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Sample records for alkali basaltic magmas

  1. Complex subvolcanic magma plumbing system of an alkali basaltic maar-diatreme volcano (Elie Ness, Fife, Scotland)

    NASA Astrophysics Data System (ADS)

    Gernon, T. M.; Upton, B. G. J.; Ugra, R.; Yücel, C.; Taylor, R. N.; Elliott, H.

    2016-11-01

    Alkali basaltic diatremes such as Elie Ness (Fife, Scotland) expose a range of volcanic lithofacies that points to a complex, multi-stage emplacement history. Here, basanites contain phenocrysts including pyrope garnet and sub-calcic augites from depths of 60 km. Volcanic rocks from all units, pyroclastic and hypabyssal, are characterised by rare earth element (REE) patterns that show continuous enrichment from heavy REE (HREE) to light REE (LREE), and high Zr/Y that are consistent with retention of garnet in the mantle source during melting of peridotite in a garnet lherzolite facies. Erupted garnets are euhedral and unresorbed, signifying rapid ascent through the lithosphere. The magmas also transported abundant pyroxenitic clasts, cognate with the basanite host, from shallower depths ( 35-40 km). These clasts exhibit wide variation in texture, mode and mineralogy, consistent with growth from a range of compositionally diverse melts. Further, clinopyroxene phenocrysts from both the hypabyssal and pyroclastic units exhibit a very wide compositional range, indicative of polybaric fractionation and magma mixing. This is attributed to stalling of earlier magmas in the lower crust - principally from 22 to 28 km - as indicated by pyroxene thermobarometry. Many clinopyroxenes display chemical zoning profiles, occasionally with mantles and rims of higher magnesium number (Mg#) suggesting the magmas were mobilised by juvenile basanite magma. The tuffs also contain alkali feldspar megacrysts together with Fe-clinopyroxene, zircon and related salic xenoliths, of the 'anorthoclasite suite' - inferred to have crystallised at upper mantle to lower crustal depths from salic magma in advance of the mafic host magmas. Despite evidence for entrainment of heterogeneous crystal mushes, the rapidly ascending melts experienced negligible crustal contamination. The complex association of phenocrysts, megacrysts and autoliths at Elie Ness indicates thorough mixing in a dynamic system

  2. Recycled oceanic crust and marine sediment in the source of alkali basalts in Shandong, eastern China: Evidence from magma water content and oxygen isotopes

    NASA Astrophysics Data System (ADS)

    Liu, Jia; Xia, Qun-Ke; Deloule, Etienne; Chen, Huan; Feng, Min

    2015-12-01

    The magma water contents and cpx δ18O values in alkali basalts from the Fuyanyshan (FYS) volcano in Shandong, eastern China, were investigated by an inverse calculation based on the water content of clinopyroxene (cpx) phenocrysts, the ivAlcpx-dependent water partitioning coefficient Dwatercpx>/melt, and secondary ion mass spectrometer, respectively. The calculated water content (H2O wt.) of magma ranges from 0.58% to 3.89%. It positively correlates with heavy rare earth element concentrations and bulk rock 87Sr/86Sr ratios, and it negatively correlates with Nb/U ratios. However, it is not correlated with bulk Mg# (Mg# = 100 × Mg / (Mg + Fe)) and (La/Yb)n (n represents primitive mantle normalization). Combined with the rather homogenous distribution of water content within cpx grains, these correlations indicate that the water variations among different samples represent the original magma signature, rather than results of a shallow process, such as degassing and diffusion. The δ18O of cpx phenocrysts varies from 3.6‰ to 6.3‰ (±0.5‰, 2SD), which may be best explained by the involvement of components from the lower and upper oceanic crust with marine sediments within the mantle source. The H2O/Ce ratios of the calculated melts range from 113 to 696 and form a positive trend with bulk rock 87Sr/86Sr, which cannot be explained by the recycled Sulu eclogite or by the metasomatized lithospheric mantle. Our modeling calculation shows that the decoupling of ɛHf and ɛNd could be caused by the involvement of marine sediments. Combing the high Ba/Th ratios, positive Sr spikes, and low Ce/Pb ratios for the Fuyanshan basalts, we suggest that the hydrous nature of the FYS basalts was derived from the hydrous mantle transition zone with ancient sediments.

  3. Mare basalt magma source region and mare basalt magma genesis

    SciTech Connect

    Binder, A.B.

    1982-11-15

    Given the available data, we find that the wide range of mare basaltic material characteristics can be explained by a model in which: (1) The mare basalt magma source region lies between the crust-mantle boundary and a maximum depth of 200 km and consists of a relatively uniform peridotite containing 73--80% olivine, 11--14% pyroxene, 4--8% plagioclase, 0.2--9% ilmenite and 1--1.5% chromite. (2) The source region consists of two or more density-graded rhythmic bands, whose compositions grade from that of the very low TiO/sub 2/ magma source regions (0.2% ilmenite) to that of the very high TiO/sub 2/ magma source regions (9% ilmenite). These density-graded bands are proposed to have formed as co-crystallizing olivine, pyroxene, plagioclase, ilmenite, and chromite settled out of a convecting magma (which was also parental to the crust) in which these crystals were suspended. Since the settling rates of the different minerals were governed by Stoke's law, the heavier minerals settled out more rapidly and therefore earlier than the lighter minerals. Thus the crystal assemblages deposited nearest the descending side of each convection cell were enriched in heavy ilmenite and chromite with respect to lighter olivine and pyroxene and very much lighter plagioclase. The reverse being the case for those units deposited near the ascending sides of the convection cells.

  4. 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.

  5. Basaltic injections into floored silicic magma chambers

    NASA Astrophysics Data System (ADS)

    Wiebe, R. A.

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

  6. Vesiculation of basaltic magma during eruption

    USGS Publications Warehouse

    Mangan, M.T.; Cashman, K.V.; Newman, S.

    1993-01-01

    Vesicle size distributions in vent lavas from the Pu'u "O'o-Kupaianaha eruption of Kilauea volcano are used to estimate nucleation and growth rates of H2O-rich gas bubbles in basaltic magma nearing the earth's surface (???120 m depth). By using well-constrained estimates for the depth of volatile exsolution and magma ascent rate, nucleation rates of 35.9 events.cm-3.s-1 and growth rates of 3.2 ?? 10-4cm/s are determined directly from size-distribution data. The results are consistent with diffusion-controlled growth as predicted by a parabolic growth law. -from Authors

  7. Voluminous granitic magmas from common basaltic sources

    USGS Publications Warehouse

    Sisson, T.W.; Ratajeski, K.; Hankins, W.B.; Glazner, A.F.

    2005-01-01

    Granitic-rhyolitic liquids were produced experimentally from moderately hydrous (1.7-2.3 wt% H2O) medium-to-high K basaltic compositions at 700 MPa and f O2 controlled from Ni-NiO -1.3 to +4. Amount and composition of evolved liquids and coexisting mineral assemblages vary with fO2 and temperature, with melt being more evolved at higher fO2s, where coexisting mineral assemblages are more plagioclase- and Fe-Ti oxide-rich and amphibole-poor. At fO2 of Ni-NiO +1, typical for many silicic magmas, the samples produce 12-25 wt% granitic-rhyolitic liquid, amounts varying with bulk composition. Medium-to-high K basalts are common in subduction-related magmatic arcs, and near-solidus true granite or rhyolite liquids can form widely, and in geologically significant quantities, by advanced crystallization-differentiation or by low-degree partial remelting of mantle-derived basaltic sources. Previously differentiated or weathered materials may be involved in generating specific felsic magmas, but are not required for such magmas to be voluminous or to have the K-rich granitic compositions typical of the upper continental crust. ?? Springer-Verlag 2005.

  8. 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

  9. Ultramafic inclusions and host alkali olivine basalts of the southern coastal plain of the Red Sea, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Ghent, Edward D.; Coleman, Robert Griffin; Hadley, Donald G.

    1979-01-01

    A variety of mafic and ultramafic inclusions occur within the pyroclastic components of the Al Birk basalt, erupted on the southern Red Sea coastal plain of Saudi Arabia from Pleistocene time to the present. Depleted harzburgites are the only inclusions contained within the basalts that were erupted through Miocene oceanic crust (15 km thick) in the vicinity of Jizan, whereas to the north in the vicinity of Al Birk, alkali basalts that were erupted through a thicker Precambrian crust (48 km thick) contain mixtures of harzburgites, cumulate gabbro, and websterite inclusions accompanied by large (> 2 cm) megacrysts of glassy alumina-rich clinopyroxene, plagioclase, and spinel. Microprobe analyses of individual minerals from the harzburgites, websterites, and cumulate gabbros reveal variations in composition that can be related to a complex mantle history during the evolution of the alkali basalts. Clinopyroxene and plagioclase megacrysts may represent early phases that crystallized from the alkali olivine basalt magma at depths less than 35 km. Layered websterites and gabbros with cumulate plagioclase and clinopyroxene may represent continuing crystallization of the alkali olivine basalt magma in the lower crust when basaltic magma was not rapidly ascending. It is significant that the megacrysts and cumulate inclusions apparently form only where the magmas have traversed the Precambrian crust, whereas the harzburgite-bearing basalts that penetrated a much thinner Miocene oceanic crust reveal no evidence of mantle fractionation. These alkali olivine basalts and their contained inclusions are related in time to present-day rifting in the Red Sea axial trough. The onshore, deep-seated, undersaturated magmas are separated from the shallow Red Sea rift subalkaline basalts by only 170 km. The contemporaneity of alkaline olivine and subalkaline basalts requires that they must relate directly to the separation of the Arabian plate from the African plate.

  10. Volatile degassing of basaltic achondrite parent bodies Evidence from alkali elements and phosphorus

    NASA Technical Reports Server (NTRS)

    Mittlefehldt, David W.

    1987-01-01

    The Na, K, Rb, Cs, and P abundances in eucrites, diogenites, basaltic clasts from polymict eucrite, howardites, and mesosiderites are examined, and compared with an average of highly incompatible refractory (AHIR) elements normalized to cosmic abundances. It is observed that basaltic eucrites and basaltic clasts show a positive correlation between K, Rb, and Cs, and alkali element/AHIR ratios; the volatile loss of the alkali elements from the basalt affects the parent body inventory of volatile elements. The data reveal that for diogenites, the alkali /AHIR ratios are 1.4-2 times greater than in basaltic eucrites and are more variable; and the negative relation between K, Rb, Cs, and the alkali/AHIR ratio correlate with progressive alkali loss through volatile outgassing during crystallization of one or more magmas resulting in a greater than 90 percent loss of the volatile element inventory from the parent body. It is also detected that P displays volatile loss from the basaltic eucrites and elevated P/AHIR ratios in diogenites.

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

    PubMed

    Hamilton, W

    1964-10-30

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

  12. Assesment of Alkali Resistance of Basalt Used as Concrete Aggregates

    NASA Astrophysics Data System (ADS)

    al-Swaidani, Aref M.; Baddoura, Mohammad K.; Aliyan, Samira D.; Choeb, Walid

    2015-11-01

    The objective of this paper is to report a part of an ongoing research on the influence of using crushed basalt as aggregates on one of durability-related properties of concrete (i.e. alkali-silica reaction which is the most common form of Alkali-Aggregate Reaction). Alkali resistance has been assessed through several methods specified in the American Standards. Results of petrographic examination, chemical test (ASTM C289) and accelerated mortar bar test (ASTM C1260) have particularly been reported. In addition, the weight change and compressive strength of 28 days cured concrete containing basaltic aggregates were also reported after 90 days of exposure to 10% NaOH solution. Dolomite aggregate were used in the latter test for comparison. The experimental results revealed that basaltic rocks quarried from As-Swaida'a region were suitable for production of aggregates for concrete. According to the test results, the studied basalt aggregates can be classified as innocuous with regard to alkali-silica reaction. Further, the 10% sodium hydroxide attack did not affect the compressive strength of concrete.

  13. Exploring the relationship between Assimilation and Fractional Crystallization of Basalts with the Magma Chamber Simulator (MCS)

    NASA Astrophysics Data System (ADS)

    Creamer, J. B.; Bohrson, W. A.; Spera, F. J.; Ghiorso, M. S.

    2010-12-01

    Assimilation of partially melted country rock into cooling and Fractionally Crystallizing magma bodies (AFC) is well known but dynamic process that has been explored by laboratory experiments and study of natural occurrences. Case studies of magmatic systems frequently invoke models that feature mass ratios of assimilation to fractional crystallization (e) that are constant. This study explores the relationship between assimilation and fractional crystallization, as affected by magma and country rock composition, water contents, and pressure using the Magma Chamber Simulator (MCS). The MCS is a computational tool that combines the framework of mass and energy conservation equations (EC-RAFC) approach of Spera and Bohrson (2001, 2002, 2003) and Bohrson and Spera (2001, 2003) with the phase equilibria modeling capabilities of MELTS (Ghiorso and Sack 1995). Using MCS results, it is found that e is often hugely dependent on even minor variations in system composition, and that e often varies systematically (usually increasing with time) during an individual instance of AFC, by up to an order of magnitude. A well-documented effect of increasing the water content of magmas is the suppression of crystallization. Indeed, among different types of basalt (Mid-Ocean Ridge Basalt MORB, High-Alumina Basalt HAB, Alkali Basalt AB), assimilation of dry gabbro (e~0.7) is less efficient than assimilation of hydrated gabbro (e~1.5-2.5). However, the effect on efficiency of assimilation, e, of magma water content, though pronounced, is more complex. Generally, however, wet magmas can yield scenarios with higher e values due to the suppression of plagioclase crystallization, which has a relatively large enthalpy of formation. The effect of higher pressure on AFC systems, all else being equal, is quite variable. For example, a MORB, HAB, or AB assimilating gabbro at 1kbar yields an e value of ~1.5. If the pressure is elevated to 5 kbar, the same systems yield an e value of ~0.3. The

  14. The carbon dioxide solubility in alkali basalts: an experimental study

    NASA Astrophysics Data System (ADS)

    Lesne, Priscille; Scaillet, Bruno; Pichavant, Michel; Beny, Jean-Michel

    2011-07-01

    Experiments were conducted to determine CO2 solubilities in alkali basalts from Vesuvius, Etna and Stromboli volcanoes. The basaltic melts were equilibrated with nearly pure CO2 at 1,200°C under oxidizing conditions and at pressures ranging from 269 to 2,060 bars. CO2 solubility was determined by FTIR measurements. The results show that alkalis have a strong effect on the CO2 solubility and confirm and refine the relationship between the compositional parameter Π devised by Dixon (Am Mineral 82:368-378, 1997) and the CO2 solubility. A general thermodynamic model for CO2 solubility in basaltic melts is defined for pressures up to 2 kbars. Based on the assumption that O2- and CO{3/2-} mix ideally, we have: begin{gathered} K(P,T) = {{X_{{{{CO}}3^{2 - } }}m (P,T)}/{X_{{{{O}^{2 - } }}m × f_{{{{CO}}2 }} (P,T)}}} \\ K(P,T) = {{X_{{{{CO}}3^{2 - } }}m (P,T)} {/ {{{X_{{{{CO}}3^{2 - } }}m (P,T)} {( {X_{{{{O}}^{2 - } }}m × f_{{{{CO}}2 }} (P,T)} ).}}} . kern-νlldelimiterspace} {( {X_{{{{O}}^{2 - } }}m × f_{{{{CO}}2 }} (P,T)} ).}} \\ Then, from the thermodynamic model, we obtain ln K 0 = 0.893 Π - 15.247. The new CO2 solubility model yields saturation pressures lower by as much as 50% relative to some existing models when applied to volatile-rich alkali basalts.

  15. Thermobarometry for spinel lherzolite xenoliths in alkali basalts

    NASA Astrophysics Data System (ADS)

    Ozawa, Kazuhito; Youbi, Nasrrddine; Boumehdi, Moulay Ahmed; Nagahara, Hiroko

    2016-04-01

    geothermobarometry based on reactions with large and distinct volume changes, is necessary. Specification of mineral domains and their components representing the thermal state of the mantle just before xenolith extraction is one of the major tasks for the establishment of reliable geothermobarometry for spinel lherzolite xenoliths. Systematic variations of such mineralogical information among xenoliths transported by a single volcanic eruption guarantees proper estimation of a mantle geotherm. For the development of such geobarometry, it is important to choose appropriate xenolith locality, where previous studies provide enough information and where many xenolith samples are available for extending a range of derivation depth. Spinel lherzolite xenoliths in alkali basalts from Bou Ibalhatene maars in the Middle Atlas in Morocco are suitable study target. Geochemical, geochronological, petrological, and rheological aspects of the spinel lherzolite xenoliths have been studied (Raffone et al. 2009; El Messbahi et al., 2015; Witting et al., 2010; El Azzouzi et al., 2010), which show that they represent fragments of the lithospheric mantle formed and modified since 1.7Ga before their extraction from Miocene to recent. We have pinpointed portions of minerals in the xenolith samples and their components representing condition just before their entrapment in magmas, on which appropriate geothermobarometers are applied and detected ~0.5GPa pressure difference (1.5-2.0GPa) for ~100°C variation in temperatures (950-1050°C).

  16. Petrochemistry of a xenolith-bearing Neogene alkali olivine basalt from northeastern Iran

    NASA Astrophysics Data System (ADS)

    Saadat, Saeed; Stern, Charles R.

    2012-05-01

    A small isolated Neogene, possibly Quaternary, monogenetic alkali olivine basalt cone in northeastern Iran contains both mantle peridotite and crustal gabbroic xenoliths, as well as plagioclase megacrysts. The basaltic magma rose to the surface along pathways associated with local extension at the junction between the N-S right-lateral and E-W left-lateral strike slip faults that form the northeastern boundary of the Lut microcontinental block. This basalt is enriched in LREE relative to HREE, and has trace-element ratios similar to that of oceanic island basalts (OIB). Its 87Sr/86Sr (0.705013 to 0.705252), 143Nd/144Nd (0.512735 to 0.512738), and Pb isotopic compositions all fall in the field of OIB derived from enriched (EM-2) mantle. It formed by mixing of small melt fractions from both garnet-bearing asthenospheric and spinel-facies lithospheric mantle. Plagioclase (An26-32) megacrysts, up to 4 cm in length, have euhedral crystal faces and show no evidence of reaction with the host basalt. Their trace-element concentrations suggest that these megacrysts are co-genetic with the basalt host, although their 87Sr/86Sr (0.704796) and 143Nd/144Nd (0.512687) ratios are different than this basalt. Round to angular, medium-grained granoblastic meta-igneous gabbroic xenoliths, ranging from ~ 1 to 6 cm in dimension, are derived from the lower continental crust. Spinel-peridotite xenoliths equilibrated in the subcontinental lithosphere at depths of 30 to 60 km and temperatures of 965 °C to 1065 °C. These xenoliths do not preserve evidence of extensive metasomatic enrichment as has been inferred for the mantle below the Damavand volcano further to the west in north-central Iran, and clinopyroxenes separated from two different mantle xenoliths have 87Sr/86Sr (0.704309 and 0.704593) and 143Nd/144Nd (0.512798) ratios which are less radiogenic than either their host alkali basalt or Damavand basalts, implying significant regional variations in the composition and extent of

  17. Geochemistry of Kauai volcanics and a mixing model for the origin of Hawaiian alkali basalts

    NASA Astrophysics Data System (ADS)

    Feigenson, Mark D.

    1984-09-01

    A comprehensive model is developed to explain the major, trace element and strontium and neodymium isotopic characteristics of alkali basalts from Hawaii. The model is similar to that of Chen and Frey (1983) in that it requires mixing of a small melt fraction of MORB-source material with another component to generate the alkalic suite of a particular Hawaiian volcano. It differs from the Chen and Frey model in that the other end-member must be different from primitive mantle if it is to be consistent with both trace element and isotopic data. Alkali basalts and tholeiites from Kauai analyzed in this study show a nearly complete transition in Sr and Nd isotopes. There is a relatively well-constrained array on a Nd-Sr isotope correlation plot that can be explained by two-component mixing of Kauai tholeiite magma and a small amount of melt of East Pacific Rise source rock. After corrections are made for fractional crystallization (involving primarily clinopyroxene and olivine), the Sr and Ba concentrations of Kauai lavas plot along mixing curves defined by the above sources, providing positive tests of the mixing hypothesis. Implications of this model are: (1) the main source of Hawaiian shield-building tholeiites is a mixture of subducted crust, primitive mantle and depleted asthenosphere that has been homogenized prior to melting, (2) early alkalic volcanism (as at Loihi seamount) will be characterized by greater isotopic heterogeneity than will late-stage alkali basalt production, and (3) there are two fundamentally distinct types of alkalic lavas erupted towards the end of magmatism at a given Hawaiian volcano. One represents smaller degrees of melting of the same source that generated shield-building tholeiites (Kohala-type); the other derives from the mixed source discussed in this paper (Haleakala-, Kauai-type).

  18. The magma storage capacity of Mt. Etna's feeding system constrained by four decades of alkali enrichment in erupted lavas

    NASA Astrophysics Data System (ADS)

    Allard, Patrick; Corsaro, Rosanna; Métrich, Nicole

    2015-04-01

    Deciphering the magma plumbing system of volcanoes is fundamental to improved understanding of their behaviour and forecasting of their eruptions. Mount Etna, in Sicily, is one of the most active basaltic volcanoes on Earth, built upon a 20-km thick continental crust at the collision boundary between the African and Eurasian plates. Seismic tomography and inversion of natural seismic data have revealed a complex feeding system that includes a huge vertical plutonic body and magma ponding zones in coincidence with the main lithological discontinuities in the crust (at ca. 8-10 km and 2-3 km depth b.s.l.). However, limitations in spatial resolution hamper accurate size estimate of these magma ponding zones. Here we use the remarkable trend of alkali enrichment observed in Etnean lavas since the early seventies and their cumulated erupted volumes to provide an updated estimate of the magma storage capacity of the volcano feeding system. The temporal evolution of K2O/Th and Rb/Th ratios - unaffected by magma differentiation processes - tracks the replenishment of Etna's plumbing system by a new, more alkaline trachybasaltic magma that has gradually mixed with the former resident magma. In a few occasions (e.g. 1974, 1998, 2001-2002) this new magma could reach the surface without pre-eruptive homogeneization in the mixing cell, producing highest eruption rates. Such variations indicate a complex storage system, made of sills and dykes, in which long-term mixing processes but also separate storage or upraise of some magma batches can happen. Combining with the co-erupted magma volumes, we estimate an overall magma storage capacity beneath Etna that is larger than previously inferred from radioactive disequilibria in lavas or SO2 gas fluxes. Our new estimate could be usefully compared with the results from recent seismic tomography realized within the framework of the European MED-SUV project (Mediterranean Supersite Volcanoes).

  19. Role of syn-eruptive plagioclase disequilibrium crystallization in basaltic magma ascent dynamics.

    PubMed

    La Spina, G; Burton, M; De' Michieli Vitturi, M; Arzilli, F

    2016-12-12

    Timescales of magma ascent in conduit models are typically assumed to be much longer than crystallization and gas exsolution for basaltic eruptions. However, it is now recognized that basaltic magmas may rise fast enough for disequilibrium processes to play a key role on the ascent dynamics. The quantification of the characteristic times for crystallization and exsolution processes are fundamental to our understanding of such disequilibria and ascent dynamics. Here we use observations from Mount Etna's 2001 eruption and a magma ascent model to constrain timescales for crystallization and exsolution processes. Our results show that plagioclase reaches equilibrium in 1-2 h, whereas ascent times were <1 h. Using these new constraints on disequilibrium plagioclase crystallization we also reproduce observed crystal abundances for different basaltic eruptions. The strong relation between magma ascent rate and disequilibrium crystallization and exsolution plays a key role in controlling eruption dynamics in basaltic volcanism.

  20. Role of syn-eruptive plagioclase disequilibrium crystallization in basaltic magma ascent dynamics

    NASA Astrophysics Data System (ADS)

    La Spina, G.; Burton, M.; de'Michieli Vitturi, M.; Arzilli, F.

    2016-12-01

    Timescales of magma ascent in conduit models are typically assumed to be much longer than crystallization and gas exsolution for basaltic eruptions. However, it is now recognized that basaltic magmas may rise fast enough for disequilibrium processes to play a key role on the ascent dynamics. The quantification of the characteristic times for crystallization and exsolution processes are fundamental to our understanding of such disequilibria and ascent dynamics. Here we use observations from Mount Etna's 2001 eruption and a magma ascent model to constrain timescales for crystallization and exsolution processes. Our results show that plagioclase reaches equilibrium in 1-2 h, whereas ascent times were <1 h. Using these new constraints on disequilibrium plagioclase crystallization we also reproduce observed crystal abundances for different basaltic eruptions. The strong relation between magma ascent rate and disequilibrium crystallization and exsolution plays a key role in controlling eruption dynamics in basaltic volcanism.

  1. Role of syn-eruptive plagioclase disequilibrium crystallization in basaltic magma ascent dynamics

    PubMed Central

    La Spina, G.; Burton, M.; de' Michieli Vitturi, M.; Arzilli, F.

    2016-01-01

    Timescales of magma ascent in conduit models are typically assumed to be much longer than crystallization and gas exsolution for basaltic eruptions. However, it is now recognized that basaltic magmas may rise fast enough for disequilibrium processes to play a key role on the ascent dynamics. The quantification of the characteristic times for crystallization and exsolution processes are fundamental to our understanding of such disequilibria and ascent dynamics. Here we use observations from Mount Etna's 2001 eruption and a magma ascent model to constrain timescales for crystallization and exsolution processes. Our results show that plagioclase reaches equilibrium in 1–2 h, whereas ascent times were <1 h. Using these new constraints on disequilibrium plagioclase crystallization we also reproduce observed crystal abundances for different basaltic eruptions. The strong relation between magma ascent rate and disequilibrium crystallization and exsolution plays a key role in controlling eruption dynamics in basaltic volcanism. PMID:27941750

  2. Phase equilibria along a basalt-rhyolite mixing line: implications for the origin of calc-alkaline intermediate magmas

    NASA Astrophysics Data System (ADS)

    Ussler, William; Glazner, Allen F.

    1989-02-01

    One-atmosphere, anhydrous phase equilibria determined for alkali basalt/high-silica rhyolite mixtures provide a model for crystallization of natural calc-alkaline mixed magmas. The compositional trend defined by these mixtures mimics the trends of many continental calc-alkaline volcanic suites. As with many naturally occurring suites, the mixtures studied straddle the low-pressure olivine-plagioclase-augite thermal divide. Magma mixing provides a convenient method for magmas to cross this thermal divide in the absence of magnetite crystallization. For the mixtures, Mg-rich olivine (Fo82 87) coexists alone with liquid over an exceptionally large range of temperature and silica content (up to 63 wt% SiO2). This indicates that the Mg-rich olivines found in many andesites and dacites are not necessarily out of equilibrium with the host magma, as is commonly assumed. Such crystals may be either primary phenocrysts, or inherited phenocrysts derived from a mafic magma that mixed with a silicic magma. For the bulk compositions studied, the distribution of Fe and Mg between olivine and liquid ( K D ) is equal to 0.3 and is independent of temperature and composition. This result extends to silicic andesites the applicability of K D arguments for tests of equilibrium between olivine and groundmass and for modeling of fractional crystallization. In contrast, the distribution of calcium and sodium between plagioclase and liquid varies significantly with temperature and composition. Therefore, plagioclase-liquid K D s cannot be used for fractional crystallization modeling or as a test of equilibrium. Calcic plagioclase from a basalt will be close to equilibrium with andesitic mixtures, but sodic plagioclase from a rhyolite will be greatly out of equilibrium. This explains the common observation that calcic plagioclase crystals in hybrid andesites are generally close to textural equilibrium with the surrounding groundmass, but sodic plagioclase crystals generally show remelting

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

    PubMed

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

    2015-11-19

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

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

    PubMed Central

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

    2015-01-01

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

  5. The alkali basaltic and picritic Magmatism in Minusa and Kusnetsk basin, geochemical study

    NASA Astrophysics Data System (ADS)

    Firsov, Andrei; Ashchepkov, Igor; Rikhvanov, Leonid; Wald, Alexandr

    2015-04-01

    The alkali basalts and picrites are widely distributed within the Minusa depressions. They manifest quite different episodes of the magmatic activity and plumes. Some of them relate to late Devonian which are parallel to magmatism in Vilyui rift and Tungus basin as well as to Agul basaltic plateau in Sayan Foothills and in Kuznetsk Alatau (385 -360 Ma) and are mainly represented by the alkali basalts (Rikhvanov et al., 1991). The others are close in time to the Late Devonian kimberlitic basaltic magmatism and camptonite dykes in West Sayan. The Early stage of the Permian -Triassic super plume in Minusa and Kusnetsk basin 250 -254 Ma (Rikhvanov et al., 1991). The major pulse of magmatic activity at 248 -245 MA was not appeared in southern margin. But the latest which is represented in Meimecha province Northern Siberia But the late or new Early Triassic stage at 230 -240 Ma was again manifested by the appearance of the alkali picrite ankaratrite dykes. The later alkaline magmatism in Late Jurassic - Cretaceaus stages which was appeared in the Northern Siberian provinces appeared in Southern Siberia were much less pronounced. The Latest episode of the Mezo- Cenozoic activity (Kutolin, Frolova, 1970; Ashchepkov et al., 1995) in the Kopiev uplift with the abundant mantle xenoliths in magma manifest another stages which possibly is related to the hydrous plumes. The trace elements of the magmas in the Minusa depression show rather high concentration if the incompatible elements in all stages which suggest primary enrichment in the metasomatic components probably due to the ancient subducted related magmatism starting from the Devonian stage (Vorontsov et al., 2013) which had the model ages of about 0.9 Ga (Vrublevskii et al., 2014 ). The high melting stages which should be followed by the depletion and homogenization of the source mantle at the Superplume stage and the erupted volcanic still demonstrated rather high La/Yb rations. An thus the alkali picrite volcanic of

  6. Genesis of calc-alkali andesite magma in a hydrous mantle-crust boundary: Petrology of lherzolite xenoliths from the Ichinomegata crater, Oga peninsula, northeast Japan, part II

    NASA Astrophysics Data System (ADS)

    Takahashi, Eiichi

    1986-09-01

    The Ichinomegata volcano, northwestern Honshu, Japan, consisting of three explosion craters, is characterized by the presence of contemporaneous basalt (high-alkali tholeiite) and calc-alkali andesite and a variety of mafic and ultramafic xenoliths of deep-seated origin. The population of the rock types decreases exponentially as a function of increasing depth of their origin. Based on the Ichinomegata xenolith mineralogy, it is inferred that the lower crust and uppermost mantle beneath this area is partially hydrated, consisting dominantly of hornblende gabbro and hornblende-bearing spinel lherzolite, respectively. Chemical analysis on spinel-pyroxene symplectite (so called garnet pseudomorph) in some Ichinomegata lherzolites suggests a calcic-plagioclase primary chemistry rather than garnet. In lherzolite xenoliths which have undergone a preheating event, primary partial melting textures are observed. The composition of the glass formed along the grain boundaries of the partially melted lherzolites are similar to those produced in hydrous melting experiments on natural peridotite at about 10 kbar between 1000 and 1100°C. The high-alkali tholeiite and calc-alkali andesite of the Ichinomegata volcano are considered to have been formed by the following two-stage melting processes; (1) derivation of the basalt magma from partial melting of a peridotite diapir in the upper mantle at 40-50 km depth; (2) derivation of the calc-alkali andesite magma at 25-30 km depth by wet partial melting of the rocks at the mantle/crust boundary caused by emplacement of hot basaltic magma body. It is proposed that similar wet partial melting takes place more extensively beneath major island-arc volcanoes in the world, because the lower crust and the upper mantle beneath them may be hydrated due to continuous water supply from the subducting plate, and the amount of heat energy liberated at the mantle/crust boundary would be much larger in major stratovolcanoes than in the

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

    NASA Technical Reports Server (NTRS)

    Treiman, Allan H.

    1996-01-01

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

  8. Igneous Rocks of the East Pacific Rise: The alkali volcanic suite appear to be differentiated from a tholeiitic basalt extruded from the mantle.

    PubMed

    Engel, A E; Engel, C G

    1964-10-23

    The apical parts of large volcanoes along the East Pacific Rise (islands and seamounts) are encrusted with rocks of the alkali volcanic suite (alkali basalt, andesine- and oligoclase-andesite, and trachyte). In contrast, the more submerged parts of the Rise are largely composed of a tholeiitic basalt which has low concentrations of K, P, U, Th, Pb, and Ti. This tholeiitic basalt is either the predominant or the only magma generated in the earth's mantle under oceanic ridges and rises. It is at least 1000-fold more abundant than the alkali suite, which is probably derived from tholeiitic basalt by magmatic differentiation in and immediately below the larger volcanoes. Distinction of oceanic tholeiites from almost all continental tholeiites is possible on the simple basis of total potassium content, with the discontinuity at 0.3 to 0.5 percent K(2)O by weight. Oceanic tholeiites also are readily distinguished from some 19 out of 20 basalts of oceanic islands and seamount cappings by having less than 0.3 percent K(2)O by weight and more than 48 percent SiO(2). Deep drilling into oceanic volcanoes should, however, core basalts transitional between the oceanic tholeiites and the presumed derivative alkali basalts. The composition of the oceanic tholeiites suggests that the mantle under the East Pacific Rise contains less than 0.10 percent potassium oxide by weight; 0.1 part per million of uranium and 0.4 part of thorium; a potassium:rubidium ratio of about 1200 and a potassium: uranium ratio of about 10(4).

  9. Alkali basalts and enclosed ultramafic xenoliths near Ushuaia, Tierra Del Fuego, Argentina.

    PubMed

    Acevedo, Rogelio Daniel

    2016-01-01

    At the southernmost part of Tierra del Fuego a few outcrops and erratic boulders of alkali basaltic rocks with ultramafic enclaves have been studied. Alkali basalt plugs or pipes hitherto identified are scarce, and host rocks are constituted by slates that belong to Mesozoic deposition. The petrography, texture and composition of the basalt and xenoliths were investigated by petrographic microscope and electron microprobe analysis. Xenocrysts of amphibole and alkali feldspar, phenocrysts of nepheline, olivine, spinel, phlogopite and Fe-Ti minerals (10 %) and a diversity of xenoliths, mainly lherzolitic, pyroxenite and wehrlitic nodules (15 %), but also from metamorphic rocks provenance, are contained in the basalt groundmass (75 %). This finer-grained material is made up of laths or needles of plagioclase, pyroxene, opaque minerals, apatite and glass, with intersertal, hyalopilitic and pilotaxitic. Locally, rock has an even granoblastic texture. Former amygdules are filled by analcite, zeolites, sodalite and calcite. The normative classification, based on nepheline content, conclude that this rock is an alkali basalt. The chemical classification, considering immobile elements as Zr/TiO2 versus Nb/Y indicate an alkali basalt too and plots over the TAS diagram fall in the foidite (Na-rich or nephelinite) and basanite fields. The REE patterns are fractionated (La/Yb primitive mantle normalized is approximately 30). The K-Ar isotopic technique on individual macrocrysts gave ages of 146 ± 5 Ma (amphibole) and 127 ± 4 Ma (alkali feldspar); and K-Ar whole rock datum reported 8.3 ± 0.3 Ma. Nevertheless, fertile samples show geochemical features typical of deep derived material thus, based on the position in the actual tectonic setting, indicate that the basalt is older than its isotopic age.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  11. Basaltic Shergottite NWA 856: Differentiation of a Martian Magma

    NASA Technical Reports Server (NTRS)

    Ferdous, J.; Brandon, A. D.; Peslier, A. H.; Pirotte, Z.

    2016-01-01

    NWA 856 or Djel Ibone, is a basaltic shergottite discovered as a single stone of 320 g in South Morocco in April, 2001. This meteorite is fresh, i.e. shows minimal terrestrial weathering for a desert find. No shergottite discovered in North Africa can be paired with NWA 856. The purpose of this study is to constrain its crystallization history using textural observations, crystallization sequence modeling and in-situ trace element analysis in order to understand differentiation in shergottite magmatic systems.

  12. Mineralogy, geochemistry and expansion testing of an alkali-reactive basalt from western Anatolia, Turkey

    SciTech Connect

    Copuroglu, Oguzhan; Andic-Cakir, Ozge; Broekmans, Maarten A.T.M.; Kuehnel, Radko

    2009-07-15

    In this paper, the alkali-silica reaction performance of a basalt rock from western Anatolia, Turkey is reported. It is observed that the rock causes severe gel formation in the concrete microbar test. It appears that the main source of expansion is the reactive glassy phase of the basalt matrix having approximately 70% of SiO{sub 2}. The study presents the microstructural characteristics of unreacted and reacted basalt aggregate by optical and electron microscopy and discusses the possible reaction mechanism. Microstructural analysis revealed that the dissolution of silica is overwhelming in the matrix of the basalt and it eventually generates four consequences: (1) Formation of alkali-silica reaction gel at the aggregate perimeter, (2) increased porosity and permeability of the basalt matrix, (3) reduction of mechanical properties of the aggregate and (4) additional gel formation within the aggregate. It is concluded that the basalt rock is highly prone to alkali-silica reaction. As an aggregate, this rock is not suitable for concrete production.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  14. Volatile Behavior in Lunar and Terrestrial Basalts During Shock: Implications for Martian Magmas

    NASA Technical Reports Server (NTRS)

    Chaklader, Johny; Shearer, C. K.; Hoerz, F.; Newsom, H. E.

    2004-01-01

    The amount of water in martian magmas has significant ramifications for the martian atmosphere-hydrosphere cycle. Large D-enrichments have been observed in kaersutitic amphiboles in Zagami, Chassigny and Shergotty meteorites (delta-D values up to 4400 per mil) suggesting that substantial amounts of H escaped Mars in its past. Furthermore, martian meteorites with inclusions of biotite and apatite imply possible origins in a hydrous mantle. However, whether martian magmas ever possessed considerable proportions of water remains controversial and unclear. The H-content of mica and amphibole melt inclusions has been found to be low, while bulk-rock H2O content is also low ranging from 0.013 to 0.035 wt. % in Shergotty. Hydrous martian magmas were considered responsible for light lithophile element (LLE) zoning patterns observed in Nakhlite and Shergottite pyroxenes. Since LLEs, such as Li and B, partition into aqueous fluids at temperatures greater than 350 C, workers interpreted Li-B depletions in pyroxene rims as evidence that supercritical fluid exsolution occurred during magma degassing. In that many martian basalts experienced substantial shock (15-45 GPa) it is possible that the magmatic volatile record preserved in martian basalts has been disturbed. Previous shock experiments suggest that shock processes may effect water content and H/D. To better understand the possible effects of shock on this volatile record, we are studying the redistribution of volatile elements in naturally and experimentally shocked basalts. Here, we report the initial results from shocked basalts associated with the Lonar Crater, India and an experimentally shocked lunar basalt.

  15. Oxygen isotope studies on placer sapphire and ruby in the Chanthaburi-Trat alkali basaltic gemfield, Thailand

    NASA Astrophysics Data System (ADS)

    Yui, Tzen-Fu; Wu, Chao-Ming; Limtrakun, Phisit; Sricharn, Weerapan; Boonsoong, Apichet

    2006-02-01

    Placer sapphire and ruby are common in the western zone and the central/eastern zone, respectively, of the Chanthaburi-Trat (C-T) alkali basaltic gemfield in southeastern Thailand. Sapphires have O-isotope composition in the range from + 5.1‰ to + 6.2‰, while rubies, from + 1.3‰ to + 4.2‰. These data clearly show that the C-T placer sapphires and rubies should have a different primary genesis. Olivine in the nearby alkali basalts exhibits a narrow range of O-isotope composition, i.e., from + 4.8‰ to + 5.0‰, demonstrating that the C-T placer gem corundums cannot be phenocrysts of these basalts. The homogeneous O-isotope compositions of sapphires, combined with other available data, strongly suggest that these sapphires most probably have originally crystallized from evolved mantle magmas at lower crust/upper mantle depths. The varied O-isotope compositions of rubies are consistent with the previous suggestion that these rubies originally formed in mafic metamorphic rocks under upper mantle conditions, although the O-isotope data also require that the mafic rocks would have experienced an earlier surface (sea) water-rock interaction history. Consistent with the available data, a suggestion with garnet pyroxenite in the sub-continental mantle as the primary source for these placer gem corundums is tentatively proposed. The surface distribution of sapphire or ruby in the studied area may be a sign of composition variation of garnet pyroxenite underneath.

  16. Ascent and eruption of basaltic magma on the earth and moon

    NASA Astrophysics Data System (ADS)

    Wilson, L.; Head, J. W.

    1981-04-01

    The ascent and emplacement of basaltic magma on the earth and moon is modeled by the application of geological and physical observations and constraints. Relatively simple mathematical models of the motion of gas/liquid mixtures are shown to be adequate in the treatment of basaltic eruptions, provided that allowance is made for the coalescence of gas bubbles and that realistic geological and petrochemical constraints are applied to the numerical values of variables. Because gas exsolution from magmas on the earth and moon commonly occur at depths of less than 2 km, it is generally convenient to consider separately the rise of bubble-free magmatic liquid at depth in a planetary crust and the more complex motions occurring near the surface with gas exsolution.

  17. Temperature evolution during magma ascent in basaltic effusive eruptions: A numerical application to Stromboli volcano

    NASA Astrophysics Data System (ADS)

    La Spina, G.; Burton, M.; de'Michieli Vitturi, M.

    2015-09-01

    The dynamics of magma ascent are controlled by the complex, interdependent processes of crystallisation, rheological evolution, gas exsolution, outgassing, non-ideal gas expansion and temperature evolution. Temperature changes within the conduit, in particular, play a key role on ascent dynamics, since temperature strongly controls the crystallisation process, which in turn has an impact on viscosity and thus on magma ascent rate. The cooling produced by gas expansion is opposed by the heat produced by crystallisation, and therefore the temperature profile within the conduit is quite complex. This complexity means that unravelling the dynamics controlling magma ascent requires a numerical model. Unfortunately, comprehensive, integrated models with full thermodynamic treatment of multiple phases and rheological evolution are challenging to produce, due to the numerical challenges involved. Until now, models have tended to focus on aspects of the problem, without a holistic approach in which petrological, thermodynamic, rheological and degassing processes, and their interactions, were all explicitly addressed and quantified. Here, we present a new, multiphase steady-state model for magma ascent in which the main physical and chemical processes, such as crystallisation, degassing, outgassing, rheological evolution and temperature variations, are quantitatively calculated. Basaltic magma's crystallisation and flow are sensitive to initial temperature and volatile content, and therefore we investigate temperature variations during magma ascent in a basaltic system with a range of volatile contents. As a test case, we use one of the most well-studied recent basaltic effusive eruptions: the 2007 eruption of Stromboli, Italy. Assuming equilibrium crystallisation and exsolution, we compare the solutions obtained both with and without an isothermal constraint, finding that temperature variations within the conduit have a significant influence on the ascent dynamics and

  18. Magma mixing at mid-ocean ridges - Evidence from legs 45 and 46-DSDP. [petrologic and geochemical study of basalts

    NASA Technical Reports Server (NTRS)

    Dungan, M. A.; Long, P. E.; Rhodes, J. M.

    1978-01-01

    An integrated petrologic and geochemical study of basalts recovered in Legs 45 and 46 (DSDP) has indicated, on the basis of disequilibrium mineralogy, that these moderately evolved basalts are mixtures of primitive mantle-derived tholeiites with more evolved magmas. Plagioclase phenocrysts are characterized by substantial diversity in composition and zoning pattern. Many olivine and plagioclase phenocrysts are too refractory to be in equilibrium with liquids of the host basalt composition but possess a composition consistent with crystallization from a primitive mantle-derived basalt liquid. On the basis of melt inclusions trapped in the olivine phenocrysts, features of the primitive melt are estimated. It is suggested that subvolcanic magma chambers beneath midocean ridges receive periodic injections of this primitive melt and its attendant phenocrysts which mix with fractionated chamber-bound magmas, resulting in observed moderately evolved lavas.

  19. The formation of plagioclase chains during convective transfer in basaltic magma

    PubMed

    Philpotts; Dickson

    2000-07-06

    The basaltic rock in the lower part of the thick Holyoke lava flow in Connecticut and Massachusetts has been shown to have a remarkable texture, with crystals of feldspar linked together in a continuous three-dimensional network of chains. Heating experiments have revealed that this network persists to temperatures where the rock is 75% liquid, and therefore the network was interpreted to have formed at an early stage of crystallization and to have played an important role in the compaction of crystal mush in the lower part of the flow. Despite the texture's importance to our understanding of how such basalt flows form, the origin of the texture has remained uncertain. Here we show that, although the network is present in the lower third of the flow, it was actually formed in the upper solidification front and was transported down in plumes of dense crystal mush. Convection of this type has been postulated for intrusive magma chambers, but corroborative field evidence has been equivocal, especially in lava lakes and flows. Preservation of the roof-generated texture in the lower part of a thick flood-basalt flow therefore constitutes important evidence for the role of convection in the solidification and differentiation of a simple magma sheet.

  20. Evolution of carbonated melt to alkali basalt in the South China Sea

    NASA Astrophysics Data System (ADS)

    Zhang, Guo-Liang; Chen, Li-Hui; Jackson, Matthew G.; Hofmann, Albrecht W.

    2017-01-01

    CO2 is considered to play a key role in the melting of the deep upper mantle, and carbonated silicate melts have been widely predicted by partial melting experiments to exist at mantle depths of greater than 80 km. However, such melts have not been shown to exist in nature. Thus, the relationship between CO2 and the origin of silicate melts is highly speculative. Here we present geochemical analyses of rocks sampled from the South China Sea, at the Integrated Ocean Discovery Program Site U1431. We identify natural carbonated silicate melts, which are enriched in light rare earth elements and depleted in Nb and Ta, and show that they were continuously transformed to alkali basalts that are less enriched in light rare earth elements and enriched in Nb and Ta. This shows that carbonated silicate melts can survive in the shallow mantle and penetrate through the hot asthenosphere. Carbonated silicate melts were converted to alkali basaltic melts through reactions with the lithospheric mantle, during which precipitation of apatite accounts for reduction of light rare earth elements and genesis of positive Nb-Ta anomalies. We propose that an extremely thin lithosphere (less than 20 km in the South China Sea) facilitates extrusion of the carbonated silicate melts, whereas a thickened lithosphere tends to modify carbonated silicate melt to alkali basalt.

  1. Constraining Open-System Processes in the Generation of Basaltic Magma Using 87Sr/86Sr of Individual Minerals and Melt Inclusions, Pisgah Crater, Ca

    NASA Astrophysics Data System (ADS)

    Ramos, F. C.; Wolff, J. A.

    2002-12-01

    Basaltic magmas have been extensively used to infer the geochemical nature of mantle sources. Studies which make such inferences typically focus on basalts that are characterized by assumed primary magma characteristics such as high MgO contents. Such characteristics are typically used as justification to discount or suggest only a minimal influence of open-system modifications, such as those resulting from crustal assimilation. Often, very little effort is made to more thoroughly eliminate this possibility because it is very difficult to identify and constrain such effects especially if the assimilated crust is mafic in character. Alkali basalts and hawaiities erupted at Pisgah Crater in the Mojave Desert of California result from open-system processes yet still retain high MgO (6-8%) contents. The specific processes responsible for extensive trace element and isotopic variations in these basalts, however, are in dispute. Glazner et al. (1991) suggest that Pisgah Crater trace element and isotopic variations originate from assimilation of mafic crust while Reiners (2002) suggests that such variations result from mixing of mantle-derived garnet peridotite and garnet pyroxenite magmas. Large 87Sr/86Sr variations among and within individual plagioclase, clinopyroxene, amphibole, groundmass, and melt inclusions in olivine attest to the effects of open-system processes and indicate a complex mixing process (i.e., not two-component mixing) that occurred up to the time of eruption (Ramos et al, in prep). 87Sr/86Sr of minerals indicate that early and intermediate erupted lavas retain relatively uncontaminated signatures while the latest erupted lavas reflect much higher 87Sr/86Sr, consistent with contamination at crustal pressures (i.e., within the plagioclase stability field). Major element compositions of melt inclusions hosted in olivine confirm the presence of highly evolved magmas (e.g., MgO: 0.5 to 3%, SiO2: 52-57%) in later erupted lavas. Whole grain olivine

  2. Enriched asthenosphere melting beneath the nascent North African margin: trace element and Nd isotope evidence in middle-late Triassic alkali basalts from central Sicily (Italy)

    NASA Astrophysics Data System (ADS)

    Cirrincione, Rosolino; Fiannacca, Patrizia; Lustrino, Michele; Romano, Vanessa; Tranchina, Annunziata; Villa, Igor M.

    2016-03-01

    During the dismembering of the Pangea supercontinent, middle-late Triassic sub-volcanic alkaline rocks were emplaced in central Sicily. These rocks have an alkali basaltic composition and show OIB-like incompatible element patterns in primitive mantle-normalized diagrams (e.g., enrichments in HFSE and LREE coupled with high HFSE/LILE ratios), as well as slightly positive \\varepsilon_{Nd} values. Only subtle effects of crustal contamination at shallow depths emerge from geochemical data. These characteristics are very different compared with the Permian calcalkaline magmas from elsewhere in SW Europe still carrying the geochemical signature of modifications related to the Variscan orogeny. The mineralogical, geochemical and isotopic compositions of the investigated samples from central Sicily are also different from the coeval shoshonitic volcano-plutonic formations of Southern Alps (Dolomites). The incompatible element composition and Nd isotopic ratios are consistent with low-degree partial melting of a moderately depleted asthenospheric mantle source, with a negligible involvement of the thinned continental crust. The studied alkaline basalts represent the only known evidence of a segment of the Triassic rift system associated with early Pangea breakup in central Sicily. The close similarity of the central Sicily Triassic alkali basalts with coeval basalts emplaced along former orogenic sutures across the peri-Mediterranean area suggests a common origin related, at least partly, to asthenospheric passive upwelling following the tectonic collapse of the Variscan Belt. These rocks provide new constraints on the spatial-temporal distribution, magma source evolution and geodynamic meaning of the widespread Permo-Triassic basic magmatism developed after the end of the Variscan Orogeny in southwestern Europe.

  3. Tidal Dissipation in Basalt Magma Chambers - Implications for Io's Loki Patera and Icy Satellite Cores

    NASA Astrophysics Data System (ADS)

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

    2006-05-01

    We discuss tidal dissipation in molten basaltic magma and the results from model application to Io and Enceladus. Magma is a non-newtonian liquid with a complex rheology dependent on interactions between different phases: liquid, crystals and bubbles, resulting in a slurry with each component responding differently to temperature and stress. This study is based on results obtained for terrestrial basalts. For example, the evolution of crystal content as a function of temperature has been described for basalts [e.g., 1]. The behavior of cyclically stressed basalt has been observed in laboratory for frequencies corresponding to seismic waves between 1 and 200 sec. [e.g., 2-5]. While this frequency range is outside the range of dynamical frequencies considered in planetary sciences, these results show variations of the response as a function of the wavelength of the structure involved in the response. From the trend observed at low frequencies we extrapolate these data to tidal frequencies encountered at Io and Enceladus. We apply this result to a silicate magma chamber deep in Enceladus's core. Such a magma body has been proposed by Matson et al. [6, 7] as a heat source for keeping Enceladus warm over geological time and ultimately powering the observed volcanism [8]. We also apply the model to the 'magma sea' at Loki Patera [9] the source of 10-20% of Io's heat flow. In both cases we evaluate how much tidal dissipation can be produced. Our objectives are to chart the development and long-term evolution of magma chambers on bodies heavily influenced by tidal dissipation. From consideration of the relevant processes taking place over appropriate timescales, results show that self- regulation mechanisms are in place, such that crystal content and heat production remain in equilibrium over geological time. Our preliminary results support long-term preservation of a magma chamber in Enceladus' core. Coupled thermal-orbital modeling also indicates consistency between this

  4. Apollo 14 mare basalt petrogenesis - Assimilation of KREEP-like components by a fractionating magma

    NASA Technical Reports Server (NTRS)

    Neal, Clive R.; Taylor, Lawrence A.; Lindstrom, Marilyn M.

    1988-01-01

    Based on analysis of whole rock and mineral data from 22 samples, it is shown that the trace element characteristics of 14321 high-AL mare basalts exhibit variations that cannot be related to short-range mixing alone. It is suggested that the five groups defined for Apollo 14 high-Al basalts are due to sampling. It is found that the addition of new data results in a continuum of compositions. Detailed trace element modeling demonstrates that a primitive parental magma evolves by assimilation and fractional crystallization (AFC) with KREEP. The ratio of mass assimilated to mass crystallized is found to be 0.22. It is suggested that this AFC process occurs within the lunar crust and that the fractionating phases are effectively removed from the system.

  5. Recent volcanism in the Siqueiros transform fault: Picritic basalts and implications for MORB magma genesis

    USGS Publications Warehouse

    Perfit, M.R.; Fornari, D.J.; Ridley, W.I.; Kirk, P.D.; Casey, J.; Kastens, K.A.; Reynolds, J.R.; Edwards, M.; Desonie, D.; Shuster, R.; Paradis, S.

    1996-01-01

    Small constructional volcanic landforms and very fresh-looking lava flows are present along one of the inferred active strike-slip faults that connect two small spreading centers (A and B) in the western portion of the Siqueiros transform domain. The most primitive lavas (picritic and olivine-phyric basalts), exclusively recovered from the young-looking flows within the A-B strike-slip fault, contain millimeter-sized olivine phenocrysts (up to 20 modal%) that have a limited compositional range (Fo91.5-Fo89.5) and complexly zoned Cr-Al spinels. High-MgO (9.5-10.6 wt%) glasses sampled from the young lava flows contain 1-7% olivine phenocrysts (Fo90.5-Fo89) that could have formed by equilibrium crystallization from basaltic melts with Mg# values between 71 and 74. These high MgO (and high Al2O3) glasses may be near-primary melts from incompatible-element depleted oceanic mantle and little modified by crustal mixing and/or fractionation processes. Phase chemistry and major element systematics indicate that the picritic basalts are not primary liquids and formed by the accumulation of olivine and minor spinel from high-MgO melts (10% < MgO < 14%). Compared to typical N-MORB from the East Pacific Rise, the Siqueiros lavas are more primitive and depleted in incompatible elements. Phase equilibria calculations and comparisons with experimental data and trace element modeling support this hypothesis. They indicate such primary mid-ocean ridge basalt magmas formed by 10-18% accumulative decompression melting in the spinel peridotite field (but small amounts of melting in the garnet peridotite field are not precluded). The compositional variations of the primitive magmas may result from the accumulation of different small batch melt fractions from a polybaric melting column.

  6. Limestone Assimilation by Basaltic Magmas: an Experimental re-Assessment and Application to Italian Volcanoes

    NASA Astrophysics Data System (ADS)

    Gaillard, F.; Iacono Marziano, G.; Pichavant, M.

    2007-12-01

    Based on field observations, Daly proposed hundred years ago that limestone assimilation could generate silica undersaturated magma. Discarded by successive studies this process is here re-assessed by an experimental survey and is proposed as a differentiation mechanisms operating in the plumbing system of Italian Plio- Quaternary volcanoes. The widespread presence of sedimentary limestone in their basement, the abundant high temperature skarns in their eruptive products and their important CO2 emissions make carbonate assimilation in the plumbing system of Italian volcanoes a central question, which, however, has been poorly addressed by specific studies. Experimental results of Ca-Mg carbonate assimilation by hydrated mafic magmas in the range 1050-1150°C, 0.1- 500 MPa are here reported. Two types of experiments have been performed in internally heated pressure vessels to simulate magma-carbonate interactions. In the first type we characterized equilibrium phase diagram of basaltic system as a function of variable amount of added carbonate (up to 20 wt percent of the total charge). In all experiments, carbonates completely breakdown and no immiscible carbonate melts are observed. MgO and CaO are essentially incorporated in clinopyroxene and olivine, while CO2 is partitioned between the fluid phase and the silicate glass, with a strong preference for the fluid. The major effect of carbonate incorporation on liquidus phase equilibria is to favor the massive crystallization of Ca-rich clinopyroxene (accompanied by leucite for some starting magma compositions) and the consumption of the other phases crystallizing in carbonate-free conditions (olivine, plagioclase, Fe-Ti oxides). Crystallization of pyroxene from carbonate consumes magmatic SiO2 leading to silica undersaturated residual liquid. Such desilication trend is recognized in several magmatic series emitted in Italy strongly suggesting that assimilation of carbonate is an important regional process. The

  7. Sulfur in Hydrous, Oxidized Basaltic Magmas: Phase Equilibria and Melt Solubilities

    NASA Astrophysics Data System (ADS)

    Pichavant, M.; Scaillet, B.; di Carlo, I.; Rotolo, S.; Metrich, N.

    2006-05-01

    Basaltic magmas from subduction zone settings are typically S-rich and may be the ultimate source of sulfur in vapor phases emitted during eruptions of more silicic systems. To understand processes of sulfur recycling in subduction zones, the behaviour of S in hydrous, oxidized, mafic arc magmas must be known. Although experimental data on S-bearing basaltic melts are available for dry conditions, and under both reduced and oxidized fO2, no study has yet examined the effect of S in hydrous mafic melts. In this work, 3 starting compositions were investigated, a basaltic andesite, a K basalt and a picritic basalt. For each composition, experimental data for S-added (1 wt % elemental sulfur) and S-free charges were obtained under similar P-T- H2O-fO2. All experiments were performed at 4 kbar and at either 950 ° C (basaltic andesite), 1100 ° C (K basalt) or 1150 ° C (picritic basalt). These were carried out in an internally heated vessel pressurized with Ar-H2 mixtures and fitted with a drop-quench device, and lasted for between 15 and 99 h. Either Au (950 ° C) or AuPd alloys (1100 and 1150 ° C) were used as containers. These latter perform satisfactorily under strongly oxidizing conditions, i.e., for fO2 above NNO+1 at 1100 and 1150 ° C. Below NNO+1, Pd- Au-S-Fe phases appear in the charges, suggesting extensive interaction between S and the capsule material. Experimental redox conditions, determined from Ni-Pd-O sensors, ranged between NNO+1.3 to +4.1 (basaltic andesite), +0.6 to +2.0 (K basalt), and +0.3 to +3.6 (picritic basalt). H2O concentrations in melt ranged from 8.2 wt % (basaltic andesite), decreasing to 2.2-3.9 wt % (K basalt) and 2.5-5.0 wt % (picritic basalt). All 3 compositions studied crystallize anhydrite and Fe-Ni-S-O sulphide as saturating S-bearing phases, anhydrite at high fO2 and sulphide at lower fO2, although melt composition also influences their stability. Anhydrite is present at a fO2 as low as NNO+1.5 in the K basalt. In the picritic

  8. Geochemical insights into the role of metasomatic hornblendite in generating alkali basalts

    NASA Astrophysics Data System (ADS)

    Dai, Li-Qun; Zhao, Zi-Fu; Zheng, Yong-Fei

    2014-10-01

    petrology suggested the role of hornblendite in generating alkali basalt. This mechanism is confirmed by an integrated study of major-trace elements and radiogenic isotopes for Mesozoic alkali basalts from the Qinling orogen in China. The alkali basalts have high contents of MgO (4.8-11.1 wt %, Mg# = 47-69), Na2O + K2O (2.9-5.4 wt %), TiO2 (2.0-3.1 wt %) but low content of SiO2 (41.4-49.6 wt %), which are generally silica-undersaturated with normative minerals of nepheline and olivine. They exhibit OIB-like trace element distribution patterns, with enrichment of LILE and LREE but no depletion of HFSE relative to the primitive mantle. They also show relatively depleted Sr-Nd-Hf isotope compositions, with low initial 87Sr/86Sr ratios of 0.7028-0.7058, positive ɛNd(t) values of 4.0-9.8 and ɛHf(t) values of 8.8-13.5 for whole-rock, and positive ɛHf(t) values of 5.2-16.4 for zircon. Such element and isotope features indicate their origination from the juvenile subcontinental lithospheric mantle (SCLM) source with involvement of crustal components. The alkali basalts generally have high K2O/Na2O ratios, and high K2O and TiO2 contents, suggesting their derivation from partial melting of hornblendite-rich mantle lithology. They also exhibit variable K/La and Ti/La ratios that are correlated with (La/Yb)N ratios, indicating a geochemical heterogeneity of the SCLM source. Taken together, all the above geochemical features can be accounted for by partial melting of a hornblendite-rich SCLM source. The hornblendite would be generated by reaction of the juvenile SCLM wedge peridotite with hydrous felsic melts derived from subducted Palaeotethyan oceanic crust at the slab-mantle interface in the subduction channel. Therefore, orogenic alkali basalts record recycling of the subducted fossil oceanic crust, and the metasomatic hornblendite is an important lithology in local SCLM domains above fossil subduction channels.

  9. Short Timescales for Crustal Residence, Transport and Contamination of Flood Basalt Magma: Crystal Isotope Stratigraphy of the Columbia River Basalt Group.

    NASA Astrophysics Data System (ADS)

    Tollstrup, D. L.; Ramos, F. C.; Wolff, J. A.

    2002-12-01

    Geochemical studies of continental flood basalt magmas provide evidence for contributions from one or more enriched reservoirs. There is, however, no consensus on the role of continental crust as a major source of enriched signatures. With its stratigraphy defined and mapped at the scale of individual flows, the Columbia River Basalt Group (CRBG) is the most thoroughly studied continental flood basalt province in the world. Its tectonic position (overlying both thin accreted Mesozoic crust and thick ancient cratonic crust) makes the CRBG ideal for isolating the contribution of crust in the petrogenesis of continental flood basalts. Many flows are plagioclase-phyric. Because plagioclase in basaltic magmas can be assumed to have grown at crustal pressures, growth layers in plagioclase phenocrysts record changes in the chemical and isotopic composition of the magma occurring at crustal depths. We have initiated a micro-sampling study utilizing laser ablation multicollector ICP-MS (ThermoFinnigan Neptuner) to analyze 87Sr/86Sr variability in plagioclase and clinopyroxene phenocrysts (where present) and associated groundmass. Initial results are: 1) plagioclase and clinopyroxene phenocrysts within CRBG lavas are overall less radiogenic than host groundmass and 2) plagioclase phenocrysts are commonly zoned from less radiogenic cores to more radiogenic rims. The rims may have similar compositions to, or be less radiogenic than, host groundmass. One-dimensional diffusion modeling applied to observed 87Sr/86Sr zoning and crystal/groundmass gradients constrains phenocryst residence times, and the timescale of crustal-level petrogenetic events that modified CRBG magmas. Residence times for phenocrysts in their final host liquid may be as little as 10 years prior to quenching. These results require that the 87Sr/86Sr composition of the CRBG magmas increased rapidly with time at crustal pressures during and after phenocryst growth. This could result from mixing between magmas

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

    SciTech Connect

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

    1993-03-01

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

  11. 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.

  12. Basaltic Magma-Water Interaction on Earth: Recognition Criteria To Aid Planetary Mapping on Mars (Invited)

    NASA Astrophysics Data System (ADS)

    Skilling, I. P.; Graettinger, A. H.; Mercurio, E.; McGarvie, D.; Edwards, B. R.

    2013-12-01

    The interaction of basaltic magma with frozen/liquid water or wet sediment is a very common process on Earth, resulting in a wide array of explosively and non-explosively generated products at the micron to kilometre scale. A variety of products and edifices on Mars have also been interpreted as having formed by such interaction, but with the exception of rootless cones, such interpretations are rarely unequivocal. This talk focuses on terrestrial process recognition criteria at a scale, orientation (vertical) and erosion level that is relevant to Mars geological mapping. In this context, we emphasise intrusions with peperite margins and wide hydrothermal haloes, steep margins of ice-contact lava flows, subaerial-subaqueous lava delta transitions, lava domains with distinctive water-cooled jointing, edifices that are dominated by slumped and rotated beds, and the presence of surrounding fluvial deposits and erosion. The most common products of magma-water interaction on Earth are subaqueously emplaced lava flows, which are dominated by pillow lavas. Though pillows are not easy to distinguish from subaerial pahoehoe toes at the resolution of most remote imagery, they are commonly associated with distinctively jointed lava domains, which are usually on a larger scale, including areas of water-cooled jointing (curvicolumnar, blocky etc), lava-filled tubes, which often display radial jointing, and steep talus deposits of joint-block breccia. Subaqueous basaltic lavas emplaced in an ice-confined environment may also display near-vertical ice-contact margins, draped by curtains of elongate pillows or cavities formed from melting of included ice-blocks. Subaerial lava flows that transition into water also develop large-scale foreset-bedding close to the angle of repose, which should be easily visible, at least in oblique imagery. As the majority of the Martian surface is more deeply eroded than most areas of terrestrial basaltic volcanism, it is important to discuss

  13. Uptaking of plagioclase xenocryst into H2O-rich rear-arc basaltic magma

    NASA Astrophysics Data System (ADS)

    Hamada, M.

    2015-12-01

    Kuritani et al. (2013, Mineral. Petrol.) and Kuritani et al. (2014, Contrib. Mineral. Petrol.) estimated genetic conditions of primary arc magmas beneath the Iwate volcano (a frontal arc volcano in the northeast Japan arc) and the Sannome-gata volcano (a rear-arc volcano in the northeast Japan arc) based on analyses of volcanic rocks and numerical simulation. They estimated that H2O concentrations of primary melts are 4-5 wt.% beneath the Iwate volcano and 6-7 wt.% beneath the Sannnome-gata volcano, respectively. Their arguments mean that primary melts beneath frontal-arc volcanoes and rear-arc volcanoes are both H2O-rich, yet there has been no direct evidence to support their arguments at the Sannnome-gata volcano because volcanic rocks are either almost aphyric and/or almost no melt inclusions were found. Hydrogen concentration in nominally anhydrous minerals serves as a hygrometer of arc basaltic melts (e.g., Hamada et al. 2013, Earth Planet. Sci. Lett.). In this study, hydrogen concentration of plagioclase as a crustal xenocryst was analyzed to estimate H2O concentration of basaltic melt coexisted with plagioclase before the eruption. Plagioclase xenocrists were separated from crushed scoria which erupted from the Sannome-gata volcano 20,000-24,000 years ago. Composition of the plagioclase core is homogeneous and ranges from An30 through An35. The rim is 150 to 200-μm-thick dusty zone whose composition is around An60, suggesting that the rim crystallized rapidly from degassed basaltic melt. The profiles of infrared absorption area per unit thickness across the plagioclase core were obtained using Fourier Transform InfraRed spectrometer (FTIR). The inner core contains hydrogen of about 60 wt. ppm H2O, and hydrogen concentration elevates at outer core. Hydrogen concentration at the outermost core of plagioclase is >200 wt. ppm H2O, suggesting that plagioclase xenocrists were taken by hydrous melt (H2O>5 wt.%; Hamada et al. 2014, Earth Planet. Sci. Lett.) and

  14. Alkaline melt - peridotite reaction as a potential mechanism for the nephelinite-alkali basalt transition observed in intraplate volcanoes

    NASA Astrophysics Data System (ADS)

    Pilet, S.; Rochat, L. L.; Baker, M. B.; Stolper, E. M.

    2013-12-01

    Melt-peridotite reaction is a process that can significantly modify the compositions of melts as they transit the mantle. Depending on the silica activity of the liquid such interaction can cause either the dissolution of olivine (ol) with associated precipitation of orthopyroxene (opx), or opx dissolution and ol precipitation. Here we show that the reaction between alkaline melts and peridotite at pressures of 1.5-3 GPa can reproduce the range of mafic compositions seen in intraplate volcanoes. Alkaline lavas from continental volcanoes or oceanic islands underlain by thick lithosphere (>50 km) are characterized by a compositional continuum from nephelinites to alkali olivine basalts (and sometimes to tholeiites). This continuum is associated with a decrease in incompatible trace-element concentrations from nephelinitic to less alkaline magmas. This continuum is classically interpreted as reflecting an increase in the degree of partial melting of a common source. However, no experiments on mantle lithologies (peridotite, pyroxenite) have reproduced the observed compositional spectrum (or even the observed range of silica contents: ~40 to 48 wt. % SiO2). Further, the decreases in HREE concentrations in lavas along the continuum (i.e., nephelinites to alkali olivine basalts/tholeiites) seem difficult to explain by increasing degrees of partial melting of a common source. Alternatively, this continuum could be explained by reaction between nephelinitic/basanitic liquid and peridotite [1, 2]. To test this hypothesis, we performed 'sandwich' experiments in which a layer of hornblendite (producing nephelinitic liquids upon melting [2]) was packed between layers of moderately depleted peridotite. Experiments were performed at 1.5, 2.5, and 3 GPa and temperatures of 1225-1450°C. The melts produced by the reaction are significantly richer in SiO2 (~4-5 wt. %) than the initial alkaline liquid; this increase is explained by the dissolution of opx at all three pressures and

  15. Rheological Properties of Ascending Magma at a Basaltic Andesitic System: Puy De La Vache, France As a Case Study

    NASA Astrophysics Data System (ADS)

    Sanchez, L.; Sehlke, A.; Harris, A. J. L.; Whittington, A. G.; Menand, T.

    2014-12-01

    Eruptions at basaltic andesitic systems are often characterized by effusive behavior. However, an increasing number of examples around the World indicate that these magmas, with low degrees of differentiation and basic compositions, have the capacity to produce explosive eruptions; thus presenting a considerable hazard. Volcanoes in the Chaîne des Puys (France), more specically the Puy de la Vache volcano, are good examples of explosive activity at basaltic andesitic centers. A combination of factors can explain this behavior: high magma ascent rate, high content of dissolved gases and high crystal contents. The latter leads to an increase in magma viscosity. The rheological properties of the magma control the eruptive style; viscosity itself strongly depends on composition, temperature, crystal fraction and vesicularity. In particular, an increase in crystal content may drastically change the composition of the residual melt and adds rigid particles to the mixture, inducing a complex strain rate dependence. Here, we are interested in the rheology of basaltic andesitic magmas as a function of crystal content. To quantify the effect of crystals on the viscosity, we measured the stress-strain relationship of the remelted Puy de la Vache lava by concentric cylinder viscometry at super and subliquidus conditions. Concurrently, we performed a textural analysis to determine the crystal fraction at each temperature. We also measured viscosities close to the glass transition using a parallel plate viscometer. We then compared the measured viscosities with those obtained from calculations using existing models. With the experimentally obtained stress-strain rate relationship of the magma at different temperatures and crystal fractions, our goal is to design a model where viscosity varies across the conduit depending on the shear stress and strain rate conditions. This will allow us to characterize the potential explosive behavior of basaltic to andesitic magmas.

  16. Evidence for Magma-Mixing and Disequilibrium in 'Primitive' Basaltic Andesites From Mount Shasta, Northern California

    NASA Astrophysics Data System (ADS)

    Leeman, W. P.; Streck, M. J.; Chesley, J. T.; Tonarini, S.

    2005-12-01

    High-Mg basaltic andesites near Mt. Shasta volcano have been considered fundamental to establishing the existence of exceptionally water-rich primary magmas in this system, implying significant slab-derived fluid fluxes into the underlying mantle wedge (Grove et al., 2002). This notion was reinvestigated via new mineralogical and geochemical studies of fresh scoria blocks from the Whaleback volcano (loc. S17; Anderson,1979). These high-Mg andesites (58% SiO2, 8.5% MgO, Mg# = 76, 120 ppm Ni, 550 ppm Cr) carry small dunitic xenoliths and xeno/phenocrysts (ol+opx+cpx). Plagioclase is not a liquidus phase. Electron microprobe traverses and back-scattered images show that mafic silicates, particularly pyroxenes, have complex histories. Olivine compositions of larger crystals and interiors are often above Fo90 up to Fo94 whereas microphenocrysts and rims of larger crystals are ~Fo87. Complexities among pyroxenes include: (a) Cores of opx and cpx with low Mg# (~67) containing melt inclusions; this evidence indicates these pyroxenes crystallized from magma of roughly dacitic composition; (b) Virtually all low Mg# grains are resorbed and have overgrowths (~20 microns) of high Mg# (87-92) that may be internally zoned arriving at a Mg# near 80 at the outermost euhedral rim; (c) Another variant is orthopyroxene with 'wormy' texture and either a thin (~15 microns) euhedral overgrowth or anhedral outline; compositions of resorbed interiors and overgrowth are similar ( Mg# range: 80 to 90), but distribution of lower and higher Mg# in resorbed areas is patchy whereas any compositional zoning of overgrowth follows crystal shape and arrives again at a Mg# of ~80 at the outermost rim. These data record mixing of diverse magmas (dacite and one or more basaltic liquids) combined with entrainment of ultramafic crystal debris during wall rock contamination, and eventual cooling and equilibration. Low Al2O3 contents in the pyroxenes imply that these minerals grew at relatively low

  17. Generation of CO2-rich melts during basalt magma ascent and degassing

    NASA Astrophysics Data System (ADS)

    Pichavant, Michel; Di Carlo, Ida; Rotolo, Silvio G.; Scaillet, Bruno; Burgisser, Alain; Le Gall, Nolwenn; Martel, Caroline

    2013-08-01

    To test mechanisms of basaltic magma degassing, continuous decompressions of volatile-bearing (2.7-3.8 wt% H2O, 600-1,300 ppm CO2) Stromboli melts were performed from 250-200 to 50-25 MPa at 1,180-1,140 °C. Ascent rates were varied from 0.25 to ~1.5 m/s. Glasses after decompression show a wide range of textures, from totally bubble-free to bubble-rich, the latter with bubble number densities from 104 to 106 cm-3, similar to Stromboli pumices. Vesicularities range from 0 to ~20 vol%. Final melt H2O concentrations are homogeneous and always close to solubilities. In contrast, the rate of vesiculation controls the final melt CO2 concentration. High vesicularity charges have glass CO2 concentrations that follow theoretical equilibrium degassing paths, whereas glasses from low vesicularity charges show marked deviations from equilibrium, with CO2 concentrations up to one order of magnitude higher than solubilities. FTIR profiles and maps reveal glass CO2 concentration gradients near the gas-melt interface. Our results stress the importance of bubble nucleation and growth, and of volatile diffusivities, for basaltic melt degassing. Two characteristic distances, the gas interface distance (distance either between bubbles or to gas-melt interfaces) and the volatile diffusion distance, control the degassing process. Melts containing numerous and large bubbles have gas interface distances shorter than volatile diffusion distances, and degassing proceeds by equilibrium partitioning of CO2 and H2O between melt and gas bubbles. For melts where either bubble nucleation is inhibited or bubble growth is limited, gas interface distances are longer than volatile diffusion distances. Degassing proceeds by diffusive volatile transfer at the gas-melt interface and is kinetically limited by the diffusivities of volatiles in the melt. Our experiments show that CO2-oversaturated melts can be generated as a result of magma decompression. They provide a new explanation for the occurrence

  18. Petrogenesis of basaltic volcanic rocks from the Pribilof Islands, Alaska, by melting of metasomatically enriched depleted lithosphere, crystallization differentiation, and magma mixing

    USGS Publications Warehouse

    Chang, J.M.; Feeley, T.C.; Deraps, M.R.

    2009-01-01

    The Pribilof Islands, Alaska, are located in the Bering Sea in a continental intraplate setting. In this study we examine the petrology and geochemistry of volcanic rocks from St. Paul (0??54-0??003 Ma) and St. George (2??8-1??4 Ma) Islands, the two largest Pribilof Islands. Rocks from St. George can be divided into three groups: group 1 is a high-MgO, low-SiO. 2 suite composed primarily of basanites; group 2 is a high-MgO, high-SiO 2 suite consisting predominantly of alkali basalts; group 3 is an intermediate- to low-MgO suite that includes plagioclase-phyric subalkali basalts and hawaiites. Major and trace element geochemistry suggests that groups 1 and 2 formed by small-degree partial melting of amphibole-bearing to amphibole-free garnet peridotite. Group 1 rocks were the earliest melts produced from the most hydrous parts of the mantle, as they show the strongest geochemical signature of amphibole in their source. The suite of rocks from St. Paul ranges from 14??4 to 4??2 wt % MgO at relatively constant SiO 2 contents (43??1-47??3 wt %). The most primitive St. Paul rocks are modeled as mixtures between magmas with compositions similar to groups 1 and 2 from St. George Island, which subsequently fractionated olivine, clinopyroxene, and spinel to form more evolved rocks. Plagioclase-phyric group 3 rocks from St. George are modeled as mixtures between an evolved melt similar to the evolved magmas on St. Paul and a fractionated group 2 end-member from St. George. Mantle potential temperatures estimated for primitive basanites and alkali basalts are ???1400??C and are similar to those of mid-ocean ridge basalts (MORB). Similarly, 87Sr/. 86Sr and 143Nd/. 144Nd values for all rocks are MORB-like, in the range of 0??702704-0??703035 and 0??513026-0??513109, respectively. 208Pb/. 204Pb vs 206Pb/. 204Pb values lie near the MORB end-member but show a linear trend towards HIMU (high time-integrated 238U/. 204Pb). Despite isotopic similarities to MORB, many of the major and

  19. Halogen degassing during ascent and eruption of water-poor basaltic magma

    USGS Publications Warehouse

    Edmonds, M.; Gerlach, T.M.; Herd, Richard A.

    2009-01-01

    A study of volcanic gas composition and matrix glass volatile concentrations has allowed a model for halogen degassing to be formulated for K??lauea Volcano, Hawai'i. Volcanic gases emitted during 2004-2005 were characterised by a molar SO2/HCl of 10-64, with a mean of 33; and a molar HF/HCl of 0-5, with a mean of 1.0 (from approximately 2500 measurements). The HF/HCl ratio was more variable than the SO2/HCl ratio, and the two correlate weakly. Variations in ratio took place over rapid timescales (seconds). Matrix glasses of Pele's tears erupted in 2006 have a mean S, Cl and F content of 67, 85 and 173??ppm respectively, but are associated with a large range in S/F. A model is developed that describes the open system degassing of halogens from parental magmas, using the glass data from this study, previously published results and parameterisation of sulphur degassing from previous work. The results illustrate that halogen degassing takes place at pressures of < 1??MPa, equivalent to < ~ 35??m in the conduit. Fluid-melt partition coefficients for Cl and F are low (< 1.5); F only degasses appreciably at < 0.1??MPa above atmospheric pressure, virtually at the top of the magma column. This model reproduces the volcanic gas data and other observations of volcanic activity well and is consistent with other studies of halogen degassing from basaltic magmas. The model suggests that variation in volcanic gas halogen ratios is caused by exsolution and gas-melt separation at low pressures in the conduit. There is no evidence that either diffusive fractionation or near-vent chemical reactions involving halogens is important in the system, although these processes cannot be ruled out. The fluxes of HCl and HF from K??lauea during 2004-5 were ~ 25 and 12??t/d respectively. ?? 2008 Elsevier B.V.

  20. Tectonic focusing of voluminous basaltic eruptions in magma-deficient backarc rifts

    NASA Astrophysics Data System (ADS)

    Anderson, Melissa O.; Hannington, Mark D.; Haase, Karsten; Schwarz-Schampera, Ulrich; Augustin, Nico; McConachy, Timothy F.; Allen, Katie

    2016-04-01

    The Coriolis Troughs of the New Hebrides subduction zone are among the youngest backarc rifts in the world. They reach depths of >3 km, despite their small size (<100 km in length and only 25-45 km wide) and their proximity to the arc front (˜50 km). The narrow, deep graben morphology is characteristic of magma-deficient arc rifts in the early stages of backarc extension, where the rate of extension and subsidence exceeds the magmatic input. Unexpectedly, the youngest graben, the Vate Trough, contains a centrally-located 1000-m tall and 14-km wide shield volcano with a large, 5 × 8 km breached summit caldera. The Nifonea axial volcano has a volume of ˜126 km3, reflecting unusually high extrusion rates, given its young age (<3 Ma), and the summit caldera hosts the remnants of a large lava lake, the first described from a submarine backarc setting. Extensive diffuse hydrothermal venting and several clusters of black smoker chimneys, with the highest recorded fluid temperatures (368 °C) in the SW Pacific, occur on the youngest lava flows. Comparison with similar axial volcanoes on the mid-ocean ridges suggests that the 46 ×106 m3 of sheet flows in the caldera could have been erupted in <30 hours. The focusing of voluminous basaltic eruptions into an otherwise magma-deficient backarc has been linked to strong left-lateral transtension caused by clockwise rotation and segmentation of the southern portion of the arc after collision with d'Entrecasteaux ridge. This study shows that the upper plate stresses can result in dramatic variability in magma supply and hydrothermal activity at the earliest stages of arc rifting and could explain the wide range of melt compositions, volcanic styles and mineral deposit types found in nascent backarc rifts.

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

    SciTech Connect

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

    1990-06-01

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

  2. High water contents in basaltic magmas from Irazú Volcano, Costa Rica

    NASA Astrophysics Data System (ADS)

    Benjamin, Ezra R.; Plank, Terry; Wade, Jennifer A.; Kelley, Katherine A.; Hauri, Erik H.; Alvarado, Guillermo E.

    2007-11-01

    Irazú volcano, in Costa Rica, erupts magmas unusually enriched in incompatible trace elements (e.g., K, REE) relative to most other arc volcanoes worldwide. Previous studies place this enrichment in the mantle, with minimal inputs from the subducting slab. In order to test the subduction vs. mantle hypotheses, we present here the first published measurements of the pre-eruptive volatile content of Irazú magmas. Olivine-hosted melt inclusions from basaltic-andesite scoria from the 1723 eruption are volatile-rich, containing > 3 wt.% H 2O, > 200 ppm CO 2, > 2500 ppm S, > 2200 ppm Cl and > 1800 ppm F. The average composition of the 1723 melt inclusions is very similar to that of the host scoria (SiO 2 = 54% SiO 2), although inclusions include more mafic (48% SiO 2) and felsic (57% SiO 2) compositions. The 1723 melt inclusions have the same trace element characteristics (e.g., Ba/La) as the host scoria, ruling out exotic crustal or mantle sources. Together, the melt inclusions and their host olivines (Fo 87-79) define a closed-system ascent path (150-20 MPa) of coupled degassing, crystallization, and cooling (1075-1045 °C). The maximum H 2O measured in the melt inclusions and the shape of the degassing path together constrain the pre-eruptive H 2O content to 3.2-3.5 wt.%, significantly higher than in ocean island basalts, but typical of arc magmas. The high H 2O in Irazú melts, coupled with their high Cl/K 2O, are inconsistent with enriched mantle with minimal slab fluid addition. We propose instead that subducting input is the dominant contributor to Irazú's geochemical compositions. Galapagos-derived seamounts and volcaniclastics are currently entering the trench near Irazú, and provide to the Irazú source both volatiles (from seafloor hydration and chlorination) and ocean-island-type trace elements and isotopes. A few percent of subducted Galapagos volcanics added to MORB mantle can create Irazú compositions quantitatively, provided elements are further

  3. 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

  4. The influence of magmatic differentiation on the oxidation state of Fe in a basaltic arc magma

    SciTech Connect

    Kelley, Katherine A.; Cottrell, Elizabeth

    2012-05-09

    Subduction zone basalts are more oxidized than basalts from other tectonic settings (e.g., higher Fe{sup 3+}/{Sigma}Fe), and this contrast may play a central role in the unique geochemical processes that generate arc and continental crust. The processes generating oxidized arc magmas, however, are poorly constrained, although they appear inherently linked to subduction. Near-surface differentiation processes unique to arc settings might drive oxidation of magmas that originate in equilibrium with a relatively reduced mantle source. Alternatively, arc magmas could record the oxidation conditions of a relatively oxidized mantle source. Here, we present new measurements of olivine-hosted melt inclusions from a single eruption of Agrigan volcano, Marianas, in order to test the influence of differentiation processes vs. source conditions on the Fe{sup 3+}/{Sigma}Fe ratio, a proxy for system oxygen fugacity (fO{sub 2}). We determined Fe{sup 3+}/{Sigma}Fe ratios in glass inclusions using {mu}-XANES and couple these data with major elements, dissolved volatiles, and trace elements. After correcting for post-entrapment crystallization, Fe{sup 3+}/{Sigma}Fe ratios in the Agrigan melt inclusions (0.219 to 0.282), and their modeled fO{sub 2}s ({Delta}QFM + 1.0 to + 1.8), are uniformly more oxidized than MORB, and preserve a portion of the evolution of this magma from 5.7 to 3.2 wt.% MgO. Fractionation of olivine {+-} clinopyroxene {+-} plagioclase should increase Fe{sup 3+}/{Sigma}Fe as MgO decreases in the melt, but the data show Fe{sup 3+}/{Sigma}Fe ratios decreasing as MgO decreases below 5 wt.% MgO. The major element trajectories, taken in combination with this strong reduction trend, are inconsistent with crystallization of common ferromagnesian phases found in the bulk Agrigan sample, including magnetite. Rather, decreasing Fe{sup 3+}/{Sigma}Fe ratios correlate with decreasing S concentrations, suggesting that electronic exchanges associated with SO{sub 2} degassing may

  5. CO2-rich melts generated during basalt magma ascent and degassing

    NASA Astrophysics Data System (ADS)

    Pichavant, M.; Di Carlo, I.; Rotolo, S.; Scaillet, B.; Burgisser, A.; Martel, C.

    2012-12-01

    To test mechanisms of basaltic magma degassing, experimental decompressions of volatile-bearing (2.7-3.8 wt% H2O, 600-1300 ppm CO2) Stromboli melts have been performed from 250-200 to 50-25 MPa at 1180-1140°C. Ascent rates were varied from 0.25 to ~ 1.5 m/s. Both the synthesis experiments that served to produce the volatile-bearing pre-decompression melts and the decompression experiments were performed in an internally heated vessel pressurized with Ar-H2 mixtures and fitted with a rapid-quench device. Charges were examined microscopically and by SEM. Vesicularities (% bubbles) were determined from image analysis on polished surfaces and in a few cases from X-ray microtomography. Electron microprobe analysis of post-decompression glasses shows that Fe loss to Au80Pd20 capsules is negligible. Concentrations of H2O and CO2 in both the pre- and post-decompression glasses, as well as their spatial distribution in the charge, were determined by FTIR. Glasses after decompression show a large range of vesicularities, from totally bubble-free to bubble-rich (~ 20 vol% bubbles), the latter with bubble number densities from 104 to 106/cm3, similar to Stromboli pumices. Bubble-poor or bubble-free samples (< 5 vol% bubbles) come from experiments decompressed either at constant rates to 50 MPa or at variable rates to 25 MPa. The bubble-rich charges are found among those decompressed under constant and fast ascent rates to 25 MPa. This suggest that, for our melt composition and dissolved volatile concentrations, homogeneous bubble nucleation requires a pressure drop of at least 150 MPa to be initiated. Varying ascent rates along the decompression path has a significant influence on bubble nucleation. Final melt H2O concentrations are homogeneous and in all cases close to solubilities. In contrast, the post-decompression melt CO2 concentrations are inversely correlated with vesicularities. Bubble-rich glasses have CO2 concentrations that follow theoretical closed

  6. Li, B - Behavior in Lunar Basalts During Shock and Thermal Metamorphism: Implications for H2O in Martian Magmas

    NASA Technical Reports Server (NTRS)

    Chaklader, Johny; Shearer, C. K.; Horz, F.

    2005-01-01

    Introduction: The water-content of Martian magmas is a topic of debate among researchers. Some Martian basalts are characterized with melt inclusions of biotite, apatite and amphibole; phases typically associated with hydration reactions on Earth [1-3]. However, the H-content of melt inclusions from these basalts is low, and bulk-rock H2O-contents range from a meager 0.013 to 0.035 wt. % in Shergotty [4]. Nonetheless, researchers note that low present-day water contents do not preclude a once hydrous past [5]. Since light lithophile elements (LLE), such as Li and B, partition into aqueous fluids at T > 350 C, workers proposed that Li-B depletions in pyroxene rims of Nakhlite and Shergottite basalts reflect the loss of several weight percent water from Martian magmas during crystallization [6]. Since similar depletions were observed in pyroxene rims from completely dry lunar basalts, it is likely that alternative mechanisms also contribute to the distribution of elements such as Li and B [7]. Given that many Martian basalts have experienced considerable shock pressures (15-45 GPa), it is possible that shock and subsequent thermal metamorphism may have influenced the volatile element records of these basalts [8]. In order to better understand the distribution of Li and B, we are studying the effects of crystal chemistry, shock pressure, and thermal metamorphism in pyroxenes from lunar basalts. Below, we discuss results from experimentally shocked and thermally metamorphosed Apollo 11, 10017 (A-11) and Apollo 17, 75035 (A-17) basalts.

  7. Experimental forward approach to alkali-rich magma generation from the metasomatized mantle: Melting of mantle xenoliths from Tallante (Murcia, Spain)

    NASA Astrophysics Data System (ADS)

    Manjón-Cabeza Córdoba, Antonio; Castro, Antonio; Moreno-Ventas, Ignacio; López-Ruiz, José; María Cebriá, Jose

    2014-05-01

    Alkali-rich volcanism is a wide spread characteristic of the circum Mediterranean terrains. One of the outcrops of this kind of magmas is the "Cabezo Negro" Volcano in Tallante (Murcia, Spain). The "Cabezo Negro" lavas are alkali-rich basalts, with a Na/K ratio higher than 1, that were erupted between 3 and 2 My ago. Previous experiments have shown that the origin of alkali-rich series can be attributed to an Amphibole-rich metasomatized mantle. Continuing this work, we have carried out several forward experiments at the piston cylinder apparatus under different P-T conditions starting from a sample from a metasomatized mantle xenolith hosted in those lavas. The chosen xenoliths are amphibole bearing clinopyroxenites. Although there are some of them that are phlogopite-bearing, we have worked with those bearing only pargasite as a hydrous phase, in order to ease the understanding of the role of the amphibole in the melting process. The experiments were carried out at conditions ranging from 10 to 20 kbar and from 1000 to 1300 °C mostly of them were "dry", but those under higher pressures were also under water saturated conditions. The results show compositions of melts that are very similar to those that can be found in the k-rich magmas around the Alpine Mediterranean orogenes. In particular, silica, the alkalis and the K/Na ratio tend to decrease with temperature and to increase with pressure for the experiments under dry conditions, to sum up, approaching to the amphibole stability-solidus line. For those under water saturated (and higher pressure) conditions, however, a slight increase of those values can occur with increasing temperature. Since in this kind of metasomatized mantle amphibole seems to draw the solidus line, we have have analyzed the REE and other trace-element relations between amphiboles and the obtained melts seeking for the origin of particular REE affinities that can be found in post-orogenic magmas with adakitic or sanukitic signatures.

  8. The roles of fractional crystallization, magma mixing, crystal mush remobilization and volatile-melt interactions in the genesis of a young basalt-peralkaline rhyolite suite, the greater Olkaria volcanic complex, Kenya Rift valley

    USGS Publications Warehouse

    Macdonald, R.; Belkin, H.E.; Fitton, J.G.; Rogers, N.W.; Nejbert, K.; Tindle, A.G.; Marshall, A.S.

    2008-01-01

    The Greater Olkaria Volcanic Complex is a young (???20 ka) multi-centred lava and dome field dominated by the eruption of peralkaline rhyolites. Basaltic and trachytic magmas have been erupted peripherally to the complex and also form, with mugearites and benmoreites, an extensive suite of magmatic inclusions in the rhyolites. The eruptive rocks commonly represent mixed magmas and the magmatic inclusions are themselves two-, three- or four-component mixes. All rock types may carry xenocrysts of alkali feldspar, and less commonly plagioclase, derived from magma mixing and by remobilization of crystal mushes and/or plutonic rocks. Xenoliths in the range gabbro-syenite are common in the lavas and magmatic inclusions, the more salic varieties sometimes containing silicic glass representing partial melts and ranging in composition from anorthite ?? corundum- to acmite-normative. The peralkaline varieties are broadly similar, in major element terms, to the eruptive peralkaline rhyolites. The basalt-trachyte suite formed by a combination of fractional crystallization, magma mixing and resorption of earlier-formed crystals. Matrix glass in metaluminous trachytes has a peralkaline rhyolitic composition, indicating that the eruptive rhyolites may have formed by fractional crystallization of trachyte. Anomalous trace element enrichments (e.g. ??? 2000 ppm Y in a benmoreite) and negative Ce anomalies may have resulted from various Na- and K-enriched fluids evolving from melts of intermediate composition and either being lost from the system or enriched in other parts of the reservoirs. A small group of nepheline-normative, usually peralkaline, magmatic inclusions was formed by fluid transfer between peralkaline rhyolitic and benmoreitic magmas. The plumbing system of the complex consists of several independent reservoirs and conduits, repeatedly recharged by batches of mafic magma, with ubiquitous magma mixing. ?? The Author 2008. Published by Oxford University Press. All

  9. 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

  10. Influence of an ocean on the propagation of magmas within an oceanic basaltic shield volcano

    NASA Astrophysics Data System (ADS)

    Le Corvec, Nicolas; McGovern, Patrick

    2015-04-01

    Basaltic shield volcanoes are a common feature on Earth and mostly occur within oceans, forming volcanic islands (e.g. Hawaii (USA), Galapagos (Ecuador), and recently Niijima (Japan)). As the volcano grows it will reach and emerge from the water surface and continue to grow above it. The deformation affecting the volcanic edifice may be influenced by the presence of the water level. We investigate how the presence of an ocean affects the state of stress within a volcanic edifice and thus magma propagation and fault formation. Using COMSOL Multiphysics, axisymmetric elastic models of a volcanic edifice overlying an elastic lithosphere were created. The volcanic edifice (height of ~6000 m and radius of ~ 60 km) was built either instantaneously or iteratively by adding new layers of equivalent volume on top of each other. In the later process, the resulting stress and geometry from the one step is transferred to the next as initial conditions. Thus each new layer overlies a deformed and stressed model. The water load was modeled with a boundary condition at the surface of the model. In the case of an instantaneous volcano different water level were studied, for an iteratively growing volcano the water level was set up to 4000 m. We compared the deformation of the volcanic edifice and lithosphere and the stress orientation and magnitude in half-space and flexural models with the presence or not of an ocean. The preliminary results show 1- major differences in the resulting state of stress between an instantaneous and an iteratively built volcanic edifice, similar to the results of Galgana et al. (2011) and McGovern and Solomon (1993), respectively; 2- the presence of an ocean decreases the amount of flexural response, which decreases the magnitude of differential stress within the models; and 3- stress orientation within the volcano and lithosphere in also influence of an ocean. Those results provide new insights on the state of stress and deformation of oceanic

  11. Along-arc Variations in Subduction Inputs and Mantle Source in Cascadia: Insights from Basaltic Arc Magmas

    NASA Astrophysics Data System (ADS)

    Johnson, E. R.; Walowski, K. J.; Wallace, P. J.; DeBari, S. M.; Bindeman, I. N.

    2015-12-01

    The Cascade arc spans ~1300 km from northern California into southern British Columbia, and basaltic magmas have erupted throughout the arc. The compositions of arc basalts are particularly useful in discerning mantle origins and inputs to the magmatic system, as basalts have undergone less differentiation en route to the surface. This presentation will draw on both existing datasets and new research to summarize our knowledge of Cascades arc basalt geochemistry and explore along-arc variability in mantle compositions and subduction recycling (oceanic crust and sediment). Cascades basalts are highly variable in composition; at least five types of primitive basalts erupt in the arc, with calc-alkaline basalts (CAB) and low-K tholeiites (LKT, also called high-alumina olivine tholeiites) being the most common. Such variability has been suggested to correlate with mantle heterogeneities and/or mantle melting processes, with CAB originating from fluid-fluxing of the mantle and LKT representing decompression melts (e.g., Leeman et al., 1990; Schmidt et al., 2008). However, recent work has suggested that, at least in some localities, CAB and LKT magmas could originate from a common mantle source (Mullen et al., 2014). A compilation of published primitive (>7 wt% MgO) basaltic magma compositions illustrates potential mantle heterogeneity along the arc, as well as variations in subduction recycling. Increases in melt H2O contents, radiogenic isotopes, oxygen isotopes, and LILE from north to south along the arc commonly suggest an increase in the amount of subduction component added to the mantle beneath the southern Cascades. The origin of the subduction component (crust vs. sediment) appears variable as well. With recent work on the seafloor sediments offshore of the north Cascades (Carpentier et al., 2010, 2013, 2014), researchers have been able to model the contributions of subducted sediment and crust to the north Cascades arc magmas and have suggested that sediment

  12. Water content in arc basaltic magma in the Northeast Japan and Izu arcs: an estimate from Ca/Na partitioning between plagioclase and melt

    NASA Astrophysics Data System (ADS)

    Ushioda, Masashi; Takahashi, Eiichi; Hamada, Morihisa; Suzuki, Toshihiro

    2014-12-01

    The variation in water content of arc basaltic magmas in the Northeast Japan arc and the Izu arc was estimated using a simple plagioclase phenocryst hygrometer. In order to construct a plagioclase phenocryst hygrometer optimized for arc basalt magmas, we have conducted high-pressure melting experiments of relatively primitive basalt from the Miyakejima volcano, a frontal-arc volcano in the Izu arc. As a result of the experiments, we found that the Ca/Na partition coefficient between plagioclase and hydrous basaltic melt increases linearly with an increase in H2O content in the melts. We then selected from literature geochemical data sets of relatively primitive basaltic rocks with no evidence of magma mixing and the most frequent Ca-rich plagioclase phenocrysts from 15 basaltic arc volcanoes including both frontal-arc and rear-arc volcanoes. In the 15 volcanoes studied, plagioclase phenocrysts of high anorthite content (An > 90) were commonly observed, whereas plagioclase phenocrysts in rear arc volcanoes usually had a lower anorthite content (90 > An > 80). In all volcanoes studied, the estimated H2O content of basaltic magma was at least 3 wt.% H2O or higher. The magmas of volcanoes located on the volcanic front have about 5 wt.% H2O in magma whereas those from the rear-arc side are slightly lower in H2O content.

  13. Assimilation of rhyolitic magma by basaltic recharge in the Bruneau-Jarbidge eruptive center, Snake River Plain (USA)

    NASA Astrophysics Data System (ADS)

    Morgavi, D.; de Campos, C. P.; Lavallee, Y.; Morgan, L. A.; Perugini, D.; Dingwell, D. B.

    2010-12-01

    Volcanic and magmatic activities in the Snake River Plain (SRP) have been characterised by a notably bimodal geochemical signature. The Bruneau-Jarbidge eruptive center (BJEC), in the southwestern SRP, is a fine example in which basaltic magma injection led to partial melting of the crust and different degrees of assimilation and eruption (Leeman et al., 2008). The BJEC is a 95 km by 55 km structural basin formed, ca.12 to 8 Ma, by multiple eruptions of rhyolitic pyroclastic and lava flows. The silicic eruptive phase is intercalated with a series of basaltic lava flows (e.g. Bonnichsen et al., 2008). Here, we assess the physical and chemical interaction of basaltic and rhyolitic magmas to help constrain the time scales of assimilation in the older southwestern SRP magma reservoirs. The Mary’s Creek basalt (MCB) and the Cougar Point Tuff unit V (CPTV) were chosen as end-members, based on work by Cathey and Nash (2009). The experimental procedure is: 1) geochemical analysis of the original samples using x-ray fluorescence (XRF) and electron microprobe, 2) determination of the temperature dependence of the viscosity of each sample using concentric cylinder and micropenetration methods, 3) magmatic assimilation of the end-members using a Couette geometry, and 4) geochemical analysis of the mixed product. Our geochemical analysis confirms that our end-members contain 49 wt. % SiO2 (MCB) and 76 wt. % SiO2 (CPTV), (c.f., Cathey and Nash, 2009). The dry superliquidus viscosities indicate that at 1450 °C, the CPTV and MCB melts have a viscosities of ~1.2x10^4 Pa*s and ~3x10^0 Pa*s, respectively - yielding a viscosity ratio of rhyolitic to basaltic magma of ca. 4x10^3. Assimilation experiments are being performed at 1450 °C, under laminar fluid conditions (Reynolds number of ca. 10^-7). Although recent numerical models (e.g., Jellinek and Kerr, 1999) suggest magma mixing to be inefficient under low Reynolds numbers and high viscosity ratios, we are hereby testing whether

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

    SciTech Connect

    Powers, P.M. . Geology Dept.)

    1993-03-01

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

  15. Chemical stratigraphy of the Paraná basalt succession in western Uruguay: further evidence for the diachronous nature of the Paraná magma types

    NASA Astrophysics Data System (ADS)

    Turner, S. P.; Peate, D. W.; Hawkesworth, C. J.; Mantovani, M. S. M.

    1999-11-01

    An important issue in the study of continental flood basalt provinces concerns whether chemically defined magma types have chronological significance. Relevant to this debate, we present important findings based on new major and trace element geochemical data on lavas from three drill holes in western Uruguay which intersect up to 718 m of the Paraná basalt succession. The lava pile here consists of Paranapanema lavas overlain by widespread Gramado lavas and one rare Esmeralda lava. The occurrence of Paranapanema lavas beneath Gramado lavas is the reverse of the magma type stratigraphy of the Paraná flood basalt pile further north in Brazil. This provides evidence, independent of isotopic dating, that in the Paraná, magma types are not chronostratigraphic. The simultaneous eruption of different magma types suggests that the spatial and temporal distribution of magma types reflects the sub-crustal distribution of distinct source regions inferred to lie within the lithospheric mantle.

  16. La/Sm ratios in mare basalts as a consequence of mafic cumulate fractionation from an initial lunar magma

    NASA Technical Reports Server (NTRS)

    Shaffer, E. E.; Brophy, J. G.; Basu, A.

    1991-01-01

    A model is constructed for the La/Sm ratio and the abundance of chrondrite-normalized La in different proportions of partial melts of a mafic cumulate source that might have settled to the bottom of an initial lunar magma ocean prior to any plagioclase separation. It is proposed that La/Sm ratios and chrondrite-normalized La abundances of common mare basalts are found in partial melts only if: the mafic cumulate consists mostly of clinopyroxene, a very low fraction of the cumulate melts, and the cumulate represents a moderate to high proportion of the crystallization of the initial magma ocean. Only if the partitioning of clinopyroxene is forced to mimic plagioclase (DLa is greater than DSm) do the present modeling results become compatible with the scenario for producing appropriate parent melts of mare basalts from mafic cumulates. It is found unlikely that parent melts of mare basalts were produced from mafic cumulates of an initial lunar magma ocean that had not had any plagioclase crystallization.

  17. Very high potassium (VHK) basalt - Complications in mare basalt petrogenesis

    NASA Technical Reports Server (NTRS)

    Shervais, J. W.; Taylor, L. A.; Laul, J. C.; Shih, C.-Y.; Nyquist, L. E.

    1985-01-01

    The first comprehensive report on the petrology and geochemistry of Apollo 14 VHK (Very High Potassium) basalts and their implications for lunar evolution is presented. The reported data are most consistent with the hypothesis that VHK basalts formed through the partial assimilation of granite by a normal low-Ti, high-Al mare basalt magma. Assimilation was preceded by the diffusion-controlled exchange of alkalis and Ba between basalt magma and the low-temperature melt fraction of the granite. Hypotheses involving volatile/nonvolatile fractionations or long-term enrichment of the source regions in K are inconsistent with the suprachondritic Ba/La ratios and low initial Sr-87/Sr-86 ratios of VHK basalt. An important implication of this conclusion is that granite should be a significant component of the lunar crust at the Apollo 14 site.

  18. Petrology and geochemistry of alkali gabbronorites from Lunar Breccia 67975

    NASA Astrophysics Data System (ADS)

    James, Odette B.; Lindstrom, Marilyn M.; Flohr, Marta K.

    Clasts of an unusual type of lunar highlands igneous rock, alkali gabbronorite, have been found in Apollo 16 breccia 67975. The alkali gabbronorites form two distinct subgroups, magnesian and ferroan. Modes and bulk compositions are highly varied. The magnesian alkali gabbronorites are composed of bytownitic plagioclase (Or2-5An82-89), hypersthene (Wo3-5En49-62), augite (Wo39-42En36-44), a silica mineral, and trace Ba-rich K-feldspar. The ferroan alkali gabbronorites are composed of ternary plagioclase (Or11-22An65-74), pigeonite (Wo6-9En35-47), augite (Wo38-40En29-35), Ba-rich K-feldspar, and a silica mineral. Trace minerals in both subgroups are apatite, REE-rich whitlockite, and zircon. The magnesian and ferroan alkali gabbronorites appear to have formed by progressive differentiation of the same, or closely related, parent magmas; the compositional data indicate that these magmas were REE-rich. The ternary plagioclase is probably a high-temperature metastable phase formed during crystallization. In composition and mineralogy, the 67975 alkali gabbronorites show many similarities to Apollo 12 and 14 alkali norites, alkali gabbronorites, and alkali anorthosites, and all these rocks together constitute a distinctive alkali suite. In addition, the alkali gabbronorites show some similarities to KREEP basalts, Mg-norites, and some felsites. These data suggest genetic links between some or all of these types of pristine rocks. Two types of relationships are possible. The first is that alkali-suite rocks crystallized in plutons of KREEP basalt magma, and KREEP basalts are their extrusive equivalents. The second is that the alkali-suite rocks and some felsites all crystallized in plutons of Mg-norite parent magmas, and KREEP basalt magmas formed by remelting of these plutons. Additional studies are needed to resolve which of these hypotheses is correct.

  19. Petrology and geochemistry of alkali gabbronorites from lunar breccia 67975

    NASA Astrophysics Data System (ADS)

    James, Odette B.; Lindstrom, Marilyn M.; Flohr, Marta K.

    1987-09-01

    Clasts of an unusual type of lunar highlands igneous rock, alkali gabbronorite, have been found in Apollo 16 breccia 67975. The alkali gabbronorites form two distinct subgroups, magnesian and ferroan. Modes and bulk compositions are highly varied. The magnesian alkali gabbronorites are composed of bytownitic plagioclase (Or2-5An82-89), hypersthene (Wo3-5En49-62), augite (Wo39-42En36-44), a silica mineral, and trace Ba-rich K-feldspar. The ferroan alkali gabbronorites are composed of ternary plagioclase (Or11-22An65-74), pigeonite (Wo6-9En35-47), augite (Wo38-40En29-35), Ba-rich K-feldspar, and a silica mineral. Trace minerals in both subgroups are apatite, REE-rich whitlockite, and zircon. The magnesian and ferroan alkali gabbronorites appear to have formed by progressive differentiation of the same, or closely related, parent magmas; the compositional data indicate that these magmas were REE-rich. The ternary plagioclase is probably a high-temperature metastable phase formed during crystallization. In composition and mineralogy, the 67975 alkali gabbronorites show many similarities to Appllo 12 and 14 alkali norites, alkali gabbronorites, and alkali anorthosites, and all these rocks together constitute a distinctive alkali suite. In addition, the alkali gabbronorites, show some similarities to KREEP basalts, Mg-norites, and some felsites. These data suggest genetic links between some or all of these types of pristine rocks. Two types of relationships are possible. The first is that alkali-suite rocks crystallized in plutons of KREEP basalt magma, and KREEP basalts are their extrusive equivalents. The second is that the alkali-suite rocks and some felsites all crystallized in plutons of Mg-norite parent magmas, and KREEP basalt magmas formed by remelting of these plutons. Additional studies are needed to resolve which of these hypotheses is correct.

  20. Experimental magma mixing between rhyolitic and basaltic melts: implications for the Bruneau-Jarbidge magmatism, Snake River Plain (USA)

    NASA Astrophysics Data System (ADS)

    Morgavi, D.; Perugini, D.; De Campos, C. P.; Dingwell, D. B.; Lavallee, Y.; Morgan, L. A.

    2011-12-01

    Volcanic activity in the Snake River Plain (SRP) is bimodal (rhyolitic-basaltic) in geochemical character. The Bruneau-Jarbidge eruptive center (BJEC; southwestern SRP) is a 95 km by 55 km structural basin formed ca.12 to 8 Ma by multiple eruptions of rhyolitic pyroclastic and lava flows, intercalated with a series of basaltic lavas. In the BJEC, underplating of basaltic magmas induced crustal melting and partial assimilation (Leeman et al., 2008). The purpose of this study is to investigate experimentally the physical and chemical interactions between basaltic and rhyolitic magmas and to evaluate whether this process can explain the variation in major and trace element in the BJEC rhyolitic units. The Mary's Creek basalt and the Cougar Point Tuff rhyolite (unit V) were chosen for their end-member signature in the following mixing experiments. First, the temperature dependence of viscosity of each sample has been investigated at superliquidus temperatures (>ca.1200 °C) using a concentric cylinder rheometer. Second, two setups have been used to assess the potential for mixing: 1) three alternating layers of each end-member where mixed (at 1200 to 1600 °C) by density-driven overturn in a Pt80Rh20 crucible; and 2) an offset journal bearing geometry where efficient, controlled chaotic flow fields have been obtained (at 1300, 1350 and 1400°C) by stretching and folding dynamics (e.g., De Campos et al., 2011). Mass fractions of the rhyolitic-to-basaltic melts were 50-50 for the density-driven experiments and 80-20 for the chaotic mixing experiments. Samples resulting from the mixing experiments were analyzed for major and minor elements, and compared to chemical compositional range observed in the BJEC. Experimental results indicate that despite the high viscosity contrast (10^3 Pa s), the end-members show efficient mutual contamination and thus mix on timescale of hours to weeks depending on the surface area of the end-member interface. Inter-elemental plots display a

  1. Rapid high-silica magma generation in basalt-dominated rift settings

    NASA Astrophysics Data System (ADS)

    Berg, Sylvia E.; Troll, Valentin R.; Burchardt, Steffi; Deegan, Frances M.; Riishuus, Morten S.; Whitehouse, Martin J.; Harris, Chris; Freda, Carmela; Ellis, Ben S.; Krumbholz, Michael; Gústafsson, Ludvik E.

    2015-04-01

    The processes that drive large-scale silicic magmatism in basalt-dominated provinces have been widely debated for decades, with Iceland being at the centre of this discussion [1-5]. Iceland hosts large accumulations of silicic rocks in a largely basaltic oceanic setting that is considered by some workers to resemble the situation documented for the Hadean [6-7]. We have investigated the time scales and processes of silicic volcanism in the largest complete pulse of Neogene rift-related silicic magmatism preserved in Iceland (>450 km3), which is a potential analogue of initial continent nucleation in early Earth. Borgarfjörður Eystri in NE-Iceland hosts silicic rocks in excess of 20 vol.%, which exceeds the ≤12 vol% usual for Iceland [3,8]. New SIMS zircon ages document that the dominantly explosive silicic pulse was generated within a ≤2 Myr window (13.5 ± 0.2 to 12.2 ± 03 Ma), and sub-mantle zircon δ18O values (1.2 to 4.5 ± 0.2‰, n=337) indicate ≤33% assimilation of low-δ18O hydrothermally-altered crust (δ18O=0‰), with intense crustal melting at 12.5 Ma, followed by rapid termination of silicic magma production once crustal fertility declined [9]. This silicic outburst was likely caused by extensive rift flank volcanism due to a rift relocation and a flare of the Iceland plume [4,10] that triggered large-scale crustal melting and generated mixed-origin silicic melts. High-silica melt production from a basaltic parent was replicated in a set of new partial melting experiments of regional hydrated basalts, conducted at 800-900°C and 150 MPa, that produced silicic melt pockets up to 77 wt.% SiO2. Moreover, Ti-in-zircon thermometry from Borgarfjörður Eystri give a zircon crystallisation temperature ~713°C (Ti range from 2.4 to 22.1 ppm, average=7.7 ppm, n=142), which is lower than recorded elsewhere in Iceland [11], but closely overlaps with the zircon crystallisation temperatures documented for Hadean zircon populations [11-13], hinting at

  2. Degassing of Mid-Ocean Ridge Basalts during Magma Ascent and Lava Emplacement

    NASA Astrophysics Data System (ADS)

    Gardner, J. E.; Jackson, B. A.; Clow, T. W.; Soule, S. A.

    2014-12-01

    Mid-ocean ridge basalt (MORB) glasses are often supersaturated in CO2. Indeed, volatile saturation pressures, estimated from dissolved CO2 and H2O concentrations, exceed eruption pressures (seafloor collection depths) by up to 45-50 MPa. It is thought that rapid ascent to the surface promotes disequilibrium degassing by kinetically limiting bubble nucleation and growth. This study uses supersaturated MORB glasses to experimentally investigate degassing kinetics in order to constrain magma ascent and flow rates. Glasses used were recovered at the fissure of the 2005-06 eruption of the East Pacific Rise, and are supersaturated by about 38 MPa and contain ~105 bubbles/cm3, the largest of which are ~35 µm in size. Away from the fissure, CO2 concentrations decrease as bubble sizes increase dramatically along the flow length, with bubbles reaching 94 µm in size. Nucleation is being studied by heating samples at 1225 °C and 200 MPa, and then rapidly decompressing them to low pressures, holding them at low pressure for various amounts of time, and then rapidly quenching them. Samples quenched at 200 MPa are bubble free and contain about 550 ppm CO2, indicating that all original bubbles resorb. Preliminary results show that samples decompressed to 12-21 MPa nucleate ~105 bubbles/cm3 after two minutes, but nucleate many orders of magnitude more after ten minutes, number densities that far exceed those in the natural samples. Samples decompressed to 52 MPa nucleate ~105 bubbles/cm3 after 10 minutes. These preliminary results suggest that bubble nucleation in MORB occurs at relatively high pressures, and then bubble growth suppresses further nucleation at lower pressures. Such a scenario suggests that MORB magmas may not ascend as rapidly as predicted. Bubble growth at low pressure is being studied by rapidly heating glassy vent samples to 1225 °C at 70 MPa, then decompressing and holding them at ~25 MPa for various amounts of time. Mean bubble size increases steadily by

  3. Magma Supply at the Arctic Gakkel Ridge: Constraints from Peridotites and Basalts

    NASA Astrophysics Data System (ADS)

    Sun, C.; Dick, H. J.; Hellebrand, E.; Snow, J. E.

    2015-12-01

    Crustal thickness in global ridge systems is widely believed to be nearly uniform (~7 km) at slow- and fast-spreading mid-ocean ridges, but appears significantly thinner (< ~4 km) at ultraslow-spreading ridges. At the slowest-spreading Arctic Gakkel Ridge, the crust becomes extremely thin (1.4 - 2.9 km; [1]). The thin crust at the Gakkel and other ultraslow-spreading ridges, has been attributed to lithosphere thickening, ancient mantle depletion, lower mantle temperature, ridge obliquity, and melt retention/focusing. To better understand the magma supply at ultraslow-spreading ridges, we examined melting dynamics by linking peridotites and basalts dredged along the Gakkel Ridge. We analyzed rare earth elements in clinopyroxene from 84 residual peridotites, and estimated melting parameters for individual samples through nonlinear least squares analyses. The degrees of melting show a large variation but mainly center at around 7% assuming a somewhat arbitrary but widely used depleted MORB mantle starting composition. Thermobarometry on published primitive basaltic glasses from [2] indicates that the mantle potential temperature at the Gakkel Ridge is ~50°C cooler than that at the East Pacific Rise. The ridge-scale low-degree melting and lower mantle potential temperature place the final depth of melting at ~30 km and a melt thickness of 1.0 or 2.9 km for a triangular or trapezoidal melting regime, respectively. The final melting depth is consistent with excess conductive cooling and lithosphere thickening suggested by geodynamic models, while the estimated melt thickness is comparable to the seismic crust (1.4 - 2.9 km; [1]). The general agreement among geochemical analyses, seismic measurements, and geodynamic models supports that lower mantle potential temperature and thick lithosphere determine the ridge-scale low-degree melting and thin crust at the Gakkel Ridge, while melt retention/focusing and excess ancient mantle depletion are perhaps locally important at

  4. Influence of an ocean on the propagation of magmas within an oceanic basaltic shield volcano

    NASA Astrophysics Data System (ADS)

    Le Corvec, N.; McGovern, P. J., Jr.

    2014-12-01

    Basaltic shield volcanoes are a common feature on Earth and mostly occur within oceans, forming volcanic islands (e.g. Hawaii (USA), Galapagos (Ecuador), and recently Niijima (Japan)). As the volcano grows it will reach and emerge from the water surface and continue to grow above it. The deformation affecting the volcanic edifice may be influenced by the presence of the water level. We investigate how the presence of an ocean affects the state of stress within a volcanic edifice and thus magma propagation and fault formation. Using COMSOL Multiphysics, axisymmetric elastic models of a volcanic edifice overlying an elastic lithosphere were created. The volcanic edifice (height of ~6000 m and radius of ~ 60 km) was built either instantaneously or iteratively by adding new layers of equivalent volume on top of each other. In the later process, the resulting stress and geometry from the one step is transferred to the next as initial conditions. Thus each new layer overlies a deformed and stressed model. The water load was modeled with a boundary condition at the surface of the model. In the case of an instantaneous volcano different water level were studied, for an iteratively growing volcano the water level was set up to 4000 m. We compared the deformation of the volcanic edifice and lithosphere and the stress orientation and magnitude in half-space and flexural models with the presence or not of an ocean. The preliminary results show 1- major differences in the resulting state of stress between an instantaneous and an iteratively built volcanic edifice, similar to the results of [Galgana et al., 2011] and [McGovern and Solomon, 1993], respectively; 2- the presence of an ocean decreases the amount of flexural response, which decreases the magnitude of differential stress within the models; and 3- stress orientation within the volcano and lithosphere in also influence of an ocean. Those results provide new insights on the state of stress and deformation of oceanic

  5. Composition of basalts from the Mid-Atlantic Ridge

    USGS Publications Warehouse

    Engel, A.E.J.; Engel, C.G.

    1964-01-01

    Studies of volcanic rocks in dredge hauls from the submerged parts of the Mid-Atlantic Ridge suggest that it consists largely of tholeiitic basalt with low values of K, Ti, and P. In contrast, the volcanic islands which form the elevated caps on the Ridge are built of alkali basalt with high values of Ti, Fe3+, P, Na, and K. This distinct correlation between the form of the volcanic structures, elevation above the sea floor, and composition suggests that the islands of alkali basalt are derived from a parent tholeiitic magma by differentiation in shallow reservoirs. The volume of low-potassium tholeiites along the Mid-Atlantic Ridge and elsewhere in the oceans appears to be many times that of the alkali basalts exposed on oceanic islands. Tholeiitic basalts with about 0.2 K2O appear to be the primary and predominant magma erupted on the oceanic floor.

  6. Retention of inherited Ar by alkali feldspar xenocrysts in a magma: Kinetic constraints from Ba zoning profiles

    NASA Astrophysics Data System (ADS)

    Renne, Paul R.; Mulcahy, Sean R.; Cassata, William S.; Morgan, Leah E.; Kelley, Simon P.; Hlusko, Leslea J.; Njau, Jackson K.

    2012-09-01

    40Ar/39Ar dating of volcanic alkali feldspars provides critical age constraints on many geological phenomena. A key assumption is that alkali feldspar phenocrysts in magmas contain no initial radiogenic 40Ar (40Ar∗), and begin to accumulate 40Ar∗ only after eruption. This assumption is shown to fail dramatically in the case of a phonolitic lava from southern Tanzania that contains partially resorbed xenocrystic cores which host inherited 40Ar manifest in 40Ar/39Ar age spectra. Magmatic overgrowths on the xenocrysts display variable oscillatory zoning with episodic pulses of Ba enrichment and intervals of resorption. Ba concentration profiles across contrasting compositional zones are interpreted as diffusion couples. Inferred temperature time histories recorded by these profiles reveal significant variations between phenocrysts. Combined with Ar diffusion kinetics for alkali feldspars and magma temperature inferred from two feldspar thermometry, the results indicate that >1% inherited 40Ar can be retained in such xenocrysts despite immersion in magma at ˜900 °C for tens to >100 years. In cases where the age contrast between inherited and magmatic feldspars is less pronounced, the age biasing effect of incompletely degassed xenocrysts may easily go undetected.

  7. Basaltic melt evolution of the Hengill volcanic system, SW Iceland, and evidence for clinopyroxene assimilation in primitive tholeiitic magmas

    SciTech Connect

    Troennes, R.G. )

    1990-09-10

    The thick oceanic crust of Iceland is formed by tholeiitic central volcanoes arranged in en echelon patterns along the 40-50 km wide rift zones. The Hengill central volcano in the southwestern rift zone has produced 25-30 km{sup 3} of hyaloclastites and lava during the last 0.11 m.y., with maximum productivity during the isostatic rebound following the degalciations 0.13 and 0.01 m.y. ago. The petrographic relations of pillow rim and hyaloclastite glass indicate that the basaltic melts were saturated with olivine and plagioclase, except for the most primitive ones that were undersaturated with plagioclase. Saturation with clinopyroxene was reached in some of the intermediate and evolved basaltic melts. Corroded and partly resorbed crystals of clinopyroxene and partly disintegrated gabbro nodules with resorbed clinopyroxene indicate that selective assimilation contributed to the evolution of the most primitive melts. The intermediate and evolved basaltic glass compositions fall along the low-pressure cotectic for mid-ocean ridge basalt (MORB) compositions saturated with olivine, plagioclase, and clinopyroxene, but the primitive glasses fall well inside the low-pressure olivine + plagioclase primary phase volume. The dense picritic magmas were driven to the surface by magmatic overpressure in the mantle at an early deglaciation stage characterized by the absence of large, trapping magma chambers in the lower crust. The assimilation of clinopyroxene in these melts could proceed by direct contact with the solidified cumulate sequences and gabbro intrusions. Clinopyroxene assimilation in combination with olivine fractionation may also contribute to the chemical evolution of some of the most primitive MORB magmas.

  8. Petrological processes in mantle plume heads: Evidence from study of mantle xenoliths in the late Cenozoic alkali Fe-Ti basalts in Western Syria

    NASA Astrophysics Data System (ADS)

    Sharkov, Evgenii

    2015-04-01

    It is consensus now that within-plate magmatism is considered with ascending of mantle plumes and adiabatic melting of their head. At the same time composition of the plumes' matter and conditions of its adiabatic melting are unclear yet. The major source of objective information about it can be mantle xenoliths in alkali basalts and basanites which represent fragments of material of the plume heads above magma-generation zone. They are not represent material in melting zone, however, carry important information about material of modern mantle plumes, its phase composition and components, involved in melting. Populations of mantle xenoliths in basalts are characterized by surprising sameness in the world and represented by two major types: (1) dominated rocks of ``green'' series, and (2) more rare rocks of ``black'' series, which formed veins in the ``green'' series matrix. It can evidence about common composition of plume material in global scale. In other words, the both series of xenoliths represent two types of material of thermochemical mantle plumes, ascended from core-mantle boundary (Maruyama, 1994; Dobretsov et al., 2001). The same types of xenoliths are found in basalts and basanites of Western Syria (Sharkov et al., 1996). Rocks of ``green'' series are represented by Sp peridotites with cataclastic and protogranular structures and vary in composition from dominated spinel lherzolites to spinel harzburgites and rare spinel pyroxenites (websterites). It is probably evidence about incomplete homogenizing of the plume head matter, where material, underwent by partial melting, adjoins with more fertile material. Such heterogeneity was survived due to quick cooling of upper rim of the plume head in contact with relatively cold lithosphere. Essential role among xenoliths of the ``black'' series play Al-Ti-augite and water-bearing phases like hornblende (kaersutute) and Ti-phlogopite. Rocks of this series are represented by wehrlite, clinopyroxenite, amphibole

  9. Geochemical characteristics of hydrous basaltic magmas due to assimilation and fractional crystallization: the Ikoma gabbroic complex, southwest Japan

    NASA Astrophysics Data System (ADS)

    Koizumi, N.; Okudaira, T.; Ogawa, D.; Yamashita, K.; Suda, Y.

    2016-10-01

    To clarify the processes that occur in hydrous basaltic magma chambers, we have undertaken detailed petrological and geochemical analyses of mafic and intermediate rocks from the Ikoma gabbroic complex, southwest Japan. The complex consists mainly of hornblende gabbros, hornblende gabbronorites, and hornblende leucogabbros. The hornblende leucogabbros are characterized by low TiO2 and high CaO contents, whereas the hornblende gabbronorites have high TiO2 and low CaO contents. The initial 87Sr/86Sr ratios (SrI) of the hornblende gabbronorites and hornblende gabbros are higher than those of the hornblende leucogabbros and plagioclase, and they may have resulted from a higher degree of assimilation of metasediments. The geochemical features of the hornblende leucogabbros and hornblende gabbronorites can be explained by accumulation of plagioclase and ilmenite, respectively, in a hybrid magma that formed by chemical interaction between mafic magma and metasediment, whereas the hornblende gabbros were produced by a high degree of crustal assimilation and fractional crystallization of this hybrid magma. As a result of the density differences between crystals and melt, the Ikoma gabbroic rocks formed by the accumulation of plagioclase in the middle of the magma chamber and by the accumulation of ilmenite in the bottom of the chamber. Taking into account the subsequent assimilation and fractional crystallization, our observations suggest an enriched mantle (SrI = ~0.7071) as the source material for the Ikoma gabbros.

  10. Immiscible separation of metalliferous Fe/ Ti-oxide melts from fractionating alkali basalt: P-T-fO2 conditions and two-liquid elemental partitioning

    NASA Astrophysics Data System (ADS)

    Hurai, Vratislav; Simon, Klaus; Wiechert, Uwe; Hoefs, Jochen; Konečný, Patrik; Huraiová, Monika; Pironon, Jacques; Lipka, Jozef

    Globules of iron-dominated (59-69 wt% FeOtot) and titanium-dominated (43.5 wt% TiO2) oxide melts have been detected in igneous xenoliths from Pliocene-to-Pleistocene alkali basalts of the Western Carpathians. Fluid inclusion and mineral composition data indicate immiscible separation of the high-iron-oxide melt (HIM) at magmatic temperatures. The HIM separation occurred during clinopyroxene (augite) accumulation in an alkali trachybasalt and continued during crystallization of amphibole (kaersutite) and K-feldspar (anorthoclase), the latter coexisting with trachyte and alkalic rhyolite residual melts. Some HIM was also expelled from sub-alkalic rhyolite (70-77% SiO2), coexisting with An27-45 plagioclase and quartz in granitic (tonalite-trondhjemite) xenoliths. Oxygen fugacities during HIM separation range from -1.4to +0.6log units around the QFM buffer. A close genetic relationship between HIM-hosted xenoliths and mantle-derived basaltic magma is documented by mineral 18O values ranging from 4.9 to 5.9‰ V-SMOW. δD values of gabbroic kaersutite between -61 and -86‰ V-SMOW are in agreement with a presumed primary magmatic water source. Most trace elements, except Li, Rb and Cs, have preferentially partitioned into the HIM. The HIM/Si-melt partition coefficients for transition elements (Sc, V, Cr, Co, Ni) and base metals (Zn, Cu, Mo) are between 2-160, resulting in extreme enrichment in the HIM. La and Ce also concentrate in the silicic melt, whereas Tb-Tm in the HIM. Hence, the immiscible separation causes REE fractionation and produces residual silicic melt enriched in LREE and depleted in HREE. The weak fractionation among Tb-Tm and Yb, Lu can be attributed to recurrent extraction of the HIM from the magmatic system, while flat HREE chondrite-normalized patterns are interpreted to indicate no or little loss of the HIM.

  11. Geochemical and oxygen isotope signatures of mantle corundum megacrysts from the Mbuji-Mayi kimberlite, Democratic Republic of Congo, and the Changle alkali basalt, China

    NASA Astrophysics Data System (ADS)

    Giuliani, Gaston; Pivin, Marjorie; Fallick, Anthony E.; Ohnenstetter, Daniel; Song, Yucai; Demaiffe, Daniel

    2015-01-01

    Oxygen isotope signatures of ruby and sapphire megacrysts, combined with trace-element analysis, from the Mbuji-Mayi kimberlite, Democratic Republic of Congo, and the Changle alkali basalt, China, provide clues to specify their origin in the deep Earth. At Mbuji-Mayi, pink sapphires have δ18O values in the range 4.3 to 5.4‰ (N = 10) with a mean of 4.9 ± 0.4‰, and rubies from 5.5 to 5.6‰ (N = 3). The Ga/Mg ratio of pink sapphires is between 1.9 and 3.9, and in rubies, between 0.6 and 2.6. The blue or yellow sapphires from Changle have δ18O values from 4.6 to 5.2 ‰, with a mean of 4.9 ± 0.2‰ (N = 9). The Ga/Mg ratio is between 5.7 and 11.3. The homogenous isotopic composition of ruby suggests a derivation from upper mantle xenoliths (garnet lherzolite, pyroxenite) or metagabbros and/or lower crustal garnet clinopyroxenite eclogite-type xenoliths included in kimberlites. Data from the pink sapphires from Mbuji-Mayi suggest a mantle origin, but different probable protoliths: either subducted oceanic protolith transformed into eclogite with δ18O values buffered to the mantle value, or clinopyroxenite protoliths in peridotite. The Changle sapphires have a mantle O-isotope signature. They probably formed in syenitic magmas produced by low degree partial melting of a spinel lherzolite source. The kimberlite and the alkali basalt acted as gem conveyors from the upper mantle up to the surface.

  12. Water content in arc basaltic magma in the Northeast Japan and Izu arcs: an estimate from Ca/Na partitioning between plagioclase and melt

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The variation in water content of arc basaltic magmas in the Northeast Japan arc and the Izu arc was estimatedusing a simple plagioclase phenocryst hygrometer. In order to construct a plagioclase phenocryst hygrometeroptimized for arc basalt magmas, we have conducted hydrous melting experiments of relatively primitive basaltfrom the Miyakejima volcano, a frontal-arc volcano in the Izu arc. As a result of the experiments, we found that theCa/Na partition coefficient between plagioclase and hydrous basaltic melt increases linearly with an increase in H2Ocontent in the melts. We then compiled published geochemical data sets of relatively primitive basaltic rocks with no evidence of magma mixing and the most frequent Ca-rich plagioclase phenocrysts from 15 basaltic arc volcanoesincluding both frontal-arc and rear-arc volcanoes. In the 15 volcanoes studied, plagioclase phenocrysts of high anorthitecontent (An > 90) were commonly observed, whereas plagioclase phenocrysts in rear arc volcanoes usually had a loweranorthite content (90 > An > 80). In all volcanoes studied, the estimated H2O content of basaltic magma was at least3 wt.% H2O or higher. The magmas of volcanoes located on the volcanic front have about 5 wt.% H2O in magmawhereas those from the rear-arc side are slightly lower in H2O content.

  13. Understanding Magma Storage Conditions that Produce Highly Explosive Monogenetic Basaltic Eruptions Using Olivine-Hosted Melt Inclusions from Sunset Crater, AZ

    NASA Astrophysics Data System (ADS)

    Allison, C. M.; Roggensack, K.; Clarke, A. B.

    2014-12-01

    To investigate mechanisms of explosive basaltic volcanism, we studied the ca. 1085 AD Sunset Crater eruption in the San Francisco Volcanic Field (SFVF) of northern Arizona. This eruption, the youngest in the SFVF, first featured fissure eruptions (explosive phases 1-2) and a small lava flow, and then activity narrowed to a central vent producing explosive phases 3-8 and two additional lava flows. While the first two phases were Strombolian-style explosions, middle phases (3-5) were subplinian in character and produced an anomalously large tephra deposit. The final phases (6-8) are poorly characterized at this stage. The total erupted volume of lava and tephra is >0.7 km3 DRE of alkali olivine basalt with a large proportion of crystal-free glass and low phenocryst content. We studied 82 primary melt inclusions (MIs) in the largest tephra units (explosive phases 3, 4) to investigate magma volatiles and storage conditions. To prioritize primary volatile contents, we picked rapidly quenched free olivine crystals (Fo 81-85; 0.5-2 mm) and selected large volume MIs (50-180 μm) located near crystal cores for analysis. We observed vapor bubbles in all MIs and also noted rare occurrences of CO2-rich gas inclusions. MIs show little major element variability suggesting little crystal fractionation (K2O 0.8-1.1 wt.%). Post-entrapment crystallization is also minor (2-9%). The MI compositions from the two phases largely overlap, with phase 4 skewed to slightly higher K2O. FTIR spectroscopy shows that the MIs are relatively dry and CO2-rich. Water abundances vary 0.8-1.6 wt.% with a median of 1.25 wt.%, while most MIs have CO2 abundances 1,600-3,400 ppm. Phases 3 and 4 are essentially identical in water content. CO2 contents of phases 3 and 4 show considerable overlap, however the phase 4 MIs are skewed toward high CO2 (>2,500 ppm). These results require a minimum MI entrapment depth of ~11 km from fluid saturation constraints. Overall, the MIs indicate a largely homogeneous

  14. Isotopic and chemical evidence concerning the genesis and contamination of basaltic and rhyolitic magma beneath the Yellowstone Plateau Volcanic Field

    USGS Publications Warehouse

    Hildreth, W.; Halliday, A.N.; Christiansen, R.L.

    1991-01-01

    Since 2.2 Ma, the Yellowstone Plateau Volcanic Field has produced ~6000 km3 of rhyolite tuffs and lavas in >60 separate eruptions, as well as ~100 km3 of tholeiitic basalt from >50 vents peripheral to the silicic focus. Intermediate eruptive products are absent. Early postcollapse rhyolites show large shifts in Nd, Sr, Pb, and O isotopic composition caused by assimilation of roof rocks and hydrothermal brines during collapse and resurgence. Younger intracaldera rhyolite lavas record partial isotopic recovery toward precaldera ratios. Thirteen extracaldera rhyolites show none of these effects and have sources independent of the subcaldera magma system. Contributions from the Archaean crust have extreme values and wide ranges of Nd-, Sr, and Pb-isotope ratios, but Yellowstone rhyolites have moderate values and limited ranges. This requires their deep-crustal sources to have been pervasively hybridized by distributed intrusion of Cenozoic basalt, most of which was probably contemporaneous with the Pliocene and Quaternary volcanism. Most Yellowstone basalts had undergone cryptic clinopyroxene fractionation in the lower crust or crust-mantle transition zone and, having also ascended through or adjacent to crustal zones of silicic-magma generation, most underwent some crustal contamination. -from Authors

  15. Petrochemistry, age and isotopic composition of alkali basalts from Ponape Island, Western Pacific

    USGS Publications Warehouse

    Dixon, T.H.; Batiza, Rodey; Futa, K.; Martin, D.

    1984-01-01

    Eleven analyzed lava samples from Ponape Island are alkali olivine basalt, basanite and basanitoid. Most lavas are aphyric or sparsely phyric (< 10% phenocrysts) and have phenocrysts of olivine (Fo77-80), clinopyroxene and titanomagnetite, and microphenocrysts of plagioclase (An53-68) in a fine-grained groundmass of olivine, clinopyroxene, plagioclase, opaques, potassic oligoclase, ?? nepheline and accessary phases. Oxygen isotope and Fe2O3 FeO data suggest that most samples are fresh, although H2O contents are high. Xenoliths of chromite-bearing harzburgites and dunites, both with cumulate textures occur in one locality. Major- and trace-element concentrations are similar to other oceanic volcanic islands. Most major elements and compatible trace elements vary systematically with respect to the Mg number [ 100Mg (Mg + Fe2+)]. In contrast, the incompatible trace elements do not correlate with the Mg number, but do covary with other incompatible elements. Simple closed-system shallow fractionation cannot be invoked to explain the observed chemical variation in the lavas. Derivation of the fractionated lavas (Mg number = 66-48) probably involved polybaric crystal fractionation from a high-Mg-number parental liquid. In addition, variable-source concentration of a trace-element-rich minor phase is postulated. However, the mantle was homogeneous with respect to the ratio of 87Sr 86Sr. New KAr age data are not consistent with the hypothesis that Ponape and the Caroline Ridge represent a simple "hot spot". ?? 1984.

  16. Origin of basaltic magmas of Perşani volcanic field, Romania: A combined whole rock and mineral scale investigation

    NASA Astrophysics Data System (ADS)

    Harangi, Szabolcs; Sági, Tamás; Seghedi, Ioan; Ntaflos, Theodoros

    2013-11-01

    The Perşani volcanic field is a low-volume flux monogenetic volcanic field in the Carpathian-Pannonian region, eastern-central Europe. Volcanic activity occurred intermittently from 1200 ka to 600 ka, forming lava flow fields, scoria cones and maars. Selected basalts from the initial and younger active phases were investigated for major and trace element contents and mineral compositions. Bulk compositions are close to those of the primitive magmas; only 5-12% olivine and minor spinel fractionation occurred at 1300-1350 °C, followed by clinopyroxenes at about 1250 °C and 0.8-1.2 GPa. Melt generation occurred in the depth range from 85-90 km to 60 km. The estimated mantle potential temperature, 1350-1420 °C, is the lowest in the Pannonian Basin. It suggests that no thermal anomaly exists in the upper mantle beneath the Perşani area and that the mafic magmas were formed by decompression melting under relatively thin continental lithosphere. The mantle source of the magmas could be slightly heterogeneous, but is dominantly variously depleted MORB-source peridotite, as suggested by the olivine and spinel composition. Based on the Cr-numbers of the spinels, two coherent compositional groups (0.38-0.45 and 0.23-0.32, respectively) can be distinguished that correspond to the older and younger volcanic products. This indicates a change in the mantle source region during the volcanic activity as also inferred from the bulk rock major and trace element data. The younger basaltic magmas were generated by lower degree of melting, from a deeper and compositionally slightly different mantle source compared to the older ones. The mantle source character of the Perşani magmas is akin to that of many other alkaline basalt volcanic fields in the Mediterranean close to orogenic areas. The magma ascent rate is estimated based on compositional traverses across olivine xenocrysts using variations of Ca content. Two heating events are recognized; the first one lasted about 1

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

    USGS Publications Warehouse

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

    1985-01-01

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

  18. Geochemistry of the Quaternary alkali basalts of Garrotxa (NE Volcanic Province, Spain): a case of double enrichment of the mantle lithosphere

    NASA Astrophysics Data System (ADS)

    Cebriá, J. M.; López-Ruiz, J.; Doblas, M.; Oyarzun, R.; Hertogen, J.; Benito, R.

    2000-11-01

    The area of Garrotxa (also known as the Olot area) represents the most recent (700,000-11,500 y) and better preserved area of magmatic activity in the NE Volcanic Province of Spain (NEVP). This region comprises a suite of intracontinental leucite basanites, nepheline basanites and alkali olivine basalts, which in most cases represent primary or nearly primary liquids. The geochemical characteristics of these lavas are very similar to the analogous petrologic types of other Cenozoic volcanics of Europe, which are intermediate between HIMU, DM and EM1. Quantitative trace element modeling, suggests derivation from an enriched mantle source by degrees of melting that progressively increased from the leucite basanites (˜4%) to the olivine basalts (˜16%). However, the relatively more variable Sr-Nd-Pb isotope signature of the magmas suggests the participation of at least two distinct components in the mantle source: (1) a sublithospheric one with a geochemical signature similar to the magmas of Calatrava (Central Spain) and other basalts of Europe; and (2) an enriched lithospheric component with a K-bearing phase present. The geochemical model proposed here involves the generation of a hybrid mantle lithosphere source produced by the infiltration of the sublithospheric liquids into enriched domains of the mantle lithosphere, shortly before the melting event that generated the Garrotxa lavas. The available geological data suggest that the first enrichment event of the mantle lithosphere under the NEVP could be the result of Late Variscan mantle upwelling triggered by the extensional collapse of the Variscan orogen during the Permo-Carboniferous. By Jurassic/Cretaceous time, large-scale NNE-directed sublithospheric mantle channeling of thermally and chemically anomalous plume material was placed under the Iberian Peninsula and Central Europe. However, the geodynamic conditions in the NEVP did not favor magmatism, which could not take place until the Cenozoic after

  19. Seismic constraints on basaltic underplating and probably magma conduits beneath the Hong Kong region, coastal region of SE China

    NASA Astrophysics Data System (ADS)

    Xia, S.; Xu, H.; Qiu, X.; Zhao, M.

    2012-12-01

    Hong Kong lies on the SE margin of the Cathaysia Block. Mesozoic plutonic and volcanic rocks crop out over approximately 85% of the land area of Hong Kong. E- and ENE-trending axes of extension, and transtension were dominant. NW-trending faults increased in importance with time, and their intersections with ENE-trending faults influenced the loci of volcanic centres. Basaltic underplating has been thought to play an important role in providing the necessary heat to cause partial melting of lower and middle crust, and generation of granitic magmas. By using both crustal refraction and reflection travel times from two offshore shot lines with a three-dimensional of land-based seismometer network, the three-dimensional (3D) velocity model has been obtained beneath the coastal area near Hong Kong. In order to assess the reliability of 3D velocity model from the challenging source-receiver configuration, we performed a series of Checkerboard resolution tests and MonteCarlo test. The application of this combination of model assessment methods has allowed us to validate the 3D model given the challenging imaging conditions. The results reveal high velocity (> 7.2km/s) anomaly in the lowermost crust which locates the intersection loci of NE- and NW-trending faults, implying that the basaltic underplating exists beneath the coastal area near Hong Kong and the NE- and NW-trending intersecting faults could play an important role in probably magma conduits.

  20. Basalt Magma, Whisky and Tequila: finely-crafted mixes of small liquid batches that defy the parent liquid concept but whose complexities teach us much

    NASA Astrophysics Data System (ADS)

    Rubin, K. H.; Sinton, J. M.; Perfit, M. R.

    2015-12-01

    Basalt is the most ubiquitous magma type we know of in the solar system. It comes in various varieties manifested as compositional sub groups, erupts from a wide variety of volcanic systems and tectonic settings, and its eruptions span many order of magnitude in duration and volume. Igneous petrology, thermodynamics, geochemistry, and geodynamical modelling have been used to develop a sophisticated understanding of source lithologies, compositions and formation conditions (e.g., pressure and temperature) for parent melts and their subsequent transport, storage and evolution. These demonstrate some striking systematics as a function of volcano tectonic setting (on Earth). Yet much like Whisky, what makes it into the bottle, or the eruption, is a mixture of different liquids with unique characteristics, sometimes stirred so well that successive batches are indistinguishable, and sometimes stirred more incompletely, preserving small batch characters that are unique. Recently, geochemical and petrological studies in high spatial density within the products of individual eruptions have shown chemical and mineralogical evidence for incompletely mixed heterogeneous magmas in a majority of systems examined, begging the question of when, if ever, is it realistic to speak of a single parent magma composition, and even in cases where it apparently is, if these are instead just more thoroughly stirred multi-parent magmas. For instance, do monogenetic fields really erupt basalts of more varied parent melt compositions than large hot spot and flood basalt eruptions, or are they just more poorly stirred? This presentation will focus on work by ourselves and others constraining spatial and temporal single-eruption basaltic magma histories at different settings, using them to unravel the time and space scales of magma formation and mixing, how these translate to the assembly of an erupted basalt magma, and the implications for deducing things about and from presumed parents.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  2. Alkali basalts and leucitites in an extensional intracontinental plate setting: The late Cenozoic Calatrava Volcanic Province (central Spain)

    NASA Astrophysics Data System (ADS)

    Cebriá, J.-M.; López-Ruiz, J.

    1995-04-01

    The Calatrava Volcanic Province (CVP) of central Spain is characterised by a intracontinental plate magmatic association of leucitites, melilitites, nephelinites and olivine basalts extruded during the late Miocene to Quaternary. Most of the rocks represent relatively primitive magmas and less than 45% have experienced small degrees ( < 25%) of crystal fractionation. Melilitites, nephelinites and olivine basalts form a suite generated by variable degrees of partial melting ( F = 5-17%) of a nearly homogeneous enriched (up to x18 chondritic values for the highly incompatible elements and × 3 for the moderately incompatible) mantle source, composed of Ol+Opx+Cpx+Gt+Phl. The leucitites appear to be derived by low degrees of partial melting ( ~ 4%) from a different mantle source, characterized by higher Rb, Ba, K and 87Sr enrichment and the presence of residual apatite. Phlogopite contributed to the leucititic liquids in a higher proportion than in the basaltic suite whereas clinopyroxene participated in lower amounts. The geochemical characteristics of the primary liquids suggest a contribution from two source components: (1) a subcontinental lithospheric component which appears to be a strongly enriched garnet-lherzolite with phlogopite ± apatite and (2) an asthenospheric diapir component with characteristics similar to the HIMU reservoir. These conclusions combined with geophysical observations indicate that the CVP magmatism could develop in two stages. In a first stage, a HIMU-like mantle diapir would trigger magma generation in the overlying subcontinental lithosphere by melting of pervasive enriched streaks or veins with phlogopite + apatite, giving rise to small amounts of leucititic liquids and to initial extension of the upper crust. In subsequent steps the extension developed, the lithosphere becomes stripped of its enriched components and the asthenospheric diapir starts to melt giving rise to the basaltic liquids which are virtually OIB-like magmas. This

  3. First data on magma ascent and residence times retrieved from Fe-Mg and trace element zonation in olivine phenocrysts from Kamchatka basalts

    NASA Astrophysics Data System (ADS)

    Gordeychik, Boris; Churikova, Tatiana; Kronz, Andreas; Simakin, Alexander; Wörner, Gerhard

    2016-04-01

    Compositional zonation in olivine phenocrysts and diffusion modelling have been used in the last ten years to estimate magma residence times and the duration of magma ascent. The fundamental assumption is that mixing with newly injected magma into a reservoir triggers diffusional exchange between mafic olivine crystals and more evolved magma and that this magma mixing eventually triggers eruption. If depth of mixing is known, this translates to ascent rates of magmas to the surface. We applied this approach to a series of different arc basalt lavas from Kamchatka to constrain the rates of magma ascent and magma resident in what is one of the most active subduction zones in the world that is also dominated by an abundance of unusually mafic magmas. Our sample collection cover the principal modes of arc magmatism in Kamchatka: from different volcanic complexes (stratovolcano, dikes, summit eruptions, monogenetic cones), of different age (from Late-Pleistocene to Holocene and recent eruptions), from different magmatic regimes (long-lived volcanoes vs. monogenetic eruptions) and different major element composition (from basalt to basaltic andesite of different geochemical character including LILE enrichments). We analyzed and modelled zonation profiles for a range of elements with different diffusivities (e.g. Mg-Fe, Ca, Ni, Mn, Cr) to assess the role of variable diffusivities as a function of major and trace elements in the olivines from different P-T conditions. First data were obtained on samples from the Klyuchevskoy, Shiveluch and Tolbachik, including recent most eruption in 2012/2013. These data show that for some samples the zonation patterns are much more complex than is usually observed: high-Mg olivines at different volcanoes have very different zonation patterns, including normally, reversely zoned grains or even show highly complex repetitive zonation that indicate large compositional changes in the surrounding magma at very short time scales (years). Thus

  4. NanoSIMS results from olivine-hosted melt embayments: Magma ascent rate during explosive basaltic eruptions

    NASA Astrophysics Data System (ADS)

    Lloyd, Alexander S.; Ruprecht, Philipp; Hauri, Erik H.; Rose, William; Gonnermann, Helge M.; Plank, Terry

    2014-08-01

    pressure (> 145 MPa), with similar decompression rates to the single-stage model for the shallower stage. The magma ascent rates reported here are among the first for explosive basaltic eruptions and demonstrate the potential of the embayment method for quantifying magmatic timescales associated with eruptions of different vigor.

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

    NASA Astrophysics Data System (ADS)

    Bagnardi, Marco

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

  6. Residual glasses and melt inclusions in basalts from DSDP Legs 45 and 46 - Evidence for magma mixing. [Deep Sea Drilling Project

    NASA Technical Reports Server (NTRS)

    Dungan, M. A.; Rhodes, J. M.

    1978-01-01

    Microprobe analyses of natural glasses in basalts recovered by Legs 45 and 46 of the Deep Sea Drilling Project are reported and interpreted in the context of other geochemical, petrographic and experimental data on the same rocks (Rhodes et al., 1978). Residual glass compositions in the moderately evolved aphyritic and abundantly phyric basalts within each site indicate that none of the units is related to any other or to a common parent by simple fractional crystallization. The compositional trends, extensive disequilibrium textures in the plagioclase phenocrysts and the presence in evolved lavas of refractory plagioclase and olivine phenocrysts bearing primitive melt inclusions provide evidence that magma mixing had a major role in the genesis of the Leg 45 and 46 basalts. The magma parental to these basalts was most likely characterized by high Mg/(Mg + Fe/+2/), CaO/Al2O3, CaO/Na2O and low lithophile concentrations. A mixing model involving incremental enrichment of magmaphile elements by repeated episodes of mixing of relatively primitive and moderately evolved magmas, followed by a small amount of fractionation is consistent with the characteristics of the basalts studied.

  7. A strontium and neodymium isotopic study of Apollo 17 high-Ti mare basalts - Resolution of ages, evolution of magmas, and origins of source heterogeneities

    NASA Technical Reports Server (NTRS)

    Paces, James B.; Neal, Clive R.; Taylor, Lawrence A.; Nakai, Shun'ichi; Halliday, Alex N.

    1991-01-01

    The geochronological and compositional differences between previously identified magma types (A, B1, B2, and C) were investigated using high-precision Rb-Sr and Sm-Nd isotopic data for a set of Apollo 17 high-Ti mare basalt samples chosen to span the range of each of the magma types. These data, combined with previously reported geochemical ages, suggest that Apollo 17 volcanism was initially dominated by an eruption of Type B basalts. Data obtained from new whole-rock Sr and Nd isotopic analyses exhibited distinct differences in initial Sr and Nd isotopic compositions between Types A, B1, B2, and C basalts and were found to be consistent with existing petrogenetic models.

  8. The impact of degassing on the oxidation state of basaltic magmas: A case study of Kīlauea volcano

    NASA Astrophysics Data System (ADS)

    Moussallam, Yves; Edmonds, Marie; Scaillet, Bruno; Peters, Nial; Gennaro, Emanuela; Sides, Issy; Oppenheimer, Clive

    2016-09-01

    Volcanic emissions link the oxidation state of the Earth's mantle to the composition of the atmosphere. Whether the oxidation state of an ascending magma follows a redox buffer - hence preserving mantle conditions - or deviates as a consequence of degassing remains under debate. Thus, further progress is required before erupted basalts can be used to infer the redox state of the upper mantle or the composition of their co-emitted gases to the atmosphere. Here we present the results of X-ray absorption near-edge structure (XANES) spectroscopy at the iron K-edge carried out for a series of melt inclusions and matrix glasses from ejecta associated with three eruptions of Kīlauea volcano (Hawai'i). We show that the oxidation state of these melts is strongly correlated with their volatile content, particularly in respect of water and sulfur contents. We argue that sulfur degassing has played a major role in the observed reduction of iron in the melt, while the degassing of H2O and CO2 appears to have had a negligible effect on the melt oxidation state under the conditions investigated. Using gas-melt equilibrium degassing models, we relate the oxidation state of the melt to the composition of the gases emitted at Kīlauea. Our measurements and modelling yield a lower constraint on the oxygen fugacity of the mantle source beneath Kīlauea volcano, which we infer to be near the nickel nickel-oxide (NNO) buffer. Our findings should be widely applicable to other basaltic systems and we predict that the oxidation state of the mantle underneath most hotspot volcanoes is more oxidised than that of the associated lavas. We also suggest that whether the oxidation states of a basalt (in particular MORB) reflects that of its source, is primarily determined by the extent of sulfur degassing.

  9. Calculated diffusion coefficients and the growth rate of olivine in a basalt magma

    NASA Technical Reports Server (NTRS)

    Donaldson, C. H.

    1975-01-01

    Concentration gradients in glass adjacent to skeletal olivines in a basalt have been examined by electron probe. The glass is depleted in Mg, Fe, and Cr and enriched in Si, Al, Na, and Ca relative to that far from olivine. Ionic diffusion coefficients for the glass compositions are calculated from temperature, ionic radius and melt viscosity, using the Stokes-Einstein relation. At 1170 C, the diffusion coefficient of Mg(2+) ions in the basalt is 4.5 billionths sq cm per sec. Comparison with measured diffusion coefficients in a mugearite suggests this value may be 16 times too small. The concentration gradient data and the diffusion coefficients are used to calculate instantaneous olivine growth rates. Growth necessarily preceded emplacement such that the composition of the crystals plus the enclosing glass need not be that of a melt. The computed olivine growth rates are compatible with the rate of crystallization deduced for the Skaegaard intrusion.

  10. Major element evolution of basaltic magmas: a comparison of the information in CMAS and ALFE projections

    NASA Astrophysics Data System (ADS)

    Reid, John B.; Steig, Eric; Bryan, Wilfred B.

    1989-03-01

    Basalt petrologists disagree as to whether the commonly used projection, forsterite-diopside-silica, in the system CMAS (CaO-MgO-Al2O3-SiO2), can adequately resolve differences in basaltic glass compositions for purposes of petrogenetic modelling. Here, we suggest than an analogous plot, the aluminium-factor diagram (ALFE) of Nesbitt and Cramer (1981), has greater diagnostic value than Fo-Di-Sil. A plot of molar (Al2O2-CaO-Na2O-K2O)/(FeO + MgO) vs FeO/(FeO + MgO), it produces more coherent patterns both for experimental basalt glasses, and for natural lavas. It is, like Fo-Di-Sil, a projection through plagioclase, but has the advantage that it monitors changes in Fe/(Fe + Mg) in melts and associated crystalline phases, and is particularly useful in assessing the timing of clinopyroxene crystallization in a suite of lavas. The diagram owes its greater resolving power to the fact that the computation of its coordinates is less sensitive to analytical uncertainty than for Fo-Di-Sil. In the latter diagram, normative quartz is calculated as a residual and thus manifests the uncertainties in all the major elements.

  11. Volatile budget of Eyjafjallajokull magmas

    NASA Astrophysics Data System (ADS)

    Sigurdsson, H.; Mandeville, C. W.

    2010-12-01

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

  12. Petrogenesis of Mare Basalts, Mg-Rich Suites and SNC Parent Magmas

    NASA Technical Reports Server (NTRS)

    Hess, Paul C.

    2004-01-01

    The successful models for the internal evolution of the Moon must consider the volume, distribution, timing, composition and, ultimately, the petrogenesis of mare basaltic volcanism. Indeed, given the paucity of geophysical data, the internal state of the Moon in the past can be gleaned only be unraveling the petrogenesis of the various igneous products on the Moon and, particularly, the mare basalts. most useful in constraining the depth and composition of their source region [Delano, 1980] despite having undergone a certain degree of shallow level olivine crystallization.The bulk of the lunar volcanic glass suite can be modeled as the partial melting products of an olivine + orthopyroxene source region deep within the lunar mantle. Ti02 contents vary from 0.2 wt % -1 7.0wt [Shearer and Papike, 1993]. Values that extreme would seem to require a Ti- bearing phase such as ilmenite in the source of the high-Ti (but not in the VLT source) because a source region of primitive LMO olivine and orthopyroxene, even when melted in small degrees cannot account for the observed range of Ti02 compositions. The picritic glasses are undersaturated with respect to ilmenite at all pressures investigated therefore ilmenite must have been consumed during melting, leaving an ilmenite free residue and an undersaturated melt [Delano, 1980, Longhi, 1992, Elkins et al, 2000 among others]. Multi- saturation pressures for the glasses potentially represent the last depths at which the liquids equilibrated with a harzburgite residue before ascending to the surface. These occur at great depths within the lunar mantle. Because the liquids have suffered some amount of crystal fractionation, this is at best a minimum depth. If the melts are mixtures, then it is only an average depth of melting. Multisaturation, nevertheless, is still a strong constraint on source mineralogy, revealing that the generation of the lunar basalts was dominated by melting of olivine and orthopyroxene.

  13. Deep mixing of mantle melts beneath continental flood basalt provinces: Constraints from olivine-hosted melt inclusions in primitive magmas

    NASA Astrophysics Data System (ADS)

    Jennings, Eleanor S.; Gibson, Sally A.; Maclennan, John; Heinonen, Jussi S.

    2017-01-01

    We present major and trace element compositions of 154 re-homogenised olivine-hosted melt inclusions found in primitive rocks (picrites and ferropicrites) from the Mesozoic Paraná-Etendeka and Karoo Continental Flood Basalt (CFB) provinces. The major element compositions of the melt inclusions, especially their Fe/Mg ratios, are variable and erratic, and attributed to the re-homogenisation process during sample preparation. In contrast, the trace element compositions of both the picrite and ferropicrite olivine-hosted melt inclusions are remarkably uniform and closely reflect those of the host whole-rocks, except in a small subset affected by hydrothermal alteration. The Paraná-Etendeka picrites and ferropicrites are petrogenetically related to the more evolved and voluminous flood basalts, and so we propose that compositional homogeneity at the melt inclusion scale implies that the CFB parental mantle melts were well mixed prior to extensive crystallisation. The incompatible trace element homogeneity of olivine-hosted melt inclusions in Paraná-Etendeka and Karoo primitive magmatic rocks has also been identified in other CFB provinces and contrasts with findings from studies of basalts from mid-ocean ridges (e.g. Iceland and FAMOUS on the Mid Atlantic Ridge), where heterogeneity of incompatible trace elements in olivine-hosted melt inclusions is more pronounced. We suggest that the low variability in incompatible trace element contents of olivine-hosted melt inclusions in near-primitive CFB rocks, and also ocean island basalts associated with moderately thick lithosphere (e.g. Hawaii, Galápagos, Samoa), may reflect mixing along their longer transport pathways during ascent and/or a temperature contrast between the liquidus and the liquid when it arrives in the crust. These thermal paths promote mixing of mantle melts prior to their entrapment by growing olivine crystals in crustal magma chambers. Olivine-hosted melt inclusions of ferropicrites from the Paran

  14. High alumina (HA) and very high potassium (VHK) basalt clasts from Apollo 14 breccias. I - Mineralogy and Petrology - Evidence of crystallization from evolving magmas

    NASA Technical Reports Server (NTRS)

    Neal, C. R.; Taylor, L. A.; Patchen, A. D.

    1989-01-01

    The mineralogy and petrography of very high potassium (VHK) and high alumina (HA) basalts from the Apollo 14 site provide an insight into their magmatic evolution. Generally, their parageneses are similar, with olivine and chromite the early liquidus phases, followed by plagioclase and pyroxene, which crystallized together. Although late-stage ilmenite and FeNi metal occur in both VHK and HA samples, the VHKs also crystallize K-feldspar and Fa-rich olivine. Zoning of constituent minerals is similar for both basalt types, demonstrating that the parental magmas for both HA and VHK basalts became enriched in K, Na, Ca, Fe, and Ti and depleted in Mg and Al as crystallization proceeded. Enrichment of K in the VHK basalts is above that expected from normal fractional crystallization.

  15. Fluid and melt inclusions in the Mesozoic Fangcheng basalt from North China Craton: implications for magma evolution and fluid/melt-peridotite reaction

    NASA Astrophysics Data System (ADS)

    Sun, He; Xiao, Yilin; Gao, Yongjun; Lai, Jianqing; Hou, Zhenhui; Wang, Yangyang

    2013-05-01

    Melt inclusions and fluid inclusions in the Fangcheng basalt were investigated to understand the magma evolution and fluid/melt-peridotite interaction. Primary silicate melt inclusions were trapped in clinopyroxene and orthopyroxene phenocrysts in the Fangcheng basalt. Three types of melt inclusions (silicate, carbonate, and sulfide) coexisting with fluid inclusions occur in clinopyroxene xenocrysts and clinopyroxene in clinopyroxenite xenoliths. In situ laser-ablation ICP-MS analyses of major and trace element compositions on individual melt inclusions suggest that the silicate melt inclusions in clinopyroxene and orthopyroxene phenocrysts were trapped from the same basaltic magma. The decoupling of major and trace elements in the melt inclusions indicates that the magma evolution was controlled by melt crystallization and contamination from entrapped ultramafic xenoliths. Trace element patterns of melt inclusions are similar to those of the average crust of North China Craton and Yangtze Craton, suggesting a considerable crustal contribution to the magma source. Calculated parental melt of the Fangcheng basalt has features of low MgO (5.96 wt%), high Al2O3 (16.81 wt%), Sr (1,670 ppm), Y (>35 ppm), and high Sr/Y (>40), implying that subducted crustal material was involved in the genesis of the Fangcheng basalt. The coexisting fluid and melt inclusions in clinopyroxene xenocrysts and in clinopyroxene of xenoliths record a rare melt-peridotite reaction, that is olivine + carbonatitic melt1 (rich in Ca) = clinopyroxene + melt2 ± CO2. The produced melt2 is enriched in LREE and CO2 and may fertilize the mantle significantly, which we consider to be the cause for the rapid replacement of lithospheric mantle during the Mesozoic in the region.

  16. Phenomena associated with magma expansion into a drift

    SciTech Connect

    Gaffney, E. S.

    2002-01-01

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

  17. Io: Generation of Silicate Magma by Shear Melting at the Base of a Basaltic Lithosphere

    NASA Technical Reports Server (NTRS)

    Carr, M. H.

    1985-01-01

    Tidal theory and observational evidence indicates that about 1 w/sq. m. of energy is released at the surface of Io. In order to place limits on how much tidal energy can be dissipated within a rigid lithosphere, depth-temperature profiles were calculated for different lithosphere thickness assuming that the tidal energy was dissipated uniformly throughout the lithosphere. Thus a thick lithosphere implies that a significant fraction of the tidal energy is dissipated below the depth where solidus temperatures are reached. One possibility is that Io has a crust consisting of a low melting temperature fraction such as basalt, overlying a mantle of a high melting temperature fraction such as peridotite. Thus, if the lithosphere of Io is thicker than 30 km, as appears probable, then high rates of silicate volcanism are implied and a significant fraction of the tidal energy must be dissipated by viscous deformation rather than rigid flexure.

  18. Role of Subducted Basalt in the Genesis Island Arc Magmas: Evidence from Western Aleutian Seafloor Lavas

    NASA Astrophysics Data System (ADS)

    Yogodzinski, G. M.; Brown, S. T.; Kelemen, P. B.; Vervoort, J. D.; Hoernle, K.; Portnyagin, M.

    2013-12-01

    Western Aleutian seafloor lavas define a highly calc-alkaline series, with Mg numbers (Mg#, Mg/Mg+Fe) greater than 0.65 in dacitic lavas with 2-4% MgO at 63-70% SiO2. These lavas have uniformly radiogenic Hf and Nd and variable, but relatively unradiogenic, Sr and Pb, at the MORB-like end of the spectrum of island-arc lavas. Andesites and dacites have high Sr >1000 ppm, fractionated trace element patterns (Sr/Y=50-350, La/Yb=8-35, Dy/Yb=2-3.5), and low relative abundances of Nb and Ta (La/Ta=100-300), consistent with an enhanced role for residual or cumulate garnet + rutile. MORB-like isotope compositions and high MgO and Mg# relative to silica, rule out an origin for the andesites and dacites by fractional crystallization from basalt, except perhaps, by a process of melt-rock reaction with peridotite. The most fractionated trace element patterns are in western seafloor rhyodacites (69-70% SiO2), which were dredged from volcanic cones built on Bering Sea oceanic lithosphere, where the crust is probably no more than 10 km thick, and so unlikely to produce garnet during crustal melting. We interpret the western seafloor andesites and dacites to have been produced by melting of subducted MORB-like basalt in the eclogite facies, followed by interaction of the resulting high-silica melt with mantle peridotite. This interpretation is consistent with the tectonic setting in the western Aleutians, which is dominated by oblique convergence, capable of producing a relatively hot subducting plate. Western seafloor lavas define an end-member composition with MORB-like isotope compositions and fractionated trace element ratios, which falls at the end of the continuum of compositions for all Aleutian lavas. The end-member character of western seafloor lavas is clearest in plots highlighting their radiogenic Hf, Nd and strong relative depletions in Ta and Yb. The western seafloor lavas also define an end-member composition for Pb isotopes and Ce/Pb (Miller et al., Nature, 1994

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

    PubMed Central

    Kushiro, Ikuo

    2007-01-01

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

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

    PubMed

    Kushiro, Ikuo

    2007-02-01

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

  1. Major-element evidence for multiple magma batches in the evolution of Pleistocene and Holocene volcanic rocks of the Markagunt Plateau volcanic field, southwestern Utah

    SciTech Connect

    Nealey, L.D.; Maldonado, F. )

    1993-04-01

    Pearce element ratios (PER) provide an initial understanding of the evolution of Pleistocene and Holocene alkali basalt to trachyandesite magmas of the Markagunt Plateau. The magmas erupted from numerous cinder cones, shield-like centers, and dikes. Vent areas were controlled by structures (e.g., grabens) related to the tectonic evolution of the transition zone between the Basin and Range and Colorado Plateaus provinces. The cinder cone-fed basalt flows and a single dike-fed basalt flow are probably older than shield-fed basalt and trachyandesite flows. Chemically, cinder cone- and dike-fed basalt flows are more mafic than shield-fed basalt flows. Trachyandesite flows are latite and benmoreite (58.7--59.7 wt % SiO[sub 2]). PER analysis of flow chemistry indicates that the shield-fed flows represent at leas three cogenetic magma batches, that cinder cone-fed flows must be related to more than one magma batch, but that all andesite is genetically related to a common parent magma. The dike-fed basalt flow is not genetically related to any other magma type. Although several magma batches erupted, chemical variations in the magmatic series are consistent with the fractionation of the observed phenocryst phases: olivine, plagioclase, clinopyroxene, and spinel. This four-phase fractionation assemblage relates compositional differences within each basalt type better than it does the entire magmatic series. Fractionation of no single mineral phase can adequately explain chemical variations in the basaltic magmas of the Markagunt Plateau.

  2. Mechanics and Timescales of Magma Mixing Inferred by Texture and Petrology of Basalt Inclusions and Host Andesite From the 2006 Eruption of Augustine Volcano, Alaska

    NASA Astrophysics Data System (ADS)

    Vitale, M. L.; Browne, B. L.

    2010-12-01

    This study characterizes the texture, mineralogy and phenocryst disequilibrium textures in basaltic inclusions and host andesite lavas and scoria to advance our understanding of the mechanics and timescales of open system magma processes driving the 2006 eruption at Augustine Volcano, Alaska. Inclusions account for approximately 1 volume percent in all andesite lithologies emplaced during the explosive, continuous, and effusive eruption phases. In outcrop, quenched basaltic to andesite inclusions (51.3 to 57.3 weight percent SiO2) hosted by andesite lavas (59.1-62.6 weight percent SiO2) range in diameter from 1 cm to over 9 cm, are dark black and characterized by vesicular interiors, quenched and cuspate margins, and porphyritic texture. Inclusion mineralogy is dominated by phenocryst-sized plagioclase with lesser amounts of hornblende, clinopyroxene and olivine, as well as, microphenocrysts-sized plagioclase, hornblende, clinopryoxene, olivine, magnetite, ilmenite and apatite in a glassy, vesicular and acicular groundmass. Intrusion of a hotter, basaltic magma into a cooler silicic magma followed by inclusion formation through mingling processes is evidenced by (1) plagioclase crystal textures displaying (a) oscillatory zoned interiors surrounded by a dusty sieved layer and enclosed by clear, euhedral overgrowth rims, (b) coarsely-sieved interiors characterized by 0.01 mm -0.02 mm diameter melt inclusions and/or similarly sized inclusions of clinopyroxene, orthopryoxene, or hornblende, (2) Anorthite concentration profiles of engulfed host plagioclase crystals displaying contact with a basaltic magma, (3)Fe-Ti oxides from inclusions and low-silica andesite host recording core to rim temperatures ranging from 908°C to 1100°C, indicative of pre- and post- mixing temperatures, respectively, with oxygen fugacity approximately 2 log units above the nickel-nickel oxide buffer. The closest approximation of the basaltic end-member magma composition involved in magma

  3. 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.

  4. Eruptive History and Chemical Evolution of the Precaldera and Postcaldera Basalt-Dacite Sequences, Long Valley, California: Implications for Magma Sources, Current Seismic Unrest, and Future Volcanism

    USGS Publications Warehouse

    Bailey, Roy A.

    2004-01-01

    The Long Valley Volcanic Field in east-central California straddles the East Sierran frontal fault zone, overlapping the Sierra Nevada and western Basin and Range Provinces. The volcanic field overlies a mature mid-Tertiary erosional surface that truncates a basement composed mainly of Mesozoic plutons and associated roof pendants of Mesozoic metavolcanic and Paleozoic metasedimentary rocks. Long Valley volcanism began about 4 Ma during Pliocene time and has continued intermittently through the Holocene. The volcanism is separable into two basalt-rhyolite episodes: (1) an earlier, precaldera episode related to Long Valley Caldera that climaxed with eruption of the Bishop Tuff and collapse of the caldera; and (2) a later, postcaldera episode structurally related to the north-south-trending Mono-Inyo Craters fissure system, which extends from the vicinity of Mammoth Mountain northward through the west moat of the caldera to Mono Lake. Eruption of the basalt-dacite sequence of the precaldera basalt-rhyolite episode peaked volumetrically between 3.8 and 2.5 Ma; few basalts were erupted during the following 1.8 m.y. (2.5?0.7 Ma). Volcanism during this interval was dominated by eruption of the voluminous rhyolites of Glass Mountain (2.2?0.8 Ma) and formation of the Bishop Tuff magma chamber. Catastrophic rupture of the roof of this magma chamber caused eruption of the Bishop Tuff and collapse of Long Valley Caldera (760 ka), after which rhyolite eruptions resumed on the subsided caldera floor. The earliest postcaldera rhyolite flows (700?500 ka) contain quenched globular basalt enclaves (mafic magmatic inclusions), indicating that basaltic magma had reentered shallow parts of the magmatic system after a 1.8-m.y. hiatus. Later, at about 400 ka, copious basalts, as well as dacites, began erupting from vents mainly in the west moat of the caldera. These later eruptions initiated the postcaldera basalt-rhyolite episode related to the Mono-Inyo Craters fissure system, which

  5. Water and magmas: insights about the water solution mechanisms in alkali silicate melts from infrared, Raman, and 29Si solid-state NMR spectroscopies

    NASA Astrophysics Data System (ADS)

    Le Losq, Charles; Mysen, Bjorn O.; Cody, George D.

    2015-12-01

    Degassing of water during the ascent of hydrous magma in a volcanic edifice produces dramatic changes in the magma density and viscosity. This can profoundly affect the dynamics of volcanic eruptions. The water exsolution history, in turn, is driven by the water solubility and solution mechanisms in the silicate melt. Previous studies pointed to dissolved water in silicate glasses and melts existing as molecules (H2Omol species) and hydroxyl groups, OH. These latter OH groups commonly are considered bonded to Si4+ but may form other bonds, such as with alkali or alkaline-earth cations, for instance. Those forms of bonding influence the structure of hydrous melts in different ways and, therefore, their properties. As a result, exsolution of water from magmas may have different eruptive consequences depending on the initial bonding mechanisms of the dissolved water. However, despite their importance, the solution mechanisms of water in silicate melts are not clear. In particular, how chemical composition of melts affects water solubility and solution mechanism is not well understood. In the present experimental study, components of such information are reported via determination of how water interacts with the cationic network of alkali (Li, Na, and K) silicate quenched melts. Results from 29Si single-pulse magic-angle spinning nuclear magnetic resonance (29Si SP MAS NMR), infrared, and Raman spectroscopies show that decreasing the ionic radius of alkali metal cation in silicate melts results in decreasing fraction of water dissolved as OH groups. The nature of OH bonding also changes as the alkali ionic radius changes. Therefore, as the speciation and bonding of water controls the degree of polymerization of melts, water will have different effects on the transport properties of silicate melts depending on their chemical composition. This conclusion, in turn, may affect volcanic phenomena related to the viscous relaxation of hydrous magmas, such as for instance the

  6. The Sr and Nd isotopic record of Apollo 12 basalts - Implications for lunar geochemical evolution

    NASA Technical Reports Server (NTRS)

    Nyquist, L. E.; Shih, C.-Y.; Wooden, J. L.; Bansal, B. M.; Wiesmann, H.

    1979-01-01

    Alkali, alkaline earth, and rare earth element data are reported for several Apollo 12 basalts which are representative of the four Apollo 12 magma types. Results confirm the heterogeneity of the lunar mantle and show that the Sm/Nd ratio of at least the Apollo 12 ilmenite basalts was decreased by 13-24% during magma genesis. In addition, whole mare basalt Sm-Nd data are not collinear on an isochron diagram; thus it is no longer possible to explain these data via mixing of 'primitive material' and 'early differentiates' as in the hybridization and assimilation models.

  7. 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

  8. Light elements, volatiles, and stable isotopes in basaltic melt inclusions from Grenada, Lesser Antilles: Inferences for magma genesis

    NASA Astrophysics Data System (ADS)

    Bouvier, A.-S.; MéTrich, N.; Deloule, E.

    2010-09-01

    Grenada Island is located at the southern end of the Lesser Antilles. Grenada lavas display a large range in compositions which includes picrites, representing the parental melt of all Grenada suites. We present here an extensive study of major, light and volatile elements combined with δD, δ11B and δ7Li determinations of melt inclusions hosted in olivines (Fo86-91) from picritic scoriae. The major element compositions of melt inclusions encompass those of Grenada basalts. Their H2O contents typically range from 0.2 to 4.1 wt% (one value at 6.4 wt%). Such extreme range stands in contrast with typical arc magmas for a single volcanic center. The high H2O contents are associated with strongly negative values of δD (on average -140‰). Melt inclusions display a wide range in B (1.7-47 ppm) and Li (1.1-12 ppm) contents as well as in δ7Li and δ11B, which vary from -24 to 8.2‰ and from -20 to 8.9‰, respectively. Both B and Li compositions of Grenada melt inclusions suggest (i) the involvement of dehydration fluids or hydrous silicate melts derived from buried carbonate-bearing sediments, (ii) the contribution of aqueous fluids generated during the dehydration of hydrothermally altered oceanic crust, and (iii) melting of a mantle metasomatized by the addition of high δ11B, high-Cl, Li-poor fluids derived from the early dehydration of serpentinized peridotite above the slab beneath Grenada.

  9. Porosity evolution, contact metamorphism, and fluid flow in the host basalts of the Skaergaard magma-hydrothermal system

    SciTech Connect

    Manning, C.E.

    1989-01-01

    Temporal and spatial variations in porosity during contact metamorphism of the basaltic country rocks to the Skaergaard intrusion in East Greenland resulted in a complex hydrological evolution of the metamorphic aureole. Contrasts in macroscopic porosities in different lithologies led to differences in mineralogical, bulk chemical, and oxygen isotopic alteration, and units with greater macroscopic porosities record larger fluid flux during metamorphism. Calculated Darcy velocities indicate that the horizontal component of fluid flow in the aureole was toward the intrusive contact. In the actinolite + chlorite zone time-integrated fluid flux was higher in aa units ({approximately} 300 kg cm{sup {minus}2}) than in massive units ({approximately} 130 kg cm{sup {minus}2}). Approximately equal time-integrated fluxes of respectively 4 and 5 kg cm{sup {minus}2} in aa and massive units in the pyroxene zone indicate that the volume of fluid flow in the higher grade rocks was independent of primary porosity. These results are consistent with inward fluid migration in the actinolite + chlorite zone through an open network of pores whose abundance varied as a function of primary lava morphology. At higher metamorphic grades fluid fluxes were lower and were independent of primary porosity, probably as a consequence of (1) channelization of fluids due to more extensive pore filling and (2) decreasing horizontal component of flow due to upward migration of fluids near the contact. The results of this study indicate that explicit provision for rock porosity aids interpretation of the nature of fluid flow during contact metamorphism in magma-hydrothermal systems.

  10. Trace-element and Sr, Nd, Pb, and O isotopic composition of Pliocene and Quaternary alkali basalts of the Patagonian Plateau lavas of southernmost South America

    USGS Publications Warehouse

    Stern, C.R.; Frey, F.A.; Futa, K.; Zartman, R.E.; Peng, Z.; Kurtis, Kyser T.

    1990-01-01

    The Pliocene and Quaternary Patagonian alkali basalts of southernmost South America can be divided into two groups. The "cratonic" basalts erupted in areas of Cenozoic plateau volcanism and continental sedimentation and show considerable variation in 87Sr/86Sr (0.70316 to 0.70512), 143Nd/144Nd (e{open}Nd) and 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios (18.26 to 19.38, 15.53 to 15.68, and 38.30 to 39.23, respectively). These isotopic values are within the range of oceanic island basalts, as are the Ba/La, Ba/Nb, La/Nb, K/Rb, and Cs/Rb ratios of the "cratonic" basalts. In contrast, the "transitional" basalts, erupted along the western edge of the outcrop belt of the Pliocene and Quaternary plateau lavas in areas that were the locus of earlier Cenozoic Andean orogenic arc colcanism, have a much more restricted range of isotopic composition which can be approximated by 87Sr/86Sr=0.7039??0.0004, e{open}Nd, 206Pb/204Pb=18.60??0.08, 207Pb/204Pb=15.60??0.01, and 208Pb/204Pb=38.50??0.10. These isotopic values are similar to those of Andean orogenic are basalts and, compared to the "cratonic" basalts, are displaced to higher 87Sr/86Sr at a given 143Nd/144Nd and to higher 207Pb/204Pb at a given 208Pb/204Pb. The "transitional" basalts also have Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios higher than the "cratonic" and oceanic island basalts, although not as high as Andean orogenic are basalts. In contrast to the radiogenic isotopes, ??18O values for both groups of the Patagonian alkali basalts are indistinguishable and are more restricted than the range reported for Andean orogenic are basalts. Whole rock ??18O values calculated from mineral separates for both groups range from 5.3 to 6.5, while measured whole rock ??18O values range from 5.1 to 7.8. The trace element and isotopic data suggest that decreasing degrees of partial melting in association with lessened significance of subducted slabderived components are fundamental factors in the west to east transition from arc

  11. Perspectives on basaltic magma crystallization and differentiation: Lava-lake blocks erupted at Mauna Loa volcano summit, Hawaii

    USGS Publications Warehouse

    McCarter, Renee L.; Fodor, R.V.; Trusdell, Frank A.

    2006-01-01

    Explosive eruptions at Mauna Loa summit ejected coarse-grained blocks (free of lava coatings) from Moku'aweoweo caldera. Most are gabbronorites and gabbros that have 0–26 vol.% olivine and 1–29 vol.% oikocrystic orthopyroxene. Some blocks are ferrogabbros and diorites with micrographic matrices, and diorite veins (≤2 cm) cross-cut some gabbronorites and gabbros. One block is an open-textured dunite.The MgO of the gabbronorites and gabbros ranges ∼ 7–21 wt.%. Those with MgO >10 wt.% have some incompatible-element abundances (Zr, Y, REE; positive Eu anomalies) lower than those in Mauna Loa lavas of comparable MgO; gabbros (MgO <10 wt.%) generally overlap lava compositions. Olivines range Fo83–58, clinopyroxenes have Mg#s ∼83–62, and orthopyroxene Mg#s are 84–63 — all evolved beyond the mineral-Mg#s of Mauna Loa lavas. Plagioclase is An75–50. Ferrogabbro and diorite blocks have ∼ 3–5 wt.% MgO (TiO2 3.2–5.4%; K2O 0.8–1.3%; La 16–27 ppm), and a diorite vein is the most evolved (SiO2 59%, K2O 1.5%, La 38 ppm). They have clinopyroxene Mg#s 67–46, and plagioclase An57–40. The open-textured dunite has olivine ∼ Fo83.5. Seven isotope ratios are 87Sr/86Sr 0.70394–0.70374 and 143Nd/144Nd 0.51293–0.51286, and identify the suite as belonging to the Mauna Loa system.Gabbronorites and gabbros originated in solidification zones of Moku'aweoweo lava lakes where they acquired orthocumulate textures and incompatible-element depletions. These features suggest deeper and slower cooling lakes than the lava lake paradigm, Kilauea Iki, which is basalt and picrite. Clinopyroxene geobarometry suggests crystallization at <1 kbar P. Highly evolved mineral Mg#s, <75, are largely explained by cumulus phases exposed to evolving intercumulus liquids causing compositional ‘shifts.’ Ferrogabbro and diorite represent segregation veins from differentiated intercumulus liquids filter pressed into rigid zones of cooling lakes. Clinopyroxene

  12. Neogene to Quaternary basalts of the Jabal Eghei (Nuqay) area (south Libya): Two distinct volcanic events or continuous volcanism with gradual shift in magma composition?

    NASA Astrophysics Data System (ADS)

    Radivojević, Maša; Toljić, Marinko; Turki, Salah M.; Bojić, Zoran; Šarić, Kristina; Cvetković, Vladica

    2015-02-01

    This study reports and discusses a set of new K/Ar age and new petrochemical data on basalts of the Jabal Eghei (Nuqay) area (south Libya). This area is part of a > 1000 km long NNW-SSE Libyan volcanic field that stretches from the Mediterranean coastal near Tripoli to the Tibesti massif in Chad. Whole rock K/Ar ages, stratigraphy, volcanology and rock petrochemistry indicate that the Jabal Eghei developed during two volcanic events. The first occurred from the Middle Miocene to the Pliocene (K/Ar ages from ~ 16 to ~ 5 Ma) when large volumes of low aspect ratio lava flows of transitional basalts formed. The second event happened in Pliocene-mid-Pleistocene time (4-≤ 1 Ma) and it gave rise to basanite spatter to scoria pyroclastic cones and subordinate lava flow facies. The transitional basalts are less primitive and less enriched in incompatible trace elements than the basanites. Petrochemical characteristics reveal that the transitional basalts underwent weak to moderate olivine-dominated fractionation and that crustal assimilation had negligible effects. REE geochemical modeling shows that primary magmas of both transitional basalts and basanites formed by melting of a similar garnet-bearing, primitive mantle-like source with degree of melting of 3-5% and ≤ 1%, respectively. It is also demonstrated that the transitional basalts show systematic compositional changes in time because progressively younger rocks are petrochemically more similar to basanites. We argue that our data definitely prove that the age pattern along the entire Libyan volcanic field is much more complex than it was thought before.

  13. Ion microprobe studies of trace elements in Apollo 14 volcanic glass beads - Comparisons to Apollo 14 mare basalts and petrogenesis of picritic magmas

    NASA Technical Reports Server (NTRS)

    Shearer, C. K.; Papike, J. J.; Simon, S. B.; Shimizu, N.; Yurimoto, H.

    1990-01-01

    Results are presented from trace element analysis, by ion microprobe techniques, of individual glass beads representing seven compositionally distinct types of picritic glass beads from the Apollo 14 landing site. The picritic glass beads at the A-14 exhibited a wide range of primary magma compositions and a lack of petrogenetic linkage (via crystal fractionation) to crystalline basalts. The wide range of major and trace element characteristics of the picritic glass beads is consistent with derivation from mineralogically distinct sources which consist of varying proportions of olivine + orthopyroxene +/- clonopyroxene +/- ilmenite +/- plagioclase +/- KREEP component.

  14. The Chimalpahad anorthosite Complex and associated basaltic amphibolites, Nellore Schist Belt, India: Magma chamber and roof of a Proterozoic island arc

    NASA Astrophysics Data System (ADS)

    Dharma Rao, C. V.; Windley, B. F.; Choudhary, A. K.

    2011-03-01

    New major and trace element data on the Proterozoic Chimalpahad layered anorthositic Complex and associated basaltic amphibolites of the Nellore Schist Belt of South India provide new constraints on their petrogenesis and geodynamic setting. The Complex consists of layered anorthosites, leucogabbros, gabbros, ultramafic rocks and is spatially associated with basaltic amphibolites. Despite deformation and metamorphism, primary cumulate textures and igneous layering are locally well preserved throughout the Complex. Whereas the amphibolites display diverse REE systematics, the Chimalpahad anorthositic-gabbroic rocks are characterized by moderately depleted to strongly enriched LREE patterns and by flat to depleted HREE patterns. The field relations, major and trace element compositions of the basaltic amphibolites suggest that they are petrogenetically related to the anorthositic-gabbroic rocks by fractional crystallization. The anorthositic rocks and the basaltic amphibolites share the depletion of Nb relative to Th and La on primitive mantle-normalized diagrams. They exhibit signatures of arc magmatic rocks, such as high LILE and LREE relative to the HFSE and HREE, as well as high Ba/Nb, Ba/Zr, Sr/Y, La/Yb ratios that mimic chondrite-normalized REE and primitive mantle-normalized trace element patterns of arc magmas. Similarly, on log-transformed tectonic discrimination diagrams, the Chimalpahad rocks plot within the field of Phanerozoic magmatic arcs, consistent with a subduction zone origin. On the basis of field relations and geochemical characteristics, the Chimalpahad Complex is interpreted as a fragment of a magma chamber of an island arc, which is tectonically juxtaposed against its original volcanic cover. A new preliminary Sm-Nd date of anorthosite from the Chimalpahad Complex indicates a model age of 1170 Ma.

  15. Flow in the western Mediterranean shallow mantle: Insights from xenoliths in Pliocene alkali basalts from SE Iberia (eastern Betics, Spain)

    NASA Astrophysics Data System (ADS)

    Hidas, Károly; Konc, Zoltán.; Garrido, Carlos J.; Tommasi, Andréa.; Vauchez, Alain; Padrón-Navarta, José Alberto; Marchesi, Claudio; Booth-Rea, Guillermo; Acosta-Vigil, Antonio; Szabó, Csaba; Varas-Reus, María. Isabel; Gervilla, Fernando

    2016-11-01

    Mantle xenoliths in Pliocene alkali basalts of the eastern Betics (SE Iberia, Spain) are spinel ± plagioclase lherzolite, with minor harzburgite and wehrlite, displaying porphyroclastic or equigranular textures. Equigranular peridotites have olivine crystal preferred orientation (CPO) patterns similar to those of porphyroclastic xenoliths but slightly more dispersed. Olivine CPO shows [100]-fiber patterns characterized by strong alignment of [100]-axes subparallel to the stretching lineation and a girdle distribution of [010]-axes normal to it. This pattern is consistent with simple shear or transtensional deformation accommodated by dislocation creep. One xenolith provides evidence for synkinematic reactive percolation of subduction-related Si-rich melts/fluids that resulted in oriented crystallization of orthopyroxene. Despite a seemingly undeformed microstructure, the CPO in orthopyroxenite veins in composite xenoliths is identical to those of pyroxenes in the host peridotite, suggesting late-kinematic crystallization. Based on these observations, we propose that the annealing producing the equigranular microstructures was triggered by melt percolation in the shallow subcontinental lithospheric mantle coeval to the late Neogene formation of veins in composite xenoliths. Calculated seismic properties are characterized by fast propagation of P waves and polarization of fast S waves parallel to olivine [100]-axis (stretching lineation). These data are compatible with present-day seismic anisotropy observations in SE Iberia if the foliations in the lithospheric mantle are steeply dipping and lineations are subhorizontal with ENE strike, implying dominantly horizontal mantle flow in the ENE-WSW direction within vertical planes, that is, subparallel to the paleo-Iberian margin. The measured anisotropy could thus reflect a lithospheric fabric due to strike-slip deformation in the late Miocene in the context of WSW tearing of the subducted south Iberian margin

  16. Pliocene-Quaternary basalts from the Harrat Tufail, western Saudi Arabia: Recycling of ancient oceanic slabs and generation of alkaline intra-plate magma

    NASA Astrophysics Data System (ADS)

    Bakhsh, Rami A.

    2015-12-01

    Harrat Tufail represents a Caenozoic basalt suite at the western margin of the Arabian plate. This rift-related suite includes voluminous Quaternary non-vesicular basalt (with fragments of earlier Pliocene vesicular flow) that forms a cap sheet over Miocene rhyolite and minor vesicular basalt. The contact between rhyolite and the basaltic cap is erosional with remarkable denudations indicating long time gap between the felsic and mafic eruptions. The geochemical data prove alkaline, sodic and low-Ti nature of the olivine basalt cap sheet. The combined whole-rock and mineral spot analyses by the electron microprobe (EMPA) suggest magma generation from low degree of partial melting (∼5%) from spinel- and garnet-lherzolite mantle source. Derivation from a mantle source is supported by low Na content in clinopyroxene (ferroan diopside) whereas high Mg content in ilmenite is an evidence of fractional crystallization trajectory. Accordingly, the Pliocene basaltic cap of Harrat Tufail is a product of mantle melt that originates by recycling in the asthenosphere during subduction of ancient oceanic slab(s). The whole-rock chemistry suggests an ancient ocean island basaltic slab (OIB) whereas the EMPA of Al-rich spinel inclusions in olivine phenocrysts are in favour of a mid-ocean ridge basaltic source (MORB). Calculations of oxygen fugacity based on the composition of co-existing Fe-Ti oxide suggest fluctuation from highly to moderately oxidizing conditions with propagation of crystallization (log10 fO2 from -22.09 to -12.50). Clinopyroxene composition and pressure calculation indicates low-pressure (0.4-2 kbar). Cores of olivine phenocrysts formed at highest temperature (1086-1151 °C) whereas the rims and olivine micro-phenocrysts formed at 712-9-796 °C which is contemporaneous to formation of clinopyroxene at 611-782 °C. Fe-Ti oxides crystallized over a long range (652-992 °C) where it started to form at outer peripheries of olivine phenocrysts and as interstitial

  17. How does magma move inside the shallow feeder systems in basaltic volcanoes? The exceptional example of the 1809 Etna eruption (Italy)

    NASA Astrophysics Data System (ADS)

    Neri, Marco; Geshi, Nobuo

    2015-04-01

    The detection and understanding of the movement of magma at very shallow levels remains one of the most fascinating challenges of modern volcanology, since such information allows us to identify and circumscribe the most probable location for the opening of future eruptive vents. Unfortunately, it is rarely possible to observe in any detail the internal structure of the feeder system of recent eruptions. In this paper, we describe the 1809 eruption of Mt. Etna, Italy, which represents one historical and rare case where it is possible to closely observe the internal structure of the feeder system. The 1809 eruption is fairly typical of the flank eruptions occurring along the NE Rift of Etna, but with a fundamental difference: the development of the fracture field was characterized, in its central sector, by an abrupt change in eruptive style (from effusive/Strombolian to explosive phreatomagmatic), testified by the outcrops exposed along the inner walls of some craters. This transition also created the formation of cavities in the feeder system. Phreatomagmatic activity was probably triggered by the interaction between the magma and the aquifer of the volcano, precisely when the magma was migrating abruptly downwards. The understanding of these mechanisms sheds new light on a) the propagation mechanism of eruptive fractures in basaltic volcanoes such as Mt. Etna, b) how magma moves inside the feeder systems and c) how the dynamic of the magma creates conditions of variability of eruptive styles during the same eruption. These results are also useful in terms of hazard assessment, since they allow predicting different eruptive scenarios according to the dynamics of the structural system feeding the eruptions, a crucial factor in highly urbanized volcanoes.

  18. Prodigious emission rates and magma degassing budget of major, trace and radioactive volatile species from Ambrym basaltic volcano, Vanuatu island Arc

    NASA Astrophysics Data System (ADS)

    Allard, P.; Aiuppa, A.; Bani, P.; Métrich, N.; Bertagnini, A.; Gauthier, P.-J.; Shinohara, H.; Sawyer, G.; Parello, F.; Bagnato, E.; Pelletier, B.; Garaebiti, E.

    2016-08-01

    Ambrym volcano, in the Vanuatu arc, is one of the most active volcanoes of the Southwest Pacific region, where persistent lava lake and/or Strombolian activity sustains voluminous gas plume emissions. Here we report on the first comprehensive budget for the discharge of major, minor, trace and radioactive volatile species from Ambrym volcano, as well as the first data for volatiles dissolved in its basaltic magma (olivine-hosted melt inclusions). In situ MultiGAS analysis of H2O, CO2, SO2 and H2S in crater rim emissions, coupled with filter-pack determination of SO2, halogens, stable and radioactive metals demonstrates a common magmatic source for volcanic gases emitted by its two main active craters, Benbow and Marum. These share a high water content ( 93 mol%), similar S/Cl, Cl/F, Br/Cl molar ratios, similar (210Po/210Pb) and (210Bi/210Pb) activity ratios, as well as comparable proportions in most trace metals. Their difference in CO2/SO2 ratio (1.0 and 5.6-3.0, respectively) is attributed to deeper gas-melt separation at Marum (Strombolian explosions) than Benbow (lava lake degassing) during our measurements in 2007. Airborne UV sensing of the SO2 plume flux (90 kg s- 1 or 7800 tons d- 1) demonstrates a prevalent degassing contribution ( 65%) of Benbow crater in that period and allows us to quantify the total volatile fluxes during medium-level eruptive activity of the volcano. Results reveal that Ambrym ranks among the most powerful volcanic gas emitters on Earth, producing between 5% and 9% of current estimates for global subaerial volcanic emissions of H2O, CO2, HCl, Cu, Cr, Cd, Au, Cs and Tl, between 10% and 17% of SO2, HF, HBr, Hg, 210Po and 210Pb, and over 30% of Ag, Se and Sn. Global flux estimates thus need to integrate its contribution and be revised accordingly. Prodigious gas emission from Ambrym does not result from an anomalous volatile enrichment nor a differential excess degassing of its feeding basalt: this latter contains relatively modest

  19. A trachyte-syenite core within a basaltic nest: filtering of primitive injections by a multi-stage magma plumbing system (Oki-Dōzen, south-west Japan)

    NASA Astrophysics Data System (ADS)

    Brenna, Marco; Nakada, Setsuya; Miura, Daisuke; Toshida, Kiyoshi; Ito, Hisatoshi; Hokanishi, Natsumi; Nakai, Shun'ichi

    2015-08-01

    Oki-Dōzen (Japan) is a Late Miocene (7-5 Ma) intraplate alkalic volcano composed of a central trachytic pyroclastic complex surrounded by a ring-shaped succession of basaltic to trachybasaltic lavas and pyroclastic rocks and dispersed trachytic bodies. The central trachytic complex is in contact with a syenite that was intruded into the basement early Miocene volcano-sedimentary succession. In the centre of the system there are no alkalic basaltic rocks that are correlative of the outer flank ring. We present whole-rock major and trace element chemistry, Sr-Nd-Pb isotopic compositions and petrological data from the central trachytic volcanic complex and the intrusive syenite body, as well as from the outer ring basaltic succession. We also present and discuss a new set of zircon U/Pb ages collected from the central trachyte and syenite bodies. All the eruptive products of Oki-Dōzen, as well as the syenite, plot on a single liquid line of descent initiated from a mantle-derived alkalic basaltic parent. A younger (2.8 Ma) basaltic eruption (Uzuka basalt) has isotopic compositions that distinguish it from the rest of the system. Geochemical modelling indicates that magmatic differentiation through crystal fractionation and minor crustal assimilation occurred in crustal and shallow sub-volcanic magma reservoirs. In the central part of the system, a number of vertically spaced reservoirs acted as a filter, capturing basaltic dykes and hindering their ascent. In the outer region, dykes either reached the surface unhindered and erupted to form the basaltic/trachybasaltic succession or stalled at crustal levels and differentiated to trachyte before forming dispersed domes/flows. The central plumbing system "filter" resulted in a nest-shaped volcano, with a trachytic core surrounded by basaltic products, and stopped direct injection of basaltic magmas into the shallow syenitic magma reservoir, likely preventing its destabilization and explosive eruption.

  20. Assimilation of granite by basaltic magma at Burnt Lava flow, Medicine Lake volcano, northern California: Decoupling of heat and mass transfer

    USGS Publications Warehouse

    Grove, T.L.; Kinzler, R.J.; Baker, M.B.; Donnelly-Nolan, J. M.; Lesher, C.E.

    1988-01-01

    At Medicine Lake volcano, California, andesite of the Holocene Burnt Lava flow has been produced by fractional crystallization of parental high alumina basalt (HAB) accompanied by assimilation of granitic crustal material. Burnt Lava contains inclusions of quenched HAB liquid, a potential parent magma of the andesite, highly melted granitic crustal xenoliths, and xenocryst assemblages which provide a record of the fractional crystallization and crustal assimilation process. Samples of granitic crustal material occur as xenoliths in other Holocene and Pleistocene lavas, and these xenoliths are used to constrain geochemical models of the assimilation process. A large amount of assimilation accompanied fractional crystallization to produce the contaminated Burnt lava andesites. Models which assume that assimilation and fractionation occurred simultaneously estimate the ratio of assimilation to fractional crystallization (R) to be >1 and best fits to all geochemical data are at an R value of 1.35 at F=0.68. Petrologic evidence, however, indicates that the assimilation process did not involve continuous addition of granitic crust as fractionation occurred. Instead, heat and mass transfer were separated in space and time. During the assimilation process, HAB magma underwent large amounts of fractional crystallization which was not accompanied by significant amounts of assimilation. This fractionation process supplied heat to melt granitic crust. The models proposed to explain the contamination process involve fractionation, replenishment by parental HAB, and mixing of evolved and parental magmas with melted granitic crust. ?? 1988 Springer-Verlag.

  1. Magma degassing: new experiments on CO2, H2O, S and Cl between basaltic melt and fluid and development of a new thermodynamical model

    NASA Astrophysics Data System (ADS)

    Lesne, P.; Kohn, S.; Blundy, J.; Witham, F.; Behrens, H.; Botcharnikov, R. E.

    2009-12-01

    Many volcanoes are monitored and one of the main tools for predicting eruptions is analysis of the amount and compositions of gases which are emitted. In particular, measurements of SO2 and HCl are widely used, as there is normally very little SO2 or HCl in the atmosphere. In contrast, it is hard to distinguish between water and carbon dioxide released by the volcano because water and carbon dioxide are already in the atmosphere. In addition, melt inclusions can be analysed for all the dissolved gases and the pre-eruptive history of rising magma losing its dissolved gases can be worked out. Both types of measurements are very useful, but to make the most of them we need to fully understand how gases are released from the molten magma, and at what depth in the volcano. The aim of this research is therefore to study how much of each type of gas can be dissolved in the molten rock, and how the different concentrations of each gas affects the exsolution of the others. We have developed a method which involves experimentally simulating the decompression that occurs when magma ascends beneath a volcano whereby basaltic melt is equilibrated with a C-H-O-S-Cl fluid phase. Experiments were performed in an internal heated pressure vessel, at 1150°C and between 400MPa and 25MPa under oxidized conditions. To reproduce the degassing path of basaltic melt in a closed system, the initial volatile contents are always the same for each experiment. Then, quenched liquid was analysed for both major (CO2, H2O) and minor (S, Cl) components using a range of state-of-the-art analytical techniques. The composition of the fluid phase was determined by mass balance calculations. This study has elucidated, for the first time, the way in which the degassing of S and Cl from basaltic volcanoes is influenced by the presence of H2O and CO2. Water and carbon dioxide data were compared to previous H2O-CO2 models of degassing (Dixon, 1997; Newman and Lowenstern, 2002; Papale et al., 2006): these

  2. Lithospheric influences on magma compositions of late Mesozoic and Cenozoic intraplate basalts (the Older Volcanics) of Victoria, south-eastern Australia

    NASA Astrophysics Data System (ADS)

    Price, Richard C.; Nicholls, Ian A.; Day, Arthur

    2014-10-01

    distinctive convex upwards patterns but are characterised by strong depletions of K, Rb and Ba relative to Nb. In both groups there is additional subtle variation with some samples having patterns with relative enrichments in Nb, Sr and Eu and/or depletions in Pb. Group 1 basalt compositions can be approximated by quantitative models involving 2 to 10% partial melting of an originally depleted mantle composition that has been metasomatised by the addition of 2 to 3% of an enriched component with a composition similar to EM1 intraplate basalt. The trace element patterns of Group 2 basalts can be modelled by 2 to 10% partial melting of an originally depleted mantle metasomatised by the addition of 1% of a calci-carbonatite composition. When Sr isotope data for Older Volcanics are projected onto an east-west profile across the state of Victoria, they outline distinctive discontinuities in isotopic composition that appear to be related to surface and subsurface structural features within the basement. One such discontinuity has previously been identified using data for the Newer Volcanics of the Western District Province of Victoria. Lithospheric blocks present beneath southern Victoria range in age from NeoProterozoic or Cambrian to Palaeozoic and some of the lowest 87Sr/86Sr ratios are observed in basalts erupted above an older basement unit (the Selwyn Block). The inference is that there is some form of lithospheric control on basaltic magma chemistry and since a substantial proportion of Older Volcanics have the geochemical characteristics of primary magmas (high Mg# and moderate to high abundances of Ni and Cr), this could indicate that magmas have been sourced from regionally heterogeneous, variably metasomatised, sub-continental lithospheric mantle. Neither the temporal and spatial relationships of the magmatic activity that followed continental breakup nor the uplift history of the south-eastern Australian passive margin are readily explained in terms of deep mantle plume

  3. Very low Ti /VLT/ basalts - A new mare rock type from the Apollo 17 drill core

    NASA Technical Reports Server (NTRS)

    Vaniman, D. T.; Papike, J. J.

    1977-01-01

    Phaneritic fragments, vitrophyres, and glass beads of a new very low Ti (VLT) mare basalt are found in the Apollo 17 drill core. VLT lithic fragments are characterized by TiO2 content of approximately 0.5%, Mg/(Mg + Fe) of approximately 0.52, CaO/Al2O3 of approximately 0.9, and low alkali content. Although mineral systematics and modal composition of VLT basalt are similar to Apollo 12 and 15 low Ti basalts, VLT basalts cannot be related to these mare basalts by crystal fractionation. Since VLT basalt is isochemical with some of the less mafic green glasses, fractionation of VLT magma from a liquid of green-glass composition is a possibility. Spectral reflectance studies suggest that VLT-type basalts may be relatively common in mare basins.

  4. Modern analogues for Miocene to Pleistocene alkali basaltic phreatomagmatic fields in the Pannonian Basin: "soft-substrate" to "combined" aquifer controlled phreatomagmatism in intraplate volcanic fields Research Article

    NASA Astrophysics Data System (ADS)

    Németh, Károly; Cronin, Shane; Haller, Miguel; Brenna, Marco; Csillag, Gabor

    2010-09-01

    The Pannonian Basin (Central Europe) hosts numerous alkali basaltic volcanic fields in an area similar to 200 000 km2. These volcanic fields were formed in an approximate time span of 8 million years producing smallvolume volcanoes typically considered to be monogenetic. Polycyclic monogenetic volcanic complexes are also common in each field however. The original morphology of volcanic landforms, especially phreatomagmatic volcanoes, is commonly modified. by erosion, commonly aided by tectonic uplift. The phreatomagmatic volcanoes eroded to the level of their sub-surface architecture expose crater to conduit filling as well as diatreme facies of pyroclastic rock assemblages. Uncertainties due to the strong erosion influenced by tectonic uplifts, fast and broad climatic changes, vegetation cover variations, and rapidly changing fluvio-lacustrine events in the past 8 million years in the Pannonian Basin have created a need to reconstruct and visualise the paleoenvironment into which the monogenetic volcanoes erupted. Here phreatomagmatic volcanic fields of the Miocene to Pleistocene western Hungarian alkali basaltic province have been selected and compared with modern phreatomagmatic fields. It has been concluded that the Auckland Volcanic Field (AVF) in New Zealand could be viewed as a prime modern analogue for the western Hungarian phreatomagmatic fields by sharing similarities in their pyroclastic successions textures such as pyroclast morphology, type, juvenile particle ratio to accidental lithics. Beside the AVF two other, morphologically more modified volcanic fields (Pali Aike, Argentina and Jeju, Korea) show similar features to the western Hungarian examples, highlighting issues such as preservation potential of pyroclastic successions of phreatomagmatic volcanoes.

  5. Light Lithophile Elements in Natural and Experimental Phases in Martian Basalts: Implications for the Degassing of Water from Martian Magmas

    NASA Technical Reports Server (NTRS)

    Herd, C. D. K.; Treiman, A. H.; McKay, G. A.; Shearer, C. K.

    2003-01-01

    Lentz et al. argued that zoning trends in light lithophile elements (LLE) in pyroxene in Shergotty and Zagami are evidence for the degassing of magmatic water. We tested this inference by obtaining: additional LLE analyses of Shergotty and Zagami pyroxene; analyses of Pasamonte pyroxene; and silicate and phosphate partition coefficients for B and Li for martian magma and mineral compositions.

  6. The Etendeka Igneous Province: magma types and their stratigraphic distribution with implications for the evolution of the Paraná-Etendeka flood basalt province

    NASA Astrophysics Data System (ADS)

    Marsh, J. S.; Ewart, A.; Milner, S. C.; Duncan, A. R.; Miller, R. McG.

    2001-02-01

    Detailed geochemical and field data for the volcanic sequence and intrusions of the Etendeka Igneous Province are used to construct a stratigraphic framework for petrogenetic interpretation of the evolution of the Etendeka-Paraná continental flood volcanic event. Geochemical and petrographic characterization of over 1,000 analyzed samples allows 8 mafic and 17 silicic magma types to be recognized. Both silicic and mafic types can be grouped into high-Ti and low-Ti suites on the basis of elevated Ti relative to other elements. The mafic magmas are: Khumib (high-Ti), Tafelberg, Kuidas, Horingbaai, Huab, Tafelkop, Albin, and Esmeralda (all low-Ti). Amongst the silicic types, the Goboboseb, Springbok, Wereldsend, Grootberg, and Beacon low-Ti quartz latites, and the Nil Desperandum high-Ti latite have been described previously. In addition, the Hoas (low-Ti), Nadas, Sechomib, and Hoarusib, (all high-Ti) latites and the Fria (low-Ti), Sarusas, Ventura, Khoraseb, Naudé, and Elliott (all high-Ti) quartz latites are described for the first time here. There is a marked provinciality in the distribution of the high- and low-Ti suites, with the former concentrated in the Northern Etendeka region and the latter dominant in the Southern Etendeka. Stratigraphic distribution of magma types allows two new formations to be defined in the Northern Etendeka - the Khumib Formation of basaltic flows and the Skeleton Coast Formation dominated by silicic sheets. The geochemical provinciality hampers precise correlations between Northern and Southern Etendeka. Available evidence suggests that the lower part of the Awahab Formation in the Southern Etendeka is coeval with the lower part of the Khumib Formation and that the silicic units in the upper part of the Tafelberg Formation probably correlate with the Skeleton Coast Formation. The paucity of Khumib dykes in relation to Tafelberg dykes and their field relationships with regard to the volcanic sequence in the Northern Etendeka

  7. Volatile constraints on the magma supply, dynamics and plumbing system of a top-ranking basaltic gas emitter: Ambrym volcano, Vanuatu Arc

    NASA Astrophysics Data System (ADS)

    Allard, Patrick

    2016-04-01

    P. Allard1,2, A. Aiuppa3,4, P. Bani5, N. Métrich1,6, A. Bertagnini6, M. Burton7, P-J. Gauthier5, F. Parello3, H. Shinohara8, G. Sawyer9, E. Bagnato3, E. Garaebiti10 1IPGP, UMR7154 CNRS, Paris France; 2INGV, Sezione di Catania, Italy; 3DiSTEM, Palermo University, Italy; 4INGV, Sezione di Palermo, Italy; 5LMV-OPGC, Clermont-Ferrand, France; 6INGV, Sezione di Pisa, Italy; 7SEAES, University of Manchester, UK; 8Geological Survey of Japan, Tsukuba, Japan; 9Department of Geography, University of Cambridge, UK; 10GEOHAZARD, Port Vila, Vanuatu. Ambrym basaltic volcano (central Vanuatu arc) is one of the most active volcanic systems of the Southwest Pacific region, where recurrent lava lake activity sustains voluminous gas release from two main cones, Benbow and Marum, in a 12 km-wide summit caldera. In 2007-2008 we could perform the first detailed investigations of gas emissions from this very active but remote and hardly accessible intra-oceanic arc volcano, combining ground-based and airborne measurements and using both in situ and remote sensing tools. The degassing budget of major, minor, trace and radioactive volatile species reveals that Ambrym ranks amongst the three most powerful persistent emitters of magmatic volatiles at global scale [1]. Coupled with the analysis of dissolved volatiles in the feeding basalt (olivine-hosted melt inclusions), the gas emission rates imply a very high average magma supply/degassing rate of 25 m3/s - 6 times the rate at Mount Etna - from a reservoir emplaced at about 4 km depth beneath the caldera floor. The chemical composition of emitted volcanic gases is compatible with dominant closed-system ascent and degassing of the basalt, followed by open degassing at shallow depth as water exsolution becomes extensive. The modest time-averaged extrusion rate, estimated from caldera infilling over the past 2 ka, requires convective downward recycling of the denser degassed magma in conduits with diameter of order 10 m. High resolution OP

  8. Crystal preferred orientations of minerals from mantle xenoliths in alkali basaltic rocks form the Catalan Volcanic Zone (NE Spain)

    NASA Astrophysics Data System (ADS)

    Fernández-Roig, Mercè; Galán, Gumer; Mariani, Elisabetta

    2015-04-01

    Mantle xenoliths in alkali basaltic rocks from the Catalan Volcanic Zone, associated with the Neogene-Quaternary rift system in NE Spain, are formed of anhydrous spinel lherzolites and harzburgites with minor olivine websterites. Both peridotites are considered residues of variable degrees of partial melting, later affected by metasomatism, especially the harzburgites. These and the websterites display protogranular microstructures, whereas lherzolites show continuous variation between protogranular, porphyroclastic and equigranular forms. Thermometric data of new xenoliths indicate that protogranular harzburgites, lherzolites and websterites were equilibrated at higher temperatures than porphyroclastic and equigranular lherzolites. Mineral chemistry also indicates lower equilibrium pressure for porphyroclastic and equigranular lherzolites than for the protogranular ones. Crystal preferred orientations (CPOs) of olivine and pyroxenes from these new xenoliths were determined with the EBSD-SEM technique to identify the deformation stages affecting the lithospheric mantle in this zone and to assess the relationships between the deformation fabrics, processes and microstructures. Olivine CPOs in protogranular harzburgites, lherzolites and a pyroxenite display [010]-fiber patterns characterized by a strong point concentration of the [010] axis normal to the foliation and girdle distribution of [100] and [001] axes within the foliation plane. Olivine CPO symmetry in porphyroclastic and equigranular lherzolites varies continuously from [010]-fiber to orthorhombic and [100]-fiber types. The orthorhombic patterns are characterized by scattered maxima of the three axes, which are normal between them. The rare [100]-fiber patterns display strong point concentration of [100] axis, with normal girdle distribution of the other two axes, which are aligned with each other. The patterns of pyroxene CPOs are more dispersed than those of olivine, especially for clinopyroxene, but

  9. The "Large" in Large Igneous Provinces: Using Digital Geological Maps to Determine the Area, Magma Flux, and Potential Environmental Impact of the Wrangellia Flood Basalts

    NASA Astrophysics Data System (ADS)

    Scoates, J. S.; Greene, A. R.; Weis, D. A.

    2010-12-01

    Large igneous provinces (LIPs), such as continental flood basalts and oceanic plateaus, are formed by relatively short duration, massive outpourings of basalt in intraplate settings. Their emplacement has been associated with global climatic and biotic change (e.g., end-Permian Siberian LIP). The magmatic products of a LIP typically cover an area >1 Mkm2, however erosion and exhumation may substantially reduce the original area and volume of a LIP, especially oceanic plateaus that have been tectonically dispersed during accretion (e.g., Caribbean, Wrangellia). The availability of digital geologic maps from government geologic surveys now allows for measuring the precise areal distribution of remnant LIP-products, which is essential information for estimating total volumes and ultimately potential environmental effects. The Wrangellia flood basalts represent one of the best-exposed accreted oceanic plateaus on Earth. This Triassic LIP is exposed in numerous fault-bound blocks in a belt extending discontinuously for 2300 km in the Pacific Northwest of North America. It contains exposures of submarine and subaerial volcanic rocks representing composite stratigraphic thicknesses of 3.5-6 km. From recently compiled digital geologic maps (British Columbia, Yukon, Alaska), the mapped exposures of the Wrangellia flood basalts are relatively small (25,256 km2 with 75% from Vancouver Island), which leads to minimum calculated erupted volumes of up to 1.4 x 105 km3 and an estimated magma flux of 0.03 km3/yr. The original areal distribution was substantially greater, perhaps by an order of magnitude or more, as the outcrop extent does not include regions covered by younger strata and surficial deposits nor does it account for the volcanic component of the terrane that may have been subducted. However, even this minimum volumetric output rate is comparable to recent estimates of long-term volumetric eruption rates for ocean islands such as Iceland (0.02-0.04 km3/yr) and Hawaii

  10. Crystal fractionation of the basalt comendite series of the mount Edziza volcanic complex, British Columbia: Major and trace elements

    NASA Astrophysics Data System (ADS)

    Souther, J. G.; Hickson, C. J.

    1984-06-01

    The Mount Edziza Volcanic Complex in north-central British Columbia includes a group of overlapping basaltic shields, salic composite volcanoes, domes and small calderas that range in age from 7.5 Ma to less than 2000 years B.P. The volcanic assemblage is chemically bimodal, comprising voluminous alkali olivine basalt and hawaiite, a salic suite of mainly peralkaline trachyte and comendite, plus a relatively small volume of intermediate rocks (trachybasalt, tristanite, mugearite, benmoreite). The complex is the product of five cycles of magmatic activity, each of which began with alkali olivine basalt and culminated with the eruption of salic magma. The regular chemical variation shown by almost 100 major- and trace-element analyses suggests a genetic lineage between the basic and salic members of each cycle. Least-squares mathematical modelling, indicates that the salic rocks (trachyte and comendite) have formed by fractionation of observed phenocryst and cumulate nodule mineral phases from a common alkali olivine basalt parent magma. Hawaiite is thought to be a cumulate rock, formed by partial fractionation and feldspar accumulation within rising columns of primary alkali olivine basalt. Fractionation leading from alkali olivine basalt through trachybasalt and trachyte to comendite is believed to have taken place where primary basalt became trapped in large crustal reservoirs. The early removal of olivine, clinopyroxene and plagioclase, leading to a trachytic residuum, and subsequent fractionation of mainly alkali feldspar, leading to the peralkaline end members, is consistent with major- and trace-element variation and with isotopic and REE data. The chemical diversity of the complex is attributed to its location over a zone of crustal extension where mantle-derived basalt, trapped in large high-level reservoirs, underwent prolonged fractionation.

  11. Major element chemistry of Apollo 14 mare basalt clasts and highland plutonic clasts from lunar breccia 14321: Comparison with neutron activation results

    NASA Technical Reports Server (NTRS)

    Shervais, John W.; Vetter, Scott K.

    1993-01-01

    Studies of lithic components in lunar breccias have documented a wide variety of rock types and magma suites which are not found among large, discrete lunar samples. Rock types found exclusively or dominantly as clasts in breccias include KREEP basalts, VHK mare basalts, high-alumina mare basalts, olivine vitrophyres, alkali anorthosites, and magnesian anorthosites and troctolites. These miniature samples are crucial in petrogenetic studies of ancient mare basalts and the highlands crust of the western nearside, both of which have been battered by basin-forming impacts and no longer exist as distinct rock units.

  12. Assimilation of Seawater in Basaltic Magmas: Evidence Found in a Lava Pillar From Axial Seamount, Juan de Fuca Ridge

    NASA Astrophysics Data System (ADS)

    Schiffman, P.; Zierenberg, R.; Chadwick, W. W.; Clague, D. A.

    2008-12-01

    A lava pillar formed during the 1998 eruption at Axial Seamount exhibits compositional and textural evidence consistent with the direct assimilation of seawater under magmatic conditions. Glass immediately adjacent to anastomosing microfractures within 1 cm of the inner pillar wall is oxidized and significantly enriched in both Na and Cl (and depleted in Fe and K) with respect to that in selvages from the (unaffected) outer pillar wall. The affected glass contains up to 1 wt. % Cl and is enriched by ca. 2 wt. % Na2O relative to unaffected glass, consistent with a nearly 1:1 (molar) assimilation of NaCl. Glass not adjacent to microfractures in the inner pillar wall is depleted in Na, but enriched in K, with respect to the NaCl-enriched, inner pillar wall glass and the unaffected outer pillar wall glass. The 87Sr/86Sr ratio of the NaCl-enriched glass (ca. 0.704 +/- .001), as determined by LA ICPMS, is slightly elevated with respect to that of unaffected glass (ca. .703) consistent with the incorporation of a seawater-derived fluid. The presence of tiny (< 10 mm) grains of Cu-Fe- and Fe-sulfides as well as elemental Ni, Ag, and Au in the Na-depleted, K-enriched glass of the inner pillar wall implies significant reduction of this glass, presumably by hydrogen generated during seawater assimilation and oxidation of magma adjacent to microfractures. We interpret that the chemical anomalies we see in the glass of the interior pillar wall are caused by nearly instantaneous assimilation of seawater into the magma during pillar growth. Other lava pillars we have examined from Axial Seamount and elsewhere on the Juan de Fuca Ridge do not display similar features, although we have not examined a statistically significant number of samples to ascertain how widespread a process this is for seawater assimilation.

  13. Mullite-corundum-spinel-cordierite-plagioclase xenoliths in the Skaergaard Marginal Border Group: multi-stage interaction between metasediments and basaltic magma

    NASA Astrophysics Data System (ADS)

    Markl, Gregor

    2005-04-01

    Metapelitic country rocks were contact- and pyro-metamorphosed by the Tertiary Skaergaard Intrusion, East Greenland. In an initial stage of heating, while they were probably still in place within the host rock contact aureole, they overstepped a range of equilibrium and disequilibrium melting reactions and produced both a granitic melt and very refractory spinel+cordierite+plagioclase±corundum residuals. Parts of these refractory rocks were then subjected to another melting event after being entrained as xenoliths into the Skaergaard Marginal Border Group, where they experienced a temperature of about 1,000°C at a pressure of about 650 bars and at an oxygen fugacity about 0.2-0.5 log units below the FMQ buffer. Here, they underwent bulk melting, but did not mix with the Skaergaard magma, presumably because of the high viscosity contrast. The Al-rich melts crystallized to an assemblage of corundum+mullite+sillimanite+ plagioclase+spinel+rutile±tridymite±cordierite and they reacted with the surrounding basalt producing a strongly cryptically zoned rim of plagioclase (An55 close to the basalt to An90 close to the Al-rich melt). The assemblage in the inner parts of the xenoliths provides textural evidence for disequilibrium growth due to slow diffusivities in the highly viscous, probably water-free Al-rich melt. Later interaction of lower temperature ferrobasaltic to granophyric melts with the xenoliths along their margins and along cracks led to consumption of corundum and mullite and to the stable assemblage of spinel+cordierite+plagioclase+quartz+K-feldspar +magnetite+ilmenite at about 800°C.

  14. Volatile Flux and Composition at Yellowstone Reflects a Gas-Charged Hydrothermal System Above a Basalt-Fueled Silicic Magma Reservoir

    NASA Astrophysics Data System (ADS)

    Lowenstern, J. B.; Hurwitz, S.

    2007-12-01

    Recent papers have documented the immense volatile (CO2, S, Cl-, F-) flux from the Yellowstone Caldera. Carbon dioxide is estimated to escape diffusively through soils at a rate of 45,000 t d-1 (Werner and Brantley, 2003) compared with 137 t d-1 of Cl- released from hot springs into rivers (Hurwitz and others, 2007). These high volatile fluxes and the CO2/Cl- ratio of ~300 are inconsistent with simple degassing of a mid- or upper-crustal silicic intrusion. For example, if the estimated CO2-flux were supplied solely by a 104 km3 silicic-magma reservoir with 500 ppm dissolved CO2, the reservoir would be exhausted in ~1000 years, less than 0.1% of the longevity of the present Yellowstone volcanic field. Moreover, silicate melt inclusions in phenocrysts from erupted rhyolites contain abundant dissolved Cl- and F-, but minimal CO2 and S, the dominant effluents from the hydrothermal system. The carbon budget is explained best by dominant basalt degassing (~0.3 km3 a-1 of magma) in the lower and mid- crust, augmented by metamorphic devolatilization of limestone and other sediments, plus what can be sourced from overlying rhyolitic magma. The volatiles then pass into and through the near-surface hydrothermal system. The relative abundances of emitted CO2 and Cl- appear to require that the shallow subsurface beneath Yellowstone is gas-saturated down to >2 km. Fournier (1989) concluded that the diverse Yellowstone geothermal waters are ultimately derived from a deep parent fluid with 400 ppm Cl-. If Cl- and CO2 are emitted in proportion to their abundance in the hydrothermal system, then given the CO2/Cl- of 300, this parent fluid would contain 12 wt.% CO2 (5 mol%). Solubility constraints reveal that such fluid would be saturated with CO2-rich steam within the upper few kilometers. The presence of a compressible and expandable vapor phase has important implications for the origin and interpretation of ground-surface displacements at active calderas such as Yellowstone

  15. Magma differentiation rates from ( 226Ra / 230Th) and the size and power output of magma chambers

    NASA Astrophysics Data System (ADS)

    Blake, Stephen; Rogers, Nick

    2005-08-01

    We present a mathematical model for the evolution of the ( 226Ra / 230Th) activity ratio during simultaneous fractional crystallization and ageing of magma. The model is applied to published data for four volcanic suites that are independently known to have evolved by fractional crystallization. These are tholeiitic basalt from Ardoukoba, Djibouti, MORB from the East Pacific Rise, alkali basalt to mugearite from Vestmannaeyjar, Iceland, and basaltic andesites from Miyakejima, Izu-Bonin arc. In all cases ( 226Ra / 230Th) correlates with indices of fractional crystallization, such as Th, and the data fall close to model curves of constant fractional crystallization rate. The best fit rates vary from 2 to 6 × 10 - 4 yr - 1 . Consequently, the time required to generate moderately evolved magmas ( F ≤ 0.7) is of the order of 500 to 1500 yrs and closed magma chambers will have lifetimes of 1700 to 5000 yrs. These rates and timescales are argued to depend principally on the specific power output (i.e., power output per unit volume) of the magma chambers that are the sites of fractional crystallization. Equating the heat flux at the EPR to the heat flux from the sub-axial magma chamber that evolves at a rate of ca. 3 × 10 - 4 yr - 1 implies that the magma body is a sill of ca. 100 m thickness, a value which coincides with independent estimates from seismology. The similarity of the four inferred differentiation rates suggests that the specific power output of shallow magma chambers in a range of tectonic settings covers a similarly narrow range of ca. 10 to 50 MW km - 3 . Their differentiation rates are some two orders of magnitude slower than that of the basaltic Makaopuhi lava lake, Hawaii, that cooled to the atmosphere. This is consistent with the two orders of magnitude difference in heat flux between Makaopuhi and the East Pacific Rise. ( 226Ra / 230Th) data for magma suites related by fractional crystallization allow the magma differentiation rate to be estimated

  16. Insights into mantle heterogeneities: mid-ocean ridge basalt tapping an ocean island magma source in the North Fiji Basin

    NASA Astrophysics Data System (ADS)

    Brens, R., Jr.; Jenner, F. E.; Bullock, E. S.; Hauri, E. H.; Turner, S.; Rushmer, T. A.

    2015-12-01

    The North Fiji Basin (NFB), and connected Lau Basin, is located in a complex area of volcanism. The NFB is a back-arc basin (BAB) that is a result of an extinct subduction zone, incorporating the complicated geodynamics of two rotating landmasses: Fiji and the Vanuatu island arc. Collectively this makes the spreading centers of the NFB the highest producing spreading centers recorded. Here we present volatile concentrations, major, and trace element data for a previously undiscovered triple junction spreading center in the NFB. We show our enrichment samples contain some of the highest water contents yet reported from (MORB). The samples from the NFB exhibit a combination of MORB-like major chemical signatures along with high water content similar to ocean island basalts (OIB). This peculiarity in geochemistry is unlike other studied MORB or back-arc basin (to our knowledge) that is not attributed to subduction related signatures. Our results employ the use of volatiles (carbon dioxide and water) and their constraints (Nb and Ce) combined with trace element ratios to indicate a potential source for the enrichment in the North Fiji Basin. The North Fiji Basin lavas are tholeiitic with similar major element composition as averaged primitive normal MORB; with the exception of averaged K2O and P2O5, which are still within range for observed normal MORB. For a mid-ocean ridge basalt, the lavas in the NFB exhibit a large range in volatiles: H2O (0.16-0.9 wt%) and CO2 (80-359 ppm). The NFB lavas have volatile levels that exceed the range of MORB and trend toward a more enriched source. In addition, when compared to MORB, the NFB lavas are all enriched in H2O/Ce. La/Sm values in the NFB lavas range from 0.9 to 3.8 while, Gd/Yb values range from 1.2 to 2.5. The NFB lavas overlap the MORB range for both La/Sm (~1.1) and Gd/Yb (~1.3). However, they span a larger range outside of the MORB array. High La/Sm and Gd/Yb ratios (>1) are indications of deeper melting within the

  17. Early and Late Alkali Igneous Pulses and a High-3He Plume Origin for the Deccan Flood Basalts.

    PubMed

    Basu, A R; Renne, P R; Dasgupta, D K; Teichmann, F; Poreda, R J

    1993-08-13

    Several alkalic igneous complexes of nephelinite-carbonatite affinities occur in extensional zones around a region of high heat flow and positive gravity anomaly within the continental flood basalt (CFB) province of Deccan, India. Biotites from two of the complexes yield (40)Ar/(39)Ar dates of 68.53 +/- 0.16 and 68.57 +/- 0.08 million years. Biotite from a third complex, which intrudes the flood basalts, yields an (40)Ar/(39)Ar date of 64.96 +/- 0.1 1 million years. The complexes thus represent early and late magmatism with respect to the main pulse of CFB volcanism 65 million years ago. Rocks from the older complexes show a (3)He/(4)He ratio of 14.0 times the air ratio, an initial (87)Sr/(86)Sr ratio of 0.70483, and other geochemical characteristics similar to ocean island basalts; the later alkalic pulse shows isotopic evidence of crustal contamination. The data document 3.5 million years of incubation of a primitive, high-(3)He mantle plume before the rapid eruption of the Deccan CFB.

  18. A Mantle Cross-Section Through Western And Central Nevada From Young Basaltic Magmas In The Sierra Nevada And Western Great Basin

    NASA Astrophysics Data System (ADS)

    Gupta, V.; Cousens, B. L.; Henry, C. D.

    2007-12-01

    The geochemistry of basaltic magmas erupted in the Basin and Range province of the western USA has demonstrated that at least two mantle sources exist, one with a subduction signature and another with an "ocean island basalt" (OIB) signature. Here we investigate the distribution of these two sources during the Pleistocene and Holocene in a 250 km-long transect from the eastern Sierra Nevada near Reno, NV, into central Nevada. Samples were collected from young, dated mafic lava flows from the Carson Range (2.5 to 1.4 Ma), Steamboat Hills (2.6 Ma), Virginia City and Chalk Hills (1.5 to 1.44 Ma), east of Carson City (1.36 Ma), Rattlesnake Hill (1.2 to 0.9 Ma), Buffalo Valley (1.1 to 0.95 Ma), Upsal Hogback (0.6 Ma), and Soda Lake (Holocene). With the exception of Carson Range andesites, all of the lavas are alkaline basalts and basaltic trachyandesites with K2O/Na2O > 0.4. Incompatible element abundances, incompatible element ratios, and radiogenic isotope ratios vary widely between locations. Many key incompatible element ratios, such as Ce/Pb, Sr/P, Ba/Nb, and Nb/La, and isotopic ratios vary as a function of age and longitude. Lavas less than 1 Ma in age have low Ba/Nb, Sr/P, 87Sr/86Sr, 206Pb/204Pb, and high Ce/Pb and Nd/La compared to lavas greater than 1Ma in age. These ratios vary more strongly as a function of longitude, from high Ba/Nb, Sr/P, 206Pb/204Pb, 87Sr/86Sr and low Ce/Pb and Nb/La (subduction signature mantle) lavas in the Sierra Nevada margin to lavas with the opposite characteristics (OIB signature mantle) in central Nevada. La/Sm does not vary with either age or longitude. The relationship with longitude indicates that two mantle sources currently exist beneath western Nevada, subduction-modified mantle to the west and OIB-type mantle to the east, and that these two mantle types probably taper in thickness towards one another. The termination of subduction beneath the Reno area at 5-3 Ma, in conjunction with 87Sr/86Sr greater than modern Cascade arc

  19. Crystallization kinetics in magmas during decompression

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  20. Minéralogie et bilan de matière de l'altération supergène d'un basalte alcalin du Moyen Atlas MarocainMineralogy and geochemistry of supergene alteration of an alkali basalt from the Middle Atlas, Morocco

    NASA Astrophysics Data System (ADS)

    Dekayir, A.; El-Maâtaoui, M.

    2001-05-01

    In the Middle Atlas of Morocco, alkali basaltic flows record successive weathering phases during the Quaternary. In fresh basalt interior and intermediate external zones, the first weathering stage is characterised by glass dissolution and the formation of a Si-Al poorly-crystallised product. Advanced weathering phases are characterised by 10 Å halloysite, kaolinite and goethite, located within the primary minerals or as secondary products in fissures. Olivine and iddingsite are transformed into Si-rich goethite, plagioclase into halloysite and pyroxene into a mixture of halloysite + geothite. Dissolution of Ti-magnetite and ilmenite yielded Ti-rich products. In these conditions, the weathering of basalts and development of a soil matrix are accompanied by the elimination of certain chemical elements, such as Si, Ca, Na and K, and the concentration of Fe and Al. In the soil, clay minerals such as illite and vermiculite, do not have any genetic relationship with weathered basalt and were probably introduced externally.

  1. 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.

  2. Petrogenesis of Late Cenozoic basalts from North Hainan Island: Constraints from melt inclusions and their host olivines

    NASA Astrophysics Data System (ADS)

    Liu, Jian-Qiang; Ren, Zhong-Yuan; Nichols, Alexander R. L.; Song, Mao-Shuang; Qian, Sheng-Ping; Zhang, Yan; Zhao, Pei-Pei

    2015-03-01

    Melt inclusions and their host olivines in basaltic lavas provide important information about the nature of their mantle source. We present the first analyzed chemical data of olivine-hosted melt inclusions in Cenozoic basalts from the North Hainan Island and report the discovery of both tholeiitic and alkalic melt inclusions in a single rock sample. Cenozoic basalts from the Hainan Island are predominantly tholeiites with only small amounts of alkali basalts. There is a much broader compositional variation in melt inclusions than whole rocks. Compared to partial melts of mantle peridotite, the Hainan basalts have lower CaO, Na2O/TiO2, CaO/Al2O3 and Co/Fe, and higher TiO2, FeO∗, Fe/Mn, Zn/Fe and Zn/Mn. The olivine phenocrysts from the Hainan basalts contain lower Ca and Mn, and higher Ni and Fe/Mn than those of olivines crystallized from partial melts of peridotite. Projections from or towards olivine into the plane CS-MS-A for melt inclusions and whole rocks with MgO >7.5 wt% imply that the residual minerals in the source of the tholeiites are mainly clinopyroxene and garnet, possibly with some orthopyroxene, while in the source of the alkali basalts they are dominated by clinopyroxene and garnet. This indicates that a pyroxenite component could serve as the source lithology of the Hainan basalts. The OIB-like trace element compositions, with Ba, Sr, Nb and Ta positive anomalies, and Th and U negative anomalies, of the Hainan basalts suggest that a recycled oceanic crust component was involved in the source of the Hainan basalts. Based on a CMAS projection of primary magma compositions of the whole rocks and melt inclusions, we infer that a stage-2 silica-deficient pyroxenite derived from melt-peridotite reaction or mechanical mixing between recycled oceanic crust and peridotite can serve as the source lithology. Partial melts derived from such a source can match the overall compositions of the Hainan basalts better than those of MORB-eclogite and fertile

  3. Hydrogen isotope systematics of submarine basalts

    USGS Publications Warehouse

    Kyser, T.K.; O'Neil, J.R.

    1984-01-01

    The D/H ratios and water contents in fresh submarine basalts from the Mid-Atlantic Ridge, the East Pacific Rise, and Hawaii indicate that the primary D/H ratios of many submarine lavas have been altered by processes including (1) outgassing, (2) addition of seawater at magmatic temperature, and (3) low-temperature hydration of glass. Decreases in ??D and H2O+ from exteriors to interiors of pillows are explained by outgassing of water whereas inverse relations between ??D and H2O+ in basalts from the Galapagos Rise and the FAMOUS Area are attributed to outgassing of CH4 and H2. A good correlation between ??D values and H2O is observed in a suite of submarine tholeiites dredged from the Kilauea East Rift Zone where seawater (added directly to the magma), affected only the isotopic compositions of hydrogen and argon. Analyses of some glassy rims indicate that the outer millimeter of the glass can undergo lowtemperature hydration by hydroxyl groups having ??D values as low as -100. ??D values vary with H2O contents of subaerial transitional basalts from Molokai, Hawaii, and subaerial alkali basalts from the Society Islands, indicating that the primary ??D values were similar to those of submarine lavas. Extrapolations to possible unaltered ??D values and H2O contents indicate that the primary ??D values of most thoteiite and alkali basalts are near -80 ?? 5: the weight percentages of water are variable, 0.15-0.35 for MOR tholeiites, about 0.25 for Hawaiian tholeiites, and up to 1.1 for alkali basalts. The primary ??D values of -80 for most basalts are comparable to those measured for deep-seated phlogopites. These results indicate that hydrogen, in marked contrast to other elements such as Sr, Nd, Pb, and O, has a uniform isotopic composition in the mantle. This uniformity is best explained by the presence of a homogeneous reservoir of hydrogen that has existed in the mantle since the very early history of the Earth. ?? 1984.

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

    SciTech Connect

    Kovach, L.A.

    1984-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Corsaro, Rosa Anna; Métrich, Nicole

    2016-05-01

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

  6. Bubble coalescence in magmas

    NASA Technical Reports Server (NTRS)

    Herd, Richard A.; Pinkerton, Harry

    1993-01-01

    The most important factors governing the nature of volcanic eruptions are the primary volatile contents, the ways in which volatiles exsolve, and how the resulting bubbles grow and interact. In this contribution we assess the importance of bubble coalescence. The degree of coalescence in alkali basalts has been measured using Image Analysis techniques and it is suggested to be a process of considerable importance. Binary coalescence events occur every few minutes in basaltic melts with vesicularities greater than around 35 percent.

  7. Melt rock components in KREEPy breccia 15205: Petrography and mineral chemistry of KREEP basalts and quartz-normative mare basalts

    NASA Technical Reports Server (NTRS)

    Shervais, John W.; Vetter, Scott K.

    1993-01-01

    Many current models for the origin of lunar highland rocks feature as an essential component the assimilation of KREEPy material by primitive magmas parental to the Mg-rich suite and alkali suite plutonic rocks. Similar models have also been proposed for the origin of various mare basalt suites. However, any model which considers assimilation of KREEP an important petrologic process must sooner-or-later deal with the question: what is KREEP? Because pristine KREEP basalts are rare, and most known samples are small (e.g., 15382/15386), the geochemical variability of KREEP basalts is poorly known. Other KREEP compositions which are commonly used in these models include the hypothetical 'high-K KREEP' component of Warren and Wasson, which is derived from Apollo 14 soil data, and the 'superKREEP' quartz-monzodiorite 15405. Lunar breccia 15205 is a polymict regolith breccia that consists of approximately 20% KREEP basalt clasts and 20% quartz-normative basalt clasts in a KREEP-rich matrix. Bulk rock mixing calculations show that this sample comprises about 84% KREEP. The clasts range up to 1 cm in size, but most are considerably smaller. The primary aim is to characterize pristine KREEP basalts petrographically, to establish the range in chemical compositions of KREEP basalts, and to test models that were proposed for their origin. In addition, we may be able to extend the compositional range recognized in the quartz-normative basalt suite and cast some light on its origin as well. Preliminary whole rock geochemical data on the KREEP basalts are presented in a companion paper by M.M. Lindstrom and co-workers. Concentration is on petrography and mineral chemistry of these clasts, and the implications these data have for the origin of the different melt rock suites.

  8. Melt inclusions in olivine and plagioclase phenocrysts from Antarctic-Phoenix Ridge basalts: Implications for origins of N- and E-type MORB parent magmas

    NASA Astrophysics Data System (ADS)

    Choi, Sung Hi; Schiano, Pierre; Chen, Yang; Devidal, Jean-Luc; Choo, Mi Kyung; Lee, Jong-Ik

    2013-03-01

    The Antarctic-Phoenix Ridge (APR) is a fossil spreading center in the Drake Passage, Antarctic Ocean. Spreading ceased in chron C2A (ca. 3.3 Ma). Although the APR is a normal ridge that is not influenced by a hotspot, enriched (E-type) mid-ocean ridge basalt (MORB) coexists with normal (N-type) MORB in the ridge's axial region. The E-type APR basalt is relatively young (< 3.1 Ma) compared to the N-type basalt (> 3.5 Ma). The E-type basalt is characterized by elevated K2O/TiO2 (= 0.4-0.8) and (La/Sm)N (= 2.2-3.4) ratios, relative to the N-type basalt (K2O/TiO2 = 0.1-0.3; (La/Sm)N = 0.7-0.8). To better understand the compositional variation in the APR basalts and their mantle source regions through time, silicate melt inclusions in primitive olivine (Fo87-89) and plagioclase (An85-89) phenocrysts from the N-type APR basalt were studied. Rehomogenized melt inclusions were analyzed by electron microprobe and LA-ICPMS for major and trace elements. The melt inclusions are more primitive than the host basalt, with Mg#s from 67.5 to 74.1. All inclusions exhibit patterns that are depleted in the light rare earth elements. The inclusions have K2O/TiO2 from 0.1 to 0.3 and (La/Sm)N ratios from 0.4 to 0.9; these values overlap with those of the N-type APR basalt. Furthermore, the melt inclusions have elevated (Lu/Hf)N and (Sm/Nd)N ratios compared to the E-type basalts. The N-type APR basalts do not contain any melt inclusions that are enriched in incompatible elements. The E-type basalt was generated by a low degree of partial melting of a relatively incompatible-element-enriched mantle source. In contrast, chemistries of melt inclusions and N-type basalts are compatible with high degrees of partial melting of an increasingly depleted mantle source. Assuming a veined or otherwise heterogeneous mantle, the absence of E-type inclusions from the N-type host has implications for cyclic magmatic activity beneath the APR. Multi-stage mantle melting and melt extraction from a

  9. 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

  10. Melt inclusions hosted in olivine and plagioclase phenocrysts from the Antarctic-Phoenix Ridge basalts: Implications for origins of N- and E-type MORB parent magmas

    NASA Astrophysics Data System (ADS)

    Choi, S.; Schiano, P.; Chen, Y.; Devidal, J.

    2011-12-01

    The Antarctic-Phoenix Ridge (APR) is a fossil spreading center in the Drake Passage, Antarctic Ocean. Extinction of spreading occurred at the time of chron C2A (ca. 3.3 Ma). Enriched (E-type) mid-ocean ridge basalts (MORB) coexist with normal (N-type) MORB in the axial region of the APR, which is far from any known hotspots. The E-type basalts are relatively young (<3.1 Ma) compared to the N-type ones (>3.5 Ma). The E-type basalts are characterized by elevated K2O/TiO2 and (La/Sm)N ratios (K2O/TiO2 = 0.4 - 0.7; (La/Sm)N = 2.2 - 3.4) compared with the N-type basalts (K2O/TiO2 = 0.1 - 0.2; (La/Sm)N = 0.7 - 0.8). The E-type basalts are considered to have been generated by low-degree of partial melting of an enriched mantle source. In order to understand the spaciotemporal primitive melt diversity, we used silicate melt inclusions hosted in primitive olivine (Fo87-89) and plagioclase (An85-89) phenocrysts from the N-type APR basalts. Rehomogenized melt inclusions have been analyzed by electron and LA-ICPMS for major and trace elements. The homogenization temperature varies from 1205 to 1237oC for olivine hosts, and 1206 to 1247oC for plagioclase hosts. Melt inclusions have more primitive compositions than the host lavas. Melt inclusions hosted in olivine display Mg#s ranging from 67.7 to 71.9, and those in plagioclase from 67.5 to 74.1. All melt inclusions from the N-type APR basalts exhibit light rare earth element depleted patterns. They have K2O/TiO2 and (La/Sm)N ratios ranging from 0.1 to 0.3, and 0.4 to 0.9, respectively, which are overlapping with the values for N-type APR basalts. Furthermore, the melt inclusions have elevated (Lu/Hf)N and (Sm/Nd)N ratios compared with the E-type APR basalts. It should be pointed out that the N-type APR basalts do not contain any of enriched melt inclusions. These observations indicate that the N- and E-type APR basalts were produced at different depths. The chemistry of melt inclusions with N-type basalts is consistent with a

  11. Petrogenesis of a basalt-comendite-pantellerite rock suite: the Boseti Volcanic Complex (Main Ethiopian Rift)

    NASA Astrophysics Data System (ADS)

    Ronga, Fiorenzo; Lustrino, Michele; Marzoli, Andrea; Melluso, Leone

    2010-03-01

    Petrological and geochemical data for basic (alkali basalts and hawaiites) and silicic peralkaline rocks, plus rare intermediate products (mugearites and benmoreites) from the Pleistocene Boseti volcanic complex (Main Ethiopian Rift, East Africa) are reported in this work. The basalts are slightly alkaline or transitional, have peaks at Ba and Nb in the mantle-normalized diagrams and relatively low 87Sr/86Sr (0.7039-0.7044). The silicic rocks (pantellerites and comendites) are rich in sanidine and anorthoclase, with mafic phases being represented by fayalite-rich olivine, opaque oxides, aenigmatite and slightly Na-rich ferroaugite (ferrohedenbergite). These rocks were generated after prolonged fractional crystallization process (up to 90-95 %) starting from basaltic parent magmas at shallow depths and fO2 conditions near the QFM buffer. The apparent Daly Gap between mafic and evolved Boseti rocks is explained with a model involving the silicic products filling upper crustal magma chambers and erupted preferentially with respect to basic and intermediate products. Evolved liquids could have been the only magmas which filled the uppermost magma reservoirs in the crust, thus giving time to evolve towards Rb-, Zr- and Nb-rich peralkaline rhyolites in broadly closed systems.

  12. Magma Differentiation and Storage Inferred from Crystal Textures at Harrat Rahat Volcanic Field, Kingdom of Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Witter, M. R.; Mahood, G. A.; Stelten, M. E.; Downs, D. T.; Zahran, H. M.

    2015-12-01

    We present results of a petrographic study of Harrat Rahat volcanic field in western Saudi Arabia as part of a collaborative project between the U.S.G.S. and the Saudi Geological Survey. Lavas range in composition from alkali basalt to trachyphonolite. Basalts have <2-10 vol.% phenocrysts of euhedral olivine and plagioclase (± minor clinopyroxene). In intermediate lavas, phenocrysts (<5 vol.%) of olivine and plagioclase are resorbed, and plagioclase also exhibits sieve textures and strong zoning, indicative of complex magmatic histories. Trachyphonolite lavas have 0-35 vol.% large phenocrysts of anorthoclase and trace fayalitic olivine but are characterized by a size distribution of crystals that is seriate in hand specimen, so that most exceeded 45% crystals at the time of eruption. Some contain groundmass alkali amphibole. Crystal size distributions (CSD) of crystal-rich trachyphonolites produce simple linear trends (see below), which are interpreted as signifying that all the crystals are related through a common nucleation and growth history, at more or less constant pressure. Linear CSDs indicate no loss of small crystals due to reheating of magmas by recharge, no gain of small crystals due to late-stage nucleation on ascent or degassing, and no addition of large phenocrysts by crystal accumulation or magma mixing. Experimental studies demonstrate that silica-undersaturated evolved magmas like those erupted at Harrat Rahat can form by fractionation of alkali basalts at crustal depths greater than ~25 km. The observed phenocryst assemblage in the trachyphonolites, however, forms at shallow depths, ~2-4 km, according to MELTS modeling. Coupled with CSD data, this suggests that deep extraction events yield crystal-poor trachyphonolite magmas that rise to the upper crust where they undergo crystallization. Extensive shallow crystallization of trachyphonolites may have triggered eruptions by causing vapor saturation, which lowers magma density via vesiculation and

  13. Alkali content of alpine ultramafic rocks

    USGS Publications Warehouse

    Hamilton, W.; Mountjoy, W.

    1965-01-01

    The lower limit of abundance of sodium and potassium in ultramafic rocks is less than the threshold amount detectable by conventional analytical methods. By a dilutionaddition modification of the flame-spectrophotometric method, sodium and potassium have been determined in 40 specimens of alpine ultramafic rocks. Samples represent six regions in the United States and one in Australia, and include dunite, peridotite, pyroxenite, and their variably serpentinized and metamorphosed derivatives. The median value found for Na2O is 0.004 per cent, and the range of Na2O is 0.001-0.19. The median value for K2O is 0.0034 per cent and the range is 0.001-0.031 per cent. Alkali concentrations are below 0.01 per cent Na2O in 28 samples and below 0.01 per cent K2O in 35. Derivation of basalt magma from upper-mantle material similar to such ultramafic rocks, as has been postulated, is precluded by the relative amounts of sodium and potassium, which are from 200 to 600 times more abundant in basalt than in the ultramafic rocks. Similar factors apply to a number of other elements. No reasonable process could produce such concentrations in, for example, tens of thousands of cubic miles of uniform tholeiitic basalt. The ultramafic rocks might have originated either as magmatic crystal precipitates or as mantle residues left after fusion and removal of basaltic magma. Injection of ultramafic rocks to exposed positions is tectonic rather than magmatic. ?? 1965.

  14. Chemical heterogeneity of Mt. Etna magmas in the last 15 ky and inferences on their mantle sources

    NASA Astrophysics Data System (ADS)

    Corsaro, Rosa Anna; Métrich, Nicole

    2016-04-01

    Primitive basaltic magmas are crucially important in the study of geochemical heterogeneity documented in Etna magmas and their inferred mantle sources. We undertook a systematic sampling of the less evolved basalts erupted at Mt. Etna over the past few millennia, focusing on lava flows and pyroclastites emplaced during deep-dyke fed (DDF) eruptions which were driven by the rapid ascent of deeply-rooted magma intrusions that bypassed the shallow plumbing system of the volcano. All the samples were analyzed by the same laboratory to avoid analytical biases and to build up a comprehensive dataset on their major and trace element compositions in order to propose a coherent framework to interpret the geochemical fingerprints of Etna present-day basalts. Trace element modelling together with literature data for Sr isotopes gave insight into long-term magmatic processes related to different melting degrees of the heterogeneous mantle beneath Mt. Etna. DDF magma batches younger than 15 ky provide good snapshots of their mantle source heterogeneities that point to the variable involvement of clinopyroxenitic lithology, Rb-87Sr-Cl-rich fluid component(s) possibly controlled by their source mineralogy, and slab-derived fluids selectively enriched in alkalis (Rb, K). The ongoing alkali (Rb, K) enrichment of the present-day magmas, well manifest since the 1970s, is decoupled from that of Sr and Cl. This recent process is linked to mantle source composition and is concomitant with changes in both volcanological and seismotectonic patterns of the volcano. There is no evidence for any time evolution of DDF magma chemistry.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  16. Earliest Silicic Volcanism Associated with Mid-Miocene Flood Basalts: Tuffs Interbedded with Steens Basalt, Nevada and Oregon

    NASA Astrophysics Data System (ADS)

    Luckett, M.; Mahood, G. A.; Benson, T. R.

    2013-12-01

    During the main phase of Steens and Columbia River flood basalt eruptions between ~16.7 and 15.0 Ma, spatially associated silicic volcanism was widespread, ~4,000 km3 of silicic magma erupting at calderas and smaller centers dispersed across ~25,000 km2 in eastern Oregon and northern Nevada (Coble and Mahood, 2012). The oldest flood basalts erupted from a focus at Steens Mountain in eastern Oregon, where the section of lavas is ~1 km thick. The Steens Basalt thins southward to only a few flows thick in northern Nevada, either because fewer flows were emplaced this far from the focus or because fewer dikes propagated to the surface on encountering thicker continental crust and/or were intercepted by growing bodies of silicic magma that ultimately erupted in McDermitt Caldera Field (Rytuba and McKee, 1984), High Rock Caldera Complex, and the Lone Mountain/Hawks Valley center (Wypych et al., 2011). Rhyolitic tuffs have not been recognized interbedded with the basalt lavas in the type section, but we have identified several silicic tuffs interbedded with Steens Basalt in the southern Pueblo Mountains and in the Trout Creek Mountains. Although noted by previous workers (e.g., Avent, 1965; Minor, 1986; Hart et al., 1989), they have not been studied. We identified six tuffaceous intervals 20 cm to 15 m thick in the escarpment of the southern Pueblo Mountains near the Oregon-Nevada border where the Steens basalt section is ~250 m thick, with the base unexposed. Two intervals are lithic-rich, reworked volcaniclastic sediments, but four are primary or only slightly reworked sequences of fall deposits that range from fine ash to lapilli in grain size. The heat and weight of the overlying basaltic lava flows has fused the tuffs so that the upper parts of thicker tuffaceous intervals and entire thinner ones are converted to vitrophyres, with crystals of alkali feldspar × quartz × biotite typically 1-2 mm in diameter set in a dense, black, variably hydrated, glassy matrix. We

  17. Residence times of alkali feldspar phenocrysts from magma feeding the Agnano-Monte Spina Eruption (4.7 ka), Campi Flegrei caldera (Napoli, southern Italy) based on Ba-zonation modelling

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    Timescales governing the development of crustal magma reservoirs are a key for understanding magmatic processes such as ascent, storage and mixing event. An estimate of these timescales can provide important constraints for volcanic hazard assessment of active volcanoes. We studied the Agnano-Monte Spina eruption (A-MS; 4.7 ka; VEI = 4; 0.85 km3 D.R.E. of magma erupted) of the Campi Flegrei caldera, one of the most dangerous volcanic areas on Earth. The A-MS eruption has been fed by magmas varying from more to less evolved trachyte whose variable 87Sr/86Sr and trace elements features suggest magma mixing between two end-members. Ba zonation profiles of alkali feldspar phenocrysts have been determined through combined energy-dispersive and wavelength-dispersive electron microprobe analyses (EDS-WDS-EMPA). We focused on distinct compositional breaks near the rim of the crystals that likely represent the last mixing event prior to eruption. We always chose the steepest gradients close to the crystal rims, taking into account that any effects related to cutting angles or crystal orientation should give longer apparent diffusion times. Two different approaches were undertaken: (1) a quantitative Ba compositional profiles were measured by point analyses along a short transect crossing growth discontinuities and (2) grey-scale profiles were taken parallel to the acquired point profiles. Assuming that Ba dominates the backscattered electron intensities in sanidines, greyscale gradients can be used as a diffusive tracer. BSE images were processed using the ImageJ® software, in order to extract a numerical greyscale profile. In both cases, each profile was interpolated through a non-linear Boltzmann fit curve with the Mathematica® software. A few traverses done at angles smaller than 90° to the compositional boundary interface were corrected by multiplying the distance values by the sinus of the traverse angle relative to the vertical on the interface. Our preliminary

  18. Production of hybrid granitic magma at the advancing front of basaltic underplating: Inferences from the Sesia Magmatic System (south-western Alps, Italy)

    NASA Astrophysics Data System (ADS)

    Sinigoi, Silvano; Quick, James E.; Demarchi, Gabriella; Klötzli, Urs S.

    2016-05-01

    The Permian Sesia Magmatic System of the southwestern Alps displays the plumbing system beneath a Permian caldera, including a deep crustal gabbroic complex, upper crustal granite plutons and a bimodal volcanic field dominated by rhyolitic tuff filling the caldera. Isotopic compositions of the deep crustal gabbro overlap those of coeval andesitic basalts, whereas granites define a distinct, more radiogenic cluster (Sri ≈ 0.708 and 0.710, respectively). AFC computations starting from the best mafic candidate for a starting melt show that Nd and Sr isotopic compositions and trace elements of andesitic basalts may be modeled by reactive bulk assimilation of ≈ 30% of partially depleted crust and ≈ 15%-30% gabbro fractionation. Trace elements of the deep crustal gabbro cumulates require a further ≈ 60% fractionation of the andesitic basalt and loss of ≈ 40% of silica-rich residual melt. The composition of the granite plutons is consistent with a mixture of relatively constant proportions of residual melt delivered from the gabbro and anatectic melt. Chemical and field evidence leads to a conceptual model which links the production of the two granitic components to the evolution of the Mafic Complex. During the growth of the Mafic Complex, progressive incorporation of packages of crustal rocks resulted in a roughly steady state rate of assimilation. Anatectic granite originates in the hot zone of melting crust located above the advancing mafic intrusion. Upward segregation of anatectic melts facilitates the assimilation of the partially depleted restite by stoping. At each cycle of mafic intrusion and incorporation, residual and anatectic melts are produced in roughly constant proportions, because the amount of anatectic melt produced at the roof is a function of volume and latent heat of crystallization of the underplated mafic melt which in turn produces proportional amounts of hybrid gabbro cumulates and residual melt. Such a process can explain the

  19. Understanding highly explosive basaltic eruptions: Evidence from olivine-hosted melt inclusions from Sunset Crater, AZ

    NASA Astrophysics Data System (ADS)

    Allison, C. M.; Roggensack, K.; Clarke, A. B.; Alfano, F.

    2013-12-01

    Basaltic scoria cone volcanoes are the most abundant volcanic landform on Earth and occur in all tectonic settings. Basaltic magmas have lower viscosities, higher temperatures, and lower volatile contents than silicic magmas, and therefore generally have a lower potential for explosive activity. However, basaltic eruptions display great variability, from mild lava flows to more energetic explosions with large plumes. The mechanism controlling highly explosive basaltic eruptions, such as the ca. 1085 AD eruption of Sunset Crater, is poorly understood. Processes or conditions such as high volatile content in the source magma, injection of a compositionally distinct magma at depth, interaction with shallow magma reservoirs, or rapid crystallization and/or bubble nucleation in the shallow subsurface could increase explosivity of basaltic magmas. One method to test these hypotheses is melt inclusion analysis in order to constrain initial melt composition, volatile content and minimum storage depth. The San Francisco Volcanic Field (SFVF) in northern Arizona, active from 6 Ma-present, consists of over 600 volcanoes - mainly alkali basalt scoria cones along with five silicic centers. The eruption of Sunset Crater in the SFVF during the Holocene was an anomalously large basaltic explosive eruption, consisting of >8 explosive phases and 3 lava flows. Typical scoria cone-forming eruptions produce <0.1 km3 DRE of material, while the Sunset Crater tephra deposit is on the order of ~0.3 km3 DRE, with each phase characterized by volumes of 0.02-0.08 km3 DRE. The phases vary in size and style; the beginning stages of explosive activity (phases 1-2) were considerably smaller than phases 3-5, classified as subplinian. Because of the young age and desert setting of the volcano, the eruptive material is fresh and the deposit is well preserved. The bulk composition is an alkali basalt with Mg# 74. We studied 40 primary melt inclusions (MIs) hosted in 36 olivine crystals 0.5-2 mm in

  20. 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

  1. Deformation of Magma-Filled Bodies during Solidification

    NASA Astrophysics Data System (ADS)

    Gaffney, E. S.; Damjanac, B.

    2007-12-01

    As magma or lava solidifies, volatiles are concentrated in the residual liquid. The result will be expansion (including venting) or pressurization. The mechanism behind this is well-described. A rough hand calculation indicates that an alkali basalt with 4 wt% volatiles would attain attain 12 MPa with 50% crystallization at constant volume. Such pressures would easily be enough to break through the roof of a typical lava tube. If confined in a tunnel deeper in the ground, even in a relatively weak rock, crystallization would be virtually isochoric. However, in a sill at depths of only a few hundred meters, expansion could result in more nearly isobaric crystallization. In either event, before cooling enough to become a brittle solid, the outer portions of the magma would reach a viscoplastic state that could seal in any remaining vapor phase. This would allow pressures to increase further as solidification progressed. Using PELE, a computer code developed to calculate the progress of solidification (Boudreau, 2005), we calculate isochoric and isobaric equilibrium crystallization of alkali basalt and obtain pressures and viscosities as a function of temperature. For an initial pressure of 6 MPa and 0.85 weight percent water, the liquidus is 1433 K. The isochoric pressure reaches 11 MPa at 1293 K with 57% of the mass crystallized; the bulk viscosity is about 3 MPa-s, but that of the residual liquid is only 1 kPa-s. At the same temperature, the isobaric path results in 60% crystallization and a viscosity on the order of 10 kPa-s. A tabular body with these properties would be easily deformed by sagging of the roof if the viscoplastic seal were breached, resulting in a saucer shape. With 91% of the mass crystallized, the isochoric pressure exceeds 28 MPa at 1173 K. By that time, the bulk viscosity of the nearly crystallized mass is on the order of 1025 Pa-s, effectively solid, and the viscosity of the residual liquid (there is also a vapor phase) is about 50 k

  2. Externally triggered renewed bubble nucleation in basaltic magma: the 12 October 2008 eruption at Halema‘uma‘u Overlook vent, Kīlauea, Hawai‘i, USA

    USGS Publications Warehouse

    Carey, Rebecca J.; Manga, Michael; Degruyter, Wim; Swanson, Donald; Houghton, Bruce; Orr, Tim R.; Patrick, Matthew R.

    2012-01-01

    From October 2008 until present, dozens of small impulsive explosive eruptions occurred from the Overlook vent on the southeast side of Halema‘uma‘u Crater, at Kīlauea volcano, USA. These eruptions were triggered by rockfalls from the walls of the volcanic vent and conduit onto the top of the lava column. Here we use microtextural observations and data from clasts erupted during the well-characterized 12 October 2008 explosive eruption at Halema‘uma‘u to extend existing models of eruption triggering. We present a potential mechanism for this eruption by combining microtextural observations with existing geophysical and visual data sets. We measure the size and number density of bubbles preserved in juvenile ejecta using 2D images and X-ray microtomography. Our data suggest that accumulations of large bubbles with diameters of >50μm to at least millimeters existed at shallow levels within the conduit prior to the 12 October 2008 explosion. Furthermore, a high number density of small bubbles <50 μm is measured in the clasts, implying very rapid nucleation of bubbles. Visual observations, combined with preexisting geophysical data, suggest that the impact of rockfalls onto the magma free surface induces pressure changes over short timescales that (1) nucleated new additional bubbles in the shallow conduit leading to high number densities of small bubbles and (2) expanded the preexisting bubbles driving upward acceleration. The trigger of eruption and bubble nucleation is thus external to the degassing system.

  3. 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

  4. Viscosity of hydrous Etna basalt: implications for Plinian-style basaltic eruptions

    NASA Astrophysics Data System (ADS)

    Giordano, D.; Dingwell, D. B.

    Water dissolved in a silicate melt can strongly influence its physical properties and thus magma behavior during crystallization, degassing, foaming and fragmentation. Etna is a basaltic volcano whose activity is dominated by effusive eruptions which have long represented a threat to the densely populated, surrounding area. Recently, recognition of the products of a Plinian eruption (122 B.C.) has raised further issues for hazard assessment at Etna and other basaltic volcanoes. Constraining the behavior of Etna magma under conditions relevant to both effusive and explosive hazards requires viscosity data under conditions near the glass transition. Here we have investigated the viscosity of hydrous Etna lava in order to better understand eruptive processes which characterize this volcano. The experimental methods which have been used include piston cylinder synthesis of the hydrated melts, micropenetration viscometry for low-temperature viscosity measurements, and near-infrared spectroscopy for the evaluation of sample homogeneity and measurements of water content. Additionally, scanning calorimetric determinations were performed to check whether incipient crystallization had occurred. Sample compositions were determined using electron microprobe analysis and 57Fe Mössbauer spectroscopy. Results from this study are compared with previous reports of trachytic, phonolitic and model calc-alkaline rhyolite (HPG8) compositions. The viscosity of the basaltic melt (dry and wet) has been parameterized in terms of temperature and water content via the non-Arrhenian equation: log10ɛ=-4.643+(5,812.44- 427.04×H2O)/(T(K)- 499.31+28.74×ln(H2O)) where ɛ is the viscosity in Pa s, H2O is the water content in wt%, and T is the temperature in Kelvin. We observe that the viscosity of alkali basalt (at more than 0.5 wt% H2O) is similar to that of an alkaline trachyte (Agnano-Monte Spina eruption, Phlegrean Fields) and much higher than that of a peralkaline phonolite (Teide

  5. Viscosity of hydrous Etna basalt: implications for Plinian-style basaltic eruptions

    NASA Astrophysics Data System (ADS)

    Giordano, D.; Dingwell, D. B.

    2002-07-01

    Water dissolved in a silicate melt can strongly influence its physical properties and thus magma behavior during crystallization, degassing, foaming and fragmentation. Etna is a basaltic volcano whose activity is dominated by effusive eruptions which have long represented a threat to the densely populated, surrounding area. Recently, recognition of the products of a Plinian eruption (122 B.C.) has raised further issues for hazard assessment at Etna and other basaltic volcanoes. Constraining the behavior of Etna magma under conditions relevant to both effusive and explosive hazards requires viscosity data under conditions near the glass transition. Here we have investigated the viscosity of hydrous Etna lava in order to better understand eruptive processes which characterize this volcano. The experimental methods which have been used include piston cylinder synthesis of the hydrated melts, micropenetration viscometry for low-temperature viscosity measurements, and near-infrared spectroscopy for the evaluation of sample homogeneity and measurements of water content. Additionally, scanning calorimetric determinations were performed to check whether incipient crystallization had occurred. Sample compositions were determined using electron microprobe analysis and 57Fe Mössbauer spectroscopy. Results from this study are compared with previous reports of trachytic, phonolitic and model calc-alkaline rhyolite (HPG8) compositions. The viscosity of the basaltic melt (dry and wet) has been parameterized in terms of temperature and water content via the non-Arrhenian equation: log10ɛ=-4.643+(5,812.44-427.04×H2O)/(T(K)-499.31+28.74×ln(H2O)) where ɛ is the viscosity in Pa s, H2O is the water content in wt%, and T is the temperature in Kelvin. We observe that the viscosity of alkali basalt (at more than 0.5 wt% H2O) is similar to that of an alkaline trachyte (Agnano-Monte Spina eruption, Phlegrean Fields) and much higher than that of a peralkaline phonolite (Teide, Tenerife

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  7. Crystals in magma chambers

    NASA Astrophysics Data System (ADS)

    Higgins, M.

    2011-12-01

    Differentiation processes in igneous systems are one way in which the diversity of igneous rocks is produced. Traditionally, magmatic diversity is considered as variations in the overall chemical composition, such as basalt and rhyolite, but I want to extend this definition to include textural diversity. Such textural variations can be manifested as differences in the amount of crystalline (and immiscible liquid) phases and in the origin and identity of such phases. One important differentiation process is crystal-liquid separation by floatation or decantation, which clearly necessitates crystals in the magma. Hence, it is important to determine if magmas in chambers (sensu lato) have crystals. The following discussion is framed in generalities - many exceptions occur. Diabase (dolerite) dykes are a common, widespread result of regional mafic magmatism. The rims of most diabase dykes have few or no phenocrysts and crystals in the cores are commonly thought to have crystallized in place. Hence, this major mafic magmatic source did not have crystals, although compositional diversity of these dykes is commonly explained by crystal-liquid separation. This can be resolved if crystallisation was on the walls on the magma chamber. Similarly, most flood basalts are low in crystals and separation of those that are present cannot always explain the observed compositional diversity. Crystal-rich flows do occur, for example the 'Giant Plagioclase Basalts' of the Deccan series, but the crystals are thought to form or accumulate in a crystal-rich zone beneath the roof of the chamber - the rest of the chamber probably has few crystals. Some magmas from Hawaii contain significant amounts of olivine crystals, but most of these are deformed and cannot have crystallised in the chamber. In this case the crystals are thought to grow as the magma passes through a decollement zone. They may have grown on the walls or been trapped by filters. Basaltic andesite ignimbrites generally have

  8. Th-230 - U-238 series disequilibrium of the Olkaria basalts Gregory Rift Valley, Kenya: Petrogenesis

    NASA Technical Reports Server (NTRS)

    Black, S.; Macdonald, R.; Kelly, M.

    1993-01-01

    Strong mixing trends on a (Th-230/Th-232) versus Th diagram show that the basalts are mixed magmas which have undergone interaction with the crust. Instantaneous Th/U ratios are less than time integrated ones but these exceed the Th/U ratios in the MORB and OIB sources. This indicates that the mantle may have undergone some metasomatic fluxing, crustal contamination of the basalts will also enhance these ratios. Early activity on the Akira plain is represented by early basalts and hawaiites. The early basalt samples are known to predate the earliest comendites. The most recent phase of activity is represented by another cinder cone 40-50 m high being feldspar and clinopyroxene phyric. Inclusions which occur in the comendites vary in size and distribution. The largest and most porphyritic are the trachytes (up to 40 cm) with alkali feldspar phases up to 6 mm and small pyroxenes in the ground mass. The second set of inclusions are smaller (up to 10 cm) and are largely aphyric. The distribution of the inclusions are not uniform, the Broad Acres (C5) lavas contain 2-5 percent. The size of the inclusions decrease from south to north, as does the abundance of the trachytic inclusions. The major element variations in the Naivasha basalts, hawaiites and magmatic inclusions are discussed.

  9. Geochemical fingerprint of the primary magma composition in the marine tephras originated from the Baegdusan and Ulleung volcanoes

    NASA Astrophysics Data System (ADS)

    Lim, Chungwan; Kim, Seonyoung; Lee, Changyeol

    2014-12-01

    The intraplate Baegdusan (Changbai) and Ulleung volcanoes located on the border of China, North Korea, and East/Japan Sea, respectively, have been explained by appeals to both hotspots and asthenospheric mantle upwelling (wet plume) caused by the stagnant Pacific plate. To understand the origin of the Baegdusan and Ulleung volcanism, we performed geochemical analyses on the tephra deposits in the East/Japan Sea basins originating from the Baegdusan and Ulleung volcanoes. The volcanic glass in the tephra from the Baegdusan and Ulleung volcanoes ranged from alkaline trachyte to peralkaline rhyolite and from phonolite to trachyte, respectively. The tephra from the two intraplate volcanoes showed highly enriched incompatible elements, such as Tb, Nb, Hf, and Ta, distinct from those of the ordinary arc volcanoes of the Japanese islands. The straddle distribution of the Th/Yb and Ta/Yb ratios of the tephra deposits from the Baegdusan volcano may originate from the alkali basaltic magma resulting from mixing between the wet plume from the stagnant Pacific plate in the transition zone and the overlying shallow asthenospheric mantle. In contrast, the deposits from the Ulleung volcano show a minor contribution of the stagnant slab to the basaltic magma, implying either partial melting of a more enriched mantle, smaller degrees of partial melting of a garnet-bearing mantle source, or a combination of both processes as the magma genesis. Our study indicated that the Baegdusan and Ulleung volcanoes have different magma sources and evolutionary histories.

  10. Petrologic and Volcanologic Constraints on Depths of Evolved Magma Generation and Storage at Northern Harrat Rahat and Harrat Khaybar, Kingdom of Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Mahood, G. A.; Calvert, A. T.; Witter, M. R.; Stelten, M. E.; Zahran, H. M.; Shawali, J.; Hassan, K. H.; Muquyyim, F. A.; Ashur, M. S.

    2015-12-01

    We present preliminary results of a petrologic study of northern Harrat Rahat that is part of an interdisciplinary hazard assessment of this rift-related volcanic field in Saudi Arabia. Alkali basalts and hawaiites occur with mugearites and trachyphonolites. This silica-undersaturated suite is consistent with fractionation at crustal depths greater than 25 km, i.e., at pressures for which experimental studies find that sodic clinopyroxene dominates the liquidus assemblage, resulting in a differentiation trend in which SiO2 rises only moderately. Trachyphonolites lack positive Eu anomalies despite abundant anorthoclase phenocrysts, and exhibit linear crystal-size distributions indicative of a simple, one-stage crystallization history. We suggest that trachyphonolite melts are extracted from extensively crystallized alkali basalts in the middle to lower crust. Any crystals entrained from depth (e.g., sodic clinopyroxene) are resorbed during ascent of these water-poor magmas to shallow levels, where they cool and crystallize. Abundant phenocrysts and low H2O contents resulted in viscous magmas that produced numerous cryptodomes along with domes and spines that pierced the uplifts. Eruption of trachyphonolite domes was accompanied by poorly fluidized scoria flows that traveled up to 4 km from their vents. Explosive disruption of domes produced block flows that ring craters. Vulcanian deposits with accretionary lapilli and lithics of rounded metamorphic rocks point to the involvement of groundwater sourced in basinal sediments eroded from Precambrian basement. Although phreatomagmatic eruptions produced tuff rings up to 1.5 km in diameter, there is no evidence for collapse calderas, suggesting there have not been sizable reservoirs of evolving magma in the shallow crust, consistent with petrologic evidence for a deep origin of the trachyphonolite magmas. In contrast, Harrat Khaybar, which lies 140 km NNE of Harrat Rahat, erupted silica-saturated evolved magmas

  11. 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.

  12. 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

  13. Sulfide Stability of Planetary Basalts

    NASA Technical Reports Server (NTRS)

    Caiazza, C. M.; Righter, K.; Gibson, E. K., Jr.; Chesley, J. T.; Ruiz, J.

    2004-01-01

    The isotopic system, 187Re 187Os, can be used to determine the role of crust and mantle in magma genesis. In order to apply the system to natural samples, we must understand variations in Re/Os concentrations. It is thought that low [Os] and [Re] in basalts can be attributed to sulfide (FeS) saturation, as Re behaves incompatibly to high degrees of evolution until sulfide saturation occurs [1]. Previous work has shown that lunar basalts are sulfide under-saturated, and mid-ocean ridge, ocean-island and Martian (shergottites) basalts are saturated [2,3]. However, little is known about arc basalts. In this study, basaltic rocks were analyzed across the Trans-Mexican Volcanic Belt.

  14. Understanding cratonic flood basalts

    NASA Astrophysics Data System (ADS)

    Silver, Paul G.; Behn, Mark D.; Kelley, Katherine; Schmitz, Mark; Savage, Brian

    2006-05-01

    leads to the initiation and propagation of lithospheric dikes. Such a model accounts for the short eruption time of flood basalts, the evidence for lithospheric control of the eruptions, and the continued survival of cratonic lithosphere following these magmatic events. The most notable consequence of this model is that it implies the existence of large reservoirs of magma, comparable to the eruption volume of flood basalts that have been, and are still likely, present beneath stable continental lithopshere.

  15. The Plumbing System of a Highly Explosive Basaltic Volcano: Sunset Crater, AZ

    NASA Astrophysics Data System (ADS)

    Allison, C. M.; Roggensack, K.; Clarke, A. B.

    2015-12-01

    We seek to better understand highly explosive basaltic eruptions with specific focus on magmatic volatile solubility in alkali basalts and the magma plumbing system. Sunset Crater, an alkali basalt (~3.7 wt.% alkalis) scoria cone volcano, erupted explosively in 1085 AD. We analyzed 125 primary melt inclusions (MIs) from Sunset Crater tephra deposited by 2 subplinian phases and 1 Strombolian explosion to compare magma volatiles and storage conditions. We picked rapidly quenched free olivine crystals and selected large volume MIs (50-180 μm) located toward crystal cores. MIs are faceted and exhibit little major element composition variability with minor post entrapment crystallization (2-10%). MIs are relatively dry but CO2-rich. Water content varies from 0.4 wt.% to 1.5 wt.% while carbon dioxide abundance ranges between 1,150 ppm and 3,250 ppm. Most MIs contain >1 wt.% H2O and >2,150 ppm CO2. All observed MIs contain a vapor bubble, so we are evaluating MI vapor bubbles with Raman spectroscopy and re-homogenization experiments to determine the full volatile budget. Because knowledge of volatile solubility is critical to accurately interpret results from MI analyses, we measured H2O-CO2 solubility in the Sunset Crater bulk composition. Fluid-saturated experiments at 4 and 6 kbar indicate shallower entrapment pressures for these MIs than values calculated for this composition using existing models. Assuming fluid saturation, MIs record depths from 6 km to 14 km, including groupings suggesting two pauses for longer-term storage at ~6 km and ~10.5 km. We do not observe any significant differences in MIs from phases exhibiting different eruptive styles, suggesting that while a high CO2 content may drive rapid magma ascent and be partly responsible for highly explosive eruptions, shallower processes may govern the final eruptive character. To track shallow processes during magma ascent from depth of MI-entrapment up to the surface, we are examining MI re-entrants.

  16. Effect of melt composition on basalt and peridotite interaction: laboratory dissolution experiments with applications to mineral compositional variations in mantle xenoliths from the North China Craton

    NASA Astrophysics Data System (ADS)

    Wang, Chunguang; Liang, Yan; Xu, Wenliang; Dygert, Nick

    2013-11-01

    Interaction between basaltic melts and peridotites has played an important role in modifying the lithospheric and asthenospheric mantle during magma genesis in a number of tectonic settings. Compositions of basaltic melts vary considerably and may play an important role in controlling the kinetics of melt-peridotite interaction. To better understand the effect of melt composition on melt-peridotite interaction, we conducted spinel lherzolite dissolution experiments at 2 GPa and 1,425 °C using the dissolution couple method. The reacting melts include a basaltic andesite, a ferro-basalt, and an alkali basalt. Dissolution of lherzolite in the basaltic andesite and the ferro-basalt produced harzburgite-lherzolite sequences with a thin orthopyroxenite layer at the melt-harzburgite interface, whereas dissolution of lherzolite in the alkali basalt produced a dunite-harzburgite-lherzolite sequence. Systematic variations in mineral compositions across the lithological units are observed. These mineral compositional variations are attributed to grain-scale processes that involve dissolution, precipitation, and reprecipitation and depend strongly on reacting melt composition. Comparison of mineral compositional variations across the dissolution couples with those observed in mantle xenoliths from the North China Craton (NCC) helps to assess the spatial and temporal variations in the extent of siliceous melt and peridotite interaction in modifying the lithospheric mantle beneath the NCC. We found that such melt-rock interaction mainly took place in Early Cretaceous, and is responsible for the enrichment of pyroxene in the lithospheric mantle. Spatially, siliceous melt-peridotite interaction took place in the ancient orogens with thickened lower crust.

  17. Thermodynamics and Phase Equilibria of Concurrent Assimilation and Fractional Crystallization (AFC) in Crustal Magma Bodies

    NASA Astrophysics Data System (ADS)

    Creamer, J. B.; Spera, F. J.; Bohrson, W. A.; Ghiorso, M. S.

    2009-12-01

    the melt fraction in the wallrock exceeds a critical threshold fraction based on percolation theory (~ 0.05), a portion of anatectic melt is transferred to the magma such that the fraction of melt remaining in wallrock is 0.05. Results are presented where the initial mass ratio of wallrock to magma ranges from 1:10 to 1:2, pressure is varied between 0.05 to 0.5 GPa and pristine magma compositions include MORB, Alkali Basalt, and Calc-Alkaline Basalt. Oceanic gabbros, granodiorites, and pelitic metasedimentary compositions are used as wallrock representatives. Wallrock volatile compositions vary from dry to water saturated (sub-solidus), and the water content of pristine magma varies from 0.2 to 3 wt %. For each simulation only one of the aforementioned parameters is varied in order to isolate the effects of a specific variable. Each of the parameters exerts an important effect on the compositional evolution of magma undergoing concurrent AFC and is graphically portrayed.

  18. Primitive magmas at five Cascade volcanic fields: Melts from hot, heterogeneous sub-arc mantle

    USGS Publications Warehouse

    Bacon, C.R.; Bruggman, P.E.; Christiansen, R.L.; Clynne, M.A.; Donnelly-Nolan, J. M.; Hildreth, W.

    1997-01-01

    Major and trace element concentrations, including REE by isotope dilution, and Sr, Nd, Pb, and O isotope ratios have been determined for 38 mafic lavas from the Mount Adams, Crater Lake, Mount Shasta, Medicine Lake, and Lassen volcanic fields, in the Cascade arc, northwestern part of the United States. Many of the samples have a high Mg# [100Mg/(Mg + FeT) > 60] and Ni content (>140 ppm) such that we consider them to be primitive. We recognize three end-member primitive magma groups in the Cascades, characterized mainly by their trace-element and alkali-metal abundances: (1) High-alumina olivine tholeiite (HAOT) has trace element abundances similar to N-MORB, except for slightly elevated LILE, and has Eu/Eu* > 1. (2) Arc basalt and basaltic andesite have notably higher LILE contents, generally have higher SiO2 contents, are more oxidized, and have higher Cr for a given Ni abundance than HAOT. These lavas show relative depletion in HFSE, have lower HREE and higher LREE than HAOT, and have smaller Eu/Eu* (0.94-1.06). (3) Alkali basalt from the Simcoe volcanic field east of Mount Adams represents the third end-member, which contributes an intraplate geochemical signature to magma compositions. Notable geochemical features among the volcanic fields are: (1) Mount Adams rocks are richest in Fe and most incompatible elements including HFSE; (2) the most incompatible-element depleted lavas occur at Medicine Lake; (3) all centers have relatively primitive lavas with high LILE/HFSE ratios but only the Mount Adams, Lassen, and Medicine Lake volcanic fields also have relatively primitive rocks with an intraplate geochemical signature; (4) there is a tendency for increasing 87Sr/86Sr, 207Pb/204Pb, and ??18O and decreasing 206Pb/204Pb and 143Nd/144Nd from north to south. The three end-member Cascade magma types reflect contributions from three mantle components: depleted sub-arc mantle modestly enriched in LILE during ancient subduction; a modern, hydrous subduction component

  19. The petrology of the Apollo 12 pigeonite basalt suite

    NASA Technical Reports Server (NTRS)

    Baldridge, W. S.; Beaty, D. W.; Hill, S. M. R.; Albee, A. L.

    1979-01-01

    A study of the petrology of the Apollo 12 pigeonite basalt samples 12011, 12043, and 12007 is presented. In this suite, the abundances of olivine and Cr-spinel decrease with increasing grain size, while the abundances of plagioclase and ilmenite increase. The petrochemical and textural variations indicate that the pigeonite basalts were derived from the olivine basalts, but the compositional gap between the olivine and pigeonite basalts indicates that they could not have crystallized together from a single, initially homogeneous magma body.

  20. The Influence of Magma Plumbing Complexity on Low-Volume, Intraplate Volcanism

    NASA Astrophysics Data System (ADS)

    Cronin, S. J.; Brenna, M.; Nemeth, K.; Smith, I. E.; Sohn, Y.

    2010-12-01

    Monogenetic volcanoes in a continental field environment are typically conceived of as being constructed in single eruptive episodes, often involving low-volume single magma batches of alkali basalt. Well exposed pyroclastic successions at four eruptive centres (Udo, Suwolbong, Songaksan, Ilchulbong) in the Jeju Island Volcanic Field (Korea) allow detailed, stratigraphically controlled, geochemical investigations of juvenile ejecta. Despite the narrow ranges in overall magma variability, these sucessions reveal that multiple distinct magma batches may commonly be erupted during a single monogenetic eruption episode. Pyroclastic successions and chemical trends define two end-member behaviours. Uninterrupted depositional sequences have generally smooth chemical transitions, showing gradual changes in magmatic evolution. Discontinuous depositional sequences including truncation surfaces, slump beds, breccia horizons, asymmetric deposit geometries and deposit colour changes appear to coincide with renewals of magmatic activity by either a contrasting magma or a related magma batch showing a marked difference in evolution. Consequently, the entire chemical sequence of volcanoes showing the latter features, is oscillating and/or stepped, with chemical offests corresponding to the deposition breaks/transitions. We infer that uninterrupted eruptions result from open plumbing systems within which a single large dyke feeds the eruption of a single batch of magma that may be undergoing chemical evolution. Congested plumbing systems consist of dyke complexes that may give rise to asymmetrical eruptive centres and composite depositional sequences. If eruptions are sourced from individual dykes, stepped and oscillatory chemo-stratigraphic patterns result. The magmatic evolution, deep and shallow plumbing systems are intricately linked in the development of not only the variations in chemical composition erupted during a “monogenetic” eruption, but also the physical dynamics

  1. Experimental Melting Study of Basalt-Peridotite Hybrid Source: Constrains on Chemistry of Recycled Component

    NASA Astrophysics Data System (ADS)

    Gao, S.; Takahashi, E.; Matsukage, K. N.; Suzuki, T.; Kimura, J. I.

    2015-12-01

    It is believed that magma genesis of OIB is largely influenced by recycled oceanic crust component involved in the mantle plume (e.g., Hauri et al., 1996; Takahashi & Nakajima., 2002; Sobolev et al., 2007). Mallik & Dasgupta (2012) reported that the wall-rock reaction in MORB-eclogite and peridotite layered experiments produced a spectrum of tholeiitic to alkalic melts. However, the proper eclogite source composition is still under dispute. In order to figure out the geochemistry of recycled component as well as their melting process, we conducted a series of high-P, high-T experiments. Melting experiments (1~10hrs) were performed under 2.9GPa with Boyd-England type piston-cylinder (1460~1540°C for dry experiments, 1400~1500°C for hydrous experiments) and 5GPa with Kawai-type multi-anvil (1550~1650°C for dry experiments, 1350~1550°C for hydrous experiments), at the Magma Factory, Tokyo Tech. Spinel lherzolite KLB-1 (Takahashi 1986) was employed as peridotite component. Two basalts were used as recycled component: Fe-enriched Columbia River basalt (CRB72-180, Takahashi et al., 1998) and N-type MORB (NAM-7, Yasuda et al., 1994). In dry experiments below peridotite dry solidus, melt compositions ranged from basaltic andesite to tholeiite. Opx reaction band generated between basalt and peridotite layer hindered chemical reaction. On the other hand, alkali basalt was formed in hydrous run products because H2O promoted melting process in both layers. Compared with melts formed by N-MORB-peridotite runs, those layered experiments with CRB are enriched in FeO, TiO2, K2O and light REE at given MgO. In other words, melts produced by CRB-peridotite layered experiments are close to alkali basalts in OIB and tholeiite in Hawaii, while those by layered experiments with N-MORB are poor in above elements. Thus we propose that Fe-rich Archean or Proterozoic tholeiite (BVSP 1980) would be a possible candidate for recycled component in OIB source.

  2. Extensive mixing features at 27-41 Ka postcaldera trachytes at Long Valley caldera, CA: Mixing/mingling of basalt with trachyte and mobilization of young granitic material to form kspar megacrysts

    NASA Astrophysics Data System (ADS)

    Hagmann, I. J.; Mahood, G.

    2014-12-01

    Five small lava domes erupted at the NW margin of Long Valley caldera from 41 to 27 Ka. They range from trachyte (66% SiO2) to trachyandesite (60%), with the youngest lava being the most mafic. Mixing features are pervasive, with enclaves, kspar megacrysts, crystal clots of various grain sizes, compositions, and degrees of resorption indicating multiple episodes of mafic injection, mobilization of young granitic material, and mixing/mingling of alkali basalt with trachyte to alkali rhyolite magmas similar to those at Mammoth Mountain. Enclaves range from 49 to 57% SiO2 and form a mixing line with a felsic end member at 67% SiO2. In order to quantify the distribution of enclaves and large (1-4 cm), resorbed, kspar megacrysts, outcrop-scale point counting was performed at >200 locations on the lavas. Contour maps show that kspar content is highest at the vent, but mafic-intermediate enclaves are irregularly distributed. Fe-Ti oxide temperatures for the host trachytic magmas are 915-1080°C, with the coolest temperatures at flow termini. Enclave temperatures are similar, 950-1120°C, with cooler temperatures in more felsic enclaves that are typically located near flow termini, indicating prolonged thermal and chemical interaction with the host magma. Calculated pressures are 2-4 kbar for host magmas, but some mafic crystal clots yield pressures up to 12 kbar, near the Moho at Long Valley. The kspar megacrysts match the composition of phenocrysts in late-erupted Bishop Tuff, suggesting that the megacrysts originated from solidified equivalents of magma remaining after eruption of the Bishop Tuff at 760 Ka. These data suggest a model in which alkali basalts are generated in the uppermost mantle and, through AFC, evolve into trachytes. Repeated basaltic injections keep the trachyte hot and partially melt young granites, resulting in entrainment of kspar megacrysts. The most mafic enclaves in the NW domes match the alkali basalt compositions of the most mafic enclaves in

  3. The Perils of Partition: Erroneous Results from Applying D Mineral/Magma to Rocks that Equilibrated Without Magma

    NASA Astrophysics Data System (ADS)

    Treiman, A. H.

    1995-09-01

    Compositions of extraterrestrial magmas are commonly derived from mineral compositions using, using experimentally determined mineral/basalt partition coefficients, Dmineral/basalt [1]. However, Dmineral/basalts cannot be applied to minerals which have experienced post-magmatic (subsolidus or metamorphic) chemical equilibration [2]. A failure to recognize post-magmatic equilibration can lead to wildly erroneous estimates of magma compositions and unrealistic scenarios of magmatic and planetary evolution [3]. To judge the effects of subsolidus chemical equilibration, consider REE distributions in a eucrite basalt, formed from a magma with CREE = 10 x CI. Let this magma crystallize and chemically equilibrate just below its solidus to a rock consisting of 49.5% plagioclase, 49.5% pigeonite, 0.1% whitlockite (a Ca phosphate), and 0.9% minor phases no REE content (silica, Fe metal, troilite); exact proportions are not critical. The total REE content ofthe rock is unchanged at 10 x CI, and distributions of REE among its minerals can be calculated from solidus-temperature Ds, e.g., Dpigeonite/plagioclase = Dpigeonite/basalt / Dplagioclase/basalt (where Dmineral/basalts are chosen to reflect the same magma compositions and temperature). REE abundances in minerals of this equilibrated rock (Figure 1 [5]) are significantly higher than they would be in the presence of magma. For instance, if this eucrite basalt system consisted of 50% magma, 25% pigeonite, and 25% plagioclase, one calculates C(La)Pigeonite = 0 04 x CI and C(La)Plagioclase = 0.8 x CI; with no magma present (Figure 1), C(La)Pigeonite = 0.4 x CI and CLaPIagioclase = 9 x CI! In the absence of magma, the incompatible REE must go somewhere!! If a mineral grain from this rock were used with Dmineral/basalts to derive a magma composition, that "Hparent basalt" would be rich in REE (130-200 x CI), enrichmed in light REE (La/Lu = 1.6 x CI), and strongly depleted in Eu. Compare this to the original eucrite, with REE at

  4. A basalt trigger for the 1991 eruptions of Pinatubo volcano?

    USGS Publications Warehouse

    Pallister, J.S.; Hoblitt, R.P.; Reyes, A.G.

    1992-01-01

    THE eruptive products of calc-alkaline volcanos often show evidence for the mixing of basaltic and acid magmas before eruption (see, for example, refs 1, 2). These observations have led to the suggestion3 that the injection of basaltic magma into the base of a magma chamber (or the catastrophic overturn of a stably stratified chamber containing basaltic magma at its base) might trigger an eruption. Here we report evidence for the mixing of basaltic and dacitic magmas shortly before the paroxysmal eruptions of Pinatubo volcano on 15 June 1991. Andesitic scoriae erupted on 12 June contain minerals and glass with disequilibrium compositions, and are considerably more mafic than the dacitic pumices erupted on 15 June. Differences in crystal abundance and glass composition among the pumices may arise from pre-heating of the dacite magma by the underlying basaltic liquid before mixing. Degassing of this basaltic magma may also have contributed to the climatologically important sulphur dioxide emissions that accompanied the Pinatubo eruptions.

  5. Zinc and volatile element loss during planetary magma ocean phases

    NASA Astrophysics Data System (ADS)

    Dhaliwal, Jasmeet K.; Day, James M. D.; Moynier, Frédéric

    2016-10-01

    Zinc is a moderately volatile element and a key tracer of volatile depletion on planetary bodies due to lack of significant isotopic fractionation under high-temperature processes. Terrestrial basalts have δ66Zn values similar to some chondrites (+ 0.15 to 0.3‰ where [{66Zn/64Znsample/66Zn/64ZnJMC-Lyon-1} × 1000]) and elevated Zn concentrations (100 ppm). Lunar mare basalts yield a mean δ66Zn value of +1.4 ± 0.5‰ and have low Zn concentrations (~2 ppm). Late-stage lunar magmatic products, such as ferroan anorthosite, Mg-suite and Alkali suite rocks exhibit heavier δ66Zn values (+3 to +6‰). The heavy δ66Zn lunar signature is thought to reflect evaporative loss and fractionation of zinc, either during a giant impact or in a magma ocean phase.We explore conditions of volatile element loss within a lunar magma ocean (LMO) using models of Zn isotopic fractionation that are widely applicable to planetary magma oceans. For the Moon, our objective was to identify conditions that would yield a δ66Zn signature of ~ +1.4‰ within the mantle, assuming a terrestrial mantle zinc starting composition.We examine two cases of zinc evaporative fractionation: (1) lunar surface zinc fractionation that was completed prior to LMO crystallization and (2) lunar surface zinc fractionation that was concurrent with LMO crystallization. The first case resulted in a homogeneous lunar mantle and the second case yielded a stratified lunar mantle, with the greatest zinc isotopic enrichment in late-stage crystallization products. This latter case reproduces the distribution of zinc isotope compositions in lunar materials quite well.We find that hydrodynamic escape was not a dominant process in losing Zn, but that erosion of a nascent lunar atmosphere, or separation of condensates into a proto-lunar crust are possible. While lunar volatile depletion is still possible as a consequence of the giant impact, this process cannot reproduce the variable δ66Zn found in the Moon. Outgassing

  6. The Mantle and Basalt-Crust Interaction Below the Mount Taylor Volcanic Field, New Mexico

    NASA Technical Reports Server (NTRS)

    Schrader, Christian M.; Crumpler, Larry S.; Schmidt, Marick E.

    2010-01-01

    The Mount Taylor Volcanic Field (MTVF) lies on the Jemez Lineament on the southeastern margin of the Colorado Plateau. The field is centered on the Mt. Taylor composite volcano and includes Mesa Chivato to the NE and Grants Ridge to the WSW. MTVF magmatism spans approximately 3.8-1.5 Ma (K-Ar). Magmas are dominantly alkaline with mafic compositions ranging from basanite to hy-basalt and felsic compositions ranging from ne-trachyte to rhyolite. We are investigating the state of the mantle and the spatial and temporal variation in basalt-crustal interaction below the MTVF by examining mantle xenoliths and basalts in the context of new mapping and future Ar-Ar dating. The earliest dated magmatism in the field is a basanite flow south of Mt. Taylor. Mantle xenolith-bearing alkali basalts and basanites occur on Mesa Chivato and in the region of Mt. Taylor, though most basalts are peripheral to the main cone. Xenolith-bearing magmatism persists at least into the early stages of conebuilding. Preliminary examination of the mantle xenolith suite suggests it is dominantly lherzolitic but contains likely examples of both melt-depleted (harzburgitic) and melt-enriched (clinopyroxenitic) mantle. There are aphyric and crystal-poor hawaiites, some of which are hy-normative, on and near Mt. Taylor, but many of the more evolved MTVF basalts show evidence of complex histories. Mt. Taylor basalts higher in the cone-building sequence contain >40% zoned plagioclase pheno- and megacrysts. Other basalts peripheral to Mt. Taylor and at Grants Ridge contain clinopyroxene and plagioclase megacrysts and cumulate-textured xenoliths, suggesting they interacted with lower crustal cumulates. Among the questions we are addressing: What was the chemical and thermal state of the mantle recorded by the basaltic suites and xenoliths and how did it change with time? Are multiple parental basalts (Si-saturated vs. undersaturated) represented and, if so, what changes in the mantle or in the tectonic

  7. Geochemical diversity of shergottite basalts: Mixing and fractionation, and their relation to Mars surface basalts

    NASA Astrophysics Data System (ADS)

    Treiman, Allan H.; Filiberto, Justin

    2015-04-01

    The chemical compositions of shergottite meteorites, basaltic rocks from Mars, provide a broad view of the origins and differentiation of these Martian magmas. The shergottite basalts are subdivided based on their Al contents: high-Al basalts (Al > 5% wt) are distinct from low-Al basalts and olivine-phyric basalts (both with Al < 4.5% wt). Abundance ratios of highly incompatible elements (e.g., Th, La) are comparable in all the shergottites. Abundances of less incompatible elements (e.g., Ti, Lu, Hf) in olivine-phyric and low-Al basalts correlate well with each other, but the element abundance ratios are not constant; this suggests mixing between components, both depleted and enriched. High-Al shergottites deviate from these trends consistent with silicate mineral fractionation. The "depleted" component is similar to the Yamato-980459 magma; approximately, 67% crystal fractionation of this magma would yield a melt with trace element abundances like QUE 94201. The "enriched" component is like the parent magma for NWA 1068; approximately, 30% crystal fractionation from it would yield a melt with trace element abundances like the Los Angeles shergottite. This component mixing is consistent with radiogenic isotope and oxygen fugacity data. These mixing relations are consistent with the compositions of many of the Gusev crater basalts analyzed on Mars by the Spirit rover (although with only a few elements to compare). Other Mars basalts fall off the mixing relations (e.g., Wishstone at Gusev, Gale crater rocks). Their compositions imply that basalt source areas in Mars include significant complexities that are not present in the source areas for the shergottite basalts.

  8. Water Content of Lunar Alkali Fedlspar

    NASA Technical Reports Server (NTRS)

    Mills, R. D.; Simon, J. I.; Wang, J.; Alexander, C. M. O'D.; Hauri, E. H.

    2016-01-01

    Detection of indigenous hydrogen in a diversity of lunar materials, including volcanic glass, melt inclusions, apatite, and plagioclase suggests water may have played a role in the chemical differentiation of the Moon. Spectroscopic data from the Moon indicate a positive correlation between water and Th. Modeling of lunar magma ocean crystallization predicts a similar chemical differentiation with the highest levels of water in the K- and Th-rich melt residuum of the magma ocean (i.e. urKREEP). Until now, the only sample-based estimates of water content of KREEP-rich magmas come from measurements of OH, F, and Cl in lunar apatites, which suggest a water concentration of < 1 ppm in urKREEP. Using these data, predict that the bulk water content of the magma ocean would have <10 ppm. In contrast, estimate water contents of 320 ppm for the bulk Moon and 1.4 wt % for urKREEP from plagioclase in ferroan anorthosites. Results and interpretation: NanoSIMS data from granitic clasts from Apollo sample 15405,78 show that alkali feldspar, a common mineral in K-enriched rocks, can have approx. 20 ppm of water, which implies magmatic water contents of approx. 1 wt % in the high-silica magmas. This estimate is 2 to 3 orders of magnitude higher than that estimated from apatite in similar rocks. However, the Cl and F contents of apatite in chemically similar rocks suggest that these melts also had high Cl/F ratios, which leads to spuriously low water estimates from the apatite. We can only estimate the minimum water content of urKREEP (+ bulk Moon) from our alkali feldspar data because of the unknown amount of degassing that led to the formation of the granites. Assuming a reasonable 10 to 100 times enrichment of water from urKREEP into the granites produces an estimate of 100-1000 ppm of water for the urKREEP reservoir. Using the modeling of and the 100-1000 ppm of water in urKREEP suggests a minimum bulk silicate Moon water content between 2 and 20 ppm. However, hydrogen loss was

  9. Precaldera lavas of the southeast San Juan Volcanic Field: Parent magmas and crustal interactions

    NASA Astrophysics Data System (ADS)

    Colucci, M. T.; Dungan, M. A.; Ferguson, K. M.; Lipman, P. W.; Moorbath, S.

    1991-07-01

    Early intermediate composition volcanic rocks of the Oligocene (circa 34-29 Ma) southeast San Juan volcanic field, southern Colorado, comprise the Conejos Formation. Conejos lavas include both high-K calc-alkaline and alkaline magma series (54-69% SiO2) ranging in composition from basaltic andesite (basaltic trachyandesite) to dacite (trachydacite). The subsequent Platoro caldera complex (29-27 Ma) was superimposed on a cluster of broadly precursory Conejos stratocones. Precaldera volcanism occurred in three pulses corresponding to three time-stratigraphic members: (1) the Horseshoe Mountain member, (2) the Rock Creek member, and (3) the Willow Mountain member. Each member exhibits distinctive phenocryst modes and incompatible trace element contents. Horseshoe Mountain lavas (hornblende-phyric) have relatively low alkali and incompatible element abundances, Rock Creek lavas (anhydrous phenocrysts) and ash-flow tuffs have the highest abundances, and Willow Mountain lavas (diverse mineralogy) are intermediate. All Conejos lavas exhibit low ratios of lead (206Pb/204Pb = 17.5 to 18.2) and neodymium (ɛNd = -8 to -4) isotopes and high 87Sr/86Sr (0.7045 to 0.7056) compared to depleted asthenospheric mantle. These values lie between those of likely mantle compositions and the isotopic composition of Proterozoic crust of the southern Rocky Mountains. Mafic lavas of the Horseshoe Mountain member have the lowest Pb and Nd isotope ratios among Conejos members but trend toward higher isotopic values with increasing degrees of differentiation. Compositions within the Rock Creek series trend toward higher Pb and lower Nd isotope ratios with increasing SiO2. Willow mountain volcanic sequences define diverse chemical-isotopic correlations. We interpret the chemical and isotopic differences observed between mafic lavas of each member to reflect derivation from compositionally distinct mantle derived parent magmas that have experienced extensive deep level crustal contamination

  10. 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

  11. Basaltic cannibalism at Thrihnukagigur volcano, Iceland

    NASA Astrophysics Data System (ADS)

    Hudak, M. R.; Feineman, M. D.; La Femina, P. C.; Geirsson, H.

    2014-12-01

    Magmatic assimilation of felsic continental crust is a well-documented, relatively common phenomenon. The extent to which basaltic crust is assimilated by magmas, on the other hand, is not well known. Basaltic cannibalism, or the wholesale incorporation of basaltic crustal material into a basaltic magma, is thought to be uncommon because basalt requires more energy than higher silica rocks to melt. Basaltic materials that are unconsolidated, poorly crystalline, or palagonitized may be more easily ingested than fully crystallized massive basalt, thus allowing basaltic cannibalism to occur. Thrihnukagigur volcano, SW Iceland, offers a unique exposure of a buried cinder cone within its evacuated conduit, 100 m below the main vent. The unconsolidated tephra is cross-cut by a NNE-trending dike, which runs across the ceiling of this cave to a vent that produced lava and tephra during the ~4 Ka fissure eruption. Preliminary petrographic and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) analyses indicate that there are two populations of plagioclase present in the system - Population One is stubby (aspect ratio < 1.7) with disequilibrium textures and low Ba/Sr ratios while Population Two is elongate (aspect ratio > 2.1), subhedral to euhedral, and has much higher Ba/Sr ratios. Population One crystals are observed in the cinder cone, dike, and surface lavas, whereas Population Two crystals are observed only in the dike and surface lavas. This suggests that a magma crystallizing a single elongate population of plagioclase intruded the cinder cone and rapidly assimilated the tephra, incorporating the stubbier population of phenocrysts. This conceptual model for basaltic cannibalism is supported by field observations of large-scale erosion upward into the tephra, which is coated by magma flow-back indicating that magma was involved in the thermal etching. While the unique exposure at Thrihnukagigur makes it an exceptional place to investigate basaltic

  12. 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.

  13. 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

  14. Chemical and isotopic constraints on the petrogenesis of the large mare basalt clast in breccia 15459

    NASA Technical Reports Server (NTRS)

    Nyquist, L.; Lindstrom, M.; Bansal, B.; Mittlefehldt, D.; Shih, C.-Y.

    1989-01-01

    Results are presented that demonstrate that the large mare basalt clast in Apollo 15 breccia 15459 may represent one or more independent magma types. The complex nonequilibrium pyroxene and plagioclase compositions and relatively abundant mesostasis suggest that the 15459 clast is not a slowly cooled crystal cumulate. The addition of about 40 percent olivine to an olivine-normative basalt parental magma is found to be necessary to explain the high MgO abundances of picritic basalts by the accumulation of olivine in the magma. The present clast has a slightly younger age and a slightly higher Sr-87/Sr-86 ratio than most Apollo 15 basalts.

  15. Chemistry and fluxes of magmatic gases powering the explosive trachyandesitic phase of Eyjafjallajokull 2010 eruption: constraints on degassing magma volumes and processes

    NASA Astrophysics Data System (ADS)

    Allard, P.; Burton, M. R.; Oskarsson, N.; Michel, A.; Polacci, M.

    2010-12-01

    The 2010 Eyjafjallajökull eruption developed in two distinct phases, with initial lateral effusion of alkali basalt since March 20, followed by highly explosive extrusion of a quite homogenous and crystal-poor trachyandesitic magma [1] through the central volcano ice cap between April 14 and May 24. As usual, magmatic volatiles played a key role in the eruption dynamics. Here we report on the chemical composition and the mass output of magmatic gases powering intense explosive activity during the second eruptive phase in early May. On May 8 we could measure the composition of magmatic gases directly issuing from the eruptive vents, by using OP-FTIR spectroscopy from the crater rim (~900 m distance) and molten lava blocks as IR radiation source. FTIR spectra reveal a variable mixture between two gas components equally rich in H2O (91.3 mol%) and CO2 (8%) but differing in their SO2/HCl ratio (up to 3.5 for the main one and 0.5 for the Cl-richer second one). Analysis of S-Cl-F in ash leachates and in ash and lava bomb samples (pyrohydrolysis) show that this second component was generated by greater chlorine loss during extensive magma fragmentation into fine ash. S/Cl and Cl/F ratios from both these analyses and solar occultation FTIR plume sensing indicate a modest fluorine content in emitted gas and its preferential adsorption onto solid particles during plume transport. DOAS traverses under the volcanic plume (4-6 km height), though hampered by dense ash load, gave most reliable SO2 fluxes of 4500-6600 tons d-1 on May 9, consistent with OMI satellite data [2]. These imply the daily co-emission of 7.2x105 tons of H2O, 1.5x105 tons of CO2, 2000 tons of HCl and ≤200 tons of HF. Eyjafjallajökull thus produced more hydrous and relatively CO2-poorer gas, in much greater quantities, during that stage than during its first basaltic phase [3]. Linear variations of dissolved S with TiO2/FeO ratio in nearby Katla alkali magmas [4] suggest possible pre-eruptive S contents

  16. Oxygen isotope composition of mafic magmas at Vesuvius

    NASA Astrophysics Data System (ADS)

    Dallai, L.; Cioni, R.; Boschi, C.; D'Oriano, C.

    2009-12-01

    The oxygen isotope composition of olivine and clinopyroxene from four plinian (AD 79 Pompeii, 3960 BP Avellino), subplinian (AD 472 Pollena) and violent strombolian (Middle Age activity) eruptions were measured to constrain the nature and evolution of the primary magmas of the last 4000 years of Mt. Vesuvius activity. A large set of mm-sized crystals was accurately separated from selected juvenile material of the four eruptions. Crystals were analyzed for their major and trace element compositions (EPMA, Laser Ablation ICP-MS), and for 18O/16O ratios. As oxygen isotope composition of uncontaminated mantle rocks on world-wide scale is well constrained (δ18Oolivine = 5.2 ± 0.3; δ18Ocpx = 5.6 ± 0.3 ‰), the measured values can be conveniently used to monitor the effects of assimilation/contamination of crustal rocks in the evolution of the primary magmas. Instead, typically uncontaminated mantle values are hardly recovered in Italian Quaternary magmas, mostly due to the widespread occurrence of crustal contamination of the primary magmas during their ascent to the surface (e.g. Alban Hills, Ernici Mts., and Aeolian Islands). Low δ18O values have been measured in olivine from Pompeii eruption (δ18Oolivine = 5.54 ± 0.03‰), whereas higher O-compositions are recorded in mafic minerals from pumices or scoria of the other three eruptions. Measured olivine and clinopyroxene share quite homogeneous chemical compositions (Olivine Fo 85-90 ; Diopside En 45-48, respectively), and represent phases crystallized in near primary mafic magmas, as also constrained by their trace element compositions. Data on melt inclusions hosted in crystals of these compositions have been largely collected in the past demonstrating that they crystallized from mafic melt, basaltic to tephritic in composition. Published data on volatile content of these melt inclusions reveal the coexistence of dissolved water and carbon dioxide, and a minimum trapping pressure around 200-300 MPa, suggesting

  17. Tachylyte in Cenozoic basaltic lavas from the Czech Republic and Iceland: contrasting compositional trends

    NASA Astrophysics Data System (ADS)

    Ulrych, Jaromír; Krmíček, Lukáš; Teschner, Claudia; Řanda, Zdeněk; Skála, Roman; Jonášová, Šárka; Fediuk, Ferry; Adamovič, Jiří; Pokorný, Richard

    2016-11-01

    Tachylytes from rift-related volcanic rocks were recognized as: (i) irregular veinlets in host alkaline lava flows of the Kozákov volcano, Czech Republic, (ii) (sub)angular xenoliths in alkaline lava of the feeding channel of the Bukovec volcano, Czech Republic, and (iii) paleosurface of a tholeiitic lava flow from Hafrafell, Iceland. The tachylyte from Kozákov is phonotephrite to tephriphonolite in composition while that from Bukovec corresponds to trachyandesite to tephriphonolite. Both glass and host rock from Hafrafell are of tholeiitic basalt composition. The tachylyte from Kozákov, compared with the host rock, revealed a substantial enrichment in major elements such as Si, Al and alkalis along with Rb, Sr, Ba, Nb, Zr, REE, Th and U. The tachylyte from Bukovec displays contrasting trends in the incompatible element contents. The similarity in composition of the Hafrafell tachylyte paleosurface layer and parental tholeiitic basalt is characteristic for lavas. The host/parent rocks and tachylytes have similar initial Sr-Nd characteristics testifying for their co-magmatic sources. The initial ɛNd values of host/parent rocks and tachylytes from the Bohemian Massif (+3.4 to +3.9) and those from Iceland (+6.3) are interpreted as primary magma values. Only the tachylyte from Bukovec shows a different ɛNd value of -2.1, corresponding to a xenolith of primarily sedimentary/metamorphic origin. The tachylyte from Kozákov is a product of an additional late magmatic portion of fluids penetrating through an irregular fissure system of basaltic lava. The Bukovec tachylyte is represented by xenoliths originated during the interaction of ascending basaltic melt with granitoids or orthogneisses, whereas the Hafrafell tachylyte is a product of a rapid cooling on the surface of a basalt flow.

  18. Are flood basalt eruptions monogenetic or polygenetic?

    NASA Astrophysics Data System (ADS)

    Sheth, Hetu C.; Cañón-Tapia, Edgardo

    2015-11-01

    A fundamental classification of volcanoes divides them into "monogenetic" and "polygenetic." We discuss whether flood basalt fields, the largest volcanic provinces, are monogenetic or polygenetic. A polygenetic volcano, whether a shield volcano or a stratovolcano, erupts from the same dominant conduit for millions of years (excepting volumetrically small flank eruptions). A flood basalt province, built from different eruptive fissures dispersed over wide areas, can be considered a polygenetic volcano without any dominant vent. However, in the same characteristic, a flood basalt province resembles a monogenetic volcanic field, with only the difference that individual eruptions in the latter are much smaller. This leads to the question how a flood basalt province can be two very different phenomena at the same time. Individual flood basalt eruptions have previously been considered monogenetic, contrasted by only their high magma output (and lava fluidity) with typical "small-volume monogenetic" volcanoes. Field data from Hawaiian shield volcanoes, Iceland, and the Deccan Traps show that whereas many feeder dykes were single magma injections, and the eruptions can be considered "large monogenetic" eruptions, multiple dykes are equally abundant. They indicate that the same dyke fissure repeatedly transported separate magma batches, feeding an eruption which was thus polygenetic by even the restricted definition (the same magma conduit). This recognition helps in understanding the volcanological, stratigraphic, and geochemical complexity of flood basalts. The need for clear concepts and terminology is, however, strong. We give reasons for replacing "monogenetic volcanic fields" with "diffuse volcanic fields" and for dropping the term "polygenetic" and describing such volcanoes simply and specifically as "shield volcanoes," "stratovolcanoes," and "flood basalt fields."

  19. Mid-Tertiary magmatism in western Big Bend National Park, Texas, U.S.A.: Evolution of basaltic source regions and generation of peralkaline rhyolite

    NASA Astrophysics Data System (ADS)

    Parker, Don F.; Ren, Minghua; Adams, David T.; Tsai, Heng; Long, Leon E.

    2012-07-01

    then descended as magmatism died out. Variation within Burro Mesa Rhyolite is best explained by fractional crystallization of a mix of alkali feldspar, fayalite and Fe-Ti oxide. Comendite of the Burro Mesa Rhyolite evolved from trachyte as batches in relatively small independent magma systems, as suggested by widespread occurrence of trachytic magma enclaves within Burro Mesa lava and results of fractionation modeling. Trachyte may have been derived by fractional crystallization of intermediate magma similar to that erupted as part of Bee Mountain Basalt. ɛNdt values of trachyte lava (0.745) and two samples of Burro Mesa Rhyolite (- 0.52 and 1.52) are consistent with the above models. In all, ~ 5 wt.% comendite may be produced from 100 parts of parental trachybasalt. Negative Nb anomalies in some Bee Mountain, Tule Mountain Trachyte and Burro Mesa incompatible element plots may have been inherited from lithospheric mantle rather than from a descending plate associated with subduction. Late phase basalts lack such a Nb anomaly, as do all of our Alamo Creek analyses but one. Even if some slab fluids partially metasomatized lithospheric mantle, these igneous rocks are much more typical of continental rifts than continental arcs. We relate Big Bend magmatism to asthenospheric mantle upwelling accompanying foundering of the subducted Farallon slab as the convergence rate between the North American and the Farallon plates decreased beginning about 50 Ma. Upwelling asthenosphere heated the base of the continental lithosphere, producing the Alamo Creek series; magmatism climaxed with main phase magmatism generated within middle continental lithosphere, and then, accompanying regional extension, gradually died out by 18 Ma.

  20. Isotopic characteristics of mantle sources for Quaternary continental alkaline magmas in the northern Canadian Cordillera

    NASA Astrophysics Data System (ADS)

    Carignan, Jean; Ludden, John; Francis, Don

    1994-12-01

    Three mantle compositions are identified as potential source end members for Quaternary to recent alkaline volcanic rocks from Fort Selkirk, Llangorse-Hirschfeld, Alligator Lake and Mt. Edziza in the northern Canadian Cordillera. These are: (1) an amphibole-rich source, characterized by unradiogenic Sr, Nd and Pb, from which the olivine nephelinite lavas formed, (2) the continental lithospheric mantle which is characterised by high Pb-207/Pb-204 and appears to be involved in the formation of the alkali olivine basalts of Fort Selkirk, and (3) a mantle with radiogenic Pb and unradiogenic Sr (HIMU-type) represented by lavas from Mt. Edziza. The Mt. Edziza volcano is the largest of the volcanic centres in the region, and is considered to reflect melting of sublithospheric mantle of HIMU composition below central British Columbia. Incipient melting of amphibole-veined subcontinental mantle lithosphere resulted from plume upwelling and/or transtensional pressure release and produced the small nephelinite to olivine basalt centres of the northern Cordilleran Province. The source of the nephelinite magmas is slightly more radiogenic than present-day Pacific Mid-Ocean ridge basalts (MORB), and is best represented by the most depleted component of the Aleutian magmas. This suggests enrichment of the subcontinental lithosphere in the northern Cordillera by melts of this isotopic composition during Cretaceous subduction. The Alligator Lake complex is anomalous and charaterized by the most radiogenic lavas. Despite the presence of crustal xenoliths there is no clear geochemical signature for crustal contamination and, in contrast to the other volcanic centers which were erupted through the Intermontain Belt, the lavas of this center may have been derived from a highly radiogenic lithospheric mantle beneath the Coast Plutonic complex.

  1. Basaltic maar-diatreme volcanism in the Lower Carboniferous of the Limerick Basin (SW Ireland)

    NASA Astrophysics Data System (ADS)

    Elliott, H. A. L.; Gernon, T. M.; Roberts, S.; Hewson, C.

    2015-05-01

    Lead-zinc exploration drilling within the Limerick Basin (SW Ireland) has revealed the deep internal architecture and extra-crater deposits of five alkali-basaltic maar-diatremes. These were emplaced as part of a regional north-east south-west tectonomagmatic trend during the Lower Carboniferous Period. Field relationships and textural observations suggest that the diatremes erupted into a shallow submarine environment. Limerick trace element data indicates a genetic relationship between the diatremes and extra-crater successions of the Knockroe Formation, which records multiple diatreme filling and emptying cycles. Deposition was controlled largely by bathymetry defined by the surrounding Waulsortian carbonate mounds. An initial non-diatreme forming eruption stage occurred at the water-sediment interface, with magma-water interaction prevented by high magma ascent rates. This was followed by seawater incursion and the onset of phreatomagmatic activity. Magma-water interaction generated poorly vesicular blocky clasts, although the co-occurrence of plastically deformed and highly vesicular clasts indicate that phreatomagmatic and magmatic processes were not mutually exclusive. At a later stage, the diatreme filled with a slurry of juvenile lapilli and country rock lithic clasts, homogenised by the action of debris jets. The resulting extra-crater deposits eventually emerged above sea level, so that water ingress significantly declined, and late-stage magmatic processes became dominant. These deposits, largely confined to the deep vents, incorporate high concentrations of partially sintered globular and large `raggy' lapilli showing evidence for heat retention. Our study provides new insights into the dynamics and evolution of basaltic diatremes erupting into a shallow water (20-120 m) submarine environment.

  2. Orientation of the eruption fissures controlled by a shallow magma chamber in Miyakejima

    NASA Astrophysics Data System (ADS)

    Geshi, Nobuo; Oikawa, Teruki

    2016-11-01

    Orientation of the eruption fissures and composition of the lavas of the Miyakejima volcano indicate tectonic influence of a shallow magma chamber on the distribution of eruption fissures. We examined the distributions and magmatic compositions of 23 fissures that formed within the last 2800 years, based on a field survey and a new dataset of 14C ages. The dominant orientation of the eruption fissures in the central portion of the volcano was found to be NE-SW, which is perpendicular to the direction of regional maximum horizontal compressive stress (σHmax). Magmas that show evidences of magma mixing between basaltic and andesitic magmas erupted mainly from the eruption fissures with a higher offset angle from the regional σHmax direction. The presence of a shallow dike-shaped magma chamber controls the distribution of the eruption fissures. The injection of basaltic magma into the shallow andesitic magma chamber caused the temporal rise of internal magmatic pressure in the shallow magma chamber. Dikes extending from the andesitic magma chamber intrude along the local compressive stress field which is generated by the internal excess pressure of the andesitic magma chamber. As the result, the eruption fissures trend parallel to the elongation direction of the shallow magma chamber. Injection of basaltic magma into the shallow andesitic magma chamber caused the magma mixing. Some basaltic dikes from the deep-seated magma chamber reach the ground surface without intersection with the andesitic magma chamber. The patterns of the eruption fissures can be modified in the future as was observed in the case of the destruction of the shallow magma chamber during the 2000 AD eruption.

  3. Mobility and fluxes of major, minor and trace metals during basalt weathering and groundwater transport at Mt. Etna volcano (Sicily)

    SciTech Connect

    Aiuppa, A.; Allard, P.; D'Alessandro, W.; Michel, A.; Parello, F.; Treuil, M.; Valenza, M.

    2000-06-01

    The concentrations and fluxes of major, minor and trace metals were determined in 53 samples of groundwaters from around Mt. Etna, in order to evaluate the conditions and extent of alkali basalt weathering by waters enriched in magma-derived CO{sub 2} and the contribution of aqueous transport to the overall metal discharge of the volcano. The authors show that gaseous input of magmatic volatile metals into the Etnean aquifer is small or negligible, being limited by cooling of the rising fluids. Basalt leaching by weakly acidic, CO{sub 2}-charged water is the overwhelming source of metals and appears to be more extensive in two sectors of the S-SW (Paterno) and E (Zafferana) volcano flanks, where out flowing groundwaters are the richest in metals and bicarbonate of magmatic origin. Thermodynamic modeling of the results allows evaluation of the relative mobility and chemical speciation of various elements during their partitioning between solid and liquid phases through the weathering process. At Mt. Etna, poorly mobile elements (Al, Th, Fe) are preferentially retained in the solid residue of weathering, while alkalis, alkaline earth and oxo-anion-forming elements (As, Se, Sb, Mo) are more mobile and released to the aqueous system. Transition metals display an intermediate behavior and are strongly dependent on either the redox conditions (Mn, Cr, V) or solid surface-related processes (V, Zn, Cu).

  4. Petrologic models of 15388, a unique Apollo 15 mare basalt

    NASA Technical Reports Server (NTRS)

    Hughes, S. S.; Dasch, E. J.; Nyquist, L. E.

    1993-01-01

    Mare basalt 15388, a feldspathic microgabbro from the Apennine Front, is chemically and petrographically distinct from Apollo 15 picritic, olivine-normative (ON), and quartz-normative basalts. The evolved chemistry, coarse texture, lack of olivine, and occurrence of cristobalite in 15388 argue for derivation by a late-stage magmatic process that is significantly removed from parental magma. It either crystallized from a magma evolved from the more mafic Apollo 15 basalts, or it crystallized from a currently unrepresented magma. Rb-Sr and Sm-Nd isotopic systematics yield isochron ages of 3.391 plus or minus 0.036 and 3.42 plus or minus 0.07 Ga, respectively, and epsilon(sub Nd) = 8.6 plus or minus 2.4, which is relatively high for Apollo 15 mare basalts. In contrast to chemical patterns of average Apollo 15 ON basalts and Apollo 15 picritic basalt, 15388 has a strongly positive LREE slope, high Ti, shallower HREE slope and a slightly positive Eu anomaly. These features argue against 15388 evolution by simple olivine fractionation of a parental ON or picritic basalt magma, although olivine is a dominant liquidus phase in both potential parents.

  5. Magma mixing induced by particle settling

    NASA Astrophysics Data System (ADS)

    Renggli, Christian J.; Wiesmaier, Sebastian; De Campos, Cristina P.; Hess, Kai-Uwe; Dingwell, Donald B.

    2016-11-01

    A time series of experiments at high temperature have been performed to investigate the influence of particle settling on magma mixing. A natural rhyolite glass was held above a natural basalt glass in a platinum crucible. After melting of the glasses at superliquidus temperatures, a platinum sphere was placed on the upper surface of the rhyolitic melt and sank into the experimental column (rhyolitic melt above basaltic melt). Upon falling through the rhyolitic-basaltic melt interface, the Pt sphere entrained a filament of rhyolitic melt in its further fall. The quenched products of the experiments were imaged using X-ray microCT methods. The images of our time series of experiments document the formation of a rhyolite filament as it is entrained into the underlying basalt by the falling platinum sphere. When the Pt particle reached the bottom of the crucible, the entrained rhyolitic filament started to ascend buoyantly up to the initial rhyolitic-basaltic interface. This generated a significant thickness increase of a comingled "melange" layer at the interface due to "liquid rope coiling" and piling up of the filament. As a consequence, the basalt/rhyolite interface was greatly enlarged and diffusive hybridisation greatly accelerated. Further, bubbles, originating at the interface, are observed to have risen into the overlying rhyolite dragging basalt filaments with them. Upon crossing the basalt/rhyolite interface, the bubbles have non-spherical shapes as they adapt to the differing surface tensions of basaltic and rhyolitic melts. Major element profiles, measured across the rhyolite filaments, exhibit asymmetrical shapes from the rhyolite into the basalt. Na and Ti reveal uphill diffusion from the rhyolite towards the interface in the filament cross sections. These results reveal the potential qualitative complexity of the mingling process between rhyolitic and basaltic magmas in the presence of sinking crystals. They imply that crystal-rich magma mingling may

  6. Lunar ferroan anorthosites and mare basalt sources - The mixed connection

    NASA Astrophysics Data System (ADS)

    Ryder, Graham

    1991-11-01

    Global overturn of a hot, gravitationally unstable lunar mantle immediately following the solidification of a magma ocean explains several characteristics of lunar petrology. Lunar mare basalt sources are inferred to be depleted in europium and alumina. These depletions are consensually attributed to complementary plagioclase floating from a magma ocean. However, in contrast to the mare basalt source parent magma, the ferroan anorthosite parent magma was more evolved by virtue of its lower Mg/Fe ratio and Ni abundances, although less evolved in its poverty of clinopyroxene constituents, flat rare earth pattern, and lower incompatible element abundances. The europium anomaly in mare sources is inferred to be present at 400 km depth, too deep to have been directly influenced by plagioclase crystallization. Massive overturning of the post-magma ocean mantle would have carried down clinopyroxene, ilmenite, and phases containing fractionated rare earths, europium anomalies, and some heat-producing radionuclides.

  7. Lunar ferroan anorthosites and mare basalt sources - The mixed connection

    NASA Technical Reports Server (NTRS)

    Ryder, Graham

    1991-01-01

    Global overturn of a hot, gravitationally unstable lunar mantle immediately following the solidification of a magma ocean explains several characteristics of lunar petrology. Lunar mare basalt sources are inferred to be depleted in europium and alumina. These depletions are consensually attributed to complementary plagioclase floating from a magma ocean. However, in contrast to the mare basalt source parent magma, the ferroan anorthosite parent magma was more evolved by virtue of its lower Mg/Fe ratio and Ni abundances, although less evolved in its poverty of clinopyroxene constituents, flat rare earth pattern, and lower incompatible element abundances. The europium anomaly in mare sources is inferred to be present at 400 km depth, too deep to have been directly influenced by plagioclase crystallization. Massive overturning of the post-magma ocean mantle would have carried down clinopyroxene, ilmenite, and phases containing fractionated rare earths, europium anomalies, and some heat-producing radionuclides.

  8. Making rhyolite in a basalt crucible

    NASA Astrophysics Data System (ADS)

    Eichelberger, John

    2016-04-01

    Iceland has long attracted the attention of those concerned with the origin of rhyolitic magmas and indeed of granitic continental crust, because it presents no alternative for such magmas other than deriving them from a basaltic source. Hydrothermally altered basalt has been identified as the progenitor. The fact that rhyolite erupts as pure liquid requires a process of melt-crustal separation that is highly efficient despite the high viscosity of rhyolite melt. Volcanoes in Iceland are foci of basaltic magma injection along the divergent plate boundary. Repeated injection produces remelting, digestion, and sometimes expulsion or lateral withdrawal of material resulting in a caldera, a "crucible" holding down-dropped and interlayered lava flows, tephras, and injected sills. Once melting of this charge begins, a great deal of heat is absorbed in the phase change. Just 1% change in crystallinity per degree gives a melt-present body an effective heat capacity >5 times the subsolidus case. Temperature is thus buffered at the solidus and melt composition at rhyolite. Basalt inputs are episodic ("fires") so likely the resulting generation of rhyolite by melting is too. If frequent enough to offset cooling between events, rhyolite melt extractions will accumulate as a rhyolite magma reservoir rather than as discrete crystallized sills. Evidently, such magma bodies can survive multiple firings without themselves erupting, as the 1875 eruption of Askja Caldera of 0.3 km3 of rhyolite equilibrated at 2-km depth without previous leakage over a ten-millennium period and the surprise discovery of rhyolite magma at 2-km depth in Krafla suggest. Water is required for melting; otherwise melting cannot begin at a temperature lower than that of the heat source. Because the solubility of water in melt is pressure-dependent and almost zero at surface pressure, there must be a minimum depth at which basalt-induced melting can occur and a rhyolite reservoir sustained. In practice, the

  9. Lu-Hf constraints on the evolution of lunar basalts

    NASA Technical Reports Server (NTRS)

    Fujimaki, H.; Tatsumoto, M.

    1984-01-01

    It is shown that a cumulate-remelting model best explains the recently acquired data on the Lu-Hf systematics of lunar mare basalts. The model is constructed using Lu and Hf concentration data and is strengthened by Hf isotopic evidence of Unruh et al. (1984). It is shown that the similarity in MgO/FeO ratios and Cr2O3 content in high-Ti and low-Ti basalts are not important constraints on lunar basalt petrogenesis. The model demonstrates that even the very low Ti or green glass samples are remelting products of a cumulate formed after at least 80-90 percent of the lunar magma ocean had solidified. In the model, all the mare basalts and green glasses were derived from 100-150 km depth in the lunar mantle. The Lu-Hf systematics of KREEP basalts clearly indicate that they would be the final residual liquid of the lunar magma ocean.

  10. Constraints on volatile concentrations of pre-eruptive lunar magma

    NASA Astrophysics Data System (ADS)

    Xu, Yingkui; Zhu, Dan; Wang, Shijie

    2014-04-01

    Until recently, the Moon had long been thought to be depleted of volatiles such as H2O, S, COx and Cl2. Researchers have recently measured volatile concentrations in the minerals, glasses and inclusions of lunar samples, and the results show that lunar rocks contain volatiles that are more similar to terrestrial materials than was previously thought. Mare basalts are located on the Earth-facing hemisphere in large impact basins, and they are not representative of the feldspathic highlands. Thus, it is likely that the density of lunar mafic magma exceeds that of the highland rocks based on buoyancy alone. According to this observational fact, we calculate the density of mare basalt to give a constraint for the maximum amount of water mare basalt can contain because water can effectively decrease the density of mare magma. Our result shows that water contained in the pre-eruptive magma could not have been more than 1000 ppm; otherwise, the density of very-low-Ti basaltic magma would be less than that of the highland rocks. Additionally, if magma contains other species of volatiles such as C-O, S, F, or Cl2, the water in the pre-eruptive magma would have to be much less than 1000 ppm because volatiles such as CO2 can effectively decrease the solubility of water in silicate melts. Based on these calculations on densities and a comparison with water in MORB, we conclude that the moon's water is not as great as has been recently suggested.

  11. Submarine basalt from the Revillagigedo Islands region, Mexico

    USGS Publications Warehouse

    Moore, J.G.

    1970-01-01

    Ocean-floor dredging and submarine photography in the Revillagigedo region off the west coast of Mexico reveal that the dominant exposed rock of the submarine part of the large island-forming volcanoes (Roca Partida and San Benedicto) is a uniform alkali pillow basalt; more siliceous rocks are exposed on the upper, subaerial parts of the volcanoes. Basalts dredged from smaller seamounts along the Clarion fracture zone south of the Revillagigedo Islands are tholeiitic pillow basalts. Pillows of alkali basalts are more vesicular than Hawaiian tholeiitic pillows collected from the same depths. This difference probably reflects a higher original volatile content of the alkali basalts. Manganese-iron oxide nodules common in several dredge hauls generally contain nucleii of rhyolitic pumice or basalt pillow fragments. The pumice floated to its present site from subaerial eruptions, became waterlogged and sank, and was then coated with manganese-iron oxides. The thickness of palagonite rinds on the glassy pillow fragments is proportional to the thickness of manganese-iron oxide layers, and both are a measure of the age of the nodule. Both oldest basalts (10-100 m.y.) and youngest (less than 1 m.y.) are along the Clarion fracture zone, whereas basalts from Roca Partida and San Benedicto volcanoes are of intermediate age. ?? 1970.

  12. Pressure of Partial Crystallization of Katla Magmas: Implications for Magma Chamber Depth and for the Magma Plumbing System

    NASA Astrophysics Data System (ADS)

    Tenison, A.; Kelley, D. F.; Barton, M.

    2012-12-01

    Iceland is home to some of the most active volcanoes in the world, and recent eruptions emphasize the need for additional studies to better understand the volcanism and tectonics in this region. Historical patterns of eruptive activity and an increase in seismic activity suggest that Katla is showing signs of an impending eruption. The last major eruption in 1918 caused massive flooding and deposited enough sediment to extend part of Iceland's southern shoreline by 5 km. It also generated sufficient ash over many weeks to cause a brief drop in global temperature. A future eruption similar to the 1918 event could have serious global consequences, including severe disruptions in air travel, short-term global cooling, and shortened growing seasons. Relatively few studies have focused on establishing the depth of the main magma chamber beneath Katla, although knowledge of magma chamber depth is essential for constraining models for magma evolution and for understanding the eruption dynamics of this volcano. The results of seismic and geodetic studies suggest the presence of a shallow magma body at a depth of 2-4 km, but do not provide firm evidence for the presence of deeper chambers in contrast to results obtained for other volcanoes in Iceland. Studies of volcanic ash layers reveal a history of alternating cycles of basaltic and silicic eruptions. We suggest that the shallow magma chamber is primarily the source of silica-rich magma, and postulate that there must be one or more additional chambers in the middle or deep crust that serve as the storage site of the basaltic magma erupted as lava and ash. We have tested this proposal by calculating the pressures of partial crystallization for basalts erupted at Katla using petrological methods. These pressures can be converted to depths and the results provide insight into the likely configuration of the magma plumbing system. Published analyses of volcanic glasses (lava, ash and hyaloclastite) were used as input data

  13. Lunar mare versus terrestrial mid-ocean ridge basalts - Planetary constraints on basaltic volcanism

    NASA Technical Reports Server (NTRS)

    Papike, J. J.; Bence, A. E.

    1978-01-01

    Major differences which exist between terrestrial midocean ridge basalts (MORBs) and lunar mare basalts reflect the different planetary characteristics of earth and moon. MORBs are enriched in aluminum and have higher Mg/(Mg + Fe(2+)). These features reflect a more aluminum- and magnesium-rich mantle source for MORBs. Mare basalts are depleted in sodium and potassium relative to MORBs and, consequently, mare feldspars are depleted in the albite component relative to MORB feldspars; these features are a reflection of the alkali-depleted nature of the moon relative to earth. The oxygen fugacities that obtained during MORB petrogenesis follow the quartz-magnetite-fayalite buffer curve very closely, while those of mare basalts are several orders of magnitude lower. This results in reduced valence states for Fe, Cr, and Ti in mare basalts, which, in turn, has a significant effect on mineral-melt partitioning.

  14. 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.

  15. Primary melt from Sannome-gata volcano, NE Japan arc: constraints on generation conditions of rear-arc magmas

    NASA Astrophysics Data System (ADS)

    Kuritani, T.; Yoshida, T.; Kimura, J.; Takahashi, T.; Hirahara, Y.; Miyazaki, T.; Senda, R.; Chang, Q.; Ito, Y.

    2013-12-01

    Material and energy transport in subduction zones has played an important role in Earth's evolution, and has been investigated extensively in petrological, geochemical, experimental, numerical, and geophysical studies. In these approaches, petrological and geochemical studies on arc basalts have remarkably contributed to the quantitative understanding of subduction-zone processes. However, a more rigorous understanding is limited by the fact that primary magmas generated in the mantle erupt only very occasionally without significant thermal and mechanical interaction with the crust. In this study, the conditions under which arc magma is generated are estimated using primary basalts from the Sannome-gata volcano, located in the rear of the NE Japan arc. The NE Japan arc has been investigated extensively, and is one of the best-documented volcanic arcs on Earth. Therefore, the reliable estimates of the magma generation conditions are expected to contribute to gaining a better understanding of subduction-zone processes. The Sannome-gata maar is located in the Oga Peninsula, NE Japan. The age of the volcanic activity is 20-24 ka (Kitamura 1990). We have examined the petrology and geochemistry of basaltic scoria samples that were collected from scoria fall deposits, outcropping around 500 m southwest of the Sannome-gata maar (Yoshinaga and Nakagawa 1999). The scoriae occur with abundant mantle and crustal xenoliths, suggesting that the magma ascended rapidly from the upper mantle. They show significant variations in their whole-rock compositions (7.9-11.1 wt.% in MgO). High-MgO scoriae (MgO > ~9.5 wt.%) have mostly homogeneous 87Sr/86Sr ratios (~0.70318), whereas low-MgO scoriae (MgO <~9 wt.%) have higher 87Sr/86Sr ratios (>0.70327); ratios tend to increase with decreasing MgO content. The high-MgO scoriae are aphyric, containing ~5 vol.% olivine microphenocrysts with Mg# of up to 90. In contrast, the low-MgO scoriae have crustal xenocrysts of plagioclase, alkali

  16. Volatiles and the tempo of flood basalt magmatism

    NASA Astrophysics Data System (ADS)

    Black, Benjamin A.; Manga, Michael

    2017-01-01

    Individual flood basalt lavas often exceed 103 km3 in volume, and many such lavas erupt during emplacement of flood basalt provinces. The large volume of individual flood basalt lavas implies correspondingly large magma reservoirs within or at the base of the crust. To erupt, some fraction of this magma must become buoyant and overpressure must be sufficient to encourage failure and dike propagation. The overpressure associated with a new injection of magma is inversely proportional to the total reservoir volume, and as a large magma body heats the surrounding rocks thermally activated creep will relax isotropic overpressure more rapidly. Here, we examine the viability of buoyancy overpressure as a trigger for continental flood basalt eruptions. We employ a new one-dimensional model that combines volatile exsolution, bubble growth and rise, assimilation, and permeable fluid escape from Moho-depth and crustal chambers. We investigate the temporal evolution of degassing and the eruptibility of magmas using the Siberian Traps flood basalts as a test case. We suggest that the volatile inventory set during mantle melting and redistributed via bubble motion controls ascent of magma into and through the crust, thereby regulating the tempo of flood basalt magmatism. Volatile-rich melts from low degrees of partial melting of the mantle are buoyant and erupt to the surface with little staging or crustal interaction. Melts with moderate volatile budgets accumulate in large, mostly molten magma chambers at the Moho or in the lower crust. These large magma bodies may remain buoyant and poised to erupt-triggered by volatile-rich recharge or external stresses-for ∼106 yr. If and when such chambers fail, enormous volumes of magma can ascend into the upper crust, staging at shallow levels and initiating substantial assimilation that contributes to pulses of large-volume flood basalt eruption. Our model further predicts that the Siberian Traps may have released 1019-1020 g of CO2

  17. Megacrystic Clinopyroxene Basalts Sample A Deep Crustal Underplate To The Mount Taylor Volcanic Field, New Mexico

    NASA Astrophysics Data System (ADS)

    Schmidt, M. E.; Schrader, C. M.; Crumpler, L. S.; Wolff, J. A.

    2012-12-01

    The alkaline and compositionally diverse (basanite to high-Si rhyolite) Mount Taylor Volcanic Field (MTVF), New Mexico comprises 4 regions that cover ~75 x 40 km2: (1) Mount Taylor, a large composite volcano and a surrounding field of basaltic vents; (2) Grants Ridge, constructed of topaz rhyolitic ignimbrite and coulees; (3) Mesa Chivato, a plateau of alkali basalts and mugearitic to trachytic domes; and (4) the Rio Puero basaltic necks. Distributed throughout its history (~3.6 to 1.26 Ma; Crumpler and Goff, 2012) and area (excepting Rio Puerco Necks) is a texturally distinct family of differentiated basalts (Mg# 43.2-53.4). These basalts contain resorbed and moth-eaten megacrysts (up to 2 cm) of plagioclase, clinopyroxene, and olivine ±Ti-magnetite ±ilmenite ±rare orthopyroxene. Some megacrystic lava flows have gabbroic cumulate inclusions with mineral compositions similar to the megacrysts, suggesting a common origin. For instance, gabbroic and megacrystic clinopyroxenes form linear positive arrays in TiO2 (0.2-2.3 wt%) with respect to Al2O3 (0.7-9.3 wt%). The lowest Al clinopyroxenes are found in a gabbroic inclusion and are associated with partially melted intercumulus orthopyroxene. Megacrystic and gabbroic plagioclase (An 41-80) in 4 representative thin sections were analyzed for 87Sr/86Sr by Laser Ablation ICP-MS. 87Sr/86Sr values for the suite range from 0.7036 to 0.7047. The low 87Sr/86Sr plagioclases (0.7036 to 0.7037) are associated with high Ti-Al clinopyroxenes. Likewise, the higher 87Sr/86Sr plagioclases (0.7043 to 0.7047) are associated with the low-Al clinopyroxenes. Taken together, these megacrysts track the differentiation of an intrusive body (or related bodies) from alkaline to Si-saturated conditions by fractional crystallization and crustal assimilation. The intrusive body likely underplates portions of the MTVF that have generated silicic magmas (Mount Taylor, Grants Ridge, Mesa Chivato). Although disequilibrium is implied by resorbed

  18. Characterization of mesostasis regions in lunar basalts: Understanding late-stage melt evolution and its influence on apatite formation

    NASA Astrophysics Data System (ADS)

    Potts, Nicola J.; TartèSe, Romain; Anand, Mahesh; Westrenen, Wim; Griffiths, Alexandra A.; Barrett, Thomas J.; Franchi, Ian A.

    2016-09-01

    Recent studies geared toward understanding the volatile abundances of the lunar interior have focused on the volatile-bearing accessory mineral apatite. Translating measurements of volatile abundances in lunar apatite into the volatile inventory of the silicate melts from which they crystallized, and ultimately of the mantle source regions of lunar magmas, however, has proved more difficult than initially thought. In this contribution, we report a detailed characterization of mesostasis regions in four Apollo mare basalts (10044, 12064, 15058, and 70035) in order to ascertain the compositions of the melts from which apatite crystallized. The texture, modal mineralogy, and reconstructed bulk composition of these mesostasis regions vary greatly within and between samples. There is no clear relationship between bulk-rock basaltic composition and that of bulk-mesostasis regions, indicating that bulk-rock composition may have little influence on mesostasis compositions. The development of individual melt pockets, combined with the occurrence of silicate liquid immiscibility, exerts greater control on the composition and texture of mesostasis regions. In general, the reconstructed late-stage lunar melts have roughly andesitic to dacitic compositions with low alkali contents, displaying much higher SiO2 abundances than the bulk compositions of their host magmatic rocks. Relevant partition coefficients for apatite-melt volatile partitioning under lunar conditions should, therefore, be derived from experiments conducted using intermediate compositions instead of compositions representing mare basalts.

  19. Columbia River flood basalts from a centralized crustal magmatic system

    NASA Astrophysics Data System (ADS)

    Wolff, J. A.; Ramos, F. C.; Hart, G. L.; Patterson, J. D.; Brandon, A. D.

    2008-03-01

    The Columbia River Basalt Group in the northwestern United States, comprising about 230,000 cubic kilometres of rock, exhibits unusual patterns in lava distribution, geochemistry and its apparent relationship to regional tectonics. Consequently, there is little consensus on the origin of its magmas. Here, we examine the isotopic ratios of Sr, Nd, Pb and Os and trace-element abundances in Columbia River basalts. The results suggest that most of the lava was produced when magma derived from a mantle plume assimilated continental crust in a central magma chamber system located at the boundary between the North American craton and the accreted terranes of Idaho and Oregon. Other, related basalts are the product of mixing between the mantle plume and different types of regional upper mantle. Magma was then transported over a wide region by an extensive network of dykes, a process that has been identified in other flood basalt provinces as well. Interactions of the plume with surrounding upper mantle, and of mantle-derived magmas with regional crust, provide a relatively simple model to explain the more unusual features of the main-phase Columbia River Basalts.

  20. Bubble Growth in Lunar Basalts

    NASA Astrophysics Data System (ADS)

    Zhang, Y.

    2009-05-01

    Although Moon is usually said to be volatile-"free", lunar basalts are often vesicular with mm-size bubbles. The vesicular nature of the lunar basalts suggests that they contained some initial gas concentration. A recent publication estimated volatile concentrations in lunar basalts (Saal et al. 2008). This report investigates bubble growth on Moon and compares with that on Earth. Under conditions relevant to lunar basalts, bubble growth in a finite melt shell (i.e., growth of multiple regularly-spaced bubbles) is calculated following Proussevitch and Sahagian (1998) and Liu and Zhang (2000). Initial H2O content of 700 ppm (Saal et al. 2008) or lower is used and the effect of other volatiles (such as carbon dioxide, halogens, and sulfur) is ignored. H2O solubility at low pressures (Liu et al. 2005), concentration-dependent diffusivity in basalt (Zhang and Stolper 1991), and lunar basalt viscosity (Murase and McBirney 1970) are used. Because lunar atmospheric pressure is essentially zero, the confining pressure on bubbles is completely supplied by the overlying magma. Due to low H2O content in lunar basaltic melt (700 ppm H2O corresponds to a saturation pressure of 75 kPa), H2O bubbles only grow in the upper 16 m of a basalt flow or lake. A depth of 20 mm corresponds to a confining pressure of 100 Pa. Hence, vesicular lunar rocks come from very shallow depth. Some findings from the modeling are as follows. (a) Due to low confining pressure as well as low viscosity, even though volatile concentration is very low, bubble growth rate is extremely high, much higher than typical bubble growth rates in terrestrial melts. Hence, mm-size bubbles in lunar basalts are not strange. (b) Because the pertinent pressures are so low, bubble pressure due to surface tension plays a main role in lunar bubble growth, contrary to terrestrial cases. (c) Time scale to reach equilibrium bubble size increases as the confining pressure increases. References: (1) Liu Y, Zhang YX (2000) Earth

  1. Phonolites and peralkaline rhyolites from a single magma source in the mantle : A new look at some Black Hills rocks

    SciTech Connect

    Kirchner, J.G. . Dept. of Geography-Geology)

    1993-03-01

    A re-evaluation of existing data from the Deer Mountain-Terry Peak-Sugarloaf Mountain area of the Black Hills, plus some new data, suggests the real possibility that both silica-undersaturated and silica-oversaturated alkaline-peralkaline rocks evolved from the same mantle-derived parent magma. Mineralogically, aegirine rhyolites, phonolites, a minette and the mantle are linked by an association of Mg-rich olivine-phlogopite structures, zenocrystic phlogopite and diopside-cored pyroxene phenocrysts. Trends of silica vs. major elements, trace elements (V,Sc,Ni) and MgO/FeOt are continuous and preclude being fortuitous. Peralkalinity also increases with silica in a well-defined trend. Increasing ferric oxide to total iron oxide indicates increasing oxygen fugacity with silica saturation. A mantle origin for the phonolites is supported by Sr-isotope data of Beintema (1986) and Beintema and Montgomery (1986). Higher Sr-isotope ratios for the aegirine rhyolites, suggesting a lower crustal origin, actually may result from magmatic processes, as shown by others for ocean island basalt-phonolite-comendite associations. Early fractionation of mafic phases drives trends away from the Ne-minimum on the residua diagram, indicating that magma evolution took place above residua temperatures, thus avoiding the thermal divide. Later fractionation of alkali feldspars accounts for variation in the aegirine rhyolites. Rising alkalies and oxygen explain variations in peralkalinity and ferric iron content. Pressure-dependent immiscibility possibly may be the cause of a silica gap in rock types, as rocks with low quartz contents are not found, except as phaneritic inclusions. A model is suggested in which either a fractionating minette or trachyte magma could yield the series of rocks under study.

  2. 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

    /86Sr)i that are too high, and ??(T)Nd that are too low, to represent the expected isotopic composition of typical depleted mantle. However, gabbro xenoliths with typical depleted-mantle isotopic compositions are found in the plutons. This situation requires either an additional enriched mantle component to provide the parental magma for these plutons, or some mechanism of crustal contamination of the parent magma that did not cause significant crystallization and differentiation of the magma to more felsic compositions. Thermodynamic modeling indicates that assimilation of alkali- and water-rich partial melt of the metapelite country rock by fractionating, near-liquidus basaltic magma could cause significant contamination while suppressing significant crystallization and differentiation.

  3. Strontium Isotopes and Magma Dynamics

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  4. Geochemical characteristics of the "Mid-Alkaline Basalts" from the "adventive cones" of Piton de la Fournaise volcano (La Réunion Island)

    NASA Astrophysics Data System (ADS)

    Valer, Marina; Bachèlery, Patrick; Schiano, Pierre; Upton, Brian G. J.

    2016-04-01

    Piton de la Fournaise, the youngest volcano of La Réunion Island, is renowned for being frequently active. Its lavas (younger than ~450 ka) have been subdivided into three compositional groups (see Lénat et al. 2012 for a review). Almost all recent and historical lavas belong to two of these groups: "cotectic basalts" and "olivine-rich basalts", marked by a constant CaO/Al2O3 ratio of ~0.8, and MgO content ranging from 5 to 30 wt % reflecting different degrees of olivine accumulation. Whereas that current activity is mainly located within the "Enclos Fouqué" caldera, ~100 strombolian cones lie on the volcano's flanks, thought to date from ~300 years to a few thousand years. Our study focuses on these "adventive cones", by studying bulk-rock major and trace element compositions, isotopic compositions, mineral phases and olivine-hosted melt inclusions. The bulk-rock compositions correspond to the third group of the Piton de la Fournaise lavas (see above), called the "mid-alkaline basalts". They mainly consist of magnesian basalts at 7.55 - 10.24 wt% MgO and CaO/Al2O3 values down to 0.55. At constant MgO content, this group shows higher alkali content and a relative deficiency in Ca compared to the historic basalts. The "adventive cones" lavas usually contain magnesian olivine crystals (Fo > 86). Such crystals are not at the equilibrium with their host lava, raising thus the question of the recycling processes. The volatile contents of these olivine-hosted melt inclusions (work in progress) will allow to determine if such magnesian olivine crystals come from deep storage levels, as previously proposed by Bureau et al. (1998; 1999). The specific geochemistry the "adventive cones" lavas is attributed either to a high-pressure fractionation of a clinopyroxene-rich assemblage (Albarède et al. 1997), or to an assimilation process involving wehrlite-gabbro cumulates (e.g. Salaün et al. 2010). Although the trace element data show that the source of these magmas is

  5. Phase relations of a high-Mg basalt from the Aleutian Island arc - Implications for primary island arc basalts and high-Al basalts

    NASA Technical Reports Server (NTRS)

    Gust, D. A.; Perfit, M. R.

    1987-01-01

    An experimental investigation of a primitive high-Mg basalt, MK-15, collected from lava flows of the Unalaska Island in the Aleutian Island arc has been conducted in order to study primary and parental island arc basalts and the development of island arc magmas. The results suggest a model in which high-Al basalts are generated by moderate amounts of crystal fractionation from more primitive (high Mg/Mg + Fe, lower Al2O3) basaltic magmas near the arc crust-mantle boundary. Somewhere between 20-30 depth, significant amounts of clinopyroxene and olivine, with lesser amounts of spinel and possibly amphibole, fractionate, forming layer of olivine-clinopyroxenite at the base of the arc crust.

  6. Magma vesiculation and pyroclastic volcanism on Venus

    NASA Astrophysics Data System (ADS)

    Garvin, J. B.; Head, J. W.; Wilson, L.

    1982-11-01

    Theoretical consideration of the magma vesiculation process under observed and inferred venusian surface conditions suggests that vesicles should form in basaltic melts, especially if CO2 is the primary magmatic volatile. However, the high surface atmospheric pressure (about 90 bars) and density on Venus retard bubble coalescence and disruption sufficiently to make explosive volcanism unlikely. The products of explosive volcanism (fire fountains, convecting eruption clouds, pyroclastic flows, and topography-mantling deposits of ash, spatter, and scoria) should be rare on Venus, and effusive eruptions should dominate. The volume fraction of vesicles in basaltic rocks on Venus are predicted to be less than in chemically similar rocks on earth. Detection of pyroclastic landforms or eruption products on Venus would indicate either abnormally high volatile contents of Venus magmas (2.5-4 wt%) or different environmental conditions (e.g., lower atmospheric pressure) in previous geologic history.

  7. Thermochemistry and melting properties of basalt

    NASA Astrophysics Data System (ADS)

    Bouhifd, M. A.; Besson, P.; Courtial, P.; Gérardin, C.; Navrotsky, A.; Richet, P.

    2007-06-01

    The heat capacities of the liquid, glassy and crystalline phases of an alkali basalt have been determined from relative enthalpies measured between 400 and 1,800 K. Values given by available models of calculation generally agree to within 2% of these results. As derived from the new data and the enthalpy of vitrification measured at 973 K by oxide-melt drop solution calorimetry for the same sample, the enthalpy of fusion of this basalt increases from 15.4 kJ/mol at 1,000 K to 33.6 kJ/mol at 1,800 K. Comparisons between the enthalpies of fusion of basalt and model compositions confirm the small magnitude of the enthalpy of mixing between the molten mineral components of the liquids. Minor variations in the chemical composition have only a small effect in the heat capacity and the enthalpy of melting of basalt. The enthalpies of formation at 298 K from the oxides of the crystallized and glass phases of this alkali basalt are -112.2 and -98.5 kJ/mol, respectively, for a gram formula weight based on one mole of oxide components.

  8. Experimental Study of Lunar and SNC Magmas

    NASA Technical Reports Server (NTRS)

    Rutherford, Malcolm J.

    2004-01-01

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

  9. Chlorine in Lunar Basalts

    NASA Technical Reports Server (NTRS)

    Barnes, J. J.; Anand, M.; Franchi, I. A.

    2017-01-01

    In the context of the lunar magma ocean (LMO) model, it is anticipated that chlorine (and other volatiles) should have been concentrated in the late-stage LMO residual melts (i.e., the dregs enriched in incompatible elements such as K, REEs, and P, collectively called KREEP, and in its primitive form - urKREEP, [1]), given its incompatibility in mafic minerals like olivine and pyroxene, which were the dominant phases that crystallized early in the cumulate pile of the LMO (e.g., [2]). When compared to chondritic meteorites and terrestrial rocks (e.g., [3-4]), lunar samples often display heavy chlorine isotope compositions [5-9]. Boyce et al. [8] found a correlation between delta Cl-37 (sub Ap) and bulk-rock incompatible trace elements (ITEs) in lunar basalts, and used this to propose that early degassing of Cl (likely as metal chlorides) from the LMO led to progressive enrichment in remaining LMO melt in Cl-37over Cl-35- the early degassing model. Barnes et al. [9] suggested that relatively late degassing of chlorine from urKREEP (to yield delta Cl-37 (sub urKREEP greater than +25 per mille) followed by variable mixing between KREEPy melts and mantle cumulates (characterized by delta Cl-370 per mille) could explain the majority of Cl isotope data from igneous lunar samples. In order to better understand the processes involved in giving rise to the heavy chlorine isotope compositions of lunar samples, we have performed an in situ study of chlorine isotopes and abundances of volatiles in lunar apatite from a diverse suite of lunar basalts spanning a range of geochemical types.

  10. Climate Throughout Geologic Time Has Been Controlled Primarily by the Balance Between Cooling Caused by Major Explosive Eruptions of Evolved Magmas Typical of Island Arcs and Warming Caused by Voluminous Effusive Eruptions of Basaltic Magma Typical of Subaerial Ocean Ridges and Island Chains

    NASA Astrophysics Data System (ADS)

    Ward, P. L.

    2014-12-01

    Most volcanic eruptions deplete ozone ~6% for a few years, allowing more high-energy, ultraviolet-B radiation to warm earth. Record low levels of total column ozone followed the 1991 explosive eruption of Pinatubo. Yet 6% depletion also followed the smaller and more effusive eruptions of Eyjafjallajökull (2010) and Grímsvötn (2011) in Iceland. Explosive volcanoes also eject 10-20 megatons of sulfur dioxide into the lower stratosphere, forming sulfuric-acid aerosols that reflect and diffuse sunlight causing a net cooling of ~0.5°C for 3 years. High rates of explosive volcanos cool earth into ice ages while high rates of effusive basaltic volcanism in Iceland between 11,500 and 9,500 years ago clearly warmed Earth out of the last ice age depositing sulfate recorded in ice cores in Greenland. Basalts from these eruptions are observed as tuyas in Iceland dated during this period. The 25 Dansgaard-Oeschger abrupt warmings are contemporaneous with increased sulfate in Greenland and with the few older dates available for tuyas in Iceland. Extensive flood basalts were formed during the Paleocene Eocene Thermal Maximum and during times of most major mass extinctions when global temperatures rose substantially, with fossil evidence for ozone depletion. Greenhouse-gas theory assumes electromagnetic radiation travels through space as waves and therefore thermal energy reaching earth is proportional to the square of wave amplitude. Thus the change in energy reaching Earth due to ozone depletion is considered small compared to infrared energy absorbed by greenhouse gases. But waves travel in matter and there is no matter in space. Electromagnetic energy is transmitted as frequency, as shown by radio signals, where energy equals frequency times the Planck constant. Thus thermal energy reaching earth when ozone is depleted is 50 times thermal energy involved in greenhouse gases. Global warming from 1970 to 1998 was caused primarily by 3% ozone depletion due to anthropogenic

  11. Germanium abundances in lunar basalts - Evidence of mantle metasomatism?

    NASA Technical Reports Server (NTRS)

    Dickinson, T.; Taylor, G. J.; Keil, K.; Bild, R. W.

    1989-01-01

    To fill in gaps in the present Ge database, mare basalts were analyzed for Ge and other elements by RNAA and INAA. Mare basalts from Apollo 11, 12, 15, and 17 landing sites are rather uniform in Ge abundance, but Apollo 14 aluminous mare basalts and KREEP are enriched in Ge by factors of up to 300 compared to typical mare basalts. These Ge enrichments are not associated with other siderophile element enrichments and thus are not due to differences in the amount of metal segregated during core formation. Based on crystal-chemical and interelement variations, it does not appear that the observed Ge enrichments are due to silicate liquid immiscibility. KREEP basalt source regions may have been metasomatized, and Apollo 14 aluminous mare basalt magmas may have become enriched in Ge by interacting with these metasomatized areas. The presence of volatile- and Ge-rich regions in the moon suggest that the moon was never totally molten.

  12. Hotspots, basalts, and the evolution of the mantle.

    PubMed

    Anderson, D L

    1981-07-03

    The trace element concentration patterns of continental and ocean island basalts and of mid-ocean ridge basalts are complementary. The relative sizes of the source regions for these fundamentally different basalt types can be estimated from the trace element enrichment-depletion patterns. Their combined volume occupies most of the mantle above the 670 kilometer discontinuity. The source regions separated as a result of early mantle differentiation and crystal fractionation from the resulting melt. The mid-ocean ridge basalts source evolved from an eclogite cumulate that lost its late-stage enriched fluids at various times to the shallower mantle and continental crust. The mid-ocean ridge basalts source is rich in garnet and clinopyroxene, whereas the continental and ocean island basalt source is a garnet peridotite that has experienced secondary enrichment. These relationships are consistent with the evolution of a terrestrial magma ocean.

  13. Loki Patera: A Magma Sea Story

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  14. Convection and mixing in magma chambers

    NASA Astrophysics Data System (ADS)

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

    1986-08-01

    released continuously during crystallization and rises to the top of the chamber with little mixing. Overturning of a gas-rich mafic lower layer into a cooler silicic layer can cause a sudden quenching, with the rapid release of gas which could trigger an explosive eruption. Mixing can also occur during eruption, as two layers are drawn up simultaneously from a stratified chamber when a critical flow velocity is exceeded, and they then mix in the outlet vent. Laboratory experiments suggest, however, that magma mixing is inhibited by large viscosity differences, both during the filling and emptying of a magma chamber. Scaling these results to magmas indicates that a basaltic magma can flow into the bottom of a chamber containing rhyolite with little or no mixing between them, and that these two magma types can also flow out through the same exit vent with limited mixing. Each of the phenomena discussed in this review has been studied, at least in a qualitative way, using laboratory experiments to identify and understand a significant physical process occurring in magma chambers. The field of geological fluid mechanics and its application to these problems is still very new, and further advances seem assured as new phenomena are identified and more detailed and quantitative analogue experiments are developed to study them.

  15. Chemical Zoning of Feldspars in Lunar Granitoids: Implications for the Origins of Lunar Silicic Magmas

    NASA Technical Reports Server (NTRS)

    Mills, R. D; Simon, J. I.; Alexander, C.M. O'D.; Wang, J.; Christoffersen, R.; Rahman, Z..

    2014-01-01

    Fine-scale chemical and textural measurements of alkali and plagioclase feldspars in the Apollo granitoids (ex. Fig. 1) can be used to address their petrologic origin(s). Recent findings suggest that these granitoids may hold clues of global importance, rather than of only local significance for small-scale fractionation. Observations of morphological features that resemble silicic domes on the unsampled portion of the Moon suggest that local, sizable net-works of high-silica melt (>65 wt % SiO2) were present during crust-formation. Remote sensing data from these regions suggest high concentrations of Si and heat-producing elements (K, U, and Th). To help under-stand the role of high-silica melts in the chemical differentiation of the Moon, three questions must be answered: (1) when were these magmas generated?, (2) what was the source material?, and (3) were these magmas produced from internal differentiation. or impact melting and crystallization? Here we focus on #3. It is difficult to produce high-silica melts solely by fractional crystallization. Partial melting of preexisting crust may therefore also have been important and pos-sibly the primary mechanism that produced the silicic magmas on the Moon. Experimental studies demonstrate that partial melting of gabbroic rock under mildly hydrated conditions can produce high-silica compositions and it has been suggested by that partial melting by basaltic underplating is the mechanism by which high-silica melts were produced on the Moon. TEM and SIMS analyses, coordinated with isotopic dating and tracer studies, can help test whether the minerals in the Apollo granitoids formed in a plutonic setting or were the result of impact-induced partial melting. We analyzed granitoid clasts from 3 Apollo samples: polymict breccia 12013,141, crystalline-matrix breccia 14303,353, and breccia 15405,78

  16. Degassing-driven crystallisation in basalts

    NASA Astrophysics Data System (ADS)

    Applegarth, L. J.; Tuffen, H.; James, M. R.; Pinkerton, H.

    2013-01-01

    Syn-eruptive crystallisation can drastically increase magma viscosity, with profound implications for conduit dynamics, lava emplacement and volcanic hazards. There is growing evidence that crystallisation is not only cooling-driven, but can also occur almost isothermally during decompression-induced degassing on ascent from depth. Here we review field and experimental evidence for degassing-driven crystallisation in a range of magma compositions. We then present new results showing, for the first time, experimental evidence for this process in basaltic magma. Our experiments use simultaneous thermogravimetric analysis and differential scanning calorimetry coupled with mass spectrometry (TGA-DSC-MS) to monitor degassing patterns and thermal events during heating and cooling of porphyritic basaltic samples from Mt. Etna, Italy. The partly degassed samples, which contained 0.39-0.81 wt.% total volatiles in the glass fraction, were subjected to two cycles of heating from ambient to 1250 °C. On the first heating, TGA data show that 30-60% of the total volatiles degassed slowly at < 1050 °C, and that the degassing rate increased rapidly above this temperature. DSC data indicate that this rapid increase in the degassing rate was closely followed (≤ 3.4 min) by a strongly exothermic event, which is interpreted as crystallisation. Enthalpies measured for this event suggest that up to 35% of the sample crystallises, a value supported by petrographic observations of samples quenched after the event. As neither degassing nor crystallisation was observed at high temperature during the second heating cycle we infer that the events on first heating constitute degassing-driven crystallisation. The rapidity and magnitude of the crystallisation response to degassing indicates that this process may strongly affect the rheology of basaltic magma in shallow conduits and lava flows, and thus influence the hazards posed by basaltic volcanism.

  17. Pb isotopic heterogeneity in basaltic phenocrysts

    SciTech Connect

    Bryce, Julia G.; DePaolo, Donald J.

    2002-06-01

    The Pb isotopic compositions of phenocrystic phases in young basaltic lavas have been investigated using the Getty-DePaolo method (Getty S. J. and DePaolo D. J. [1995] Quaternary geochronology by the U-Th-Pb method. Geochim. Cosmochim. Acta 59, 3267 3272), which allows for the resolution of small isotopic differences. Phenocryst, matrix, and whole rock analyses were made on samples from the 17 Myr-old Imnaha basalts of the Columbia River Group, a zero-age MORB from the Mid-Atlantic Ridge, and a ca. 260 kyr-old tholeiite from Mount Etna. Plagioclase feldspar phenocrysts have low-(U, Th)/Pb, and in each sample the plagioclase has significantly lower 206Pb/207Pb and 208Pb/207Pb values than whole rock, matrix, and magnetite-rich separates. The Pb isotopic contrast between plagioclase and matrix/whole rock is found in three samples with varying grain sizes (0.5 2 cm for the Imnaha basalt and MORB and <1 mm for the Etna sample) from different tectonic settings, suggesting that these results are not unique. The isotopic contrasts are only slightly smaller in magnitude than the variations exhibited by whole rock samples from the region. The Imnaha basalts also have Sr isotopic heterogeneity evident only in plagioclase phenocrysts, but the MORB and Etna lavas do not. The isotopic heterogeneities reflect magma mixing, and indicate that isotopically diverse magmas were mixed together just prior to eruption. The results reinforce indications from melt inclusion studies that magma source region isotopic heterogeneities have large amplitudes at short length scales, and that the isotopic variations imparted to the magmas are not entirely homogenized during segregation and transport processes.

  18. Interpreting chemical compositions of small scale basaltic systems: A review

    NASA Astrophysics Data System (ADS)

    McGee, Lucy E.; Smith, Ian E. M.

    2016-10-01

    Small scale basaltic magmatic systems occur in all of the major tectonic environments of planet Earth and are characteristically expressed at the Earth's surface as fields of small monogenetic cones. The chemical compositions of the materials that make up these cones reflect processes of magma generation and differentiation that occur in their plumbing system. The volumes of magmas involved are very small and significantly their compositional ranges reveal remarkably complex processes which are overwhelmed or homogenized in larger scale systems. Commonly, compositions are basaltic, alkalic and enriched in light rare earth elements and large ion lithophile elements, although the spectrum extends from highly enriched nephelinites to subalkalic and tholeiitic basalts. Isotopic analyses of rocks from volcanic fields almost always display compositions which can only be explained by the interaction of two or more mantle sources. Ultimately their basaltic magmas originate by small scale melting of mantle sources. Compositional variety is testament to melting processes at different depths, a range of melting proportions, a heterogeneous source and fractionation, magma mixing and assimilation within the plumbing system that brings magmas to the surface. The fact that such a variety of compositions is preserved in a single field shows that isolation of individual melting events and their ascent is an important and possibly defining feature of monogenetic volcanism, as well as the window their chemical behavior provides into the complex process of melt generation and extraction in the Earth's upper mantle.

  19. Germanium abundances in lunar basalts: Evidence of mantle metasomatism

    SciTech Connect

    Dickinson, T.; Taylor, G.J.; Keil, T.K.; Bild, R.W.

    1988-01-01

    To fill in gaps in the present Ge data base, mare basalts were analyzed for Ge and other elements by RNAA and INAA. Mare basalts from Apollo 11, 12, 15, 17 landing sites are rather uniform in Ge abundance, but Apollo 14 aluminous mare basalts and KREEP are enriched in Ge by factors of up to 300 compared to typical mare basalts. These Ge enrichments are not associated with other siderophile element enrichments and, thus, are not due to differences in the amount of metal segregated during core formation. Based on crystal-chemical and inter-element variations, it does not appear that the observed Ge enrichments are due to silicate liquid immiscibility. Elemental ratios in Apollo 14 aluminous mare basalts, green and orange glass, average basalts and KREEP suggest that incorporation of late accreting material into the source regions or interaction of the magmas with primitive undifferentiated material is not a likely cause for the observed Ge enrichments. We speculate that the most plausible explanation for these Ge enrichments is complexing and concentration of Ge by F, Cl or S in volatile phases. In this manner, the KREEP basalt source regions may have been metasomatized and Apollo 14 aluminous mare basalt magmas may have become enriched in Ge by interacting with these metasomatized areas. The presence of volatile- and Ge-rich regions in the Moon suggests that the Moon was never totally molten. 71 refs., 1 fig., 6 tabs.

  20. Hanford basalt flow mineralogy

    SciTech Connect

    Ames, L.L.

    1980-09-01

    Mineralogy of the core samples from five core wells was examined in some detail. The primary mineralogy study included an optical examination of polished mounts, photomicrographs, chemical analyses of feldspars, pyroxenes, metallic oxides and microcrystalline groundmasses and determination from the chemical analyses of the varieties of feldspars, pyroxenes and metallic oxides. From the primary mineralogy data, a firm understanding of the average Hanford basalt flow primary mineralogy emerged. The average primary feldspar was a laboradorite, the average pyroxene was an augite and the average metallic oxide was a solid solution of ilmenite and magnetite. Secondary mineralization consisted of vug filling and joint coating, chiefly with a nontronite-beidellite clay, several zeolites, quartz, calcite, and opal. Specific flow units also were examined to determine the possibility of using the mineralogy to trace flows between core wells. These included units of the Pomona, the Umatilla and a high chromium flow just below the Huntzinger. In the Umatilla, or high barium flow, the compositional variation of the feldspars was unique in range. The pyroxenes in the Pomona were relatively highly zoned and accumulated chromium. The high chromium flow contained chromium spinels that graded in chromium content into simple magnetites very low in chromium content. A study of the statistical relationships of flow unit chemical constituents showed that flow unit constituents could be roughly correlated between wells. The probable cause of the correlation was on-going physical-chemical changes in the source magma.

  1. Thermal and rheological controls on magma migration in dikes: Examples from the east rift zone of Kilauea volcano, Hawaii

    NASA Technical Reports Server (NTRS)

    Parfitt, E. A.; Wilson, L.; Pinkerton, H.

    1993-01-01

    Long-lived eruptions from basaltic volcanoes involving episodic or steady activity indicate that a delicate balance has been struck between the rate of magma cooling in the dike system feeding the vent and the rate of magma supply to the dike system from a reservoir. We describe some key factors, involving the relationships between magma temperature, magma rheology, and dike geometry that control the nature of such eruptions.

  2. Dredged trachyte and basalt from kodiak seamount and the adjacent aleutian trench, alaska.

    PubMed

    Forbes, R B; Hoskin, C M

    1969-10-24

    Blocky fragments of aegirine-augite trachyte (with accompanying icerafted gravels.) were recovered from the upper slopes of Kodiak Seamount in several dredge hauls. An alkali basalt pillow segment was also dredged from a moatlike depression, at a depth of 5000 meters, near the west base of the seamount. These retrievals confirm the volcanic origin of Kodiak Seamount and further support the view of Engel, Engel, and Havens that the higher elevations of seamounts are composed of alkali basalts or related variants.

  3. Carbon solution and partitioning between metallic and silicate melts in a shallow magma ocean: Implications for the origin and distribution of terrestrial carbon

    NASA Astrophysics Data System (ADS)

    Dasgupta, Rajdeep; Chi, Han; Shimizu, Nobumichi; Buono, Antonio S.; Walker, David

    2013-02-01

    The origin of bulk silicate Earth carbon inventory is unknown and the fate of carbon during the early Earth differentiation and core formation is a missing link in the evolution of the terrestrial carbon cycle. Here we present high pressure (P)-temperature (T) experiments that offer new constraints upon the partitioning of carbon between metallic and silicate melt in a shallow magma ocean. Experiments were performed at 1-5 GPa, 1600-2100 °C on mixtures of synthetic or natural silicates (tholeiitic basalt/alkali basalt/komatiite/fertile peridotite) and Fe-Ni-C ± Co ± S contained in graphite or MgO capsules. All the experiments produced immiscible Fe-rich metallic and silicate melts at oxygen fugacity (fO2) between ˜IW-1.5 and IW-1.9. Carbon and hydrogen concentrations of basaltic glasses and non-glassy quenched silicate melts were determined using secondary ionization mass spectrometry (SIMS) and speciation of dissolved C-O-H volatiles in silicate glasses was studied using Raman spectroscopy. Carbon contents of metallic melts were determined using both electron microprobe and SIMS. Our experiments indicate that at core-forming, reduced conditions, carbon in deep mafic-ultramafic magmas may dissolve primarily as various hydrogenated species but the total carbon storage capacity, although is significantly higher than solubility of CO2 under similar conditions, remains low (<500 ppm). The total carbon content in our reduced melts at graphite saturation increases with increasing melt depolymerization (NBO/T), consistent with recent spectroscopic studies, and modestly with increasing hydration. Carbon behaves as a metal-loving element during core-mantle separation and our experimental DCmetal/silicate varies between ˜4750 and ⩾150 and increases with increasing pressure and decreases with increasing temperature and melt NBO/T. Our data suggest that if only a trace amount of carbon (˜730 ppm C) was available during early Earth differentiation, most of it was

  4. Occurrence and Mineral Chemistry of High Pressure Phases, Potrillo Basalt, Southcentral New Mexico. M.S. Thesis Final Technical Report, 1 Jun. 1980 - 31 May 1982

    NASA Technical Reports Server (NTRS)

    Sheffield, T. M.

    1982-01-01

    The presence of an older plagioclase-rich basalt and a younger olivine-rich basalt were confirmed by modal and chemical analysis. Chemical analysis also confirmed the presence of flows that are tholeiitic in composition and could be remnants of an original tholeittic parent magma. Eruptions from different levels of a differentiated magma chamber are proposed to account for the two members.

  5. Petrogenesis of coeval sodic and potassic alkaline magmas at Spanish Peaks, Colorado: Magmatism related to the opening of the Rio Grande rift

    NASA Astrophysics Data System (ADS)

    Lord, A. Brooke Hamil; McGregor, Heath; Roden, Michael F.; Salters, Vincent J. M.; Sarafian, Adam; Leahy, Rory

    2016-07-01

    Approximately coeval, relatively primitive (∼5-10% MgO with exception of a trachyandesite) alkaline mafic dikes and sills at or near Spanish Peaks, CO are divided into relatively sodic and potassic varieties on the basis of K2O/Na2O. Many of these dikes are true lamprophyres. In spite of variable alkali element ratios, the alkaline rocks share a number of geochemical similarities: high LIL element contents, high Ba and similar Sr, Nd and Hf isotope ratios near that of Bulk Earth. One important difference is that the potassic rocks are characterized by lower Al2O3 contents, typically less than 12 wt.%, than the sodic dikes/sills which typically have more than 13 wt.% Al2O3, and this difference is independent of MgO content. We attribute the distinct Al2O3 contents to varying pressure during melting: a mica-bearing, Al-poor vein assemblage for the potassic magmas melted at higher pressure than an aluminous amphibole-bearing vein assemblage for the sodic magmas. Remarkable isotopic and trace element similarities with approximately contemporaneous, nearby Rio Grande rift-related basalts in the San Luis Valley, indicate that the magmatism at Spanish Peaks was rift-related, and that lithosphere sources were shared between some rift magmas and those at Spanish Peaks. High Zn/Fe ratios in the Spanish Peaks mafic rocks point to a clinopyroxene- and garnet-rich source such as lithosphere veined by pyroxenite or eclogite. Lithospheric melting was possibly triggered by foundering of cool, dense lithosphere beneath the Rio Grande rift during the initiation of rifting with the potassic parent magmas generated by higher pressure melting of the foundered lithosphere than the sodic parent magmas. This process, caused by gravitational instability of the lithosphere (Elkins-Tanton, 2007) may be common beneath active continental rifts.

  6. Trace-element modelling of mare basalt parental melts: Implications for a heterogeneous lunar mantle

    NASA Astrophysics Data System (ADS)

    Hallis, L. J.; Anand, M.; Strekopytov, S.

    2014-06-01

    The heterogeneous-source model of mare basalt formation indicates that Lunar Magma Ocean (LMO) overturn produced an uneven mixture of early-formed olivine and pyroxene, and late-formed, ilmenite-rich cumulates, which subsequently partially melted to give rise to mare magmas. These heterogeneous cumulate source regions would not only have been characterised by different mineral modal abundances, but also by different trace element compositions. The aim of this work was to investigate the petrology and geochemistry of a diverse suite of Apollo mare basalts, and utilise trace-element modelling in order to understand their petrogenetic history. Chemical modelling confirms that the mare basalts were produced by relatively small degrees of partial melting (<10%) of the LMO cumulates, and that the dominant melting type (batch vs. fractional) varies among different basalt groups. Similarly, single-source mineralogy cannot be applied to all mare basalt types, confirming that the lunar mantle was heterogeneous at the time of generation of mare magmas. Plagioclase is not required in the source of most mare basalts, with the notable exception of the Apollo 14 high-Al basalts. Addition of more than 1% plagioclase to the source of other basalts produces weaker negative Eu anomalies than those observed in the samples. AFC calculations demonstrate the compositional differences between materials assimilated into the Apollo 14 high-Al and Apollo 11 high-K mare basalt partial melts, highlighting the complexities of mare basalt petrogenesis.

  7. New Insights to the Mid Miocene Calc-alkaline Lavas of the Strawberry Volcanics, NE Oregon Surrounded by the Coeval Tholeiitic Columbia River Basalt Province

    NASA Astrophysics Data System (ADS)

    Steiner, A. R.; Streck, M. J.

    2013-12-01

    The Strawberry Volcanics (SV) of NE Oregon were distributed over 3,400 km2 during the mid-Miocene and comprise a diverse volcanic suite, which span the range of compositions from basalt to rhyolite. The predominant composition of this volcanic suite is calc-alkaline (CA) basaltic andesite and andesite, although tholeiitic (TH) lavas of basalt to andesite occur as well. The coeval flood basalts of the Columbia River province surround the SV. Here we will discuss new ages and geochemical data, and present a new geologic map and stratigraphy of the SV. The SV are emplaced on top of pre-Tertiary accreted terranes of the Blue Mountain Province, Mesozoic plutonic rocks, and older Tertiary volcanic rocks thought to be mostly Oligocene of age. Massive rhyolites (~300 m thick) are exposed mainly along the western flank and underlie the intermediate composition lavas. In the southern portion of this study area, alkali basaltic lavas, thought to be late Miocene to early Pliocene in age, erupted and overlie the SV. In addition, several regional ignimbrites reach into the area. The 9.7 Ma Devine Canyon Tuff and the 7.1 Ma Rattlesnake Tuff also overlie the SV. The 15.9-15.4 Ma Dinner Creek Tuff is mid-Miocene, and clear stratigraphic relationships are found in areas where the tuff is intercalated between thick SV lava flows. All of the basalts of the SV are TH and are dominated by phenocryst-poor (≤2%) lithologies. These basalts have an ophitic texture dominated by plagioclase, clinopyroxene and olivine (often weathered to iddingsite). Basalts and basaltic andesites have olivine Fo #'s ranging from 44 at the rims (where weathered to iddingsite) and as high as 88 at cores. Pyroxene Mg #'s range from 65 to 85. Andesites of the SV are sub-alkaline, and like the basalts, are exceedingly phenocryst-poor (≤3%) with microphenocrysts of plagioclase and lesser pyroxene and olivine, which occasionally occur as crystal clots of ~1-3 mm instead of single crystals. In addition, minimal

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

    SciTech Connect

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

    1988-09-10

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

  9. Neodymium isotopes in flood basalts from the Siberian Platform and inferences about their mantle sources

    PubMed Central

    DePaolo, D. J.; Wasserburg, G. J.

    1979-01-01

    The initial isotopic compositions of Nd and Sr in basalts from the Central Siberian Plateau and other major continental flood basalts are reported. The continental flood basalts appear to be the product of partial melting of mantle sources that consist of relatively primitive undifferentiated material and are clearly distinct from midocean ridge basalts, which sample mantle reservoirs that have been modified by extraction of continental crust earlier in earth history. These observations provide fundamental constraints on models of mantle structure and dynamics. Isotopic effects of crustal contamination are clearly recognizable in some continental flood basalts, but these effects can be distinguished from isotopic patterns inherited from the mantle magma sources. PMID:16592671

  10. Neodymium isotopes in flood basalts from the Siberian Platform and inferences about their mantle sources.

    PubMed

    Depaolo, D J; Wasserburg, G J

    1979-07-01

    The initial isotopic compositions of Nd and Sr in basalts from the Central Siberian Plateau and other major continental flood basalts are reported. The continental flood basalts appear to be the product of partial melting of mantle sources that consist of relatively primitive undifferentiated material and are clearly distinct from midocean ridge basalts, which sample mantle reservoirs that have been modified by extraction of continental crust earlier in earth history. These observations provide fundamental constraints on models of mantle structure and dynamics. Isotopic effects of crustal contamination are clearly recognizable in some continental flood basalts, but these effects can be distinguished from isotopic patterns inherited from the mantle magma sources.

  11. New Insights into Basaltic Balloon Formation during Submarine Eruptions

    NASA Astrophysics Data System (ADS)

    Carey, S.; Kelly, J.; Rosi, M.; Pistolesi, M.; Marani, M.; Roman, C.; Croff Bell, K. L.

    2014-12-01

    Remotely operated vehicle (ROV) explorations in the area of the 1891 Foerstner submarine eruption (Pantelleria, Italy) during cruise NA-018 of the E/V Nautilus has provided the first examination of the vent site of a basaltic balloon-forming eruption. Ultra high-resolution bathymetric mapping defined a mound-like vent morphology in water depths of ~250 meter, constructed dominantly of highly vesicular scoriaceous fragments with minor pillow lava flows. The formation of floating basaltic balloons that reached the surface of the Strait of Sicily during the eruption is attributed to a hybrid Strombolian eruption mechanism that involved pre-concentration of volatiles into gas-rich portions of magma beneath the vent. An important difference of this Strombolian mechanism compared to its subaerial counterpart is the occurrence of buoyant magma discharge in the submarine environment caused by localized high gas contents. The added buoyancy flux modifies the fluid dynamic configuration of magma venting on the seafloor allowing for detachment of highly-inflated parcels of gas-rich magma. Some of these parcels contain large gas cavities that are enveloped in a partially quenched shell and maintain sufficient buoyancy to rise to the sea surface as a basaltic balloon. The majority of the vesicular magma maintains only partial positive buoyancy or negative buoyancy and is explosively fragmented to form large quantities of decimeter-scale fragments that accumulate close to the vent. Formation of the basaltic balloons is thus considered a somewhat accidental process that involves a subset of the total erupted volume of magma during the eruption. Suitable conditions for balloon formation include low magma viscosity, pre-concentration of gas, and moderate pressures (i.e.water depth). The dampening effect of seawater greatly reduces the dispersal of pyroclasts resulting in a mound-like vent morphology compared to subaerial scoria cones typically associated with Strombolian activity.

  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. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  14. Deep magma feeding system of Fuji volcano, Japan

    NASA Astrophysics Data System (ADS)

    Takahashi, E.; Asano, K.; Nakajima, J.

    2012-12-01

    Fuji volcano is known for its perfect cone shape and it is the largest among Japanese Quaternary volcanoes. For the last 100kya, Fuji has erupted dominantly basalt magma (>>99 vol%), but its eruption style changed (from debris flow and tephra dominant Ko-Fuji or Older Fuji, to lava flow dominant Shin-Fuji or Younger Fuji) at ~15 kya BP. The incompatible trace element composition of the magma changed abruptly between Ko-Fuji and Shin-Fuji. The origin of the voluminous yet monotonous basalt production and the simultaneous changes in volcanic style and magma chemistry in Fuji volcano have been discussed but remain unanswered. Here we report the first high-pressure melting experimental results on Fuji Basalt (Hoei-IV, AD1707) and demonstrate that its main magma chamber is located at ca.25km depth (Asano et al, this conference). We also show seismic tomographic images of Fuji volcano for the first time, which reveal the existence of strong upwelling flow in the mantle and its connection to the voluminous lower crustal magma chamber (Fig.1). The chemistry of Fuji magma is buffered by a lower crustal AFC magma chamber located at 25-35km depth. Mantle derived primitive basalt (FeO/MgO~1.0, saturated with mantle peridotite assemblage, oliv+opx+cpx) changes to evolved basalt (FeO/MgO~2.0, saturated with lower crustal gabbroic assemblage, opx+cpx+pl) by the AFC process. Very frequent low frequency earthquakes just above the magma chamber (red circles in Fig.1) may be due to the injection of basalt magma and/or fluids (Ukawa, 2007). The total lack of silica-rich rocks (basaltic andesite and andesite) in Fuji volcano must be due to the special location of the volcano. As shown in Fig.1 (solid line), the plate boundary between the Eurasia plate and the subducting Phillipine sea plate is located just beneath Fuji volcano (~5 km depth). Large tectonic stress and deformation associated with the plate boundary inhibit the survival of a shallow level magma chamber, which would allow

  15. Origin of yellow glasses associated with Apollo 15 KREEP basalt fragments

    NASA Technical Reports Server (NTRS)

    Basu, Abhijit; Holmberg, Beth B.; Molinaroli, Emanuela

    1992-01-01

    The occurrence and chemical compositions of some uncommon yellow to yellowish orange glasses associated with KREEP basalt fragments in Apollo 15 solids of possibly pyroclastic origins are discussed. The glasses show compositional variations that are compatible with igneous fractionation trends. A scenario is described in which late-stage KREEP basalt magmas erupted violently enough to fragment and incorporate previously crystallized basalts and deposited pyroclastic material on the moon.

  16. Ibitira: A basaltic achondrite from a distinct parent asteroid

    NASA Technical Reports Server (NTRS)

    Mittlefehldt, David W.

    2004-01-01

    I have done detailed petrologic study of Ibitira, nominally classified as a basaltic eucrite. The Fe/Mn ratio of Ibitira pyroxenes with <10 mole % wollastonite component is 36.4 0.4, and is well-resolved from those of five basaltic eucrites studied for comparison; 31.2-32.2. Data for the latter completely overlap. Ibitira pyroxenes have lower Fe/Mg than the basaltic eucrite pyroxenes. Thus, the higher Fe/Mn ratio does not reflect a simple difference in oxidation state. Ibitira also has an oxygen isotopic composition, alkali element contents and a Ti/Hf ratio that distinguish it from basaltic eucrites. These differences support derivation from a distinct parent asteroid. Ibitira is the first recognized representative of the fifth known asteroidal basaltic crust.

  17. Vesicularity and CO2 in mid-ocean ridge basalt

    USGS Publications Warehouse

    Moore, J.G.

    1979-01-01

    Vesicles and included CO2are enriched in deep-sea basalts that are also enriched in light rare earth and incompatible elements. This enrichment probably results from a unique deep mantle origin of such melts but may have been modified by CO2 bubbles rising in shallow magma chambers. ?? 1979 Nature Publishing Group.

  18. Genetic relations of oceanic basalts as indicated by lead isotopes

    USGS Publications Warehouse

    Tatsumoto, M.

    1966-01-01

    The isotopic compositions of lead and the concentrations of lead, uranium, and thorium in samples of oceanic tholeiite and alkali suites are determined, and the genetic relations of the oceanic basalts are discussed. Lead of the oceanic tholeiites has a varying lead-206 : lead-204 ratio between 17.8 and 18.8, while leads of the alkali basalt suites from Easter Island and Guadalupe Island are very radiogenic with lead-206 : lead-204 ratios between 19.3 and 20.4. It is concluded that (i) the isotopic composition of lead in oceanic tholeiite suggests that the upper mantle source region of the tholeiite was differentiated from an original mantle material more than 1 billion years ago and that the upper mantle is not homogeneous at the present time, (ii) less than 20 million years was required for the crystal differentiation within the alkali suite from Easter Island, (iii) no crustal contamination was involved in the course of differentiation of rocks from Easter Island; however, some crustal contamination may have affected Guadalupe Island rocks, and (iv) alkali basalt may be produced from the tholeiite in the oceanic region by crystal differentiation. Alternatively the difference in the isotopic composition of lead in oceanic basalts may be produced by partial melting at different depths of a differentiated upper mantle.

  19. An estimate of the juvenile sulfur content of basalt

    USGS Publications Warehouse

    Moore, J.G.; Fabbi, Brent P.

    1971-01-01

    Sulfur analyses by X-ray fluorescence give an average content of 107 ppm for 9 samples of fresh subaerially-erupted oceanic basalt and 680 ppm for 38 samples of submarine erupted basalt. This difference is the result of retention of sulfur in basalt quenched on the sea floor and loss of sulfur in basalt by degassing at the surface. The outer glassy part of submarine erupted basalt contains 800??150 ppm sulfur, and this amount is regarded as an estimate of the juvenile sulfur content of the basalt melt from the mantle. The slower cooled interiors of basalt pillows are depleted relative to the rims owing to degassing and escape through surface fractures. Available samples of deep-sea basalts do not indicate a difference in original sulfur content between low-K tholeiite, Hawaiian tholeiite, and alkali basalt. The H2O/S ratio of analyzed volcanic gases is generally lower than the H2O/S ratio of gases presumed lost from surface lavas as determined by chemical differences between pillow rims and surface lavas. This enrichment of volcanic gases in sulfur relative to water may result from a greater degassing of sulfur relative to water from shallow intrusive bodies beneath the volcano. ?? 1971 Springer-Verlag.

  20. Can we identify source lithology of basalt?

    PubMed Central

    Yang, Zong-Feng; Zhou, Jun-Hong

    2013-01-01

    The nature of source rocks of basaltic magmas plays a fundamental role in understanding the composition, structure and evolution of the solid earth. However, identification of source lithology of basalts remains uncertainty. Using a parameterization of multi-decadal melting experiments on a variety of peridotite and pyroxenite, we show here that a parameter called FC3MS value (FeO/CaO-3*MgO/SiO2, all in wt%) can identify most pyroxenite-derived basalts. The continental oceanic island basalt-like volcanic rocks (MgO>7.5%) (C-OIB) in eastern China and Mongolia are too high in the FC3MS value to be derived from peridotite source. The majority of the C-OIB in phase diagrams are equilibrium with garnet and clinopyroxene, indicating that garnet pyroxenite is the dominant source lithology. Our results demonstrate that many reputed evolved low magnesian C-OIBs in fact represent primary pyroxenite melts, suggesting that many previous geological and petrological interpretations of basalts based on the single peridotite model need to be reconsidered. PMID:23676779

  1. Can we identify source lithology of basalt?

    PubMed

    Yang, Zong-Feng; Zhou, Jun-Hong

    2013-01-01

    The nature of source rocks of basaltic magmas plays a fundamental role in understanding the composition, structure and evolution of the solid earth. However, identification of source lithology of basalts remains uncertainty. Using a parameterization of multi-decadal melting experiments on a variety of peridotite and pyroxenite, we show here that a parameter called FC3MS value (FeO/CaO-3*MgO/SiO2, all in wt%) can identify most pyroxenite-derived basalts. The continental oceanic island basalt-like volcanic rocks (MgO>7.5%) (C-OIB) in eastern China and Mongolia are too high in the FC3MS value to be derived from peridotite source. The majority of the C-OIB in phase diagrams are equilibrium with garnet and clinopyroxene, indicating that garnet pyroxenite is the dominant source lithology. Our results demonstrate that many reputed evolved low magnesian C-OIBs in fact represent primary pyroxenite melts, suggesting that many previous geological and petrological interpretations of basalts based on the single peridotite model need to be reconsidered.

  2. The petrogenesis of primary mid-ocean ridge basalts

    NASA Technical Reports Server (NTRS)

    Elthon, Don

    1990-01-01

    The nature of primary mid-ocean ridge basalts (MORB) is reviewed from the primary-magma composition point of view. The concept of primary MORB magma used in the study stipulates that melting of the mantle produces a discrete identifiable magma that separates from the mantle and ascends toward the surface. Constraints from abyssal peridotites are considered along with constraints from high-pressure phase equilibria studies with emphasis on partial melting of mantle peridotites, basalt-peridotite sandwich techniques, high-pressure experiments on MORB-type compositions, and constraints on the pressure of origin from mineral compositions. Compositional variations in primitive MORB glasses are discussed, and possible models for the origin of these glasses are presented.

  3. Petrological, magnetic and chemical properties of basalt dredged from an abyssal hill in the North-east pacific

    USGS Publications Warehouse

    Luyendyk, B.P.; Engel, C.G.

    1969-01-01

    OVER the years, samples of basalt from the oceanic crust have been taken mainly from seamounts, fracture zones and ridge and rise crests1-6, and rarely from the vast fields of abyssal hills which cover a large part of the deep-sea floor. The basalt sampled from the deeper regions of the oceanic crust (for example, on fault scarps) is a distinct variety of tholeiitic basalt, while alkali basalt is restricted to the volcanic edifices4. Oceanic tholeiitic basalt differs from alkali basalt and continental tholeiite chiefly in having a relatively low percentage of K2O (0.2 weight per cent)4. Some authors have speculated that this type of tholeiitic basalt is the major extrusion from the upper mantle and constitutes the predominant rock type in the upper oceanic crust. ?? 1969 Nature Publishing Group.

  4. 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.

  5. A new lunar high-Ti basalt type defined from clasts in Apollo 16 breccia 60639

    NASA Astrophysics Data System (ADS)

    Fagan, A. L.; Neal, C. R.

    2016-01-01

    This paper reports the detailed examination of three basalt clasts from Apollo 16 breccia 60639 that represent a new variant of high-Ti basalt returned from the Moon by the Apollo 16 mission. Mineral chemistry and whole-rock analyses were conducted on aliquots from three clasts (breccia matrix, basalt, and basalt + breccia matrix). The basalt clasts, which are not overtly porphyritic, contain compositionally zoned pyroxene, olivine, and plagioclase crystals that represent the evolution of the magma during crystallization; ilmenite does not exhibit major-element compositional zoning within individual crystals. Mineral compositions are distinct between the basalt and breccia matrix lithologies. In addition, whole-rock analyses identify clear compositional differences between the basalt and breccia matrix lithologies in both major and trace element concentrations. The composition of the mixed lithology aliquots (i.e., basalt + breccia matrix) do not indicate simple two component mixing (i.e., compositions are not intermediate to the basalt and breccia end-members); this apparent incongruity can be accounted for by adding ∼19-40% plagioclase to an amalgamation of the average basalt and individual breccia clast compositions via impact mixing. Whole-rock analyses are consistent with previous analyses of one 60639 basalt clast, which were interpreted to indicate chemical similarity with Apollo 11 and 17 basalts. However, both major and trace elements suggest that the 60639 basalt clasts examined here have compositions that are distinct from Apollo 11 and 17 high-Ti basalts. Although the 60639 basalt clasts have similar characteristics to a variety of previously identified basalt types, the more extensive whole-rock analyses reported here indicate that they represent a type of Apollo high-Ti basalt heretofore unrecognized in the Apollo and lunar meteorite collections. By placing these new analyses in the context of other mare basalt compositions, a petrogenetic model for

  6. Origin of rhyolite by crustal melting and the nature of parental magmas in the Oligocene Conejos Formation, San Juan Mountains, Colorado, USA

    NASA Astrophysics Data System (ADS)

    Parker, D. F.; Ghosh, A.; Price, C. W.; Rinard, B. D.; Cullers, R. L.; Ren, M.

    2005-01-01

    Four closely spaced volcanoes (Summer Coon; Twin Mountains; Del Norte; Carnero Creek) form the east-central cluster of Conejos volcanic centers. These Conejos rocks range from high-K basaltic andesite to rhyolite, with andesite volumetrically the most abundant. Summer Coon and Twin Mountains are composite volcanoes. The Del Norte and Carnero Creek volcanoes are deeply eroded dacite shields. Rhyolite (10% of our Conejos analyses but a much smaller percentage by volume) is only known from Summer Coon and Twin Mountains volcanoes, although high-SiO 2 dacite occurs in the Del Norte volcano. The younger Hinsdale Formation contains a related series ranging from transitional basalt to high-K andesite; we use Hinsdale Formation analyses to represent Conejos parental magmas. Conejos and Hinsdale magmas evolved through AFC processes: Basalt, after interacting with lower crust, assimilated low K/Rb crust, similar in some ways to Taylor and McLennan (Taylor, S.R., and McLennan, S.M., 1985, The continental crust: its composition and evolution. Oxford, Blackwell Scientific.) model upper crust; main series basaltic andesite fractionated to high-K andesite; rhyolite was produced by melting of high K/Ba upper crustal rocks similar to granite gneiss known from inclusions and basement outcrops. Some rhyolite may have been back-mixed into fractionating andesite and dacite. Field evidence for assimilation includes sanidinite-facies, partially melted, gneiss blocks up to 1 m in diameter. Temperature estimates (1100-900 ° C) from two-pyroxene equilibria are consistent with this interpretation, as are the sparsely porphyritic nature of the most-evolved rhyolites and the absence of phenocrystic alkali feldspar. Our study supports the conclusions of previous workers on AFC processes in similar, but generally more mafic, Conejos magmas of the southeastern San Juan Mountains. Our results, however, emphasize the importance of crustal melting in the generation of Conejos rhyolite. We further

  7. Modeling Central American basalts using the Arc Basalt Simulator

    NASA Astrophysics Data System (ADS)

    Feigenson, M.; Carr, M. J.

    2011-12-01

    We have used the Arc Basalt Simulator (ABS), developed by JI Kimura, to explore the conditions and components of melting beneath the Central American volcanic front. ABS is a comprehensive forward model that incorporates slab dehydration and melting and mantle wedge fluxing and melting using realistic P-T conditions and experimentally determined phase relations. We have applied ABS versions 3 and 4 to model representative magma types in Nicaragua, which span a broad geochemical range including proximal high- and low-Ti lavas in Nicaragua. Sr-Nd-Pb data require appropriate selection of previously identified sources, including: separate carbonate and hemipelagic sediments, DMM, an enriched mantle isotopically similar to the alkaline basalts of Yojoa, a Himu-influenced mantle derived from Galapagos material and altered oceanic crust (AOC) derived from both MORB and Galapagos seamounts. Following the dry solidus, the dominant arc basalts, exemplified by Cerro Negro lavas, can be generated at about 80-90 km where lawsonite and zoisite break down, releasing LILEs into a hydrous fluid that travels into the wedge. The fluid-triggered melting occurs just above the garnet stability field in the wedge to fit the HREEs. Below 90 Km, slab melting begins and the AOC component dominates, generating a fluid with little or no HFSE depletions, consistent with the unusual high-Ti lavas found in Nicaragua. However, the isotopic data require a much lower sediment input for the high-Ti lavas (consistent with 10Be results on the high-Ti lavas) and an enriched component for the AOC and/or mantle wedge. Following the wet solidus, fits to the Cerro Negro magma only occur in the absence of phengite in the AOC and with the presence of HFSE attracting minerals, rutile, zircon and allanite. The depth of the best fit is 135 km, consistent with current best estimates of the depth to the seismic zone beneath Cerro Negro. Below 150 km, the high-Ti lavas can be generated if the HFSE retaining

  8. A tale of two magmas, Fuego, Guatemala

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  9. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  10. An Apollo 15 Mare Basalt Fragment and Lunar Mare Provinces

    NASA Technical Reports Server (NTRS)

    Ryder, Graham; Burling, Trina Cox

    1996-01-01

    Lunar sample 15474,4 is a tiny fragment of olivine-augite vitrophyre that is a mare basalt. Although petroraphically distinct from all other Apollo 15 samples, it has been ignored since its first brief description. Our new petrographic and mineral chemical data show that the olivines and pyroxenes are distinct from those in other basalts. The basalt cooled and solidified extremely rapidly; some of the olivine might be cumulate or crystallized prior to extrusion. Bulk-chemical data show that the sample is probably similar to an evolved Apollo 15 olivine-normative basalt in major elements but is distinct in its rare earth element pattern. Its chemical composition and petrography both show that 15474,4 cannot be derived from other Apollo 15 mare basalts by shallow-level crystal fractionation. It represents a distinct extrusion of magma. Nonetheless, the chemical features that 15474,4 has in common with other Apollo 15 mare basalts, including the high FeO/Sc, the general similarity of the rare earth element pattern, and the common (and chondritic) TiO2/Sm ratio, emphasize the concept of a geochemical province at the Apollo 15 site that is distinct from basalts and provinces elsewhere. In making a consistent picture for the derivation of all of the Apollo 15 basalts, both the commonalities and the differences among the basalts must be explained. The Apollo 15 commonalities and differences suggest that the sources must have consisted of major silicate phases with the same composition but with varied amounts of a magma trapped from a contemporary magma ocean. They probably had a high olivine/pyroxene ratio and underwent small and reasonably consistent degrees of partial melting to produce the basalts. These inferences may be inconsistent with models that suggest greatly different depths of melting among basalts, primitive sources for the green glasses, or extensive olivine fractionation during ascent. An integrated approach to lunar mare provinces, of which the Apollo 15

  11. Endeavour basalt geology and petrology

    NASA Astrophysics Data System (ADS)

    Gill, J. B.; Stakes, J.; Ramos, F.; Michael, P.; Stakes, D.

    2005-12-01

    We report major and trace element and isotope data from 250 basalt samples recently collected by submersible from the axial valley and flanks of the Endeavour segment of the Juan de Fuca Ridge. Off-axis volcanism is abundant on both flanks which are mirror images of one another geologically. Axial valley walls up to 1 km off axis appear to be steps of in tact but variably fractured sheet, lobate, and hackly lava flows similar to the youngest lavas seen in collapse features in the axis. Coverage by pillow terrane increases with distance off axis and coverage becomes complete after 1 km. The similarity of the two flanks suggests that the currently asymmetric axial magma chamber (van Ark et al., 2004) may be shorter-lived than the off-axis volcanism. MgO contents range from 6.0-8.5% and generally are lower on the flanks consistent with consistently cooler chamber edges there. La/Yb ratios vary 3-fold within 100 m in the axial valley, with normalized La/Sm = 0.8-2.5 in contrast to constant Sr and Nd isotopes. However, Th/U and 230Th/232Th ratios vary only slightly in the axial valley, which may enable dating of off-axis samples. H2O/Ce is less than 170, typical of values throughout much of the Pacific. Variations in depth and degree of melting, and in source composition, are implied. At times, these heterogeneities escaped homogenization in axial magma chambers. Cl concentrations and Cl/K ratios are surprisingly low considering the active hydrothermal systems in close proximity and the potential for brine incorporation into the magma chamber.

  12. Time scales of crystal mixing in magma mushes

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  13. Differentiation of an Apollo 12 picrite magma

    NASA Technical Reports Server (NTRS)

    Walker, D.; Hays, J. F.; Longhi, J.; Kirkpatrick, R. J.

    1976-01-01

    The Apollo 12 olivine basalt suite shows a strong positive correlation of grain size with normative olivine content. This correlation is interpreted to mean that the suite of samples represents the basal portion of a cooling unit which differentiated by simple olivine settling. The grain size of plagioclase observed in the coarsest samples indicates the cooling unit may have been as much as 30 m thick. The amount of olivine concentration observed in the suite is quantitatively internally consistent with simple olivine settling in a magma body of this size which has the composition of the chill margin.

  14. Ir, Ru, Pt, and Pd in basalts and komatiites: New constraints for the geochemical behavior of the platinum-group elements in the mantle

    SciTech Connect

    Rehkaemper, M.; Halliday, A.N.; Fitton, J.G.; Lee, D.C.; Wieneke, M.; Arndt, N.T.

    1999-11-01

    The concentrations of the platinum-group elements (PGE) Ir, Ru, Pt, and Pd were determined in 18 mantle-derived basalts from a variety of tectonic settings and six komatiites from three locations. All analyses were performed using isotope dilution, Carius tube digestion, and the precise technique of multiple collector inductively coupled plasma mass spectrometry. Multiple analyses of two samples indicate external reproducibilities, based upon separate dissolutions, or approximately 2--9% in the ppt to ppb concentration range. Mid-ocean ridge basalts from the Kolbeinsey Ridge, tholeiites from Iceland and alkali basalts from the Cameroon Line define three individual samples suites that are characterized by distinct major, trace, and platinum-group element systematics. All three-sample suites display correlations of the PGE with MgO, Ni, and Cr. The new analytical results are employed to constrain the geochemical behavior of the PGE during the formation and differentiation of mantle-derived melts. The PGE are inferred to be compatible in sulfides during partial melting with sulfide-silicate melt partition coefficients of {approximately}1 x 10{sup 4}. The fractionated PGE patterns of mantle melts re a consequence of the incompatibility of Pd in nonsulfide phases, whereas Ir and Ru must be compatible in at least one other mantle phase. Model calculations indicate that PGE alloys or spinel may be responsible for the higher compatibility of the latter elements during partial melting. It is further demonstrated that the shape of the melting regime has a profound effect on the PGE systematics of mantle magmas. The systematic trends of the three samples suites in plots of PGE against Ni and Cr are the results of magma differentiation processes that involve fractional crystallization of silicate minerals and the concurrent segregation of an immiscible sulfide liquid. The behavior of the PGE during magma fractionation indicates that the segregated sulfides probably equilibrate

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

    NASA Astrophysics Data System (ADS)

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

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

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

    NASA Astrophysics Data System (ADS)

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

    1995-06-01

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

  17. 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

  18. Alkali metal nitrate purification

    DOEpatents

    Fiorucci, Louis C.; Morgan, Michael J.

    1986-02-04

    A process is disclosed for removing contaminants from impure alkali metal nitrates containing them. The process comprises heating the impure alkali metal nitrates in solution form or molten form at a temperature and for a time sufficient to effect precipitation of solid impurities and separating the solid impurities from the resulting purified alkali metal nitrates. The resulting purified alkali metal nitrates in solution form may be heated to evaporate water therefrom to produce purified molten alkali metal nitrates suitable for use as a heat transfer medium. If desired, the purified molten form may be granulated and cooled to form discrete solid particles of purified alkali metal nitrates.

  19. The global pattern of trace-element distributions in ocean floor basalts.

    PubMed

    O'Neill, Hugh St C; Jenner, Frances E

    2012-11-29

    The magmatic layers of the oceanic crust are created at constructive plate margins by partial melting of the mantle as it wells up. The chemistry of ocean floor basalts, the most accessible product of this magmatism, is studied for the insights it yields into the compositional heterogeneity of the mantle and its thermal structure. However, before eruption, parental magma compositions are modified at crustal pressures by a process that has usually been assumed to be fractional crystallization. Here we show that the global distributions of trace elements in ocean floor basalts describe a systematic pattern that cannot be explained by simple fractional crystallization alone, but is due to cycling of magma through the global ensemble of magma chambers. Variability in both major and incompatible trace-element contents about the average global pattern is due to fluctuations in the magma fluxes into and out of the chambers, and their depth, as well as to differences in the composition of the parental magmas.

  20. Basalt generation at the Apollo 12 site. Part 2: Source heterogeneity, multiple melts, and crustal contamination

    NASA Technical Reports Server (NTRS)

    Neal, Clive R.; Hacker, Matthew D.; Snyder, Gregory A.; Taylor, Lawrence A.; Liu, Yun-Gang; Schmitt, Roman A.

    1994-01-01

    The petrogenesis of Apollo 12 mare basalts has been examined with emphasis on trace-element ratios and abundances. Vitrophyric basalts were used as parental compositions for the modeling, and proportions of fractionating phases were determined using the MAGFOX prograqm of Longhi (1991). Crystal fractionation processes within crustal and sub-crustal magma chambers are evaluated as a function of pressure. Knowledge of the fractionating phases allows trace-element variations to be considered as either source related or as a product of post-magma-generation processes. For the ilmenite and olivine basalts, trace-element variations are inherited from the source, but the pigeonite basalt data have been interpreted with open-system evolution processes through crustal assimilation. Three groups of basalts have been examined: (1) Pigeonite basalts-produced by the assimilation of lunar crustal material by a parental melt (up to 3% assimilation and 10% crystal fractionation, with an 'r' value of 0.3). (2) Ilmenite basalts-produced by variable degrees of partial melting (4-8%) of a source of olivine, pigeonite, augite, and plagioclase, brought together by overturn of the Lunar Magma Ocean (LMO) cumulate pile. After generation, which did not exhaust any of the minerals in the source, these melts experienced closed-system crystal fractionation/accumulation. (3) Olivine basalts-produced by variable degrees of partial melting (5-10%) of a source of olivine, pigeonite, and augite. After generation, again without exhausting any of the minerals in the source, these melts evolved through crystal accumulation. The evolved liquid counterparts of these cumulates have not been sampled. The source compositions for the ilmenite and olivine basalts were calculated by assuming that the vitrophyric compositions were primary and the magmas were produced by non-modal batch melting. Although the magnitude is unclear, evaluation of these source regions indicates that both be composed of early- and

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

    NASA Technical Reports Server (NTRS)

    Treiman, Allan H.

    1996-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  3. Large Pb Isotopic Variations in Pre-shield Stage Kilauea Magmas

    NASA Astrophysics Data System (ADS)

    Shimizu, N.; Sisson, T. W.; Layne, G. D.

    2001-12-01

    Volcaniclastic sediments found from a scarp below the mid-slope bench at water depths between 3,000 and 5,000m offshore south of Kilauea, Hawaii, contain abundant glass shards that represent submarine eruptions from an ancestral Kilauea volcano (Lipman et al., 2000; Sisson et al., 2001). Their major element compositions range from tholeiites/transitional basalts to alkali basalts to basanites and nephelinites. Pb isotopic compositions of the glasses were determined using a Cameca IMS 1270 ion microprobe at Woods Hole Oceanographic Institution. Replicate analyses of basalt glass stnadards show that 208Pb/206Pb and 207Pb/206Pb ratios could be determined in basalt glasses with external precisions better than 0.15% (1σ ) in a spot of 30 μ m across. Results show that: (1) a range of Pb isotopic compositions observed in the glasses are much greater than the entire spectrum of the Hawaiian volcanics. 208Pb/206Pb ratios vary from 2.099 to 2.004 and 207Pb/206Pb from 0.864 to 0.805. (2) There appear to be three distinct compositions, with each being represented by diverse magmatic compositions. There appears to be no significant mixing between them, and they form a linear array in a 208/206 vs 207/206 space, encompassing the entire Hawaiian Pb isotopic composition array. The least radiogenic composition (208Pb/206Pb=2.099, 207Pb/206Pb=0.864) in on an extension of the Honolulu Volcanics array, whereas the most radiogenic composition (208Pb/206Pb=2.004, 207Pb/206Pb=0.805) is far more radiogenic than any known Hawaiian magmas. The intermediate composition (208Pb/206Pb=2.041, 207Pb/206Pb=0.827) is close to the "Kea" endmember composition proposed by Eiler et al. (1998). The ancestral Kilauea nephelinites are derived from two distinct sources with radiogenic compositions and are quite distinct from all other Hawaiian post-erosional nephelinites. It is evident that diverse sources were tapped during the pre-shield stage Kilauea magmatism, and that melts erupted without mixing

  4. Is plagioclase removal responsible for the negative Eu anomaly in the source regions of mare basalts

    SciTech Connect

    Shearer, C.K.; Papike, J.J. )

    1989-12-01

    The nearly ubiquitous presence of a negative Eu anomaly in the mare basalts has been suggested to indicate prior separation and flotation of plagioclase from the basalt source region during its crystallization from a lunar magma ocean (LMO). Are there any mare basalts derived from a mantle source which did not experience prior plagioclase separation Crystal chemical rationale for REE substitution in pyroxene suggests that the combination of REE size and charge, M2 site characteristics of pyroxene, fO{sub 2}, magma chemistry, and temperature may account for the negative Eu anomaly in the source region of some types of primitive, low TiO{sub 2} mare basalts. This origin for the negative Eu anomaly does not preclude the possibility of the LMO as many mare basalts still require prior plagioclase crystallization and separation and/or hybridization involving a KREEP component.

  5. Is plagioclase removal responsible for the negative Eu anomaly in the source regions of mare basalts?

    NASA Technical Reports Server (NTRS)

    Shearer, C. K.; Papike, J. J.

    1989-01-01

    The nearly ubiquitous presence of a negative Eu anomaly in the mare basalts has been suggested to indicate prior separation and flotation of plagioclase from the basalt source region during its crystallization from a lunar magma ocean (LMO). Are there any mare basalts derived from a mantle source which did not experience prior plagioclase separation? Crystal chemical rationale for REE substitution in pyroxene suggests that the combination of REE size and charge, M2 site characteristics of pyroxene, fO2, magma chemistry, and temperature may account for the negative Eu anomaly in the source region of some types of primitive, low TiO2 mare basalts. This origin for the negative Eu anomaly does not preclude the possibility of the LMO as many mare basalts still require prior plagioclase crystallization and separation and/or hybridization involving a KREEP component.

  6. Eruption and emplacement of a basaltic welded ignimbrite during caldera formation on Gran Canaria

    NASA Astrophysics Data System (ADS)

    Freundt, Armin; Schmincke, Hans-Ulrich

    1995-02-01

    The 14.1 Ma old composite ignimbrite cooling unit P1 (45 km3) on Gran Canaria comprises a lower mixed rhyolite-trachyte tuff, a central rhyolite-basalt mixed tuff, and a slightly rhyolite-contaminated basaltic tuff at the top. The basaltic tuff is compositionally zoned with (a) an upward change in basalt composition to higher MgO content (4.3 5.2 wt.%), (b) variably admixed rhyolite or trachyte (commonly <5 wt.%), and (c) an upward increasing abundance of basaltic and plutonic lithic fragments and cognate cumulate fragments. The basaltic tuff is divided into three structural units: (I) the welded basaltic ignimbrite, which forms the thickest part (c. 95 vol.%) and is the main subject of the present paper; (II) poorly consolidated massive, bomb- and block-rich beds interpreted as phreatomagmatic pyroclastic flow deposits; and (III) various facies of reworked basaltic tuff. Tuff unit I is a basaltic ignimbrite rather than a lava flow because of the absence of top and bottom breccias, radial sheet-like distribution around the central Tejeda caldera, thickening in valleys but also covering higher ground, and local erosion of the underlying P1 ash. A gradual transition from dense rock in the interior to ash at the top of the basaltic ignimbrite reflects a decrease in welding; the shape of the welding profile is typical for emplacement temperatures well above the minimum welding temperature. A similar transition occurs at the base where the ignimbrite was emplaced on cold ground in distal sections. In proximal sections the base is dense where it was emplaced on hot felsic P1 tuff. The intensity of welding, especially at the base, and the presence of spherical particles and of mantled and composite particles formed by accretion and coalescence in a viscous state imply that the flow was a suspension of hot magma droplets. The flow most likely had to be density stratified and highly turbulent to prevent massive coalescence and collapse. Model calculations suggest eruption

  7. Geochemical and isotopic studies of syenites from the Yamato Mountains, East Antarctica: Implications for the origin of syenitic magmas

    NASA Astrophysics Data System (ADS)

    Zhao, J.-X.; Shiraishi, K.; Ellis, D. J.; Sheraton, J. W.

    1995-04-01

    , it is proposed that the syenites were generated by fractionation and magma mixing (with a crystal melt) of a Si-undersaturated alkali basaltic magma in a lower-crust magma chamber, followed by further crystal fractionation/cumulate-melt unmixing at middle to upper crustal levels (<5 kbars). Tectonically, it is proposed that the syenites were probably formed within the hinterland of the proposed Cambrian continental collision zone, with the parental magma being derived ultimately by partial melting of the metasomatised mantle wedge above the deepest part of the subduction zone. Similar models may also apply to the origin of some post-tectonic alkaline dikes in East Antarctica, with their sources being the continental lithospheric mantle previously modified by subduction-related processes.

  8. Calculation of water-bearing primary basalt and estimation of source mantle conditions beneath arcs: PRIMACALC2 model for WINDOWS

    NASA Astrophysics Data System (ADS)

    Kimura, Jun-Ichi; Ariskin, Alexey A.

    2014-04-01

    present a new method for estimating the composition of water-bearing primary arc basalt and its source mantle conditions. The PRIMACALC2 model uses a thermodynamic fractional crystallization model COMAGMAT3.72 and runs with an Excel macro to examine the mantle equilibrium and trace element calculations of a primary basalt. COMAGMAT3.72 calculates magma fractionation in 0-10 kb at various compositions, pressure, oxygen fugacity, and water content, but is only applicable for forward calculations. PRIMACALC2 first calculates the provisional composition of a primary basalt from an observed magma. The basalt composition is then calculated by COMAGMAT3.72 for crystallization. Differences in elemental concentrations between observed and the closest-match calculated magmas are then adjusted in the primary basalt. Further iteration continues until the calculated magma composition converges with the observed magma, resulting in the primary basalt composition. Once the fitting is satisfied, back calculations of trace elements are made using stepwise addition of fractionated minerals. Mantle equilibrium of the primary basalt is tested using the Fo-NiO relationship of olivine in equilibrium with the primary basalt, and thus with the source mantle. Source mantle pressure, temperature, and degree of melting are estimated using petrogenetic grids based on experimental data obtained in anhydrous systems. Mantle melting temperature in a hydrous system is computed by adjusting T with a parameterization for a water-bearing system. PRIMACALC2 can be used either in dry or water-bearing arc magmas and is also applicable to mid-ocean ridge basalts and nonalkalic ocean island basalts.

  9. Experimental constraints on CO2 and H2O in the Martian mantle and primary magmas

    NASA Technical Reports Server (NTRS)

    Holloway, John R.; Domanik, Kenneth J.; Cocheo, Peter A.

    1993-01-01

    We present new data on the stability of hornblende in a Martian mantle composition, on CO2 solubility in iron-rich basaltic magmas, and on the solubility of H2O in an alkalic basaltic magma. These new data are combined with a summary of data from the literature to present a summary of the current state of our estimates of solubilities of H2O and CO2 in probable Martian magmas and the stability of hornblende in a slightly hydrous mantle. The new results suggest that hornblende stability is not sensitive to the Mg/(Mg+Fe) ratio (mg#) of the mantle, that is the results for terrestrial mantle compositions are similar to the more iron-rich Martian composition. Likewise, CO2 solubility in iron-rich tholeiitic basaltic magmas is similar to iron-poor terrestrial compositions. The solubility of H2O has been measured in an alkalic basaltic (basanite) composition for the first time, and it is significantly lower than predicted for models of water solubility in magmas. The lack of mg# dependence observed in hornblende stability and on CO2 solubility that in many cases terrestrial results can be applied to Martian compositions. This conclusion does not apply to other phenomena such as primary magma compositions and major mantle mineral mineralogy.

  10. Vapor segregation and loss in basaltic melts

    USGS Publications Warehouse

    Edmonds, M.; Gerlach, T.M.

    2007-01-01

    Measurements of volcanic gases at Pu'u'O??'o??, Kilauea Volcano, Hawai'i, reveal distinct degassing regimes with respect to vapor segregation and loss during effusive activity in 2004-2005. Three styles of vapor loss are distinguished by the chemical character of the emitted volcanic gases, measured by open path Fourier transform infrared spectroscopy: 1 persistent continuous gas emission, 2 gas piston events, and 3 lava spattering. Persistent continuous gas emission is associated with magma ascent and degassing beneath the crater vents, then eruption of the degassed magma from flank vents. Gas piston events are the result of static gas accumulation at depths of 400-900 m beneath Pu'u'O??'o??. A CO2-rich gas slug travels up the conduit at a few meters per second, displacing magma as it expands. Lava spattering occurs due to dynamic bubble coalescence in a column of relatively stagnant magma. The Large gas bubbles are H2O rich and are generated by open-system degassing at depths of <150 m. Static gas accumulation and dynamic bubble coalescence are both manifestations of vapor segregation in basaltic melts, but their implications differ. Accumulation and segregation of CO2-rich vapor at depth does not deplete the melt of H2O (required to drive lava fountains near to the surface) and therefore gas piston events can occur interspersed with lava fountaining activity. Lava spattering, however, efficiently strips H2O-rich vapor from magma beneath the crater vents; the magma must then erupt effusively from vents on the flank of the cone. ?? 2007 The Geological Society of America.

  11. Products of a Subglacial Flood Basalt Eruption

    NASA Astrophysics Data System (ADS)

    Gorny, C. F.; White, J. D. L.; Gudmundsson, M. T.

    2015-12-01

    The Snæbýlisheiði unit, SE Iceland, is a ca. 26 km³ elongate, flat-topped ridge of volcaniclastic debris coupled with and intruded by coherent basalt stretching over 34 km from the eruption site perpendicular to the rift fissure source. It formed from a single subglacial flood basalt eruption during a recent glaciation, and its elongation reflects glacial control on dispersal via the hydraulic potential gradient at the glacier's base, which drove towards the glacier terminus the meltwater+debris formed during the eruption by quenching and fragmentation. High magma discharge and outgassing drove segregation of magma into down-flow propagating intrusions. Edifice growth was mediated by the extent of ice melting, extent and efficiency of meltwater+debris drainage, and hydraulic gradients locally favoring meltwater accumulation. Eruption style reflected magma flux, edifice stability, and accessibility of water to the vent area via flooding or infiltration. Deposits reflect these competing factors in their chaotic internal organization and stratigraphy, limited lithofacies continuity, and diverse particle populations from multiple source vents. Linear growth of the ridge down-gradient from the eruption site was driven primarily by propagation and continuous fragmentation of shoaling intrusions that formed an interconnected intrusive complex with extensive peperites. Advance was along gently meandering and locally bifurcating sub-ice conduits within hyaloclastite with sheet-lobe levees and lobate fingered intrusions. Irregular dikes, apophyses, horns, and tendrils extended from the main body and generated voluminous lapilli tuff and contorticlasts while providing additional heat to the system. Prolonged transport and deposition of debris produced complexly bedded volcaniclastic deposits derived from and intruded by the basalt sheet. The bedding and depositional features of volcaniclastic debris and relationship to their adjacent intrusions suggest transport and

  12. Using 40Ar/39Ar ages of intercalated silicic tuffs to date flood basalts: Precise ages for Steens Basalt Member of the Columbia River Basalt Group

    NASA Astrophysics Data System (ADS)

    Mahood, Gail A.; Benson, Thomas R.

    2017-02-01

    To establish causality between flood basalt eruptions and extinction events and global environmental effects recorded by isotopic excursions in marine sediments, highly accurate and precise ages for the flood basalts are required. But flood basalts are intrinsically difficult to date. We illustrate how 40Ar/39Ar feldspar ages for silicic tuffs intercalated with and overlying sections of Steens Basalt, the earliest lavas of the Middle Miocene Columbia River Basalt Group in the northwestern United States, provide high-precision ages that, for the first time, make it possible to resolve age differences with stratigraphic position within a section of these flood lavas. The stratigraphically lowest rhyolitic tuff, a fall deposit, yielded an age of 16.592 ± ± 0.028 Ma (FCs = 28.02 Ma), and the uppermost, the alkali rhyolite ignimbrite Tuff of Oregon Canyon, is 16.468 ± ± 0.014 Ma. The argon and stratigraphic data indicate that Steens Basalt eruptions occurred from ∼16.64 to 16.43 Ma in the southern end of its distribution. We estimate that the Steens Mountain geomagnetic reversal occurred at 16.496 ± ± 0.028 Ma (±0.18 Ma total error). Our estimates of the timing for initiation of volcanism and volumetric eruptive rates do not seem to support volcanic forcing by the initial stages of Columbia River Basalt Group eruptions as an explanation for the abrupt warming and carbonate dissolution at the beginning of the Miocene Climatic Optimum.

  13. Milk-alkali syndrome

    MedlinePlus

    ... this page: //medlineplus.gov/ency/article/000332.htm Milk-alkali syndrome To use the sharing features on this page, please enable JavaScript. Milk-alkali syndrome is a condition in which there ...

  14. 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.

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

    SciTech Connect

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

    1992-04-01

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

  16. Workshop on Mare Volcanism and Basalt Petrogenesis: Astounding Fundamental Concepts (AFC) Developed Over the Last Fifteen Years

    NASA Technical Reports Server (NTRS)

    Taylor, Lawrence A. (Editor); Longi, John (Editor)

    1991-01-01

    Papers presented at the workshop on mare volcanism and basalt petrogenesis are compiled. The discussion of recent ideas and concepts within the context of this workshop permitted to catch up on the developments over the last 15 years. The following subject areas were covered: (1) geological setting; (2) magma evolution and source regions; (3) magma source and ascent processes; and (4) history of volcanism.

  17. Nature of basalt-deep crust interaction in the petrogenesis of a potassium-rich, silicic-dominated eruptive system, Davis Mountain volcanic field, west Texas

    SciTech Connect

    Ward, R.L.; Walker, J.A. . Dept. of Geology)

    1993-04-01

    The Davis Mountain volcanic field (DMVF) is one of several silicic-dominated eruptive centers that constitute the bulk of the Trans Pecos volcanic province (TPVP). New major-, trace element, and Pb-O isotope data on local granulite-facies xenoliths and the DMVF are used in evaluating the extent of basalt-deep crust interaction to produce voluminous silicic lavas and -ignimbrites. The DMVF (39.3--35.4 Ma) is a high-K, alkali basalt-potassic trachybasalt-shoshonite-latite-trachyte-rhyolite volcanoplutonic series with the evolved members being silica-saturated. DMF silicic rocks are characterized by high concentrations of Rb, Th, U, and K, low-[sup 18]O and have a broad range in Pb isotopes. These characteristics are inconsistent with an origin by partial melting of a Rb-Th-U depleted, unradiogenic Pb granulitic deep crust. However, distinctly different Pb isotope compositions between mafic and silicic rocks preclude an origin by fractional crystallization alone. Multistage-AFC involving a mantle-source, various proportions of OL-CPX-PLAG-KSPAR-MAG-AP-BIO-QTZ-aenigmatite-ZR differentiation, limited (<10%) amounts of deep and upper crustal contamination, and mixing between mafic and silicic magmas can satisfactorily account for the observed chemical and isotopic variation in the DMVF.

  18. Calderas and magma reservoirs

    NASA Astrophysics Data System (ADS)

    Cashman, Katharine V.; Giordano, Guido

    2014-11-01

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

  19. Isotope geochemistry of early Kilauea magmas from the submarine Hilina bench: The nature of the Hilina mantle component

    USGS Publications Warehouse

    Kimura, Jun-Ichi; Sisson, Thomas W.; Nakano, Natsuko; Coombs, Michelle L.; Lipman, Peter W.

    2006-01-01

    Submarine lavas recovered from the Hilina bench region, offshore Kilauea, Hawaii Island provide information on ancient Kilauea volcano and the geochemical components of the Hawaiian hotspot. Alkalic lavas, including nephelinite, basanite, hawaiite, and alkali basalt, dominate the earliest stage of Kilauea magmatism. Transitional basalt pillow lavas are an intermediate phase, preceding development of the voluminous tholeiitic subaerial shield and submarine Puna Ridge. Most alkalic through transitional lavas are quite uniform in Sr–Nd–Pb isotopes, supporting the interpretation that variable extent partial melting of a relatively homogeneous source was responsible for much of the geochemical diversity of early Kilauea magmas (Sisson et al., 2002). These samples are among the highest 206Pb/204Pb known from Hawaii and may represent melts from a distinct geochemical and isotopic end-member involved in the generation of most Hawaiian tholeiites. This end-member is similar to the postulated literature Kea component, but we propose that it should be renamed Hilina, to avoid confusion with the geographically defined Kea-trend volcanoes. Isotopic compositions of some shield-stage Kilauea tholeiites overlap the Hilina end-member but most deviate far into the interior of the isotopic field defined by magmas from other Hawaiian volcanoes, reflecting the introduction of melt contributions from both “Koolau” (high 87Sr/86Sr, low 206Pb/204Pb) and depleted (low 87Sr/86Sr, intermediate 206Pb/204Pb) source materials. This shift in isotopic character from nearly uniform, end-member, and alkalic, to diverse and tholeiitic corresponds with the major increase in Kilauea's magmatic productivity. Two popular geodynamic models can account for these relations: (1) The upwelling mantle source could be concentrically zoned in both chemical/isotopic composition, and in speed/extent of upwelling, with Hilina (and Loihi) components situated in the weakly ascending margins and the

  20. Carbon and its isotopes in mid-oceanic basaltic glasses

    NASA Technical Reports Server (NTRS)

    Des Marais, D. J.; Moore, J. G.

    1984-01-01

    Sample surface carbon, mantle carbon dioxide in vesicles, and mantle carbon dissolved in glasses, are the three carbon components evident in the 11 mid-oceanic basalts presently analyzed. The total carbon content may be controlled by the depth of the shallowest ridge magma chamber, and carbon isotopic fractionation accompanies magma degassing. Using He-3 and carbon data for submarine hydrothermal fluids, the present day midoceanic ridge carbon flux is approximately estimated to be 1.0 x 10 to the 13th g C/yr, requiring 8 Gyr to accumulate the earth's present crustal carbon inventory.

  1. Carbon Solution in Core-Forming Magma Ocean Conditions: Implications for the Origin and Distribution of Terrestrial Carbon

    NASA Astrophysics Data System (ADS)

    Dasgupta, R.; Chi, H.; Walker, D.; Shimizu, N.; Buono, A. S.

    2012-12-01

    The origin of bulk silicate Earth carbon inventory is poorly known and the fate of the element during the early Earth differentiation and core formation is a missing link in the evolution of the terrestrial carbon cycle. Here we present high pressure-temperature experiments that simulate metal-silicate equilibria in a shallow magma ocean. Experiments were performed at 1-5 GPa, 1600-2100 °C on mixtures of synthetic or natural silicates (tholeiitic basalt/ alkali basalt/ komatiite/ fertile peridotite) and Fe-Ni-C±Co±S contained in graphite or MgO capsules. All the experiments produced immiscible Fe-rich metallic and silicate melts at oxygen fugacity (fO2) between ~IW-1.5 and IW-1.9. Carbon and hydrogen concentrations of basaltic glasses and non-glassy quenched silicate melts were determined using secondary ionization mass spectrometry (SIMS) and speciation of dissolved C-O-H volatiles in silicate glasses was constrained using Raman spectroscopy. Carbon contents of metallic melts were determined using both electron microprobe and SIMS. Our experiments indicate that at core-forming, reduced conditions, carbon in mafic-ultramafic magmas dissolves primarily as various hydrogenated species and the total carbon storage capacity, although is significantly higher than solubility of CO2 under similar conditions, remains low (<500 ppm). The total carbon content in our reduced melts at graphite saturation increases with increasing melt depolymerization (NBO/T), consistent with recent spectroscopic studies [1], and modestly with increasing hydration. Carbon behaves as a metal loving element during core-mantle separation and metal/silicate carbon partition coefficient, DC varies between ~3500 and ≥150 and increases with increasing pressure and decreases with increasing temperature and melt NBO/T. Extrapolation of our data to the plausible conditions of core-mantle equilibration suggest that if only a trace amount of carbon (~730 ppm C; [2]) was available during early Earth

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  3. Magmatic inclusions in rhyolites, contaminated basalts, and compositional zonation beneath the Coso volcanic field, California

    USGS Publications Warehouse

    Bacon, C.R.; Metz, J.

    1984-01-01

    Basaltic lava flows and high-silica rhyolite domes form the Pleistocene part of the Coso volcanic field in southeastern California. The distribution of vents maps the areal zonation inferred for the upper parts of the Coso magmatic system. Subalkalic basalts (<50% SiO2) were erupted well away from the rhyolite field at any given time. Compositional variation among these basalts can be ascribed to crystal fractionation. Erupted volumes of these basalts decrease with increasing differentiation. Mafic lavas containing up to 58% SiO2, erupted adjacent to the rhyolite field, formed by mixing of basaltic and silicic magma. Basaltic magma interacted with crustal rocks to form other SiO2-rich mafic lavas erupted near the Sierra Nevada fault zone. Several rhyolite domes in the Coso volcanic field contain sparse andesitic inclusions (55-61% SiO2). Pillow-like forms, intricate commingling and local diffusive mixing of andesite and rhyolite at contacts, concentric vesicle distribution, and crystal morphologies indicative of undercooling show that inclusions were incorporated in their rhyolitic hosts as blobs of magma. Inclusions were probably dispersed throughout small volumes of rhyolitic magma by convective (mechanical) mixing. Inclusion magma was formed by mixing (hybridization) at the interface between basaltic and rhyolitic magmas that coexisted in vertically zoned igneous systems. Relict phenocrysts and the bulk compositions of inclusions suggest that silicic endmembers were less differentiated than erupted high-silica rhyolite. Changes in inferred endmembers of magma mixtures with time suggest that the steepness of chemical gradients near the silicic/mafic interface in the zoned reservoir may have decreased as the system matured, although a high-silica rhyolitic cap persisted. The Coso example is an extreme case of large thermal and compositional contrast between inclusion and host magmas; lesser differences between intermediate composition magmas and inclusions lead to

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

    NASA Astrophysics Data System (ADS)

    Marsh, Bruce D.; Coleman, Neil M.

    2009-05-01

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

  5. Crustal influence in the generation of continental flood basalts

    NASA Technical Reports Server (NTRS)

    Carlson, R. W.; Lugmair, G. W.; Macdougall, J. D.

    1981-01-01

    The suggestion that primordial undifferentiated material may exist in the earth's mantle has recently been revived on the strength of Nd isotope data for two types of young continental rocks - flood basalts and kimberlites. The limited published data show a clustering of Nd isotopic compositions close to those for meteorites with chondritic relative rare-earth (REE) abundance. In contrast, data are presented for samples from the Columbia flood basalt province of the northwestern United States which show large isotopic variability suggestive of mixing processes acting after the separation of the primary magmas from their mantle source.

  6. Copper systematics in arc magmas and implications for crust-mantle differentiation.

    PubMed

    Lee, Cin-Ty A; Luffi, Peter; Chin, Emily J; Bouchet, Romain; Dasgupta, Rajdeep; Morton, Douglas M; Le Roux, Veronique; Yin, Qing-zhu; Jin, Daphne

    2012-04-06

    Arc magmas are important building blocks of the continental crust. Because many arc lavas are oxidized, continent formation is thought to be associated with oxidizing conditions. On the basis of copper's (Cu's) affinity for reduced sulfur phases, we tracked the redox state of arc magmas from mantle source to emplacement in the crust. Primary arc and mid-ocean ridge basalts have identical Cu contents, indicating that the redox states of primitive arc magmas are indistinguishable from that of mid-ocean ridge basalts. During magmatic differentiation, the Cu content of most arc magmas decreases markedly because of sulfide segregation. Because a similar depletion in Cu characterizes global continental crust, the formation of sulfide-bearing cumulates under reducing conditions may be a critical step in continent formation.

  7. 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.

  8. Basaltic fragments in lunar feldspathic meteorites: Connecting sample analyses to orbital remote sensing

    NASA Astrophysics Data System (ADS)

    Robinson, Katharine L.; Treiman, Allan H.; Joy, Katherine H.

    2012-03-01

    The feldspathic lunar meteorites contain rare fragments of crystalline basalts. We analyzed 16 basalt fragments from four feldspathic lunar meteorites (Allan Hills [ALHA] 81005, MacAlpine Hills [MAC] 88104/88105, Queen Alexandra Range [QUE] 93069, Miller Range [MIL] 07006) and utilized literature data for another (Dhofar [Dho] 1180). We compositionally classify basalt fragments according to their magma's estimated TiO2 contents, which we derive for crystalline basalts from pyroxene TiO2 and the mineral-melt Ti distribution coefficient. Overall, most of the basalt fragments are low-Ti basalts (1-6% TiO2), with a significant proportion of very-low-Ti basalts (<1% TiO2). Only a few basalt clasts were high-Ti or intermediate Ti types (>10% TiO2 and 6-10% TiO2, respectively). This distribution of basalt TiO2 abundances is nearly identical to that obtained from orbital remote sensing of the moon (both UV-Vis from Clementine, and gamma ray from Lunar Prospector). However, the distribution of TiO2 abundances is unlike those of the Apollo and Luna returned samples: we observe a paucity of high-Ti basalts. The compositional types of basalt differs from meteorite to meteorite, which implies that all basalt subtypes are not randomly distributed on the Moon, i.e., the basalt fragments in each meteorite probably represent basalts in the neighborhood of the meteorite launch site. These differences in basalt chemistry and classifications may be useful in identifying the source regions of some feldspathic meteorites. Some of the basalt fragments probably originate from ancient cryptomaria, and so may hold clues to the petrogenesis of the Moon's oldest volcanism.

  9. Magma Dynamics at Yucca Mountain, Nevada

    SciTech Connect

    D. Krier

    2005-08-29

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

  10. The production of intermediate magmas through magma mixing and commingling: Evidence from the Hoover Dam Volcanics, Mohave County, Arizona and Clark County, Nevada

    SciTech Connect

    Mills, J.G. Jr. . Dept. of Geoscience)

    1993-04-01

    The Hoover Dam Volcanic section ([approximately]14 Ma) is composed of the reversely-zoned dacitic tuff of Hoover Dam, Switchyard basaltic andesite, Sugarloaf dacite, Black Canyon dacite and Kingman Wash basaltic andesite (Mills, 1985). The origin of this suite is best explained by the commingling and mixing of end-member mafic and felsic magmas. These end-member magmas were most likely formed by partial melting of the mantle and subsequent advective heating and melting of the crust respectively. Textural evidence for these processes is observed in the Black Canyon dacite which contains enclaves of basaltic andesite, and, in the Paint Pots pluton which contains commingled basaltic andesite and monzonite. The Black Canyon dacite is a biotite (4%), homblende (1%) and plagioclase 10% phyric dacite flow which contains up to 5% enclaves of basaltic andesite. The enclaves contain 54 wt% SiO[sub 2], 7.22 ppm Tl, 65 ppm Rb, 1,274 ppm Sr and 1,810 ppm Ba. The gray to purplish-red enclaves have crenulate margins, are commonly vesiculated and contain phenocrysts of biotite (< 1%), hornblende ([much lt]1%), plagioclase (1%) and clinopyroxene( ) (2%). Chemically, the enclaves are distinct from the Switchyard and Kingman Wash basaltic andesites. The enclaves most likely represent a more primitive magma from which the Switchyard and Kingman Wash basaltic andesites were derived. These two units were subsequently chemically modified by mixing with crustal melt and/or crystal fractionation. The presence of a small, clinopyroxenite xenolith (clinopyroxene 90%, garnet 5%, plagioclase 4%) within one of the enclaves indicates an upper mantle source for the enclave magma.

  11. Degassing of reduced carbon from planetary basalts

    PubMed Central

    Wetzel, Diane T.; Rutherford, Malcolm J.; Jacobsen, Steven D.; Hauri, Erik H.; Saal, Alberto E.

    2013-01-01

    Degassing of planetary interiors through surface volcanism plays an important role in the evolution of planetary bodies and atmospheres. On Earth, carbon dioxide and water are the primary volatile species in magmas. However, little is known about the speciation and degassing of carbon in magmas formed on other planets (i.e., Moon, Mars, Mercury), where the mantle oxidation state [oxygen fugacity (fO2)] is different from that of the Earth. Using experiments on a lunar basalt composition, we confirm that carbon dissolves as carbonate at an fO2 higher than -0.55 relative to the iron wustite oxygen buffer (IW-0.55), whereas at a lower fO2, we discover that carbon is present mainly as iron pentacarbonyl and in smaller amounts as methane in the melt. The transition of carbon speciation in mantle-derived melts at fO2 less than IW-0.55 is associated with a decrease in carbon solubility by a factor of 2. Thus, the fO2 controls carbon speciation and solubility in mantle-derived melts even more than previous data indicate, and the degassing of reduced carbon from Fe-rich basalts on planetary bodies would produce methane-bearing, CO-rich early atmospheres with a strong greenhouse potential. PMID:23569260

  12. Degassing of reduced carbon from planetary basalts.

    PubMed

    Wetzel, Diane T; Rutherford, Malcolm J; Jacobsen, Steven D; Hauri, Erik H; Saal, Alberto E

    2013-05-14

    Degassing of planetary interiors through surface volcanism plays an important role in the evolution of planetary bodies and atmospheres. On Earth, carbon dioxide and water are the primary volatile species in magmas. However, little is known about the speciation and degassing of carbon in magmas formed on other planets (i.e., Moon, Mars, Mercury), where the mantle oxidation state [oxygen fugacity (fO2)] is different from that of the Earth. Using experiments on a lunar basalt composition, we confirm that carbon dissolves as carbonate at an fO2 higher than -0.55 relative to the iron wustite oxygen buffer (IW-0.55), whereas at a lower fO2, we discover that carbon is present mainly as iron pentacarbonyl and in smaller amounts as methane in the melt. The transition of carbon speciation in mantle-derived melts at fO2 less than IW-0.55 is associated with a decrease in carbon solubility by a factor of 2. Thus, the fO2 controls carbon speciation and solubility in mantle-derived melts even more than previous data indicate, and the degassing of reduced carbon from Fe-rich basalts on planetary bodies would produce methane-bearing, CO-rich early atmospheres with a strong greenhouse potential.

  13. Staged storage and magma convection at Ambrym volcano, Vanuatu

    NASA Astrophysics Data System (ADS)

    Sheehan, Fionnuala; Barclay, Jenni

    2016-08-01

    New mineral-melt thermobarometry and mineral chemistry data are presented for basaltic scoriae erupted from the Mbwelesu crater of Ambrym volcano, Vanuatu, during persistent lava lake activity in 2005 and 2007. These data reveal crystallisation conditions and enable the first detailed attempt at reconstruction of the central magma plumbing system of Ambrym volcano. Pressures and temperatures of magma crystallisation at Ambrym are poorly constrained. This study focuses on characterising the magma conditions underlying the quasi-permanent lava lakes at the basaltic central vents, and examines petrological evidence for magma circulation. Mineral-melt equilibria for clinopyroxene, olivine and plagioclase allow estimation of pressures and temperatures of crystallisation, and reveal two major regions of crystallisation, at 24-29 km and 11-18 km depth, in agreement with indications from earthquake data of crustal storage levels at c. 25-29 km and 12-21 km depth. Temperature estimates are 1150-1170 °C for the deeper region, and 1110-1140 °C in the mid-crustal region, with lower temperatures of 1090-1100 °C for late-stage crystallisation. More primitive plagioclase antecrysts are thought to sample a slightly more mafic melt at sub-Moho depths. Resorption textures combined with effectively constant mafic mineral compositions suggest phenocryst convection in a storage region of consistent magma composition. In addition, basalt erupted at Ambrym has predominantly maintained a constant composition throughout the volcanic succession. This, coupled with recurrent periods of elevated central vent activity on the scale of months, suggest frequent magmatic recharge via steady-state melt generation at Ambrym.

  14. Pyroclastic deposits of the Mount Edgecumbe volcanic field, southeast Alaska: eruptions of a stratified magma chamber

    USGS Publications Warehouse

    Riehle, J.R.; Champion, D.E.; Brew, D.A.; Lanphere, M.A.

    1992-01-01

    The Mount Edgecumbe volcanic field in southeastern Alaska consists of 5-6 km3 (DRE) of postglacial pyroclasts that overlie Pleistocene lavas. All eleven pyroclast vents align with the long axis of the field, implying that the pyroclast magma conduits followed a crustal fissure. Most of these vents had previously erupted lavas that are compositionally similar to the pyroclasts, so a persistent magma system (chamber) had likely evolved by the onset of the pyroclastic eruptions. The pyroclastic sequence was deposited in about a millennium and is remarkable for a wide range of upward-increasing silica contents (51-72% SiO2), which is consistent with rise of coexisting magmas at different rates governed by their viscosity. Basaltic and andesitic lava flows have erupted throughout the lifetime of the field. Rhyolite erupted late; we infer that it formed early but was hindered from rising by its high viscosity. Most of the magmas-and all siliceous ones-erupted from vents on the central fissure. Basalt has not erupted from the center of the field during at least the latter part of its lifetime. Thus the field may illustrate basalt underplating: heat and mass flux are concentrated at the center of a stratified magma chamber in which a cap of siliceous melt blocks the rise of basalt. Major-element, strontium isotope, and mineral compositions of unaltered pyroclasts are broadly similar to those of older lavas of similar SiO2 content. Slightly fewer phenocrysts, inherited grains, and trace amphibole in pyroclastic magmas may be due simply to faster rise and less undercooling and degassing before eruption relative to the lavas. Dacite occurs only in the youngest deposits; the magma formed by mixing of andesitic and rhyolitic magmas erupted shortly before by the dacitic vents. ?? 1992.

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

    PubMed

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

    2015-09-01

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

  16. The chlorine isotope fingerprint of the lunar magma ocean

    PubMed Central

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

    2015-01-01

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

  17. Melt density and the efficiency of fractional crystallization for the generation of phonolite magmas

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    The natural Plateau phonolites from the Kenya rift exceed the total combined volume of phonolite lava found elsewhere in the world by several orders of magnitude [1]. These alkali-rich magmas are thought to form as fractionation products from low-silica, primary compositions such as nephelinite and melililite [2] or are generated directly within the mantle by melting or fractionation [3]. Although the density contrast between melt and crystal has an important effect on crystal fractionation and magma differentiation rates, density data for alkaline magmas typically found in continental rift zone setting is not available, precluding the assessment of the efficiency of crystal fractionation processes as a mechanism to generate phonolitic melts. We present in-situ density measurements of phonolitic melts at crustal and upper mantle conditions (1.0-3.1 GPa, 1585-1855 K) using synchrotron X-ray absorption in a Paris-Edinburgh press [4]. The starting material is a synthetic haplo-phonolite glass based on the Plateau flood phonolites from the Kenya rift [5]. Single-crystal diamond cylinders were used as sample containers and the density was determined as a function of pressure and temperature from the X-ray absorption contrast between the sample and the diamond capsule. The results were 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. The equation of state is calibrated up to 3.1 GPa, but can be reliably extrapolated to higher pressures; melt densities range from 2.45 g/cm3 up to 2.62 g/cm3 for a depth of 30 to 60 km, respectively - A comparison of our results with literature data shows that the compressibility of silicate melts decreases with increasing silica content in a similar manner observed for silicate glasses: phonolitic melts are more compressible than peridotitic and basaltic melts. The low compressibility of phonolites causes small

  18. Role of mechanical erosion in controlling the effusion rate of basaltic eruptions

    NASA Astrophysics Data System (ADS)

    Piombo, Antonello; Tallarico, Andrea; Dragoni, Michele

    2016-09-01

    In many basaltic eruptions, observations show that the effusion rate of magma has a typical dependence on time: the effusion rate curves show first a period of increasing and later a decreasing phase by a maximum value. We present a model to explain this behavior by the emptying of a magma reservoir through a vertical cylindrical conduit with elliptical cross section, coupled with the its widening due to mechanical erosion, produced by the magma flow. The model can reproduce the observed dependence on time of effusion rate in basaltic eruptions. Eruption duration and the maximum value of effusion rate depend on the size of magma chamber, on lava viscosity and strongly on erosion rate per unit traction.

  19. The solubility of olivine in basaltic liquids - An ionic model

    NASA Technical Reports Server (NTRS)

    Herzberg, C. T.

    1979-01-01

    A model is presented which enables the temperature at which olivine is in equilibrium with any alkali-depleted basaltic compound to be calculated to within + or - 30 C. It is noted that the error increases substantially when applied to terrestrial basalts which contain several weight percent alkalis. In addition the model predicts and quantifies the reduced activity of SiO4(4-) monomers due to increasing SiO2 concentrations in the melt. It is shown that the coordination of alumina in melts which precipitate olivine only appears to be dominantly octahedral, while titanium acts as a polmerizing agent by interconnecting previously isolated SiO4(4-) monomers. It is concluded that the model is sufficiently sensitive to show that there are small repulsive forces between Mg(2+) and calcium ions which are in association with normative diopside in the melt.

  20. Iron Redox Systematics of Shergottites and Martian Magmas

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  1. Petrology and geochemistry of Cenozoic intra-plate basalts in east-central China: Constraints on recycling of an oceanic slab in the source region

    NASA Astrophysics Data System (ADS)

    Li, Yan-Qing; Ma, Chang-Qian; Robinson, Paul T.

    2016-10-01

    Cenozoic mafic rocks in Jiangsu and Anhui Provinces, east-central China are chiefly basanites and alkali olivine basalts with subordinate tholeiites, which were erupted in three stages; Paleogene, Neogene and Quaternary. The rocks become increasingly alkaline as they become younger. On a primitive mantle-normalized multi-element plot, these lavas exhibit typical OIB-like trace element patterns, including enrichment in most incompatible elements (LILE and HFSE) and negative K and Pb anomalies. The compositions of the mafic rocks indicate that they were derived from a mantle source mainly containing clinopyroxene and garnet, most probably a mixture of pyroxenite/eclogite and peridotite. A mineral equilibrium projection shows that all the mafic magmas were produced at pressures of 3-4 GPa, implying an asthenospheric origin. Their positive Ba and Sr anomalies and relatively high 87Sr/86Sr ratios suggest derivation from an EM1-type mantle source. However, poor correlations between 87Sr/86Sr and 143Nd/144Nd indicate an isotopically heterogeneous source for the magmas, including DMM, EM1 and EM2, representing mantle peridotite, recycled ancient oceanic crust and seafloor sedimentary rocks, respectively. Variable correlations between 87Sr/86Sr and 143Nd/144Nd ratios, CaO-MgO contents and Eu/Eu* and Ce/Ce* anomalies with rock type imply that marine sediments (plus variable amounts of oceanic crust) and peridotites were the dominant source lithologies of the basanites, whereas recycled oceanic crust (pyroxenite/eclogite) was the main source of the weakly alkaline basalts. This hypothesis is supported by seismic tomographic images of the mantle beneath the region, which show the presence of a stagnant subducted slab in the mantle transition zone. Thus, we propose a petrological model in which a hybrid magma column originated from the mantle transition zone and assimilated some of the overlying peridotite during upwelling, to become the parental magmas of these mafic rocks

  2. Subduction zone mantle enrichment by fluids and Zr-Hf-depleted crustal melts as indicated by backarc basalts of the Southern Volcanic Zone, Argentina

    NASA Astrophysics Data System (ADS)

    Holm, Paul M.; Søager, Nina; Alfastsen, Mads; Bertotto, Gustavo W.

    2016-10-01

    We aim to identify the components metasomatizing the mantle above the subducting Nazca plate under part of the Andean Southern Volcanic Zone (SVZ). We present new major and ICP-MS trace element and Sr, Nd and high-precision Pb isotope analyses of primitive olivine-phyric alkali basalts from the Northern Segment Volcanic Field, part of the Payenia province in the backarc of the Transitional SVZ. One new 40Ar-39Ar age determination confirms the Late Pleistocene age of this most northerly part of the province. All analysed rocks have typical subduction zone type incompatible element enrichment, and the rocks of the Northern Segment, together with the neighbouring Nevado Volcanic Field, have isotopic compositions intermediate between adjacent Transitional SVZ arc rocks and southern Payenia OIB-type basaltic rocks. Modelling the Ba-Th-Sm variation we demonstrate that fluids as well as 1-2% melts of upper continental crust (UCC) enriched their mantle sources, and La-Nb-Sm variations additionally indicate that the pre-metasomatic sources ranged from strongly depleted to undepleted mantle. Low Eu/Eu* and Sr/Nd also show evidence for a UCC component in the source. The contribution of Chile Trench sediments to the magmas seems insignificant. The Zr/Sm and Hf/Sm ratios are relatively low in many of the Northern Segment rocks, ranging down to 17 and 0.45, respectively, which, together with relatively high Th/U, is argued to indicate that the metasomatizing crustal melts were derived by partial melting of subducted UCC that had residual zircon, in contrast to the UCC melts added to Transitional SVZ arc magmas. Mixing between depleted and undepleted mantle, enriched by UCC and fluids, is suggested by Sr, Nd and Pb isotopes of the Northern Segment and Nevado magmas. The metasomatized undepleted mantle south of the Northern Segment is suggested to be part of upwelling OIB-type mantle, whereas the pre-metasomatically depleted mantle also can be found as a component in some arc

  3. 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

  4. Evidence for pressure-release melting beneath magmatic arcs from basalt at Galunggung, Indonesia

    USGS Publications Warehouse

    Sisson, T.W.; Bronto, S.

    1998-01-01

    The melting of peridotite in the mantle wedge above subduction zones is generally believed to involve hydrous fluids derived from the subducting slab. But if mantle peridotite is upwelling within the wedge, melting due to pressure release could also contribute to magma production. Here we present measurements of the volatile content of primitive magmas from Galunggung volcano in the Indonesian are which indicate that these magmas were derived from the pressure-release melting of hot mantle peridotite. The samples that we have analysed consist of mafic glass inclusions in high-magnesium basalts. The inclusions contain uniformly low H2O concentrations (0.21-0.38 wt%), yet relatively high levels of CO2 (up to 750 p.p.m.) indicating that the low H2O concentrations are primary and not due to degassing of the magma. Results from previous anhydrous melting experiments on a chemically similar Aleutian basalts indicate that the Galunggung high-magnesium basalts were last in equilibrium with peridotite at ~1,320 ??C and 1.2 GPa. These high temperatures at shallow sub-crustal levels (about 300-600 ??C hotter than predicted by geodynamic models), combined with the production of nearly H2O- free basaltic melts, provide strong evidence that pressure-release melting due to upwelling in the sub-are mantle has taken place. Regional low- potassium and low-H2O (ref. 5) basalts found in the Cascade are indicate that such upwelling-induced melting can be widespread.

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

    USGS Publications Warehouse

    Clynne, M.A.

    1999-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

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

  7. Dike injection and magma mixing in Kenya rift volcanoes

    NASA Astrophysics Data System (ADS)

    Anthony, E. Y.; Espejel, V.; Biggs, J.

    2009-12-01

    A nexus of volcanoes in the rift graben at approximately the latitude of Nairobi consist of central vent trachyte, phonolite, and peralkaline rhyolite and cinder cone and fissure-fed flows of basalt to benmoreite. The volcanoes are referred to as the Central Kenya Peralkaline Province (CKPP, Macdonald and Scaillet, 2006, Lithos 91, 59-73) and formed by a combination of processes including fractional crystallization, magma mixing, and volatile transport (Ren et al., 2006, Lithos 91, 109-124; Macdonald et al., 2008, JPet 49, 1515-1547). This presentation focuses on magma mixing for trachytes and phonolites for Suswa rocks, which are the southernmost part of the CKPP. We also explore the contribution of magma process studies to the interpretation of recent geodetic data, which indicate inflation/deflation of up to 21 cm for Kenyan volcanoes from 1997 to present (Biggs et al., 2009, Geology, in press). Incontrovertible evidence for magma mixing is found in field evidence, where a basaltic trachyandesite ash horizon is found interbedded with syncaldera trachyte (Skilling, 1993, J. Geol. Society London 150, 885-896), hand-specimen and thin-section petrography, and disequilibrium mineral chemistry. Precaldera lavas contain a homogeneous group of anorthoclase crystals with An content 6% or less. Syncaldera samples contain this same group and two other populations: polysynthetic twinned labradorite and andesine and anorthoclase with An content of 17%. Textures for all three groups indicate disequilibrium. Postcaldera flows contain the high and low An anorthoclase populations but lack the polysynthetic twinned labradorite and andesine. These observations suggest a model of injection of mafic magmas via diking into shallow trachtytic magma systems. Recent geodetic studies of dike injection and subsequent seismic/volcanic activity in both Ethiopia and Lengai point to the ongoing importance of these processes to rift evolution in East Africa.

  8. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  9. Watching magma from space

    USGS Publications Warehouse

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

    2000-01-01

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

  10. Testing the Origins of Basalt Fragments fro Apollo 16

    NASA Technical Reports Server (NTRS)

    Donohue, P. H.; Stevens, R. E.; Neal, C. R.; Zeigler, R. A.

    2013-01-01

    Several 2-4 mm regolith fragments of basalt from the Apollo 16 site were recently described by [1]. These included a high-Ti vitrophyric basalts (60603,10-16) and one very-low-titanium (VLT) crystalline basalt (65703,9-13). As Apollo 16 was the only highlands sample return mission distant from the maria, identification of basaltic samples at the site indicates input from remote sites via impact processes [1]. However, distinguishing between impact melt and pristine basalt can be notoriously difficult and requires significant sample material [2-6]. The crystal stratigraphy method utilizes essentially non-destructive methods to make these distinctions [7,8]. Crystal stratigraphy combines quantitative petrography in the form of crystal size distributions (CSDs) coupled with mineral geochemistry to reveal the petrogenetic history of samples. The classic CSD plot of crystal size versus population density can reveal insights on growth/cooling rates, residence times, and magma history which in turn can be used to evaluate basaltic vs impact melt origin [7-9]. Electron microprobe (EMP) and laser ablation (LA)-ICP-MS analyses of mineral phases complement textural investigations. Trace element variations document subtle changes occurring during the formation of the samples, and are key in the interpretation and preservation of this rare lunar sample collection.

  11. Hotspots, basalts, and the evolution of the mantle

    NASA Technical Reports Server (NTRS)

    Anderson, D. L.

    1981-01-01

    It is noted that the trace element concentration patterns of continental and ocean island basalts and of mid-ocean ridge basalts are complementary. Estimates of the relative sizes of the source regions for these fundamentally different basalt types can be arrived at from the trace element enrichment-depletion patterns. Their combined volume occupies the greater part of the mantle above the 670 km discontinuity. It is pointed out that the source regions separated as a result of early mantle differentiation and crystal fractionation from the resulting melt. The mid-ocean ridge basalts source evolved from an eclogite cumulate that gave up its late-stage enriched fluids at various times to the shallower mantle and continental crust. The mid-ocean ridge basalts source is rich in garnet and clinopyroxene, while the continental and ocean island basalt source is a garnet peridotite that has experienced secondary enrichment. These relationships are found to be consistent with the evolution of a terrestrial magma ocean.

  12. High alumina (HA) and very high potassium (VHK) basalt clasts from Apollo 14 breccias. II - Whole rock geochemistry - Further evidence for combined assimilation and fractional crystallization within the lunar crust

    NASA Technical Reports Server (NTRS)

    Neal, C. R.; Taylor, L. A.; Schmitt, R. A.; Hughes, S. S.; Lindstrom, M. M.

    1989-01-01

    The understanding of basalt petrogenesis at the Apollo 14 site has increased markedly due to the study of 'new' samples from breccia 'pull-apart' efforts. Whole-rock compositions of 26 new high alumina (HA) and 7 very high potassium (VHK) basalts emphasize the importance of combined assimilation and fractional crystallization in a lunar regime. Previously formulated models for HA and VHK basalt petrogenesis are modified in order to accomodate these new data, although modeling parameters are essentially the same. The required range in HA basalt compositions is generated by the assimilation of KREEP by a 'primitive' parental magma. The VHK basalts can be generated by three parental HA basalts assimilating granite. Results indicate that VHK basalt compositions are dominated by the parental magma, and only up to 8 percent granite assimilation is required. This modeling indicates that at least three VHK basalt flows must be present at the Apollo 14 site.

  13. Long-Term Volumetric Eruption Rates and Magma Budgets

    SciTech Connect

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

    2005-01-01

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

  14. Magma storage under Iceland's Eastern Volcanic Zone

    NASA Astrophysics Data System (ADS)

    Maclennan, J.; Neave, D.; Hartley, M. E.; Edmonds, M.; Thordarson, T.; Morgan, D. J.

    2014-12-01

    The Eastern Volcanic Zone (EVZ) of Iceland is defined by a number of volcanic systems and large basaltic eruptions occur both through central volcanoes (e.g. Grímsvötn) and on associated fissure rows (e.g. Laki, Eldgjá). We have collected a large quantity of micro-analytical data from a number of EVZ eruptions, with the aim of identifying common processes that occur in the premonitory stages of significant volcanic events. Here, we focus on the AD 1783 Laki event, the early postglacial Saksunarvatn tephra and the sub-glacially erupted Skuggafjöll tindar and for each of these eruptions we have >100 olivine-hosted or plagioclase-hosted melt inclusion analyses for major, trace and volatile elements. These large datasets are vital for understanding the history of melt evolution in the plumbing system of basaltic volcanoes. Diverse trace element compositions in melt inclusions hosted in primitive macrocrysts (i.e. Fo>84, An>84) indicate that the mantle melts supplied to the plumbing system of EVZ eruptions are highly variable in composition. Concurrent mixing and crystallisation of these melts occurs in crustal magma bodies. The levels of the deepest of these magma bodies are not well constrained by EVZ petrology, with only a handful of high-CO2 melt inclusions from Laki providing evidence for magma supply from >5 kbar. In contrast, the volatile contents of melt inclusions in evolved macrocrysts, which are close to equilibrium with the carrier liquids, indicate that final depths of inclusion entrapment are 0.5-2 kbar. The major element composition of the matrix glasses shows that the final pressure of equilibration between the melt and its macrocryst phases also occurred at 0.5-2 kbar. The relationship between these pressures and seismic/geodetic estimates of chamber depths needs to be carefully evaluated. The melt inclusion and macrocryst compositional record indicates that injection of porphyritic, gas-rich primitive melt into evolved/enriched and degassed shallow

  15. Carbon dioxide in magmas and implications for hydrothermal systems

    USGS Publications Warehouse

    Lowenstern, J. B.

    2001-01-01

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

  16. Evidence for variations in magma production along oceanic spreading centers - A critical appraisal

    NASA Technical Reports Server (NTRS)

    Karson, J. A.; Elthon, D.

    1987-01-01

    Recent studies of the oceanic lithosphere near fracture zones have resulted in the proposal that the 'magma budget', defined as the amount of magma delivered to magma chambers or conduits beneath a spreading center for a given amount of spreading, decreases as fracture zones are approached. Geochemical variations in basaltic glasses collected near fracture zones are consistent with a decrease in partial melting as fracture zones are approached, but they could also be produced by variations in open-system magmatic processes with no change in the extent of partial melting. Although a decrease in the magma budget as fracture zones are approached is consistent with these data, so are alternative models that incorporate a constant magma budget.

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

    PubMed

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

    2014-12-15

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

  18. The magmatic plumbing of the submarine Hachijo NW volcanic chain, Hachijojima, Japan: Long-distance magma transport?

    NASA Astrophysics Data System (ADS)

    Ishizuka, Osamu; Geshi, Nobuo; Itoh, Jun'ichi; Kawanabe, Yoshihisa; Tuzino, Taqumi

    2008-08-01

    Recent geophysical observations on basaltic composite volcanoes in Izu-Bonin arc reveal the process of long-distance lateral magma transport within arc crust. To clarify a long-distance magma transport system of the basaltic arc volcano from geological and petrological aspects, we investigated 20-km-long submarine volcanic chains (Hachijo NW chain and Hachijo-kojima chain) and cones on the northeastern slope (NE edifices) as well as subaerial satellite cones nested Hachijo Nishiyama volcano in the northern Izu arc front. Basalts from Hachijo NW chain have more primitive composition than those from other edifices. The composition of the Hachijo NW chain basalts is controlled by fractional crystallization, while plagioclase accumulation occurred in NE edifices and subaerial satellite cones. Trace element and isotopic characteristics indicate that the same basaltic primary magma is involved in all sections of the volcano. This leads us to consider that magma was transported long distances between the Nishiyama volcano and the Hachijo NW chain. Primitive magma was laterally transported NNW for at least 20 km in the middle to lower crust (10-20 km deep) from Nishiyama volcano with only minimal crustal level modifications and formed Hachijo NW chain. On the other hand, magmas experienced crystal fractionation and accumulation at shallow magma chamber beneath Nishiyama volcano seems to have been transported in a short distance (<5 km) and formed NE trending edifices and subaerial satellite cones. The long-distance magma transport seems to be controlled by a regional extensional stress regime, while short-distance transport may be controlled by local stress regime affected by load of main volcanic edifice.

  19. Influence of pre-eruptive storage conditions and volatile contents on explosive Plinian style eruptions of basic magma

    NASA Astrophysics Data System (ADS)

    Goepfert, Katherine; Gardner, James E.

    2010-07-01

    Sub-Plinian to Plinian eruptions of basic magma present a challenge to modeling volcanic behavior because many models rely on magma becoming viscous enough during ascent to behave brittlely and cause fragmentation. Such models are unable, however, to strain low viscosity magma fast enough for it to behave brittlely. That assumes that such magmas actually have low viscosities, but the rare Plinian eruptions of basic magma may in fact result from them being anomalously viscous. Here, we examine two such eruptions, the 122 B.C. eruption of hawaiitic basalt from Mt. Etna and the late Pleistocene eruption of basaltic andesite from Masaya Caldera, to test whether they were anomalously viscous. We carried out hydrothermal experiments on both magmas and analyzed glass inclusions in plagioclase phenocrysts from each to determine their most likely pre-eruptive temperatures and water contents. We find that the hawaiite was last stored at 1,000-1,020°C, whereas the basaltic andesite was last stored at 1,010-1,060°C, and that both were water saturated with ˜3.0 wt.% water dissolved in them. Such water contents are not high enough to trigger Plinian explosive behavior, as much more hydrous basic magmas erupt less violently. In addition, despite being relatively cool, the viscosities of both magmas would range from ˜102.2-2.5 Pa s before erupting to ˜104 Pa s when essentially degassed, all of which are too fluid to cause brittle disruption. Without invoking special external forces to explain all such eruptions, one of the more plausible explanations is that when the bubble content reaches some critical value the fragile foam-like magma disrupts. The rarity of Plinian eruptions of basic magma may be because such magmas must ascend fast enough to retain their bubbles.

  20. 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.

  1. 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.

  2. Zr and Nb partition coefficients - Implications for the genesis of mare basalts, KREEP, and sea floor basalts

    NASA Technical Reports Server (NTRS)

    Mccallum, I. S.; Charette, M. P.

    1978-01-01

    The distribution coefficients of Zr and Nb have been found between armalcolite, ilmenite, clinopyroxene, rutile, plagioclase, and a coexisting high-Ti mare basalt melt in the 1105-1128 C temperature range. Henry's Law is not broken over the compositional range evaluated. The distribution coefficients of clinopyroxene are strongly dependent on melt and crystal compositions. The Al2O3 activity in the melt is a strong controlling parameter. It is concluded that: (1) Apollo 11 (low K) and Apollo 17 high-Ti mare basalts may have been generated by the partial melting of an ilmenite-rich cumulate, (2) Apollo 11 (high K) basalts may have been generated by a small amount of partial melting of a more fractionated ilmenite-rich cumulate, (3) KREEP magmas may have been formed as residual melts produced by fractional crystallization of the lunar magma ocean, and (4) anomalous (type II) MOR basalts may have been generated by small degrees of partial melting of a relatively undepleted mantle with clinopyroxene remaining in the residium.

  3. A chemical model for generating the sources of mare basalts - Combined equilibrium and fractional crystallization of the lunar magmasphere

    NASA Technical Reports Server (NTRS)

    Snyder, Gregory A.; Taylor, Lawrence A.; Neal, Clive R.

    1992-01-01

    A chemical model for simulating the sources of the lunar mare basalts was developed by considering a modified mafic cumulate source formed during the combined equilibrium and fractional crystallization of a lunar magma ocean (LMO). The parameters which influence the initial LMO and its subsequent crystallization are examined, and both trace and major elements are modeled. It is shown that major elements tightly constrain the composition of mare basalt sources and the pathways to their creation. The ability of this LMO model to generate viable mare basalt source regions was tested through a case study involving the high-Ti basalts.

  4. 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.

  5. Enrichment of basalt and mixing of dacite in the rootzone of a large rhyolite chamber: inclusions and pumices from the Rattlesnake Tuff, Oregon

    NASA Astrophysics Data System (ADS)

    Streck, Martin J.; Grunder, Anita L.

    A variety of cognate basalt to basaltic andesite inclusions and dacite pumices occur in the 7-Ma Rattlesnake Tuff of eastern Oregon. The tuff represents 280km3 of high-silica rhyolite magma zoned from highly differentiated rhyolite near the roof to less evolved rhyolite at deeper levels. The mafic inclusions provide a window into the processes acting beneath a large silicic chamber. Quenched basaltic andesite inclusions are substantially enriched in incompatible trace elements compared to regional primitive high-alumina olivine tholeiite (HAOT) lavas, but continuous chemical and mineralogical trends indicate a genetic relationship between them. Basaltic andesite evolved from primitive basalt mainly through protracted crystal fractionation and multiple cycles (>=10) of mafic recharge, which enriched incompatible elements while maintaining a mafic bulk composition. The crystal fractionation history is partially preserved in the mineralogy of crystal-rich inclusions (olivine, plagioclase+/-clinopyroxene) and the recharge history is supported by the presence of mafic inclusions containing olivines of Fo80. Small amounts of assimilation ( 2%) of high-silica rhyolite magma improves the calculated fit between observed and modeled enrichments in basaltic andesite and reduces the number of fractionation and recharge cycles needed. The composition of dacite pumices is consistent with mixing of equal proportions of basaltic andesite and least-evolved, high-silica rhyolite. In support of the mixing model, most dacite pumices have a bimodal mineral assemblage with crystals of rhyolitic and basaltic parentage. Equilibrium dacite phenocrysts are rare. Dacites are mainly the product of mingling of basaltic andesite and rhyolite before or during eruption and to a lesser extent of equilibration between the two. The Rattlesnake magma column illustrates the feedback between mafic and silicic magmas that drives differentiation in both. Low-density rhyolite traps basalts and induces

  6. Modeling the Time-dependent Changes in Electrical Conductivity of Basaltic Melts With Redox State

    NASA Astrophysics Data System (ADS)

    Pommier, A.; Gaillard, F.; Pichavant, M.

    2008-12-01

    The electrical conductivity σ is an efficient probe of mass transfer processes within silicate melts and magmas. Little attention has been given to the influence of redox state (fO2) on the melts conductivity. We present an experimental setup allowing electrical conductivity measurements for basaltic melts under variable fO2. We demonstrate a significant dependence of σ with fO2, allowing to characterize in situ the mechanisms and kinetics of redox changes in the melt. Experiments were conducted on basalts from Pu'u 'O'o, Hawaii, and Mt.Vesuvius, Italy. Measurements were performed cylindrical glass samples (OD: 6mm, ID: 1mm, L: 8mm) using an impedance spectrometer. Experiments were conducted in a 1atm vertical furnace, from 1200°C to 1400°C. Variable gas atmosphere (air, CO2 or CO-CO2 gas mixtures) were used, imposing ΔNNO from -1 to +7. Electrical conductivities were determined for the two melts at constant fO2, different T (constant fO2) and constant T, different fO2 (variable fO2) obtained by changing the gas composition. Isothermal reduction and oxidation cycles were performed. Glasses quenched from different T and fO2 conditions were analyzed by electron microprobe, the FeO concentration was determined by wet chemistry. In constant fO2 experiments, a small but detectable effect of fO2 on σ is evidenced. At 1300°C, the difference in the Kilauea sample conductivity between reduced (ΔNNO=-1) and oxidized (ΔNNO=+7) fO2 is <1(ohm.m)-1, the sample being more conductive when reduced. The temperature dependence of σ was fitted using Arrhenian equations, the activation energy Ea being 100kJ/mol. Sodium was identified as the main charge carrier in the melts. The fO2-effect on σ can thus be attributed to the influence of the Fe2+/Fe3+ ratio on sodium mobility. The fO2-dependence of σ was included in the model of Pommier et al.(2008), allowing the conductivity of natural melts to be calculated as a function of T, P, H2O, and fO2. Variable fO2 experiments

  7. How did the Lunar Magma Ocean crystallize?

    NASA Astrophysics Data System (ADS)

    Davenport, J.; Neal, C. R.

    2012-12-01

    It is generally accepted that the lunar crust and at least the uppermost (500 km) mantle was formed by crystallization of a magma ocean. How the magma ocean cooled and crystallized is still under debate. Parameters such as bulk composition, lunar magma ocean (LMO) crystallization method (fractional vs. equilibrium), depth of the LMO, and time for LMO solidification (effects of tidal heating mechanisms, insulating crustal lid, etc.) are still under debate. Neal (2001, JGR 106, 27865-27885) argues for the presence of garnet in the deep lunar mantle via compositional differences between low- and high-Ti mare basalts and volcanic glasses. Neal (2001) suggests that these compositional differences are due to the presence of garnet in the source regions of certain volcanic glass bead groups. As Neal (2001, JGR 106, 27865-27885) points out, determining if there is garnet in the lunar mantle is important in determining if the LMO was a "whole-Moon" event or if it was limited to certain areas. In the latter case, garnet would have been preserved in the lunar mantle and would have been used in the source material for some of the volcanic glasses. High-pressure experimental work concludes that with the right T-P conditions (2.5-4.5 GPa and 1675-1800° C) there could be a garnet-bearing pyroxene rich protolith at ~500 km depth. This also has significant implications for the bulk Al2O3 composition of the initial bulk Moon. If the LMO was not global, the volcanic glass beads that show evidence of garnet in their sources were formed from the deep, primitive lunar mantle, it begs the questions how was the non-LMO regions of the Moon formed and what was it's bulk composition? To try to answer these questions, it is necessary to thoroughly model the evolution of the LMO and then use that work to model the sources and formation of mare basalts, the volcanic glass beads, and other regions in question. To begin to answer these questions, we developed a scenario we have termed reverse

  8. Nanoparticulate mineral matter from basalt dust wastes.

    PubMed

    Dalmora, Adilson C; Ramos, Claudete G; Querol, Xavier; Kautzmann, Rubens M; Oliveira, Marcos L S; Taffarel, Silvio R; Moreno, Teresa; Silva, Luis F O

    2016-02-01

    Ultra-fine and nano-particles derived from basalt dust wastes (BDW) during "stonemeal" soil fertilizer application have been the subject of some concern recently around the world for their possible adverse effects on human health and environmental pollution. Samples of BDW utilized were obtained from companies in the mining district of Nova Prata in southern Brazil for chemical characterization and nano-mineralogy investigation, using an integrated application of advanced characterization techniques such as X-ray diffraction (XRD), High Resolution-Transmission Electron microscopy (HR-TEM)/(Energy Dispersive Spectroscopy) EDS/(selected-area diffraction pattern) SAED, Field Emission-Scanning Electron Microscopy (FE-SEM)/EDS and granulometric distribution analysis. The investigation has revealed that BDW materials are dominated by SiO2, Al2O3 and Fe2O3, with a complex micromineralogy including alkali feldspar, augite, barite, labradorite, hematite, heulandrite, gypsum, kaolinite, quartz, and smectite. In addition we have identified a number of trace metals such as Cd, Cu, Cr, Zn that are preferentially concentrated into the finer, inhalable, dust fraction and could so present a health hazard in the urban areas around the basalt mining zone. The implication of this observation is that use of these nanometric-sized particulates as soil fertilizer may present different health challenges to those of conventional fertilizers, inviting future work regarding the relative toxicities of these materials. Our investigation on the particle size distribution, nano-particle mineralogy and chemical composition in typical BDW samples highlights the need to develop cleaning procedures to minimise exposure to these natural fertilizing basalt dust wastes and is thus of direct relevance to both the industrial sector of basalt mining and to agriculture in the region.

  9. A cellular automaton model for the rise of magma

    NASA Astrophysics Data System (ADS)

    Piegari, Ester; di Maio, Rosa; Milano, Leopoldo; Scandone, Roberto

    2010-05-01

    structure, we have introduced in our model the presence of dissolved gas in the liquid. We relax the previous approximation made on the magma presence field n and treat it not as a step function, but as a continuous function, whose values reduce when pressure decreases as magma rises towards the surface. In particular, we focus on the modeling of Mt. Somma-Vesuvius volcano and, therefore, we consider basaltic magmas.

  10. CONDITIONS LEADING TO SUDDEN RELEASE OF MAGMA PRESSURE

    SciTech Connect

    B. Damjanac; E.S. Gaffney

    2005-08-26

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

  11. Production of isotopic variability in continental basalts by cryptic crustal contamination.

    PubMed

    Glazner, A F; Farmer, G L

    1992-01-03

    Regional variations in the Nd, Sr, and Pb isotopic compositions of Neogene basalts from the western United States are commonly interpreted to originate in the subcontinental mantle. In southern California, isotopic variability is restricted to lavas that lack mantle-derived xenoliths; xenolith-bearing basalts have uniform isotopic compositions similar to those of ocean-island basalts (OIBs). Combined with available geochemical data, these observations suggest that isotopic variability at these volcanoes results from subtle crustal contamination, locally by mafic crust, of primitive OIB-like magma. Recognition of such cryptic contamination may help to reconcile local discrepancies between tectonic and isotopic views of the subcontinental mantle.

  12. Production of isotopic variability in continental basalts by cryptic crustal contamination

    SciTech Connect

    Glazner, A.F. ); Farmer, G.L. )

    1992-01-03

    Regional variations in the Nd, Sr, and Pb isotopic compositions of Neogene basalts from the western US are commonly interpreted to originate in the subcontinental mantle. In southern California, isotopic variability is restricted to lavas that lack mantle-derived xenoliths; xenolith-bearing basalts have uniform isotopic compositions similar to those of ocean-island basalts (OIBs). Combined with available geochemical data, these observations suggest that isotopic variability at these volcanoes results from subtle crustal contamination, locally by mafic crust, of primitive OIB-like magma. Recognition of such cryptic contamination may help to reconcile local discrepancies between tectonic and isotopic views of the subcontinental mantle.

  13. Magma Storage, Recharge and the Caldera Cycle at Rabaul, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Fabbro, G.; Bouvet de Maisonneuve, C.; Sindang, M.

    2015-12-01

    Many calderas have a history of repeated caldera-forming eruptions, interspersed with periods of more minor activity. Rabaul, for instance, has had at least 11 ignimbrite-forming eruptions over the last 200 ky. The most recent of these was the '1400 BP' eruption, which led to caldera collapse. Since then, there has been multiple smaller eruptions, including the ongoing activity from Tavurvur and Vulcan. An important question facing volcanology today is what controls the size of eruptions at calderas such as Rabaul.Detailed stratigraphic sampling of the 1400BP eruption reveals that prior to eruption, the magma reservoir below Rabaul contained a well-mixed dacite with whole-rock SiO2 contents of 65.0-66.4 wt%. The dacite contains a single phenocryst assemblage of plag (An44-52), cpx (En43-46Fs13-15Wo40-41), opx (En69-71Fs25-28Wo3) and magnetite, along with minor apatite. The homogeneity of the dacite is underscored by the narrow range of compositions of both the matrix glass and the melt inclusions (67.8-69.0 wt% SiO2). The only exception to this is at the top of the ignimbrite, representing some of the last magma to have been withdrawn. Dispersed throughout the dacitic pumices are darker, more mafic blebs. Streaks of mingled magma with a range of SiO2 contents, down to 59.9 wt% SiO2 are also found in the pumice, suggesting that a mafic recharge magma was intruded into the base of the reservoir shortly before eruption. High TiO2 contents rule out the direct involvement of basalt, and instead imply the magma that intruded into the reservoir was an andesite with at least 56 wt% SiO2. Phenocrysts related to this recharge magma are rare, and the crystals found in the dark blebs are identical in composition to those found in the dacite, indicating that the recharge was aphyric. The present-day, post-caldera recharge magma is different to the pre-1400 BP recharge magma: it is basaltic. This suggests that the plumbing system of Rabaul is different during the pre-caldera and

  14. Geologic Mapping of Basalt Flows: Implications for Petrology

    NASA Astrophysics Data System (ADS)

    Donnelly-Nolan, J. M.; Grove, T. L.; Champion, D. E.

    2011-12-01

    Basaltic lava flows can display a variety of compositional signatures that hold clues to P, T, and composition of the mantle from which they originated. Compositional variation within basalt flows records individual histories of mantle and crustal processes. At the Cascades rear-arc Newberry and Medicine Lake volcanoes, detailed geologic mapping of compositionally-zoned basalts indicates clearly that "drive-through" sampling of such lava flows would fail to capture the full geochemical story. For these flows, the internal stratigraphy captures the eruptive sequence that took place as the magma reservoir was tapped. Given a range of composition, or exposures of basalt that have different compositions, how does one know whether different eruptions have occurred, or whether a single compositionally-zoned eruption took place? Geologic mapping today goes well beyond traditional approaches using petrography and morphology. In addition to those basic tools, iterative use of multiple chemical analyses and, most critically, paleomagnetic sampling are essential to identifying individual basalt eruptive events. At Medicine Lake volcano in N. CA, 4 compositionally-zoned basalt flows have been documented (see Donnelly-Nolan, 2011, USGS map SIM 2927): (1) basalt of Black Crater and Ross Chimneys; this very small eruptive event produced 0.001 km3 of lava that covers 0.4 km2. SiO2 content increased from 48.3 to 50.6% as the eruption progressed; composition also correlates with latitude; (2) basalt of Giant Crater, 200-sq-km postglacial basaltic andesite to basalt that is characterized by strong variation in a variety of elements (e.g. 47.7-53.2% SiO2, 0.07-1.1% K2O) [Baker et al. 1991 JGR; Donnelly-Nolan et al. 1991 JGR]; (3) basalt of Mammoth Crater, 250-sq-km basaltic andesite to basalt also having strong SiO2 variation (48.2-56.0%), but in addition a lobe enriched in FeO and TiO2; (4) 300-sq-km basalt of Yellowjacket Butte displays limited SiO2 variation, but linear variation

  15. Diverse primitive magmas in the Cascade arc, Northern Oregon and Southern Washington

    USGS Publications Warehouse

    Conrey, R.M.; Sherrod, D.R.; Hooper, P.R.; Swanson, D.A.

    1997-01-01

    Bulk-rock major- and trace-element composition, petrography and mineral compositions are presented for a diverse suite of 22 primitive mafic lavas in the Cascade Range of northern Oregon and southern Washington. With the exception of an early Western Cascade basalt, all the rocks are younger than 7 Ma. Intensive parameters [F(H2O), f(O2), T, P] for the magmas have been inferred mostly from equilibrium olivine-liquid and plagioclase-liquid relations. Nearly anhydrous, MORB-like, low-K tholeiite was probably derived from relatively high degrees of decompression-induced melting of shallow, depleted, relatively unmetasomatized lithospheric mantle during intra-arc rifting. The degree of partial melting decreases northward along the arc, whereas the depth of average melt generation increases. OIB-like basalt represents deeper, wetter, smaller-degree melts of more enriched asthenospheric mantle, unaffected by subduction. Olivine analcimite resembles the silicate melt considered responsible for within-plate mantle metasomatism. Post-7-Ma subduction-related basalt was derived by low degrees of partial melting of subduction-metasomatized garnet lherzolite, similar to OIB-like basalt source-mantle before modification. The spectrum of subduction-related basalt from cooler and wetter (and slightly more oxidized) absarokite to progressively hotter and drier high-K calc-alkaline basalt and calc-alkaline basalt seems to be due to varying degrees of metasomatism of the deep mantle wedge by relatively cool, wet, LILE-rich absarokitic magmas coming from near the subducted slab. Early Western Cascade basalt is more typically arc-like in its composition and mineralogy, and was probably generated under H2O-rich conditions when more vigorous subduction prevailed. Depleted basaltic andesite may have been generated by low degrees of partial melting of residual harzburgite, possibly formed during the generation of early Western Cascade basalt.

  16. Additive Construction using Basalt Regolith Fines

    NASA Technical Reports Server (NTRS)

    Mueller, Robert P.; Sibille, Laurent; Hintze, Paul E.; Lippitt, Thomas C.; Mantovani, James G.; Nugent, Matthew W.; Townsend, Ivan I.

    2014-01-01

    Planetary surfaces are often covered in regolith (crushed rock), whose geologic origin is largely basalt. The lunar surface is made of small-particulate regolith and areas of boulders located in the vicinity of craters. Regolith composition also varies with location, reflecting the local bedrock geology and the nature and efficiency of the micrometeorite-impact processes. In the lowland mare areas (suitable for habitation), the regolith is composed of small granules (20 - 100 microns average size) of mare basalt and volcanic glass. Impacting micrometeorites may cause local melting, and the formation of larger glassy particles, and this regolith may contain 10-80% glass. Studies of lunar regolith are traditionally conducted with lunar regolith simulant (reconstructed soil with compositions patterned after the lunar samples returned by Apollo). The NASA Kennedy Space Center (KSC) Granular Mechanics & Regolith Operations (GMRO) lab has identified a low fidelity but economical geo-technical simulant designated as Black Point-1 (BP-1). It was found at the site of the Arizona Desert Research and Technology Studies (RATS) analog field test site at the Black Point lava flow in adjacent basalt quarry spoil mounds. This paper summarizes activities at KSC regarding the utilization of BP-1 basalt regolith and comparative work with lunar basalt simulant JSC-1A as a building material for robotic additive construction of large structures. In an effort to reduce the import or in-situ fabrication of binder additives, we focused this work on in-situ processing of regolith for construction in a single-step process after its excavation. High-temperature melting of regolith involves techniques used in glassmaking and casting (with melts of lower density and higher viscosity than those of metals), producing basaltic glass with high durability and low abrasive wear. Most Lunar simulants melt at temperatures above 1100 C, although melt processing of terrestrial regolith at 1500 C is not

  17. Pressure conditions for the solidification of the Skaergaard intrusion: Eruption of East Greenland flood basalts in less than 300,000 years

    NASA Astrophysics Data System (ADS)

    Larsen, Rune B.; Tegner, Christian

    2006-11-01

    Primary granophyres are differentiated from olivine tholeiitic magma and occur interstitially throughout the cumulus stratigraphy of the Skaergaard intrusion, East Greenland. Samples from the Lower Zones a-c (LZa-c), the Middle Zone (MZ) and the Sandwich Horizon (SH) are included in the present study together with granophyric accumulations in gabbroic pegmatite from LZa-c. Fluid inclusions in quartz and the mineral assemblage in the granophyres record the pressure under which the Skaergaard intrusion crystallised. Pegmatitic granophyre from LZa-c consists mainly of quartz, plagioclase (An 4-7) and alkali feldspar (Or 40-80) enclosing an earlier formed assemblage of ferrohastingsitic and ferroedenitic hornblende, fayalite (Fo 4-5), titanite, biotite and fluor-apatite. Granophyric quartz, albite and alkali feldspar crystallised from water-saturated granitic melts near eutectic minimum conditions between 680 and 660 °C. The pressure of granophyre crystallisation was modelled by the intercept between fluid inclusion isochores and the minimum melt solidus for granitic compositions. Pressures, recalculated to the roof pendant of the intrusion, are 0.7 ± 0.5 for LZa, 2.0 ± 0.2 for LZb-c, 2.3 ± 0.8 for MZ (the Triple Group level) and 3.3 ± 1.3 kb for SH. Amphibole geobarometry, independently, confirm the pressure estimates for pegmatitic granophyres in LZa-c. The granophyres formed as the intrusion cooled through the minimum melt solidus in LZa, LZb, LZc, MZ and SH, respectively. The pressure increase from LZa to SH granophyres is explained by progressive burial during cooling of the intrusion and contemporaneous outpouring of 5.3-6.3 ± 2.7 km of flood basalts during the initial opening of the Northeast Atlantic Ocean. Accordingly, the Skaergaard intrusion evolved from a subvolcanic magma chamber at emplacement to a more deep-seated igneous system during terminal crystallization when the majority of the intercumulus phases formed. The present cooling history suggests

  18. Petrogenesis of basalt-comendite and basalt-pantellerite suites, Terceira, Azores, and some implications for the origin of ocean-island rhyolites

    NASA Astrophysics Data System (ADS)

    Mungall, J. E.; Martin, R. F.

    1995-02-01

    Petrogenetic modeling of the Recent lava succession of Santa Barbara and Pico Alto volcanoes and associated basaltic lavas indicates that there are two discrete lava series present, one erupted from the axial rift linking the two central volcanoes and one associated with monogenetic cones scattered around the flanks of Santa Barbara. The felsic lavas of both volcanoes are peralkaline and appear to be derived from associated basalts by fractional crystallization of an assemblage including essential amphibole. Trace element abundances in the felsic lavas, particularly those of Sr and REE, cannot be reconciled with an origin through partial melting of basaltic material at the base of the volcanic pile. The difference between the comenditic and pantelleritic differentiation trends of Santa Barbara and Pico Alto is attributed primarily to FO2 control of the crystallizing assemblage, probably related to thermal dissociation of magmatic water in the Santa Barbara magma chamber. This effect may be augmented by minor differences in parent basaltic compositions, the Pico Alto pantellerites being derived from the rift basalts whereas the Santa Barbara comendites are derived from the off-rift basalts. A compositional gap between 54 and 64% silica content in the lavas is not present if the suite is extended to include co-magmatic hypabyssal xenoliths, leading to the inference that the gap in this and other bimodal suites results solely from a relative inability of magma of intermediate composition to erupt.

  19. A preliminary analysis of lunar extra-mare basalts - Distribution, compositions, ages, volumes, and eruption styles

    NASA Technical Reports Server (NTRS)

    Whitford-Stark, J. L.

    1982-01-01

    Extra-mare basalts occupy 8.5% of the lunar basalt area and comprise 1% of the total mare basalt volume. They are preferentially located where the crust is thin and topographically low. In terms of age, eruption style, and composition they are as variable as the mare basalts. In some instances extrusion in extra-mare craters was preceded by floor-fracturing whereas in other cases it apparently was not. The volume of lava erupted may have been controlled more by the volume of magma produced than by hydrostatic effects. A minimum of nearly 1300 separate basalt eruptions is indicated; the true value could be nearer 30,000 separate eruptions.

  20. Variation of volatile concentration in a magma system of Satsuma-Iwojima volcano deduced from melt inclusion analyses

    NASA Astrophysics Data System (ADS)

    Saito, G.; Kazahaya, K.; Shinohara, H.; Stimac, J.; Kawanabe, Y.

    2001-08-01

    Chemical analyses of 30 melt inclusions from Satsuma-Iwojima volcano, Japan, were carried out to investigate volatile evolution in a magma chamber beneath the volcano from about 6300 yr BP to the present. Large variations in volatile concentrations of melts were observed. (1) Water concentration of rhyolitic melts decreases with time; 3-4.6 wt.% at the time of latest caldera-forming eruption of Takeshima pyroclastic flow deposit (ca. 6300 yr BP), 3 wt.% for small pyroclastic flow (ca. 1300 yr BP) of Iwodake, post-caldera rhyolitic dome, and 0.7-1.4 wt.% for submarine lava eruption (Showa-Iwojima) in 1934. (2) Rhyolitic melts of the Takeshima and Iwodake eruptions contained CO 2 of less than 40 ppm, while the Showa-Iwojima melt has higher CO 2 concentration of up to 140 ppm. (3) Water and CO 2 concentrations of basaltic to andesitic melt of Inamuradake, a post-caldera basaltic scoria cone, are 1.2-2.8 wt.% and ≤290 ppm, respectively. Volatile evolution in the magma chamber is interpreted as follows: (1) the rhyolitic magma at the time of the latest caldera-forming eruption (ca. 6300 yr BP) was gas-saturated due to pressure variation in the magma chamber because the large variation in water concentration of the melt was attributed to exsolution of volatile in the magma prior to the eruption. Iwodake eruption (ca. 1300 yr BP) was caused by a remnant of the caldera-forming rhyolitic magma, suggested from the similarity of major element composition between these magmas. (2) Volatile composition of the Showa-Iwojima rhyolitic melt agrees with that of magmatic gases presently discharging from a summit of Iwodake, indicating the low pressure degassing condition. (3) The degassing of the magma chamber by magma convection in a conduit of Iwodake during non-eruptive but active degassing period for longer than 800 years decreased water concentration of the rhyolitic magma. (4) Geological and petrological observations indicate that a stratified magma chamber, which consists

  1. 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.

  2. 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.

  3. Pillow basalts of the Angayucham terrane: Oceanic plateau and island crust accreted to the Brooks Range

    NASA Astrophysics Data System (ADS)

    Pallister, John S.; Budahn, James R.; Murchey, Benita L.

    1989-11-01

    The Angayucham Mountains (north margin of the Yukon-Koyukuk province) are made up of an imbricate stack of four to eight east-west trending, steeply dipping, fault slabs composed of Paleozoic (Devonian to Mississippean), Middle to Late Triassic, and Early Jurassic oceanic upper crustal rocks (pillow basalt, subordinate diabase, basaltic tuff, and radiolarian chert). Field relations and geochemical characteristics of the basaltic rocks suggest that the fault slabs were derived from an oceanic plateau or island setting and were emplaced onto the Brooks Range continental margin. The basalts are variably metamorphosed to prehnite-pumpellyite and low-greenschist facies. Major element analyses suggest that many are hypersthene-normative olivine tholeiites. Classification based on immobile trace elements confirms the tholeiitic character of most of the basalts but suggests that some had primary compositions transitional to alkali basalt. Although field and petrographic features of the basalts are similar, trace element characteristics allow definition of geographically distinct suites. A central outcrop belt along the crest of the mountains is made up of basalt with relatively flat rare earth element (REE) patterns. This belt is flanked to the north and south by LREE (light rare earth element)-enriched basalts. Radiolarian and conodont ages from interpillow and interlayered chert and limestone indicate that the central belt of basalts is Triassic in age, the southern belt is Jurassic in age, and the northern belt contains a mixture of Paleozoic and Mesozoic ages. Data for most of the basalts cluster in the "within-plate basalt" fields of trace element discriminant diagrams; none have trace-element characteristics of island arc basalt. The Triassic and Jurassic basalts are geochemically most akin to modern oceanic plateau and island basalts. Field evidence also favors an oceanic plateau or island setting. The great composite thickness of pillow basalt probably resulted

  4. Nd-Sr isotopes, petrochemistry, and origin of the Siberian flood basalts, USSR

    SciTech Connect

    Sharma, M.; Basu, A.R. ); Nesterenko, G.V. )

    1991-04-01

    The Siberian Flood Basalt Province (SFBP) of Permo-Triassic age is one of the largest flood basalt provinces with an estimated area of exposure of 337 000 km{sup 2}, average thickness of 1 km, and a magma volume of 337 000 km{sup 3}. Forty-seven basaltic rocks from two main subprovinces, Norilsk (5-10{percent} of area, thickness up to 3 km) and Putorana (90-95{percent} of area, thickness of more than 2 km), were selected, on the basis of petrography and volcano-stratigraphic relation, for major-element analysis. Twenty-six of these basalts, twelve from Norilsk and fourteen from Putorana, were analyzed for Nd- and Sr-isotopic compositions. The Norilsk and Putorana basalts show some contrasting behavior in terms of the ratios of the highly incompatible elements of Ti, P, and K as a function of their Mg. The Norilsk basalts are more variable, suggesting the role of fractional crystallization-assimilation in their evolution. In contrast, the Putorana basalts show remarkable uniformity in their bulk chemical compositions. In Nd- and Sr-isotopic space, most of the Siberian basalts also fall within the field defined by the ocean island basalts data, implying common mantle sources. It is concluded that the SFBP originated by hotspot volcanism due to the rise of a large and relatively primitive lower mantle-derived plume beneath the Siberian continent.

  5. Alkali metal ionization detector

    DOEpatents

    Bauerle, James E.; Reed, William H.; Berkey, Edgar

    1978-01-01

    Variations in the conventional filament and collector electrodes of an alkali metal ionization detector, including the substitution of helical electrode configurations for either the conventional wire filament or flat plate collector; or, the substitution of a plurality of discrete filament electrodes providing an in situ capability for transferring from an operationally defective filament electrode to a previously unused filament electrode without removing the alkali metal ionization detector from the monitored environment. In particular, the helical collector arrangement which is coaxially disposed about the filament electrode, i.e. the thermal ionizer, provides an improved collection of positive ions developed by the filament electrode. The helical filament design, on the other hand, provides the advantage of an increased surface area for ionization of alkali metal-bearing species in a monitored gas environment as well as providing a relatively strong electric field for collecting the ions at the collector electrode about which the helical filament electrode is coaxially positioned. Alternatively, both the filament and collector electrodes can be helical. Furthermore, the operation of the conventional alkali metal ionization detector as a leak detector can be simplified as to cost and complexity, by operating the detector at a reduced collector potential while maintaining the sensitivity of the alkali metal ionization detector adequate for the relatively low concentration of alkali vapor and aerosol typically encountered in leak detection applications.

  6. Investigating magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions.

    NASA Astrophysics Data System (ADS)

    Dahren, Börje; Troll, Valentin R.; Andersson, Ulf-Bertil; Chadwick, Jane P.; Gardner, Mairi F.

    2010-05-01

    Improving our understanding of magma plumbing and storage remains one of the major challenges for petrologists and volcanologists today. This is especially true for explosive volcanoes, where constraints on magma plumbing are essential for predicting dynamic changes in future activity and thus for hazard mitigation. This study aims to investigate the magma plumbing system at Anak Krakatau; the post-collapse cone situated on the rim of the 1883 Krakatau caldera. Since 1927, Anak Krakatau has been highly active, growing at a rate of ~8 cm/week. The methods employed are a.) clinopyroxene-melt thermo-barometry [1,2] b.) plagioclase-melt thermo-barometry [3] c.) clinopyroxene composition barometry [2,4] and d.) olivine-melt thermometry [5]. The minerals analysed are from basaltic-andesites erupted between 1990-2002, with an average modal composition of 70% groundmass, 25% plagioclase, 4% clinopyroxene and <1% olivine. Clinopyroxenes are homogenous and display no obvious zoning. Plagioclases are considerably more heterogenous, exhibiting complex zoning and An content between An45-80. In addition, mineral compositions of older clinopyroxenes, erupted between 1883-1981, are used for comparison [6,7]. Previously, both seismic [8] and petrological studies [6,7,9] have addressed the magma plumbing beneath Anak Krakatau. Interestingly, petrological studies indicate shallow magma storage in the region of 2-8 km, while the seismic evidence points towards a mid-crustal and a deep storage, at 9 and 22 km respectively. Our results imply that clinopyroxene presently crystallizes in a mid-crustal storage region (8-12 km), a previously identified depth level for magma storage, using seismic methods [8]. Plagioclases, in turn, form at shallower depths (4-6 km), in concert with previous petrological studies [6,7,9]. Pre-1981 clinopyroxenes record deeper levels of storage (8-22 km), indicating that there may have been an overall shallowing of the plumbing system over the last ~40 years

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  8. 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.

  9. Jorullo Volcano, Michoacan, Mexico: the earliest stages of fractionation in calc-alkaline magmas

    SciTech Connect

    Luhr, J.; Carmichael, I.S.E.

    1985-01-01

    Between 1759 and 1774, Jorullo Volcano and four associated cinder cones erupted approximately 2 km/sup 3/ of magma which evolved progressively with time from early ol-hy-normative primitive basalts (Mgnumber=73, 516 ppm Cr, 260 ppm Ni) to late-stage qtz-hy-normative basaltic andesites. All lavas contain <6 vol% phenocrysts of magnesian olivine (fO/sub 90-70/) with Cr-Al-Mg spinel inclusions, and microphenocrysts of plagioclase and augite. Smooth whole-rock major and trace element compositional trends through the suite can be largely modeled by simple crystal fractionation of olivine, augite, plagioclase, and minor spinel. In order for augite and plagioclase to have been near-liquidus phases, the modeled crystal fractionation event must have occurred at lower-crustal to upper-mantle pressures (8-15 Kb). The crystals actually present in the Jorullo lavas, however, formed at low pressures. Compared to modeled abundances, La, Ce, Rb, Sr, Ba, Hf, Th, and Ta are anomalously enriched in the late-stage basaltic andesites and Dy, Yb, and Lu are anomalously depleted. These discrepancies apparently indicate the importance of other magma-chamber processes. Most high-alumina basalts reported in the literature have 18 to 21 wt% Al/sub 2/O/sub 3/, but are too depleted in MgO, Cr, and Ni to be direct mantle products. These high-alumina basalts have probably undergone significant fractionation of olivine, augite, plagioclase, and spinel from primitive parental basalt similar to the early Jorullo magmas. For hydraulic reasons, such primitive basalts are rarely erupted in mature arcs, and may be completely absent from mature stratovolcanoes.

  10. Identifying recycled ash in basaltic eruptions

    NASA Astrophysics Data System (ADS)

    D'Oriano, Claudia; Bertagnini, Antonella; Cioni, Raffaello; Pompilio, Massimo

    2014-07-01

    Deposits of mid-intensity basaltic explosive eruptions are characterized by the coexistence of different types of juvenile clasts, which show a large variability of external properties and texture, reflecting alternatively the effects of primary processes related to magma storage or ascent, or of syn-eruptive modifications occurred during or immediately after their ejection. If fragments fall back within the crater area before being re-ejected during the ensuing activity, they are subject to thermally- and chemically-induced alterations. These `recycled' clasts can be considered as cognate lithic for the eruption/explosion they derive. Their exact identification has consequences for a correct interpretation of eruption dynamics, with important implications for hazard assessment. On ash erupted during selected basaltic eruptions (at Stromboli, Etna, Vesuvius, Gaua-Vanuatu), we have identified a set of characteristics that can be associated with the occurrence of intra-crater recycling processes, based also on the comparison with results of reheating experiments performed on primary juvenile material, at variable temperature and under different redox conditions.

  11. Identifying recycled ash in basaltic eruptions.

    PubMed

    D'Oriano, Claudia; Bertagnini, Antonella; Cioni, Raffaello; Pompilio, Massimo

    2014-07-28

    Deposits of mid-intensity basaltic explosive eruptions are characterized by the coexistence of different types of juvenile clasts, which show a large variability of external properties and texture, reflecting alternatively the effects of primary processes related to magma storage or ascent, or of syn-eruptive modifications occurred during or immediately after their ejection. If fragments fall back within the crater area before being re-ejected during the ensuing activity, they are subject to thermally- and chemically-induced alterations. These 'recycled' clasts can be considered as cognate lithic for the eruption/explosion they derive. Their exact identification has consequences for a correct interpretation of eruption dynamics, with important implications for hazard assessment. On ash erupted during selected basaltic eruptions (at Stromboli, Etna, Vesuvius, Gaua-Vanuatu), we have identified a set of characteristics that can be associated with the occurrence of intra-crater recycling processes, based also on the comparison with results of reheating experiments performed on primary juvenile material, at variable temperature and under different redox conditions.

  12. Identifying recycled ash in basaltic eruptions

    PubMed Central

    D'Oriano, Claudia; Bertagnini, Antonella; Cioni, Raffaello; Pompilio, Massimo

    2014-01-01

    Deposits of mid-intensity basaltic explosive eruptions are characterized by the coexistence of different types of juvenile clasts, which show a large variability of external properties and texture, reflecting alternatively the effects of primary processes related to magma storage or ascent, or of syn-eruptive modifications occurred during or immediately after their ejection. If fragments fall back within the crater area before being re-ejected during the ensuing activity, they are subject to thermally- and chemically-induced alterations. These ‘recycled' clasts can be considered as cognate lithic for the eruption/explosion they derive. Their exact identification has consequences for a correct interpretation of eruption dynamics, with important implications for hazard assessment. On ash erupted during selected basaltic eruptions (at Stromboli, Etna, Vesuvius, Gaua-Vanuatu), we have identified a set of characteristics that can be associated with the occurrence of intra-crater recycling processes, based also on the comparison with results of reheating experiments performed on primary juvenile material, at variable temperature and under different redox conditions. PMID:25069064

  13. How important is the role of crystal fractionation in making intermediate magmas? Insights from Zr and P systematics

    NASA Astrophysics Data System (ADS)

    Lee, Cin-Ty A.; Bachmann, Olivier

    2014-05-01

    Most magmatism on Earth forms by direct melting of the mantle, generating basalts at the low silica end of the terrestrial compositional spectrum. However, most subduction zone magmas erupted or sampled at the surface are basalt-andesitic to andesitic and hence have higher Si contents. Endmember hypotheses for the origin of andesites are: (1) direct melting of the mantle at water-saturated conditions, (2) partial re-melting of altered basaltic crust, (3) crystal fractionation of arc basalts in crustal magma chambers, and (4) mixing of mafic magmas with high Si crust or magmas, e.g., dacite-rhyolite. Here, we explore the possibility of using Zr and P systematics to evaluate the importance of some of these processes. Direct melting of the mantle generates magmas with low Zr (<50 ppm) and P2O5 (<0.2 wt.%). Crystal-liquid segregation should drive an increase in P and Zr in the residual magma because the magma is initially undersaturated in zircon and apatite. With further cooling and crystallization, apatite followed by zircon will saturate, causing P and Zr to decrease so that most rhyolites and granites will have low P and Zr (high temperature rhyolites may never saturate in zircon and will maintain high Zr contents). Mixing of basalts with rhyolites having low P and Zr should generate coupled decreases in Zr and P with increasing SiO2. Here, we show that Zr (>100 ppm) and P2O5 (>0.2 wt.%) in island- and continental-arc magmas initially increase to levels higher than what can be achieved if andesites form by direct mantle melting. As Si increases, both Zr and P decrease with Zr decreasing at higher Si, and hence lagging the decrease in P. These systematics, particularly the decoupled decrease in Zr and P, cannot be explained by mixing, and instead, are more easily explained if andesites are dominantly formed by crystal-liquid segregation from moderately hydrous basalt, wherein P and Zr are controlled, respectively, by early and later saturation in apatite and zircon

  14. The role of bubble ascent in magma mixing

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  15. Magma deformation and emplacement in rhyolitic dykes

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  16. The Magma Chamber Simulator: Modeling the Impact of Wall Rock Composition on Mafic Magmas during Assimilation-Fractional Crystallization

    NASA Astrophysics Data System (ADS)

    Creamer, J. B.; Spera, F. J.; Bohrson, W. A.; Ghiorso, M. S.

    2012-12-01

    C while in the second example features a WR beginning at 700oC due to prior regional heating from magmatic activity. In the first example, the Magma only experiences FC as it completely crystallizes before the WR is heated above the solidus. In the second example, identical beyond WR starting temperature, the Magma begins to receive anatectic melt from the granitic WR after ~10% of its original mass has crystallized. Once the Magma in the AFC example has reached an SiO2 content of 60 wt.%, the relative masses of 'initial Magma melt' : 'remaining melt in Magma' : 'cumulates' : 'cumulative anatectic melt added' is 1:1.4:0.1:0.5 as orthopyroxene follows olivine crystallization once assimilation begins. At the equivalent point of 60 wt.% SiO2 in the first FC-only case, these mass ratios sit at 1:0.35:0.65:0, as clinopyroxene and plagioclase follow olivine crystallization. In the second example with AFC, the assimilation dramatically modifies the chemical evolution of the magma as described above until a point where, in the WR, alkali feldspar has been exhausted by partial melting at the plag-kspar-qtz ternary minimum and the WR melt production rate slows for given heat input. Beyond these examples, the influence of WR composition on the chemical trends of an evolving set of mafic magmas undergoing AFC is portrayed.

  17. Crystallization of the magma ocean

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  18. Efficiency of differentiation in the Skaergaard magma chamber

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  19. Molybdenite saturation in silicic magmas: Occurrence and petrological implications

    USGS Publications Warehouse

    Audetat, A.; Dolejs, D.; Lowenstern, J. B.

    2011-01-01

    We identified molybdenite (MoS2) as an accessory magmatic phase in 13 out of 27 felsic magma systems examined worldwide. The molybdenite occurs as small (<20 ??m) triangular or hexagonal platelets included in quartz phenocrysts. Laser-ablation inductively coupled plasma mass spectrometry analyses of melt inclusions in molybdenite-saturated samples reveal 1-13 ppm Mo in the melt and geochemical signatures that imply a strong link to continental rift basalt-rhyolite associations. In contrast, arc-associated rhyolites are rarely molybdenite-saturated, despite similar Mo concentrations. This systematic dependence on tectonic setting seems to reflect the higher oxidation state of arc magmas compared with within-plate magmas. A thermodynamic model devised to investigate the effects of T, f O2 and f S2 on molybdenite solubility reliably predicts measured Mo concentrations in molybdenite-saturated samples if the magmas are assumed to have been saturated also in pyrrhotite. Whereas pyrrhotite microphenocrysts have been observed in some of these samples, they have not been observed from other molybdenite-bearing magmas. Based on the strong influence of f S2 on molybdenite solubility we calculate that also these latter magmas must have been at (or very close to) pyrrhotite saturation. In this case the Mo concentration of molybdenite-saturated melts can be used to constrain both magmatic f O2 and f S2 if temperature is known independently (e.g. by zircon saturation thermometry). Our model thus permits evaluation of magmatic f S2, which is an important variable but is difficult to estimate otherwise, particularly in slowly cooled rocks. ?? The Author 2011. Published by Oxford University Press. All rights reserved.

  20. Sloshing of a bubbly magma reservoir as a mechanism of triggered eruptions

    NASA Astrophysics Data System (ADS)

    Namiki, Atsuko; Rivalta, Eleonora; Woith, Heiko; Walter, Thomas R.

    2016-06-01

    Large earthquakes sometimes activate volcanoes both in the near field as well as in the far field. One possible explanation is that shaking may increase the mobility of the volcanic gases stored in magma reservoirs and conduits. Here experimentally and theoretically we investigate how sloshing, the oscillatory motion of fluids contained in a shaking tank, may affect the presence and stability of bubbles and foams, with important implications for magma conduits and reservoirs. We adopt this concept from engineering: severe earthquakes are known to induce sloshing and damage petroleum tanks. Sloshing occurs in a partially filled tank or a fully filled tank with density-stratified fluids. These conditions are met at open summit conduits or at sealed magma reservoirs where a bubbly magma layer overlays a newly injected denser magma layer. We conducted sloshing experiments by shaking a rectangular tank partially filled with liquids, bubbly fluids (foams) and fully filled with density-stratified fluids; i.e., a foam layer overlying a liquid layer. In experiments with foams, we find that foam collapse occurs for oscillations near the resonance frequency of the fluid layer. Low viscosity and large bubble size favor foam collapse during sloshing. In the layered case, the collapsed foam mixes with the underlying liquid layer. Based on scaling considerations, we constrain the conditions for the occurrence of foam collapse in natural magma reservoirs. We find that seismic waves with lower frequencies < 1 Hz, usually excited by large earthquakes, can resonate with magma reservoirs whose width is > 0.5 m. Strong ground motion > 0.1 m s- 1 can excite sloshing with sufficient amplitude to collapse a magma foam in an open conduit or a foam overlying basaltic magma in a closed magma reservoir. The gas released from the collapsed foam may infiltrate the rock or diffuse through pores, enhancing heat transfer, or may generate a gas slug to cause a magmatic eruption. The overturn in the

  1. Lu-Hf and Sm-Nd evolution in lunar mare basalts

    NASA Technical Reports Server (NTRS)

    Unruh, D. M.; Tatsumoto, M.; Stille, P.; Patchett, P. J.

    1984-01-01

    Existing cumulate remelting models for mare basalt genesis are evaluated in light of Lu-Hf, Rb-Sr, Sm-Nd data and overall REE characteristics in order to determine the simplest model that can account for these data. A data base for comparing Lu-Hf evolution in the lunar mantle as inferred from Lu-Hf analyses of oceanic basalts is presented along with a preliminary comparison of Lu-Hf and Sm-Nd evolution betwee mare basalts and terrestrial oceanic basalts. It is found that Lu/Hf characteristics of mare basalts cannot be explained in terms of modal melting of cumulate sources formed from a magma ocean with chondritic Lu/Hf. The data are consistent with a model in which the cumulate sources formed from a light REE + HF-enriched magma ocean. Nonmodal melting of ilmenite in the sources is also required. The Lu-Hf data suggest that even the high-Ti basalt sources contained no more than about 3 percent ilmenite.

  2. Apparatus enables accurate determination of alkali oxides in alkali metals

    NASA Technical Reports Server (NTRS)

    Dupraw, W. A.; Gahn, R. F.; Graab, J. W.; Maple, W. E.; Rosenblum, L.

    1966-01-01

    Evacuated apparatus determines the alkali oxide content of an alkali metal by separating the metal from the oxide by amalgamation with mercury. The apparatus prevents oxygen and moisture from inadvertently entering the system during the sampling and analytical procedure.

  3. The influence of geometry on the ascent of magma in open fissures

    NASA Astrophysics Data System (ADS)

    Giberti, G.; Wilson, L.

    1990-09-01

    During steady eruption, the flow conditions (emitted mass flux, exit velocity and exit pressure) depend on the geometry of the conduit in which the eruption occurs. This dependence is examined for the onedimensional, isothermal ascent of a homogeneous basaltic magma with an aqueous volatile phase and newtonian rheology. By fixing the geometry of the feeding fissure, the mass flux flowing in steady conditions can be determined at any depth, as well the magma pressure and vertical velocity. Flow behaviour is analysed for three fissure shapes: constant width, slowly upward narrowing and lenticular. In all the cases examined the magma arrives at the earth's surface with a pressure greater than atmospheric. The results are compared with those obtained when a lithostatic pressure gradient is assumed for the magma column. Some speculations are made, moreover, about the change in eruption style, if conduit geometry varies during a non-steady phase.

  4. From Map Unit to Magma Chamber: Understanding the 2006 Eruption of Augustine Volcano

    NASA Astrophysics Data System (ADS)

    Coombs, M.; Bull, K.; Cervelli, P.; Larsen, J.; Mandeville, C.; Nye, C.; Tilman, M.; Vallance, J.; Wallace, K.; Webster, J.

    2007-12-01

    In 2006, Augustine Volcano once again sprang to life and erupted ~70 x 106 m3 of magma during three eruptive phases. Variations in magma composition, eruptive style, and deformation of the edifice provide clues to the ascent and interaction of magmas prior to and during the three-month-long eruption. Genetically unrelated end members basaltic andesite (56.5 wt% SiO2) and dacite (63.3 wt% SiO2) bracket erupted magma compositions. Products from all three eruptive phases contain both end members though proportions varied with time, and many pyroclasts have mixing textures. Initial Vulcanian explosions in mid-January 2006 (explosive phase) erupted small-volumes (~14 x 106 m3 DRE) of basaltic andesite as ash fall and pyroclastic flows. In late January, explosions transitioned to continuous "boil over" at the vent (continuous phase), producing relatively voluminous (28.5 x 106 m3 DRE) block-and-ash flows that are rich in dacite and banded clasts. In early February, explosive activity gave way to effusion of basaltic andesite lava (effusive phase; 32 x 106 m3 DRE) highlighted by a pulse of increased effusion from March 7-14. Effusive activity ceased by the end of March. Geophysical and petrologic evidence lead us to a hypothetical series of magmatic processes that drove the eruption. The presence of amphibole in all eruptive products indicates that magma storage must have been within the amphibole stability field at depths greater than ~4 km, in agreement with elevated water (2 - 4 wt% by difference) and chlorine (2400 - 4900 ppm) contents in melt inclusions. Precursory unrest took the form of six months of volcano-tectonic earthquakes and island-wide uplift and radial displacement (recorded by GPS), all centered near sea level. Preliminary textural analysis of the explosively erupted basaltic andesite indicates that it did not undergo the degree of decompression-driven crystallization expected if it had accumulated at sea level (~40 MPa) for longer than a few days. This

  5. Götzenite- and combeite-bearing mineral assemblages in peralkaline nephelinite at Nyiragongo, East African Rift: Recrystallization around a degassing alkaline magma chamber

    NASA Astrophysics Data System (ADS)

    Andersen, T.; Elburg, M.; Erambert, M.

    2012-04-01

    In most igneous rocks, the high field strength elements (HFSE) titanium and zirconium reside in minerals such as ilmenite, titanite, zircon and baddelyite. In some highly peralkaline igneous rocks (agpaitic nepheline syenite, elpidite granite) these minerals are not stable, and the HFSE form complex, Na-, Ca- and volatile bearing silicate minerals. The central crater of Nyiragongo volcano in the East African Rift has a semi-permanent lava lake which may be regarded as a high-level magma chamber open to the atmosphere. The lavas and pyroclastic rocks of Nyiragongo range in composition from olivine melilitite to nephelinite and minor alkali olivine basalt. The nephelinites range from metaluminous to peralkaline compositions, including strongly peralkaline combeite nephelinite. In fresh peralkaline nephelinite, titanium is hosted in different minerals or mineral assemblages with titanomagnetite ± perovskite ± Ti-rich clinopyroxene, but in some holocrystalline, thermally metamorphosed nephelinites, götzenite (ideally Na2Ca5Ti(Si2O7)2F4) is the main Ti-bearing mineral. Götzenite is stable with combeite (Na2Ca2Si3O9), diopside and kirschsteinite, which replace primary magmatic minerals and glassy groundmass. The compositions of coexisting nepheline and kalsilite suggest recrystallization temperatures between 500 and 600 °C. A chemographic analysis of the sub-solidus mineral assemblages of götzenite-bearing and götzenite-free peralkaline nephelinite suggests that götzenite is stabilized by elevated fluorine activity combined with moderately high (for nephelinite) silica activity. At increasing peralkalinity, götzenite is likely to break down to perovskite-bearing mineral assemblages coexisting with combeite. The presence of götzenite- and combeite-bearing nephelinite at Nyiragongo is due to the influence of fluorine-rich fluids degassing from magma stored in the lava lake.

  6. The Middle Fork Plutonic Complex: A plutonic association of coeval peralkaline and metaluminous magmas in the north-central Alaska Range

    SciTech Connect

    Solie, D.N.

    1988-01-01

    The 57 m.y. Middle Fork Plutonic Complex (MFPC) intrudes Paleozoic metasedimentary rocks south of the Farewell Fault zone in the north-central Alaska Range. Though spatially related to the late Cretaceous - Early Tertiary subduction-related Alaska Range batholith, MFPC is more characteristic of an extensional or anorogenic setting. A swarm of basalt, hawaiite and rhyolite dikes east of the complex intruded, and was intruded by, the plutonic rocks. Approximately 30% of the exposed rock in the 125 km[sup 2] complex is hedenbergite - fayalite syenite, [approx equal]20% is peralkalin arfvedsonite-biotite alkali-feldspar granite (AF granite), and [le]20% is pyroxene-olivine-biotite gabbro. The rest is a mixed unit including clinopyroxene-biotite-amphibole diorite, and hornblende-biotite granite (HB granite). K-Ar and Rb-Sr radiometric dating of rock types shows that they are coeval. Their close spatial and temporal relationships led to complex magmatic interactions. Calculated initial [sup 87]Sr/[sup 86]Sr for gabbro and diorite group is around 0.705 to 0.706. HB granites are heterogeneous, but fall mostly around 0.707 to 0.708. Hypersolvus syenites and AF granites form an isochron with initial [sup 87]Sr/[sup 86]Sr of 0.70965. These groupings suggest that at least three different magmas formed the MFPC; scatter of isotopic data reflects mutual contamination and assimilation. Consanguinous hypersolvus syenite and AF granite mineralogy appears to be controlled by fluorine in the magma chamber. Eruptive stratigraphy, as predicted by intrusive history of MFPC, compares favorably with volcanic stratigraphies of peralkaline volcanic systems worldwide, and MFPC may be modelled as the root zone of a peralkaline volcanic system.

  7. Alkali metal ion battery with bimetallic electrode

    DOEpatents

    Boysen, Dane A; Bradwell, David J; Jiang, Kai; Kim, Hojong; Ortiz, Luis A; Sadoway, Donald R; Tomaszowska, Alina A; Wei, Weifeng; Wang, Kangli

    2015-04-07

    Electrochemical cells having molten electrodes having an alkali metal provide receipt and delivery of power by transporting atoms of the alkali metal between electrode environments of disparate chemical potentials through an electrochemical pathway comprising a salt of the alkali metal. The chemical potential of the alkali metal is decreased when combined with one or more non-alkali metals, thus producing a voltage between an electrode comprising the molten the alkali metal and the electrode comprising the combined alkali/non-alkali metals.

  8. Ideas about Acids and Alkalis.

    ERIC Educational Resources Information Center

    Toplis, Rob

    1998-01-01

    Investigates students' ideas, conceptions, and misconceptions about acids and alkalis before and after a teaching sequence in a small-scale research project. Concludes that student understanding of acids and alkalis is lacking. (DDR)

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

    NASA Astrophysics Data System (ADS)

    Lowenstern, J. B.; Hurwitz, S.

    2012-12-01

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

  10. 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…

  11. Methods of recovering alkali metals

    DOEpatents

    Krumhansl, James L; Rigali, Mark J

    2014-03-04

    Approaches for alkali metal extraction, sequestration and recovery are described. For example, a method of recovering alkali metals includes providing a CST or CST-like (e.g., small pore zeolite) material. The alkali metal species is scavenged from the liquid mixture by the CST or CST-like material. The alkali metal species is extracted from the CST or CST-like material.

  12. Petrogenesis of the Northwest Africa 4734 basaltic lunar meteorite

    NASA Astrophysics Data System (ADS)

    Wang, Ying; Hsu, Weibiao; Guan, Yunbin; Li, Xianhua; Li, Qiuli; Liu, Yu; Tang, Guoqiang

    2012-09-01

    We report the petrography, mineralogy, trace element abundance geochemistry, and Pb-Pb geochronology of the lunar meteorite Northwest Africa (NWA) 4734 and make a comparison with the LaPaz Icefield (LAP) 02205/02224 low-Ti lunar basaltic meteorites. NWA 4734 is an unbrecciated low-Ti mare basalt composed mainly of subophitic-textured pyroxene (60 vol%) and plagioclase (30%). Pyroxene, plagioclase, and olivine exhibit large compositional variations and intra-grain chemical zoning. Pyroxene and plagioclase in NWA 4734 have rare earth element (REE) concentrations and patterns similar to those of the LAPs. The crystallization age of NWA 4734, determined in situ in baddeleyite, is 3073 ± 15 Ma (2σ), nearly identical to that of the LAPs (3039 ± 12 Ma). NWA 4734 and the LAPs have similar textures, modal abundances, mineral chemistry, and crystallization ages, and are most likely source-crater paired on the Moon. One baddeleyite grain in LAP 02224 displays distinctively older and spatially variable ages, from 3349 ± 62 to 3611 ± 62 Ma (2σ), similar to another baddeleyite grain (3109 ± 29 to 3547 ± 21 Ma) reported by Zhang et al. (2010) for the same meteorite. Raman spectra, cathodoluminescence, and stoichiometric studies of the baddeleyite suggest that the two older grains were not endogenic but were trap