore seismic line that extends along the axis of the Salton Trough, parallel to the direction of plate motion, constrains rifted crustal structure. Crystalline basement (~5 km/s) generally occurs at ~4 km depth, but is at 2-3 km depth in a localized region beneath the Salton Buttes and Salton Sea geothermal field. This crystalline rock is interpreted to be late Pliocene to Quaternary Colorado River sediment that has been metamorphosed by high heat flow to a depth of at least 10km. The shallower basement under the volcanic and geothermal field is due to more intense metamorphism and hydrothermal alteration in this region of extreme heat flow. Faster velocity (6.2-6.4 km/s) observed at 10-13 km depth might be the remains of ruptured pre-existing crust or might be produced by deeper magmatism. Seismic travel times indicate

  6. Revealing magma degassing below closed-conduit active volcanoes: Geochemical features of volcanic rocks versus fumarolic fluids at Vulcano (Aeolian Islands, Italy)

    NASA Astrophysics Data System (ADS)

    Mandarano, Michela; Paonita, Antonio; Martelli, Mauro; Viccaro, Marco; Nicotra, Eugenio; Millar, Ian L.

    2016-04-01

    The elemental and isotopic compositions of noble gases (He, Ne, and Ar) in olivine- and clinopyroxene-hosted fluid inclusions have been measured for rocks at various degrees of evolution and belonging to high-K calcalkaline-shoshonitic and shoshonitic-potassic series in order to cover the entire volcanological history of Vulcano Island (Italy). The major- and trace-element concentrations and the Sr- and Pb-isotope compositions for whole rocks were integrated with data obtained from the fluid inclusions. 3He/4He in fluid inclusions is within the range of 3.30 and 5.94 R/Ra, being lower than the theoretical value for the deep magmatic source expected for Vulcano Island (6.0-6.2 R/Ra). 3He/4He of the magmatic source is almost constant throughout the volcanic history of Vulcano. Integration of the He- and Sr-isotope systematics leads to the conclusion that a decrease in the He-isotope ratio of the rocks is mainly due to the assimilation of 10-25% of a crustal component similar to the Calabrian basement. 3He/4He shows a negative correlation with Sr isotopes except for the last-erupted Vulcanello latites (Punta del Roveto), which have anomalously high He isotope ratios. This anomaly has been attributed to a flushing process by fluids coming from the deepest reservoirs, since an input of deep magmatic volatiles with high 3He/4He values increases the He-isotope ratio without changing 87Sr/86Sr. A comparison of the He-isotope ratios between fluid inclusions and fumarolic gases shows that only the basalts of La Sommata and the latites of Vulcanello have comparable values. Taking into account that the latites of Vulcanello relate to one of the most-recent eruptions at Vulcano (in the 17th century), we infer that the most probable magma which actually feeds the fumarolic emissions is a latitic body that ponded at about 3-3.5 km of depth and is flushed by fluids coming from a deeper and basic magma.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  8. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  10. Convective Regimes in Crystallizing Basaltic Magma Chambers

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Gudmundsson, Agust

    2012-09-01

    -situ tensile strength of the host rock, 0.5-9 MPa. These in-situ strength estimates are based on hydraulic fracture measurements in drill-holes worldwide down to crustal depths of about 9 km. These measurements do not support some recent magma-chamber stress models that predict (a) extra gravity-related wall-parallel stresses at the boundaries of magma chambers and (b) magma-chamber excess pressures prior to rupture of as much as hundreds of mega-pascals, particularly at great depths. General stress models of magma chambers are of two main types: analytical and numerical. Earlier analytical models were based on a nucleus-of-strain source (a 'point pressure source') for the magma chamber, and have been very useful for rough estimates of magma-chamber depths from surface deformation during unrest periods. More recent models assume the magma chamber to be axisymmetric ellipsoids or, in two-dimensions, ellipses of various shapes. Nearly all these models use the excess pressure in the chamber as the only loading (since lithostatic stress effects are then automatically taken into account), assume the chamber to be totally molten, and predict similar local stress fields. The predicted stress fields are generally in agreement with the world-wide stress measurements in drill-holes and, in particular, with the in-situ tensile-strength estimates. Recent numerical models consider magma-chambers of various (ideal) shapes and sizes in relation to their depths below the Earth's surface. They also take into account crustal heterogeneities and anisotropies; in particular the effects of the effects of a nearby free surface and horizontal and inclined (dipping) mechanical layering. The results show that the free surface may have strong effects on the local stresses if the chamber is comparatively close to the surface. The mechanical layering, however, may have even stronger effects. For realistic layering, and other heterogeneities, the numerical models predict complex local stresses around

  12. Lead isotope constraints on the origin of andesite and dacite magmas at Tungurahua volcano (Ecuador)

    NASA Astrophysics Data System (ADS)

    Nauret, Francois; Ancellin, Marie-Anne; Vlastelic, Ivan; Tournigand, Pierre-Yves; Samaniego, Pablo; Le Pennec, Jean Luc; Gannoun, Mouhcine; Hidalgo, Silvana; Schiano, Pierre

    2016-04-01

    Understanding the occurrence of large explosive eruptions involving silica-rich magmas at mostly andesitic volcanoes is crucial for volcanic hazard assessment Here we focus on the well-known active Tungurahua volcano (Ecuador), specifically its eruptive sequence for the last 3000 years BP, which are characterized by VEI 3 explosive events involving mostly homogeneous andesitic compositions (56-59 wt.% SiO2). However, some large eruptions (VEI ≥ 4) involving andesitic and dacitic magmas (up to 66 wt.% SiO2) also occur at 3000 BP, 1250 BP and 1886 AD. An additional outburst of siliceous magmas occurred during the last eruptive eruption of this volcano in 2006 [1]. Volcanic products at Tungurahua are described as been generated by a binary mixing between a silica-rich and a silica-poor end-member, but the origin of these components was not discussed [2]. Major, trace elements and Sr-Nd-Pb isotopes were used to investigate the genesis of the andesites and dacites. Andesites are heterogeneous in terms of Pb isotopes (206Pb/204Pb: 18.189-19.154, 207Pb/204Pb:15.658-15.696, 208Pb/204Pb: 38.752-38.918, 207Pb/206Pb: 0.8240-0.8275) but homogeneous in terms of major-trace element. Dacite are characterized by homogenous and low 207Pb/206Pb (0.8235±0.0001), very low Nb/U (1.97 to 4.49) and Ce/Pb (2.52-2.99) and high Th/La ratios (0.24 to 0.49). Triangular distribution of data in major element or trace element ratio vs. Pb isotopes plots suggests that at least three components control geochemical variability at Tungurahua. We interpret andesite compositions as reflecting mainly a deep mixture of two mantle components, with small addition of crustal material. We suggest that dacite results from a mixing between various andesite compositions and a larger amount of a contaminant derived from the volcanic basement of the Tungurahua made of late Cretaceous to Palaeogene oceanic plateau basalts and volcano-sedimentary rocks volcanic. Since andesite and dacite occur during the same

  13. Isotopic zonations in silicic magma chambers

    SciTech Connect

    Johnson, C.M. )

    1989-12-01

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

  14. Crustal structure beneath Southwestern Mexico

    NASA Astrophysics Data System (ADS)

    Suhardja, S.; Grand, S.; Wilson, D.; Guzman Speziale, M.; Gomez Gonzalez, J.; Ni, J.; Dominguez Reyes, T.

    2007-12-01

    The MARS ( Mapping the Rivera Subduction zone ) project started in January 2006 deploying 50 broadband seismometers across southwestern Mexico for one and a half year duration. The stations were deployed in Jalisco, Michoacan and Colima states. The goal of the project is to understand the geometry of the Rivera and Cocos subducting plates and the effect of the subduction on the overriding plate. In this study, we employ the teleseismic receiver function technique to map out the lateral variation in Moho depth as well as the Vp/Vs ratio of the crust in this tectonically and magmatically active area. The ambiguity between the delay time of Ps and crustal Vp/Vs ratio is reduced by stacking later phases, the PpPs and PpSs + PsPs, for different values of Moho depth and Vp/Vs ratio (Zhu et al. ). An average crustal depth and crustal Vp/Vs ratio is obtained by finding the highest combination of parameters that give the largest amplitude stack. We find that the average Moho depth is 39 km but varies significantly from 25 to 45 km thick. The average crustal Vp/Vs ratio is 1.82 but is also variable ranging from 1.7 to 1.9. We will discuss correlations of crustal thickness and Vp/Vs ratio with crustal composition and magmatic activity.

  15. Magma Recharge and Emerging Heterogeneity in Prolonged Strombolian and Vulcanian Eruptions

    NASA Astrophysics Data System (ADS)

    Ruprecht, P.; Plank, T.

    2011-12-01

    Volcanoes that erupt mafic to intermediate compositions frequently show prolonged eruptive phases of months to years after decades or more of repose. Such eruptions are characterized by quasi-continuous strombolian and vulcanian behavior. Understanding the driving force that sustains this prolonged activity is important for hazard mitigation and may provide important insights into our knowledge of the shallow crustal plumbing system of such volcanoes. While volcanic gases may be indicative of magma recharge, gas measurements are still relatively rare and absent for many past eruptions. Textural and geochemical studies of crystal zoning are an alternative to derive time scales and frequencies of magma recharge. In order to identify distinct magma batches and their temporal relationship to the eruptive sequence, we have obtained by LA-ICPMS multi-element zoning patterns for olivines from the VEI 3, 1963-65 eruption of Irazu volcano (Costa Rica) for elements that span a wide range of diffusivities (Fe-Mg, Mn, Li, Ca, P, Sc, Ti V, Cr, Mn, Fe-Mg, Co, Ni, Zn). The 1963-65 eruption is characterized by vulcanian and strombolian phases involving basaltic andesites of fairly uniform composition (54-57 wt% SiO2). In three samples spanning most of the eruption we identify olivines (Fo70-91) of different origin (mantle-derived, crustal cumulates and 1963-65 growth). The initial phase is dominated by mantle-melt derived olivines with a thin low Fo rim consistent with decompression growth over a few weeks and a slightly normal zoned interior (Fo84-90) resulting from an extended time of diffusive exchange with intermediate compositions on the order of tens of years - a time scale comparable to the repose time of Irazu volcano. Thus, the low amplitude variations observed in the interior of the olivines may record previous recharge activity during the last eruptive phase in 1939-40. The later eruptive sequence of the 1963-65 eruption continues to have olivines from the early stage

  16. Magma generation at a large, hyperactive silicic volcano (Taupo, New Zealand) revealed by U-Th and U-Pb systematics in zircons

    USGS Publications Warehouse

    Charlier, B.L.A.; Wilson, C.J.N.; Lowenstern, J. B.; Blake, S.; van Calsteren, P.W.; Davidson, J.P.

    2005-01-01

    Young (crustal magmatic systems. Up to and including the 26??5 ka 530 km 3 Oruanui eruption, magmatic systems were contemporaneous but geographically separated. Subsequently they have been separated in time and have vented from geographically overlapping areas. Single-crystal (secondary ionization mass spectrometry) and multiple-crystal (thermal ionization mass spectrometry) zircon model-age data are presented from nine representative eruption deposits from ??? 45 to ???3??5 ka. Zircon yields vary by three orders of magnitude, correlating with the degrees of zircon saturation in the magmas, and influencing the spectra of model ages. Two adjacent magma systems active up to 26??5 ka show wholly contrasting model-age spectra. The smaller system shows a simple unimodal distribution. The larger system, using data from three eruptions, shows bimodal model-age spectra. An older ???100 ka peak is interpreted to represent zircons (antecrysts) derived from older silicic mush or plutonic rocks, and a younger peak to represent zircons (phenocrysts) that grew in the magma body immediately prior to eruption. Post-26??5 ka magma batches show contrasting age spectra, consistent with a mixture of antecrysts, phenocrysts and, in two examples, xenocrysts from Quaternary plutonic and Mesozoic-Palaeozoic metasedimentary rocks. The model-age spectra, coupled with zircon-dissolution modelling, highlight contrasts between short-term silicic magma generation at Taupo, by bulk remobilization of crystal mush and assimilation of metasediment and/or silicic plutonic basement rocks, and the longer-term processes of fractionation from crustally contaminated mafic melts. Contrasts between adjacent or successive magma systems are attributed to differences in positions of the source and root zones within contrasting domains in the quartzo-feldspathic (<15 km deep) crust below

  17. Late Quaternary tectonic activity and crustal shortening rate of the Bogda mountain area, eastern Tian Shan, China

    NASA Astrophysics Data System (ADS)

    Wu, Chuanyong; Wu, Guodong; Shen, Jun; Dai, Xunye; Chen, Jianbo; Song, Heping

    2016-04-01

    The Bogda mountain range is the highest range among the northern Tian Shan mountains. Based on geologic and geomorphologic field surveys, trench excavation and optically stimulated luminescence (OSL) dating, we targeted the active Fukang fault along the Bogda mountain range and identified the late Quaternary deformation characteristics of this area. We found that the Fukang fault dislocated different geomorphic surfaces of the northern Bogda piedmont. The vertical fault displacement corresponds to the topographic relief of the Bogda over long time scales. Since the late Quaternary, the crustal shortening rate was estimated to be 0.90 ± 0.20 mm/yr, which is less than that of the western segment of the northern Tian Shan. We interpret the Bogda fold and thrust belt to be a thick-skinned structure, since a high angle thrust fault bounds the Bogda mountain range and the foreland basin. The deformation characteristics of this region have been dominated by vertical uplift, and the component of propagation toward the basin has been very limited. This tectonic deformation is evidenced as vertical growth. Although the deformation rate is small, the uplift amplitude is very significant in this region.

  18. Damping scaling factors for elastic response spectra for shallow crustal earthquakes in active tectonic regions: "average" horizontal component

    USGS Publications Warehouse

    Rezaeian, Sanaz; Bozorgnia, Yousef; Idriss, I.M.; Abrahamson, Norman; Campbell, Kenneth; Silva, Walter

    2014-01-01

    Ground motion prediction equations (GMPEs) for elastic response spectra are typically developed at a 5% viscous damping ratio. In reality, however, structural and nonstructural systems can have other damping ratios. This paper develops a new model for a damping scaling factor (DSF) that can be used to adjust the 5% damped spectral ordinates predicted by a GMPE for damping ratios between 0.5% to 30%. The model is developed based on empirical data from worldwide shallow crustal earthquakes in active tectonic regions. Dependencies of the DSF on potential predictor variables, such as the damping ratio, spectral period, ground motion duration, moment magnitude, source-to-site distance, and site conditions, are examined. The strong influence of duration is captured by the inclusion of both magnitude and distance in the DSF model. Site conditions show weak influence on the DSF. The proposed damping scaling model provides functional forms for the median and logarithmic standard deviation of DSF, and is developed for both RotD50 and GMRotI50 horizontal components. A follow-up paper develops a DSF model for vertical ground motion.

  19. Deep Borehole Measurements for Characterizing the Magma/Hydrothermal System at Long Valley Caldera, CA

    SciTech Connect

    Carrrigan, Charles R.

    1989-03-21

    The Magma Energy Program of the Geothermal Technology Division is scheduled to begin drilling a deep (6 km) exploration well in Long Valley Caldera, California in 1989. The drilling site is near the center of the caldera which is associated with numerous shallow (5-7 km) geophysical anomalies. This deep well will present an unparalleled opportunity to test and validate geophysical techniques for locating magma as well as a test of the theory that magma is still present at drillable depths within the central portion of the caldera. If, indeed, drilling indicates magma, the geothermal community will then be afforded the unique possibility of examining the coupling between magmatic and hydrothermal regimes in a major volcanic system. Goals of planned seismic experiments that involve the well include the investigation of local crustal structure down to depths of 10 km as well as the determination of mechanisms for local seismicity and deformation. Borehole electrical and electromagnetic surveys will increase the volume and depth of rock investigated by the well through consideration of the conductive structure of the hydrothermal and underlying regimes. Currently active processes involving magma injection will be studied through observation of changes in pore pressure and strain. Measurements of in situ stress from recovered cores and hydraulic fracture tests will be used in conjunction with uplift data to determine those models for magmatic injection and inflation that are most applicable. Finally, studies of the thermal regime will be directed toward elucidating the coupling between the magmatic source region and the more shallow hydrothermal system in the caldera fill. To achieve this will require careful logging of borehole fluid temperature and chemistry. In addition, studies of rock/fluid interactions through core and fluid samples will allow physical characterization of the transition zone between hydrothermal and magmatic regimes.

  20. Magma genesis of the pre-extensional early miocene silicic pyroclastic rocks of the Pannonian Basin

    NASA Astrophysics Data System (ADS)

    Olah, I.; Harangi, Sz.

    2003-04-01

    The Neogene evolution of the Pannonian Basin was accompanied with various volcanic activities started with explosive eruptions of silicic magmas followed by formation of calc-alkaline and alkaline volcanic rocks and subordinate potassic-ultrapotassic volcanic products. The Miocene silicic ignimbrites and pyroclastic fall deposits cover a large region in the Pannonian Basin and therefore have a great stratigraphic significance. In addition, they have strong geodynamic implications because they were formed just before and coeval with the extensional formation of the Pannonian Basin. Traditionally, they are divided into three horizons; however, our new geochemical and volcanologic data do not prove the existence of these three separate units. In this paper, we are focusing on the oldest, pre-extensional silicic pyroclastic rocks. Based on the detailed investigation of the main mineral phases (e.g., plagioclases, amphibole, biotite) and the accessory minerals, especially zircons, we suggest a complex magmagenesis including mixing of mantle derived and crustal derived melts. Detailed zircon morphology studies involving the method of Pupin and CL image analysis proved that it could be used to correlate the scattered localities. In addition, these data showed systematic change in the magmagenesis of the different occurrences. Early Miocene silicic ignimbrites from the southern part of the Pannonian Basin contain greater mantle component, whereas those from the northern regions could involve more crustal component. In addition, zoning patterns and mineral chemical data of the pehnocrysts suggest non-equilibrium crystallization process in an open system magma chamber.

  1. Magma chamber dynamics constrained by crystal isotope stratigraphy

    NASA Astrophysics Data System (ADS)

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

    2003-04-01

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

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

    NASA Astrophysics Data System (ADS)

    Yamasaki, T.

    2015-12-01

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

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

    SciTech Connect

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

    1993-04-01

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

  4. TerraSAR InSAR Investigation of Active Crustal Deformation

    NASA Astrophysics Data System (ADS)

    Lei, L.; Burgmann, R.

    2009-12-01

    We aim to utilize advanced analysis of TerraSAR-X data to investigate the dynamics and interactions of solid Earth deformation processes, such as earthquakes and fault creep, and Earth surface processes, such as land subsidence and groundwater movements, in a densely populated, urban region, the San Francisco Bay Area. Ongoing deformation imaging reveals a number of natural hazards including elastic strain accumulation about seismologic faults, active landsliding, land subsidence and rebound, and settling of unconsolidated sediments that are highly susceptible to liquefaction. Up to now, we have ordered and received 20 more TerraSAR-X Spotlight Single Look Complex (SLC) images and a few Stripmap SLC images delivered by DLR and got a few preliminary results. The TerraSAR-X images were acquired over the San Francisco Bay Area particularly around an area of active landsliding, coastal subsidence and shallow Hayward fault creep near the city of Berkeley. Berkeley is situated between latitude 37.45 and 38.00, longitude 237.30 and 238.00. The data acquisition interval is from November, 2008 to now. Four types of Spotlight images and one type of Stripmap images in time sequence were ordered and acquired: spot_012, spot_038, spot_049, spot_075 and strip_003, having different look angles and pass directions. Access to the SAR data is via ftp about 10 days after acquisition date. The data is supplied in TerraSAR-X standard SLC COSAR (COmplex SAR) format with orbital information in an Extensible Markup Language (XML) header. The file contains integer real-complex components with double sampling and calibration constants for values. I am using ROI_PAC to do the interferograms. But ROI_PAC was designed to process the raw data rather SLC images. So there are some problems in azimuth processing with TerraSAR SLC data especially the Spotlight data. We now have some preliminary results of Stripmap interferograms and Spotlight interferograms but still work on those problems and

  5. Determining the Magma Genesis of Mo Porphyry Deposits

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  6. Magma generation on Mars: Estimated volumes through time

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald; Schneid, B.

    1991-01-01

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

  7. Investigating Compositional Links Between Arc Magmas And The Subducted Altered Oceanic Crust

    NASA Astrophysics Data System (ADS)

    Straub, S. M.

    2015-12-01

    Arc magmatism is causally related to the recycling of materials from the subducting plate. Numerous studies showed that the recycled material flux is dominated by recycled continental crust (oceanic sediment, eroded crust) and altered oceanic igneous crust (AOC). The crustal component is highly enriched, and thus its signal in arc magmas can readily be distinguished from mantle wedge contributions. In contrast, the impact of the AOC flux is much more difficult to detect, since the AOC isotopically resembles the mantle. Mass balance studies of arc input and output suggest that the recycled flux from the thick (6000 meter on average) AOC may buffer the flux of the recycled continental crust to the point of concealment in arc settings where the latter is volumetrically minor. In particular, highly fluid- mobile elements Sr and Pb in arc magmas are strongly influenced by the AOC, implying that the arc chemistry may allow for inferring the Sr and Pb isotopic composition of the subducted AOC. This hypothesis is being tested by a compilation of published data of high-quality trace element and isotope compositions from global arcs. In agreement with previous studies, our results confirm that the Sr-rich fluids released from the AOC control the arc Sr isotopes, whereby the slightly elevated 87Sr/86Sr (up to 0.705) of many arcs may principally reflect the similarly elevated Sr isotope ratios of the AOC rather than a recycled crustal component. In contrast, the arc Pb isotope ratios are influenced by both the AOC and the recycled crustal component which create the typical binary mixing arrays. These arrays should then point to the Pb isotope composition of the AOC and the recycled crust, respectively. However, as the proportions of these end members may strongly vary in arc magmas, the exact 206Pb/204Pb of the subducted AOC in a given setting is challenging. Remarkably, the Pb isotope systematics from well-constrained western Aleutian (minimal sediment subduction) and central

  8. Vertical crustal motion of active plate convergence in Taiwan derived from tide gauge, altimetry, and GPS data

    NASA Astrophysics Data System (ADS)

    Chang, Emmy T. Y.; Chao, Benjamin F.; Chiang, Chieh-Chung; Hwang, Cheinway

    2012-11-01

    Located at the converging junction between the Eurasian and Philippine Sea plates, the island of Taiwan is subject to an active lithospheric deformation as well as seismicity. Taking the difference between the satellite altimetry data (ALT) that give the absolute sea level variation and the tide gauge data (TG) that record the relative sea level variation, we obtain the absolute vertical crustal motion of the tide gauge sites. We use 20 TG stations along the west and east coasts of Taiwan along with the ALT measurements from the TOPEX/Poseidon-Jason satellites in the nearby waters. The ALT-TG results are compared with vertical GPS measurements in discussing vertical motion. We find a general subsidence of the entire Taiwan coast during the past two decades. The west coast sees no prominent vertical motion but with a severe local subsidence due to the over-withdrawal of groundwater. On the east coast, the ALT-TG results in the northern section demonstrate a northward dipping motion. The elastic thickness of the neighboring oceanic lithosphere modeled as an elastic plate with the flexure of the subducting plate shows that the adjacent Philippine Sea plate should be an old, thick oceanic plate, which could drag the slab into the mantle as manifested in a gentle northward subsidence in the northeast Taiwan. In the southern section of the east coast, the ALT-TG results reveal a segmented or undulating pattern in the vertical-motion rates. Judging from the different behaviors between the co-seismic and interseismic vertical motions marked by the major earthquakes during the studied period, we postulate a temporal saw-tooth scenario for the deformation in phases. It demonstrates the opposite motions under different mechanisms in the frontal sections of the subduction zone, which can be understood with lateral collision and slab dragging subject to varied temporal and spatial dependences.

  9. Groundwater pressure changes and crustal deformation before and after the 2007 and 2014 eruptions of Mt. Ontake

    NASA Astrophysics Data System (ADS)

    Koizumi, Naoji; Sato, Tsutomu; Kitagawa, Yuichi; Ochi, Tadafumi

    2016-03-01

    Volcanic activity generally causes crustal deformation, which sometimes induces groundwater changes, and both of these phenomena are sometimes detected before volcanic eruptions. Therefore, investigations of crustal deformation and groundwater changes can be useful for predicting volcanic eruptions. The Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, has been observing groundwater pressure at Ohtaki observatory (GOT) since 1998. GOT is about 10 km southeast of the summit of Mt. Ontake. During this observation period, Mt. Ontake has erupted twice, in 2007 and in 2014. Before the 2007 eruption, the groundwater pressure at GOT clearly dropped, but it did not change before or after the 2014 eruption. These observations are consistent with the crustal deformation observed by Global Navigation Satellite System stations of the Geospatial Information Authority of Japan. The difference between the 2007 and 2014 eruptions can be explained if a relatively large magma intrusion occurred before the 2007 eruption but no or a small magma intrusion before the 2014 eruption.

  10. Seismic evidence of magma transport in Eyjafjallajökull during 2009-2010 (Invited)

    NASA Astrophysics Data System (ADS)

    Hjaltadottir, S.; Vogfjord, K. S.

    2010-12-01

    The ice-capped central volcano Eyjafjallajökull in South-Iceland erupted in March and April 2010, after nearly 190 years of dormancy. Its last eruption occurred at the summit in 1821-23 and only two other eruptions are known during historic time in Iceland (last 1100 years). However, the volcano had shown signs of repeated magmatic activity since 1992, with the last intrusion episode occurring 10 years before the latest events. We have used relocated earthquakes recorded during 2009-2010 to track magma transport in the volcano during the recent intrusion and eruption episode. Only three major swarms were recorded in Eyjafjallajökull during the last 20 years. These occurred in 1994, 1996 and in 1999-2000. The 1996 swarm occurred at 20-25 km depth, near the Moho with no crustal uplift detected during the swarm, probably due to its great depth. However, the other two swarms occurred in the intermediate and upper crust and were accompanied by uplift centered at the southern flank caused by 4.5-6.5 km deep intrusions. The latest swarm activity began late in March 2009 when several deep earthquakes were recorded near the Moho. The swarm activity continued during June-August and was followed by a southward movement of a close GPS-station which indicated the formation of a new but small intrusion beneath the southern flank. After four quiet months the activity picked up again in late December. Similar to 1994, 1999 and 2009, the main activity was clustered approximately east of the summit at 9-11 km and 2-4 km depth. This pattern changed in late February when the seismicity partly migrated towards SSE, indicating the formation of a series of dykes at 4-9 km depth and again on 3 March with dramatic rise in intensity and the foci forming an E-W trending segment east of the main cluster. On 17 March the seismicity started to ascent towards the surface beneath the ice-cap but on 20 March the magma took a turn in the uppermost 2-3 km towards the first eruption site at the ice

  11. The petrogenesis of sodic island arc magmas at Savo volcano, Solomon Islands

    NASA Astrophysics Data System (ADS)

    Smith, D. J.; Petterson, M. G.; Saunders, A. D.; Millar, I. L.; Jenkin, G. R. T.; Toba, T.; Naden, J.; Cook, J. M.

    2009-12-01

    Savo, Solomon Islands, is a historically active volcano dominated by sodic, alkaline lavas, and pyroclastic rocks with up to 7.5 wt% Na2O, and high Sr, arc-like trace element chemistry. The suite is dominated by mugearites (plagioclase-clinopyroxene-magnetite ± amphibole ± olivine) and trachytes (plagioclase-amphibole-magnetite ± biotite). The presence of hydrous minerals (amphibole, biotite) indicates relatively wet magmas. In such melts, plagioclase is relatively unstable relative to iron oxides and ferromagnesian silicates; it is the latter minerals (particularly hornblende) that dominate cumulate nodules at Savo and drive the chemical differentiation of the suite, with a limited role for plagioclase. This is potentially occurring in a crustal “hot zone”, with major chemical differentiation occurring at depth. Batches of magma ascend periodically, where they are subject to decompression, water saturation and further cooling, resulting in closed-system crystallisation of plagioclase, and ultimately the production of sodic, crystal and feldspar-rich, high-Sr rocks. The sodic and hydrous nature of the parental magmas is interpreted to be the result of partial melting of metasomatised mantle, but radiogenic isotope data (Pb, Sr, Nd) cannot uniquely identify the source of the metasomatic agent.

  12. Magma ascent pathways associated with large mountains on Io

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  13. Why do Martian Magmas erupt?

    NASA Astrophysics Data System (ADS)

    Balta, J. B.; McSween, H. Y.

    2011-12-01

    crust [7]. If these melts were to stall at this depth, they would begin crystallizing pyroxene and become denser with crystallization, possibly trapping them at the base of the crust. However, as Martian magmas do erupt, some liquids must be able to bypass this crustal filter. One mechanism for driving eruption is magmatic water. Addition of 1 wt.% H2O to a melt reduces the magnitude of the density increase by stabilizing olivine relative to pyroxene (increasing the crossover pressure by 1-2 kb depending on liquid composition) and decreasing the liquid density by 0.08 g/cc. Alternatively, other volatiles, such as chlorine and CO2, have different effects, stabilizing pyroxene relative to olivine, with ~0.8 wt.% Cl causing pyroxene to remain the liquidus phase down to pressures of 7-8 kb [8,9], within the Martian crust. Therefore, melts rich in volatiles other than water may be more likely to stall within the Martian crust leading to cumulate formation, while water rich magmas crystallize olivine and pass through the crust, erupting as the basalts on the surface. [1] Stolper and Walker, 1980. [2] Greshake et al., 2004. [3] Monders et al., 2007. [4] Filiberto et al., 2010. [5] Balta et al., 2011, in prep. [6] Ghiorso and Sack, 1995. [7] Wieczorek and Zuber, 2004 [8] Filiberto and Treiman, 2009 [9] Balta et al., 2011, J. Petrol, in press.

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

    NASA Astrophysics Data System (ADS)

    Ulusoy, Ezgi; Kagan Kadioglu, Yusuf

    2016-04-01

    calkalkaline in character.Geochemical features include moderate to slightly elevated large ion lithophile elements (LILE) and slightly depleted high field strength element (HFSE) in patterns. According to petrographic, minerological and geochemical studies gabbroic rocks are products of mantle products with contaminated by crustal components and during magmatic activity mantle addition continuing with varying proportions during cycling of magma intrusion in the Strandja Massif.

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

    USGS Publications Warehouse

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

    2000-01-01

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

  16. Formation of continental crust in a temporally linked arc magma system from 5 to 30 km depth: ~ 90 Ma plutonism in the Cascades Crystalline Core composite arc section

    NASA Astrophysics Data System (ADS)

    Ratschbacher, B. C.; Miller, J. S.; Kent, A. J.; Miller, R. B.; Anderson, J. L.; Paterson, S. R.

    2015-12-01

    Continental crust has an andesitic bulk composition with a mafic lower crust and a granodioritic upper crust. The formation of stratified continental crust in general and the vertical extent of processes active in arc crustal columns leading to the differentiation of primitive, mantle-derived melts entering the lower crust are highly debated. To investigate where in the crustal column magma mixing, fractionation, assimilation and crystal growth occur and to what extent, we study the ~ 90 Ma magmatic flare-up event of the Cascades arc, a magma plumbing system from ~ 5 to 30 km depth. We focus on three intrusive complexes, emplaced at different depths during major regional shortening in an exceptionally thick crust (≥ 55 km1) but which are temporally related: the upper crustal Black Peak intrusion (1-3 kbar at 3.7 to 11 km; ~ 86.8 to 91.7 Ma2), the mid-crustal Mt. Stuart intrusion (3.5-4.0 kbar at 13 to 15 km; 90.8 and 96.3 Ma3) and the deep crustal Tenpeak intrusion (7 to 10 kbar at 25 to 37 km; 89.7 to 92.3 Ma4). These intrusive complexes are well characterized by geochronology showing that they have been constructed incrementally by multiple magma batches over their lifespans and thus allow the monitoring and comparison of geochemical parameters over time at different depths. We use a combination of whole rock major and trace element data and isotopes combined with detailed investigation of amphibole, which has been recognized to be important in the generation of calc-alkaline rocks in arcs to test the following hypotheses: (a) compositional bimodality is produced in the lower crust, whereas upper crustal levels are dominated by mixing to form intermediate compositions, or (b) differentiation occurs throughout the crustal column with different crystallizing phases and their compositions controlling the bulk chemistry. 1. Miller et al. 2009: GSA Special Paper 456, p. 125-149 2. Shea 2014: PhD thesis, Massachusetts Institute of Technology 3. Anderson et al. 2012

  17. Eruptive stratigraphy of the Tatara-San Pedro complex, 36°S, sourthern volcanic zone, Chilean Andes: reconstruction method and implications for magma evolution at long-lived arc volcanic centers

    USGS Publications Warehouse

    Dungan, M.A.; Wulff, A.; Thompson, R.

    2001-01-01

    The Quaternary Tatara-San Pedro volcanic complex (36°S, Chilean Andes) comprises eight or more unconformity-bound volcanic sequences, representing variably preserved erosional remnants of volcanic centers generated during 930 ky of activity. The internal eruptive histories of several dominantly mafic to intermediate sequences have been reconstructed, on the basis of correlations of whole-rock major and trace element chemistry of flows between multiple sampled sections, but with critical contributions from photogrammetric, geochronologic, and paleomagnetic data. Many groups of flows representing discrete eruptive events define internal variation trends that reflect extrusion of heterogeneous or rapidly evolving magna batches from conduit-reservoir systems in which open-system processes typically played a large role. Long-term progressive evolution trends are extremely rare and the magma compositions of successive eruptive events rarely lie on precisely the same differentiation trend, even where they have evolved from similar parent magmas by similar processes. These observations are not consistent with magma differentiation in large long-lived reservoirs, but they may be accommodated by diverse interactions between newly arrived magma inputs and multiple resident pockets of evolved magma and / or crystal mush residing in conduit-dominated subvolcanic reservoirs. Without constraints provided by the reconstructed stratigraphic relations, the framework for petrologic modeling would be far different. A well-established eruptive stratigraphy may provide independent constraints on the petrologic processes involved in magma evolution-simply on the basis of the specific order in which diverse, broadly cogenetic magmas have been erupted. The Tatara-San Pedro complex includes lavas ranging from primitive basalt to high-SiO2 rhyolite, and although the dominant erupted magma type was basaltic andesite ( 52-55 wt % SiO2) each sequence is characterized by unique proportions of

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    USGS Publications Warehouse

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

    2015-01-01

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

  20. Magma Genesis of Sakurajima, the Quaternary post- Aira caldera volcano, southern Kyushu Island, Japan

    NASA Astrophysics Data System (ADS)

    Shibata, T.; Suzuki, J.; Yoshikawa, M.; Kobayashi, T.; Miki, D.; Takemura, K.

    2012-12-01

    Sakurajima volcano is the Quaternary post-caldera volcano of Aira caldera, which was caused by the eruption of huge amount of silicic pyroclastics, situated on Ryukyu arc, southern Kyushu Island, Japan. This volcano is quite active, so it can be considered that the preparation of next caldera-forming eruption with huge amount of silicic magma is proceeding. It is, therefore, expected that the investigation of magma genesis of Sakurajima volcano give us information for the mechanism generating huge amount of silicic magma, which cause the caldera formation. We analyzed major and trace elements with Sr, Nd and Pb isotopic compositions of volcanic rocks from Sakurajima volcano. We sampled (ol) - opx - cpx - pl andesite and dacite from almost all the volcanic units defined by Fukuyama and Ono (1981). In addition to Sakurajima samples, we also studied basaltic rocks erupted at pre-caldera stage of the Aira caldera to estimate the primary magma of Sakurajima volcano. Major and trace element variations generally show linear trends on the Harker diagrams, with the exception of P2O5 and TiO2. Based on the trend of P2O5 vs.SiO2, we divided studied samples low-P (P2O5 < 0.15 wt. %) and high-P (P2O5 > 0.15 wt. %) groups and these groups also display two distinct trends on TiO2-SiO2 diagram. The composition of trace elements shows typical island arc character as depletion of Nb and enrichments of Rb, K and Pb, suggesting addition of aqueous fluids to the mantle wedge. The Zr and Nb concentrations make a liner trend (Zr/Nb = 27) and this trend across from tend of MORB (Zr/Nb = 35) to that of crustal materials (Zr/Nb=17). The Sr, Nd and Pb isotopic compositions broadly plot to on the mixing curve connecting MORB-type mantle and sediments of the Philippine Sea Plate, indicating that the primary magma was generated by partial melting of MORB-type mantle wedge, which was hydrated with fluids derived from the subducted Philippine Sea sediments. But we found that our data plot apart

  1. Slip reversals on active normal faults related to the inflation and deflation of magma chambers: Numerical modeling with application to the Yellowstone-Teton region

    NASA Astrophysics Data System (ADS)

    Hampel, Andrea; Hetzel, Ralf

    2008-04-01

    Earthquakes and coseismic slip on faults are the common response of Earth's crust to plate-tectonic forces. Here we demonstrate, using three-dimensional numerical experiments, that pulses of magmatic activity may alter the slip behavior of nearby tectonic faults by causing unusual aseismic creep and even reversals in the sense of slip. We apply our results to the Teton normal fault, Wyoming, which experienced hitherto unexplained episodes of reverse and normal creep between 1988 and 2001, to show that its anomalous behavior can be explained by inflation and deflation of two magma chambers beneath the Yellowstone caldera. Our findings imply a strong coupling between magmatism and tectonic faulting, which requires coordinated monitoring of both processes to improve our understanding of the resulting spatial and temporal strain pattern.

  2. Long-term evolution of erupted magma chemistry

    NASA Astrophysics Data System (ADS)

    Caricchi, L.; Simpson, G.

    2014-12-01

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

  3. Experimental Magma Mixing and Mingling in Volcanic Environments

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  4. Silicic magma generation at Askja volcano, Iceland

    NASA Astrophysics Data System (ADS)

    Sigmarsson, O.

    2009-04-01

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

  5. Chapter 9 The magma feeding system of Somma-Vesuvius (Italy) strato-volcano: new inferences from a review of geochemical and Sr, Nd, Pb and O isotope data

    USGS Publications Warehouse

    Piochi, M.; de Vivo, B.; Ayuso, R.A.

    2006-01-01

    A large database of major, trace and isotope (Sr, Nd, Pb, O) data exists for rocks produced by the volcanic activity of Somma-Vesuvius volcano. Variation diagrams strongly suggest a major role for evolutionary processes such as fractional crystallization, contamination, crystal trapping and magma maxing, occurring after magma genesis in the mantle. Most mafic magmas are enriched in LILE (Light Ion Lithophile Elements; K. Rb, Ba), REE (Ce, Sm) and Y, show small Nb-Ta negative anomalies, and have values of Nb/Zr at about 0.15. Enrichments in LILE, REE, Nb and Ta do not correlate with Sr isotope values or degree of both K enrichment and silica undersaturation. The results indicate mantle source heterogeneity produced by slab-derived components beneath the volcano. However, the Sr isotope values of Somma-Vesuvius increase from 0.7071 up to 0.7081 with transport through the uppermost 11-12 km of the crust. The Sr isotope variation suggests that the crustal component affected the magmas during ascent through the lithosphere to the surface. Our new geochemical assessment based on chemical, isotopic and fluid inclusion data points to the existence of three main levels of magma storage. Two of the levels are deep and may represent long-lived reservoirs; the uppermost crustal level probably coincides with the volcanic conduit. The deeper level of magma storage is deeper than 12 km and fed the 1944 AD eruption. The intermediate level coincides with the seismic discontinuity detected by Zollo et al. (1996) at about 8 km. This intermediate level supplies magmas with 87Sr/86Sr values between 0.7071 and 0.7074, and ??O18<8% that typically erupted both during interplinian (i.e. 1906 AD) and sub-plinian (472 AD, 1631 AD) events. The shallowest level of magma storage at about 5 km was the site of magma chambers for the Pompei and Avellino plinian eruptions. New investigations are necessary to verify the proposed magma feeding system. ?? 2006 Elsevier B.V. All rights reserved.

  6. Magma evolution and ascent at the Craters of the Moon and neighboring volcanic fields, southern Idaho, USA: implications for the evolution of polygenetic and monogenetic volcanic fields

    USGS Publications Warehouse

    Putirka, Keith D.; Kuntz, Mel A.; Unruh, Daniel M.; Vaid, Nitin

    2009-01-01

    The evolution of polygenetic and monogenetic volcanic fields must reflect differences in magma processing during ascent. To assess their evolution we use thermobarometry and geochemistry to evaluate ascent paths for neighboring, nearly coeval volcanic fields in the Snake River Plain, in south-central Idaho, derived from (1) dominantly Holocene polygenetic evolved lavas from the Craters of the Moon lava field (COME) and (2) Quaternary non-evolved, olivine tholeiites (NEOT) from nearby monogenetic volcanic fields. These data show that NEOT have high magmatic temperatures (1205 + or - 27 degrees C) and a narrow temperature range (50 degrees C). Prolonged storage of COME magmas allows them to evolve to higher 87Sr/86Sr and SiO2, and lower MgO and 143Nd/144Nd. Most importantly, ascent paths control evolution: NEOT often erupt near the axis of the plain where high-flux (Yellowstone-related), pre-Holocene magmatic activity replaces granitic middle crust with basaltic sills, resulting in a net increase in NEOT magma buoyancy. COME flows erupt off-axis, where felsic crustal lithologies sometimes remain intact, providing a barrier to ascent and a source for crustal contamination. A three-stage ascent process explains the entire range of erupted compositions. Stage 1 (40-20 km): picrites are transported to the middle crust, undergoing partial crystallization of olivine + or - clinopyroxene. COME magmas pass through unarmored conduits and assimilate 1% or less of ancient gabbroic crust having high Sr and 87Sr/86Sr and low SiO2. Stage 2 (20-10 km): magmas are stored within the middle crust, and evolve to moderate MgO (10%). NEOT magmas, reaching 10% MgO, are positively buoyant and migrate through the middle crust. COME magmas remain negatively buoyant and so crystallize further and assimilate middle crust. Stage 3 (15-0 km): final ascent and eruption occurs when volatile contents, increased by differentiation, are sufficient (1-2 wt % H2O) to provide magma buoyancy through the

  7. 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

  8. Describing the chemical character of a magma

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  9. Intrusion Triggering of Explosive Eruptions: Lessons Learned from EYJAFJALLAJÖKULL 2010 Eruptions and Crustal Deformation Studies

    NASA Astrophysics Data System (ADS)

    Sigmundsson, F.; Hreinsdottir, S.; Hooper, A. J.; Arnadottir, T.; Pedersen, R.; Roberts, M. J.; Oskarsson, N.; Auriac, A.; Decriem, J.; Einarsson, P.; Geirsson, H.; Hensch, M.; Ofeigsson, B. G.; Sturkell, E. C.; Sveinbjornsson, H.; Feigl, K.

    2010-12-01

    Gradual inflation of magma chambers often precedes eruptions at highly active volcanoes. During eruptions, rapid deflation occurs as magma flows out and pressure is reduced. Less is known about the deformation style at moderately active volcanoes, such as Eyjafjallajökull, Iceland, where an explosive summit eruption of trachyandesite beginning on 14 April 2010 caused exceptional disruption to air traffic. This eruption was preceded by an effusive flank eruption of olivine basalt from 20 March - 12 April 2010. Geodetic and seismic observations revealed the growth of an intrusive complex in the roots of the volcano during three months prior to eruptions. After initial horizontal growth, modelling indicates both horizontal and sub-vertical growth in three weeks prior the first eruption. The behaviour is attributed to subsurface variations in crustal stress and strength originating from complicated volcano foundations. A low-density layer may capture magma allowing pressure to build before an intrusion can ascend towards higher levels. The intrusive complex was formed by olivine basalt as erupted on the volcano flank 20 March - 12 April; the intrusive growth halted at the onset of this eruption. Deformation associated with the eruption onset was minor as the dike had reached close to the surface in the days before. Isolated eruptive vents opening on long-dormant volcanoes may represent magma leaking upwards from extensive pre-eruptive intrusions formed at depth. A deflation source activated during the summit eruption of trachyandesite is distinct from, and adjacent to, all documented sources of inflation in the volcano roots. Olivine basalt magma which recharged the volcano appears to have triggered the summit eruption, although the exact mode of triggering is uncertain. Scenarios include stress triggering or propagation of olivine basalt into more evolved magma. The trachyandesite includes crystals that can be remnants of minor recent intrusion of olivine basalt

  10. A proposal of monitoring and forecasting system for crustal activity in and around Japan using a large-scale high-fidelity finite element simulation codes

    NASA Astrophysics Data System (ADS)

    Hori, T.; Ichimura, T.

    2015-12-01

    Here we propose a system for monitoring and forecasting of crustal activity, especially great interplate earthquake generation and its preparation processes in subduction zone. Basically, we model great earthquake generation as frictional instability on the subjecting plate boundary. So, spatio-temporal variation in slip velocity on the plate interface should be monitored and forecasted. Although, we can obtain continuous dense surface deformation data on land and partly at the sea bottom, the data obtained are not fully utilized for monitoring and forecasting. It is necessary to develop a physics-based data analysis system including (1) a structural model with the 3D geometry of the plate interface and the material property such as elasticity and viscosity, (2) calculation code for crustal deformation and seismic wave propagation using (1), (3) inverse analysis or data assimilation code both for structure and fault slip using (1)&(2). To accomplish this, it is at least necessary to develop highly reliable large-scale simulation code to calculate crustal deformation and seismic wave propagation for 3D heterogeneous structure. Actually, Ichimura et al. (2014, SC14) has developed unstructured FE non-linear seismic wave simulation code, which achieved physics-based urban earthquake simulation enhanced by 10.7 BlnDOF x 30 K time-step. Ichimura et al. (2013, GJI) has developed high fidelity FEM simulation code with mesh generator to calculate crustal deformation in and around Japan with complicated surface topography and subducting plate geometry for 1km mesh. Further, for inverse analyses, Errol et al. (2012, BSSA) has developed waveform inversion code for modeling 3D crustal structure, and Agata et al. (2015, this meeting) has improved the high fidelity FEM code to apply an adjoint method for estimating fault slip and asthenosphere viscosity. Hence, we have large-scale simulation and analysis tools for monitoring. Furthermore, we are developing the methods for

  11. Detailed crustal structure of the North China and its implication for seismicity

    NASA Astrophysics Data System (ADS)

    Jiang, Wenliang; Wang, Xin; Tian, Tian; Zhang, Jingfa; Wang, Donglei

    2014-02-01

    Since the Mesozoic-Cenozoic era the North China Craton has experienced an important tectonic transition and it has given rise to complicated crustal structure and strong earthquake activity. Based on the large-scale surface gravity data, we studied the detailed crustal structure and seismogenic mechanism of the North China. The results indicate that the North China presents typical characteristics of adjoining depression and uplift, alternating basins and hills, inhomogeneous density and also great differences in crustal structure and Moho topography. The upper and middle crustal structures are dominated by the NNE-striking tectonic units, with many faults cut down to the middle crust. The lower crust is characterized by the folding-structure, with high and low-density placed alternately from west to east, presenting lateral heterogeneous feature. Adjusted by the gravity isostasy, Moho topography of the North China fluctuates greatly. Compared with the North China Basin, crustal thickness in the Western Taihang, northern Yanshan and Luzhong areas are much thicker while those densities are lower than the North China Basin. The dominating tectonic direction of the Moho topography strikes NE to NNE and undulates alternately from west to east. The epicenters are mostly concentrated in the upper and middle crust, especially the transitional areas between the high and low-gravity anomalies. The Tancheng earthquake in 1668, Sanhe earthquake in 1673, Tangshan earthquake in 1976, and all other seismic tectonic zones of the North China are all distributed in area where magma moves strongly beneath the crust, which is considered to be related to the movement of the high density, unstable and heat flows along the deep passage from the uppermost and asthenosphere due to the subduction of the Pacific slab towards the Eurasian plate.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  13. Dynamics of a large, restless, rhyolitic magma system at Laguna del Maule, southern Andes, Chile

    USGS Publications Warehouse

    Singer, Brad S.; Andersen, Nathan L.; Le Mével, Hélène; Feigl, Kurt L.; DeMets, Charles; Tikoff, Basil; Thurber, Clifford H.; Jicha, Brian R.; Cardonna, Carlos; Córdova, Loreto; Gil, Fernando; Unsworth, Martyn J.; Williams-Jones, Glyn; Miller, Craig W.; Fierstein, Judith; Hildreth, Edward; Vazquez, Jorge A.

    2014-01-01

    Explosive eruptions of large-volume rhyolitic magma systems are common in the geologic record and pose a major potential threat to society. Unlike other natural hazards, such as earthquakes and tsunamis, a large rhyolitic volcano may provide warning signs long before a caldera-forming eruption occurs. Yet, these signs—and what they imply about magma-crust dynamics—are not well known. This is because we have learned how these systems form, grow, and erupt mainly from the study of ash flow tuffs deposited tens to hundreds of thousands of years ago or more, or from the geophysical imaging of the unerupted portions of the reservoirs beneath the associated calderas. The Laguna del Maule Volcanic Field, Chile, includes an unusually large and recent concentration of silicic eruptions. Since 2007, the crust there has been inflating at an astonishing rate of at least 25 cm/yr. This unique opportunity to investigate the dynamics of a large rhyolitic system while magma migration, reservoir growth, and crustal deformation are actively under way is stimulating a new international collaboration. Findings thus far lead to the hypothesis that the silicic vents have tapped an extensive layer of crystal-poor, rhyolitic melt that began to form atop a magmatic mush zone that was established by ca. 20 ka with a renewed phase of rhyolite eruptions during the Holocene. Modeling of surface deformation, magnetotelluric data, and gravity changes suggest that magma is currently intruding at a depth of ~5 km. The next phase of this investigation seeks to enlarge the sets of geophysical and geochemical data and to use these observations in numerical models of system dynamics.

  14. Tectonic activity as a significant source of crustal tetrafluoromethane emissions to the atmosphere: Observations in groundwaters along the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Deeds, Daniel A.; Kulongoski, Justin T.; Mühle, Jens; Weiss, Ray F.

    2015-02-01

    Tetrafluoromethane (CF4) concentrations were measured in 14 groundwater samples from the Cuyama Valley, Mil Potrero and Cuddy Valley aquifers along the Big Bend section of the San Andreas Fault System (SAFS) in California to assess whether tectonic activity in this region is a significant source of crustal CF4 to the atmosphere. Dissolved CF4 concentrations in all groundwater samples but one were elevated with respect to estimated recharge concentrations including entrainment of excess air during recharge (Cre; ∼30 fmol kg-1 H2O), indicating subsurface addition of CF4 to these groundwaters. Groundwaters in the Cuyama Valley contain small CF4 excesses (0.1-9 times Cre), which may be attributed to an in situ release from weathering and a minor addition of deep crustal CF4 introduced to the shallow groundwater through nearby faults. CF4 excesses in groundwaters within 200 m of the SAFS are larger (10-980 times Cre) and indicate the presence of a deep crustal flux of CF4 that is likely associated with the physical alteration of silicate minerals in the shear zone of the SAFS. Extrapolating CF4 flux rates observed in this study to the full extent of the SAFS (1300 km × 20-100 km) suggests that the SAFS potentially emits (0.3- 1) ×10-1 kg CF4 yr-1 to the Earth's surface. For comparison, the chemical weathering of ∼ 7.5 ×104km2 of granitic rock in California is estimated to release (0.019- 3.2) ×10-1 kg CF4 yr-1. Tectonic activity is likely an important, and potentially the dominant, driver of natural emissions of CF4 to the atmosphere. Variations in preindustrial atmospheric CF4 as observed in paleo-archives such as ice cores may therefore represent changes in both continental weathering and tectonic activity, including changes driven by variations in continental ice cover during glacial-interglacial transitions.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  16. The interpretation of crustal dynamics data in terms of plate interactions and active tectonics of the Anatolian Plate and surrounding regions in the Middle East

    NASA Technical Reports Server (NTRS)

    Toksoz, M. Nafi

    1987-01-01

    The primary effort in this study during the past year has been directed along two separate lines: (1) expanding finite element models to include the entire Anatolian plate, the Aegean Sea and the Northeastern Mediterranean Sea, and (2) investigating the relationship between fault geometry and earthquake activity for the North Anatolian and similar strike-slip faults (e.g., San Andreas Fault). Both efforts are designed to provide an improved basis for interpreting the Crustal Dynamics measurements NASA has planned for this region. The initial phases of both investigations have been completed and the results are being prepared for publication. These investigations are described briefly.

  17. Pliocene-Quaternary crustal melting in central and northern Tibet and insights into crustal flow

    PubMed Central

    Wang, Qiang; Hawkesworth, Chris J.; Wyman, Derek; Chung, Sun-Lin; Wu, Fu-Yuan; Li, Xian-Hua; Li, Zheng-Xiang; Gou, Guo-Ning; Zhang, Xiu-Zheng; Tang, Gong-Jian; Dan, Wei; Ma, Lin; Dong, Yan-Hui

    2016-01-01

    There is considerable controversy over the nature of geophysically recognized low-velocity–high-conductivity zones (LV–HCZs) within the Tibetan crust, and their role in models for the development of the Tibetan Plateau. Here we report petrological and geochemical data on magmas erupted 4.7–0.3 Myr ago in central and northern Tibet, demonstrating that they were generated by partial melting of crustal rocks at temperatures of 700–1,050 °C and pressures of 0.5–1.5 GPa. Thus Pliocene-Quaternary melting of crustal rocks occurred at depths of 15–50 km in areas where the LV–HCZs have been recognized. This provides new petrological evidence that the LV–HCZs are sources of partial melt. It is inferred that crustal melting played a key role in triggering crustal weakening and outward crustal flow in the expansion of the Tibetan Plateau. PMID:27307135

  18. Sr-O isotope systematics in the Campi Flegrei magma systems

    NASA Astrophysics Data System (ADS)

    Wörner, Gerhard; Iovine, Raffaella; Carmine Mazzeo, Fabio; D'Antonio, Massimo; Arienzo, Ilenia; Civetta, Lucia; Orsi, Giovanni

    2016-04-01

    a large range mostly between 7 and 10 ‰ VSMOW, maximum and minimum values reach from ~11 to ~6 ‰ VSMOW. Our data obtained so far show compositions that are very different from typical mantle values and that span a very large range towards heavy δ18O values compared to other magmatic compositions from the Italian Peninsula. We compare our clinopyroxene and olivine data with published clinopyroxene and olivine O-isotope data from other Italian volcanic centers (Alban Hills, Mts. Ernici, Ischia, Mt. Vesuvius, Aeolian Islands, Tuscany and Sardinia) and from subduction zones worldwide (Kamchatka, Lesser Antilles, Indonesia and Central Andean ignimbrites). Distinct trends and sources are recognized: (1) serpentinized mantle (Kamchatka), (2) sediment-enrichment in the mantle source (Indonesia, Vesuvius), (3) magma assimilation by old radiogenic continental crust (Alban Hills, Tuscany, Ischia), (4) assimilation by mafic crust (Andes). Sr-O-isotope values of Campi Flegrei and Vesuvius magmas fall on the same vertical trend in Sr-O isotope space that deviates profoundly from all other subduction-related magmas. This indicates that magmas are derived from (a) a mantle source variably modified by pelagic sediments (as for Vesuvius) that were later (b) assimilated by highly δ18O-enriched crustal material that did not further significantly affect the Sr-isotope composition. From Sr-O isotope relations, this crustal signal could be introduced through interaction with Mesozoic limestone and/or low-T altered volcanic material from previous volcanic activity in the Campi Flegrei caldera.

  19. 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. 

  20. The Active Solid Earth

    NASA Astrophysics Data System (ADS)

    Ebinger, Cynthia

    2016-04-01

    Dynamic processes in Earth's crust, mantle and core shape Earth's surface and magnetic field over time scales of seconds to millennia, and even longer time scales as recorded in the ca. 4 Ga rock record. Our focus is the earthquake-volcano deformation cycles that occur over human time scales, and their comparison with time-averaged deformation studies, with emphasis on mantle plume provinces where magma and volatile release and vertical tectonics are readily detectable. Active deformation processes at continental and oceanic rift and back arc zones provide critical constraints on mantle dynamics, the role of fluids (volatiles, magma, water), and plate rheology. For example, recent studies of the East African rift zone, which formed above one of Earth's largest mantle upwellings reveal that magma production and volatile release rates are comparable to those of magmatic arcs, the archetypal zones of continental crustal creation. Finite-length faults achieve some plate deformation, but magma intrusion in the form of dikes accommodates extension in continental, back-arc, and oceanic rifts, and intrusion as sills causes permanent uplift that modulates the local time-space scales of earthquakes and volcanoes. Volatile release from magma intrusion may reduce fault friction and permeability, facilitating aseismic slip and creating magma pathways. We explore the implications of active deformation studies to models of the time-averaged structure of plume and extensional provinces in continental and oceanic plate settings.

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

    SciTech Connect

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

    1998-10-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

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

    USGS Publications Warehouse

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

    2015-01-01

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

  4. Collision zone magmatism aids continental crustal growth

    NASA Astrophysics Data System (ADS)

    Savov, Ivan; Meliksetian, Khachatur; Ralf, Halama; Gevorg, Navasardian; Chuck, Connor; Massimo, D'Antonio; Samuele, Agostini; Osamu, Ishizuka; Sergei, Karapetian; Arkadi, Karakhanian

    2014-05-01

    The continental crust has a broadly andesitic bulk composition and is predominantly generated at convergent margins. However, estimates of the bulk composition of oceanic arcs indicate a bulk composition closer to basalt than to andesite. Hence, reworking processes that transform basaltic island arc crust into andesitic continental crust are essential[1] and explaining growth of andesitic continental crust via accretion of arc crustal fragments remains problematic. Recent studies of magmatism in the Great Tibetan Plateau[2], as site of multiple and still active continent-continent collisions, have proposed that andesitic CC is generated via amalgamation of large volumes of collision-related felsic magmas generated by melting of hydrated oceanic crust with mantle geochemical signatures. We aim to test this hypothesis by evaluating geochemical data from the volcanically and tectonically active Lesser Caucasus region (Armenia, Azerbaijan, Georgia and E. Turkey), as the only other region where active continent-continent collision takes place. We will benefit from the newly compiled volcano-tectonic database of collision-related volcanic and plutonic rocks of Armenia that is comparable in quality and detail to the one available on Tibet. Our dataset combines several detailed studies from the large Aragats shield volcano[3] and associated monogenetic volcanic fields (near the capital city of Yerevan), as well as > 500 Quaternary to Holocene volcanoes from Gegham, Vardenis and Syunik volcanic highlands (toward Armenia-Nagorno-Karabakh-Azerbaijan-Iran border). The Armenian collision-related magmatism is diverse in volume, composition, eruption style and volatile contents. Interestingly, the majority of exposed volcanics are andesitic in composition. Nearly all collision-related volcanic rocks, even the highly differentiated dacite and rhyolite ignimbrites, have elevated Sr concentrations and 87Sr/86Sr and 143Nd/144Nd ratios varying only little (average ~ 0.7043 and ~ 0

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

    NASA Astrophysics Data System (ADS)

    Schreiber, Ulrich; Berberich, Gabriele

    2013-04-01

    . 2002). Our research findings suggest that due to the slow movement rates of active tectonic faults, an estimated 18 km³ magma chamber within the brittle fracture section of the earth's crust beneath the Laacher See (v. d. Bogaard & Schmincke 1984) cannot be confirmed yet. Another discrepancy is given by a comparison of modeling of caldera evolution (Acocella 2007) with the Laacher See Caldera formation. The Laacher See caldera has a volume of 0.5 km³ with regard to the pre-eruptive surface (Viereck & v.d. Bogaard 1986). According to v. d. Bogaard & Schmincke (1984) a volume of 6.3 km³ dry rock equivalent of lava and basic rock was erupted. This magnitude is contradictory to the calculated 0.5 km³ volume of the Laacher See caldera. A volume compensation of approx. 6 km³ which could have prevented a further subsidence of the magma chamber cannot be a scientific possible explanation. This hypothesis is strengthened by performed sonar recordings of the post-eruptive Laacher See sediment layers which do not show any displacements that might indicate a doming caused by magma. Estimations of the erupted tephra volume provided the basis for the calculation of the size of the Laacher See magma chamber (v.d. Bogaard 1983), but there is no statistical significant data set with regard to spatial distribution of the erupted tephra amount. Our findings show an overestimation of the tephra thickness in published isopach maps of the Westerwald. Therefore, an order of magnitude smaller magma chamber stretched over a longer vertical crustal section can help to better match the given tectonic movement rates and the size of the caldera. To estimate the future development of the East Eifel volcanic field, a good knowledge of the active tectonics is an absolute prerequisite. Along the "Laacher See Strike-slip Fault", an area of intensive micro-seismicity and a new seismically active zone with local magnitudes up to 4 has developed over the last 40 years (Hinzen 2003). In the last

  6. 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

  7. Subterranean fragmentation of magma during conduit initiation and evolution in the shallow plumbing system of the small-volume Jagged Rocks volcanoes (Hopi Buttes Volcanic Field, Arizona, USA)

    NASA Astrophysics Data System (ADS)

    Re, Giuseppe; White, James D. L.; Muirhead, James D.; Ort, Michael H.

    2016-08-01

    Monogenetic volcanoes have limited magma supply and lack long-lived sustained magma plumbing systems. They erupt once, often from multiple vents and sometimes over several years, and are rarely or never re-activated. Eruptive behavior is very sensitive to physical processes (e.g., volatile exsolution, magma-water interaction) occurring in the later stages of magma ascent at shallow crustal depths (<1 km), which yield a spectrum of eruptive styles including weak to moderate explosive activity, violent phreatomagmatism, and lava effusion. Jagged Rocks Complex in the late Miocene Hopi Buttes Volcanic field (Arizona, USA) exposes the frozen remnants of the feeding systems for one or a few monogenetic volcanoes. It provides information on how a shallow magmatic plumbing system evolved within a stable non-marine sedimentary basin, and the processes by which magma flowing through dikes fragmented and conduits were formed. We have identified three main types of fragmental deposits, (1) buds (which emerge from dikes), (2) pyroclastic massifs, and (3) diatremes; these represent three different styles and intensities of shallow-depth magma fragmentation. They may develop successively and at different sites during the evolution of a monogenetic volcano. The deposits consist of a mixture of pyroclasts with varying degrees of welding and country-rock debris in various proportions. Pyroclasts are commonly welded together, but also reveal in places features consistent with phreatomagmatism, such as blocky shapes, dense groundmasses, and composite clasts (loaded and cored). The extent of fragmentation and the formation of subterranean open space controlled the nature of the particles and the architecture and geometry of these conduit structures and their deposits.

  8. 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.

  9. Geochronology and magma sources of Elbrus volcano (Greater Caucasus, Russia)

    NASA Astrophysics Data System (ADS)

    Lebedev, Vladimir

    2010-05-01

    Elbrus volcano (5642m), the largest Quaternary volcano in the European part of the Russia, is situated within the central part of Greater Caucasus mountain system at the watershed of Black and Caspian seas. Complex isotope-geochronological studies showed that the Elbrus volcano experienced long (approximately 200-250 thousands years) discrete evolution, with protracted periods of igneous quiescence (approximately 50 ka) between large-scale eruptions. The volcanic activity of Elbrus is subdivided into three phases: Middle-Neopleistocene (225-170 ka), Late Neopleistocene (110-70 ka), and Late Neopleistocene-Holocene (less than 35 ka). No eruptions presumably occurred during 'quiescence' periods, while the volcano was dormant or revealed only insignificant explosive eruptions and postmagmatic activity. Volcanic rocks of the Elbrus volcano are represented by biotite-hypersthene-plagioclase calc-alcaline dacites (65.2-70.4% SiO2, and 6.4-7.9% K2O+Na2O at 2.7-3.9% K2O). Petrogeochemical and isotope-geochemical signatures of Elbrus dacitic lavas (87Sr/86Sr - 0.70535-0.70636, Eps(Nd) from +0.8 to -2.3, 206Pb/204Pb - 18.631-18.671, 207Pb/204Pb - 15.649-15.660, and 208Pb/204Pb = 38.811-38.847) point to their mantle-crustal origin. It was found that hybrid parental magmas of the volcano were formed due to mixing and/or contamination of deep-seated mantle melts by Paleozoic upper crustal material of the Greater Caucasus. The temporal evolution of isotope characteristics for lavas of Elbrus volcano is well described by a Sr-Nd mixing hyperbole between mantle source of 'Common'-type and estimated average composition of the Paleozoic upper crust of the Greater Caucasus. It was shown that, with time, the proportions of mantle material in the parental magmas of Elbrus gently increased: from ~60% at the Middle-Neopleistocene phase of activity to ~80% at the Late Neopleistocene-Holocene phase, which indicates an increase of the activity of deep-seated source at decreasing input of

  10. Magma energy: a feasible alternative

    SciTech Connect

    Colp, J.L.

    1980-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1987-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  14. NASA plan for international crustal dynamics studies

    NASA Technical Reports Server (NTRS)

    1979-01-01

    The international activities being planned as part of the NASA geodynamics program are described. Methods of studying the Earth's crustal movements and deformation characteristics are discussed. The significance of the eventual formalations of earthquake predictions methods is also discussed.

  15. 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.

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

    USGS Publications Warehouse

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

    1993-01-01

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

  17. 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

  18. Bimodal magmatism produced by progressively inhibited crustal assimilation.

    PubMed

    Meade, F C; Troll, V R; Ellam, R M; Freda, C; Font, L; Donaldson, C H; Klonowska, I

    2014-01-01

    The origin of bimodal (mafic-felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose 'progressively inhibited crustal assimilation' (PICA) as a major cause of bimodality in continental volcanism. PMID:24947142

  19. Bimodal magmatism produced by progressively inhibited crustal assimilation

    NASA Astrophysics Data System (ADS)

    Meade, F. C.; Troll, V. R.; Ellam, R. M.; Freda, C.; Font, L.; Donaldson, C. H.; Klonowska, I.

    2014-06-01

    The origin of bimodal (mafic-felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose ‘progressively inhibited crustal assimilation’ (PICA) as a major cause of bimodality in continental volcanism.

  20. The three stages of magma ocean cooling

    NASA Technical Reports Server (NTRS)

    Warren, Paul H.

    1992-01-01

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

  1. Relative Roles of Source Composition, Fractional Crystallization and Crustal Contamination in the Petrogenesis of Andean Volcanic Rocks

    NASA Astrophysics Data System (ADS)

    Thorpe, R. S.; Francis, P. W.; O'Callaghan, L.

    1984-04-01

    There are well established differences in the chemical and isotopic characteristics of the calc-alkaline basalt--andesite--decite--rhyolite association of the northern (n.v.z.), central (c.v.z.) and southern volcanic zones (s.v.z.) of the South American Andes. Volcanic rocks of the alkaline basalt--trachyte association occur within and to the east of these active volcanic zones. The chemical and isotopic characteristics of the n.v.z. basaltic andesites and andesites and the s.v.z. basalts, basaltic andesites and andesites are consistent with derivation by fractional crystallization of basaltic parent magmas formed by partial melting of the asthenospheric mantle wedge containing components from subducted oceanic lithosphere. Conversely, the alkaline lavas are derived from basaltic parent magmas formed from mantle of `within-plate' character. Recent basaltic andesites from the Cerro Galan volcanic centre to the SE of the c.v.z. are derived from mantle containing both subduction zone and within-plate components, and have experienced assimilation and fractional crystallization (a.f.c.) during uprise through the continental crust. The c.v.z. basaltic andesites are derived from mantle containing subduction-zone components, probably accompanied by a.f.c. within the continental crust. Some c.v.z. lavas and pyroclastic rocks show petrological and geochemical evidence for magma mixing. The petrogenesis of the c.v.z. lavas is therefore a complex process in which magmas derived from heterogeneous mantle experience assimilation, fractional crystallization, and magma mixing during uprise through the continental crust. Active Andean volcanoes of the calc-alkaline basalt--andesite--dacite rhyolite association occur within a northern (n.v.z.), central (c.v.z.) and southern volcanic zone (s.v.z.) (figure 9). Alkaline volcanic rocks occur within and to the east of these zones. The n.v.z. and s.v.z. lavas have chemical and isotope characteristics consistent with an origin by

  2. Linking rapid magma reservoir assembly and eruption trigger mechanisms at evolved Yellowstone-type supervolcanoes

    USGS Publications Warehouse

    Wotzlaw, J.F.; Bindeman, I.N.; Watts, Kathryn E.; Schmitt, A.K.; Caricchi, L.; Schaltegger, U.

    2014-01-01

    The geological record contains evidence of volcanic eruptions that were as much as two orders of magnitude larger than the most voluminous eruption experienced by modern civilizations, the A.D. 1815 Tambora (Indonesia) eruption. Perhaps nowhere on Earth are deposits of such supereruptions more prominent than in the Snake River Plain–Yellowstone Plateau (SRP-YP) volcanic province (northwest United States). While magmatic activity at Yellowstone is still ongoing, the Heise volcanic field in eastern Idaho represents the youngest complete caldera cycle in the SRP-YP, and thus is particularly instructive for current and future volcanic activity at Yellowstone. The Heise caldera cycle culminated 4.5 Ma ago in the eruption of the ∼1800 km3 Kilgore Tuff. Accessory zircons in the Kilgore Tuff display significant intercrystalline and intracrystalline oxygen isotopic heterogeneity, and the vast majority are 18O depleted. This suggests that zircons crystallized from isotopically distinct magma batches that were generated by remelting of subcaldera silicic rocks previously altered by low-δ18O meteoric-hydrothermal fluids. Prior to eruption these magma batches were assembled and homogenized into a single voluminous reservoir. U-Pb geochronology of isotopically diverse zircons using chemical abrasion–isotope dilution–thermal ionization mass spectrometry yielded indistinguishable crystallization ages with a weighted mean 206Pb/238U date of 4.4876 ± 0.0023 Ma (MSWD = 1.5; n = 24). These zircon crystallization ages are also indistinguishable from the sanidine 40Ar/39Ar dates, and thus zircons crystallized close to eruption. This requires that shallow crustal melting, assembly of isolated batches into a supervolcanic magma reservoir, homogenization, and eruption occurred extremely rapidly, within the resolution of our geochronology (103–104 yr). The crystal-scale image of the reservoir configuration, with several isolated magma batches, is very similar to the

  3. Near Surface Controls on Magma Fragmentation and Ash Generation during Contemporaneous Magmatic and Phreatomagmatic Activity: Insights from the 2500BC Hverfjall Fires, Iceland

    NASA Astrophysics Data System (ADS)

    Liu, E. J.; Cashman, K. V.; Rust, A.; Hoskuldsson, A.

    2014-12-01

    Magma-water interaction (MWI) influences both eruption style and resulting pyroclast grain size (and transport properties). We explore both the mechanisms and consequences of MWI by examining tephra deposits from the 2500BC Hverfjall Fires within the Krafla fissure system, northern Iceland. Here, contemporaneous fissure vents spanned sub-aerial to shallow lacustrine environments, causing both dry magmatic and variably wet phreatomagmatic activity. As all vents shared the same initial magma composition, the range of pyroclastic (ash fall, wet surge, dry surge and scoria) deposits provides an excellent sample suite to explore fragmentation mechanisms under different near-surface conditions. Sample analysis of the opening phreatomagmatic phase shows that ash components of individual size fractions exhibit a linear increase [from 8% (1φ) to 77% (>4φ)] in the proportion of dense blocky fragments with decreasing size (Figure). The proportion of vesicular particles decreases concurrently, but shards comprise an increasing proportion of the vesicular size fraction [from 6% (1φ) to 70% (>4φ)]. Free crystals, lithic and microcrystalline grains are ~10% of all size classes. We compare these morphological data to (1) bubble size distributions (BSDs) and (2) the spatial distribution of preserved volatiles in matrix glass, which record the degassing history and pressure/rate of quenching, respectively. Measured BSDs for quenched Pele's tears within the opening phreatomagmatic ash deposit show a modal bubble diameter of 20-30 µm (by number) or 150-200 µm (by volume), comparable to those from Kilauea Iki fire fountains in Hawaii. Elevated dissolved sulphur concentrations (≤ 550 ppm) in phreatomagmatic ash compared to magmatic scoria (~180 ppm), however, suggests either faster quench rates and/or greater fragmentation depths. To discriminate between these alternatives, we analyse BSDs in ash from the magmatic phase, which requires determining the optimal particle size for

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  5. 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.

  6. 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

  7. 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.

  8. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  11. The crustal structure of the southern Argentine margin

    NASA Astrophysics Data System (ADS)

    Becker, Katharina; Franke, Dieter; Schnabel, Michael; Schreckenberger, Bernd; Heyde, Ingo; Krawczyk, Charlotte M.

    2012-06-01

    Multichannel reflection seismic profiles, combined with gravimetric and magnetic data provide insight into the crustal structure of the southernmost Argentine margin, at the transition from a rifted to a transform margin and outline the extent of the North Falkland Graben. Based on these data, we establish a regional stratigraphic model for the post-rift sediments, comprising six marker horizons with a new formation in the Barremian/Lower Cretaceous. Our observations support that a N-S trending subsidiary branch of the North Falkland Graben continues along the continental shelf and slope to the Argentine basin. During the rift phase, a wide shelf area was affected by the E-W extension, subsequently forming the North Falkland Graben and the subsidiary branch along which finally breakup occurred. We propose the division of the margin in two segments: a N-S trending rifted margin and an E-W trending transform margin. This is further underpinned by crustal scale gravity modelling. Three different tectono-dynamic processes shaped the study area. (1) The Triassic/Early Jurassic extensional phase resulting in the formation of the North Falkland Graben and additional narrower rift grabens ended synchronously with the breakup of the South Atlantic in the early Valanginian. (2) Extensional phase related to the opening of the South Atlantic. (3) The transform margin was active in the study area from about Hauterivian times and activity lasted until late Cretaceous/early Cenozoic. Both, the rifted margin and the transform margin are magma-poor. Very limited structures may have a volcanic origin but are suggested to be post-rift. The oceanic crust was found to be unusually thin, indicating a deficit in magma supply during formation. These findings in combination with the proposed breakup age in the early Valanginian that considerably predates the formation of the Paraná-Etendeka continental flood basalt provinces in Brazil and Namibia question the influence of the Tristan da

  12. Petrological cannibalism: the chemical and textural consequences of incremental magma body growth

    NASA Astrophysics Data System (ADS)

    Cashman, Kathy; Blundy, Jon

    2013-09-01

    fluxing the reservoir with CO2-rich vapors that are either released from deeper in the system or transported with the recharge magma. Temperature fluctuations of 20-40 °C, on the other hand, are an inevitable consequence of incremental, or pulsed, assembly of crustal magma bodies wherein each pulse interacts with ancestral, stored magmas. We venture that this "petrological cannibalism" accounts for much of the plagioclase zoning and textural complexity seen not only at Mount St. Helens but also at arc magmas generally. More broadly we suggest that the magma reservoir below Mount St. Helens is dominated by crystal mush and fed by frequent inputs of hotter, but compositionally similar, magma, coupled with episodes of magma ascent from one storage region to another. This view both accords with other independent constraints on the subvolcanic system at Mount St. Helens and supports an emerging view of many active magmatic systems as dominantly super-solidus, rather than subliquidus, bodies.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  14. Tectonic activity as a significant source of crustal tetrafluoromethane emissions to the atmosphere: observations in groundwaters along the San Andreas Fault

    USGS Publications Warehouse

    Deeds, Daniel A.; Kulongoski, Justin T.; Muhle, Jens; Weiss, Ray F.

    2015-01-01

    Tetrafluoromethane (CF4) concentrations were measured in 14 groundwater samples from the Cuyama Valley, Mil Potrero and Cuddy Valley aquifers along the Big Bend section of the San Andreas Fault System (SAFS) in California to assess whether tectonic activity in this region is a significant source of crustal CF4 to the atmosphere. Dissolved CF4 concentrations in all groundwater samples but one were elevated with respect to estimated recharge concentrations including entrainment of excess air during recharge (CreCre; ∼30 fmol kg−1 H2O), indicating subsurface addition of CF4 to these groundwaters. Groundwaters in the Cuyama Valley contain small CF4 excesses (0.1–9 times CreCre), which may be attributed to an in situ release from weathering and a minor addition of deep crustal CF4 introduced to the shallow groundwater through nearby faults. CF4 excesses in groundwaters within 200 m of the SAFS are larger (10–980 times CreCre) and indicate the presence of a deep crustal flux of CF4 that is likely associated with the physical alteration of silicate minerals in the shear zone of the SAFS. Extrapolating CF4 flux rates observed in this study to the full extent of the SAFS (1300 km × 20–100 km) suggests that the SAFS potentially emits (0.3–1)×10−1 kg(0.3–1)×10−1 kg CF4 yr−1 to the Earth's surface. For comparison, the chemical weathering of ∼7.5×104 km2∼7.5×104 km2 of granitic rock in California is estimated to release (0.019–3.2)×10−1 kg(0.019–3.2)×10−1 kg CF4 yr−1. Tectonic activity is likely an important, and potentially the dominant, driver of natural emissions of CF4 to the atmosphere. Variations in preindustrial atmospheric CF4 as observed in paleo-archives such as ice cores may therefore represent changes in both continental weathering and tectonic activity, including changes driven by variations in continental ice cover during glacial–interglacial transitions.

  15. The Role of Magma Mixing in Creating Magmatic Diversity

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  16. Geology of magma systems: background and review

    SciTech Connect

    Peterfreund, A.R.

    1981-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  18. Seismic constraints on the nature of lower crustal reflectors beneath the extending Southern Transition Zone of the Colorado Plateau, Arizona

    USGS Publications Warehouse

    Parsons, Thomas E.; Howie, John M.; Thompson, George A.

    1992-01-01

    We determine the reflection polarity and exploit variations in P and S wave reflectivity and P wave amplitude versus offset (AVO) to constrain the origin of lower crustal reflectivity observed on new three-component seismic data recorded across the structural transition of the Colorado Plateau. The near vertical incidence reflection data were collected by Stanford University in 1989 as part of the U.S. Geological Survey Pacific to Arizona Crustal Experiment that traversed the Arizona Transition Zone of the Colorado Plateau. The results of independent waveform modeling methods are consistent with much of the lower crustal reflectivity resulting from thin, high-impedance layers. The reflection polarity of the cleanest lower crustal events is positive, which implies that these reflections result from high-velocity contrasts, and the waveform character indicates that the reflectors are probably layers less than or approximately equal to 200 m thick. The lower crustal events are generally less reflective to incident S waves than to P waves, which agrees with the predicted behavior of high-velocity mafic layering. Analysis of the P wave AVO character of lower crustal reflections demonstrates that the events maintain a constant amplitude with offset, which is most consistent with a mafic-layering model. One exception is a high-amplitude (10 dB above background) event near the base of lower crustal reflectivity which abruptly decreases in amplitude at increasing offsets. The event has a pronounced S wave response, which along with its negative AVO trend is a possible indication of the presence of fluids in the lower crust. The Arizona Transition Zone is an active but weakly extended province, which causes us to discard models of lower crustal layering resulting from shearing because of the high degree of strain required to create such layers. Instead, we favor horizontal basaltic intrusions as the primary origin of high-impedance reflectors based on (1) The fact that

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

    NASA Astrophysics Data System (ADS)

    Black, Benjamin A.; Manga, Michael

    2016-06-01

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

  20. Crustal accretion and deformation processes above the Galápagos hotspot

    NASA Astrophysics Data System (ADS)

    Ebinger, C. J.; Davidge, L.; Ruiz, M. C.; Bagnardi, M.; Amelung, F.; Tepp, G.; Cote, D. M.

    2012-12-01

    Ocean island volcanoes initiate and grow as plates move over mantle upwellings, producing chains of volcanoes with long-lived magmatic plumbing systems that store mantle melts. Pressure changes that accompany the arrival of new batches of melt into the magma chamber, or the release of magma to surface eruptions and/or dikes, cause surface deformation, and changes in state-of-stress in the overlying rocks. Nowhere are these surface variations more pronounced than along the chain of 7 active volcanoes in the western Galápagos, each of which has a large, deep summit caldera. Our aim is to evaluate the relative importance of magma intrusion, circumferential and intra-caldera faulting, radial dike intrusions, and sill emplacement to volcano deformation during inter-eruption periods. The SIGNET 2009-11 seismic array on Isabela Island, Galápagos recorded nearly 2000 local earthquakes that provide constraints on magma storage and fault systems accommodating the rapid volcano inflation. Seismicity largely is restricted to the uppermost 2 km of Sierra Negra, excepting the pipe-like zone beneath the eastern side of the caldera; depths of earthquakes on Alcedo and the shallow platform outside the array are poorly constrained. Seismicity is localized around the caldera ring fault system and the sinuous ridge within the caldera. The orientation of reverse fault mechanisms suggest that the intra-caldera ridge formed through compression of the > 2 km-thick lid above the magma chamber, consistent with slip along inward-dipping ring faults. Swarms of seismicity coincide with aligned chains of cinder cones and vents between Sierra Negra and Cerro Azul, between Sierra Negra and Alcedo, between Sierra Negra and Santa Cruz volcanoes, and along the southern flank of Isabela Island, suggesting ongoing dike intrusion and/or degassing. Migrating swarms of seismicity initiating in the caldera may mark small volume radial dike intrusions. Deformation is not restricted to the ring fault

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

    NASA Astrophysics Data System (ADS)

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

    1985-09-01

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

  2. 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.

  3. Is the Valles caldera entering a new cycle of activity?

    SciTech Connect

    Wolff, J.A.; Gardner, J.N.

    1995-05-01

    The Valles caldera formed during two major rhyolitic ignimbrite eruptive episodes (the Bandelier Tuff) at 1.61 and 1.22 Ma, after some 12 m.y. of activity in the Jemez Mountains volcanic field, New Mexico. Several subsequent eruptions between 1.22 and 0.52 Ma produced dominantly high-silica rhyolite lava domes and tephras within the caldera. These were followed by a dormancy of 0.46 m.y. prior to the most recent intracaldera activity, the longest hiatus since the inception of the Bandelier magma system at approximately 1.8 Ma. The youngest volcanic activity at approximately 60 ka produced the SW moat rhyolites, a series of lavas and tuffs that display abundant petrologic evidence of being newly generated melts. Petrographic textures conform closely to published predictions for silicic magmas generated by intrusion of basaltic magma into continental crust. The Valles caldera may currently be the site of renewed silicic magma generation, induced by intrusion of mafic magma at depth. Recent seismic investigations revealed the presence of a large low-velocity anomaly in the lower crust beneath the caldera. The generally aseismic character of the caldera, despite abundant regional seismicity, may be attributed to a heated crustal column, the local effect of 13 m.y. of magmatism and emplacement of mid-crustal plutons. 24 refs., 3 figs.

  4. From Magma Oceans to Plates: A Habitability Transition in the Earth's Early History

    NASA Astrophysics Data System (ADS)

    Olson, P.

    2014-04-01

    Scenarios for Earth's early history link the development and maintenance of habitable surface conditions to the transition from a dynamical regime dominated by near-surface magma oceans to one dominated by mobile plate tectonics. Plate tectonics is considered necessary for maintaining a vigorous rock cycle that buffers atmospheric CO2 with negative feedbacks involving balances between crustal uplift, erosion, weathering, and volcanism. Heat transfer through the mantle by plate tectonics also promotes dynamo activity in the core, thereby generating a long-lived magnetic field to inhibit gas escape from the atmosphere and provide a radiation shield for the near-surface environment. In this talk I review various hypotheses about the thermal evolution of the Earth, focusing on the implications for early Earth history of the transition from magma oceans and magmatic heat transport to plate tectonics and mantle heat transport by solid-state flow. In addition to summarizing some of the observational constraints and the physical controls on the timing of this transition, I review current ideas on the bifurcation from mobile plates to single plate (stagnant lid) forms of mantle convection, showing how this bifurcation can lead to a lack of habitability in single-plate terrestrial planets such as Venus.

  5. Deep-crustal seismicity in volcanic regions by fluid-enhanced wallrock embrittlement

    NASA Astrophysics Data System (ADS)

    Sisson, T. W.; Power, J. A.

    2013-12-01

    Spatial association of deep long-period (DLP) seismicity with volcanoes [1,2], spectral frequencies resembling shallow events attributed to fluid motions, and temporal associations with some eruptions, prompt the interpretation that DLPs mark the locations of magma, or magma with percolating exsolved vapor, in the mid and lower crust. However, various factors are more consistent with the events taking place in the walls surrounding the hot aseismic cores of deep magmatic systems, due to expelled magmatic fluids elevating pore pressures and reducing wall rock brittle strengths, or possibly in largely solidified peripheral intrusions embrittled by interstitial residual melt. First, although exceptions are known, deep seismic events are typically displaced to one or more sides of the locus of volcanism. Compilation of >1000 mid to deep crustal DLP and volcano tectonic events from the Aleutian arc, plotted as radial distance from the respective volcanic locus vs. depth, shows a minimum of events beneath the volcanic loci, encased in a downward broadening halo of events, typically displaced about 6 km to the sides of the volcanic locus. Lateral offsets of deep events are also well established for volcanoes of the Washington Cascades [3], averaging 7.5×4.5(1σ) km, and for some centers in California [1]. Second, while mafic parental magmas can have high concentrations of H2O (CO2 concentrations are comparatively negligible), H2O is highly soluble at mid to lower crustal pressures and will not exsolve appreciably until advanced crystallization and second boiling. Deep vapor exsolution will proceed gradually, delayed well after replenishment events, due to slow cooling and crystallization in the hot deep crust. Exsolution dominantly at high crystallinities argues against bubbles moving through largely liquid replenishing magmas as a major cause of DLPs. Third, isotherms around the mid to deep crustal portions of magmatic systems will propagate outward with time1/2 due to

  6. Crustal processes of the Mid-Ocean Ridge

    USGS Publications Warehouse

    Ballard, Richard D.; Craig, H.; Edmond, J.; Einaudi, M.; Holcomb, R.; Holland, H.D.; Hopson, C.A.; Luyendyk, B.P.; Macdonald, K.; Morton, J.; Orcutt, J.; Sleep, N.

    1981-01-01

    Independent geological and geophysical investigations of the Mid-Ocean Ridge system have begun to focus on the nature of the magma chamber system underlying its central axis. Thermal models predict the existence of a steady-state chamber beneath a thin crustal lid ranging in thickness from 2 to 13 kilometers. The only aspect of the system that these models fail to account for is the extremely slow spreading rates. Seismological studies reveal the existence of a low-velocity zone beneath segments of the East Pacific Rise, which is thought to correspond to a chamber system having a half-width of approximately 5 to 10 kilometers. These estimates compare favorably with those derived separately through petrological investigations of deep-sea drilling results, various sampling programs, and field and laboratory studies of ophiolites. The chamber is thought to be wing-shaped and to remain continuously open; it is thought to be fed from the center while simultaneously solidifying at the sides as spreading carries the two halves apart. Progressive fractionation occurs by crystal settling coupled with repeated replenishment and magma mixing in an open steady-state system. Near-bottom studies reveal that the zone of extrusion above the chamber is narrow, but its eruptive history is cyclic in nature, in conflict with the predictions of a steady-state model. On-bottom gravity data at 21 ??N on the East Pacific Rise reveal a negative gravity anomaly that may be related to the uppermost part of the chamber. The anomaly is only 2 kilometers wide and 1 kilometer below the sea floor. This feature may be associated with a short-term upper magma reservoir. The cyclic volcanic activity is directly related to the active phase of hydrothermal circulation responsible for the observed negative thermal anomaly. The volume of water associated with this circulation is equal to the entire ocean volume passing through the accretion zone approximately every 8 million years. This is about 0

  7. Crustal processes of the mid-ocean ridge.

    PubMed

    1981-07-01

    Independent geological and geophysical investigations of the Mid-Ocean Ridge system have begun to focus on the nature of the magma chamber system underlying its central axis. Thermal models predict the existence of a steady-state chamber beneath a thin crustal lid ranging in thickness from 2 to 13 kilometers. The only aspect of the system that these models fail to account for is the extremely slow spreading rates. Seismological studies reveal the existence of a low-velocity zone beneath segments of the East Pacific Rise, which is thought to correspond to a chamber system having a half-width of approximately 5 to 10 kilometers. These estimates compare favorably with those derived separately through petrological investigations of deep-sea drilling results, various sampling programs, and field and laboratory studies of ophiolites. The chamber is thought to be wing-shaped and to remain continuously open; it is thought to be fed from the center while simultaneously solidifying at the sides as spreading carries the two halves apart. Progressive fractionation occurs by crystal settling coupled with repeated replenishment and magma mixing in an open steady-state system. Near-bottom studies reveal that the zone of extrusion above the chamber is narrow, but its eruptive history is cyclic in nature, in conflict with the predictions of a steady-state model. On-bottom gravity data at 21 degrees N on the East Pacific Rise reveal a negative gravity anomaly that may be related to the uppermost part of the chamber. The anomaly is only 2 kilometers wide and 1 kilometer below the sea floor. This feature may be associated with a short-term upper magma reservoir. The cyclic volcanic activity is directly related to the active phase of hydrothermal circulation responsible for the observed negative thermal anomaly. The volume of water associated with this circulation is equal to the entire ocean volume passing through the accretion zone approximately every 8 million years. This is about 0

  8. Three-dimensional crustal structure in the Southern Alps region of New Zealand from inversion of local earthquake and active source data

    NASA Astrophysics Data System (ADS)

    Eberhart-Phillips, Donna; Bannister, Stephen

    2002-10-01

    P and S-P arrival time data from 311 earthquakes and several thousand offshore and onshore shots have been used in simultaneous inversion for hypocenters, three-dimensional (3-D) Vp and Vp/Vs models in the Southern Alps region, New Zealand. The combined data result in a highly nonuniform ray path distribution, and linked nodes are used in sparsely sampled areas. Gravity data are used to improve the model below 20-km depth, where it is poorly sampled by local earthquakes. The crustal Vp from 5 to 25 km depth is fairly uniform, generally ranging from 5.5 to 6.5 km/s, typical of graywacke and schist. Active fault zones tend to be correlated with low-velocity zones. Where the Alpine fault is primarily strike slip, it is characterized by a vertical low-velocity zone, to at least 15-km depth. Where the fault is dipping and has a large dip-slip component, it is characterized by a large region of low velocity above and southeast of the fault, to at least 14-km depth, consistent with fluids and fracture density from active deformation. A large high-velocity, high-resistivity feature in the eastern Southern Alps may represent Mesozoic schist of higher metamorphic grade than its surroundings, which is relatively rigid and serves to both reduce deformation in the overlying basin and concentrate deformation in the adjoining low-velocity region. The imaged crustal root is deepest 80-km south of Mt. Cook and is asymmetric with a sharper gradient on the northwestern side. The approximate Moho shows regional variation, with 5-10 km thicker crust in Otago than Canterbury.

  9. Icelandic Volcanoes Geohazard Supersite and FUTUREVOLC: role of interferometric synthetic aperture radar to identify renewed unrest and track magma movement beneath the most active volcanoes in Iceland

    NASA Astrophysics Data System (ADS)

    Parks, Michelle; Dumont, Stéphanie; Spaans, Karsten; Drouin, Vincent; Sigmundsson, Freysteinn; Hooper, Andrew; Michalczewska, Karolina; Ófeigsson, Benedikt

    2014-05-01

    FUTUREVOLC is an integrated volcano monitoring project, funded by the European Commission (FP7) and led by the University of Iceland and the Icelandic Meteorological Office (IMO). The project is a European collaborative effort, comprising 26 partners, aimed at integrating ground based and satellite observations for improved monitoring and evaluation of volcanic hazards. Iceland has also recently been declared a Geohazard Supersite by the Committee on Earth Observation Satellites, based on its propensity for relatively frequent eruptions and their potentially hazardous, long ranging effects. Generating a long-term time series of ground displacements is key to gaining a better understanding of sub-volcanic processes, including the detection of new melt and migration of magma within the crust. The focus of the FUTUREVOLC deformation team is to generate and interpret an extended time series of high resolution deformation measurements derived from InSAR observations, in the vicinity of the four most active volcanoes in Iceland: Grímsvötn, Katla, Hekla and Bárdarbunga. A comprehensive network of continuous deformation monitoring equipment, led by IMO and collaborators, is already deployed at these volcanoes, including GPS, tilt and borehole strainmeters. InSAR observations are complementary to field based measurements and their high spatial resolution assists in resolving the geometry and location of the source of the deformation. InSAR and tilt measurements at Hekla indicate renewed melt supply to a sub-volcanic reservoir after the last eruption in 2000. Recent deformation studies utilising data spanning this eruption, have provided insight into the shallow plumbing system which may explain the large reduction in eruption repose interval following the 1970 eruption. Although InSAR and GPS observations at Katla volcano (between 2001 and 2009) suggest no indication of magma induced deformation outside the ice-cap, it is possible that a small flood at Mýrdalsjökull in

  10. Continental crustal composition and lower crustal models

    NASA Technical Reports Server (NTRS)

    Taylor, S. R.

    1983-01-01

    The composition of the upper crust is well established as being close to that of granodiorite. The upper crustal composition is reflected in the uniform REE abundances in shales which represent an homogenization of the various REE patterns. This composition can only persist to depths of 10-15 km, for heat flow and geochemical balance reasons. The composition of the total crust is model dependent. One constraint is that it should be capable of generating the upper granodioritic (S.L.) crust by partial melting within the crust. This composition is based on the andesite model, which assumes that the total crust has grown by accretion of island arc material. A representation of the growth rate of the continental crust is shown. The composition of the lower crust, which comprises 60-80% of the continental crust, remains a major unknown factor for models of terrestrial crustal evolution. Two approaches are used to model the lower crust.

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  12. Crustal recycling by subduction erosion in the central Mexican Volcanic Belt

    NASA Astrophysics Data System (ADS)

    Straub, Susanne M.; Gómez-Tuena, Arturo; Bindeman, Ilya N.; Bolge, Louise L.; Brandl, Philipp A.; Espinasa-Perena, Ramón; Solari, Luigi; Stuart, Finlay M.; Vannucchi, Paola; Zellmer, Georg F.

    2015-10-01

    Recycling of upper plate crust in subduction zones, or 'subduction erosion', is a major mechanism of crustal destruction at convergent margins. However, assessing the impact of eroded crust on arc magmas is difficult owing to the compositional similarity between the eroded crust, trench sediment and arc crustal basement that may all contribute to arc magma formation. Here we compare Sr-Nd-Pb-Hf and trace element data of crustal input material to Sr-Nd-Pb-Hf-He-O isotope chemistry of a well-characterized series of olivine-phyric, high-Mg# basalts to dacites in the central Mexican Volcanic Belt (MVB). Basaltic to andesitic magmas crystallize high-Ni olivines that have high mantle-like 3He/4He = 7-8 Ra and high crustal δ18Omelt = +6.3-8.5‰ implying their host magmas to be near-primary melts from a mantle infiltrated by slab-derived crustal components. Remarkably, their Hf-Nd isotope and Nd/Hf trace element systematics rule out the trench sediment as the recycled crust end member, and imply that the coastal and offshore granodiorites are the dominant recycled crust component. Sr-Nd-Pb-Hf isotope modeling shows that the granodiorites control the highly to moderately incompatible elements in the calc-alkaline arc magmas, together with lesser additions of Pb- and Sr-rich fluids from subducted mid-oceanic ridge basalt (MORB)-type altered oceanic crust (AOC). Nd-Hf mass balance suggests that the granodiorite exceeds the flux of the trench sediment by at least 9-10 times, corresponding to a flux of ⩾79-88 km3/km/Myr into the subduction zone. At an estimated thickness of 1500-1700 m, the granodiorite may buoyantly rise as bulk 'slab diapirs' into the mantle melt region and impose its trace element signature (e.g., Th/La, Nb/Ta) on the prevalent calc-alkaline arc magmas. Deep slab melting and local recycling of other slab components such as oceanic seamounts further diversify the MVB magmas by producing rare, strongly fractionated high-La magmas and a minor population of

  13. Magmatic Differentiation Exposed on a Crustal Scale: A Field Example from Sierra Valle Fértil, Argentina

    NASA Astrophysics Data System (ADS)

    Banik, T. J.; Bergantz, G. W.; Bachmann, O.

    2010-12-01

    Two endmember models of magmatic arc assembly have been proposed: (1) a model where an upper-crust silicic magma body is fed by a lower-crust mafic source area with the mid-crust largely uninvolved, serving as a transport zone, and (2), a model of progressive and spatially continuous construction of arc basement that requires a few million years of thermal maturation before voluminous silicic magmas accumulate in the upper crust. One way to assess the generality of these two models is to look at crustal cross-sections. A particularly well-exposed example of such a cross-section is within the Ordovician Famatinian magmatic arc, a 1500 km long suite of magmatic units ranging from deep mafic to shallower intermediate plutonic bodies and silicic eruptive products. The deepest complete section of the arc is exposed in the Sierras Valle Fértil-La Huerta (SVF) with magmatic crystallization pressures ranging from greater than 8 kb to 4 kb. The SVF displays continuous outcrop that preserves the geological record of the magmatic role of igneous input, thermal prograde processes, and assimilation during arc crust assembly, thereby allowing us to construct a time-composition-volume evolution of the SVF arc section. Field observations—such as large, multiply intruded gabbro bodies interspersed with metapelitic septa, the absence of regional vertical structures, a sharp horizontal contact between mafic and felsic units, minor pelite assimilation, and no remelting of precursory mafic forerunners (amphibolites)—constrain possible processes of magmatic differentiation and preserve complex features indicative of emplacement during a common thermal prograde event. CA-ID-TIMS U-Pb geochronology from gabbroic, dioritic, and granodioritic rocks in the SVF yields crystallization ages from 471.47 Ma to 467.14 Ma. This 4.33 Myr time frame for the initial construction and evolution of arc crust is consistent with examples from continental and oceanic arcs that indicate an active

  14. Crustal-scale degassing and igneous mush re-organisation: a generic concept applied to episodic volcanism at the Soufrière Hills Volcano Montserrat

    NASA Astrophysics Data System (ADS)

    R Stephen J, S.; Cashman, K. V.

    2015-12-01

    A complete theory of episodic volcanism is lacking. Melt generation related to large scale tectonic processes is likely continuous but surface volcanic activity is typically episodic; for most volcanoes short-lived eruptions alternate with long periods of dormancy. Many models of volcanic activity and geophysical unrest are framed by a conceptual model of shallow magma chamber recharge, in which various phenomena are attributed to magma transport from deeper levels. While many aspects of volcanism are explained by this concept it has little explanatory power for key aspects of volcanism, including time scales of dormancy, eruption duration and eruption magnitude. Extensive trans-crustal igneous systems develop beneath active volcanoes in which much of the system is in a mushy state in which buoyancy-driven segregation of melt and magmatic fluid occurs to form layers, which are inherently unstable. We postulate that such systems are prone to destabilisation in which segregating layers amalgamate to form ephemeral magma chambers and in which melts and magmatic fluids decouple. Periods of dormancy relate to slow processes of segregation while short periods of volcanic unrest and eruption relate to episodic and rapid processes of destabilisation of the mush system. In this conceptual framework volatiles rather than magma recharge plays the key role in the dynamics of the shallow parts of the magmatic systems. Magma ascent during episodes of destabilisation does not itself cause pressurisation because melts and crystals are near incompressible, while volatile exsolution and decompression results in major pressure changes that can lead to unrest and eruption. These concepts are applied to the interpretation of stratigraphic, geochronological, geophysical, geochemical, petrological and volcanological data of volcanic activity at the Soufrière Hills Volcano (SHV), Montserrat.

  15. Magma feeding 2011 unrest at Turrialba volcano: insights from noble gas geochemistry

    NASA Astrophysics Data System (ADS)

    Di Piazza, A.; Barberi, F.; Carapezza, M.; Rizzo, A.; Romano, C.; De Astis, G.

    2013-12-01

    After almost 150 years of quiescence accompanied by weak fumarolic activity, Turrialba volcano (Costa Rica Central Cordillera) is showing signals of potential reawakening. Since 1996, the degassing has become more intense with the extension of the fumarolic field, the opening of new fractures and the occurrence of phreatic explosions (2010-2013). Here, we present a noble gas isotope investigation of crater fumaroles and of fluid inclusions hosted in olivines and pyroxenes from lavas and scoria erupted in the last 10 ka. The 3He/4He ratio of fluid inclusions from the most mafic eruptive products (SiO2=52.5wt% and MgO=6wt%) varies from 7.86 to 8.07 Ra, while that from andesite lavas varies from 7.03 to 7.18 Ra. The most evolved products (SiO2=63wt% and MgO=3wt%) display the lowest 3He/4He ratio (Rc/Ra=6.5). The He isotope values of the most mafic products are in the range of typical arc volcanoes (7-8 Ra), suggesting that contamination of the mantle wedge below the volcano by crustal He is negligible. On the other hand, the lowest values of 3He/4He ratio measured in the most silicic rocks of the series (dacitic) could be representative of a crustal contamination undergone by magma in the plumbing system of Turrialba. The fumaroles collected in 2007-2011 show an helium isotope composition of 7.50-7.96 Ra, which is well in the range of that measured in fluid inclusions from more mafic and recently erupted rocks. This implies that magma involved in the ongoing unrest phase and feeding the crater fumarolic field has petrological and geochemical features comparable to the basaltic-andesitic rocks analyzed in this study. In addition, long-term monitoring of He isotope composition carried out in the last years at Turrialba displays a progressive increase of 3He/4He ratios, which could be related to the simultaneous unrest testified by the increased seismic activity. We infer that this variation could be related to a refill of the plumbing system by 3He-rich magmas, which

  16. Isotopic Disequilibrium and High-Crystallinity Magma Ascent: Clues to the Temporal Restriction of Proterozoic Anorthosites

    NASA Astrophysics Data System (ADS)

    Bybee, G. M.

    2014-12-01

    Many Proterozoic anorthosite massifs show crustal isotopic signatures that have fuelled debate regarding the source (mantle vs. lower crust) of these temporally restricted magmas. The models advocating a mantle derivation for these rocks suggest that lower crustal assimilation plays an important role in developing the isotopic signature of the massifs, but no evidence exists to support this. We make use of Sr, Nd and Pb isotopic compositions of anorthosites from the Mealy Mountains Intrusive Suite (MMIS), the Nain Plutonic Suite (NPS) and the Rogaland Anorthosite Province (RAP), their internal mineral phases and comagmatic, high-pressure pyroxene megacrysts, which represent samples from various stages of the polybaric ascent of the magmas, to probe the origin of the crustal isotopic signatures and assess the importance of differentiation at lower crustal depths. Study of the MMIS and NPS is instructive as each is intruded into crust of significantly different age and isotopic composition. We observe varying degrees of internal isotopic disequilibrium, enforcing the notion that the nature of the crustal assimilant has a profound influence on the chemical signature of the magmas (Fig. 1). We also find unexpected patterns of internal isotopic disequilibrium, such as isotopically depleted orthopyroxene relative to plagioclase (Fig. 1), which suggests that anorthosite petrogenesis is not a "simple" case of progressive crustal contamination during polybaric magma ascent, but is more likely to involve significant differentiation and solidification at lower crust depths. The 100 m.y. magmatic timescales observed in these anorthosite systems may be caused by significant magmatic differentiation at Moho/lower crustal levels, as well as formation in long-lived arc environments. These long-lived magmatic timescales contrast with recent observations suggesting that the duration of magma ascent from the Moho to surface in arc environments is on the order of months to years. Such

  17. 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

  18. The L-SCAN Experiment: Mapping the Axial Magma Chamber Beneath the Eastern Lau Spreading Center

    NASA Astrophysics Data System (ADS)

    Allison, C. M.; Dunn, R.; Brooks, K.; Conder, J. A.; Martinez, F.; Conley, M. M.

    2009-12-01

    The L-SCAN (Lau Spreading Center Active-source Investigation) seismic experiment was designed to examine the relationship between melt supply and magmatic, tectonic, and hydrothermal processes along the Eastern Lau Spreading Center (a RIDGE2000 focus site). This 3-D active-source ocean-bottom-seismometer experiment covers a 100-km-long section of the spreading center, which exhibits significant along-strike variability in seafloor morphology, tectonics, crustal magma storage, and hydrothermal venting. Presumably these changes arise from variations in mantle melt supply. During the seismic experiment, we deployed 84 4-component ocean bottom seismometers (OBS), obtained from the OBSIP national instrument pool, over a 40 x 100 sq. km area centered on the ridge at 20°30'S. Sixty-five seismic lines (50-150 km in length) were shot using the R/V M. G. Langseth's 36-element airgun source, generating ~1 million seismic travel time observations. The experiment extends across three ridge segments, separated by two overlapping spreading centers. The southern segment exhibits an ‘inflated’ cross-sectional area and is underlain by an axial-magma-chamber seismic reflector (as detected by a previous MCS seismic study). We present a preliminary analysis of the L-SCAN refraction data collected along this ridge segment. Travel times of P-wave seismic energy were measured and compared for ray paths as a function of distance from the ridge axis, thereby allowing us to map, to first order, the location of the crustal low-velocity zone that extends beneath the AMC reflector. Only P-wave energy that has traveled within ~2-3 km of the ridge axis clearly exhibits the travel time delays indicative of a crustal low-velocity "mush” zone. We have not yet examined the deeper, Moho- and mantle-turning P-wave arrivals. It has been previously observed that high-temperature venting along this ridge segment is restricted to a narrow region at the ridge axis. We suggest a model in which a

  19. Heterogeneous Os isotope compositions in the Kalatongke sulfide deposit, NW China: the role of crustal contamination

    NASA Astrophysics Data System (ADS)

    Gao, Jian-Feng; Zhou, Mei-Fu; Lightfoot, Peter C.; Qu, Wenjun

    2012-10-01

    Re-Os isotope compositions of mantle-derived magmas are highly sensitive to crustal contamination because the crust and mantle have very different Os isotope compositions. Crustal contamination may trigger S saturation and thus the formation of magmatic Ni-Cu-(PGE) sulfide deposits. The ˜287-Ma Kalatongke norite intrusion of NW China are hosted in carboniferous tuffaceous rocks and contain both disseminated and massive sulfide mineralization. The Re-Os isotope compositions in the intrusion are highly variable. Norite and massive sulfide ores have γ Os values ranging from +59 to +160 and a Re-Os isochron age of 239 ± 51 Ma, whereas disseminated sulfide ores have γ Os values from +117 to +198 and a Re-Os isochron age of 349 ± 34 Ma. The variability of Os isotope compositions can be explained as the emplacement of two distinct magma pulses. Massive sulfide ores and barren norite in the intrusion formed from the same magma pulse, whereas the disseminated sulfide ores with more radiogenic Os isotopes formed from another magma pulse which underwent different degrees of crustal contamination. Re-Os isotopes may not be suitable for dating sulfide-bearing intrusions that underwent variable degrees of crustal contamination to form magmatic sulfide deposits.

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

    NASA Astrophysics Data System (ADS)

    Karlstrom, Leif; Dufek, Josef; Manga, Michael

    2009-10-01

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

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

    PubMed

    Blundy, Jon; Cashman, Kathy; Humphreys, Madeleine

    2006-09-01

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

  2. Re-Os isotopic evidence for a lower crustal origin of massif-type anorthosites

    PubMed

    Schiellerup; Lambert; Prestvik; Robins; McBride; Larsen

    2000-06-15

    Massif-type anorthosites are large igneous complexes of Proterozoic age. They are almost monomineralic, representing vast accumulations of plagioclase with subordinate pyroxene or olivine and Fe-Ti oxides--the 930-Myr-old Rogaland anorthosite province in southwest Norway represents one of the youngest known expressions of such magmatism. The source of the magma and geodynamic setting of massif-type anorthosites remain long-standing controversies in Precambrian geology, with no consensus existing as to the nature of the parental magmas or whether these magmas primarily originate in the Earth's mantle or crust. At present, massif-type anorthosites are believed to have crystallized from either crustally contaminated mantle-derived melts that have fractionated olivine and pyroxenes at depth or primary aluminous gabbroic to jotunitic melts derived from the lower continental crust. Here we report rhenium and osmium isotopic data from the Rogaland anorthosite province that strongly support a lower crustal source for the parental magmas. There is no evidence of significantly older crust in southwest Scandinavia and models invoking crustal contamination of mantle-derived magmas fail to account for the isotopic data from the Rogaland province. Initial osmium and neodymium isotopic values testify to the melting of mafic source rocks in the lower crust with an age of 1,400-1,550 Myr. PMID:10866196

  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. Oxygen isotope evolution of the Lake Owyhee volcanic field, Oregon, and implications for low-δ18O magmas of the Snake River Plain - Yellowstone hotspot

    NASA Astrophysics Data System (ADS)

    Blum, T.; Kitajima, K.; Nakashima, D.; Valley, J. W.

    2013-12-01

    generated by the superposition of high hotspot-derived thermal fluxes on active extensional structures (OIG extension in the LOVF, and Basin and Range rifting in the CSRP) thereby increasing meteoric water transport to depth and generating conditions for regional scale hydrothermal alteration of the crust. The intricacies of deformation rate and style, and the resulting crustal permeability-depth relations along the hotspot track, offer a qualitative explanation for low-δ18O magmas being pervasive in the CSRP, but restricted to post-caldera and late stage ignimbrites in the eastern SRP centers. This model has significant implications for the evolution of SRP-Y systems, as the thermal inputs required to drive both hydrothermal alteration and crustal melting complicate production of long-lived shallow crustal magma chambers. In addition, this model adds to a growing data set (e.g. Tangbai-Dabie-Sulu province, British Tertiary Igneous Province, etc.) demonstrating low-δ18O magmas can be generated in conjunction with regional scale hydrothermal alteration of the crust, and that this process has occurred throughout the geologic past where extensional tectonics and high thermal fluxes are superimposed.

  5. Continental Lower-crustal Flow: Channel Flow and Laminar Flow

    NASA Astrophysics Data System (ADS)

    LI, Dewei

    Numerous geological, geophysical and geochemical investigations and finite element modeling indicate that crustal flow layers exist in the continental crust. Both channel flow model and laminar flow model have been created to explain the flow laws and flow mechanisms. As revealed by the channel flow model, a low-viscosity channel in middle to lower crust in orogen or plateau with thick crust and high elevation would flow outward from mountain root in response to lateral pressure gradient resulted from topographic loading or to denudation. However, according to the laminar flow model proposed based on investigation of the Qinghai-Tibet plateau, circulative movement of crustal lithologies with different rheological properties between basin and orogen would occur, under the driving forces resulted from dehydration and melting of subduction plate on active continental margin and from thermal energy related to upwelling and diapiring of intercontinental mantle plume or its gravitational interactions. Similarly, when driven by gravity, the softened or melted substances of the lower crust in a basin would flow laterally toward adjacent mountain root, which would result in a thinned basin crust and a thickened orogenic crust. Partially melted magma within the thickened orogenic lower crust would cause vertical movement of metamorphic rocks of lower to middle crust due to density inversion, and the vertical main stress induced by thermal underplating of lower crust would in turn lead to formation of metamorphic core complexes and low-angle detachment fault systems. Lateral spreading of uplifting mountain due to gravitation potential would result in thrust fault systems on the border between mountain and basin. Meanwhile, detritus produced synchronously by intense erosion of uplifting mountain would be transported and deposited along the marginal deep depression in the foreland basin dragged by lower crust flow. Channel flow is similar to laminar flow in a variety of aspects

  6. 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

    state. These sulfides may retain some highly siderophile elements in the source, but are unlikely to be sufficiently voluminous to significantly affect the budget of more modestly sulfide-compatible and more abundant elements such as Cu and Mo. These primary magmas can therefore be considered to be largely Cu-Mo-undepleted, although highly siderophile elements such as Au and platinum group elements (PGE) may be depleted unless no sulfides remain in the source. The latter condition seems unlikely during active subduction because of the continuous flux of fresh sulfur from the slab, but may occur during post-subduction re-melting (leading to potentially Au-rich post-subduction porphyry and alkalic-type epithermal systems). Lower crustal differentiation of main-stage arc magmas results in some loss of Cu to residual or cumulate sulfides, but again the amount appears to be minor, and does not drastically reduce the Cu content of derivative intermediate-composition melts. Fractionation and devolatilization affect the oxidation state of the magma in competing ways, but, while crystallization and segregation of Fe3 +-rich magnetite can cause reduction in reduced to moderately oxidized evolved magmas, this effect appears to be outweighed by the oxidative effects of degassing reduced or weakly oxidized gaseous species such as H2, H2S, and SIVO2, and preferential solvation and removal of Fe2 + in saline hydrothermal fluids. Consequently, most arc magmatic suites show slight increases in oxidation state during differentiation, reaching typical values of ΔFMQ = + 1 to + 2. This oxidation state is significant, because it corresponds to the transition from dissolved sulfide to sulfate dominance in magmas. It has been shown that Cu and Au solubilities in silicate magma increase up to this level (ΔFMQ ≈ + 1), but while Cu solubility continues to increase at higher oxidation states, Au shows a precipitous drop as sulfide, which solvates Au in the melt, is converted to sulfate. This

  7. 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

  8. A three-dimensional Vp, Vs, and Vp/Vs crustal structure in Fujian, Southeast China, from active- and passive-source experiments

    NASA Astrophysics Data System (ADS)

    Cai, Hui-Teng; Kuo-Chen, Hao; Jin, Xin; Wang, Chien-Ying; Huang, Bor-Shouh; Yen, Horng-Yuan

    2015-11-01

    Fujian, Southeastern China, has experienced multistage tectonic activities since the Neoproterozoic Era and is currently influenced by collision between the Eurasian and Philippine Sea plates. Topography, fault zones, and patterns of seismicity are the imprints of tectonic evolution. Historically, there have been several catastrophic earthquakes in the southeastern part of Fujian. To understand the crustal structure related to the fault zones, we performed Vp, Vs, and Vp/Vs travel-time tomography using joint inversion of active and passive sources. A total of 75,827 and 31,044 arrivals of P and S waves, respectively, from 33 explosions and 2543 earthquakes are used in our study. As a result, seismicity has indicated that two NE strike seismogenic zones, the Zhenghe-Dapu and Changle-Zhaoan fault zones, are currently active. Low Vp/Vs ratios in inland Fujian imply that the crust is mainly composed of felsic rocks as part of the Eurasian continental crust, which is consistent with geological observations at the surface. Based on Vp tomography, the thickness of the crust along the coastline is shallower than that on land, which is related to higher heat flow and the Bouguer anomaly. This shallow crust phenomenon near the coastline could be related to the regional extensional stress: the remaining structure of the back-arc extension that stretched the continental crust during the Mesozoic Era or/and the Cenozoic extension due to South China sea opening in Taiwan Strait.

  9. Geochemistry of basalts from small eruptive centers near Villarrica stratovolcano, Chile: Evidence for lithospheric mantle components in continental arc magmas

    NASA Astrophysics Data System (ADS)

    Hickey-Vargas, R.; Sun, M.; Holbik, S.

    2016-07-01

    In the Central Southern Volcanic Zone (CSVZ) of the Andes, the location of stratovolcanoes and monogenetic small eruptive centers (SEC) is controlled by the Liquiñe-Ofqui Fault Zone (LOFZ), a trench-parallel strike-slip feature of over 1000 km length. The geochemistry of basalts from SEC is different from those of stratovolcanoes, and are termed Type 2 and Type 1 basalts, respectively. In the region of Villarrica stratovolcano, contemporaneous SEC are more MgO-rich, and have greater light rare earth element (LREE) enrichment, lower 87Sr/86Sr and 143Nd/144Nd, and lower ratios of large ion lithophile elements (LILE) to LREE and high field strength elements (HFSE). A unique finding in this region is that basalts from one SEC, San Jorge, has Type 1 character, similar to basalts from Villarrica stratovolcano. Type 1 basalts from Villarrica and San Jorge SEC have strong signals from time-sensitive tracers of subduction input, such as high 10Be/9Be and high (238U/230Th), while Type 2 SEC have low 10Be/9Be and (238U/230Th) near secular equilibrium. Based on new trace element, radiogenic isotope and mineral analyses, we propose that Type 1 basaltic magma erupted at San Jorge SEC and Villarrica stratovolcano forms by melting of the ambient actively subduction-modified asthenosphere, while Type 2 SEC incorporate melts of pyroxenite residing in the supra-subduction zone mantle lithosphere. This scenario is consistent with the close proximity of the volcanic features and their inferred depths of magma separation. The pyroxenite forms from arc magma produced during earlier episodes of subduction modification and magmatism, which extend back >300 Ma along this segment of the western South American margin. Type 2 basaltic magmas may reach the surface during LOFZ-related decompression events, and they may also be a normal but episodic part of the magma supply to large stratovolcanoes, resulting in cryptic geochemical variations over time. The presence and mobilization of stored

  10. 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.

  11. Reworked old crust-derived shoshonitic magma: The Guarany pluton, Northeastern Brazil

    NASA Astrophysics Data System (ADS)

    Ferreira, Valderez P.; Sial, Alcides N.; Pimentel, Marcio M.; Armstrong, Richard; Guimarães, Ignez P.; da Silva Filho, Adejardo F.; de Lima, Mariucha Maria C.; da Silva, Thyego R.

    2015-09-01

    The 572 Ma Guarany stock consists of magmatic epidote-bearing hornblende monzodiorite to biotite granite that intruded Paleoproterozoic orthogneisses about 10 km inland from the coast in northeastern Brazil. Co-magmatic diorite enclaves and dikes are abundant throughout the pluton. The monzodiorite-granite pluton and diorite enclaves are shoshonitic and display continuous trends in variation diagrams. They display chemical and isotopic characteristics of crustal melts, such as enrichment in incompatible elements, high back-calculated initial 87Sr/86Sr ratios (avg. 0.71253), negative εNd (0.57Ga) values (avg. - 14.58), as well as high and variable (+ 9.1 to + 11.1‰VSMOW) δ18O (zircon) values. Correlations between O-isotope and whole-rock silica contents, as well as initial 87Sr/86Sr ratios with 1/Sr concentrations, suggest hybridization of a lower continental crustal melt with more felsic crustal rocks, concomitant with fractional crystallization. Amphibole chemistry and whole rock Zr, TiO2 and P2O5 contents suggest magma solidification at a pressure ~ 7 kbar and near liquidus temperature ~ 900 °C. The parental magma was likely formed by partial melting of old (tDM = 2.0 Ga) amphibolitic lower continental crustal rocks, in a post-collisional setting, probably triggered by underplating of mantle-derived mafic magma during the period of relaxation after collision.

  12. Crustal Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick T.; Ravat, D.; Frawley, James J.

    1999-01-01

    Cosmos 49, Polar Orbit Geophysical Observatory (POGO) (Orbiting Geophysical Observatory (OGO-2, 4 and 6)) and Magsat have been the only low-earth orbiting satellites to measure the crustal magnetic field on a global scale. These missions revealed the presence of long- wavelength (> 500 km) crustal anomalies predominantly located over continents. Ground based methods were, for the most part, unable to record these very large-scale features; no doubt due to the problems of assembling continental scale maps from numerous smaller surveys acquired over many years. Questions arose as to the source and nature of these long-wave length anomalies. As a result there was a great stimulant given to the study of the magnetic properties of the lower crust and upper mantle. Some indication as to the nature of these deep sources has been provided by the recent results from the deep crustal drilling programs. In addition, the mechanism of magnetization, induced or remanent, was largely unknown. For computational ease these anomalies were considered to result solely from induced magnetization. However, recent results from Mars Orbiter Laser Altimeter (MOLA), a magnetometer-bearing mission to Mars, have revealed crustal anomalies with dimensions similar to the largest anomalies on Earth. These Martian features could only have been produced by remanent magnetization, since Mars lacks an inducing field. The origin of long-wavelength crustal anomalies, however, has not been completely determined. Several large crustal magnetic anomalies (e.g., Bangui, Kursk, Kiruna and Central Europe) will be discussed and the role of future satellite magnetometer missions (Orsted, SUNSAT and Champ) in their interpretation evaluated.

  13. Crustal and upper mantle structures beneath Cenozoic volcanoes on the board of China and North Korea.

    NASA Astrophysics Data System (ADS)

    Rhie, J.; Kim, S.

    2015-12-01

    The Cenozoic-to-recent volcanoes on the border of China and North Korea are recognized as continental intraplate volcanoes. Despite of much work, the origin and mechanism of the volcanoes remain as an issue of debate, due to their complex and long-lived volcanic activities and lack of detailed information for the crust and upper mantle structures. In this work, ambient noise analysis is performed to image lithospheric structures beneath the volcanoes and surrounding regions using continuous broadband recordings of two temporary networks (1998-1999 PASSCAL array and a part of the 2009-2011 NECASSArray). To better constrain the entire depths of lithosphere in the estimated 3-D velocity structure, we utilize the spectral auto-correlation (SPAC) method and a Bayesian inversion technique to measure phase velocity dispersion data and to obtain shear-wave velocity structures, respectively. We developed a novel grid-search technique for more stable SPAC measurements, and obtained phase velocity data are compared and combined with group and phase velocity data from the conventional frequency-time analysis. Hierarchical and trans-dimensional techniques are implemented in the Bayesian method to estimate more rigorous models and associated uncertainties. The estimated 3-D model shows slower velocity (~0.3 km/s) at the bottom of lithosphere (>60 km) and less modified thick-crust beneath the volcanoes compared to other regions in the model. This suggests our model favors the theory of magma underplating, crustal assimilation, and less volume of magma supply from upper mantle.

  14. Oman Ophiolite Structural Constraints Complement Models of Crustal Accretion at the EAST Pacific RISE

    NASA Astrophysics Data System (ADS)

    Nicolas, A. A.; Jousselin, D.; Boudier, F. I.

    2014-12-01

    This review documents significant similarities between East Pacific Rise (EPR), especially EPR at 9°-10°N and the Oman ophiolites. Both share comparable fast spreading rates, size and their dominant source of information that is mainly geophysical in EPR and structural in Oman. In these respects, they are remarkably complementary. Mantle upwelling zones at the EPR and mantle diapirs in Oman have a similar size and spacing. They punctually introduce basaltic melt and heat in the accreting crust, thus controlling elementary segments structure and activity. A tent-shaped magma chamber fits onto the diapir head, the top of which is a Mantle Transition Zone (MTZ) that stores, modifies, and injects the modified melt into the upper Axial Melt Lens (AML) beneath the lid. This MTZ-AML connection is central in crustal accretion, as documented in Oman. Heat from the diapir is captured above the Moho by the magma chamber and escapes through its walls, into a thin thermal boundary layer that bounds the chamber. Beyond, seawater at lower temperatures feeds smokers on the seafloor.

  15. Chemical versus temporal controls on the evolution of tholeiitic and calc-alkaline magmas at two volcanoes in the Alaska-Aleutian arc

    USGS Publications Warehouse

    George, R.; Turner, S.; Hawkesworth, C.; Bacon, C.R.; Nye, C.; Stelling, P.; Dreher, S.

    2004-01-01

    The Alaska-Aleutian island arc is well known for erupting both tholeiitic and calc-alkaline magmas. To investigate the relative roles of chemical and temporal controls in generating these contrasting liquid lines of descent we have undertaken a detailed study of tholeiitic lavas from Akutan volcano in the oceanic A1eutian arc and calc-alkaline products from Aniakchak volcano on the continental A1askan Peninsula. The differences do not appear to be linked to parental magma composition. The Akutan lavas can be explained by closed-system magmatic evolution, whereas curvilinear trace element trends and a large range in 87 Sr/86 Sr isotope ratios in the Aniakchak data appear to require the combined effects of fractional crystallization, assimilation and magma mixing. Both magmatic suites preserve a similar range in 226 Ra-230 Th disequilibria, which suggests that the time scale of crustal residence of magmas beneath both these volcanoes was similar, and of the order of several thousand years. This is consistent with numerical estimates of the time scales for crystallization caused by cooling in convecting crustal magma chambers. During that time interval the tholeiitic Akutan magmas underwent restricted, closed-system, compositional evolution. In contrast, the calc-alkaline magmas beneath Aniakchak volcano underwent significant open-system compositional evolution. Combining these results with data from other studies we suggest that differentiation is faster in calc-alkaline and potassic magma series than in tholeiitic series, owing to a combination of greater extents of assimilation, magma mixing and cooling.

  16. Complex igneous processes and the formation of the primitive lunar crustal rocks

    NASA Technical Reports Server (NTRS)

    Longhi, J.; Boudreau, A. E.

    1979-01-01

    Crystallization of a magma ocean with initial chondritic Ca/Al and REE ratios such as proposed by Taylor and Bence (TB, 1975), is capable of producing the suite of primitive crustal rocks if the magma ocean underwent locally extensive assimilation and mixing in its upper layers as preliminary steps in formation of an anorthositic crust. Lunar anorthosites were the earliest permanent crustal rocks to form the result of multiple cycles of suspension and assimilation of plagioclase in liquids fractionating olivine and pyroxene. There may be two series of Mg-rich cumulate rocks: one which developed as a result of the equilibration of anorthositic crust with the magma ocean; the other which formed in the later stages of the magma ocean during an epoch of magma mixing and ilmenite crystallization. This second series may be related to KREEP genesis. It is noted that crystallization of the magma ocean had two components: a low pressure component which produced a highly fractionated and heterogeneous crust growing downward and a high pressure component which filled in the ocean from the bottom up, mostly with olivine and low-Ca pyroxene.

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

    NASA Astrophysics Data System (ADS)

    Rollinson, H.

    2003-04-01

    from a deeper structural level. There is also a close relationship between the hornblendite phase of the intrusion and the intrusion breccias, for hornblendite is present as inclusions in the breccias, but in one case is intruded along the margins of a breccia dyke. The presence of multiple co-genetic, immiscible magmas and of intrusion breccias in the Panozero sanukitoid intrusion suggests: (a) multiple magmas at upper crustal level linked through magmatic differentiation at depth, (b) that the current level of exposure represents a high structural level in the intrusion (i.e. near the roof), (c) the importance of water at a late stage of magmatic evolution.

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

    PubMed

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

    2014-01-01

    Mixing between magmas is thought to affect a variety of processes, from the growth of continental crust to the triggering of volcanic eruptions, but its thermophysical viability remains unclear. Here, by using high-pressure mixing experiments and thermal calculations, we show that hybridization during single-intrusive events requires injection of high proportions of the replenishing magma during short periods, producing magmas with 55-58 wt% SiO2 when the mafic end-member is basaltic. High strain rates and gas-rich conditions may produce more felsic hybrids. The incremental growth of crustal reservoirs limits the production of hybrids to the waning stage of pluton assembly and to small portions of it. Large-scale mixing appears to be more efficient at lower crustal conditions, but requires higher proportions of mafic melt, producing more mafic hybrids than in shallow reservoirs. Altogether, our results show that hybrid arc magmas correspond to periods of enhanced magma production at depth. PMID:25500902

  19. Chronological evidence that the Moon is either young or did not have a global magma ocean.

    PubMed

    Borg, Lars E; Connelly, James N; Boyet, Maud; Carlson, Richard W

    2011-09-01

    Chemical evolution of planetary bodies, ranging from asteroids to the large rocky planets, is thought to begin with differentiation through solidification of magma oceans many hundreds of kilometres in depth. The Earth's Moon is the archetypical example of this type of differentiation. Evidence for a lunar magma ocean is derived largely from the widespread distribution, compositional and mineralogical characteristics, and ancient ages inferred for the ferroan anorthosite (FAN) suite of lunar crustal rocks. The FANs are considered to be primary lunar flotation-cumulate crust that crystallized in the latter stages of magma ocean solidification. According to this theory, FANs represent the oldest lunar crustal rock type. Attempts to date this rock suite have yielded ambiguous results, however, because individual isochron measurements are typically incompatible with the geochemical make-up of the samples, and have not been confirmed by additional isotopic systems. By making improvements to the standard isotopic techniques, we report here the age of crystallization of FAN 60025 using the (207)Pb-(206)Pb, (147)Sm-(143)Nd and (146)Sm-(142)Nd isotopic systems to be 4,360 ± 3 million years. This extraordinarily young age requires that either the Moon solidified significantly later than most previous estimates or the long-held assumption that FANs are flotation cumulates of a primordial magma ocean is incorrect. If the latter is correct, then much of the lunar crust may have been produced by non-magma-ocean processes, such as serial magmatism. PMID:21849974

  20. Upper Crustal Seismic Velocity Structure of the Endeavour Segment, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Weekly, R. T.; Wilcock, W. S.; Toomey, D. R.; Hooft, E. E.; Wells, A. E.

    2010-12-01

    We report preliminary results from an active-source seismic tomography experiment that was conducted along the intermediate-spreading Endeavour Segment of the Juan de Fuca Ridge in 2009. The overarching objective of the experiment is to test competing hypotheses for what governs the scale and intensity of magmatic and hydrothermal processes at mid-ocean ridges. Previous models of crustal accretion inferred that ridge-basin topography observed at the Endeavour results from alternating periods of enhanced or reduced magma supply from the mantle. Alternatively, a recent seismic reflection study has imaged a crustal magma chamber underlying the central portion of the Endeavour, which may indicate that variations in seafloor topography instead result from dike-induced faulting that occurs within the upper crust, adjacent to the axial magma chamber. The first model predicts a thicker high-porosity eruptive layer and lower velocities beneath topographic highs, while the second model is compatible with a uniform pattern of volcanic accretion. The experiment used 68 four-component ocean-bottom seismometers (OBSs) at 64 sites to record 5,567 airgun shots from the 6600 in3 airgun array of the R/V Marcus G. Langseth. Three nested shooting grids were collected to image the three-dimensional crustal and upper mantle velocity structure of the segment at multiple spatial scales. We use first-arriving crustal phases (Pg) recorded by the two grids with the densest shot-receiver spacing, the 24 x 8 km2 vent field grid and the 60 x 20 km2 crustal grid, to image the fine-scale (< 1 km) three-dimensional velocity structure of the upper few kilometers of crust at the segment scale. We employ a non-linear tomographic method that utilizes a shortest-path ray-tracing algorithm with columns of nodes sheared vertically to include effects of seafloor topography. To date, we have manually picked 13,000 Pg phases located within 10 km of 17 OBSs. The full analysis will include ~40,000 Pg travel

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Annen, C.

    2007-12-01

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

  3. The potential for crustal resources on Mars

    NASA Technical Reports Server (NTRS)

    Cordell, Bruce M.; Gillett, Stephen L.

    1991-01-01

    Martian resources pose not only an interesting scientific challenge but also have immense astronautical significance because of their ability to enhance mission efficiency, lower launch and program costs, and stimulate the development of large Mars surface facilities. Although much terrestrial mineralization is associated with plate tectonics and Mars apparently possesses a thick, stationary lithosphere, the presence of crustal swells, rifting, volcanism, and abundant volatiles indicates that a number of sedimentary, hydrothermal, dry-magma mineral concentration processes may have operated on Mars. For example, in Colorado Plateau-style (roll-front) deposits, uranium precipitation is localized by redox variations in groundwater. Also, evaporites (either in salt pans or even interstitially in pore spaces) might concentrate Cl, Li, and K. Many Martian impact craters have been modified by volcanism and probably have been affected by rising magma bodies interacting with ground ice or water. Such conditions might produce hydrothermal circulations and element concentrations. If the high sulfur content found by the Viking landers typifies Martian abundances, sulfide ore bodies may have been formed locally. Mineral-rich Africa seems to share many volcanic and tectonic characteristics with portions of Mars and may suggest Mars' potential mineral wealth. For example, the rifts of Valles Marineris are similar to the rifts in east Africa, and may both result from a large mantle plume rising from the interior and disrupting the surface. The gigantic Bushveld complex of South Africa, an ancient layered igneous intrusion that contains ores of chromium and Pt-group metals, illustrates the sort of dry-magma processes that also could have formed local element concentrations on Mars, especially early in the planet's history when heat flow was higher.

  4. Crustal Evolution Introduced.

    ERIC Educational Resources Information Center

    Stoever, Edward C., Jr.; Korporaal, Arie R.

    1979-01-01

    Detailed are the origins, development, and implementation of the Crustal Evolution Education Project (CEEP). This group has produced, for use in earth science and other classes in grades 8-10, a series of instructional modules based on current scientific research in the composition, history, and processes of the earth's crust. (BT)

  5. Tracing crustal contamination along the Java segment of the Sunda Arc, Indonesia

    NASA Astrophysics Data System (ADS)

    Jolis, E. M.; Troll, V.; Deegan, F.; Blythe, L.; Harris, C.; Freda, C.; Hilton, D.; Chadwick, J.; Van Helden, M.

    2012-04-01

    Arc magmas typically display chemical and petrographic characteristics indicative of crustal input. Crustal contamination can take place either in the mantle source region or as magma traverses the upper crust (e.g. [1]). While source contamination is generally considered the dominant process (e.g. [2]), late-stage crustal contamination has been recognised at volcanic arcs too (e.g. [3]). In light of this, we aim to test the extent of upper crustal versus source contamination along the Java segment of the Sunda arc, which, due its variable upper crustal structure, is an exemplary natural laboratory. We present a detailed geochemical study of 7 volcanoes along a traverse from Anak-Krakatau in the Sunda strait through Java and Bali, to characterise the impact of the overlying crust on arc magma composition. Using rock and mineral elemental geochemistry, radiogenic (Sr, Nd and Pb) and, stable (O) isotopes, we show a correlation between upper crustal composition and the degree of upper crustal contamination. We find an increase in 87Sr/86Sr and δ18O values, and a decrease in 143Nd/144Nd values from Krakatau towards Merapi, indicating substantial crustal input from the thick continental basement present. Volcanoes to the east of Merapi and the Progo-Muria fault transition zone, where the upper crust is thinner, in turn, show considerably less crustal input in their isotopic signatures, indicating a stronger influence of the mantle source. Our new data represent a systematic and high-resolution arc-wide sampling effort that allows us to distinguish the effects of the upper crust on the compositional spectrum of individual volcanic systems along the Sunda arc. [1] Davidson, J.P, Hora, J.M, Garrison, J.M & Dungan, M.A 2005. Crustal Forensics in Arc Magmas. J. Geotherm. Res. 140, 157-170; [2] Debaille, V., Doucelance, R., Weis, D., & Schiano, P. 2005. Geochim. Cosmochim. Acta, 70,723-741; [3] Gasparon, M., Hilton, D.R., & Varne, R. 1994. Earth Planet. Sci. Lett., 126, 15-22.

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

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

  7. Magma evolution of Quaternary minor volcanic centres in southern Peru, Central Andes

    NASA Astrophysics Data System (ADS)

    Delacour, Adélie; Gerbe, Marie-Christine; Thouret, Jean-Claude; Wörner, Gerhard; Paquereau-Lebti, Perrine

    2007-04-01

    Minor centres in the Central Volcanic Zone (CVZ) of the Andes occur in different places and are essential indicators of magmatic processes leading to formation of composite volcano. The Andahua Orcopampa and Huambo monogenetic fields are located in a unique tectonic setting, in and along the margins of a deep valley. This valley, oblique to the NW SE-trend of the CVZ, is located between two composite volcanoes (Nevado Coropuna to the east and Nevado Sabancaya to the west). Structural analysis of these volcanic fields, based on SPOT satellite images, indicates four main groups of faults. These faults may have controlled magma ascent and the distribution of most centres in this deep valley shaped by en-echelon faulting. Morphometric criteria and 14C age dating attest to four main periods of activity: Late Pleistocene, Early to Middle Holocene, Late Holocene and Historic. The two most interesting features of the cones are the wide compositional range of their lavas (52.1 to 68.1 wt.% SiO2) and the unusual occurrence of mafic lavas (olivine-rich basaltic andesites and basaltic andesites). Occurrence of such minor volcanic centres and mafic magmas in the CVZ may provide clues about the magma source in southern Peru. Such information is otherwise difficult to obtain because lavas produced by composite volcanoes are affected by shallow processes that strongly mask source signatures. Major, trace, and rare earth elements, as well as Sr-, Nd-, Pb- and O-isotope data obtained on high-K calc-alkaline lavas of the Andahua Orcopampa and Huambo volcanic province characterise their source and their evolution. These lavas display a range comparable to those of the CVZ composite volcanoes for radiogenic and stable isotopes (87Sr/86Sr: 0.70591 0.70694, 143Nd/144Nd: 0.512317 0.512509, 206Pb/204Pb: 18.30 18.63, 207Pb/204Pb: 15.57 15.60, 208Pb/204Pb: 38.49 38.64, and δ 18O: 7.1 10.0‰ SMOW), attesting to involvement of a crustal component. Sediment is absent from the Peru Chile

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

    NASA Astrophysics Data System (ADS)

    Jellinek, M.; Depaolo, D.

    2008-12-01

    the related rates of melt production and extraction. Isotopic studies, parameterized mantle convection calculations and varied geophysical observations suggest that mantle melt production rates in regions not associated with hot mantle plumes are order 10-4 to 10-2 km3 yr-1. Isotopic studies and heat balance considerations indicate that the supply to the mid crust can be increased by factors of 2-10 as a result of lower crustal melting. Applying these constraints on the average supply along with the corresponding thermal structure in the crust (also determined, in part, by the nature of mantle heat transfer) and reasonable crustal mechanical properties we identify conditions in which the storage of crystal-rich magma is favored. Additional effects and implications related to time-dependent magma supplies, varied chamber shapes, wall rock rheologies and background crustal stress regimes will also be discussed.

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

    NASA Astrophysics Data System (ADS)

    Rhodes, J. M.

    2013-12-01

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

  10. Late Cenozoic crustal extension and magmatism, southern Death Valley region, California

    USGS Publications Warehouse

    Calzia, J.P.; Rämö, O.T.

    2000-01-01

    The late Cenozoic geologic history of the southern Death Valley region is characterized by coeval crustal extension and magamatism. Crustal extension is accommodated by numerous listric and planar normal faults as well as right- and left-lateral strike slip faults. The normal faults sip 30°-50° near the surface and flatten and merge leozoic miogeoclinal rocks; the strike-slip faults act as tear faults between crustal blocks that have extended at different times and at different rates. Crustal extension began 13.4-13.1 Ma and migrated northwestward with time; undeformed basalt flows and lacustrine deposits suggest that extension stopped in this region (but continued north of the Death Valley graben) between 5 and 7 Ma. Estimates of crustal extension in this region vary from 30-50 percent to more than 100 percent. Magmatic rocks syntectonic with crustal extension in the southern Death Valley region include 12.4-6.4 Ma granitic rocks as well as bimodal 14.0-4.0 Ma volcanic rocks. Geochemical and isotopic evidence suggest that the granitic rocks get younger and less alkalic from south to north; the volcanic rocks become more mafic with less evidence of crustal interaction as they get younger. The close spatial and temporal relation between crustal extension and magmatism suggest a genetic and probably a dynamic relation between these geologic processes. We propose a rectonic-magmatic model that requires heat to be transported into the crust by mantle-derived mafic magmas. These magmas pond at lithologic or rheologic boundaries, begin the crystallize, and partially melt the surrounding crustal rocks. With time, the thermally weakened crust is extended (given a regional extensional stress field) concurrent with granitic magmatism and bimodal volcanism.

  11. Heat transfer in magma in situ

    SciTech Connect

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

    1983-12-16

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

  12. Mantle and crustal contributions to continental flood volcanism

    USGS Publications Warehouse

    Arndt, N.T.; Czamanske, G.K.; Wooden, J.L.; Fedorenko, V.A.

    1993-01-01

    Arndt, N.T., Czamanske, G.K., Wooden, J.L. and Fedorenko, V.A., 1993. Mantle and crustal contributions to continental flood volcanism. In: M.J.R. Wortel, U. Hansen and R. Sabadini (Editors), Relationships between Mantle Processes and Geological Processes at or near the Earth's Surface. Tectonophysics, 223: 39-52. Most continental flood basalts are enriched in incompatible elements and have high initial 87Sr/86Sr ratios and low ??{lunate}Nd values. Many are depleted in Nb and Ta. The commonly-held view that these characteristics are inherited directly from a source in metasomatized lithospheric mantle is inconsistent with the following arguments: (1) thermomechanical modelling demonstrates that flood basalt magmas come mainly from an asthenospheric or plume source, with minimal direct melting of the continental lithospheric mantle. The low water contents of most flood basalts argue against proposals that hydrous lithosphere was the source. (2) Lithospheric mantle normally has low concentrations of incompatible elements, and chondrite-normalized Nb and Ta contents similar to those of other incompatible elements. Such material cannot be the unmodified source of Nb-Ta-depleted basalts such as those from the Karoo, Ferrar, or Columbia River provinces. We suggest there are two main controls on the compositions of continental flood basalts. The first is lithospheric thickness, which strongly influences the depth and degree of mantle melting of a plume or asthenospheric source, and thus has an important influence on the composition of primary magmas. All liquids formed by partial melting of peridotite at sub-lithosphere depths are highly magnesian (20-25 wt.% MgO) but have variable trace-element contents. Where the lithosphere is thick, the source melts at high pressure, garnet is present, the degree of melting is low, and trace-element concentrations are high. This type of magma evolves to produce the high-Ti type of continental flood basalt. Where the lithosphere is

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  14. 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.

  15. Long-distance magma transport from arc volcanoes inferred from the submarine eruptive fissures offshore Izu-Oshima volcano, Izu-Bonin arc

    NASA Astrophysics Data System (ADS)

    Ishizuka, Osamu; Geshi, Nobuo; Kawanabe, Yoshihisa; Ogitsu, Itaru; Taylor, Rex N.; Tuzino, Taqumi; Sakamoto, Izumi; Arai, Kohsaku; Nakano, Shun

    2014-09-01

    Long-distance lateral magma transport away from volcanic centers in island arcs is emerging as a common phenomenon where the regional stress regime is favorable. It should also be recognized as an important factor in the construction and growth of island arcs, and a potential trigger for devastating eruptions. In this contribution, we report on recent investigations into the magma dynamics of Izu-Oshima volcano, an active basaltic volcano with an extensive fissure system. Izu-Oshima is flanked by numerous, subparallel NW-SE trending submarine ridges extending up to 22 km to the NW and the SE from the central vent. During a recent submersible survey we have identified that these ridges are fissures which erupted basaltic spatter and lava flows. Furthermore, lavas are petrographically similar along each ridge, while there are noticeable differences between ridges. The subparallel ridges are observed to transect a series of seamounts - the Izu-Tobu monogenetic volcanoes - which are dispersed across this area of the rear-arc. However, there are consistent petrographic and chemical differences between these seamounts and the ridges, indicating that they have different magma sources, yet, they are essentially bounding each other in dive tracks. The most appropriate scenario for their development is one where the Izu-Tobu Volcanoes are fed by an "in-situ" underlying source, while the NW-SE ridges are fed by lateral magma transport from Izu-Oshima. Magma erupted from each ridge is of a consistent geochemistry along its length, but has experienced crystal fractionation and some plagioclase accumulation. Compositions of the ridges are also very similar to lavas from the subaerial cones that can be traced down the flanks of Izu-Oshima. This implies that pairs of subaerial cones and submarine ridges represent the locus of magma transport events away from the storage system beneath Izu-Oshima. Hence, magma from this crustal reservoir moved upward to feed the on-edifice cones

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

    NASA Astrophysics Data System (ADS)

    Browning, John; Gudmundsson, Agust

    2015-12-01

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

  17. Crustal structure of the Caribbean-northeastern South America arc-continent collision zone

    NASA Astrophysics Data System (ADS)

    Christeson, Gail L.; Mann, Paul; Escalona, Alejandro; Aitken, Trevor J.

    2008-08-01

    We present the results of a 568-km-long regional wide-angle seismic profile conducted in the southeastern Caribbean that crosses an active island arc, a remnant arc, two basins possibly floored by oceanic crust, an allochthonous terrane of forearc affinity, and the passive margin of northern South America. The velocity structures of the Late Cretaceous Aves Ridge remnant arc and Miocene and younger Lesser Antilles arc are remarkably similar, which implies that magmatic processes have remained moderately steady over time. Crustal thickness is ˜26 km at the Aves Ridge and ˜24 km at the Lesser Antilles arc. In comparison to the Izu-Bonin and Aleutian arcs, the Lesser Antilles arc is thinner and has no evidence for a lower crustal cumulate layer, which is consistent with the estimated low magma production rates of the Lesser Antilles arc. Crustal thickness beneath the Grenada and Tobago basins is 4-10 km, and the velocity structure suggests that these basins could be floored by oceanic crust. A decrease of ˜1 km/s in average seismic velocity of the upper crust is observed from NW to SE across the North Coast fault zone; we argue that this marks the suture between the far-traveled Caribbean arc and the passive margin of the South American continent. Current strike-slip motion between the Caribbean and South American plates is located ˜30 km to the south, and thus material originally deposited on the South American passive margin has now been transferred to the Caribbean plate.

  18. Origin and evolution of overlapping calc-alkaline and alkaline magmas: The Late Palaeozoic post-collisional igneous province of Transbaikalia (Russia)

    NASA Astrophysics Data System (ADS)

    Litvinovsky, B. A.; Tsygankov, A. A.; Jahn, B. M.; Katzir, Y.; Be'eri-Shlevin, Y.

    2011-08-01

    The Late Palaeozoic voluminous magmatism in Transbaikalia, Russia (a territory of > 600,000 km 2 to the east of Lake Baikal) is highly diverse and complex. Of special interest are (1) the significant overlap in time between magmatic suites commonly ascribed to post-collisional and within-plate settings and (2) the provenance of the coeval, but distinct, granitoid magmas that are closely spaced within a large region. Magmatic activity lasted almost continuously from ~ 330 Ma to ~ 275 Ma and included five igneous suites occupying a total area of ~ 200,000 km 2: (1) the Barguzin suite of high-K calc-alkaline granite (330-310 Ma); (2 and 3) the coeval Chivyrkui suite of low-silica calc-alkaline granitoids and the Zaza suite of high-K calc-alkaline to alkaline granite and quartz syenite which were emplaced between 305 and 285 Ma; and (4 and 5) the partially overlapped in time Lower-Selenga monzonite-syenite suite (285-278 Ma) and the Early-Kunalei suite of alkali-feldspar and peralkaline quartz syenite and granite (281-275 Ma). The overall increase in alkalinity of the granitoids with time reflects the progress from post-collisional to within-plate settings. However, a ~ 20 m.y. long transitional period during which both calc-alkaline and alkaline granitoids were emplaced indicates the coexistence of thickened (batholiths) and thinned (rift) crustal tracts. Sr-Nd-O isotope and elemental geochemical data suggest that the relative contribution of mantle-derived components to the generation of silicic magmas progressively increased with time. The high-K calc-alkaline granite magmas that formed the Angara-Vitim batholith were generated by high degree melting of supracrustal metamorphic rocks [ɛNd(t) = - 5.7 to - 7.7; δ 18O(Qtz) = 12‰], with minor contribution of H 2O and K from the underplated mafic magma (the convective diffusion model). The coeval calc-alkaline Chivyrkui suite and the transitional to alkaline Zaza suite formed as a result of mixing of crustal silicic

  19. Oxygen Isotope Trajectories of Crystallizing Arc Magmas

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  20. Magma Dynamics in Dome-Building Volcanoes

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  1. Magma Piracy in the Southern Mariana Backarc

    NASA Astrophysics Data System (ADS)

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

    2001-12-01

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

  2. 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.

  3. The Pb isotopic compositions of lower crustal xenoliths and the evolution of lower crustal Pb

    NASA Astrophysics Data System (ADS)

    Rudnick, Roberta L.; Goldstein, Steven L.

    1990-05-01

    Pb isotopic compositions for three suites of well-characterized granulite facies xenoliths from a diversity of crustal settings (the Chudleigh and McBride volcanic provinces, Queensland, Australia and the Eifel volcanics, West Germany) are presented here. All three suites plot to the right of the 4.57 Ga geochron, similar to the published Pb results of other mafic granulite xenoliths. Correlations between Sr, Nd and Pb isotopes in the three suites measured here point to an origin by mixing of mantle-derived basaltic magmas with lower crust at the time of basaltic underplating (i.e., < 100 Ma for Chudleigh, ˜ 300 Ma for McBride, ˜ 450 Ma for Eifel). Because the Pb concentration of the continental crust is much greater than that of mantle-derived basaltic magmas, the Pb isotopic compositions of the magmas are shifted dramatically by the mixing, allowing delineation of the isotopic characteristics of the lower crust. In all three cases, this lower crust had radiogenic Pb and Sr isotopic compositions and unradiogenic Nd isotopic compositions, yielding Proterozoic Nd model ages. Such radiogenic lower crust contrasts markedly with the Pb isotopic characteristics of most Precambrian granulite facies terrains. Whereas the Nd isotopes reflect the average age of crust formation, the Pb isotopic characteristics of the lower crust appear to be a function of the tectonothermal age of the crust: unradiogenic Pb can only develop in regions which have remained stable for long time periods (e.g., cratons), whereas in areas where orogenies have occurred subsequent to crustal formation, the Pb isotopic composition of the lower crust is "rejuvenated" through mixing with radiogenic Pb from upper crust and mantle-derived magmas. Thus, after orogeny, the Pb isotopic composition of the lower crust resembles that of the upper crust. On the basis of this proposed orogenic age-Pb isotope correlation, we estimate the Pb isotopic composition of the lower crust using the data for granulite

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

    NASA Astrophysics Data System (ADS)

    Bateman, Roger

    1984-12-01

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

  5. Compositional dependence of lower crustal viscosity

    NASA Astrophysics Data System (ADS)

    Shinevar, William J.; Behn, Mark D.; Hirth, Greg

    2015-10-01

    We calculate the viscosity structure of the lower continental crust as a function of its bulk composition using multiphase mixing theory. We use the Gibbs free-energy minimization routine Perple_X to calculate mineral assemblages for different crustal compositions under pressure and temperature conditions appropriate for the lower continental crust. The effective aggregate viscosities are then calculated using a rheologic mixing model and flow laws for the major crust-forming minerals. We investigate the viscosity of two lower crustal compositions: (i) basaltic (53 wt % SiO2) and (ii) andesitic (64 wt % SiO2). The andesitic model predicts aggregate viscosities similar to feldspar and approximately 1 order of magnitude greater than that of wet quartz. The viscosity range calculated for the andesitic crustal composition (particularly when hydrous phases are stable) is most similar to independent estimates of lower crust viscosity in actively deforming regions based on postglacial isostatic rebound, postseismic relaxation, and paleolake shoreline deflection.

  6. Assimilation by Lunar Mare Basalts: Melting of Crustal Material and Dissolution of Anorthite

    NASA Technical Reports Server (NTRS)

    Finnila, A. B.; Hess, P. C.; Rutherford, M. J.

    1994-01-01

    We discuss techniques for calculating the amount of crustal assimilation possible in lunar magma chambers and dikes based on thermal energy balances, kinetic rates, and simple fluid mechanical constraints. Assuming parent magmas of picritic compositions, we demonstrate the limits on the capacity of such magmas to melt and dissolve wall rock of anorthitic, troctolitic, noritic, and KREEP (quartz monzodiorite) compositions. Significant melting of the plagioclase-rich crustal lithologies requires turbulent convection in the assimilating magma and an efficient method of mixing in the relatively buoyant and viscous new melt. Even when this occurs, the major element chemistry of the picritic magmas will change by less than 1-2 wt %. Diffusion coefficients measured for Al2O3 from an iron-free basalt and an orange glass composition are 10(exp -12) m(exp 2) s(exp -1) at 1340 C and 10(exp -11) m(exp 2) s(exp -1) at 1390 C. These rates are too slow to allow dissolution of plagioclase to significantly affect magma compositions. Picritic magmas can melt significant quantities of KREEP, which suggests that their trace element chemistry may still be affected by assimilation processes; however, mixing viscous melts of KREEP composition with the fluid picritic magmas could be prohibitively difficult. We conclude that only a small part of the total major element chemical variation in the mare basalt and volcanic glass collection is due to assimilation/fractional crystallization processes near the lunar surface. Instead, most of the chemical variation in the lunar basalts and volcanic glasses must result from assimilation at deeper levels or from having distinct source regions in a heterogeneous lunar mantle.

  7. Assimilation by lunar mare basalts: Melting of crustal material and dissolution of anorthite

    NASA Technical Reports Server (NTRS)

    Finnila, A. B.; Hess, P. C.; Rutherford, M. J.

    1994-01-01

    We discuss techniques for calculating the amount of crustal assimilation possible in lunar magma chambers and dikes based on thermal energy balances, kinetic rates, and simple fluid mechanical constraints. Assuming parent magmas of picritic compositions, we demonstrate the limits on the capacity of such magmas to melt and dissolve wall rock of anorthitic, troctolitic, noritic, and KREEP (quartz monzodiorite) compositions. Significant melting of the plagioclase-rich crustal lithologies requires turbulent convection in the assimilating magma and an efficient method of mixing in the relatively buoyant and viscous new melt. Even when this occurs, the major element chemistry of the picritic magmas will change by less than 1-2 wt %. Diffusion coefficients measured for Al2O3 from an iron-free basalt and an orange glass composition are 10(exp -12) sq m/s at 1340 C and 10(exp -11) sq m/s at 1390 C. These rates are too slow to allow dissolution of plagioclase to significantly affect magma compositions. Picritic magmas can melt significant quantities of KREEP, which suggests that their trace element chemistry may still be affected by assimilation processes; however, mixing viscous melts of KREEP composition with the fluid picritic magmas could be prohibitively difficult. We conclude that only a small part of the total major element chemical variation in the mare basalt and volcanic glass collection is due to assimilation/fractional crystallization processes near the lunar surface. Instead, most of the chemical variation in the lunar basalts and volcanic glasses must result from assimilation at deeper levels or from having distinct source regions in a heterogeneous lunar mantle.

  8. Composition and origin of basaltic magma of the Hawaiian Islands

    USGS Publications Warehouse

    Powers, H.A.

    1955-01-01

    Silica-saturated basaltic magma is the source of the voluminous lava flows, erupted frequently and rapidly in the primitive shield-building stage of activity, that form the bulk of each Hawaiian volcano. This magma may be available in batches that differ slightly in free silica content from batch to batch both at the same and at different volcanoes; differentiation by fractionation of olivine does not occur within this primitive magma. Silica-deficient basaltic magma, enriched in alkali, is the source of commonly porphyritic lava flows erupted less frequently and in relatively negligible volume during a declining and decadent stage of activity at some Hawaiian volcanoes. Differentiation by fractionation of olivine, plagioclase and augite is evident among these lavas, but does not account for the silica deficiency or the alkali enrichment. Most of the data of Hawaiian volcanism and petrology can be explained by a hypothesis that batches of magma are melted from crystalline paridotite by a recurrent process (distortion of the equatorial bulge by forced and free nutational stresses) that accomplishes the melting only of the plagioclase and pyroxene component but not the excess olivine and more refractory components within a zone of fixed and limited depth. Eruption exhausts the supply of meltable magma under a given locality and, in the absence of more violent melting processes, leaves a stratum of crystalline refractory components. ?? 1955.

  9. 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