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Sample records for partially melted zone

  1. Modeling of formation of intraplate partial melting zones

    NASA Astrophysics Data System (ADS)

    Perepechko, Y. V.; Sorokin, K. E.

    2010-12-01

    This study suggests the mathematical model of dynamics of partial melting in lithosphere causing formation of magmatic systems. The intraplate magmatic systems can be formed at achievement of required thermodynamic conditions, which can be developed due to the following mechanisms: contact heating; decompression melting at mantle matter penetration into lithosphere; and heating by filtering mantle melts and fluids in the weakened lithosphere zones above the asthenospheric structure related to a hotspot. The most efficient mechanism from the point of time and heating degree is the latter one. It is heating of lithosphere matter by mantle melts and fluids, which is especially important for development of melting sites in these systems. At formation of intraplate magmatic systems the fluid is filtered in a porous medium, porous matrix melts partially, and finally a granulated medium is formed there. To decrease the processes of heat and mass transfer in this system, the equations of dynamics of multiphase multivelocity media are derived in this study. In contrast to the Darcy-type models used in previous studies, the suggested two-velocity hydrodynamics theory describing fluid motions in a porous medium with complex reology is the thermodynamically consistent one and allows the description of nonstationary nonlinear processes. The governing equations of the model describe both the process of filtration through the deformed porous matrix and hydrodynamics of heterophase granulated medium without pressure equilibrium in phases. The work was supported by the grants 08-05-00467, 09-05-00602, 09-05-01084 from the Russian Foundation for Basic Research.

  2. The formation and chemistry of low degree hydrous partial melt on top of the transition zone

    NASA Astrophysics Data System (ADS)

    Frost, Daniel J.; Mookherjee, Mainak

    2010-05-01

    There is some geophysical evidence for the presence of silicate melt on top of the 410 km seismic discontinuity. It has also been argued that the difference in the water storage capacity of upper mantle versus transition zone minerals may cause dehydration melting as material up-wells across the 410. Studies have proposed that hydrous partial melts may be neutrally buoyant in the mantle at these conditions. In order to assess these possibilities it is important to determine the likely composition of small degree hydrous melts at these conditions and to measure the H2O contents of mantle minerals coexisting with this melt phase. The composition of a hydrous melt in equilibrium with a mantle peridotite composition has been determined at conditions of the 410 and 1450°C. Sandwich experiments were performed where an 'initial-guess' hydrous melt composition was equilibrated with 50% anhydrous peridotite. The resulting melt composition was used to assemble a further melt, which was then equilibrated in the same way. After several iterations it was possible to derive a melt composition, which was in equilibrium with a mineral assemblage identical to that observed for an anhydrous peridotite composition at the same conditions. We assess whether this melt composition could be neutrally buoyant at 410km. The 410 km discontinuity may also correspond to a transition in redox state in the mantle from a reducing transition zone to a less reduced upper mantle. Volatiles may also collect and induce melting at this horizon due to the oxidation of a rising mobile reduced fluid phase containing CH4. Minerals in mantle upwelling out of a hydrous melt layer would be expected to have H2O contents close to saturation; however, this may not be the case if the melt layer also contains other volatile components such as CO2 or CH4, which further lower the H2O activity in the melt. We assess ranges of melt compositions that may be in equilibrium with minerals containing relatively low H2O

  3. Partially melted zone in aluminum welds -- Liquation mechanism and directional solidification

    SciTech Connect

    Huang, C.; Kou, S.

    2000-05-01

    Aluminum Alloy 2219 was welded by gas metal arc welding and the microstructure was examined in the partially melted zone (PMZ), which is a narrow region immediately outside the fusion zone. Extensive liquation was observed at three different locations: at large {theta} (Al{sub 2}Cu) particles, along grain boundaries (GBs) and at numerous isolated points within grains. Liquation was initiated at the eutectic temperature T{sub E}, by the eutectic reaction {alpha} + {theta} {r_arrow} L{sub E} and intensified by further melting, above T{sub E}, of the {alpha} matrix surrounding the eutectic liquid (L{sub E}). The microstructure of the liquated-and-solidified GB material is intriguing. First, the material consisted of a new GB of mostly thin, divorced eutectic and a eutectic-free strip of {alpha} immediately next to it. Second, within an individual grain, the strip was along the top and the side facing the weld. Third, with respect to the weld, the strip was always behind the new GB. These three characteristics point to an important phenomenon, that is, solidification of the liquated GB is directional - upward and toward the weld, as a result of the temperature gradients across the PMZ. A thin, brittle eutectic GB and a soft ductile {alpha} strip side by side are expected to be much weaker than a normal GB before welding.

  4. Copper isotope fractionation during partial melting and melt percolation in the upper mantle: Evidence from massif peridotites in Ivrea-Verbano Zone, Italian Alps

    NASA Astrophysics Data System (ADS)

    Huang, Jian; Huang, Fang; Wang, Zaicong; Zhang, Xingchao; Yu, Huimin

    2017-08-01

    To investigate the behavior of Cu isotopes during partial melting and melt percolation in the mantle, we have analyzed Cu isotopic compositions of a suite of well-characterized Paleozoic peridotites from the Balmuccia and Baldissero massifs in the Ivrea-Verbano Zone (IVZ, Northern Italy). Our results show that fresh lherzolites and harzburgites have a large variation of δ65Cu ranging from -0.133 to 0.379‰, which are negatively correlated with Al2O3 contents as well as incompatible platinum-group (e.g., Pd) and chalcophile element (e.g., Cu, S, Se, and Te) contents. The high δ65Cu can be explained by Cu isotope fractionation during partial melting of a sulfide-bearing peridotite source, with the light isotope (63Cu) preferentially entering the melts. The low δ65Cu can be attributed to precipitation of sulfides enriched in 63Cu during sulfur-saturated melt percolation. Replacive dunites from the Balmuccia massif display high δ65Cu from 0.544 to 0.610‰ with lower Re, Pd, S, Se, and Te contents and lower Pd/Ir ratios relative to lherzolites, which may result from dissolution of sulfides during interactions between S-undersaturated melts and lherzolites at high melt/rock ratios. Thus, our results suggest that partial melting and melt percolation largely account for the Cu isotopic heterogeneity of the upper mantle. The correlation between δ65Cu and Cu contents of the lherzolites and harzburgites was used to model Cu isotope fractionation during partial melting of a sulfide-bearing peridotite, because Cu is predominantly hosted in sulfide. The modelling results indicate an isotope fractionation factor of αmelt-peridotite = 0.99980-0.99965 (i.e., 103lnαmelt-peridotite = -0.20 to -0.35‰). In order to explain the Cu isotopic systematics of komatiites and mid-ocean ridge basalts reported previously, the estimated αmelt-peridotite was used to simulate Cu isotopic variations in melts generated by variable degrees of mantle melting. The results suggest that high

  5. Strain heating in process zones; implications for metamorphism and partial melting in the lithosphere

    NASA Astrophysics Data System (ADS)

    Devès, Maud H.; Tait, Stephen R.; King, Geoffrey C. P.; Grandin, Raphaël

    2014-05-01

    Since the late 1970s, most earth scientists have discounted the plausibility of melting by shear-strain heating because temperature-dependent creep rheology leads to negative feedback and self-regulation. This paper presents a new model of distributed shear-strain heating that can account for the genesis of large volumes of magmas in both the crust and the mantle of the lithosphere. The kinematic (geometry and rates) frustration associated with incompatible fault junctions (e.g. triple-junction) prevents localisation of all strain on the major faults. Instead, deformation distributes off the main faults forming a large process zone that deforms still at high rates under both brittle and ductile conditions. The increased size of the shear-heated region minimises conductive heat loss, compared with that commonly associated with narrow shear zones, thus promoting strong heating and melting under reasonable rheological assumptions. Given the large volume of the heated zone, large volumes of melt can be generated even at small melt fractions.

  6. Enhancement of Polycrystal Anelasticity Just Before Partial Melting: Experimental Evidence and Implications for Seismic Low Velocity Zones

    NASA Astrophysics Data System (ADS)

    Takei, Y.; Yamauchi, H.

    2016-12-01

    Seismic low velocity zones have been detected around the volcanic source regions in the upper mantle, where partial melting is expected to occur. Therefore, many attempts have been made to get information about melt from the seismic images. Effects of partial melting on the seismic velocity have long been studied by focusing on the direct effect of melt (such as, poroelastic effect), which works in the presence of melt. However, the attempts by using the direct effect have encountered several fundamental difficulties. First, geochemical studies have shown that the amount of melt present during partial melting is about 0.1% (e.g., McKenzie, 2000, CG). Because the direct effect is generally very small for a very small melt fraction, it is difficult to explain the relatively large velocity reduction consistently with the geochemical constraints. Second, a seismic tomographic study by Priestley and McKenzie (2006, 2013, EPSL) in the Pacific mantle captured a steep reduction of seismic shear wave velocity just below the dry peridotite solidus, which cannot be explained by the direct effect. Rock anelasticity, which can cause a low velocity by grain boundary sliding even without melt (e.g., Faul & Jackson, 2005, JGR), has been considered as a key to solve these problems. However, due to the difficulty of high temperature experiments, we have had a limited understanding of rock anelasticity at the seismic frequencies. Therefore, by using a rock analogue (organic polycrystals), we performed a careful measurement of polycrystal anelasticity continuously from below to above the solidus temperature, and captured a significant enhancement of anelasticity just below the solidus temperature in the absence of melt. The model of anelasticity obtained from our data explains well the steep reduction of VS captured in the Pacific mantle. Moreover, unlike the direct effect, the newly recognized effect is large even when only a small amount of melt is generated at the solidus, and

  7. Microstructure formation in partially melted zone during gas tungsten arc welding of AZ91 Mg cast alloy

    SciTech Connect

    Zhu Tianping Chen, Zhan W.; Gao Wei

    2008-11-15

    During gas tungsten arc (GTA) welding of AZ91 Mg cast alloy, constitutional liquid forms locally in the original interdendritic regions in the partially melted zone (PMZ). The PMZ re-solidification behaviour has not been well understood. In this study, the gradual change of the re-solidification microstructure within PMZ from base metal side to weld metal side was characterised. High cooling rate experiments using Gleeble thermal simulator were also conducted to understand the morphological change of the {alpha}-Mg/{beta}-Mg{sub 17}Al{sub 12} phase interface formed during re-solidification after partial melting. It was found that the original partially divorced eutectic structure has become a more regular eutectic phase in most of the PMZ, although close to the fusion boundary the re-solidified eutectic is again a divorced one. Proceeding the eutectic re-solidification, if the degree of partial melting is sufficiently high, {alpha}-Mg re-solidified with a cellular growth, resulting in a serrated interface between {alpha}-Mg and {alpha}-Mg/{beta}-Mg{sub 17}Al{sub 12} in the weld sample and between {alpha}-Mg and {beta}-Mg{sub 17}Al{sub 12} (fully divorced eutectic) in Gleeble samples. The morphological changes affected by the peak temperature and cooling rate are also explained.

  8. Microstructures and crystallographic fabric evolution during melt-present and melt-absent conditions in the partially molten middle crust: the Patos shear zone (Borborema Province, NE Brazil)

    NASA Astrophysics Data System (ADS)

    Ferreira Viegas, Luís Gustavo; Archanjo, Carlos; Vauchez, Alain

    2013-04-01

    The Patos shear zone is an exposed segment of the partially molten middle crust characterized by a 600 km long, E-trending transcurrent structure that deforms the Precambrian rocks of the Borborema Province. High-temperature (HT) mylonites with low melt fractions (~ 5%) constitute most of the shear belt, while a narrow strip of highly strained mylonites to ultramylonites outlines its southern margin. Migmatites and "transitional" mylonites occur sandwiched between these tectonites. A progressive microfabric development is recorded from melt-bearing mylonites to high-strain ultramylonites. A microstructural study was carried out to understand the fabric evolution from melt-assisted to melt-absent deformation. Fabrics were investigated by optical and scanning electron microscopy (SEM), and crystallographic preferred orientations were measured by Electron Backscatter Diffraction (EBSD). Melt-bearing HT-mylonites display solid-state microstructures with coarse quartz ribbons and sutured grain boundaries. K-feldspar clasts are often fractured and show peripheral myrmekite. Towards the contact with anatexites the microfabric becomes typically magmatic with abundant interstitial quartz. Transitional mylonites, located immediately south of the migmatites, are marked by progressive grain size reduction of recrystallized felsic phases. High-strain mylonites have a fine-grained quartz-feldspar matrix with relics of quartz ribbons and fractured K-feldspar. Melt-bearing mylonites display quartz [0001] axes forming maxima mainly on Y, while quartz fabrics in the anatexite are weaker and diffuse, suggesting deformation in the magmatic state. In transitional and high-strain mylonites the measured quartz CPOs show [0001] concentrations between Z and Y. K-feldspar and plagioclase fabrics record mainly the activity of (010)[001] and (010)[100] slip systems in all rock types, with local activity of the (100)[010] slip system in the transitional mylonites. These data suggest that the

  9. Effects of water, depth and temperature on partial melting of mantle-wedge fluxed by hydrous sediment-melt in subduction zones

    NASA Astrophysics Data System (ADS)

    Mallik, Ananya; Dasgupta, Rajdeep; Tsuno, Kyusei; Nelson, Jared

    2016-12-01

    This study investigates the partial melting of variable bulk H2O-bearing parcels of mantle-wedge hybridized by partial melt derived from subducted metapelites, at pressure-temperature (P-T) conditions applicable to the hotter core of the mantle beneath volcanic arcs. Experiments are performed on mixtures of 25% sediment-melt and 75% fertile peridotite, from 1200 to 1300 °C, at 2 and 3 GPa, with bulk H2O concentrations of 4 and 6 wt.%. Combining the results from these experiments with previous experiments containing 2 wt.% bulk H2O (Mallik et al., 2015), it is observed that all melt compositions, except those produced in the lowest bulk H2O experiments at 3 GPa, are saturated with olivine and orthopyroxene. Also, higher bulk H2O concentration increases melt fraction at the same P-T condition, and causes exhaustion of garnet, phlogopite and clinopyroxene at lower temperatures, for a given pressure. The activity coefficient of silica (ϒSiO2) for olivine-orthopyroxene saturated melt compositions (where the activity of silica, aSiO2 , is buffered by the reaction olivine + SiO2 = orthopyroxene) from this study and from mantle melting studies in the literature are calculated. In melt compositions generated at 2 GPa or shallower, with increasing H2O concentration, ϒSiO2 increases from <1 to ∼1, indicating a transition from non-ideal mixing as OH- in the melt (ϒSiO2 <1) to ideal mixing as molecular H2O (ϒSiO2 ∼1). At pressures >2 GPa, ϒSiO2 >1 at higher H2O concentrations in the melt, indicate requirement of excess energy to incorporate molecular H2O in the silicate melt structure, along with a preference for bridging species and polyhedral edge decorations. With vapor saturation in the presence of melt, ϒSiO2 decreases indicating approach towards ideal mixing of H2O in silicate melt. For similar H2O concentrations in the melt, ϒSiO2 for olivine-orthopyroxene saturated melts at 3 GPa is higher than melts at 2 GPa or shallower. This results in melts generated at

  10. Solubility and Speciation of CO2 in Natural Rhyolitic Melts at 1.5-3.0 GPa - Implications for Carbon Flux in Subduction Zones via Sediment Partial Melts

    NASA Astrophysics Data System (ADS)

    Duncan, M. S.; Dasgupta, R.

    2012-12-01

    Sediment partial melt derived from the subducting plate is thought to be a critical agent in transport of trace elements and water to arc basalt source regions. Sediment melts may also act as significant carrier of CO2 released from subducting carbonates. However, the CO2 carrying capacity of rhyolitic melts, similar to those derived from partial melting of subducting pelitic sediments, at sub-arc depths remains unconstrained. Here we measured the solubility of CO2 in a model sediment partial melt; experiments were conducted at 1.5-3.0 GPa and 1300°C with variable water contents. The rhyolitic melt compositions were constructed with reagent grade oxides, carbonates, and hydroxides, with carbonates as the source of excess CO2 and Al(OH)3 as the source of variable water content, and were contained in AuPd capsules. All experiments produced glasses with bubbles, the latter being taken as the evidence of equilibrium vapor saturation at experimental P-T conditions. Micro-Fourier Transform Infrared spectroscopy was employed to measure the concentrations of CO2 and H2O in doubly polished, bubble-free sections of the glasses. The total CO2 solubility, CO2tot. (= CO2mol. + CO32-), of experimental melts increases with pressure and water content. For melts with H2O of ~0.5 wt.%, CO2tot. values increase and CO2mol./CO2tot. values decrease with increasing pressure from 0.68 to 1.2 wt.% and 0.95 to 0.60 from 1.5 to 3.0 GPa, respectively. In contrast to the water-poor melts, the hydrous melts with ~2 and 3.5 wt.% H2O showed the opposite CO2mol./CO2tot.-pressure trend (0.18 to 0.55 for 2 wt.% H2O and 0.04 to 0.18 for 3.5 wt.% H2O from 1.5 to 3.0 GPa). Total CO2 contents of hydrous melts were also higher at a given pressure and ranged from 0.8 to 1.5 wt.% from 1.5 to 3.0 GPa for experiments with 2 wt.% H2O and 0.9 to >1.6 wt.% from 1.5 to 3.0 GPa for experiments with 3.5 wt.% H2O. Measurements of melt inclusions and gases determined that primary arc magmas contain ≥0.3 wt.% CO2

  11. CO2 solubility and speciation in rhyolitic sediment partial melts at 1.5-3.0 GPa - Implications for carbon flux in subduction zones

    NASA Astrophysics Data System (ADS)

    Duncan, Megan S.; Dasgupta, Rajdeep

    2014-01-01

    much as 2.6-5.5 wt.% CO2 to the sub-arc mantle source regions. At saturation, 1.6-3.3 wt.% sediment partial melt relative to the mantle wedge is therefore sufficient to bring up the carbon budget of the mantle wedge to produce primary arc basalts with 0.3 wt.% CO2. Sediment plumes in mantle wedge: Sediment plumes or diapirs may form from the downgoing slab because the sediment layer atop the slab is buoyant relative to the overlying, hanging wall mantle (Currie et al., 2007; Behn et al., 2011). Via this process, sediment layers with carbonates would carry CO2 to the arc source region. Owing to the higher temperature in the mantle wedge, carbonate can breakdown. Behn et al. (2011) suggested that sediment layers as thin as 100 m, appropriate for modern arcs, could form sediment diapirs. They predicted that diapirs would form from the slab in the sub-arc region for most subduction zones today without requiring hydrous melting. H2O-rich fluid driven carbonate breakdown: Hydrous fluid flushing of the slab owing to the breakdown of hydrous minerals could drive carbonate breakdown (Kerrick and Connolly, 2001b; Grove et al., 2002; Gorman et al., 2006). The addition of water would cause decarbonation creating an H2O-CO2-rich fluid that would then flux through the overlying sediment layer, lower the solidus temperature, and trigger melting. Recent geochemical (Cooper et al., 2012) and geodynamic (van Keken, 2003; Syracuse et al., 2010) constraints suggest that the sub-arc slab top temperatures are above the hydrous fluid-present sediment solidus, thus in the presence of excess fluid, both infiltration induced decarbonation and sediment melting may occur. Hot subduction: This is relevant for subduction zones such as Cascadia and Mexico, where slab-surface temperatures are estimated to be higher (Syracuse et al., 2010). A higher temperature could cause carbonate breakdown and sediment partial melting without requiring a hydrous fluid flux. In this case a relatively dry silicate

  12. Evidence for partial melting at northern Tavan Har and relationship to Late Triassic sinistral shear in the East Gobi Fault Zone, southeastern Mongolia

    NASA Astrophysics Data System (ADS)

    Stypula, M.; Webb, L. E.; Hagen-Peter, G. A.

    2009-12-01

    We present preliminary data and interpretations from an ongoing study focused on the timing, extent, and significance of partial melting at northern Tavan Har in southeastern Mongolia. Tavan Har is a basement block within the East Gobi Fault Zone. Regional studies of the East Gobi Fault Zone reveal at least three phases of reactivation during the Mesozoic, including the formation of a Late Triassic sinistral ductile shear zone that can be traced for ~250 km along strike. The metamorphic tectonites of the shear zone exposed in the northern Tavan Har block are dominated by steeply-dipping, NE-striking foliations and subhorizontal lineations. The lithologies of northern Tavan Har consist of mylonite, ultramylonite, amphibolite-facies gneiss, granitic gneiss, and migmatite. The suite of lithologies is observed to extend to the northern margin of the study region where they are overprinted at greenschist-facies conditions and ultimately truncated by the Northern Zuunbayan Fault. The granitic gneiss is a synkinematic pluton that truncates the western margin of Tavan Har and includes vestiges of amphibolite and mylonite lithologies. The amphibolite grade tectonites represent the highest metamorphic grade in relation to the shear zone. Mylonites located throughout the shear zone exhibit WNW plunging lineations. Many generations of dikes and veining are apparent throughout the field area, revealing variable degrees of folding and cross cutting relationships. The southern margin of the migmatite zone is in fault contact with Lower Cretaceous rift basin strata. Previous argon dating determined that the timing of ductile sinistral shear at amphibolite-facies conditions occurred c. 225 Ma. The same study obtained an age of 240 Ma for hornblende from a melanosome within the migmatite unit, giving significance to the question of the timing of partial melting and its relationship to the shear zone. New mapping and structural analysis of the southern margin of the northern Tavan

  13. Reaction between Metapelite-derived Hydrous Partial Melt and Subsolidus Fertile Peridotite at 2-3 GPa - Generation of High-K Magmas in Subduction Zones

    NASA Astrophysics Data System (ADS)

    Nelson, J. M.; Mallik, A.; Dasgupta, R.

    2013-12-01

    Trace compositions of arc magmas display signatures of recycled sediments [1] and thermal and geodynamic models of subduction zones suggest that sediment contribution to sub-arc mantle occurs in the form of hydrous melts generated at the slab-mantle interface by fluid-present melting [2, 3] or in the mantle wedge by diapiric rise of downgoing sediments [4]. Partial melts of hydrous pelitic sediments are rhyolitic in P-T conditions of the mantle wedge and are out of equilibrium with the surrounding peridotite, which implies inevitable reaction between such melt and overlying peridotite. However, partial melting in the mantle wedge with slab input has mostly been studied in peridotite+H2O systems [e.g. 5] and experimental constraints on sediment-peridotite hybrid remain limited [6]. In this study, we explore the phase equilibria of a sediment melt-fluxed fertile peridotite with the aim of understanding genesis of high-K arc magmas. Experiments were performed in AuPd capsules using a piston cylinder, on a 1:3 mixture of rhyolitic melt with 7.3 wt.% H2O [3] and fertile peridotite from 1150-1350 °C at 2-3 GPa. Interstitial melt/fluid is present at 1150 °C, 2 GPa and 1150-1200 °C, 3 GPa. While residual opx+cpx+biotite are present at both pressures, olivine is present from 1200-1300 °C, 2 GPa and garnet from 1150-1300 °C, 3 GPa. Cpx and biotite disappear at 1200-1250 °C, 2 GPa and 1350 °C, 3 GPa. At 2 GPa, from 1200-1300 °C, the melt composition (on a volatile-free basis), shows an increase in SiO2 (50-51 wt.%), MgO (10-14 wt.%) and decrease in Al2O3 (16-14 wt.%), CaO (10-7 wt.%), Na2O (3-2 wt.%) and H2O (13-8 wt.%.). K2O increases from 5 to 7 wt.% till 1250 °C followed by a decrease to 5 wt.%, at 1300 °C. FeO* varies between 6 and 5 wt.%. At 3 GPa, from 1225-1350 °C, the reacted melt displays an increase in SiO2 (47-49 wt.%), FeO* (4.2-5.4 wt.%), MgO (11-14 wt.%), and decrease in Al2O3 (15-14 wt.%), CaO (12-7 wt.%), Na2O (4-3 wt.%) and H2O (16-11 wt.%). K2O

  14. Efficiency of melt extraction from partially molten regions

    NASA Astrophysics Data System (ADS)

    Hier-Majumder, S.; Abbott, M. E.; Drombosky, T.; Wimert, J. T.

    2011-12-01

    We discuss the efficiency of buoyancy-driven melt extraction in relation to the low velocity layer (LVL), atop the transition zone, and the ultralow velocity zones (ULVZ), atop the core mantle boundary. The LVL is characterized by a relatively large thickness, globally varying on the order of 30-90 km. It is inferred that the LVL is characterized by a modest amount of melting, 1% or less. The ULVZ, in contrast, is much thinner, with an average thickness of 10 km. It is also characterized by a density between 8-10% higher than the surrounding mantle, and contains up to 10% by volume melt. Three factors, frictional resistance, capillary tension, and stirring can contribute to long term melt retention in these partially molten regions. Frictional resistance to melt percolation is inversely proportional to the melt fraction squared. Consequently, the drainage efficiency of both buoyant and dense melts are reduced at low melt fractions. Strong tension on grain boundaries reduces the dihedral angle at the melt-grain triple junctions, establishing a well-connected network. Despite the presence of this well connected pathway, a larger force is required to counter the strong capillary tension and segregate melt from the matrix, especially at small melt fractions. Finally, compaction within the ULVZ stirred by convective motions in the overlying mantle can also preclude substantial drainage of melt and retain the melt over geological times.

  15. Partial melting of carbonated pelite at 3-7 GPa and deep cycling of CO2 and H2O in subduction zones

    NASA Astrophysics Data System (ADS)

    Tsuno, K.; Dasgupta, R.; Danielson, L. R.; Righter, K.

    2011-12-01

    The exchange of water and carbon dioxide between the Earth's crustal rocks and the interior is important for understanding geochemical and geophysical evolution of the planet on geologic timescale. Subduction of pelitic sediments is a key mechanism for volatile introduction to the mantle but the high-pressure behavior of H2O+ CO2 bearing sediments is only constrained for alumina-rich, low-Mg# bulk compositions [1, 2]. However, the ocean-floor sediments for many subduction zones that contain both water and CO2 are alumina-poor and have higher Mg#. To constrain the melting behavior of a model alumina poor carbonated pelite, we performed new experiments. Piston cylinder (3 GPa) and multianvil (5 and 7 GPa) experiments were conducted between 800 and 1150 °C, using a model sediment composition containing 1 wt.% H2O and 5 wt.% CO2 (trace vapor-present at subsolidus conditions). The choice of the bulk composition was aimed to model the loss of siliceous hydrous fluid during the shallow part of subduction. We determined the solidus temperatures between 800 and 850 °C at 3 GPa, 900 and 950 °C at 5 GPa, and <1000 °C at 7 GPa. The subsolidus phases include cpx, garnet, coesite, rutile, phengite, and calcitess at 3 GPa, and kyanite comes in at 5 GPa. Hydrous rhyolitic silicate melt was observed at 3 GPa and up to 1150 °C. The near-solidus melt at 5-7 GPa was K-rich and calcio-carbonatitic, in contrast to the previous experimental results in alumina-rich and low Mg# bulk composition [1, 2], which showed the stability of Al-rich trachyitic silicate melt at near-solidus temperatures up to 5 GPa, and replaced by carbonate melt only at ≥5.5 GPa. Carbonate-silicate melt immiscibility was observed at 5 GPa, 1100 °C in our study. The phengite-out boundary is located between 850 and 900 °C at 3 GPa, between 1000 and 1100 °C at 5 GPa, and <1000 °C at 7 GPa. The crystalline carbonate-out boundary is between 950 and 1000 °C at 3 and 5 GPa, and <1000 °C at 7 GPa. Comparison of

  16. Partial melting of the mafic lower oceanic crust

    NASA Astrophysics Data System (ADS)

    Leuthold, J.; Lissenberg, J. C. J.; Falloon, T.; Ulmer, P.; O'Driscoll, B.; Klimentyeva, D.

    2016-12-01

    Along oceanic spreading ridges, magma batches underplate, ascend, stall and erupt (see Fig.1). Although fractional crystallization is frequently considered the most important process, MASH processes characterize open-system igneous complexes and affects the crustal evolution of magmas. We examine the record of partial melting in lower oceanic crust gabbro cumulate from slow- (Atlantic ocean at Kane Megamullion) and fast-spreading ridges (Pacific ocean at Hess Deep). At the crystal scale, eutectic minerals are most affected by partial melting (i.e. Cpx + Plg ± Ol). Cpx oikocryst microstructure show resorption embayments related to sharp geochemical variations: compatible Cr and Al and incompatible Ti, Zr and REE decrease from core to rim, with a late-stage TiO2and REE increase. Mg#, Eu* and Sr* increase from core to rim and strongly decrease towards the outer rim. Plg shows reverse zoning. Textures and geochemical evolution are incoherent with processes such as fractional crystallization or crystallization from successive mantle-derived melts. Zoned Cpx oikocrysts result from 1) partial melting of REE-poor lower crust gabbroic cumulate, 2) hybridization with intrusive hot Cpx-undersaturated primitive mantle-derived melt and 3) refertilization. Reaction products are a Cpx-poor gabbro/troctolite residue and a hybrid melt saturated in Cpx and Plg (see Eq.1). Mineralogy, texture and chemistry of cumulate primocrysts and hot intrusive melt are modified. Outer rim crystallized from a distinct percolating late-stage reacted melt, close to solidus conditions. Hybrid melt has high SiO2 and Mg# contents and is Cr-, Zr- and REE-depleted. MELTS calculations and geochemical modelling of the hybrid melt liquid line of descent match N-MORB chemistry. Hybridization with co-genetic gabbro partial melt is a valid alternative/complementary process to explain variations in the primitive MORB geochemistry. However, the lacks of strong mineralogical and geochemical contrast between co

  17. Floating zone melting of cadmium telluride

    NASA Technical Reports Server (NTRS)

    Chang, Wen-Ming; Regel, L. L.; Wilcox, W. R.

    1992-01-01

    To produce superior crystals of cadmium telluride, floating zone melting in space has been proposed. Techniques required for floating zone melting of cadmium telluride are being developed. We have successfully float-zoned cadmium telluride on earth using square rods. A resistance heater was constructed for forming the molten zone. Evaporation of the molten zone was controlled by adding excess cadmium to the growth ampoule combined with heating of the entire ampoule. An effective method to hold the feed rod was developed. Slow rotation of the growth ampoule was proven experimentally to be necessary to achieve a complete symmetric molten zone. Most of the resultant cylindrical rods were single crystals with twins. Still needed is a suitable automatic method to control the zone length. We tried a fiber optical technique to control the zone length, but experiments showed that application of this technique to automate zone length control is unlikely to be successful.

  18. Floating zone melting of cadmium telluride

    NASA Technical Reports Server (NTRS)

    Chang, Wen-Ming; Regel, L. L.; Wilcox, W. R.

    1992-01-01

    To produce superior crystals of cadmium telluride, floating zone melting in space has been proposed. Techniques required for floating zone melting of cadmium telluride are being developed. We have successfully float-zoned cadmium telluride on earth using square rods. A resistance heater was constructed for forming the molten zone. Evaporation of the molten zone was controlled by adding excess cadmium to the growth ampoule combined with heating of the entire ampoule. An effective method to hold the feed rod was developed. Slow rotation of the growth ampoule was proven experimentally to be necessary to achieve a complete symmetric molten zone. Most of the resultant cylindrical rods were single crystals with twins. Still needed is a suitable automatic method to control the zone length. We tried a fiber optical technique to control the zone length, but experiments showed that application of this technique to automate zone length control is unlikely to be successful.

  19. Investigation of Partial Melting in Planetary Interiors using Electrical Measurements

    NASA Astrophysics Data System (ADS)

    Pommier, A.; Evans, R. L.; Leinenweber, K. D.; Kohlstedt, D. L.

    2016-12-01

    Partial melting is induced by major processes that shape the interior of terrestrial bodies and contributes to their differentiation, structure, and dynamics. Among the tools used to investigate planetary interiors, electromagnetic (EM) data probe the electrical response of planetary interiors and can detect the presence of partially molten areas. Combined with laboratory experiments on partially molten samples and petrological constraints, electrical measurements help place constraints on the amount, geometry, interconnectivity, and storage conditions of melt. In particular, electrical experiments on partially molten rocks provide a test of the likelihood of a molten lowermost mantle, as suggested for the Moon, and can be used to investigate melt alignment and distribution in active tectonic contexts on Earth. Here, we use two recent electrical conductivity datasets to investigate partially molten zones in the deep Lunar mantle and Earth's asthenosphere. Electrical experiments were performed at high temperature on 1) olivine compacts (Fo77 and Fo90) during melting experiments at 4 and 6 GPa and 2) sheared olivine (+MORB) samples at 3 GPa, with shear strains up to 7.3. All measurements were conducted using the impedance spectroscopy technique with the two-electrode method. Partial melting experiments show that at T> Tsolidus + 75°C, conductivity increases significantly, by a factor of ˜30 to 100, due to a transition from a tube-dominated network to a structure in which melt films and pools become prominent features. At higher T, a plateau suggests that the electrical response of the investigated samples lacks sensitivity to temperature at an advanced stage of melting. Comparison of our results with EM data of the Moon supports the hypothesis of the presence of interconnected melt at the base of the mantle and provides upper bounds on melt fraction. Experiments on sheared samples suggest that the presence of melt in a sheared rock will provide high conductivities

  20. Experimental evidence supports mantle partial melting in the asthenosphere

    PubMed Central

    Chantel, Julien; Manthilake, Geeth; Andrault, Denis; Novella, Davide; Yu, Tony; Wang, Yanbin

    2016-01-01

    The low-velocity zone (LVZ) is a persistent seismic feature in a broad range of geological contexts. It coincides in depth with the asthenosphere, a mantle region of lowered viscosity that may be essential to enabling plate motions. The LVZ has been proposed to originate from either partial melting or a change in the rheological properties of solid mantle minerals. The two scenarios imply drastically distinct physical and geochemical states, leading to fundamentally different conclusions on the dynamics of plate tectonics. We report in situ ultrasonic velocity measurements on a series of partially molten samples, composed of mixtures of olivine plus 0.1 to 4.0 volume % of basalt, under conditions relevant to the LVZ. Our measurements provide direct compressional (VP) and shear (VS) wave velocities and constrain attenuation as a function of melt fraction. Mantle partial melting appears to be a viable origin for the LVZ, for melt fractions as low as ~0.2%. In contrast, the presence of volatile elements appears necessary to explaining the extremely high VP/VS values observed in some local areas. The presence of melt in LVZ could play a major role in the dynamics of plate tectonics, favoring the decoupling of the plate relative to the asthenosphere. PMID:27386548

  1. Experimental evidence supports mantle partial melting in the asthenosphere.

    PubMed

    Chantel, Julien; Manthilake, Geeth; Andrault, Denis; Novella, Davide; Yu, Tony; Wang, Yanbin

    2016-05-01

    The low-velocity zone (LVZ) is a persistent seismic feature in a broad range of geological contexts. It coincides in depth with the asthenosphere, a mantle region of lowered viscosity that may be essential to enabling plate motions. The LVZ has been proposed to originate from either partial melting or a change in the rheological properties of solid mantle minerals. The two scenarios imply drastically distinct physical and geochemical states, leading to fundamentally different conclusions on the dynamics of plate tectonics. We report in situ ultrasonic velocity measurements on a series of partially molten samples, composed of mixtures of olivine plus 0.1 to 4.0 volume % of basalt, under conditions relevant to the LVZ. Our measurements provide direct compressional (V P) and shear (V S) wave velocities and constrain attenuation as a function of melt fraction. Mantle partial melting appears to be a viable origin for the LVZ, for melt fractions as low as ~0.2%. In contrast, the presence of volatile elements appears necessary to explaining the extremely high V P/V S values observed in some local areas. The presence of melt in LVZ could play a major role in the dynamics of plate tectonics, favoring the decoupling of the plate relative to the asthenosphere.

  2. The influence of partial melting and melt migration on the rheology of the continental crust

    NASA Astrophysics Data System (ADS)

    Cavalcante, Geane Carolina G.; Viegas, Gustavo; Archanjo, Carlos José; da Silva, Marcos Egydio

    2016-11-01

    The presence of melt during deformation produces a drastic change in the rheological behavior of the continental crust; rock strength is decreased even for melt fractions as low as ∼7%. At pressure/temperature conditions typical of the middle to lower crust, melt-bearing systems may play a critical role in the process of strain localization and in the overall strength of the continental lithosphere. In this contribution we focus on the role and dynamics of melt flow in two different mid-crustal settings formed during the Brasiliano orogeny: (i) a large-scale anatectic layer in an orthogonal collision belt, represented by the Carlos Chagas anatexite in southeastern Brazil, and (ii) a strike-slip setting, in which the Espinho Branco anatexite in the Patos shear zone (northeast Brazil) serves as an analogue. Both settings, located in eastern Brazil, are part of the Neoproterozoic tectonics that resulted in widespread partial melting, shear zone development and the exhumation of middle to lower crustal layers. These layers consist of compositionally heterogeneous anatexites, with variable former melt fractions and leucosome structures. The leucosomes usually form thick interconnected networks of magma that reflect a high melt content (>30%) during deformation. From a comparison of previous work based on detailed petrostructural and AMS studies of the anatexites exposed in these areas, we discuss the rheological implications caused by the accumulation of a large volume of melt "trapped" in mid-crustal levels, and by the efficient melt extraction along steep shear zones. Our analyses suggest that rocks undergoing partial melting along shear settings exhibit layers with contrasting competence, implying successive periods of weakening and strengthening. In contrast, regions where a large amount of magma accumulates lack clear evidence of competence contrast between layers, indicating that they experienced only one major stage of dramatic strength drop. This comparative

  3. The Impact of Partial Melting in the Orogenic Cycle

    NASA Astrophysics Data System (ADS)

    Rey, P. F.; Teyssier, C.; Whitney, D. L.

    2010-12-01

    Open source, community driven numerical codes available at geodynamics.org allow geologists to model orogenic processes including partial melting and its consequences during orogenic cycles. Here we explore the role of partial melting during continental subduction and its impact on the evolution of orogenic plateaux and that of migmatite-cored metamorphic core complexes. Continental subduction and orogenic plateaux: Numerical experiments show that when continental slabs buried into the mantle meet their solidus, crustal melt is confined to the slab during its ascent and ponds at the Moho (Fig. 1a). The displaced overlying crust is extruded horizontally into the weak lower crust of the continent, resulting in Earth’s surface uplift to form an orogenic plateau, and Moho downward motion to accommodate the influx of material into the lower crust. This model suggests a link between continental subduction, melting and the build up of orogenic plateaux, and show that partial melting may be a significant process in exhumation of ultrahigh-pressure (UHP) rocks. Model results are consistent with the common association of UHP rocks and migmatite. Growth and destruction of orogenic plateaux: The lateral growth of orogenic plateaux is often attributed to the flow of the plateau weak partially melted lower crust into its foreland in some cases over a distance > 1500 km in 15 myr. Using pre-thickening temperatures compatible with Tibet’s uplift history, we show that mass redistribution processes are dynamically coupled, and that CFE velocities are limited to less than 1 cm.yr-1 (~150 km in 15 myr) by cooling and crystallization of the melted channel in the foreland and by any upward deviation into metamorphic domes of the melted channel by extension in the plateau (Fig. 1b). Gravitational collapse and metamorphic core complexes: Localization of extension in the upper crust triggers convergent flow in the partially molten deep crust channel. This convergent flow leads to the

  4. A Disequilibrium Melting Spectrum: Partially Melted Crustal Xenoliths from the Wudalianchi Volcanic Field, NE China.

    NASA Astrophysics Data System (ADS)

    McLeod, C. L.; McGee, L. E.

    2015-12-01

    Disequilibrium melting has been established as a common process occurring during crustal anatexis and thus demonstrates that crustal assimilation by ascending mantle-derived magmas is likley not a closed system. Observations of extreme compositional heterogeneity within partial melts derived from crustal xenoliths have been documented in several recent examples, however, the retention or transfer of elements to and from residues and glasses, and their relative contributions to potential crustal contaminants warrants further investigation. Sampled lavas from the Huoshaoshan volcano in the Holocene Wudalianchi volcanic field of Northeast China contain crustal xenoliths which preserve a spectrum of partial melting both petrographically and geochemically, thus providing an excellent, natural example of crustal anatexis. Correlations exist between the volume of silicic glass preserved within the xenoliths and bulk rock SiO2 (70-83 wt%), Al2O3 (16-8 wt%), glass 87Sr/86Sr (0.715-0.908), abundances of elements common in feldspars and micas (Sr, Ba, Rb) and elements common in accessory minerals (Y, Zr, Nb). These correlations are likely associated with the consumption of feldspars and micas and the varying retention of accessory phases during partial melting. The xenoliths which contain the greater volumes of silicic glass and residual quartz (interpreted as being the most melted) were found within pahoehoe lava, whilst the least melted xenoliths were found within scoria of the summit cone of Huoshaoshan; thus it is interpreted that the extent of melting is linked to the immersion time in the lava. Small-scale (mm) mingling and transfer of material from the enclosing lava to the xenolith is observed, however, modelling of potential contaminant compositions is inconsistent with crustal contamination during lava petrogenesis. It is inferred that crustal contamination in sampled lavas is localized within the open magmatic system and most likely occurs at the contact zone

  5. Detection of melting atop the mantle transition zone

    NASA Astrophysics Data System (ADS)

    Hier-Majumder, S.; Keel, E. B.; Courtier, A. M.

    2012-12-01

    We explore the combined effect of thermal, chemical, and melting anomalies on shear wave velocities above the transition zone. While thermal and chemical heterogeneities influence the seismic velocities at subsolidus temperatures to some extent, the velocity structures are greatly modified in the presence of partial melting. We interpret two sets of data; ScS reflectivity beneath Coral Sea in the Southwest Pacific and receiver function analysis of P-to-S conversions beneath the Hawaiian islands. Both datasets indicate the presence of a Low Velocity Layer (LVL) at an average depth of 350 km. Temperature and subsolidus composition fail to fully explain the observed impedance contrast atop the LVL. Beneath the Coral Sea, an average melt volume fraction of 1% is necessary to explain the seismic observations, while beneath Hawaiia range of melt fractions describe the seismic signature. Melt fraction appears to increase from Northwest to Southeast along the island chain and trades off with dihedral angle.Map of calculated melt volume fraction at the Low Velocity layer (LVL) located approximately 350 km below the surface of Hawaii. The melt fraction is calculated for variations in the subsolidus basaltic component (X) and reference potential temperature (T).

  6. The role of subgrain boundaries in partial melting

    NASA Astrophysics Data System (ADS)

    Levine, Jamie S. F.; Mosher, Sharon; Rahl, Jeffrey M.

    2016-08-01

    Evidence for partial melting along subgrain boundaries in quartz and plagioclase is documented for rocks from the Lost Creek Gneiss of the Llano Uplift, central Texas, the Wet Mountains of central Colorado, and the Albany-Fraser Orogen, southwestern Australia. Domains of quartz or plagioclase crystals along subgrain boundaries are preferentially involved in partial melting over unstrained domains of these minerals. Material along subgrain boundaries in quartz and plagioclase has the same morphology as melt pseudomorphs present along grain boundaries and is commonly laterally continuous with this former grain boundary melt, indicating the material along subgrain boundaries can also be categorized as a melt pseudomorph. Subgrain boundaries consist of arrays of dislocations within a crystal lattice, and unlike fractures would not act as conduits for melt migration. Instead, the presence of former melt along subgrain boundaries requires that partial melting occurred in these locations because it is kinetically more favorable for melting reactions to occur there. Preferential melting in high strain locations may be attributed to strain energy, which provides a minor energetic contribution to the reaction and leads to preferential melting in locations with weakened bonds, and/or the presence of small quantities of water associated with dislocations, which may enhance diffusion rates or locally lower the temperature needed for partial melting.

  7. Geophysical constraints on partial melt in the upper mantle

    SciTech Connect

    Shankland, T.J.; O'Connell, R.J.; Waff, H.S.

    1981-08-01

    This paper adresses the conditions under which partial melt can exist in the mantle in order to be observed as a geophysical 'anomaly'. Typical observed anomalies are high electrical conductivity of the order of 0.1 S/m or greater, velocity decreases of 7--10%, seismic Q values less than 100, and a frequency band for seismic effects in the region mear 1 Hz. Existing theories of electrical conduction in partial melts and of frequency-dependent seismic properties together with recent measurements of melt electrical conductivity, viscosity, and partial melt texture can be used to establish requirements for melt to be observed by geophysical methods. From electrical anomalies, mainly sensitive to melt volume and its interconnection, one can require a minimum melt fraction of several percent at temperatures close to the solidus (1150/sup 0/--1300/sup 0/C). However, seismic models demand only a small volume in very flattened shapes (aspect ratio approx. =0.001, melt fraction approx.0.1%). Further, if melt configuration permits seismic dissipation in bulk, that is, there exist flattened voids intersecting more or less equant voids, then it is possible to infer melt fractions for elastic anomalies that are consistent with the several percent required for electrical anomalies. Observed equilibrium textures of partly melted peridotite together with inferred melt-solid surface energies suggest that melt on a grain size scale in a gravitational field segregates into a strongly anisotropic pattern. Thus if partial melt causes mantle geophysical anomalies, it should exist in a variety of void shapes and probably of sizes. While the association of electrical and elastic anomalies with indications of reduced density, volcanism, and high heat flow makes the hypothesis of partial melting an attractive explanation, the minimum physical requirement is for existence of relatively high temperature.

  8. Partial Melting of the Indarch (EH4) Meteorite : A Textural, Chemical and Phase Relations View of Melting and Melt Migration

    NASA Technical Reports Server (NTRS)

    McCoy, Timothy J.; Dickinson, Tamara L.; Lofgren, Gary E.

    2000-01-01

    To Test whether Aubrites can be formed by melting of enstatite Chondrites and to understand igneous processes at very low oxygen fugacities, we have conducted partial melting experiments on the Indarch (EH4) chondrite at 1000-1500 C. Silicate melting begins at 1000 C. Substantial melt migration occurs at 1300-1400 C and metal migrates out of the silicate change at 1450 C and approx. 50% silicate partial melting. As a group, our experiments contain three immiscible metallic melts 9Si-, and C-rich), two immiscible sulfide melts(Fe-and FeMgMnCa-rich) and Silicate melt. Our partial melting experiments on the Indarch (EH4) enstatite Chondrite suggest that igneous processes at low fO2 exhibit serveral unique features. The complete melting of sulfides at 1000 C suggest that aubritic sulfides are not relicts. Aubritic oldhamite may have crystallized from Ca and S complexed in the silicate melt. Significant metal-sulfide melt migration might occur at relatively low degrees of silicate partial melting. Substantial elemental exchange occurred between different melts (e.g., between sulfide and silicate, Si between silicate and metal), a feature not observed during experiments at higher fO2. This exchange may help explain the formation of aubrites from known enstatite chondrites.

  9. Melt segregation during Poiseuille flow of partially molten rocks

    NASA Astrophysics Data System (ADS)

    Quintanilla-Terminel, A.; Dillman, A. M.; Kohlstedt, D. L.

    2015-12-01

    Studies of the dynamics of partially molten regions of the Earth's mantle provide the basis necessary for understanding the chemical and physical evolution of our planet. Since we cannot directly observe processes occurring at depth, we rely on models and experiments to constrain the rheological behavior of partially molten rocks. Here, we present the results of an experimental investigation of the role of viscous anisotropy on melt segregation in partially molten rocks through Poiseuille flow experiments. Partially molten rock samples with a composition of either forsterite or anorthite plus a few percent melt were prepared from vacuum sintered powders and taken to 1200ºC at 0.1 MPa. The partially molten samples were then extruded through a channel of circular cross section under a fixed pressure gradient at 1200o to 1500oC. The melt distribution in the channel was subsequently mapped through image analyses of optical and backscattered electron microscopy images. In these experiments, melt segregates from the center toward the outer radius of the channel with the melt fraction at the outer radius increasing to twice that at the center. These results are consistent with base-state melt segregation as predicted by Takei and Holtzman (JGR, 2009), Takei and Katz (JFM, 2013) and Allwright and Katz (GJI, 2014) for sheared partially molten rocks for which viscosity is anisotropic due to the stress-induced, grain-scale alignment of melt.

  10. Evidence for partial melting in the Earth's asthenosphere

    NASA Astrophysics Data System (ADS)

    Takahashi, E.; Hirano, N.

    2005-12-01

    In the beginning of plate tectonics, the boundary between the lithosphere and the asthenosphere was considered to correspond with the solidus of the Earth's mantle (McKenzie, 1967). The presence of partial melting in the asthenosphere has been supported by the occurrences of the seismic low velocity zone, the high electric conductive layer and the experimentally determined peridotite solidus in the presence of H2O and CO2 (e.g., Anderson and Sammis, 1970; Wyllie, 1988). More recently however, the significance of partial melting in the Earth's asthenosphere has been severely criticized based on laboratory measurements on Vs and Qs of mantle material as a function temperature and pressure (e.g. Gribb and Cooper, 2000; Faul and Jackson, 2005). Karato and Jung (1998) proposed that the presence or absence of small amounts of water in olivine is the dominant factor that controls the rheology of the mantle and the presence of partial melting in the asthenosphere is unnecessary. Here we report the evidence for partial melting in the asthenosphere based on detailed fieldwork. Young alkali basalt lava (6 Ma) was found on the 130Ma old subducting Pacific plate (Hirano et al 2001, GRL). We carried out four research cruises using JAMSTEC RVs in the Western Pacific Ocean (144-153°E, 37-40°N) in order to search for the eruption site of the young alkali basalt (Hirano et al, 2005 this meeting). A cluster of small volcanic cones composed of highly vesicular (30-60 vol.%) alkali basalt (0.05 to 1 Ma) was found on flat ocean floor (149.7°E 37.5°N, 6000m deep with 300 m thick sediments). Rock samples recovered from dredges and submersible dives show chemical compositions similar to those in the Hawaiian North Arch volcanic field (Clague et al, 1990; Frey et al., 2000). REE and other trace-elements indicate that these alkali basalt magmas were formed by very small degrees of partial melting at >100km depth. Although the distribution of the studied volcanic cones is presently

  11. Dynamics of melt and water circulation in the mantle transition zone

    NASA Astrophysics Data System (ADS)

    Bercovici, David

    2010-05-01

    The presence of melt above the mantle transition zone has been predicted by several groups, and its formation has been attributed - according to the 'water filter model" (Bercovici & Karato 2003) - with causing whole mantle convection to appear geochemically layered. In recent years, various seismological studies (e.g., most recently Jasbinsek and Dueker, 2007) have collectively inferred an extensive low velocity region at 410km depth, suggestive of the predicted melt zone. The leading mechanism proposed for generating this melt zone is by dehydration melting, which is supported by modest transition-zone water concentrations inferred by electromagnetic sounding (Huang, Xu, Karato, 2005). In this mechanism, warm upwelling 'damp" transition-zone material (wadsleyite) crosses the 410km boundary, and arrives above the solidus water limit in the upper-mantle (olivine) partial melt stability field. The fate of the subsequently produced melt is important for inferring the structure, observability and stability of this melt region. The most recent models of a wet melt layer spreading along the 410km boundary and reacting with a background mantle flow predict that the layer will be several 10s of kilometers thick, and that the melt's material will be entrained into the lower mantle well before it reaches any slabs (Leahy & Bercovici, 2010). At these pressures the melt is possibly more dense than the solid, although the density cross-over point is not likely to be far above the 410km boundary. However, unless the density cross-over actually intersects the melt zone, the melt is stable to any Rayleigh-Taylor instability (Youngs & Bercovici, 2009). Finally, continued re-hydration of the transition zone is required to supply the melt layer in the presence of background mantle flow. Slabs foundering and flowing horizontally across the transition zone provide one of the best means for transporting water across the transition zone. Slabs at the bottom of the transition zone

  12. Distribution of melt during Poiseuille flow of partially molten rocks

    NASA Astrophysics Data System (ADS)

    Quintanilla-Terminel, Alejandra; Dillman, Amanda; Kohlstedt, David

    2016-04-01

    The mechanisms of melt extraction from the Earth's partially molten mantle are a key factor in the chemical and physical evolution of our planet and therefore are the topic of intense research. Since such processes cannot be observed directly, most of our understanding of the dynamics of partially molten rock relies on numerical models. Laboratory experiments are important for testing the validity of models at scales that we can observe. We designed a set of experiments to investigate the role of viscous anisotropy on melt segregation in partially molten rocks through Poiseuille flow. Partially molten rock samples composed of forsterite plus a few percent melt of different composition (anorthite, albite or lithium silicate) were prepared from high-purity nano-powders and taken to T = 1300oC at P = 0.1 MPa. The melt composition was varied in order to vary its viscosity. The partially molten samples were then extruded through a channel of circular cross section under a fixed pressure gradient. Different extrusion assemblies and consequently different flow geometries were explored. The melt distribution in the channel was subsequently mapped using image analysis on backscattered electron microscopy images and energy dispersive x-ray spectroscopy maps. In all experiments, melt segregates from the center toward the outer radius of the channel with the melt fraction at the outer radius increasing to at least twice that at the center. Furthermore, melt enriched areas are also observed in the center of the channel. The shape of the melt distribution depends on the extrusion geometry and on the melt viscosity. The segregation of melt toward the outer radius of the channel is consistent with the base-state melt segregation as predicted by viscous anisotropy theory developed by Takei and Holtzman (2009) and Takei and Katz (2014). However, the melt distribution profiles observed in our experiments have steeper gradients than the base-state melt segregation profiles described

  13. Probing the melt zone of Kilauea Iki lava lake, Kilauea volcano, Hawaii

    SciTech Connect

    Hardee, H.C.; Dunn, J.C.; Hills, R.G.; Ward, R.W.

    1981-12-01

    New drilling techniques were recently used to drill and core the melt zone of Kilauea Iki lava lake to a depth of 93 m. A partial melt zone was found to exist at depths between 58 m and 89 m consisting of 40 volume percent melt. Downhole seismic shots detonated in and below the melt zone resulted in the first in situ measurements of seismic velocity directly through well characterized partial melt zone. Periodic seismic sources were used to effectively penetrate the highly fractured hydrothermal zone of the lava lake crust. Low velocity P-wave layers (< or =2.0 km/s) were found at the surface, at 40 m depth, and at 90 m depth. Thermal convective experiments in the melt zone resulted in the first controlled in situ measurements of the interaction of water with a basaltic melt zone. Transient energy rates of 900 kW (980 kW/m/sup 2/) and steady rates of 85 kW (93 kW/m/sup 2/) were observed. The full water recovery (100%), high downhole steam temperatures (670 C), and high energy transfer rates (93 to 980 kW/m/sup 2/) observed in these thermal experiments are consistent with a closed cavity model where the injected water/steam directly contacted basaltic melt or near melt. In addition to understanding lava lakes, these seismic and thermal experiments have applications for the location of magma bodies in the crust and for the efficient extraction of energy from these bodies.

  14. An observational and thermodynamic investigation of carbonate partial melting

    NASA Astrophysics Data System (ADS)

    Floess, David; Baumgartner, Lukas P.; Vonlanthen, Pierre

    2015-01-01

    Melting experiments available in the literature show that carbonates and pelites melt at similar conditions in the crust. While partial melting of pelitic rocks is common and well-documented, reports of partial melting in carbonates are rare and ambiguous, mainly because of intensive recrystallization and the resulting lack of criteria for unequivocal identification of melting. Here we present microstructural, textural, and geochemical evidence for partial melting of calcareous dolomite marbles in the contact aureole of the Tertiary Adamello Batholith. Petrographic observations and X-ray micro-computed tomography (X-ray μCT) show that calcite crystallized either in cm- to dm-scale melt pockets, or as an interstitial phase forming an interconnected network between dolomite grains. Calcite-dolomite thermometry yields a temperature of at least 670 °C, which is well above the minimum melting temperature of ∼600 °C reported for the CaO-MgO-CO2-H2O system. Rare-earth element (REE) partition coefficients (KDcc/do) range between 9-35 for adjacent calcite-dolomite pairs. These KD values are 3-10 times higher than equilibrium values between dolomite and calcite reported in the literature. They suggest partitioning of incompatible elements into a melt phase. The δ18O and δ13C isotopic values of calcite and dolomite support this interpretation. Crystallographic orientations measured by electron backscattered diffraction (EBSD) show a clustering of c-axes for dolomite and interstitial calcite normal to the foliation plane, a typical feature for compressional deformation, whereas calcite crystallized in pockets shows a strong clustering of c-axes parallel to the pocket walls, suggesting that it crystallized after deformation had stopped. All this together suggests the formation of partial melts in these carbonates. A Schreinemaker analysis of the experimental data for a CO2-H2O fluid-saturated system indeed predicts formation of calcite-rich melt between 650-880 °C, in

  15. Secular evolution of partial melting and melt stagnation during the formation of Godzilla Mullion, Philippine Sea

    NASA Astrophysics Data System (ADS)

    Snow, J. E.; Ohara, Y.; Harigane, Y.; Michibayashi, K.; Hellebrand, E.; von der Handt, A.; Loocke, M.; Ishii, T.

    2009-12-01

    Godzilla Mullion is a large-scale low angle detachment fault (or OCC, Oceanic Core Complex) formed during backarc spreading in the Parece Vela Rift behind the Mariana arc system. Detachment spreading occurred during the time interval 15-12 Ma, before the Parece Vela Rift became extinct and the locus of back arc spreading in the system shifted to the East, to the Mariana Trough. During this time, the spreading rate varied from ~70-88 mm/year to zero (at extinction). The decline in the spreading rate, should have had profound effects on the thermal structure of the lithosphere in the rift, including include progressive thickening, decreasing degree of partial melting, and increasing melt stagnation. We have combined our preliminary data on mantle peridotite mineral chemistry to form a preliminary test of this hypothesis based on mantle peridotites from (currently) 10 sampling stations along the mullion from the cruises CSS33, KR03-01, KH07-02 and YK09-05. This test is for now based primarily on abyssal peridotite spinel chemistry (Dick and Bullen, 1982; Dick 1989). We can distinguish three distinct regions within the mullion based on spinel chemistry: (1) The Distal GM region, including sites KR03-01-D6, KH07-02-D17 and KH07-02-D7. These have a moderately depleted character, with minimum Cr-numbers between 30 and 40, and few samples with high TiO2 (an indicator of melt impregnation). (2) The Medial GM region, including stations KH07-02-D6, KR03-01-D7, KH07-02-D21 and YK09-05-6K#1142. These have a more fertile character, with minimum Cr-numbers between 14 and 22, and with the exception of KH07-02-21 (which may belong to the next group) little evidence of melt stagnation. (3) The Proximal GM region, including sites KR0301-D9 and D10 and CSS33-D1. These spinels show abundant evidence for melt reaction, including plagioclase pseudomorphs (See abstract by Loocke et al., this session) and pervasively elevated TiO2 contents and Cr-numbers in the spinels. We can interpret

  16. Impact of textural anisotropy on syn-kinematic partial melting of natural gneisses: an experimental approach.

    NASA Astrophysics Data System (ADS)

    Ganzhorn, Anne-Céline; Trap, Pierre; Arbaret, Laurent; Champallier, Rémi; Fauconnier, Julien; Labrousse, Loic; Prouteau, Gaëlle

    2015-04-01

    C experiments NOP1 was previously hydrated at room pressure and temperature. According to melt fraction, deformation of partially molten gneiss induced different strain patterns. For low melt fraction, at 750°C, deformation within the initially isotropic gneiss NOP1 is localized along large scales shear-zones oriented at about 60° from main stress component σ1. In these zones quartz grains are broken and micas are sheared. Melt is present as thin film (≥20 µm) at muscovite-quartz grain boundaries and intrudes quartz aggregates as injections parallel to σ1. For higher melt fraction, at 850°C, deformation is homogeneously distributed. In the layered gneiss PX28, deformation is partitioned between mica-rich and quartz-rich layers. For low melt fraction, at 850°C, numerous conjugate shear-bands crosscut mica-rich layers. Melt is present around muscovite grains and intrudes quartz grains in the favor of fractures. For high melt fractions, at 900°C, melt assisted creep within mica-rich layers is responsible for boudinage of the quartz-feldspar rich layers. Melt-induced veining assists the transport of melt toward inter-boudin zones. Finite strain pattern and melt distribution after deformation of PX28 attest for appearance of strong pressure gradients leading to efficient melt flow. The subsequent melt redistribution strongly enhance strain partitioning and strength weakening, as shown by differential stress vs. strain graphs. Our experiments have successfully reproduced microstructures commonly observed in migmatitic gneisses like boudinage of less fertile layers. Comparison between non-layered and layered gneisses attest for strong influence of compositional anisotropies inherited from the protolith upon melt distribution and migmatite strength.

  17. Network topology of olivine-basalt partial melts

    NASA Astrophysics Data System (ADS)

    Skemer, Philip; Chaney, Molly M.; Emmerich, Adrienne L.; Miller, Kevin J.; Zhu, Wen-lu

    2017-07-01

    The microstructural relationship between melt and solid grains in partially molten rocks influences many physical properties, including permeability, rheology, electrical conductivity and seismic wave speeds. In this study, the connectivity of melt networks in the olivine-basalt system is explored using a systematic survey of 3-D X-ray microtomographic data. Experimentally synthesized samples with 2 and 5 vol.% melt are analysed as a series of melt tubules intersecting at nodes. Each node is characterized by a coordination number (CN), which is the number of melt tubules that intersect at that location. Statistically representative volumes are described by coordination number distributions (CND). Polyhedral grains can be packed in many configurations yielding different CNDs, however widely accepted theory predicts that systems with small dihedral angles, such as olivine-basalt, should exhibit a predominant CN of four. In this study, melt objects are identified with CN = 2-8, however more than 50 per cent are CN = 4, providing experimental verification of this theoretical prediction. A conceptual model that considers the role of heterogeneity in local grain size and melt fraction is proposed to explain the formation of nodes with CN ≠ 4. Correctly identifying the melt network topology is essential to understanding the relationship between permeability and porosity, and hence the transport properties of partial molten mantle rocks.

  18. Melt-melt immiscibility as result of synchronous melting of metapelites and impure marbles at crustal depth in the Moldanubian Zone, Bohemian Massif.

    NASA Astrophysics Data System (ADS)

    Ferrero, Silvio; O´Brien, Patrick J.; Ziemann, Martin A.; Wunder, Bernd; Hecht, Lutz; Wälle, Markus

    2016-04-01

    Investigation of melt and fluid inclusions in migmatites grants access to the unadultered products of crustal melting, shedding light on the processes driving crustal differentiation. Stromatic migmatites from the Oberpfalz (Moldanubian Zone, Bohemain Massif) present a unique occurrence of calcite-rich inclusions (CRI), crystallized inclusions of anatectic melt (nanogranites) and CO2-rich inclusions, all hosted in peritectic garnet. Their distribution as clusters in the host suggests a primary nature, i.e. that they formed during garnet growth, thus testifying for the coexistence of different melts and fluid during partial melting in the middle-lower crust. CRI are generally small (≤10 μm in diameter) and, from a microstructural point of view, strikingly resemble the coexistent nanogranites, i.e. they show a well-developed negative crystal shape and have a cryptocrystalline nature. Their phase assemblage, identified via Raman spectroscopy and EDS mapping, consists of calcite, white mica and chlorite, with quartz as accessory mineral. Moreover, calcite crystals locally develop euhedral faces, further supporting the hypothesis that this phase crystallized from an originally homogeneous calcite-rich melt. Piston-cylinder re-homogenization experiments achieved nanogranites re-melting at pressure-temperature conditions consistent with geothermobarometric estimates, 800-850°C and 0.7-0.9 GPa. After having been re-heated at these conditions, the coexistent calcite-rich inclusions appear modified, with formation of internal porosity and re-crystallization of calcite in microcrystalline aggregates, suggesting that during the experimental run calcite melting was achieved. LA-ICPMS analyses show that CRIs are generally highly enriched in LILE (particularly Sr, Ba) and LREE (up to LaN ≈500, with moderate to low fractionation among LREE, La/Sm=1-9) with respect both to the host garnet and the coexistent nanogranites. The higher abundance of LREE in CRIs is consistent with

  19. The generation and composition of partial melts in the earth's mantle

    NASA Astrophysics Data System (ADS)

    Ribe, Neil M.

    1985-05-01

    A set of equations is presented which combines the constraints of fluid dynamics and multicomponent phase equilibrium to provide a unified description of partial melting in the earth's mantle. The equations are applied to a one-dimensional model for pressure-release melting of a simplified mantle material, which contains only two chemical components exhibiting either (a) complete solid solution or (b) a binary eutectic. In both cases, melting occurs over a range of depths. The unmelted crystalline residue ("matrix") is modeled as a saturated porous medium, through which the melt can migrate because of its differential buoyancy. Since melt interacts continuously with the matrix during ascent, melting occurs by equilibrium rather than fractional fusion. This equilibrium fusion is not the same as batch fusion, however, since material elements are quickly dispersed by migration of melt relative to the matrix. To a first approximation, the temperature profiles (adiabats) in the partially molten zone are independent of melt migration. The slope of the adiabats varies in inverse proportion to the number of degrees of freedom which characterizes the melting. Melting of a complete solid solution occurs along a "wet" adiabat whose slope is controlled by absorption of latent heat. Melting of a eutectic system occurs along a steeper "univariant" adiabat until one solid phase is exhausted, and subsequently along a wet adiabat. The velocity of melt migration can exceed the mantle upwelling velocity by an order of magnitude or more. The volume fraction of melt present is always less than the fraction of the material which has melted, and is unlikely to exceed a few percent. For a wide range of initial conditions, melting of a eutectic system produces erupted melts having constant major element composition and widely varying trace element composition. This result may provide a partial explanation for the characteristic major- and LIL-element patterns observed in MORB. Liquid

  20. Voluminous low-T granite: fluid present partial melting of the crust?

    NASA Astrophysics Data System (ADS)

    Hand, Martin; Barovich, Karin; Morrissey, Laura; Bockmann, Kiara; Kelsey, David; Williams, Megan

    2017-04-01

    the granites is their enriched Th concentrations compared to typical Aileron Province sub solidus metapelitic successions. However, based on continuous transects within metasedimentary rocks from a number of different regions that record transitions from sub-solidus assemblages to supra-solidus rocks petrologically characterised by typical fluid-absent peritectic assemblages (central Aileron Province, Broken Hill Zone, Ivrea-Verbano Zone), fluid-absent partial melting does not deplete Th concentrations in the residuum with respect to their sub-solidus protoliths. If these compositional transects are used as a guide to the general behaviour of Th during fluid-absent partial melting, the voluminous Th-enriched granites in the Aileron Province are unlikely to be the products of fluid-absent partial melting. This contention is supported by phase equilibria modelling of sub-solidus metasedimentary units whose detrital zircons match in age the granite-hosted xenocrysts, which indicate that temperatures in excess of 840°C are required to generate significant volumes (ie ≥ 30%) of melt under fluid-absent conditions. However, zircon saturation temperatures for the granites have a weighted mean of 776 ± 4 °C (n = 220). Because the granites contain abundant inheritance, this is an upper-T limit that also suggests fluid-absent partial melting was not the primary mechanism for granite formation. We suggest that voluminous granite formation in the Aileron Province occurred in a fluid-rich regime that was particularly effective at destabilising monazite and liberating Th into melt. Because of the propensity of monazite to destabilise in the presence of fluid, we suggest that high-grade metasedimentary terrains that are notably depleted in Th may be residuum associated with fluid-fluxed melt loss.

  1. Minority lifetime degradation of silicon wafers after electric zone melting

    NASA Astrophysics Data System (ADS)

    Wu, M. C.; Yang, C. F.; Lan, C. W.

    2015-06-01

    The degradation of minority lifetime of mono- and multi-crystalline silicon wafers after electric zone melting, a simple and contamination-free process, was investigated. The thermal-stress induced dislocations were responsible to the degradation; however, the grain size also played a crucial role. It was believed that the grain boundaries helped the relaxation of thermal stress, so that the degradation was reduced as the grain size decreased. In addition to lifetime mapping and etch pit density, photoluminescence mapping was also used to examine the electrically active defects after zone melting. Factors affecting lifetime degradation of silicon wafers after electric zone melting were examined. Small-grain multi-crystalline wafers showed better lifetime after zone melting. Twining area showed better lifetime. The formation of new grains relaxed the thermal stress mitigating lifetime degradation.

  2. The Effect of Melt Pressure on the Rheology of Compacting, Partially Molten Peridotite

    NASA Astrophysics Data System (ADS)

    Demartin, B.; Hirth, G.; Evans, B.

    2004-12-01

    The rheology of partially molten rock controls rock strength beneath spreading centers, deformation of the mantle wedge under subduction zones, and migration of melt to hot spots and volcanic arcs. Our understanding of these regions has been predominately shaped by chemical analyses of rocks and by remotely collected geophysical data. To interpret these data, however, requires knowledge of the relationships among deformation, melt topology, and melt migration. Most previous experimental studies of these relationships in partially molten rocks were conducted using undrained experiments, i.e., where melt cannot leave the matrix during deformation. For this configuration, melt pressure is inferred to roughly equal the minimum principle stress, but is actually unknown. By contrast, we have performed drained tests in which both melt pressure and compaction rates were measured independently. First, samples were synthesized by hot-isostatic pressing (HIP) fine-grained olivine power (10-38 μ m) with a prescribed amount of mid-ocean ridge basalt (MORB) powder (< 15 μ m) in a gas-medium apparatus at 1200° C and 300 MPa for 10 hours. Melt fractions (MORB contents) ranged from 0-30 %. Subsequently, samples were reinserted into the apparatus and deformed in the standard triaxial configuration. Melt flow out of the sample was accommodated by a glassy carbon bead reservoir (grain size 80-200 μ m) located above the sample. A small alumina cylinder centered within the reservoir transferred the load from the pistons to the sample. Melt pressure was controlled by regulating the pressure of argon gas in contact with the melt in the reservoir. Sample compaction was measured by recording the position of a piston with the pore pressure generator. Variations of melt fraction on the strength of drained samples at Pm = 30 or 50 MPa, where Pm is the melt pressure, affect strength in the same way as previously observed under undrained conditions. Within the uncertainty of our measurements

  3. Thermocapillary convection in zone-melting crystal growth - An open-boat physical simulation

    NASA Technical Reports Server (NTRS)

    Kim, Y. J.; Kou, Sindo

    1989-01-01

    Thermocapillary convection in a molten zone of NaNO3 contained in a boat with a free horizontal surface, that is heated from above by a centered wire heater, was studied to simulate flow in zone-melting crystal growth. Using a laser-light-cut technique and fine SiO powder as a tracer, convection in the melt zone was visualized in two different cases. In the first case, the entire melt surface was free, while in the second the melt surface was free only in the immediate vicinity of one vertical wall and was covered elsewhere, this wall being to simulate the melt/crystal interface during crystal growth. It was observed that thermocapillary convection near this wall prevailed in the first case, but was reduced significantly in the second. Since thermocapillary rather than natural convection dominated in the melt, the effect of the partial covering of the melt surface on thermocapillary convection in the melt observed in this study is expected to be similar under microgravity.

  4. Thermocapillary convection in zone-melting crystal growth - An open-boat physical simulation

    NASA Technical Reports Server (NTRS)

    Kim, Y. J.; Kou, Sindo

    1989-01-01

    Thermocapillary convection in a molten zone of NaNO3 contained in a boat with a free horizontal surface, that is heated from above by a centered wire heater, was studied to simulate flow in zone-melting crystal growth. Using a laser-light-cut technique and fine SiO powder as a tracer, convection in the melt zone was visualized in two different cases. In the first case, the entire melt surface was free, while in the second the melt surface was free only in the immediate vicinity of one vertical wall and was covered elsewhere, this wall being to simulate the melt/crystal interface during crystal growth. It was observed that thermocapillary convection near this wall prevailed in the first case, but was reduced significantly in the second. Since thermocapillary rather than natural convection dominated in the melt, the effect of the partial covering of the melt surface on thermocapillary convection in the melt observed in this study is expected to be similar under microgravity.

  5. Growth of early continental crust controlled by melting of amphibolite in subduction zones.

    PubMed

    Foley, Stephen; Tiepolo, Massimo; Vannucci, Riccardo

    2002-06-20

    It is thought that the first continental crust formed by melting of either eclogite or amphibolite, either at subduction zones or on the underside of thick oceanic crust. However, the observed compositions of early crustal rocks and experimental studies have been unable to distinguish between these possibilities. Here we show a clear contrast in trace-element ratios of melts derived from amphibolites and those from eclogites. Partial melting of low-magnesium amphibolite can explain the low niobium/tantalum and high zirconium/samarium ratios in melts, as required for the early continental crust, whereas the melting of eclogite cannot. This indicates that the earliest continental crust formed by melting of amphibolites in subduction-zone environments and not by the melting of eclogite or magnesium-rich amphibolites in the lower part of thick oceanic crust. Moreover, the low niobium/tantalum ratio seen in subduction-zone igneous rocks of all ages is evidence that the melting of rutile-eclogite has never been a volumetrically important process.

  6. Mechanical and microstructural effect of partial melting of continental crust

    NASA Astrophysics Data System (ADS)

    Fauconnier, Julien; Rosenberg, Claudio; Labrousse, Loïc; Stünitz, Holger; Jolivet, Laurent

    2017-04-01

    We present a set of experiments done in order to investigate the effect of melt on the strength and the microstructures of crustal rocks. Experiments were conducted in a Griggs-type apparatus with a mixture of 90 vol. % quartz and 10 vol. % biotite at 1 GPa confining pressure and a temperature between 700 and 900 °C. In some experiments, 5 vol. % or 10 vol. % of haplogranitic glass (HPG) powder was added to generate melt in the sample. Above the glass temperature transition (GTT), which occurs at 780 °C, HPG viscosity is 4 orders of magnitude lower than that of quartz and thus the sample strength and microstructures should be similar to those of partially molten sample. We performed a comparative study, in which samples were deformed without melt and without HPG, with HPG, but below the GTT, with HPG above the GTT, and finally with melt generated from biotite breakdown reactions. Samples with HPG above GTT and melt from biotite breakdown have the same microstructures and strength. Our data show that melt has two major consequences on the deformation of quartz-biotite aggregates : (1) while deformation is localized through a network of shear bands in experiments without melt and quartz is deformed by dislocation creep, there is no localization of the deformation with HPG or melt and the sample deformed by melt enhanced grain boundary sliding (2) melt reduces the strength of the sample but this weakening is lower than previously suggested if the long term resistance of the samples ( γ > 2.5 ) instead of peak resistance is taken into account.

  7. Partial melting of amphibolite to trondhjemite near Ykutat, Alaska

    NASA Technical Reports Server (NTRS)

    Barker, F.

    1986-01-01

    At Nunatak Fiord, 55 km NE of Yakutat, Alaska, a uniform layer of Cretaceous metabasalt approximately 3 km thick was metamorphosed to amphibolite facies and locally partially melted to trondhjemite pegmatite. Results of the rare earth element analysis performed on the amphibolite and the trondhjemite pegmatite are discussed.

  8. Modelling komatiitic melt accumulation and segregation in the transition zone

    NASA Astrophysics Data System (ADS)

    Schmeling, Harro; Arndt, Nick

    2013-04-01

    Komatiites are assumed to be the products of very hot mantle upwellings in the Archean, At such conditions melting of a chondritic mantle will take place deeply within the upper mantle or even within or below the mantle transition zone. Due to its compressibility at such pressures melt might have a higher density than olivine, but remains buoyant with respect to a pyrolitic mantle both above and below the olivine - wadsleyite phase boundary because of the presence of garnet. We study the physics of melting and melt segregation within a hot upwelling mantle flow region passing through the transition zone with particular emphasis on the effect of depth dependent density contrasts between melt and the ambient mantle. Assuming a 1D plume we solve the two-phase flow equations of the melt - matrix system accounting for matrix compaction and porosity dependent shear and bulk viscosity. We assume a constant rising velocity leading to a constant rate of melt generation. In a first model series the level of neutral buoyancy z_neutral is assumed to lie above the depth of onset of melting, i.e. there exists a region where highly dense melt may sink with respect to the rising mantle. Depending on two non-dimensional numbers (accumulation number Ac, retention number Rt) we find four regimes: 1) time-dependent melt accumulation in standing porosity waves which scale with the compaction length, 2) steady state weak melt accumulation near z_neutral , 3) no melt accumulation due to small density contrast, 4) no melt accumulation due to high matrix viscosity. In regime 4 the high mantle viscosity prohibits melt pore space opening and accumulation. In a second series the rising mantle crosses the olivine - wadsleyite phase boundary, which imposes a jump in density contrast between melt and ambient mantle, but melt is always assumed to be buoyant. In this case, a sharp melt fraction contrast forms with high melt fraction immediately above the phase boundary. In a third set of models, a

  9. Melting and crystallization of ice in partially filled nanopores.

    PubMed

    Solveyra, Estefanía González; de la Llave, Ezequiel; Scherlis, Damián A; Molinero, Valeria

    2011-12-08

    We investigate the melting and formation of ice in partially filled hydrophilic and hydrophobic nanopores of 3 nm diameter using molecular dynamics simulations with the mW water model. Above the melting temperature, the partially filled nanopores contain two water phases in coexistence: a condensed liquid plug and a surface-adsorbed phase. It has been long debated in the literature whether the surface-adsorbed phase is involved in the crystallization. We find that only the liquid plug crystallizes on cooling, producing ice I with stacks of hexagonal and cubic layers. The confined ice is wetted by a premelted liquid layer that persists in equilibrium with ice down to temperatures well below its melting point. The liquid-ice transition is first-order-like but rounded. We determine the temperature and enthalpy of melting as a function of the filling fraction of the pore. In agreement with experiments, we find that the melting temperature of the nanoconfined ice is strongly depressed with respect to the bulk T(m), it depends weakly on the filling fraction and is insensitive to the hydrophobicity of the pore wall. The state of water in the crystallized hydrophilic and hydrophobic pores, however, is not the same: the hydrophobic pore has a negligible density of the surface-adsorbed phase and higher fraction of water in the ice phase than the hydrophilic pore. The widths of the ice cores are nevertheless comparable for the hydrophobic and hydrophilic pores, and this may explain their almost identical melting temperatures. The enthalpy of melting ΔH(m), when normalized by the actual amount of ice in the pore, is indistinguishable for the hydrophobic and hydrophilic pores, insensitive to the filling fraction, and within the error bars, the same as the difference in enthalpy between bulk liquid and bulk ice evaluated at the temperature of melting of ice in the nanopores.

  10. Modelling komatiitic melt accumulation and segregation in the transition zone

    NASA Astrophysics Data System (ADS)

    Schmeling, H.; Arndt, N.

    2017-08-01

    Komatiites are probably produced in very hot mantle upwellings or plumes. Under such conditions, melting will take place deep within the upper mantle or even within the mantle transition zone. Due to its compressibility at such pressures, melt might be denser than olivine, but would remain buoyant with respect to a peridotitic mantle both above and below the olivine-wadsleyite phase boundary because of the presence of its higher temperature and denser garnet. We studied the physics of melting and melt segregation within hot upwelling mantle passing through the transition zone, with particular emphasis on the effect of depth-dependent density contrasts between melt and ambient mantle. Assuming a 1D plume, we solved the two-phase flow equations of the melt-matrix system accounting for matrix compaction and porosity-dependent shear and bulk viscosity. We assumed a constant ascent velocity and melt generation rate. In a first model series, the level of neutral buoyancy zneutr is assumed to lie above the depth of onset of melting, i.e. there exists a region where dense melt may lag behind the solid phases within the rising plume. Depending on two non-dimensional numbers (accumulation number Ac, compaction resistance number Cr) we find four regimes: 1) time-dependent melt accumulation in standing porosity waves that scale with the compaction length. The lowermost of these waves broadens with time until a high melt accumulation zone is formed in steady state. During this transient solitary porosity waves may cross the depth of neutral density and escape. 2) steady-state weak melt accumulation near zneutr, 3) no melt accumulation due to small density contrast or, 4) high matrix viscosity. In regime 4 the high mantle viscosity prevents the opening of pore space necessary to accumulate melt. In a second series, the rising mantle crosses the olivine-wadsleyite phase boundary, which imposes a jump in density contrast between melt and ambient mantle. A sharp melt porosity

  11. Melt segregation from partially molten source regions - The importance of melt density and source region size

    NASA Technical Reports Server (NTRS)

    Stolper, E.; Hager, B. H.; Walker, D.; Hays, J. F.

    1981-01-01

    An investigation is conducted regarding the changes expected in the density contrast between basic melts and peridotites with increasing pressure using the limited data available on the compressibilities of silicate melts and data on the densities of mantle minerals. It is concluded that since compressibilities of silicate melts are about an order of magnitude greater than those of mantle minerals, the density contrast between basic melts and mantle minerals must diminish significantly with increasing pressure. An earlier analysis regarding the migration of liquid in partially molten source regions conducted by Walker et al. (1978) is extended, giving particular attention to the influence of the diminished density contrast between melt and residual crystals with increasing source region depth and to the influence of source region size. This analysis leads to several generalizations concerning the factors influencing the depths at which magmas will segregate from their source regions and the degrees of partial melting that can be achieved in these source regions before melt segregation occurs.

  12. Partial structure factors reveal atomic dynamics in metallic alloy melts

    NASA Astrophysics Data System (ADS)

    Nowak, B.; Holland-Moritz, D.; Yang, F.; Voigtmann, Th.; Kordel, T.; Hansen, T. C.; Meyer, A.

    2017-07-01

    We investigate the dynamical decoupling of the diffusion coefficients of the different components in a metallic alloy melt, using a combination of neutron diffraction, isotopic substitution, and electrostatic levitation in Zr-Ni melts. We show that excess Ni atoms can diffuse more freely in a background of saturated chemical interaction, causing their dynamics to become much faster and thus decoupled than anticipated from the interparticle interactions. Based on the mode-coupling theory of the glass transition, the averaged structure as given by the partial static structure factors is able to explain the observed dynamical behavior.

  13. Identification and quantification of gabbro cumulate partial melting in mafic igneous complexes

    NASA Astrophysics Data System (ADS)

    Leuthold, J.

    2016-12-01

    In mafic magma chambers, olivine, plagioclase and clinopyroxene fractionate along the basaltic liquid line of descent. Ol-rich, troctolite and gabbro cumulates crystallize. Hot primitive magma sills are regularly injected into igneous complexes where they heat and partially melt surrounding hot rocks, percolate, hybridize and crystallize new and secondary phases (see Figure [1]). Here, I quantify the effect of gabbro cumulate partial melting and hybridization with invading primitive basalt using field observations, Cpx microtexture and core-rim geochemical profiles from the Rum sill complex (Scotland). I have run gabbro-basalt hybrid equilibrium and kinetic experiments to test the effect of gabbro assimilation on the basalt liquid and solid lines of descent. Rum poikilitic gabbro resorbed Cpx cores are overgrown by Cr-, Al-, Zr- and REE-depleted interstitial rim with high Mg#, Eu* and Sr* (see [2]). Plg is reversely zoned. Fractional crystallization fails to explain the combined dissolution texture and incoherent compatible and incompatible elements zoning. Gabbro cumulate partial melting produces a Cpx-depleted residue and a melt that is saturated in Cpx, depleted in Cr, Al, Zr and REE and with high SiO2 and Mg# contents [1]. REE-poor Cpx rim crystallized from a hybrid basalt-gabbro magma, despite a lower DREE. In picrite-gabbro kinetic experiments reacted at conditions where Ol, Plg and Cpx are stable in gabbro but only Ol is stable in primitive basalt (1210°C, NNO-2), gabbro Ol and Cpx are anhedral and reversely zoned and Plg is euhedral. In the reaction rim, Cpx is absent, Ol anhedral grains are small and Cr-Spl abundance strongly increased (to 1.8 vol%). Troctolite small-scale partial melting and hybridization with primitive basalt produces a hybrid Al-rich melt that is Spl over-saturated. Gabbro partial melting products can be very difficult to distinguish from cumulates crystallized along the basalt liquid line of descent, because of the limited

  14. Physics of deep plume melting: komatiitic melt accumulation and segregation in the transition zone

    NASA Astrophysics Data System (ADS)

    Schmeling, Harro; Arndt, Nick; Kohl, Svenja

    2014-05-01

    Komatiites are assumed to be produced in very hot mantle upwellings or plumes. Under such conditions, melting will take place deep within the upper mantle or even within or below the mantle transition zone. Due to its compressibility at such pressures, melt has a higher density than olivine. Whether it would remain buoyant with respect to a peridotitic mantle both above and below the olivine-wadsleyite phase boundary because of the presence of denser garnet remains an open issue, particularly in view of recent X-ray refraction data on molten basalts by Sanloup et al. (2013). We studied the physics of melting and melt segregation within hot upwelling mantle passing through the transition zone, with particular emphasis on the effect of depth-dependent density contrasts between melt and the ambient mantle. Assuming a 1D plume, we solved the two-phase flow equations of the melt-matrix system accounting for matrix compaction and porosity-dependent shear and bulk viscosity. We assumed a constant ascent velocity leading to a constant rate of melt generation. In a first model series, the level of neutral buoyancy zneutral is assumed to lie above the depth of onset of melting, i.e. there exists a region where dense melt may lag behind the solid phases within the rising plume. Depending on two non-dimensional numbers (accumulation number Ac, compaction resistance number Cr) we find four regimes: 1) time-dependent melt accumulation in standing and broadening porosity waves that scale with the compaction length, 2) steady-state weak melt accumulation near zneutral, 3) no melt accumulation due to small density contrast, 4) no melt accumulation due to high matrix viscosity. In regime 4 the high mantle viscosity prevents the opening of pore space and the accumulation of melt. In a second series, the rising mantle crosses the olivine-wadsleyite phase boundary, which imposes a jump in density contrast between melt and ambient mantle. In this case, a sharp melt fraction contrast

  15. Electrical conductivity of hydrous andesitic melts pertinent to subduction zones

    NASA Astrophysics Data System (ADS)

    Guo, Xuan; Li, Bin; Ni, Huaiwei; Mao, Zhu

    2017-03-01

    Andesitic magmatism and rocks are widespread at convergent plate boundaries. Electrically conductive bodies beneath subduction zone arc volcanoes, such as the Uturuncu Volcano, Bolivia, may correspond to active reservoirs of H2O-bearing andesitic magma. Laboratory measurements of electrical conductivity of hydrous andesitic melts are required to constrain the physicochemical conditions of these magma reservoirs in combination with magnetotelluric data. This experimental study investigates electrical conductivity of andesitic melts with 0.01-5.9 wt % of H2O at 1164-1573 K and 0.5-1.0 GPa in a piston cylinder apparatus using sweeping-frequency impedance spectroscopy. Electrical conductivity of andesitic melt increases with increasing temperature and H2O concentration but decreases with pressure. Across the investigated range of H2O concentration, electrical conductivity varies by 1.2-2.4 log units, indicating stronger influence of H2O for andesitic melt than for rhyolitic and dacitic melts. Using the Nernst-Einstein equation, the principal charge carrier is inferred to be Na in anhydrous melt but divalent cations in hydrous andesitic melts. The experimental data are regressed into a general electrical conductivity model for andesitic melt accounting for the pressure-temperature-H2O dependences altogether. Modeling results show that the conductive layer at >20 km depths beneath the surface of the Uturuncu Volcano could be interpreted by the presence of less than 20 vol % of H2O-rich andesitic melt (with 6-9 wt % H2O).

  16. Evidence for Partial Melting in Reflectance Spectra of 433 Eros

    NASA Technical Reports Server (NTRS)

    McFadden, L. A.; Goldman, Noah; Gaffey, M. J.; Izenberg, N. R.

    2005-01-01

    The NEAR Shoemaker spacecraft returned near-IR spectra of asteroid 433 Eros at spatial resolutions ranging from 2.5 to 100's km during its year-long orbital mission in 2000. Assuming modified Gaussian absorption bands represent the reflectance spectrum between 0.8-2.5 m we fit the average of all geometrically corrected spectra acquired by the near-IR spectrometer (NIS) with seven absorption bands. Interpretation of the absorption bands in terms of olivine and pyroxene minerals indicates that the surface of Eros contains olivine and two pyroxenes with compositions that are indicative of a partially melted assemblage. This partial melting must have occurred when the asteroid was part of a larger minor planet, prior to break up into its current elongated and irregular shape.

  17. Partial melting of secondary pyroxenite at 1 and 1.5 GPa, and its role in upwelling heterogeneous mantle

    NASA Astrophysics Data System (ADS)

    Borghini, G.; Fumagalli, P.; Rampone, E.

    2017-08-01

    We performed partial melting experiments at 1 and 1.5 GPa, and 1180-1400 °C, to investigate the melting under mantle conditions of an olivine-websterite (GV10), which represents a natural proxy of secondary (or stage 2) pyroxenite. Its subsolidus mineralogy consists of clinopyroxene, orthopyroxene, olivine and spinel (+garnet at 1.5 GPa). Solidus temperature is located between 1180 and 1200 °C at 1 GPa, and between 1230 and 1250 °C at 1.5 GPa. Orthopyroxene (±garnet), spinel and clinopyroxene are progressively consumed by melting reactions to produce olivine and melt. High coefficient of orthopyroxene in the melting reaction results in relatively high SiO2 content of low melt fractions. After orthopyroxene exhaustion, melt composition is controlled by the composition of coexisting clinopyroxene. At increasing melt fraction, CaO content of melt increases, whereas Na2O, Al2O3 and TiO2 behave as incompatible elements. Low Na2O contents reflect high partition coefficient of Na between clinopyroxene and melt (D_{{{Na}_{ 2} {O}}}^{{{cpx}/{liquid}}}). Melting of GV10 produces Quartz- to Hyperstene-normative basaltic melts that differ from peridotitic melts only in terms of lower Na2O and higher CaO contents. We model the partial melting of mantle sources made of different mixing of secondary pyroxenite and fertile lherzolite in the context of adiabatic oceanic mantle upwelling. At low potential temperatures ( T P < 1310 °C), low-degree melt fractions from secondary pyroxenite react with surrounding peridotite producing orthopyroxene-rich reaction zones (or refertilized peridotite) and refractory clinopyroxene-rich residues. At higher T P (1310-1430 °C), simultaneous melting of pyroxenite and peridotite produces mixed melts with major element compositions matching those of primitive MORBs. This reinforces the notion that secondary pyroxenite may be potential hidden components in MORB mantle source.

  18. Microstructure and levitation properties of floating zone melted YBCO samples

    SciTech Connect

    Bashkirov, Yu.A.; Fleishman, L.S.; Vdovin, A.B.; Zubritsky, I.A.; Smirnov, V.V.; Vinogradov, A.V.

    1994-07-01

    Radiation zone melting has been used to produce texture in sintered YBCO cylindrical samples. Microstructural analysis by electron microscopy and pole figure measurements reveals that the production process gives rise to a preferential orientation within large domains. D.C. transport measurements show that changes in alignment orientation can result in the inability to carry a transport current. Both a.c. magnetic field shielding and levitation properties are substantially improved by the floating zone melting, the levitation force being increased with the texture domain size growth.

  19. Highly refractory peridotites in Songshugou, Qinling orogen: Insights into partial melting and melt/fluid-rock reactions in forearc mantle

    NASA Astrophysics Data System (ADS)

    Cao, Yi; Song, Shuguang; Su, Li; Jung, Haemyeong; Niu, Yaoling

    2016-05-01

    The Songshugou ultramafic massif is located in the eastern segment of the Qinling orogenic belt, central China. It is a large spinel peridotite body dominated by coarse-grained, porphyroclastic, and fine-grained dunite with minor harzburgite, olivine clinopyroxenite, and banded/podiform chromitite. The compositions of the bulk-rock dunite and harzburgite, and the constituent olivine and spinel, together with the textures and chemical characteristics of multiphase mineral inclusions, point to the highly refractory nature of these rocks with complex histories of high-temperature boninite melt generation and boninitic melt-rock reaction, probably in a young, warm, and volatile-rich forearc lithospheric mantle setting. Additionally, a subsequent low-temperature fluid-rock reaction is also recorded by TiO2-rich spinel with Ti solubility/mobility enhanced by chloride- or fluoride-rich subduction-zone fluids as advocated by Rapp et al. (2010). The olivine clinopyroxenite, on the other hand, was likely crystallized from a residual boninitic melt that had reacted with harzburgitic residues. The ubiquitous occurrences of hydrous minerals, such as anthophyllite, tremolite, Cr-chlorite, and serpentine (stable at lower P-T crustal conditions) in the matrix, suggest that further low-temperature fluid-rock reaction (or retrograde metamorphism) has affected the original volatile-poor peridotites either in a mature and cool subduction zone, or in a continental crust during their exhumation into the Qinling collisional orogeny at early Paleozoic era, or both. The prolonged and intense ductile/brittle deformation can decrease the mineral grain size through dynamic recrystallization and fracturing, and thus aid the fluid-rock reaction or retrograde metamorphism and mineral chemical re-equilibration processes. Therefore, the Songshugou peridotites present a good example for understanding the petrogenesis and evolution of the mantle wedge, with the emphasis on the complex partial

  20. Growth of early continental crust by partial melting of eclogite.

    PubMed

    Rapp, Robert P; Shimizu, Nobumichi; Norman, Marc D

    2003-10-09

    The tectonic setting in which the first continental crust formed, and the extent to which modern processes of arc magmatism at convergent plate margins were operative on the early Earth, are matters of debate. Geochemical studies have shown that felsic rocks in both Archaean high-grade metamorphic ('grey gneiss') and low-grade granite-greenstone terranes are comprised dominantly of sodium-rich granitoids of the tonalite-trondhjemite-granodiorite (TTG) suite of rocks. Here we present direct experimental evidence showing that partial melting of hydrous basalt in the eclogite facies produces granitoid liquids with major- and trace-element compositions equivalent to Archaean TTG, including the low Nb/Ta and high Zr/Sm ratios of 'average' Archaean TTG, but from a source with initially subchondritic Nb/Ta. In modern environments, basalts with low Nb/Ta form by partial melting of subduction-modified depleted mantle, notably in intraoceanic arc settings in the forearc and back-arc regimes. These observations suggest that TTG magmatism may have taken place beneath granite-greenstone complexes developing along Archaean intraoceanic island arcs by imbricate thrust-stacking and tectonic accretion of a diversity of subduction-related terranes. Partial melting accompanying dehydration of these generally basaltic source materials at the base of thickened, 'arc-like' crust would produce compositionally appropriate TTG granitoids in equilibrium with eclogite residues.

  1. Partial melting of ultrahigh-pressure metamorphic rocks during continental collision: Evidence, time, mechanism, and effect

    NASA Astrophysics Data System (ADS)

    Chen, Yi-Xiang; Zhou, Kun; Gao, Xiao-Ying

    2017-09-01

    , depending on anatectic conditions. The extraction of such melts can greatly deplete the melt-mobile elements in residues of UHP metapelites and eclogites. The partial melting of an isotopically heterogeneous source can yield isotopic variations between melt and residue. This is primarily controlled by the type of anatectic reactions and the solubility of accessory minerals. Although much progress has been made in the partial melting of UHP metamorphic rocks during continental collision, there are still many key issues that remain to be resolved. These include discriminating peritectic minerals from metamorphic and magmatic minerals, tracing the behavior of accessory minerals during anatexis, determining the geochemical composition of melts formed at UHP conditions, and placing precise constraints on the timescale for melt-forming and melt-transport processes. The clarification of these issues may greatly advance our understanding of the intracrustal differentiation, crust-mantle interaction and crustal recycling at convergent plate margins and thus provides insights into the chemical geodynamics of subduction zones.

  2. Convective effects in float-zone and Czochralski melts

    NASA Technical Reports Server (NTRS)

    Neitzel, G. P.

    1986-01-01

    The hydrodynamics of crystal-growth melts is a relatively new research area. Numerical modeling of these processes is necessary. The work discussed herein is in two parts: numerical simulations of the flow in a Czochralski melt, and also of that in a float zone. In addition, for the float-zone case, energy stability theory will be used to determine stability bounds for the onset of oscillatory thermo-capillary flow. Convective effects in crystal-growth melts arise from a variety of mechanisms. Temperature gradients both in the direction of gravity and normal to it give rise to convection due to buoyancy effects. Rotation of the crucible and/or crystal causes a forced convection which may augment or oppose the buoyancy-driven flow. Finally, thermo-capillary forces (due to the variation of surface tension with temperature) drive surface motions which in turn generate convection in the bulk fluid. All of these mechanisms are present in either Czochralski or float-zone growth. The objective of the Czochralski modeling is to develop an accurate numerical simulation of the flow in a Czochralski silicon melt and to investigate the effects of various parameters on the flow properties. Like some earlier investigations, the intent is to simulate the effects of buoyancy, forced and thermo-capillary convection, including unsteady effects. Unlike earlier work, the aim is to include the effects of a variable free surface and freezing interface and, possibly incorporate nonaxisymmetric effects.

  3. Ascent Dynamics of Low Degree Mantle Partial Melts, Constrained from CO2 Solubility Experiments.

    NASA Astrophysics Data System (ADS)

    Moussallam, Y.; Morizet, Y.; Massuyeau, M.; Gaillard, F.

    2014-12-01

    Low degree partial melting of carbonated mantle peridotite generates strongly silica-undersaturated melts containing substantial amount of carbon dioxide (several tens of wt%). Kimberlite melts are one of these volatile-rich mantle product and are believed to ascent through the upper mantle and crust at great speed (~5 to 50 ms-1). The role of volatiles in propelling this ascent has remained poorly quantified due to experimental difficulties in quenching such compositions to a glass. In this study, we used a range of melt compositions in the Si-C-Al-Ca-Mg-Fe-Na-K-O system addressing the chemical complexity needed to closely mimic kimberlitic to carbonatitic characteristics. These melts can, furthermore, be quenched fast enough to produce a glass and be used to determine the CO2 solubility as a function of composition and pressure. Our results suggest that the solubility of CO2 decreases steadily with increasing amount of network forming cations from ~30 wt% CO2 at 12 wt% SiO2 down to ~3 wt% CO2 at 40 wt% SiO2 and that pressure has limited effect on the solubility of CO2 up until very shallow depth (~ last 3 km). This peculiar pressure-solubility relation in kimberlite melt can explain the highly explosive nature of kimberlite magma and characteristic geo-morphological features of their root zone. We present a general CO2 solubility model based on thermodynamic formalism covering a large range of melt composition from 11 to 53 wt% SiO2 spanning the transition from carbonatitic to basaltic melts at pressures up to 1500 MPa.

  4. Partial melting in amphibolites in a deep section of the Sveconorwegian Orogen, SW Sweden

    NASA Astrophysics Data System (ADS)

    Hansen, Edward; Johansson, Leif; Andersson, Jenny; LaBarge, Leah; Harlov, Daniel; Möller, Charlotte; Vincent, Stephanie

    2015-11-01

    Garnet amphibolite metataxites at the Steningekusten Nature Reserve in southwestern Sweden contain tonalitic patches and veins. Whole rock chemistry suggests that the protoliths were mafic igneous rocks with alkaline affinities. Orthopyroxene megacrysts are present in leucosome in parts of these garnet amphibolites but absent in others. Orthopyroxene megacrysts were formed by vapor-absent melting initiated by incongruent melting of biotite followed by the breakdown of hornblende. The net reaction was Bt + Hbl + Pl +/- Qtz ↔ Opx + Melt + Cpx + Gt. Melting occurred at pressures of approximately 1 GPa and temperatures which probably exceeded 800 °C. Pyroxenes are surrounded by hornblende-quartz symplectites, and hornblende in these coronas has distinctly lower concentrations of (Na + K) and Ti than that in adjacent mesosome. The hornblende rims formed upon cooling and reaction with crystallizing melt. This created a barrier to further reaction thus preserving the orthopyroxene megacrysts. Garnet amphibolite metatexites lacking pyroxene megacrysts have features characteristic of vapor-present melting including lack of peritectic phases predicted by vapor-absent melting reactions, larger amounts of leucosome (14 versus 7%), and less distinct melanosomes. The variation in these migmatites reflects open system behavior, either on a regional scale with the migration of aqueous fluids into the amphibolites or on a local scale with the migration of melt within the amphibolites. Zircons from all units have CL-dark core domains that are dated at 1415-1390 Ma. The core zones are cut and overgrown by CL-dark and CL-bright rims that are dated at 975-965 Ma. The zircon rims are thin in the mesosome but are thicker in the leucosome suggesting that they formed during migmatization. New growth of zircon associated with migmatization at ca. 970 Ma corresponds to the timing of crustal scale partial melting in the deep regions of the Sveconorwegian orogen, synchronous with east

  5. Metamorphism and partial melting of ordinary chondrites: Calculated phase equilibria

    NASA Astrophysics Data System (ADS)

    Johnson, T. E.; Benedix, G. K.; Bland, P. A.

    2016-01-01

    Constraining the metamorphic pressures (P) and temperatures (T) recorded by meteorites is key to understanding the size and thermal history of their asteroid parent bodies. New thermodynamic models calibrated to very low P for minerals and melt in terrestrial mantle peridotite permit quantitative investigation of high-T metamorphism in ordinary chondrites using phase equilibria modelling. Isochemical P-T phase diagrams based on the average composition of H, L and LL chondrite falls and contoured for the composition and abundance of olivine, ortho- and clinopyroxene, plagioclase and chromite provide a good match with values measured in so-called equilibrated (petrologic type 4-6) samples. Some compositional variables, in particular Al in orthopyroxene and Na in clinopyroxene, exhibit a strong pressure dependence when considered over a range of several kilobars, providing a means of recognising meteorites derived from the cores of asteroids with radii of several hundred kilometres, if such bodies existed at that time. At the low pressures (<1 kbar) that typify thermal metamorphism, several compositional variables are good thermometers. Although those based on Fe-Mg exchange are likely to have been reset during slow cooling, those based on coupled substitution, in particular Ca and Al in orthopyroxene and Na in clinopyroxene, are less susceptible to retrograde diffusion and are potentially more faithful recorders of peak conditions. The intersection of isopleths of these variables may allow pressures to be quantified, even at low P, permitting constraints on the minimum size of parent asteroid bodies. The phase diagrams predict the onset of partial melting at 1050-1100 °C by incongruent reactions consuming plagioclase, clinopyroxene and orthopyroxene, whose compositions change abruptly as melting proceeds. These predictions match natural observations well and support the view that type 7 chondrites represent a suprasolidus continuation of the established petrologic

  6. Consequences and Resolution of Lunar Lower Mantle Partial Melt

    NASA Astrophysics Data System (ADS)

    Fuqua, H.; Bremner, P. M.; Diamond, M. R.; Garapic, G.; Lock, S. J.; Mallik, A.; Nishikawa, Y.; Panovska, S.; Shahar, A.; Lognonne, P. H.; Panero, W. R.; Faul, U.; Panning, M. P.; Jimenez-Perez, H.; Schmerr, N. C.; Williams, Q. C.

    2014-12-01

    Existence of a partially molten layer at depth has been proposed to explain the lack of observed farside deep moonquakes, the observation of reflected phases from deep moonquakes, and the dissipation of tidal energy within the lunar interior. However, subsequent models explore the possibility that dissipation due to elevated temperatures alone can explain the observed dissipation factor (Q) and tidal love numbers. We have explored the hypothesis that high titanium melt compositions associated with lunar mantle overturn may sink to the base of the mantle, locally or regionally. We have performed forward calculations varying composition and thickness of layers to evaluate if a partially molten layer at the base of the mantle is well constrained by the observational data. Self-consistent physical parameters are calculated for each compositional model that are then compared against the observed data to determine a subset of permissible models. The data constraints considered by this study include bulk density, moment of inertia, real and imaginary parts of the Love numbers, seismic travel times, and electrical conductivity. Dynamic calculations using ASPECT have also been considered to determine the implications of early lunar mantle convection for the survivability of the partially molten layer. Finally, and as a perspective for a future NASA New Frontiers Geophysical Network, we present 1D synthetic seismograms calculated for each proposed structure of the Moon to investigate the future seismological resolution of these deep lunar structure features. This work was initiated at the CIDER 2014 program.

  7. Melt Inclusions as Windows on Subduction Zone Processes - A Retrospective

    NASA Astrophysics Data System (ADS)

    Sisson, T. W.

    2002-12-01

    A.T. (Fred) Anderson, in a series of papers in the interval 1972-1984, presented evidence from melt inclusions for high dissolved water and Cl concentrations in many subduction zone basalts through andesites. His observations, subsequently shown to be correct, were not widely accepted because (1) phase equilibrium experiments on Paricutin and Mount Hood andesites indicated moderate water concentrations, and some workers reasoned that potentially parental basalts would have been drier still, (2) common basalts lack hydrous phenocrysts, and (3) water content estimates were indirect (water-by-difference) or involved difficult, unfamiliar measurements (single inclusion manometry) and thus were discounted. Subsequent development of techniques for the direct and precise measurement of water and CO2 in melt inclusions (SIMS, FTIR), new hydrous phase-equilibrium studies on arc basalts through rhyolites, and wider appreciation of the diversity of arc magmatic suites changed this situation. Melt inclusion evidence shows that subduction zone basalts can have pre-eruptive dissolved water concentrations as high as ~6 wt% (Sisson and Layne 1993 EPSL; Roggensack et al. 1997 Science), confirming predictions from phase-equilibrium experiments (Sisson and Grove 1993a,b CMP), and supporting the now standard model of water-fluxed melting to drive arc magmatism. An important discovery, presaged in the original Anderson data, is that there is a wide range of pre-eruptive water contents in arc basalts, with some as dry as MORB (Sisson and Bronto 1998 Nature). Nearly dry arc basalts can erupt at the volcanic front (Galunggung, Java) and sporadically along the arc axis over distances of hundreds of km (Cascades, USA), in some cases in proximity to demonstrably water-rich magmatic centers (Mt. Shasta, Crater Lake). To produce dry primitive basalts requires upwelling and pressure-release melting of peridotite in the mantle wedge at temperatures (~1300° C) well above those predicted by

  8. Primary Ca-rich Carbonate Melts in the Transition Zone

    NASA Astrophysics Data System (ADS)

    Walter, M.; Bulanova, G.; Armstrong, L.; Keshav, S.; Blundy, J.; Hinton, R.; Lennie, A.

    2007-12-01

    We present new experimental and geochemical constraints on the origin of composite Ca(Ti,Si)O3 and Ca- rich majorite garnet diamond inclusions from Juina kimberlite, Brazil. The evidence reveals that the inclusions did not form as subsolidus minerals, but instead crystallized directly from calcium-rich carbonate melts during crystallization of the host diamond. Subsolidus Phase Relations. We interpret composite CaSiO3 + CaTiO3 inclusions as exsolution products from a single-phase perovskite (Pv) in the transition zone1. The MgSiO3 component in the bulk CaTiSi-Pv is exceedingly low (<0.2 mol%), unlike experimental observations of Ca-Pv coexisting with either majorite-garnet or Mg-Pv (3-7 mol%) in peridotite or eclogite2,3. Indeed, our new subsolidus phase relations show MgSiO3 increasing substantially in Ca-Pv with increasing CaTiO3- content (20-50 GPa, 2000 K). The Ca-content of the majoritic inclusions are exceptionally high (10-15 wt% CaO), also unlike in peridotite or eclogite (< 7%). Unless bizarre mantle lithologies are invoked, subsolidus paragenesis for these inclusions is effectively precluded. Melting Phase Relations. We present new experiments showing that at transition zone depths, primary melts from carbonated eclogite crystallize CaTi-rich perovskites with composition very like the inclusions, and with exceptionally low MgSiO3 (<0.2 mol%). Liquidus majorite is very calcic (10-20 wt% CaO), spanning the range of garnet inclusions. This evidence indicates that the mineral inclusions crystallized from Ca-rich carbonate melts4. Trace Element Modeling. The trace element chemistry of the inclusions as determined using SIMS techniques support a model in which the inclusions equilibrated with small-degree melts. Overall the inclusions are massively enriched in a range of incompatible trace elements, (e.g. 103 to 104 x CI in perovskite). Based on experimental mineral-melt partitioning data, calculated coexisting melts have features inherited from subducted

  9. Stannern-Trend Eucrite Petrogenesis: An Assessment of Partial Melt Contamination Models via Experimental Petrology

    NASA Astrophysics Data System (ADS)

    Crossley, S. D.; Mayne, R. G.; Lunning, N. G.; McCoy, T. J.; Greenwood, R. C.; Franchi, I. A.

    2016-08-01

    Melting experiments were performed on the eucrite, NWA 8562, in order to test the partial melt assimilation model of Stannern-trend petrogenesis. Major and trace element data will be applied to the model, and preliminary results appear to fit.

  10. Analysis of surface tension driven flow in floating zone melting

    NASA Technical Reports Server (NTRS)

    Chang, C. E.; Wilcox, W. R.

    1976-01-01

    Surface tension driven flow in a cylindrical melt suspended between two rods was investigated by numerical solution of the steady state differential equations for heat and momentum transfer. Radiation heating and electron beam heating were considered approximately. For small values of the driving force, one rotating ring was formed in the top half of the zone, and its mirror image in the bottom half. At larger driving forces, secondary cells form which probably would undergo oscillatory motion. The influence of Prandtl number, zone movement, and buoyancy on the convection was also studied. The primary resistance to mass transfer in the laminar regime was in the center of the zone rather than at the solid-liquid interfaces.

  11. Microstructure and magnetization of Y-Ba-Cu-O prepared by melt quenching, partial melting and doping

    NASA Technical Reports Server (NTRS)

    Hojaji, Hamid; Hu, Shouxiang; Michael, Karen A.; Barkatt, Aaron; Thorpe, Arthur N.; Alterescu, Sidney

    1991-01-01

    Y-Ba-Cu-O samples prepared by means of a variety of melt-based techniques exhibit high values for their magnetic properties compared with those of samples prepared by solid state sintering. These techniques include single-stage partial melting as well as melt quenching followed by a second heat treatment stage, and they have been applied to the stoichiometric 123 composition as well as to formulations containing excess yttrium or other dopants. The structure of these melt-based samples is highly aligned, and the magnetization readings exhibit large anisotropy. At 77 K and magnetic field intensities of about 2 kOe, diamagnetic susceptibilities as high as -14 x 10(exp -3) emu/g were obtained in the cases of melt-quenched samples and remanent magnetization values as high as 10 emu/g for samples prepared by partial melting.

  12. Tape casting and partial melting of Bi-2212 thick films

    SciTech Connect

    Buhl, D.; Lang, T.; Heeb, B.

    1994-12-31

    To produce Bi-2212 thick films with high critical current densities tape casting and partial melting is a promising fabrication method. Bi-2212 powder and organic additives were mixed into a slurry and tape casted onto glass by the doctor blade tape casting process. The films were cut from the green tape and partially molten on Ag foils during heat treatment. We obtained almost single-phase and well-textured films over the whole thickness of 20 {mu}m. The orientation of the (a,b)-plane of the grains were parallel to the substrate with a misalignment of less than 6{degrees}. At 77K/OT a critical current density of 15`000 A/cm{sup 2} was reached in films of the dimension 1cm x 2cm x 20{mu}m (1{mu}V/cm criterion, resistively measured). At 4K/OT the highest value was 350`000 A/cm{sup 2} (1nV/cm criterion, magnetically measured).

  13. Tape casting and partial melting of Bi-2212 thick films

    NASA Technical Reports Server (NTRS)

    Buhl, D.; Lang, TH.; Heeb, B.; Gauckler, L. J.

    1995-01-01

    To produce Bi-2212 thick films with high critical current densities tape casting and partial melting is a promising fabrication method. Bi-2212 powder and organic additives were mixed into a slurry and tape casted onto glass by the doctor blade tape casting process. The films were cut from the green tape and partially molten on Ag foils during heat treatment. We obtained almost single-phase and well-textured films over the whole thickness of 20 microns. The orientation of the (a,b)-plane of the grains was parallel to the substrate with a misalignment of less than 6 deg. At 77 K/0T a critical current density of 15, 000 A/sq cm was reached in films of the dimension 1 cm x 2 cm x 20 microns (1 micron V/cm criterion, resistively measured). At 4 K/0T the highest value was 350,000 A/sq cm (1 nV/cm criterion, magnetically measured).

  14. Tape casting and partial melting of Bi-2212 thick films

    NASA Astrophysics Data System (ADS)

    Buhl, D.; Lang, Th.; Heeb, B.; Gauckler, L. J.

    1995-04-01

    To produce Bi-2212 thick films with high critical current densities tape casting and partial melting is a promising fabrication method. Bi-2212 powder and organic additives were mixed into a slurry and tape casted onto glass by the doctor blade tape casting process. The films were cut from the green tape and partially molten on Ag foils during heat treatment. We obtained almost single-phase and well-textured films over the whole thickness of 20 microns. The orientation of the (a,b)-plane of the grains was parallel to the substrate with a misalignment of less than 6 deg. At 77 K/0T a critical current density of 15, 000 A/sq cm was reached in films of the dimension 1 cm x 2 cm x 20 microns (1 micron V/cm criterion, resistively measured). At 4 K/0T the highest value was 350,000 A/sq cm (1 nV/cm criterion, magnetically measured).

  15. Differentiation of Relatively Oxidized Planetesimals: Experimental Partial Melting of Allende at IW+1

    NASA Astrophysics Data System (ADS)

    Lunning, N. G.; McCoy, T. J.; Corrigan, C. M.; Waters, L. E.

    2016-08-01

    Partial melting experiments on CV3 chondrites reveal that oxidized differentiated planetesimals may differ in their interior mineralogy and thermal structure from more "typical" reduced differentiated planetesimals.

  16. The effect of H2O on partial melting of garnet peridotite at 3.5 GPa

    NASA Astrophysics Data System (ADS)

    Tenner, Travis J.; Hirschmann, Marc M.; Humayun, Munir

    2012-03-01

    We present experimental determinations of the influence of H2O on partial melting of garnet peridotite (+1.5, 2.5, and 5 wt. % added H2O) at 3.5 GPa and 1200-1450°C. Experiments produced complex polyphase regions of quenched melt and equilibrium partial melt compositions were reconstructed by combined EMP and LA-ICP-MS analyses. Mass balance-derived melt fractions (F) range from 0.18 to 0.33 and dissolved water contents range from 4.5 to 23.5 wt. %. One exceptional experiment quenched glass, allowing independent verification of H2O concentration by FTIR. The influence of H2O on melt production is quantified by the temperature difference required to achieve a given F under dry and wet conditions, ΔT, which is controlled by the H2O concentration in partial melts. Melts with 1.5, 5, 10, and 15 wt. % H2O yield ΔT values of 50, 150, 250, and 320°C, respectively, consistent with a cryoscopic parameterization that assumes 3 oxygens per mole of silicate melt. Based on this parameterization, we calculate that beneath oceanic ridges, peridotite H2O storage capacity increases from 0 to 240 ppm from 66 to 110 km depth. For H2O to be solely responsible for melting in the oceanic low velocity zone (LVZ) at least 5.7 wt. % H2O must be dissolved in the melt at 110 km, and considerably more (e.g., 15 wt.% at 220 km) is required for melting throughout the entire observed interval. The addition of H2O results in 3.5 GPa partial melts of garnet peridotite (normalized anhydrous) that are SiO2 and Al2O3 poor (43-50 and 9-11.5 wt. %, respectively), and MgO and CaO rich (18-27 and 7-12 wt. %, respectively) when compared to anhydrous analogues. These effects become highly pronounced deep in the upper mantle, and are opposite to the effect of H2O on melt compositions in the spinel stability field, potentially owing in part to OH-association with network modifying cations in high pressure, depolymerized melts and in part to low-temperature stabilization of garnet, which enhances CaO/Al2O

  17. Microtomography of partially molten rocks : three-dimensional melt distribution in mantle peridotite.

    SciTech Connect

    Zhu, W.; Gaetani, G.; Fusseis, F.; Montesi, L.; De Carlo, F.

    2011-04-01

    The permeability of the upper mantle controls melt segregation beneath spreading centers. Reconciling contradictory geochemical and geophysical observations at ocean ridges requires a better understanding of transport properties in partially molten rocks. Using x-ray synchrotron microtomography, we obtained three-dimensional data on melt distribution for mantle peridotite with various melt fractions. At melt fractions as low as 0.02, triple junctions along grain edges dominated the melt network; there was no evidence of an abrupt change in the fundamental character of melt extraction as melt fraction increased to 0.2. The porosity of the partially molten region beneath ocean ridges is therefore controlled by a balance between viscous compaction and melting rate, not by a change in melt topology.

  18. Microtomography of partially molten rocks: three-dimensional melt distribution in mantle peridotite.

    PubMed

    Zhu, Wenlu; Gaetani, Glenn A; Fusseis, Florian; Montési, Laurent G J; De Carlo, Francesco

    2011-04-01

    The permeability of the upper mantle controls melt segregation beneath spreading centers. Reconciling contradictory geochemical and geophysical observations at ocean ridges requires a better understanding of transport properties in partially molten rocks. Using x-ray synchrotron microtomography, we obtained three-dimensional data on melt distribution for mantle peridotite with various melt fractions. At melt fractions as low as 0.02, triple junctions along grain edges dominated the melt network; there was no evidence of an abrupt change in the fundamental character of melt extraction as melt fraction increased to 0.2. The porosity of the partially molten region beneath ocean ridges is therefore controlled by a balance between viscous compaction and melting rate, not by a change in melt topology.

  19. Axial high topography and partial melt in the crust and mantle beneath the western Galápagos Spreading Center

    USGS Publications Warehouse

    Blacic, Tanya M.; Ito, Garrett; Shah, Anjana K.; Canales, Juan Pablo; Lin, Jian

    2008-01-01

    The hot spot-influenced western Galápagos Spreading Center (GSC) has an axial topographic high that reaches heights of ∼700 m relative to seafloor depth ∼25 km from the axis. We investigate the cause of the unusual size of the axial high using a model that determines the flexural response to loads resulting from the thermal and magmatic structure of the lithosphere. The thermal structure simulated is appropriate for large amounts of cooling by hydrothermal circulation, which tends to minimize the amount of partial melt needed to explain the axial topography. Nonetheless, results reveal that the large axial high near 92°W requires that either the crust below the magma lens contains >35% partial melt or that 20% melt is present in the lower crust and at least 3% in the mantle within a narrow column (<∼10 km wide) extending to depths of 45–65 km. Because melt fractions >35% in the crust are considered unreasonable, it is likely that much of the axial high region of the GSC is underlain by a narrow region of partially molten mantle of widths approaching those imaged seismically beneath the East Pacific Rise. A narrow zone of mantle upwelling and melting, driven largely by melt buoyancy, is a plausible explanation.

  20. Lithologic melt partitioning and transport properties of partially molten harzburgite

    NASA Astrophysics Data System (ADS)

    Miller, K. J.; Zhu, W.; Montesi, L.; Gaetani, G. A.; Le Roux, V.; Xiao, X.

    2015-12-01

    Quantitative constraints on melt transport in upper mantle are critical to understanding various dynamic processes at ocean ridges. In this study, we propose that thermodynamic gradients, resulting from spatial variations in mineralogy, can unevenly partition melt between olivine and orthopyroxene (opx), the two most abundant minerals in the upper mantle. The lithologic melt partitioning leads to higher melt fraction in olivine-rich regions compared to opx-rich regions, which may have important implications for melt transport. Lithologic partitioning has been experimentally confirmed in analogue systems, such as quartz/fluorite-H2O (Watson, 1999), but has never been observed in olivine/opx-melt samples. We synthesized olivine/opx-melt (harzburgite) samples by isostatically pressing oxide-high alumina basalt mixtures at 1350 °C and 1.5 GPa in a piston-cylinder apparatus. Nominal melt fractions of 0.02 to 0.20 and a constant 3 to 2 (olivine to opx) volume ratio were tested. Experimental charges were quenched, cored, and imaged using synchrotron X-ray microtomography. The resulting 3-D images constitute digital rock samples on which local melt fraction distributions, permeabilities, and electrical conductivities were numerically quantified. Our results are strong evidence for melt partitioning between olivine and opx: local melt fractions are 10 to 50% higher around olivine than opx grains. At the same melt fraction, permeabilities of whole harzburgite samples are lower compared to monomineralic olivine-melt samples (Miller et al., 2014). However, the presence of opx negligibly affects the permeability-porosity relation unless the abundance of opx is more than 40 vol. %. In contrast, electrical conductivities of harzburgites are systematically lower than those of olivine-melt samples. Lithological melt partitioning could be another mechanism responsible for forming high-porosity melt pathways in addition to reaction infiltration instability and deformation melt bands.

  1. Recrystallization and zone melting of charged colloids by thermally induced crystallization.

    PubMed

    Shinohara, Mariko; Toyotama, Akiko; Suzuki, Misaki; Sugao, Yukihiro; Okuzono, Tohru; Uchida, Fumio; Yamanaka, Junpei

    2013-08-06

    We examined the application of recrystallization and zone-melting crystallization methods, which have been used widely to fabricate large, high-purity crystals of atomic and molecular systems, to charged colloidal crystals. Our samples were aqueous dispersions of colloidal silica (with particle diameters of d = 108 or 121 nm and particle volume fractions of ϕ = 0.035-0.05) containing the weak base pyridine. The samples crystallized upon heating because of increases in the particle charge numbers, and they melted reversibly on cooling. During the recrystallization experiments, the polycrystalline colloids were partially melted in a Peltier cooling device and then were crystallized by stopping the cooling and allowing the system to return to ambient temperature. The zone-melting crystallization was carried out by melting a narrow zone (millimeter-sized in width) of the polycrystalline colloid samples and then moving the sample slowly over a cooling device to recrystallize the molten region. Using both methods, we fabricated a few centimeter-sized crystals, starting from millimeter-sized original polycrystals when the crystallization rates were sufficiently slow (33 μm/s). Furthermore, the optical quality of the colloidal crystals, such as the half-band widths of the diffraction peaks, was significantly improved. These methods were also useful for refining. Small amounts of impurity particles (fluorescent polystyrene particles, d = 333 nm, ϕ = 5 × 10(-5)), added to the colloidal crystals, were excluded from the crystals when the crystallization rates were sufficiently slow (∼0.1 μm/s). We expect that the present findings will be useful for fabricating large, high-purity colloidal crystals.

  2. Storage of fluids and melts at subduction zones detectable by seismic tomography

    NASA Astrophysics Data System (ADS)

    Luehr, B. G.; Koulakov, I.; Rabbel, W.; Brotopuspito, K. S.; Surono, S.

    2015-12-01

    During the last decades investigations at active continental margins discovered the link between the subduction of fluid saturated oceanic plates and the process of ascent of these fluids and partial melts forming a magmatic system that leads to volcanism at the earth surface. For this purpose the geophysical structure of the mantle and crustal range above the down going slap has been imaged. Information is required about the slap, the ascent paths, as well as the reservoires of fluids and partial melts in the mantle and the crust up to the volcanoes at the surface. Statistically the distance between the volcanoes of volcanic arcs down to their Wadati Benioff zone results of approximately 100 kilometers in mean value. Surprisingly, this depth range shows pronounced seismicity at most of all subduction zones. Additionally, mineralogical laboratory investigations have shown that dehydration of the diving plate has a maximum at temperature and pressure conditions we find at around 100 km depth. The ascent of the fluids and the appearance of partial melts as well as the distribution of these materials in the crust can be resolved by seismic tomographic methods using records of local natural seismicity. With these methods these areas are corresponding to lowered seismic velocities, high Vp/Vs ratios, as well as increased attenuation of seismic shear waves. The anomalies and their time dependence are controlled by the fluids. The seismic velocity anomalies detected so far are within a range of a few per cent to more than 30% reduction. But, to explore plate boundaries large and complex amphibious experiments are required, in which active and passive seismic investigations should be combined to achieve best results. The seismic station distribution should cover an area from before the trench up to far behind the volcanic chain, to provide under favorable conditions information down to 150 km depth. Findings of different subduction zones will be compared and discussed.

  3. Design, fabrication, and evaluation of a partially melted ice particle cloud facility

    NASA Astrophysics Data System (ADS)

    Soltis, Jared T.

    High altitude ice crystal clouds created by highly convective storm cells are dangerous to jet transport aircraft because the crystals are ingested into the compressor section, partially melt, accrete, and cause roll back or flame out. Current facilities to test engine particle icing are not ideal for fundamental mixed-phase ice accretion experiments or do not generate frozen droplet clouds under representative conditions. The goal of this research was to develop a novel facility capable of testing fundamental partially melted ice particle icing physics and to collect ice accretion data related to mixed-phase ice accretion. The Penn State Icing Tunnel (PSIT) has been designed and fabricated to conduct partially melted ice particle cloud accretion. The PSIT generated a cloud with air assisted atomizing nozzles. The water droplets cool from the 60psi pressure drop as the water exited the nozzle and fully glaciate while flowing in the -11.0°C tunnel air flow. The glaciated cloud flowed through a duct in the center of the tunnel where hot air was introduced. The temperature of the duct was regulated from 3.3°C to 24°C which melted particle the frozen particle from 0% to 90%. The partially melted particle cloud impinged on a temperature controlled flat plate. Ice accretion data was taken for a range of duct temperature from 3.3°C to 24°C and plate temperature from -4.5°C to 7.0°C. The particle median volumetric diameter was 23mum, the total water content was 4.5 g/m 3, the specific humidity was 1.12g/kg, and the wet bulb temperature ranged from 1.0°C to 7.0°C depending on the duct temperature. The boundaries between ice particle bounce off, ice accretion, and water run off were determined. When the particle were totally frozen and the plate surface was below freezing, the ice particle bounced off as expected. Ice accretion was seen for all percent melts tested, but the plate temperature boundary between water runoff and ice accretion increased from 0°C at 8

  4. Melt Segregation in Extrusion and Torsion Experiments on Partially Molten Rocks

    NASA Astrophysics Data System (ADS)

    Kohlstedt, D. L.; Qi, C.; Zimmerman, M. E.

    2012-12-01

    Shear deformation of partially molten rocks results in significant segregation of the low-viscosity melt phase, producing both a broad background redistribution of melt and a pronounced localization into melt-enriched bands. Important in the process of melt segregation is the strong dependence of viscosity on melt fraction (Stevenson, 1989) combined with the anisotropic viscosity that results from a stress-induced anisotropic distribution of melt at the grain scale (Takei and Holtzman, 2009). We have investigated both types of melt segregation using narrow-channel extrusion experiments and high-strain torsion experiments. In aggregates of anorthite plus 8% melt extruded several millimeters into a 2-mm diameter tube, melt segregation leads to an increase to12% melt at the sample-tube interface and to a decrease to 6% melt at the tube center. In aggregates of olivine plus MORB deformed in torsion, melt flows from the exterior toward the interior of the sample. For a sample with an average melt content of 10% twisted to a shear strain of 10, the melt content at the outer radius is ~7%, while the melt content at the inner core is ~13%. If a few percent chromite is added to samples of olivine plus MORB to decrease the permeability and thus the compaction length, melt segregates into an anastomosing network of melt-enriched bands that are oriented ~20o to the shear plane and antithetic to the shear direction. A similar melt-enriched band structure dominates the microstructure of aggregates of anorthite plus several percent melt deformed to high strain in torsion. Both the broad-background and the local segregation of melt profoundly influence the viscosity and permeability structure not only of laboratory samples but also of partially molten regions of Earth's interior.

  5. In situ observation of partial melting in superplastic aluminum alloy composites at high temperature

    SciTech Connect

    Koike, J. . Dept. of Mechanical Engineering); Mabuchi, M. ); Higashi, K. . Dept. of Mechanical Systems Engineering)

    1995-01-01

    The possibility of partial melting and its relations to the superplasticity at high strain rates were studied with transmission electron microscopy and differential scanning calorimetry in Al-Cu-Mg(2124), Al-Mg (5052), and Al-Mg-Si (6061) alloys reinforced with Si[sub 3]N[sub 4] particles. Calorimetry measurements of all three composites showed a sharp endothermic peak at an optimum superplastic temperature. At the same temperature, transmission electron microscopy showed the melting of grain boundaries and interfaces, suggesting direct correlations between partial melting and the superplasticity. Solute segregation was also observed at boundaries and interfaces, and was discussed as causes for partial melting.

  6. Melt-bearing shear zones: analogue experiments and comparison with examples from southern Madagascar

    NASA Astrophysics Data System (ADS)

    Grujic, Djordje; Mancktelow, Neil S.

    1998-06-01

    Analogue model experiments were conducted to investigate the influence of irregularly distributed weak sites in localising strain, as an aid to understanding shear zone development in partially molten rocks. The very weak inclusions consisted of Vaseline in a homogeneous matrix of paraffin wax, which has a power-law viscous rheology. Boundary conditions were those of pure shear at constant natural strain rate and confining stress σ3. The inclusions were initially perfect cylinders with axes parallel to the intermediate bulk strain axis Y. Conjugate shear zones nucleate on the inclusions and link up to form an anastomosing pattern of high strain zones of concentrated shear surrounding much more weakly deformed pods of near coaxial strain. The zones initiate at angles near 45° to the bulk shortening axis Z but stretch and rotate towards the X axis with increasing bulk strain. All inclusions nucleate shear zones, so that with increasing development of the anastomosing pattern, weak material occurs only within the high strain zones. The restriction of migmatite leucosomes to shear zones in natural examples could also reflect a corresponding control of melt on the sites of shear zone nucleation, rather than implying accumulation from the surrounding wall-rock. The model geometry is very similar to that observed in small-scale shear zones in migmatites of southern Madagascar. Elongate zones rich in weak inclusions, originally either perpendicular or at 45° to the Z axis, were also modelled for direct comparison with the regional-scale geometry of the Pan-African high-grade 'shear zones' on Madagascar.

  7. Generation of alkaline magmas in subduction zones by melting of mélange diapirs

    NASA Astrophysics Data System (ADS)

    Cruz-Uribe, A. M.; Marschall, H.; Gaetani, G. A.; Le Roux, V.

    2016-12-01

    Alkaline lavas occur globally in subduction-related volcanic arcs. Existing explanations for the occurrence of alkaline lavas in volcanic arcs invoke at least one - and in some cases multiple - `metasomatic' events in addition to the traditional three-component mixing of altered oceanic crust (AOC), sediment melt, and depleted mantle, in order to explain the range of rock types found in a given region. These multi-stage models posit the existence of metasomatized mantle wedge peridotite containing phlogopite or amphibole-enriched veins, which partially melt when fluxed by the addition of materials from the subducted slab. The mélange diapir model is informed by observations and modeling of the subduction side of the arc system, and predicts the generation of alkaline arc magmas by advection of buoyant material from the slab-wedge interface into the mantle wedge below arcs. Here we report results from experiments in which natural mélange materials partially melted at upper mantle conditions were found to produce alkaline magmas compositionally similar to those found in arcs worldwide. The starting material for our experiments is a chlorite-omphacite fels (SY400) from the island of Syros, Greece, that is representative of a hybrid rock containing AOC, sediment, and mantle components. Melting experiments were performed using a piston cylinder apparatus at conditions relevant to the heating-decompression path of mélange diapirs (1000-1300 °C, 1.5-2.5 GPa). The compositions of experimentally produced melts range from 51-61 wt% SiO2, and fall within the trachyte and tephrite-phonolite series (7.5-12.9 wt% Na2O+K2O). Restitic phases in equilibrium with melt include clinopyroxene, garnet (at high P), phlogopite (at high P), amphibole, olivine, rutile, and ilmenite. Partial melts produced in our experiments have trace-element abundance patterns that are typical of alkaline arc lavas, such as enrichment in large ion lithophile elements (Cs, Rb, Ba, Pb, Sr) and alkalis (K

  8. Deformation mechanisms in granodiorite at effective pressures to 100 MPa and temperatures to partial melting

    SciTech Connect

    Friedman, M.; Handin, J.; Bauer, S.J.

    1981-01-01

    Deformation mechanisms in room-dry and water-saturated specimens of Charcoal Granodiorite, shortened at 10/sup -4/s/sup -1/, at effective pressures (Pe) to 100 MPa and temperatures to partial melting (less than or equal to 1050/sup 0/C) are documented with a view toward providing criteria to recognize and characterize the deformation for geological and engienering applications. Above 800/sup 0/C strength decreases dramatically at effective pressures greater than or equal to 50 MPa and water-weakening reduces strength an additional 30 to 40% at Pe = 100 MPa. Strains at failure are only 0.1 to 2.2% with macroscopic ductility (within this range) increasing as the effective pressures are increased and in wet versus dry tests. Shattering (multiple faulting) gives way to faulting along a single zone to failure without macroscopic faulting as ductility increases. Microscopically, cataclasis (extension microfracturing and thermal cracking with rigid-body motions) predominates at all conditions. Dislocation gliding contributes little to the strain. Precursive extension microfractures coalesce to produce the throughgoing faults with gouge zones exhibiting possible Riedel shears. Incipient melting, particularly in wet tests, produces a distinctive texture along feldspar grain boundaries that suggests a grain-boundary-softening effect contributes to the weakening. In addition, it is demonstrated that the presence of water does not lead to more microfractures, but to a reduction in the stresses required to initiate and propagate them.

  9. Melt in the mantle beneath the Amagmatic Zone, Southern Nevada

    NASA Astrophysics Data System (ADS)

    Rau, C. J.; Forsyth, D. W.

    2010-12-01

    Surface wave tomography of the western United States reveals the presence of an unusually slow shear wave velocity anomaly beneath a region in the Basin and Range province, sometimes termed the amagmatic gap (AMZ in figure below), which is renowned for its lack of volcanic activity. We present a model of the three-dimensional shear wave velocity structure beneath the southwestern United States constructed from the inversion of fundamental mode Rayleigh wave dispersion. The abundance of data from the deployment of the USArray provides unprecedented resolution. There is an excellent correlation between the location of slow shear wave velocity anomalies and recent (<1 Ma) volcanism (black dots below), notably along the edges of the Colorado Plateau. This correlation and the unusually low values of absolute shear velocity beneath the amagmatic gap lead us to conclude that there is melt present beneath this region. Previous studies have proposed that the preservation of cold, continental lithosphere beneath the amagmatic gap accounted for the lack of volcanism; however, this hypothesis is inconsistent with anomalously slow shear wave velocities in the 50-to-100 km depth range. Perhaps the prevalence of low angle normal faulting in this region has made it difficult for the melt to escape the mantle. Beneath an immediately adjacent region, the Southwestern Nevada volcanic field (SNVF), where volcanism was abundant 10 to 15 My ago but has since waned, significantly higher shear velocities suggest that the melt has been extracted from the mantle. We also observe fast velocities beneath the Mojave Desert, which may correlate with xenoliths from the region to indicate the presence of underplated oceanic lithosphere fragments. Shear wave velocity structure at 60, 70, and 80 km and cross section A-A'. Black dots indicate <1 Ma volcanic centers, AMZ = Amagmatic zone, SNVF = Southwestern Nevada volcanic field, CP = Colorado Plateau, IS = Isabella anomaly, WTR = Western Transverse

  10. Partial melting and recrystallization of Archeaan komatiites by residual heat from rapidly accumulated flows

    NASA Astrophysics Data System (ADS)

    Gole, Martin J.; Barnes, Stephen J.; Hill, Robin E. T.

    1990-11-01

    Spinifex-textured komatiites at Honeymoon Well, Western Australia, show evidence of partial melting and recrystallization of original igneous textures. Their textures and mineral compositions differ markedly from those typical of komatiites. Spinifex olivine plates are bent and broken, while interstitial space between spinifex and cumulus olivine is occupied by polygonal aggregates of clinopyroxene, orthopyroxene, minor olivine and plagioclase. Similar granular pyroxene-plagioclase aggregates occur as diffuse veins cutting spinifex zones and cumulate zones of the flows and, in places, form the matrix to a breccia containing corroded fragments of spinifex rock. Thermometry based on the two pyroxene assemblages yields temperatures of 1055° to 1141° C, just below the low-pressure komatiite solidus. Mineral compositions are different from those of typical komatiites: clinopyroxenes are Al-poor and Cr-rich, olivines are unusually iron-rich and depleted in Cr and Ca, and the low-Ca pyroxene is bronzite rather than the more typical pigeonite. We interpret these observations as the results of thermal metamorphism, partial remelting and subsequent slow crystallization of originally normal spinifex-textured komatiite flows. The rocks in question occupy a 40 70 m interval sandwiched between two olivine-rich units: an underlying 90 m-thick olivine adcumulate layer, forming part of the cumulate zone of a basal 160 m-thick flow, and an overlying 1 km-thick extrusive body composed mostly of olivine mesocumulate and adcumulate and capped in turn by spinifex-textured flows. Thermal modelling shows that a sinusoidal temperature profile of cool flow tops and hot flow centres would exist within this sequence shortly after eruption. Conductive thermal relaxation of this profile could reheat spinifex zones to the extent of inducing partial melting and textural reconstitution. Such reheating is largely dependent on the time interval between the emplacement of successive flows

  11. Slab melting versus slab dehydration in subduction-zone magmatism

    PubMed Central

    Mibe, Kenji; Kawamoto, Tatsuhiko; Matsukage, Kyoko N.; Fei, Yingwei; Ono, Shigeaki

    2011-01-01

    The second critical endpoint in the basalt-H2O system was directly determined by a high-pressure and high-temperature X-ray radiography technique. We found that the second critical endpoint occurs at around 3.4 GPa and 770 °C (corresponding to a depth of approximately 100 km in a subducting slab), which is much shallower than the previously estimated conditions. Our results indicate that the melting temperature of the subducting oceanic crust can no longer be defined beyond this critical condition and that the fluid released from subducting oceanic crust at depths greater than 100 km under volcanic arcs is supercritical fluid rather than aqueous fluid and/or hydrous melts. The position of the second critical endpoint explains why there is a limitation to the slab depth at which adakitic magmas are produced, as well as the origin of across-arc geochemical variations of trace elements in volcanic rocks in subduction zones. PMID:21536910

  12. Slab melting versus slab dehydration in subduction-zone magmatism.

    PubMed

    Mibe, Kenji; Kawamoto, Tatsuhiko; Matsukage, Kyoko N; Fei, Yingwei; Ono, Shigeaki

    2011-05-17

    The second critical endpoint in the basalt-H(2)O system was directly determined by a high-pressure and high-temperature X-ray radiography technique. We found that the second critical endpoint occurs at around 3.4 GPa and 770 °C (corresponding to a depth of approximately 100 km in a subducting slab), which is much shallower than the previously estimated conditions. Our results indicate that the melting temperature of the subducting oceanic crust can no longer be defined beyond this critical condition and that the fluid released from subducting oceanic crust at depths greater than 100 km under volcanic arcs is supercritical fluid rather than aqueous fluid and/or hydrous melts. The position of the second critical endpoint explains why there is a limitation to the slab depth at which adakitic magmas are produced, as well as the origin of across-arc geochemical variations of trace elements in volcanic rocks in subduction zones.

  13. Spin crossover and iron-rich dense partial melt in pyrolitic lower mantle

    NASA Astrophysics Data System (ADS)

    Hirose, K.; Tateno, S.

    2012-12-01

    Spin crossover of iron may occur not only in solids but also in melts in the lower mantle. The resulting change in Fe partitioning strongly affects the buoyancy of partial melts near the base of the mantle. Nomura et al. [2011 Nature] measured the Fe partitioning in (Mg0.89Fe0.11)2 SiO4 bulk composition over the entire mantle pressure range, demonstrating that Fe-Mg distribution coefficient KD = ([FePv]/[MgPv]) / ([Femelt]/[Mgmelt]) between (Mg,Fe)SiO3 perovskite and melt dropped from ~0.25 to <0.1 around 76 GPa, resulting in strong Fe-enrichment in melts and thereby dense partial melts in the mid-lower mantle. In contrast, the most recent experiments by Andrault et al. [2012 Nature] found much higher KD and less Fe-enrichment in partial melts formed in primitive mantle composition, suggesting that melt is not dense in the lowermost mantle. Here we extend our measurements in pyrolitic natural mantle (KLB-1 peridotite) bulk composition. The distribution coefficient KD (total Fe/Mg) was determined at 40-180 GPa by a combination of laser-heated diamond-anvil cell experiments and chemical analyses of recovered samples using field-emission-type electron microprobe (FE-EPMA). Our results demonstrate that KD between perovskite and melt is about 0.3 up to 58 GPa, consistent with earlier multi-anvil data. It then dropped to ~0.1 above 68 GPa, indicating strong Fe-enrichment in partial melts. These results are in excellent agreement with those of Nomura et al. [2011], indicating that Fe-rich partial melts are more dense than solids below 1600-km depth in the lower mantle. The observed Fe-enrichment in partial melt above 68 GPa can be explained by a spin crossover of iron in silicate melt, as discussed previously in Nomura et al. [2011].

  14. Melting Behaviour of Carbonated MORB: the transition zone carbon filter

    NASA Astrophysics Data System (ADS)

    Thomson, A. R.; Walter, M. J.; Kohn, S. C.

    2014-12-01

    The convecting mantle represents Earth's largest reservoir for volatile storage on geological timescales. Continuous outgassing in volcanic settings worldwide indicates that volatile recycling during subduction of oceanic crust is critical for the maintenance of mantle volatile contents. Subducting basaltic crust initially contains a cocktail of volatiles, but it loses effectively its entire water cargo as hydrous fluids between 70 and 300 km depending on slab temperature [1], which may leave a residual anhydrous carbonated MORB assemblage. The fate of this carbon during subduction to greater depths is important geologically due to its potential role in causing mantle melting and metasomatism. Large discrepancies exist among studies of carbonated eclogite, and results are scarce beyond 10 GPa. Here we present results of experiments on MORB containing 2.5 wt.% CO2between 3 and 21 GPa. We observe a subsolidus phase assemblage dominated by garnet, clinopyroxene and SiO2 at all pressures. At pressures lower than 7 GPa CO2 is the stable carbon phase in all runs due to the reaction dol + 2coes = cpx + CO2 [2]. Solid dolomite, magnesite and/or Na2(Ca,Mg,Fe)4(CO3)5 are observed in subsolidus experiments at higher pressure. Near-solidus melts above 7 GPa are carbonatites, with Ca# > 0.5 and alkali contents that increase with pressure. The solidus temperature of 1200 °C at 3 GPa rises to 1375 °C at 13 GPa. At higher pressure the melting temperature drops sharply by > 200 °C to ~ 1150 °C. This creates a ledge in the solidus at 13 - 15 GPa, just above or within the uppermost transition zone, which coincides with the appearance of Na2(Ca,Mg,Fe)4(CO3)5. Temperature paths for the majority of worldwide slabs [3] intersect this ledge and produce carbonatite melt that will metasomatise the overlying mantle, potentially causing a region of increased diamond formation. Only material in the coldest slabs will pass beneath the ledge and carry carbon deeper into the Earth. Thus, this

  15. Vertical zone melt growth of GaAs

    SciTech Connect

    Henry, R.L.; Nordquist, P.E.R.; Gorman, R.J.

    1993-12-31

    A Vertical Zone Melt (VZM) technique has been applied to the single crystal growth of GaAs. A pyrolytic boron nitride crucible and a (100) oriented seed were used along with liquid encapsulation by boric oxide. In the case of GaAs, the ampoule was pressurized with either argon or argensic vapor from elemental arsenic at pressures ranging from 1 to 2 atmospheres. A molten zone length of 22 mm gave a growth interface which is nearly flat and resulted in routine single crystal growth. Temperature gradients of 4{degrees}C/cm. and 9{degrees}C/cm. have produced dislocation densities of <1000/cm{sup 2} and 2000-5000/cm{sup 2} respectively for 34 mm diameter crystals of GaAs. Post growth cooling rates for GaAs have been 35, 160 and 500{degrees}C/hr. The cooling rate has been found to affect the number and size of arsenic precipitates and the EL2 concentration in the GaAs crystal. The effects of these and other growth parameters on the crystalline perfection and electrical properties of the crystals will be discussed.

  16. Effect of water on the composition of partial melts of greenstone and amphibolite

    NASA Technical Reports Server (NTRS)

    Beard, James S.; Lofgren, Gary E.

    1989-01-01

    Closed-system partial melts of hydrated, metamorphosed arc basalts and andesites (greenstones and amphibolites), where only water structurally bound in metamorphic minerals is available for melting (dehydration melting), are generally water-undersaturated, coexist with plagioclase-rich, anhydrous restites, and have compositions like island arc tonalites. In contrast, water-saturated melting at water pressures of 3 kilobars yields strongly peraluminous, low iron melts that coexist with an amphibole-bearing, plagioclase-poor restite. These melt compositions are unlike those of most natural silicic rocks. Thus, dehydration melting over a range of pressures in the crust of island arcs is a plausible mechanism for the petrogenesis of islands arc tonalite, whereas water-saturated melting at pressure of 3 kilobars and above is not.

  17. An experimental method for directly determining the interconnectivity of melt in a partially molten system

    NASA Technical Reports Server (NTRS)

    Daines, Martha J.; Richter, Frank M.

    1988-01-01

    An experimental method for directly determining the degree of interconnectivity of melt in a partially molten system is discussed using an olivine-basalt system as an example. Samarium 151 is allowed time to diffuse through mixtures of olivine and basalt powder which have texturally equilibrated at 1350 C and 13 to 15 kbars. The final distribution of samarium is determined through examination of developed radiographs of the samples. Results suggest an interconnected melt network is established at melt fractions at least as low as 1 wt pct and all melt is completely interconnected at melt fractions at least as low as 2 wt pct for the system examined.

  18. An experimental method for directly determining the interconnectivity of melt in a partially molten system

    NASA Technical Reports Server (NTRS)

    Daines, Martha J.; Richter, Frank M.

    1988-01-01

    An experimental method for directly determining the degree of interconnectivity of melt in a partially molten system is discussed using an olivine-basalt system as an example. Samarium 151 is allowed time to diffuse through mixtures of olivine and basalt powder which have texturally equilibrated at 1350 C and 13 to 15 kbars. The final distribution of samarium is determined through examination of developed radiographs of the samples. Results suggest an interconnected melt network is established at melt fractions at least as low as 1 wt pct and all melt is completely interconnected at melt fractions at least as low as 2 wt pct for the system examined.

  19. Growth of early continental crust by water-present eclogite melting in subduction zones

    NASA Astrophysics Data System (ADS)

    Laurie, A.; Stevens, G.

    2011-12-01

    The geochemistry of well preserved Paleo- to Meso-Archaean Tonalite-Trondhjemite-Granodiorite (TTG) suite rocks, such as the ca 3.45 Ga trondhjemites from the Barberton greenstone belt in South Africa, provides insight into the origins of Earth's early felsic continental crust. This is particularly well demonstrated by the high-Al2O3 variety of these magmas, such as the Barberton rocks, where the geochemistry requires that they are formed by high pressure (HP) melting of a garnet-rich metamafic source. This has been interpreted as evidence for the formation of these magmas by anatexis of the upper portions of slabs within Archaean subduction zones. Most of the experimental data relevant to Archaean TTG genesis has been generated by studies of fluid-absent melting of metabasaltic sources. However, water drives arc magmatism within Phanerozoic subduction zones and thus, understanding the behaviour of water in Archaean subduction zones, may have considerable value for understanding the genesis of these TTG magmas. Consequently, this study investigates the role of HP water-present melting of an eclogite-facies starting material, in the production of high-Al2O3 type TTG melts. Water-saturated partial melting experiments were conducted between 1.9 and 3.0GPa; and, 870°C and 900°C. The melting reaction is characterized by the breakdown of sodic Cpx, together with Qtz and H2O, to form melt in conjunction with a less sodic Cpx: Qtz + Cpx1 + Grt1 + H2O = Melt + Cpx2 + Grt2. In many of the experimental run products, melt segregated efficiently from residual crystals, allowing for the measurement of a full range of trace elements via Laser Ablation Inductively Coupled Plasma Mass Spectroscopy. The experimental glasses produced by this study have the compositions of peraluminous trondhjemites; and they are light rare earth element, Zr and Sr enriched; and heavy rare earth element, Y and Nb depleted. The compositions of the experimental glasses are similar to high-Al2O3 type

  20. Partial melting of amphibolite to trondhjemite at Nunatak Fiord, St. Elias Mountains, Alaska

    SciTech Connect

    Barker, F.; McLellan, E.L.; Plafker, G.

    1985-01-01

    At Nunatak Fiord, 55km NE of Yakutat, Alaska, a uniform layer of Cretaceous basalt ca. 3km thick was metamorphosed ca. 67 million years ago to amphibolite and locally partially melted to pegmatitic trondhjemite. Segregations of plagioclase-quartz+/-biotite rock, leucosomes in amphibolite matrix, range from stringers 5-10mm thick to blunt pods as thick as 6m. They tend to be parallel to foliation of the amphibolite, but crosscutting is common. The assemblage aluminous hornblende-plagioclase-epidote-sphene-quartz gave a hydrous melt that crystallized to plagioclase-quartz+/-biotite pegmatitic trondhjemite. 5-10% of the rock melted. Eu at 2x chondrites is positively anomalous. REE partitioning in melt/residum was controlled largely by hornblende and sphene. Though the mineralogical variability precludes quantitative modeling, partial melting of garnet-free amphibolite to heavy-REE-depleted trondhjemitic melt is a viable process.

  1. Melting Temperature and Partial Melt Chemistry of H2O-Saturated Mantle Peridotite to 11 Gigapascals

    PubMed

    Kawamoto; Holloway

    1997-04-11

    The H2O-saturated solidus of a model mantle composition (Kilborne Hole peridotite nodule, KLB-1) was determined to be just above 1000°C from 5 to 11 gigapascals. Given reasonable H2O abundances in Earth's mantle, an H2O-rich fluid could exist only in a region defined by the wet solidus and thermal stability limits of hydrous minerals, at depths between 90 and 330 kilometers. The experimental partial melts monotonously became more mafic with increasing pressure from andesitic composition at 1 gigapascal to more mafic than the starting peridotite at 10 gigapascals. Because the chemistry of the experimental partial melts is similar to that of kimberlites, it is suggested that kimberlites may be derived by low-temperature melting of an H2O-rich mantle at depths of 150 to 300 kilometers.

  2. Production of ferroan andesites by the experimental partial melting of an LL chondrite

    NASA Technical Reports Server (NTRS)

    Mcguire, J. C.; Jurewicz, A. J. G.; Jones, J. H.

    1994-01-01

    A partial melting experiment on the St. Severin (LL) chondrite produced a melt that was andesitic, having 54-60 wt% silica, at 1200 C and an oxygen fugacity of IW+2, two log units above the iron-wustite (IW) buffer. Under these same conditions, CV, CM, and L chondrites produced low-silica melts resembling angrites. This experimental study attempts to reproduce and explain this unusual result.

  3. Anomalous Enstatite Meteorites Queen Alexandra Range 94204 and Pairs: The Perplexing Question of Impact Melts or Partial Melt Residues, Either way, Unrelated to Yamato 793225

    NASA Astrophysics Data System (ADS)

    van Niekerk, D.; Keil, K.

    2012-03-01

    QUE 94204 and its seven pairs are anomalous enstatite meteorites that may either be impact melt products, or partial melt residues. We explore the petrology of these meteorites and present new findings.

  4. Redistribution of Core-forming Melt During Shear Deformation of Partially Molten Peridotite

    NASA Technical Reports Server (NTRS)

    Hustoft, J. W.; Kohlstedt, D. L.

    2002-01-01

    To investigate the role of deformation on the distribution of core-forming melt in a partially molten peridotite, samples of olivine-basalt-iron sulfide were sheared to large strains. Dramatic redistribution of sulfide and silicate melts occur during deformation. Additional information is contained in the original extended abstract.

  5. Martian crustal dichotomy and Tharsis formation by partial melting coupled to early plume migration

    NASA Astrophysics Data System (ADS)

    Šrámek, Ondřej; Zhong, Shijie

    2012-01-01

    A recently proposed model links the formation and early evolution of the Tharsis volcanic province on Mars to the preexisting hemispheric dichotomy (Zhong, 2009). A key aspect of this model is the assumption of a deep lithospheric root below the thicker crust of the southern highlands. We implemented a parameterization of partial melting into the 3-D spherical shell mantle convection code CitcomS in order to investigate whether the required lithospheric thickness variation can be generated self-consistently by partial melting when stiffening of the melt residue due to devolatilization is considered. The rate of melt production strongly depends on the mantle temperature, and additional strong coupling between the flow and partial melting is introduced through the stiffening effect on the melt residue. We find that it is possible to generate a lithospheric keel by partial melting above a single upwelling that excites a relative rotation between the one-plate lithosphere and the mantle below while producing the amount of melt distributed in a broad region constrained to one hemisphere that is necessary to form the crustal dichotomy. This scenario thus offers an internal mechanism for the Martian dichotomy formation and validates the hypothesis of Zhong (2009).

  6. A Two-Porosity Double-Lithology Model for Partial Melting, Melt Transport and Melt-Rock Reaction in the Mantle

    NASA Astrophysics Data System (ADS)

    Liang, Y.; Parmentier, M. E.

    2005-12-01

    general, the smaller these relative rates or ratios, the slower the rate at which the melt in the channel re-equilibrates with the matrix. For a given element of interest three important length scales are identified: matrix melting length (L_m); melt-rock reaction length (LMR); and a critical length for channel-matrix partitioning (L_c). The geochemical signature of the melt developed in the deep part of the melting region can be preserved via channelized flow when LMR > L_m, a condition that can be easily met for incompatible trace elements in the mantle when Xc > 10 m. For narrow channels (Xc < 1 m) significant reduction in matrix melt fraction (< 0.2%) and/or percolation of melt from the channel into the matrix continuum are needed to preserve the identity of the channelized melt. Given the chemical exchanges between the matrix and the channel continuum, the rate of matrix melting may be balanced by (or locked into) the rates of melt-rock reaction at some point in a 1-D mantle column. This dynamical rather than chemical equilibrium between the melt in the channel and that in the matrix is established when L_c > 5L_m for an incompatible element. In the limit of slow melt-rock reaction, incompatible trace elements are preferentially partitioned into the channel melt in a dynamically equilibrated double-lithology mantle. Implications of channel-matrix partitioning for partial melting, melt migration, and melt-rock reaction in a heterogeneous mantle will be discussed.

  7. Multi-stage barites in partially melted UHP eclogite: implications for fluid/melt activities during deep continental subduction in the Sulu orogenic belt

    NASA Astrophysics Data System (ADS)

    Wang, Songjie; Wang, Lu

    2015-04-01

    . Zr-in-rutile thermometry shows their formation temperature to be 586-664 oC at 1.5-2.5 GPa. Barite-bearing MS inclusions with Ba-bearing K-feldspar (type-II) connected by Kfs+Pl+Bt veinlets of in-situ phengite breakdown and thin barite veinlets along grain boundaries (type-III) are products of phengite breakdown and induced fluid flow during exhumation. These barites have witnessed the gradational separation process of melt/ fluid from miscibility on/above the second critical endpoint during UHP metamorphism, to immiscibility along the exhumation path of the subducted slab. Associated reactions from pyrite to hematite and goethite with the type-III barite ring surrounding the pyrite provide evidence for a local high oxygen fugacity environment during eclogite partial melting and subsequent melt/fluid crystallization processes. Moreover, large grain barite aggregations (type-IV) modified by amphibole+albite symplectite are most likely formed by release of molecular and hydroxyl water from anhydrous minerals of eclogite during high-grade amphibolite-facies retrogression. The growth of multi-stage barites in UHP eclogite further advances our understanding of fluid/melt transfer, crystallization processes along the subduction-exhumation path of the partially melted eclogite, broadening our knowledge of melt/fluid evolution within subduction-collision zones worldwide. REFERENCES Chen Y.X., et al., 2014, Lithos, 200, 1-21. Liu J.B., et al., 2000, Acta Petrologica Sinica 16(4), 482-484. Zeng L.S., et al., 2007, Chinese Science Bulletin, 52(21), 2995-3001. Gao X.Y., et al., 2012, Journal of Metamorphic Geology, 30(2), 193-212.

  8. Bulk YBa2Cu3O(x) superconductors through pressurized partial melt growth processing

    NASA Technical Reports Server (NTRS)

    Hu, S.; Hojaji, H.; Barkatt, A.; Boroomand, M.; Hung, M.; Buechele, A. C.; Thorpe, A. N.; Davis, D. D.; Alterescu, S.

    1992-01-01

    A novel pressurized partial melt growth process has been developed for producing large pieces of bulk Y-Ba-Cu-O superconductors. During long-time partial melt growth stage, an additional driving force for solidification is obtained by using pressurized oxygen gas. The microstructure and superconducting properties of the resulting samples were investigated. It was found that this new technique can eliminate porosity and inhomogeneity, promote large-scale grain-texturing, and improve interdomain coupling as well.

  9. Partial melting of apatite-bearing charnockite, granulite, and diorite: Melt compositions, restite mineralogy, and petrologic implications

    NASA Technical Reports Server (NTRS)

    Beard, James S.; Lofgren, Gary E.; Sinha, A. Krishna; Tollo, Richard P.

    1994-01-01

    Melting experiments (P = 6.9 kbar, T = 850-950 deg C, NNO is less than fO2 is less than HM) were done on mafic to felsic charnockites, a dioritic gneiss, and a felsic garnet granulite, all common rock types in the Grenville basement of eastern North America. A graphite-bearing granulite gneiss did not melt. Water (H2O(+) = 0.60 to 2.0 wt %) is bound in low-grade, retrograde metamorphic minerals and is consumed during the earliest stages of melting. Most melts are water-undersaturated. Melt compositions range from metaluminous, silicic granodiorite (diorite starting composition) to peraluminous or weakly metaluminous granites (all others). In general, liquids become more feldspathic, less silicic, and less peraluminous and are enriched in FeO, MgO, and TiO2 with increasing temperature. Residual feldspar mineralogy controls the CaO, K2O, and Na2O contents of the partial melts and the behavior of these elements can be used, particularly if the degree of source melting can be ascertained, to infer some aspects of the feldspar mineralogy of the source. K-feldspar, a common restite phase in the charnockite and granulite (but not the diorite) should control the behavior of Ba and, possibly, Eu in these systems and yield signatures of these elements that can distinguish source regions and, in some cases, bulk versus melt assimilation. Apatite, a common restite phase, is enriched in rare earth elements (REE), especially middle REE. Retention of apatite in the restite will result in steep, light REE-enriched patterns for melts derived from the diorite and charnockites.

  10. Dihedral angle of carbonatite melts in mantle residue near the upper mantle and transition zone

    NASA Astrophysics Data System (ADS)

    Ghosh, S. K.; Rohrbach, A.; Schmidt, M. W.

    2015-12-01

    Carbonate melts are thought to be ideal metasomatic agents in the deep upper mantle (Green & Wallace, 1988) and these melts are low in viscosities (10-1-10-3 Pa·s) compared to primitive basalt (101-102 Pa·s), furthermore the ability to form an interconnected grain-edge melt network at low melt fractions (< 1%) make carbonate melts extremely mobile. They are molten at relatively low temperatures and have solidus temperatures hundreds of degrees lower than silicate melts at >3 GPa (Dasgupta et al. 2006, Ghosh et al., 2009), dissolve a number of geochemically incompatible elements much better than silicate melts (Blundy and Dalton, 2000). Previous studies of carbonate melt dihedral angles in olivine-dominated matrices yielded 25-30oat 1-3 GPa, relatively independent of melt composition (Watson et al., 1990) and temperature (Hunter and McKenzie, 1989). Dihedral angles of carbonate melts in contact with deep mantle silicate phases (e.g. garnet, wadsleyite, and ringwoodite) which constitute more than 70 % of the deep upper mantle and transition zone have not been studied yet. We have performed multi-anvil experiments on carbonate-bearing peridotites with 5.0 wt% CO2 from 13.5 to 20 GPa 1550 oC to investigate the dihedral angle of magnesio-carbonatite melts in equilibrium with garnet, olivine (and its high-pressure polymorphs), and clinoenstatite. The dihedral angle of carbonate melts in the deep upper mantle and transition zone is ~30° for majorite garnet and olivine (and its polymorphs) dominated matrices. It does not change with increasing pressure in the range 13.5-20 GPa. Our results suggest that very low melt fractions of carbonatite melt forming in the deep upper mantle and transition zone are interconnected at melt fractions less than 0.01. Consistent with geophysical observations, this could possibly explain low velocity regions in the deep mantle and transition zone.

  11. Partially Melted UHP Eclogite in the Sulu Orogenic Belt, China and its rheological significance to deep continental subduction: Micro- to Macro-scale Evidence

    NASA Astrophysics Data System (ADS)

    Wang, Lu; Kusky, Timothy; Polat, Ali; Wang, Songjie; Jiang, Xingfu; Zong, Keqing; Wang, Junpeng; Deng, Hao; Fu, Jianmin

    2015-04-01

    . Whole-rock trace element analyses show that the leucocratic rocks, residue and peak metamorphic stage eclogite (no decompression partial melting) show well matched mass balance relationships. Melts derived from eclogite partial melting lubricated the subducted eclogite slices and facilitated their buoyant rise from mantle depths to crustal levels. Partial melting of deeply subducted eclogite is an important process in determining the rheological structure and mechanical behavior of subducted lithosphere and its rapid exhumation, controlling flow of deep lithospheric material, and for generation of melts from the upper mantle, potentially contributing to arc magmatism and growth of continental crust. Deeply subducted, partially melted eclogite from General's Hill show that eclogites can develop regularly spaced melt channels, a meter or two thick, that would act as significant seismic anomalies5. This may provide direct evidence for the nature of enigmatic 'bright zones' presented in some deep-crustal seismic reflection profiles which have been interpreted to represent areas of melt, high fluid content or unusual rock compositions6. Hermann, J. & Green, D. H. (2001). Earth Planet. Sci. Lett. 188, 149-168. Song, S.G., et al. (2014). Geochim. Cosmochim. Acta 130 42-62. Zhang, G.B., et al. (2014). Lithos, doi: 10.1016/j.lithos.2014.12.009 Gao, X. Y., et al. (2012). J. Metamorph. Geol. 30, 193-212. Wang, L., et al. (2014). Nature Communications. 5:5604 doi: 10.1038/ncomms6604. Brown, L. et al. (1996). Science 274, 1688-1690.

  12. Seismic evidence for partial melting at the root of major hot spot plumes.

    PubMed

    Yuan, Kaiqing; Romanowicz, Barbara

    2017-07-28

    Ultralow-velocity zones are localized regions of extreme material properties detected seismologically at the base of Earth's mantle. Their nature and role in mantle dynamics are poorly understood. We used shear waves diffracted at the core-mantle boundary to illuminate the root of the Iceland plume from different directions. Through waveform modeling, we detected a large ultralow-velocity zone and constrained its shape to be axisymmetric to a very good first order. We thus attribute it to partial melting of a locally thickened, denser- and hotter-than-average layer, reflecting dynamics and elevated temperatures within the plume root. Such structures are few and far apart, and they may be characteristic of the roots of some of the broad mantle plumes tomographically imaged within the large low-shear-velocity provinces in the lower mantle. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

  13. Petrofabric development during experimental partial melting and recrystallization of a mica-schist analog

    NASA Astrophysics Data System (ADS)

    Almqvist, Bjarne S. G.; Biedermann, Andrea R.; Klonowska, Iwona; Misra, Santanu

    2015-10-01

    Magnetic properties and the anisotropy of magnetic susceptibility (AMS) present promising methods to track mineral orientation and petrofabric in rocks that have undergone partial melting. In order to better understand the source of the magnetic signal in these types of rocks, the interpretation of field observations may be integrated with laboratory experiments, designed to recreate conditions of partial melting. A set of experiments is presented in this study, where synthetic foliated quartz-muscovite aggregates undergo partial melting at 300 MPa hydrostatic confining pressure and 750°C. Magnetic properties and AMS are measured before and after partial melting. Prior to partial melting, the synthetic aggregate shows a compaction-related oblate magnetic fabric, dominated by paramagnetic muscovite that contains small amounts of iron. Post experiment samples show neoblasts that crystallize from incongruent melt reactions. Most notably for the magnetic fabric, the breakdown of muscovite results in growth of secondary phases of Fe-bearing spinel and biotite. Isothermal remanence acquisition and temperature dependence of susceptibility indicate that the spinel is magnetite. The degree of magnetic anisotropy reduces significantly after partial melting, but notably the orientation of the principal axes of susceptibility mimics the AMS of the original quartz-muscovite aggregate. Additionally, the post experiment samples show a relationship between the amount of sample shortening (compaction) and the degree of magnetic anisotropy and susceptibility ellipsoid shape factor. These results suggest that petrofabrics in rocks that undergo partial melting at near hydrostatic pressure conditions may in part be inherited, or mimic, the original petrofabric of a sedimentary or metasedimentary rock.

  14. Shear-zone systems and melts: feedback relations and self-organization in orogenic belts

    NASA Astrophysics Data System (ADS)

    Brown, Michael; Solar, Gary S.

    1998-03-01

    In orogenic belts, the common spatial and temporal association of granites with crustal-scale shear-zone systems suggests melt transfer from source to upper crust was the result of a feedback relation. In this relation, the presence of melt in the crust profoundly affects the rheology, and induces localization of strain within shear-zone systems. Consequently, melt is moved out of the source preferentially along high-strain zones, which helps the system to accommodate strain. Because actively deforming orogenic belts are non-equilibrium systems, they may generate dissipative structure by self-organization; we interpret crustal-scale shear-zone systems and their associated granites as the manifestation of this self-organization. The architecture and permeability structure are controlled by the type of shear-zone system (transcurrent, normal, reverse or oblique); this is the primary control on melt transfer in orogenic belts. During active deformation, movement of melt is by percolative flow and melt essentially is pumped through the system parallel to the maximum principal finite elongation direction. If a build-up of melt pressure occurs, melt-enhanced embrittlement enables tensile and dilatant shear fracturing, and transfer of melt is by channelized flow. We illustrate feedback relations between migmatites, crustal-scale shear-zone systems and granites using examples from the Cadomian belt of western France and the northern Appalachian orogen of the eastern U.S.A. In orogenic belts dominated by transcurrent shear, where the maximum principal finite elongation direction may have a shallow to subhorizontal plunge, granite arrested during ascent through the system commonly develops C- S fabrics. This suggests percolative flow is not effective in expelling melt from these systems; the resulting build-up of melt pressure enables fracturing and channelized transfer of melt, which crystallizes during persistent deformation (e.g. the St. Malo migmatite belt, Cadomian belt

  15. Morphology of melt-rich channels formed during reaction infiltration experiments on partially molten mantle rocks

    NASA Astrophysics Data System (ADS)

    Pec, Matej; Holtzman, Benjamin; Zimmerman, Mark; Kohlstedt, David

    2016-04-01

    Geochemical, geophysical and geological observations suggest that melt extraction from the partially molten mantle occurs by some sort of channelized flow. Melt-solid reactions can lead to melt channelization due to a positive feedback between melt flow and reaction. If a melt-solid reaction increases local permeability, subsequent flow is increased as well and promotes further reaction. This process can lead to the development of high-permeability channels which emerge from background flow. In nature, anastomozing tabular dunite bodies within peridotitic massifs are thought to represent fossilized channels that formed by reactive flow. The conditions under which such channels can emerge are treated by the reaction infiltration instability (RII) theory (e.g. Szymczak and Ladd 2014). In this contribution, we report the results of a series of Darcy type experiments designed to study the development of channels due to RII in mantle lithologies (Pec et al. 2015). We sandwiched a partially molten rock between a melt source and a porous sink and annealed it at high-pressures (P = 300 MPa) and high-temperatures (T = 1200° or 1250° C) under a controlled pressure gradient (∇P = 0-100 MPa/mm) for up to 5 hours. The partially molten rock is formed by 50:50 mixtures of San Carlos olivine (Ol, Fo ˜ 88) and clinopyroxene (Cpx) with either 4, 10 or 20 vol% of alkali basalt added. The source and sink are disks of alkali basalt and porous alumina, respectively. During the experiments, silica undersaturated melt from the melt source dissolves Cpx and precipitates an iron rich Ol (Fo ˜ 82) thereby forming a Cpx-free reaction layer at the melt source - partially molten rock interface. The melt fraction in the reaction layer increases significantly (40% melt) compared to the protolith, confirming that the reaction increases the permeability of the partially molten rock. In experiments annealed under a low pressure gradient (and hence slow melt flow velocity) the reaction layer is

  16. Grain-scale alignment of melt in sheared partially molten rocks: implications for viscous anisotropy

    NASA Astrophysics Data System (ADS)

    Pec, Matej; Quintanilla-Terminel, Alejandra; Holtzman, Benjamin; Zimmerman, Mark; Kohlstedt, David

    2016-04-01

    Presence of melt significantly influences rheological properties of partially molten rocks by providing fast diffusional pathways. Under stress, melt aligns at the grain scale and this alignment induces viscous anisotropy in the deforming aggregate. One of the consequences of viscous anisotropy is melt segregation into melt-rich sheets oriented at low angle to the shear plane on much larger scales than the grain scale. The magnitude and orientation of viscous anisotropy with respect to the applied stress are important parameters for constitutive models (Takei and Holtzman 2009) that must be constrained by experimental studies. In this contribution, we analyze the shape preferred orientation (SPO) of individual grain-scale melt pockets in deformed partially molten mantle rocks. The starting materials were obtained by isostatically hot-pressing olivine + basalt and olivine + chromite + basalt powders. These partially molten rocks were deformed in general shear or torsion at a confining pressure, Pc = 300 MPa, temperature, T = 1200° - 1250° C, and strain rates of 10-3 - 10-5 s-1to finite shear strains, γ, of 0.5 - 5. After the experiment, high resolution backscattered electron images were obtained using a SEM equipped with a field emission gun. Individual melt pockets were segmented and their SPO analyzed using the paror and surfor methods and Fourier transforms (Heilbronner and Barret 2014). Melt segregation into melt-rich sheets inclined at 15° -20° antithetic with respect to the shear plane occurs in three-phase system (olivine + chromite + basalt) and in two-phase systems (olivine + basalt) twisted to high strain. The SPO of individual melt pockets within the melt-rich bands is moderately strong (b/a ≈ 0.8) and is always steeper (20° -40°) than the average melt-rich band orientation. In the two-phase system (olivine + basalt) sheared to lower strains, no distinct melt-rich sheets are observed. Individual grain-scale melt pockets are oriented at 45° -55

  17. Earth's Deep Carbon Cycle Constrained by Partial Melting of Mantle Peridotite and Eclogite

    NASA Astrophysics Data System (ADS)

    Dasgupta, R.; Hirschmann, M. M.; Withers, A. C.

    2006-05-01

    The mass of carbon in the mantle is thought to exceed that in all Earth's other reservoirs combined1 and large fluxes of carbon are cycled into and out of the mantle via subduction and volcanic emission. Devolatilization is known to release water in the mantle wedge, but release of carbon could be delayed if the relevant decarbonation reactions or solidi of oceanic crust are not encountered along P-T path of subduction. Outgassing of CO2 from the mantle also has a critical influence on Earth's climate for time scales of 108-109 yr1. The residence time for carbon in the mantle is thought to exceed the age of the Earth1,2, but it could be significantly shorter owing to pervasive deep melting beneath oceanic ridges. The dominant influx of carbon is via carbonate in altered ocean-floor basalts, which survives decarbonation during subduction. Our experiments demonstrate that solidi of carbonated eclogite remain hotter than average subduction geotherms at least as deep as transition zone3, and thus significant subducted C is delivered to the deep Earth, rather than liberated in the shallow mantle by melting. Flux of CO2 into the mantle, assuming average estimate of carbon in altered ocean crust of 0.21 wt. % CO24, can amount to 0.15 × 1015 g/yr. In upwelling mantle, however, partial melting of carbonated eclogite releases calcio-dolomitic carbonatite melt at depths near ~400 km and metasomatically implants carbonate to surrounding peridotite. Thus, volcanic release of CO2 to basalt source regions is likely controlled by the solidus of carbonated peridotite. Our recent experiments with nominally anhydrous, carbonate-bearing garnet lherzolite indicate that the solidus of peridotite with a trace amount of CO2 is ~500 °C lower than that of volatile-free peridotite at 10 GPa5. In upwelling mantle the solidus of carbonated lherzolite is ~100-200 km shallower than that of eclogite+CO2, but beneath oceanic ridges, initial melting occurs as deep as 300-330 km. For peridotite

  18. Global Cycling of Carbon Constrained by Partial Melting Experiments of Carbonated Mantle Peridotite and Eclogite

    NASA Astrophysics Data System (ADS)

    Dasgupta, R.; Hirschmann, M. M.; Withers, A. C.

    2005-12-01

    The mass of carbon stored in the mantle exceeds that in all other Earth's reservoirs combined1 and large fluxes of carbon are cycled into and out of the mantle via subduction and volcanic emission. Outgassing of CO2 from the mantle has a critical influence on Earth's climate for time scales of 108-109 yr1. The residence time for carbon in the mantle is thought to exceed the age of the Earth1,2, but it could be significantly less owing to pervasive deep melting beneath oceanic ridges. The chief flux of subducted carbon is via carbonate in altered ocean-floor basalts, which survives dehydration during subduction. Because solidi of carbonated eclogite remain hotter than average subduction geotherms at least up to transition zone3, significant subducted C is delivered to the deep Earth. In upwelling mantle, however, partial melting of carbonated eclogite releases calcio-dolomitic carbonatite melt at depths near ~400 km and metasomatically implants carbonate to surrounding peridotite. Thus, volcanic release of CO2 to basalt source regions is controlled by the solidus of carbonated peridotite. We conducted experiments with nominally anhydrous, carbonated garnet lherzolite (PERC: MixKLB-1+2.5 wt.% CO2) using Pt/C capsules in piston cylinder (3 GPa) and Walker-style multi-anvil presses (4 to 10 GPa) and between 1075-1500 °C. The stable near-solidus crystalline carbonate is dolomitess at 3 GPa and magnesitess from 4 to 10 GPa. Carbonate melt is stabilized at the solidus and crystalline carbonate disappears within 20-60°. The solidus increases from ≥1075 °C at 3 GPa to 1110-1140 °C at 4.1 GPa as the stable carbonate transforms from dolomitess to magnesitess. From 4.1 GPa, the solidus of PERC magnesite lherzolite increases to ~1500 °C at 10 GPa. In upwelling mantle the solidus of carbonated lherzolite is ~100-200 km shallower than that of eclogite+CO2, but beneath oceanic ridges, initial melting occurs as deep as 300-330 km. For peridotite with ~120-1200 ppm CO2, this

  19. Dynamics of the Axial Melt Lens/Dike transition at fast spreading ridges: assimilation and hydrous partial melting

    NASA Astrophysics Data System (ADS)

    France, L.; Ildefonse, B.; Koepke, J.

    2009-04-01

    Recent detailed field studies performed in the Oman ophiolite on the gabbro/sheeted dike transition, compared to corresponding rocks from the EPR drilled by IODP (Site 1256), constrain a general model for the dynamics of the axial melt lens (AML) present at fast spreading ridges (France et al., 2008). This model implies that the AML/dike transition is a dynamic interface migrating up- and downward, and that the isotropic gabbro horizon on top of the igneous section represents its fossilization. It is also proposed that upward migrations are associated to reheating of the base of the sheeted dike complex and to assimilation processes. Plagiogranitic lithologies are observed close to the truncated base of the dikes and are interpreted to represent frozen melts generated by partial melting of previously hydrothermalized sheeted dikes. Relicts of previously hydrothermalized lithologies are also observed in the fossil melt lens, and are associated to lithologies that have crystallized under high water activities, with clinopyroxene crystallizing before plagioclase, and An-rich plagioclase. To better understand our field data, we performed hydrous partial melting experiments at shallow pressures (0.1 GPa) under slightly oxidizing conditions (NNO oxygen buffer) and water saturated conditions on hydrothermalized sheeted dike sample from the Oman ophiolite. These experiments have been performed between 850°C and 1030°C; two additional experiments in the subsolidus regime were also conducted (750°C and 800°C). Clinopyroxenes formed during incongruent melting at low temperature (<910°C) have compositions that match those from the corresponding natural rocks (reheated base of the sheeted dike and relicts of assimilated lithologies). In particular, the characteristic low TiO2 and Al2O3 contents are reproduced. The experimental melts produced at low temperatures correspond to compositions of typical natural plagiogranites. In natural settings, these silicic liquids would be

  20. Behaviour of apatite during partial melting of metapelites and consequences for prograde suprasolidus monazite growth

    NASA Astrophysics Data System (ADS)

    Yakymchuk, Chris

    2017-03-01

    The suprasolidus behaviour of apatite and monazite is examined for an average metapelite composition using phase equilibria modelling coupled with solubility equations of these minerals. Both closed- and open-system scenarios are considered. Partial melting above the solidus requires apatite and monazite breakdown in order to saturate the anatectic melt in phosphorus and the light rare earth elements. In general, melt loss is predicted to increase the stability of apatite and monazite at high temperature. Most apatite is predicted to survive up to ultrahigh temperature conditions except for rocks with low bulk phosphorus concentrations. By contrast, most monazite is expected to be consumed by UHT conditions. Thorium substitution in monazite is expected to increase the stability of monazite to higher temperatures. The presence of LREE-rich apatite decreases the stability of monazite above the solidus, but the breakdown of this apatite during anatexis may generate prograde monazite at the apatite-melt interface in local pockets of melt oversaturation. However, prograde suprasolidus monazite along grain boundaries is expected to be consumed during further partial melting or during melt homogenization when an interconnected melt network develops. Anatectic melts are predicted to be saturated with respect to apatite except at UHT conditions and for rocks with low initial P2O5 bulk concentrations.

  1. The Behavior of Fe3+/∑Fe During Partial Melting of Spinel Lherzolite

    NASA Astrophysics Data System (ADS)

    Gaetani, G. A.

    2014-12-01

    The use of wet chemistry and X-ray absorption near edge structure (XANES) spectroscopy to determine the oxidation state of Fe in submarine glasses and olivine-hosted melt inclusions has provided important new insights into the global systematics of Fe3+/∑Fe in mid-ocean ridge basalts (MORB) [1, 2]. Because MORB are aggregates of near-fractional partial melts formed by decompression melting of variably depleted peridotite, it is difficult to judge the extent to which they directly reflect the oxidation state of the oceanic upper mantle. To provide a theoretical framework within which to interpret Fe3+/∑Fe in MORB, I have developed a model that describes the behavior of Fe3+/∑Fe during spinel lherzolite partial melting in a system closed to oxygen. Modeling is carried out by calculating the Fe3+/∑Fe of olivine using the point defect model of [3], and determining Fe3+/∑Fe of the bulk peridotite from mineral-mineral partitioning. The inter-mineral Fe3+/Fe2+ exchange coefficients are derived from Mössbauer data on natural spinel peridotites, and are parameterized in terms of oxygen fugacity, temperature, and the Fe content of the olivine. The Fe3+/∑Fe of the melt is determined by combining mass-balance with an equation relating the Fe3+/∑Fe of the melt to the fugacity of oxygen [4]. Spinel lherzolite partial melting is modeled after [5]. Modeling results indicate that oxygen fugacity does not follow the fayalite-magnetite-quartz (FMQ) buffer during partial melting. For isobaric partial melting, the system becomes reduced relative to FMQ with increasing extent of melting. This results from an increase in the FMQ buffer with increasing temperature, whereas oxygen fugacity in the peridotite remains nearly constant. Conversely, during polybaric partial melting the oxidation state of the residual peridotite increases relative to FMQ. The effective partition coefficient for Fe3+is larger than previously thought, so that a redox couple with S is not required to

  2. Separation of supercritical slab-fluids to form aqueous fluid and melt components in subduction zone magmatism.

    PubMed

    Kawamoto, Tatsuhiko; Kanzaki, Masami; Mibe, Kenji; Matsukage, Kyoko N; Ono, Shigeaki

    2012-11-13

    Subduction-zone magmatism is triggered by the addition of H(2)O-rich slab-derived components: aqueous fluid, hydrous partial melts, or supercritical fluids from the subducting slab. Geochemical analyses of island arc basalts suggest two slab-derived signatures of a melt and a fluid. These two liquids unite to a supercritical fluid under pressure and temperature conditions beyond a critical endpoint. We ascertain critical endpoints between aqueous fluids and sediment or high-Mg andesite (HMA) melts located, respectively, at 83-km and 92-km depths by using an in situ observation technique. These depths are within the mantle wedge underlying volcanic fronts, which are formed 90 to 200 km above subducting slabs. These data suggest that sediment-derived supercritical fluids, which are fed to the mantle wedge from the subducting slab, react with mantle peridotite to form HMA supercritical fluids. Such HMA supercritical fluids separate into aqueous fluids and HMA melts at 92 km depth during ascent. The aqueous fluids are fluxed into the asthenospheric mantle to form arc basalts, which are locally associated with HMAs in hot subduction zones. The separated HMA melts retain their composition in limited equilibrium with the surrounding mantle. Alternatively, they equilibrate with the surrounding mantle and change the major element chemistry to basaltic composition. However, trace element signatures of sediment-derived supercritical fluids remain more in the melt-derived magma than in the fluid-induced magma, which inherits only fluid-mobile elements from the sediment-derived supercritical fluids. Separation of slab-derived supercritical fluids into melts and aqueous fluids can elucidate the two slab-derived components observed in subduction zone magma chemistry.

  3. Separation of supercritical slab-fluids to form aqueous fluid and melt components in subduction zone magmatism

    PubMed Central

    Kawamoto, Tatsuhiko; Kanzaki, Masami; Mibe, Kenji; Ono, Shigeaki

    2012-01-01

    Subduction-zone magmatism is triggered by the addition of H2O-rich slab-derived components: aqueous fluid, hydrous partial melts, or supercritical fluids from the subducting slab. Geochemical analyses of island arc basalts suggest two slab-derived signatures of a melt and a fluid. These two liquids unite to a supercritical fluid under pressure and temperature conditions beyond a critical endpoint. We ascertain critical endpoints between aqueous fluids and sediment or high-Mg andesite (HMA) melts located, respectively, at 83-km and 92-km depths by using an in situ observation technique. These depths are within the mantle wedge underlying volcanic fronts, which are formed 90 to 200 km above subducting slabs. These data suggest that sediment-derived supercritical fluids, which are fed to the mantle wedge from the subducting slab, react with mantle peridotite to form HMA supercritical fluids. Such HMA supercritical fluids separate into aqueous fluids and HMA melts at 92 km depth during ascent. The aqueous fluids are fluxed into the asthenospheric mantle to form arc basalts, which are locally associated with HMAs in hot subduction zones. The separated HMA melts retain their composition in limited equilibrium with the surrounding mantle. Alternatively, they equilibrate with the surrounding mantle and change the major element chemistry to basaltic composition. However, trace element signatures of sediment-derived supercritical fluids remain more in the melt-derived magma than in the fluid-induced magma, which inherits only fluid-mobile elements from the sediment-derived supercritical fluids. Separation of slab-derived supercritical fluids into melts and aqueous fluids can elucidate the two slab-derived components observed in subduction zone magma chemistry. PMID:23112158

  4. Phase behavior and reactive transport of partial melt in heterogeneous mantle model

    NASA Astrophysics Data System (ADS)

    Jordan, J.; Hesse, M. A.

    2013-12-01

    The reactive transport of partial melt is the key process that leads to the chemical and physical differentiation of terrestrial planets and smaller celestial bodies. The essential role of the lithological heterogeneities during partial melting of the mantle is increasingly recognized. How far can enriched melts propagate while interacting with the ambient mantle? Can the melt flow emanating from a fertile heterogeneity be localized through a reactive infiltration feedback in a model without exogenous factors or contrived initial conditions? A full understanding of the role of heterogeneities requires reactive melt transport models that account for the phase behavior of major elements. Previous work on reactive transport in the mantle focuses on trace element partitioning; we present the first nonlinear chromatographic analysis of reactive melt transport in systems with binary solid solution. Our analysis shows that reactive melt transport in systems with binary solid solution leads to the formation of two separate reaction fronts: a slow melting/freezing front along which enthalpy change is dominant and a fast dissolution/precipitation front along which compositional changes are dominated by an ion-exchange process over enthalpy change. An intermediate state forms between these two fronts with a bulk-rock composition and enthalpy that are not necessarily bounded by the bulk-rock composition and enthalpy of either the enriched heterogeneity or the depleted ambient mantle. The formation of this intermediate state makes it difficult to anticipate the porosity changes and hence the stability of reaction fronts. Therefore, we develop a graphical representation for the solution that allows identification of the intermediate state by inspection, for all possible bulk-rock compositions and enthalpies of the heterogeneity and the ambient mantle. We apply the analysis to the partial melting of an enriched heterogeneity. This leads to the formation of moving precipitation

  5. Partial melting of deeply subducted eclogite from the Sulu orogen in China

    PubMed Central

    Wang, Lu; Kusky, Timothy M.; Polat, Ali; Wang, Songjie; Jiang, Xingfu; Zong, Keqing; Wang, Junpeng; Deng, Hao; Fu, Jianmin

    2014-01-01

    We report partial melting of an ultrahigh pressure eclogite in the Mesozoic Sulu orogen, China. Eclogitic migmatite shows successive stages of initial intragranular and grain boundary melt droplets, which grow into a three-dimensional interconnected intergranular network, then segregate and accumulate in pressure shadow areas and then merge to form melt channels and dikes that transport magma to higher in the lithosphere. Here we show, using zircon U–Pb dating and petrological analyses, that partial melting occurred at 228–219 Myr ago, shortly after peak metamorphism at 230 Myr ago. The melts and residues are complimentarily enriched and depleted in light rare earth element (LREE) compared with the original rock. Partial melting of deeply subducted eclogite is an important process in determining the rheological structure and mechanical behaviour of subducted lithosphere and its rapid exhumation, controlling the flow of deep lithospheric material, and for generation of melts from the upper mantle, potentially contributing to arc magmatism and growth of continental crust. PMID:25517619

  6. Partial melting of deeply subducted eclogite from the Sulu orogen in China.

    PubMed

    Wang, Lu; Kusky, Timothy M; Polat, Ali; Wang, Songjie; Jiang, Xingfu; Zong, Keqing; Wang, Junpeng; Deng, Hao; Fu, Jianmin

    2014-12-17

    We report partial melting of an ultrahigh pressure eclogite in the Mesozoic Sulu orogen, China. Eclogitic migmatite shows successive stages of initial intragranular and grain boundary melt droplets, which grow into a three-dimensional interconnected intergranular network, then segregate and accumulate in pressure shadow areas and then merge to form melt channels and dikes that transport magma to higher in the lithosphere. Here we show, using zircon U-Pb dating and petrological analyses, that partial melting occurred at 228-219 Myr ago, shortly after peak metamorphism at 230 Myr ago. The melts and residues are complimentarily enriched and depleted in light rare earth element (LREE) compared with the original rock. Partial melting of deeply subducted eclogite is an important process in determining the rheological structure and mechanical behaviour of subducted lithosphere and its rapid exhumation, controlling the flow of deep lithospheric material, and for generation of melts from the upper mantle, potentially contributing to arc magmatism and growth of continental crust.

  7. Contact metamorphism, partial melting and fluid flow in the granitic footwall of the South Kawishiwi Intrusion, Duluth Complex, USA

    NASA Astrophysics Data System (ADS)

    Benko, Z.; Mogessie, A.; Molnar, F.; Severson, M.; Hauck, S.; Lechler, P.; Arehart, G.

    2012-04-01

    The footwall of the South Kawishiwi Intrusion (SKI) a part of the Mesoproterozoic (1.1 Ga) Duluth Complex consists of Archean granite-gneiss, diorite, granodiorite (Giant Range Batholith), thin condensed sequences of Paleoproterozoic shale (Virginia Fm.), as well as banded iron formation (Biwabik Iron Fm). Detailed (re)logging and petrographic analysis of granitic footwall rocks in the NM-57 drillhole from the Dunka Pit area has been performed to understand metamorphic processes, partial melting, deformation and geochemical characteristics of de-volatilization or influx of fluids. In the studied drillhole the footwall consists of foliated metagranite that is intersected by mafic (dioritic) dykes of older age than the SKI. In the proximal contact zones, in the mafic dykes, the orthopyroxene+clinopyroxene+plagioclase+quartz+Fe-Ti-oxide+hornblende±biotite porphyroblasts embedded in a plagioclase+K-feldspar+orthopyroxene+apatite matrix indicate pyroxene-hornfels facies conditions. Migmatitization is revealed by the euhedral crystal faces of plagioclase and pyroxene against anhedral quartz crystals in the in-situ leucosome and by the presence of abundant in-source plagioclase±biotite leucosome veinlets. Amphibole in the melanosome of mafic dykes was formed with breakdown of biotite and implies addition of H2O to the system during partial melting. Towards the deeper zones, the partially melted metatexite-granite can be characterized by K-feldspar+plagioclase+quartz+ortho/clinopyroxene+biotite+Fe-Ti-oxide+apatite mineral assemblage. The felsic veins with either pegmatitic or aplititic textures display sharp contact both to the granite and the mafic veins. They are characterized by K-feldspar+quartz±plagioclase±muscovite mineral assemblage. Sporadic occurrence of muscovite suggest local fluid saturated conditions. Emplacement of gabbroic rocks of the SKI generated intense shear in some zones of the granitic footwall resulting in formation of biotite-rich mylonites with

  8. Petrology and Wavespeeds in Central Tibet Indicate a Partially Melted Mica-Bearing Crust

    NASA Astrophysics Data System (ADS)

    Hacker, B. R.; Ritzwoller, M. H.; Xie, J.

    2013-12-01

    S-wave speeds and Vp/Vs ratios in the middle to deep crust of Tibet are best explained by a partially melted, mica-bearing middle to lower crust with a subhorizontal to gently dipping foliation. Surface-wave tomography [e.g., Yang et al., 2012; Xie et al., 2013] shows that the central Tibetan Plateau (the Qiangtang block) is characterized by i) slow S-wave speeds of 3.3-3.5 km/s at depths from 20-25 km to 45-50 km, ii) S-wave radial anisotropy of at least 4% (Vsh > Vsv) with stronger anisotropy in the west than the east [Duret et al., 2010], and iii) whole-crust Vp/Vs ratios in the range of 1.73-1.78 [Xu et al., 2013]. The depth of the Curie temperature for magnetite inferred from satellite magnetic measurements [Alsdorf and Nelson, 1999], the depth of the α-β quartz transition inferred from Vp/Vs ratios [Mechie et al., 2004], and the equilibration pressures and temperatures of xenoliths erupted from the mid-deep crust [Hacker et al., 2000] indicate that the thermal gradient in Qiangtang is steep, reaching 1000°C at 30-40 km depth. This thermal gradient crosses the dehydration-melting solidi for crustal rocks at 20-30 km depth, implying the presence or former presence of melt in the mid-deep crust. These temperatures do not require the wholesale breakdown of mica at these depths, because F and Ti can stabilize mica to at least 1300°C [Dooley and Patino Douce, 1996]. Petrology suggests, then, that the Qiangtang middle to deep crust consists of a mica-bearing residue from which melt has been extracted or is being extracted. Wavespeeds calculated for mica-bearing rocks with a subhorizontal to gently dipping foliation and minor silicate melt are the best match to the wavespeeds and anisotropy observed by seismology. Alsdorf, D., and D. Nelson, The Tibetan satellite magnetic low: Evidence for widespread melt in the Tibetan crust?, Geology, 27, 943-946, 1999. Dooley, D.F., and A.F. Patino Douce, Fluid-absent melting of F-rich phlogopite + rutile +quartz, American

  9. Evidence for melt partitioning between olivine and orthopyroxene in partially molten harzburgite

    NASA Astrophysics Data System (ADS)

    Miller, K.; Zhu, W.; Montesi, L. G.; Le Roux, V.; Gaetani, G. A.

    2013-12-01

    During melting at mid-ocean ridges, melt is driven into an equilibrium, minimum-energy configuration by surface energy gradients between solid-solid and solid-liquid phase boundaries. Such a configuration, where melt is mostly restricted to three and four-grain junctions, acts as a porous medium through which melt can percolate to the surface. For a monomineralic system, melt is distributed evenly among all grains. However, in mineralogical heterogeneous systems, melt partitions unevenly between the various solid phases to minimize the total energy of the system. In a ocean ridge melting environment, where olivine is often juxtaposed against orthopyroxene (opx), lithologic partitioning is expected to turn olivine-rich regions into high-permeability conduits, through which melt can be quickly extracted, drastically increasing the permeability of the mantle [Zhu and Hirth, 2003]. Lithologic partitioning has been demonstrated in experiments using analogue systems [Watson, 1999]; however, to date, no experiment has confirmed its existence in partially molten mantle systems. We present experimental results that determine the degree of melt partitioning between olivine and opx in partially molten harzburgites. Samples were prepared from a powdered mixture of oxides and carbonates and then hot-pressed in a solid-media piston-cylinder apparatus at 1350°C and 1.5GPa [Zhu et al., 2011] to achieve an 82/18 vol. % ratio of olivine to opx. Prior to hot-pressing, basalt was added to the powdered mixtures in various proportions to test for lithologic partitioning across a range of melt fractions. Three-dimensional, 700nm-resolution images of our samples were obtained using synchrotron X-ray microtomography on the 2BM station of the Advanced Photon Source at Argonne National Labs. Image data were filtered using an anisotropic diffusion filter to enhance phase contrast and then segmented to produce binary representations of each phase. In order to quantitatively demonstrate

  10. Lunar highland meteorite Dhofar 026 and Apollo sample 15418: Two strongly shocked, partially melted, granulitic breccias

    USGS Publications Warehouse

    Cohen, B. A.; James, O.B.; Taylor, L.A.; Nazarov, M.A.; Barsukova, L.D.

    2004-01-01

    Studies of lunar meteorite Dhofar 026, and comparison to Apollo sample 15418, indicate that Dhofar 026 is a strongly shocked granulitic breccia (or a fragmental breccia consisting almost entirely of granulitic breccia clasts) that experienced considerable post-shock heating, probably as a result of diffusion of heat into the rock from an external, hotter source. The shock converted plagioclase to maskelynite, indicating that the shock pressure was between 30 and 45 GPa. The post-shock heating raised the rock's temperature to about 1200 ??C; as a result, the maskelynite devitrified, and extensive partial melting took place. The melting was concentrated in pyroxene-rich areas; all pyroxene melted. As the rock cooled, the partial melts crystallized with fine-grained, subophitic-poikilitic textures. Sample 15418 is a strongly shocked granulitic breccia that had a similar history, but evidence for this history is better preserved than in Dhofar 026. The fact that Dhofar 026 was previously interpreted as an impact melt breccia underscores the importance of detailed petrographic study in interpretation of lunar rocks that have complex textures. The name "impact melt" has, in past studies, been applied only to rocks in which the melt fraction formed by shock-induced total fusion. Recently, however, this name has also been applied to rocks containing melt formed by heating of the rocks by conductive heat transfer, assuming that impact is the ultimate source of the heat. We urge that the name "impact melt" be restricted to rocks in which the bulk of the melt formed by shock-induced fusion to avoid confusion engendered by applying the same name to rocks melted by different processes. ?? Meteoritical Society, 2004.

  11. 2D numerical modelling of fluid and melt percolation in the subduction zone

    NASA Astrophysics Data System (ADS)

    Dymkova, D.; Gerya, T.; Podladchikov, Y.

    2011-12-01

    Subducting slab dehydration and resulting aqueous fluid percolation triggers partial melting in the mantle wedge and is accompanied with the further melt percolation through the porous space to the region above the slab. This problem is a complex coupled chemical, thermal and mechanical process responsible for the magmatic arcs formation and change of the mantle wedge properties. We have created a two-dimensional model of a two-phase flow in a porous media solving a coupled Darcy-Stokes system of equations for two incompressible media for the case of visco-plastic rheology of solid matrix. Our system of equation is expanded for the high-porosity limits and stabilized it for the case of high porosity contrasts. Melting process is implemented according to the model of Katz (2003) where melting degree is a function of pressure, temperature, composition and water content. We use a finite-difference method with fully staggered grid in a combination with marker-in-cell technique for advection of fluid and solid phase. We performed a comparison with a benchmark of a thermal convection in a porous media in a bottom-heated box to verify the interdependency of Rayleigh and Nusselt numbers with a theoretical one. We have demonstrated the stability and robustness of the algorithm in case of strongly non-linear visco-plastic rheology of solid including cases with localization of both deformation and porous flow along spontaneously forming shear bands. We have checked our model for the forming of localized porous channels under a simple shear stress (channelling instability). Current work includes implementation of non-liner viscous rheology and elaboration on the setup of self-initiating subduction. Later we plan to include solid elasticity and fluid/solid compressibility. Also we have developed a full complexity system of equations for visco-elastic case and currently are working on numerical realisation of it to verify our simplifying assumptions for the general model

  12. Partial melting of a Pb-Sn mushy layer due to heating from above, and implications for regional melting of Earth's directionally solidified inner core

    NASA Astrophysics Data System (ADS)

    Yu, James; Bergman, Michael I.; Huguet, Ludovic; Alboussiere, Thierry

    2015-09-01

    Superimposed on the radial solidification of Earth's inner core may be hemispherical and/or regional patches of melting at the inner-outer core boundary. Little work has been carried out on partial melting of a dendritic mushy layer due to heating from above. Here we study directional solidification, annealing, and partial melting from above of Pb-rich Sn alloy ingots. We find that partial melting from above results in convection in the mushy layer, with dense, melted Pb sinking and resolidifying at a lower height, yielding a different density profile than for those ingots that are just directionally solidified, irrespective of annealing. Partial melting from above causes a greater density deeper down and a corresponding steeper density decrease nearer the top. There is also a change in microstructure. These observations may be in accordance with inferences of east-west and perhaps smaller-scale variations in seismic properties near the top of the inner core.

  13. Partial melting of UHP calc-gneiss from the Dabie Mountains

    NASA Astrophysics Data System (ADS)

    Liu, Penglei; Wu, Yao; Liu, Qiang; Zhang, Junfeng; Zhang, Li; Jin, Zhenmin

    2014-04-01

    Exhumation melting has been proposed for the ultra-high pressure (UHP) metamorphic rocks in the Dabie Mountains based on melting experiments. We document here the first petrological and mineralogical evidence demonstrating that the UHP calc-gneisses from the Ganjialing area in the Dabie Mountains experienced partial melting during early exhumation. The assemblage of garnet, phengite (Si = 3.65 pfu), coesite, rutile and carbonate preserved in the calc-gneisses indicates a peak metamorphic condition of 692-757 °C and 4.0-4.8 GPa. Partial melting is indicated by several lines of evidence: the melting textures of phengite, the feldspar-dominated films, bands, branches, blebs and veins, the euhedral K-feldspars, the intergrowth film of plagioclase and K-feldspar, the plagioclase + biotite intergrowth after garnet and the epidote poikiloblasts. Polyphase inclusions in garnet are characterized with wedge-like offshoots and serrate outlines whereas those in epidote display negative crystal shapes, which can be best interpreted by entrapment of former melts. We propose a wet melting reaction of Phn + Q ± Na-Cpx + H2O = Bt + Pl + Grt + felsic melts, which likely took place at ca.650-800 °C and ca.1.0-2.0 GPa, to interpret the melting event in the calc-gneisses. Chemical exchanges between garnet and melts produced new garnet domains with higher almandine, spessartine, MREE, HREE and Y but lower grossular, pyrope, P, Sc, Ti, V and Zr contents. Zr-in-rutile thermometer reveals a low temperature of 620-643 °C at 5 GPa, indicating a later reset for Zr in rutile. Healed fractures are suggested to be responsible for the formation of some polyphase inclusions in garnet.

  14. Melt transport through continental lithosphere by dike injection from a partially molten asthenosphere

    NASA Astrophysics Data System (ADS)

    Havlin, C.; Parmentier, E.; Hirth, G.

    2011-12-01

    The high rates of tholeitic magmatism manifested in continental flood basalts and great dike swarms during the early stages of continental rifting require the migration of melt through thick, cold lithosphere by diking. The tendency for rifts to form near mantle plumes suggests that deep melting due to the elevated temperature and volatile content of plumes is the source of melt, but the coupling between grain scale migration in the asthenosphere and growth of dikes in the lithosphere is not well defined. This study assesses the mechanical conditions for which dikes can grow to a height similar to the thickness of continental lithosphere from a partially molten source at the base of the lithosphere. A 1D model couples a network of uniformly spaced, vertical dikes to a partially molten asthenosphere in the absence of thermal effects. The dikes are treated in a simplified manner by assuming constant viscous and buoyant pressure gradients and negligible critical stress intensity factor after propagation begins. The excess fluid pressure at the crack base drives melt into the crack if the pressure is lower than that in the asthenosphere, causing the crack to grow. The partially molten asthenosphere is modeled as a two-phase medium with a matrix compaction viscosity that varies inversely with melt fraction,φ, and a permeability proportional to φ3. As melt fraction decreases near the dike entrance, the permeability decreases and crack growth slows. Thus if melt is extracted on a time scale shorter than the buoyant upwelling of melt, crack growth is self-limiting. With uniform initial melt fraction and no melt buoyancy in the asthenosphere, cracks reach greater than ~100 km if the reference compaction length is greater than ~10 km. Dikes must be spaced at least every compaction length and must have an initial height of ~100 m to grow significantly. For initial melt fractions of 0.01 to 0.05 and mantle grain sizes of 1 to 10 mm, the ratio of fluid shear viscosity to

  15. Evidence for magmatic underplating and partial melt beneath the Canary Islands derived using teleseismic receiver functions

    NASA Astrophysics Data System (ADS)

    Lodge, A.; Nippress, S. E. J.; Rietbrock, A.; García-Yeguas, A.; Ibáñez, J. M.

    2012-12-01

    In recent years, an increasing number of studies have focussed on resolving the internal structure of ocean island volcanoes. Traditionally, active source seismic experiments have been used to image the volcano edifice. Here we present results using the analysis of compressional to shear (P to S) converted seismic phases from teleseismic events, recorded by stations involved in an active source experiment "TOM-TEIDEVS" (Ibáñez et al., 2008), on the island of Tenerife, Canary Islands. We supplement this data with receiver function (RF) analysis of seismograms from the Canary Islands of Lanzarote and La Palma, applying the extended-time multitaper frequency domain cross-correlation estimation method (Helffrich, 2006). We use the neighbourhood inversion approach of Sambridge (1999a,b) to model the RFs and our results indicate magmatic underplating exists beneath all three islands, ranging from 2 to 8 km, but showing no clear correlation with the age of the island. Beneath both La Palma and Tenerife, we find localized low velocity zones (LVZs), which we interpret as due to partial melt, supported by their correlation with the location of historical earthquakes (La Palma) and recent earthquakes (Tenerife). For Lanzarote, we do not sample the most recently volcanically active region and find no evidence for a LVZ. Instead, we find a simple gradational velocity structure, with discontinuities at ˜4, 10 and 18 km depth, in line with previous studies.

  16. Partial melting of ordinary chondrites: Lost City (H) and St. Severin (LL)

    NASA Technical Reports Server (NTRS)

    Jurewicz, Amy J. G.; Jones, John H.; Weber, Egon T.; Mittlefehldt, David W.

    1993-01-01

    Eucrites and diogenites are examples of asteroidal basalts and orthopyroxenites, respectively. As they are found intermingled in howardites, which are inferred to be regolith breccias, eucrites and diogenites are thought to be genetically related. But the details of this relationship and of their individual origins remain controversial. Work by Jurewicz et al. showed that 1170-1180 C partial melts of the (anhydrous) Murchison (CM) chondrite have major element compositions extremely similar to primitive eucrites, such as Sioux County. However, the MnO contents of these melts were about half that of Sioux County, a problem for the simple partial melting model. In addition, partial melting of Murchison could not produce diogenites, because residual pyroxenes in the Murchison experiments were too Fe- and Ca-rich and were minor phases at all but the lowest temperatures. A parent magma for diogenites needs an expanded low-calcium pyroxene field. In their partial melting study of an L6 chondrite, Kushiro and Mysen found that ordinary chondrites did have an expanded low-Ca pyroxene field over that of CV chondrites (i.e., Allende), probably because ordinary chondrites have lower Mg/Si ratios. This study expands that of both Kushiro and Mysen and Jurewicz et al. to the Lost City (H) and St. Severin (LL) chondrites at temperatures ranging from 1170 to 1325 C, at an fO2 of one log unit below the iron-wuestite buffer (IW-1).

  17. The distribution of partial melt in a granitic system: The application of liquid phase sintering theory

    NASA Astrophysics Data System (ADS)

    Jurewicz, Stephen R.; Watson, E. Bruce

    1985-05-01

    Two series of experiments, four crystallization and four partial melting, were performed at 1000°C and 10 kilobars in the quartz-alkali feldspar-granitic melt system in order to determine the equilibrium melt distribution and textural adjustment processes. The melt distribution in both types of experiments was characterized by melt residing at grain edge intersections and in a few large pools scattered throughout the sample. Wetting angle measurements from both sets of experiments gave values of 44, 49, and 59 degrees for the feldspar/feldspar, feldspar/quartz, and quartz/quartz wetting angles, respectively. Interparticle welding, a process consistent with the measured wetting angles, resulted in the formation of a skeleton of solid grains with very few unattached grains in any sample. Analysis of wetting angle distributions indicates that the longest duration experiments closely approached textural equilibrium and that the distributions of observed wetting angles from both sets of experiments were nearly identical. Measurement of quartz grain sizes from the 2, 4, 7, and 14-day crystallization experiments revealed: 1) a probable cube root of time dependence for the quartz growth rate; 2) a decrease in the number of quartz grains per square micron with increasing time; 3) a normalized distribution of grain sizes that appeared stationary in time. These results were shown to be consistent with the processes observed during the liquid phase sintering of ceramic materials and suggest that identical processes may occur in natural partially-molten systems. Finally, it was shown that interfacial energy considerations lead to a model of interparticle welding (clustering) in which it is discovered that there is an equilibrium melt fraction stable along grain edges of a partially-molten crystalline aggregate. This melt fraction may be greater, equal to, or less than the equilibrium fraction of melt dictated by the pressure, temperature, and chemical potential conditions. If

  18. Partial melting of garnet lherzolite with water and carbon dioxide at 3 GPa using a new melt extraction technique: implications for intraplate magmatism

    NASA Astrophysics Data System (ADS)

    Baasner, Amrei; Médard, Etienne; Laporte, Didier; Hoffer, Géraldine

    2016-05-01

    The origin and source rocks of alkali-rich and SiO2-undersatured magmas in the Earth's upper mantle are still under debate. The garnet signature in rare earth element patterns of such magmas suggests a garnet-bearing source rock, which could be garnet lherzolite or garnet pyroxenite. Partial melting experiments were performed at 2.8 GPa and 1345-1445 °C in a piston-cylinder using mixtures of natural lherzolite with either 0.4 wt% H2O and 0.4 wt% CO2 or 0.7 wt% H2O and 0.7 wt% CO2. Different designs of AuPd capsules were used for melt extraction. The most successful design included a pentagonally shaped disc placed in the top part of the capsule for sufficient melt extraction. The degrees of partial melting range from 0.2 to 0.04 and decrease with decreasing temperature and volatile content. All samples contain olivine and orthopyroxene. The amounts of garnet and clinopyroxene decrease with increasing degree of partial melting until both minerals disappear from the residue. Depending on the capsule design, the melts quenched to a mixture of quench crystals and residual glass or to glass, allowing measurement of the volatile concentrations by Raman spectroscopy. The compositions of the partial melts range from basalts through picrobasalts to foidites. Compared to literature data for melting of dry lherzolites, the presence of H2O and CO2 reduces the SiO2 concentration and increases the MgO concentration of partial melts, but it has no observable effect on the enrichment of Na2O in the partial melts. The partial melts have compositions similar to natural melilitites from intraplate settings, which shows that SiO2-undersaturated intraplate magmas can be generated by melting of garnet lherzolite in the Earth's upper mantle in the presence of H2O and CO2.

  19. Magmatism vs mushmatism: Numerical modelling of melt migration and accumulation in partially molten crust

    NASA Astrophysics Data System (ADS)

    Roele, Katarina; Jackson, Matthew; Morgan, Joanna

    2016-04-01

    We present a quantitative model of heat and mass transport in a compacting crustal mush created by the repetitive intrusion of mantle-derived basaltic sills. At very low sill emplacement rates, we find that the maximum melt fraction remains small, far below that required to create an eruptible magma, and consistent with purely thermal models published previously. However, at intermediate (and realistic) sill emplacement rates, we observe the formation of a high melt fraction layer within a low melt fraction background. The high melt fraction layer migrates upwards towards the top of the mush (which is defined by the location of the solidus isotherm) and, despite occupying a high melt fraction, the melt in the layer has a composition corresponding to a progressively larger degree of fractionation during upwards migration, because it locally equilibrates with mush at progressively lower temperature. Thus the composition of the melt in the high melt fraction layer becomes progressively more evolved. The high melt fraction layer resembles a conventional magma chamber, but is produced by changes in bulk composition in response to melt migration, rather than the addition of heat. Indeed, such a layer can form even when the mush is cooling overall. The magma within the layer is at sufficiently high melt fraction to be eruptible, but is not located in the hottest region of the mush where the temperature is highest. This is a new method to produce a magma chamber within a crustal mush, and also to evolve the composition of the melt in the chamber. Our results show that high melt fractions need not be associated with high temperature; they also show that eruptible melt fractions can be created at much lower emplacement rates than predicted by purely thermal models. These high melt fractions are transient, and spatially localized within larger mush zones. Moreover, chemical differentiation does not require fractional crystallisation in a largely liquid magma chamber. Our

  20. Partial melting of the South Qinling orogenic crust, China: Evidence from Triassic migmatites and diorites of the Foping dome

    NASA Astrophysics Data System (ADS)

    Zhang, He; Ye, Ri-Sheng; Liu, Bing-Xiang; Wang, Yan; Zhang, Yuan-Shuo; Siebel, Wolfgang; Chen, Fukun

    2016-09-01

    The Qinling orogen was ultimately formed by suturing of the South Qinling and Yangtze blocks, but the exact timing of the final amalgamation of the two blocks has not been well established so far. Partial melting of the Qinling orogenic continental crust resulted in the generation of migmatites, and such rocks may help to decipher the chronology of such event. In this paper, we report U-Pb ages, trace element, and Hf isotopic compositions of zircons from migmatites and diorite gneisses of the Foping dome, South Qinling. Zircons from migmatites form anhedral grains of variable sizes that are characterized by complex trace element compositions. Based on zircon U-Pb ages, the migmatites can be subdivided into two groups: Group 1 migmatites mainly retain Triassic zircons with U-Pb ages of 214-211 Ma and Hf model ages of 1.46 Ga in core and rim domains; zircons from Group 2 migmatites record both Triassic ( 210 Ma) and Neoproterozoic U-Pb ages, analogous to igneous rocks of the Wudang and Yaolinghe Groups exposed in South Qinling. Zircons from the diorite gneisses yield U-Pb ages of 216-210 Ma with Hf isotopic composition (TDM2 ages of 1.46 Ga) similar to the migmatites. Evidence from whole-rock Nd isotopic analyses also points to a similar genesis between migmatites and diorite gneisses. It is proposed that Group 1 migmatites were derived by melting of Triassic diorites, while Group 2 migmatites were derived from Neoproterozoic igneous rocks, a major basement lithology of South Qinling. Partial melting of the orogenic crust took place at 214-210 Ma, approximately consistent with the retrograde metamorphism of granulites exposed along the suture zone between the South Qinling and Yangtze blocks. We suggest that the collision of these two blocks occurred prior to 215 Ma and that the Foping dome resulted from rapid collapse of an overthickened crust followed by partial melting enhanced by asthenospheric influx.

  1. Electrical Conductivity and Tomographic Imaging of Olivine-FeS Partial-Melts

    NASA Astrophysics Data System (ADS)

    Roberts, J.; Mei, S.; Ryerson, R.; Kinney, J.

    2005-05-01

    The presence, distribution, and composition of melt affect the physical properties of polycrystalline ultramafic rock and are important to our interpretation of the Earth's lower crust and upper mantle, and to our understanding of planetary core formation via liquid-metal segregation. A key issue in models of planetary core formation is the interconnectness of molten iron-sulfides in contact with silicates at high temperature and pressure. Olivine-FeS partial-melts are also considered to be possible explanations for anomalously high conductivity regions beneath mountain ranges such as the Pyrenees and Andes. The interconnectivity and tortuosity of the melt phase, in combination with the properties of the individual melt and crystal phases, have bearing on the extractability of the melt, and on the rheology, and electrical conductivity of the bulk material. We have begun an integrated study of the electrical conductivity-texture-permeability relationships of olivine-sulfide partial-melt samples. Olivine-sulfide partial-melts containing 0, 1, 3, 6, and 10% by weight non-wetting compositions (Fe64S36) and wetting compositions (Fe34S19Ni47+O2) in a San Carlos olivine matrix (Fo91) have been synthesized in a piston cylinder apparatus at 1250 C and 1 to 2 GPa. Electrical conductivity measurements of the partial-melt and the individual melt and crystalline phases have been performed in a 1-atmosphere gas-mixing furnace up to 1400 C. Additional measurements in solid medium-pressure apparatus (D-DIA, piston cylinder) have begun. Samples are characterized using X-ray microtomographic (XRCT) performed at the Advanced Light Source with spatial resolution approaching 2 microns. Determination of the 3-D structure and interconnectedness of the melt phase, combined with the electrical conductivity measurements have been used to estimate the permeability of the mixtures at various experimental conditions. Results indicate sulfur fugacity is an important parameter controlling the

  2. The behavior of Fe3+/∑Fe during partial melting of spinel lherzolite

    NASA Astrophysics Data System (ADS)

    Gaetani, Glenn A.

    2016-07-01

    This study presents an internally consistent model for the behavior of Fe3+/∑Fe during partial melting of spinel lherzolite. The Fe3+/∑Fe ratio for olivine is calculated on the basis of point defect thermodynamics, and the oxidation states of iron in the other solid phases are calculated using Fe3+/Fe2+ distribution between olivine and orthopyroxene, clinopyroxene, or spinel. Conservation of mass is used to relate the Fe3+/Fe2+ ratio of partial melt to the concentrations of Fe3+ and Fe2+ in the initial and residual solids as a function of pressure, temperature, and oxygen fugacity. Results from isobaric batch melting calculations demonstrate that the Fe3+/∑Fe ratio of the partial melt decreases with increasing melt fraction. Conversely, the Fe3+/∑Fe ratio of the partial melt increases with increasing melt fraction during decompression batch melting. The relative oxygen fugacity of the upper mantle depends on both the oxidation state of iron and mantle potential temperature. Results from incremental decompression melting calculations in which 1% melt is produced for each 100 MPa of decompression and then removed from the residual solid indicate that relative oxygen fugacity calculated from the oxidation state of iron in basaltic glass does not represent a unique value for the oceanic upper mantle but, rather, reflects conditions in the lower portion of the melting regime. A 100 °C change in mantle potential temperature produces a change in relative oxygen fugacity of ∼0.8 log units, similar to the global range inferred from mid-ocean ridge basalt glasses. It is necessary, therefore, to compare relative oxygen fugacity calculated from basaltic glass with proxies for potential temperature before drawing conclusions on heterogeneity of the oxidation state of iron in the oceanic upper mantle. Results from model calculations also suggest that the sub-arc mantle is intrinsically more oxidizing than the oceanic mantle because it is cooler. The global correlation

  3. Dynamic model of intermediate melting zones formation within the permeable lithosphere

    NASA Astrophysics Data System (ADS)

    Sorokin, Konstantin; Perepechko, Yury; Sharapov, Viktor; Chudnenko, Konstantin; Perepechko, Ludmila

    2017-04-01

    flow in course of time. According to the results of numerical simulation, the main feature of metasomatic processes in the fluid systems under study is the lack of dependence of metasomatic zoning at the far stages of system's development on the initial stage parameters. In this case the composition of metasomatic rock matrix changes monotonically along the subsurface and is determined by the composition of fluids in the magma source. Another consequence of increasing temperature is the emergence of development opportunities of partial or full local or multi-level melting zones of metasomatic rocks. The temperature of the melts in these zones exceeds the temperature of the fluid at the lower boundary of the system. The complication of the mantle fluid system's structure by introducing zones with different geodynamic parameters of filtration processes leads to more complicated nature of metasomatic zoning. This work was supported by the RFBR, grants 16-29-15131.

  4. Partial melting of basement metasedimentary rocks from the central Xolapa Complex, southern Mexico

    NASA Astrophysics Data System (ADS)

    Maldonado, R.; Corona-Chávez, P.; Poli, S.

    2013-12-01

    The Xolapa Complex in the Amuzgos region is made up of a poly-lithological metasedimentary sequence mainly consisting of garnet-sillimanite paragneisses, garnet mica schists, mafic meta-graywackes and marbles interlayered with mafic and quartz-feldspatic orthogneisses. These units as a whole constitute a highly deformed metamorphic basement, within which structural and mineralogical characteristics typical for high metamorphic grade (D1) are recognized. These features precede the development of a complex migmatitic structure which produced a wide range of metatexitic and diatexitic morphologies. The interaction between a generalized partial melting process and a syn-anatectic heterogeneous deformation process (D2) partially destroyed the internal pre-anatectic structure of the metamorphic complex. This metamorphic-migmatitic basement is affected by at least two post-anatectic ductile-fragile deformation stages (D3-D4) that produced the dislocation of D1-D2 structures, generating folds, back-thrusts and regional shear zones. Pre-anatectic paragenesis and deformation structures in lithological relicts define a prograde metamorphic path with a minimum pressure of 9 kbar and temperature >600 °C, which represents the relatively oldest recognizable crystallization stage. Subsequently, the formation of neosomes defines a new metamorphic stage at suprasolidus conditions at 750-850 °C and 7-8 kbar. The latest period of this stage evolved with the development of replacement paragenesis that indicate back reaction and rapid decompression under conditions close to the solidus at 600-700 °C and 4-4.5 kbar. Finally, the generalized presence of low temperature mineral paragenesis and deformation structures indicate the heterogeneous development of a retrograde stage at green-schist facies metamorphic conditions. The progressive consumption of residual and peritectic mineral phases in the presence of melt during decompression, controls the occurrence of cordierite and hercynite

  5. Timing and duration of partial melting and magmatism in the Variscan Montagne Noire gneiss dome (French Massif Central)

    NASA Astrophysics Data System (ADS)

    Trap, Pierre; Roger, Françoise; Cenki-Tok, Bénédicte; Paquette, Jean-Louis

    2017-03-01

    Unravelling the detailed pressure-temperature-time-deformation (P-T-t-D) evolution of magmatic and metamorphic rocks provides essential insights into the timing and duration of partial melting and related plutonism during crustal flow and migmatitic dome formation. The Montagne Noire Axial Zone (MNAZ) is a migmatitic dome located within the Variscan orogen in the southern French Massif Central. The timing of the main thermal event that was responsible for intense partial melting is still highly debated. In this study we present new laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) age data on micaschists, migmatites and granites that clarify the P-T-t-D evolution of the MNAZ. Structurally controlled samples were collected in order to constrain the timing of metamorphism, migmatization and plutonism regarding the main structural pattern D1, D2 and D3. D1 and D2 correspond to nappe stacking and dextral transpression, respectively. D3 is related to vertical shortening and coaxial thinning with a preferential NE-SW- to E-W-directed stretching. LA-ICP-MS analyses on the syntectonic Anglès, Soulié and Martys granites yielded U-Th/Pb monazite ages of 305 ± 1.5, 306 ± 1.9 and 314 ± 2 Ma, respectively. Five migmatitic rocks sampled in the eastern and central Espinouse area yielded in situ ages ranging between 312 ± 2 and 301 ± 2 Ma. Along the dome envelope, two garnet-staurolite-bearing micaschists near Saint-Pons-de-Thomières village gave in situ U-Th-Pb ages of 312.1 ± 2.1 and 309.0 ± 3.1 Ma. A fine-grained gneiss with a D3 fabrics in the eastern dome envelope yield a 208Pb/232Th mean age at 305.7 ± 3.9 Ma. All ages obtained in this study for the micaschists, migmatites and granites range between 315 and 301 Ma. We interpret this time span as the record of the high thermal event responsible for intense crustal partial melting within the lower and middle crust. The onset of partial melting occurred at ca. 315 Ma that marked the beginning of

  6. Timing and duration of partial melting and magmatism in the Variscan Montagne Noire gneiss dome (French Massif Central)

    NASA Astrophysics Data System (ADS)

    Trap, Pierre; Roger, Françoise; Cenki-Tok, Bénédicte; Paquette, Jean-Louis

    2016-11-01

    Unravelling the detailed pressure-temperature-time-deformation (P-T-t-D) evolution of magmatic and metamorphic rocks provides essential insights into the timing and duration of partial melting and related plutonism during crustal flow and migmatitic dome formation. The Montagne Noire Axial Zone (MNAZ) is a migmatitic dome located within the Variscan orogen in the southern French Massif Central. The timing of the main thermal event that was responsible for intense partial melting is still highly debated. In this study we present new laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) age data on micaschists, migmatites and granites that clarify the P-T-t-D evolution of the MNAZ. Structurally controlled samples were collected in order to constrain the timing of metamorphism, migmatization and plutonism regarding the main structural pattern D1, D2 and D3. D1 and D2 correspond to nappe stacking and dextral transpression, respectively. D3 is related to vertical shortening and coaxial thinning with a preferential NE-SW- to E-W-directed stretching. LA-ICP-MS analyses on the syntectonic Anglès, Soulié and Martys granites yielded U-Th/Pb monazite ages of 305 ± 1.5, 306 ± 1.9 and 314 ± 2 Ma, respectively. Five migmatitic rocks sampled in the eastern and central Espinouse area yielded in situ ages ranging between 312 ± 2 and 301 ± 2 Ma. Along the dome envelope, two garnet-staurolite-bearing micaschists near Saint-Pons-de-Thomières village gave in situ U-Th-Pb ages of 312.1 ± 2.1 and 309.0 ± 3.1 Ma. A fine-grained gneiss with a D3 fabrics in the eastern dome envelope yield a 208Pb/232Th mean age at 305.7 ± 3.9 Ma. All ages obtained in this study for the micaschists, migmatites and granites range between 315 and 301 Ma. We interpret this time span as the record of the high thermal event responsible for intense crustal partial melting within the lower and middle crust. The onset of partial melting occurred at ca. 315 Ma that marked the beginning of

  7. Detachment Fault Initiation and Control by Partially Molten Zones in the Lower Ocean Crust

    NASA Astrophysics Data System (ADS)

    Dick, H. J.; Natland, J. H.; MacLeod, C. J.; Robinson, P. T.

    2012-12-01

    The close association of oxide gabbro and deformation in interleaved ferrogabbro and olivine gabbro at Atlantis Bank on the SW Indian Ridge explains the formation of this enormous single-domed gabbroic oceanic core complex. ODP Holes 735B and 1105A show that the stratigraphy is defined by 100's of zones of intense deformation and strain localization in the upper 500-m where various melts percolated including late-stage iron-titanium rich melts. The latter created highly deformed oxide-rich gabbro zones at scales from millimeters to over 100 meters. Mapping by ROV, over-the-side rock drilling, dredging, and submersible shows that this stratigraphy exists uniformly over the bank. Deep drilling and sampling up the headwalls of major landslips cutting into the core complex show that the fault zone was imbricate, likely reflecting relocation of the active slip plane due to cyclic intrusion in the lower crust. The detachment originated as a high-angle fault on the rift valley wall that propagated into a zone of partially molten gabbro beneath the sheeted dikes. This zone then pinned the footwall block, creating a plutonic growth fault along which gabbro intruded beneath the ridge axis was continuously uplifted and exposed on the Antarctic plate for ~3.9 myr. The overlying basaltic carapace spread more slowly to the north on the African Plate. Textural evidence, particularly that provided by iron-titanium oxides, shows that melts migrated along complex shear zones in which several creep mechanisms operated, ranging from crystal plastic dislocation creep, diffusion creep, grain boundary sliding, and brittle deformation. More than one of these mechanisms may have occurred concurrently. Subsequently, these zones localized later solid-state creep, often producing texturally complex rocks where separation of the timing and duration of different creep mechanisms is difficult to unravel. As uplift of the plutonic section progressed, the footwall passed through the zone of diking

  8. Partial melting of the Archaean Thrym Complex of southeastern Greenland

    NASA Astrophysics Data System (ADS)

    Bagas, Leon; Næraa, Tomas; Kolb, Jochen; Reno, Barry L.; Fiorentini, Marco L.

    2013-02-01

    High-grade Archaean rocks of the remote Thrym Complex of southeastern Greenland expose a lower crustal section that formed at a depth of > 30 km at temperatures reaching 1000 °C and pressures approaching 1.5 GPa. The complex is part of the North Atlantic Craton, which is bound to the north by the Trans Hudson-Nagssugtoqidian-Ammassalik Orogen and to the south by the Makkovik-Ketilidian Orogen. The rocks in the complex include orthogneiss, migmatitic orthogneiss with banded or nebulitic fabrics, migmatite with a breccia-like structure (agmatite), and narrow bands of lensoidal mafic and ultramafic rocks (granulites) with associated widespread garnet-bearing mafic granulite, and a minor proportion of garnet-cordierite-sillimanite-biotite gneiss. The latter high-grade rocks form part of the substrate for the emplacement of the protoliths for orthogneiss that was synchronous with the ca. 2790-2700 Ma Skjoldungen Orogeny. At least two suites have been recognised in the Thrym Complex based on geochemistry. The oldest is a tholeiitic suite of mafic to ultramafic granulites, and the other is a calc-alkaline suite that includes felsic to intermediate orthogneiss. Most of the orthogneiss has a granodioritic (oldest) to quartz monzodioritic (younger) composition with rare monzogranitic, tonalitic, monzonitic and quartz dioritic protoliths. Historically, the orthogneiss units have been called TTGs, although monzogranite and tonalite are rare, and no trondhjemite is observed. In addition, they could also be called adakitic on geochemical grounds. Instead of using this terminology, which has genetic connotations, the orthogneiss is referred to as predominantly granodioritic to quartz-monzodioritic. Assuming that modern tectonics operated during the Neoarchaean, at least some of the mafic and ultramafic granulites and orthogneiss exposed in the Thrym Complex represent the root zone of a magmatic-arc that might have been relaminated around 2760 Ma during the collisional

  9. Unlocking the Secrets of the Mantle Wedge: New Insights Into Melt Generation Processes in Subduction Zones

    NASA Astrophysics Data System (ADS)

    Grove, T. L.

    2007-05-01

    Recent laboratory studies of the melting and crystallization behavior of mantle peridotite and subduction zone lavas have led to new insights into melting processes in island arc settings. Melting of the mantle wedge in the presence of H2O begins at much lower temperatures than previously thought. The solidus of mantle peridotite at 3 GPa is ~ 800 °C, which is 200 °C below previous estimates. At pressures greater than 2.4 GPa chlorite becomes a stable phase on the solidus and it remains stable until ~ 3.5 GPa. Therefore, melting over this pressure range occurs in the presence of chlorite, which contains ~ 12 wt. % H2O. Chlorite stabilized on the peridotite solidus by slab-derived H2O may be the ultimate source of H2O for subduction zone magmatism. Thus, chlorite could transport large amounts of H2O into the descending mantle wedge to depths where it can participate in melting to generate hydrous arc magmas. Our ability to identify primitive mantle melts at subduction zones has led to the following observations. 1) Primitive mantle melts show evidence of final equilibration at shallow depths near the mantle - crust boundary. 2) They contain variable amounts of dissolved H2O (up to 6 wt. %). 3) They record variable extents of melting (up to > 25 wt. %). To produce melts with such variable characteristics requires more than one melting process and requires consideration of a new type of melting called hydrous flux melting. Flux melting occurs when the H2O - rich melt initially produced on the solidus near the base of the mantle wedge ascends and continuously reacts with overlying hotter, shallower mantle. The mantle melts and magmatic H2O content is constantly diluted as the melt ascends and reacts with shallower, hotter mantle. Anhydrous mantle melts are also found in close temporal and spatial proximity to hydrous flux melts. These melts are extracted at similar depths near the top of the mantle wedge when mantle is advected up and into the wedge corner and melted

  10. The Origin of low-Sr Rhyolites by Multiple Episodes of Partial Melting

    NASA Astrophysics Data System (ADS)

    Lange, R. A.

    2008-12-01

    There is a broad, but mistaken, consensus in the literature that very low-Sr concentrations (<1-2 ppm) in high-SiO2 rhyolites requires that these rhyolites formed by extensive Rayleigh fractional crystallization and cannot have formed by partial melting of sub-solidus, felsic crust. This concept, first proposed by Halliday et al. (1991), led to a debate regarding the exact mechanism of fractional crystallization in magma chambers of significant size at the time of eruption, and how such large chambers could be thermally maintained in the shallow crust. Over time, the consensus view has shifted to a model where high-SiO2 rhyolites with low Sr contents are derived from crystalline mushes (magma chambers containing >60-90% crystals), but not by partial melting of felsic plutons. In other words, there is continued resistance to the concept that high-SiO2 rhyolites can form by partial melting of subsolidus lithologies. The primary argument against partial melting is the occurrence of rhyolites with low Sr concentrations (<1-2 ppm), which is frequently cited as an "undeniable crystal fractionation signature". Here, it is shown that this common assumption is not universally true. One of the classic examples of high-SiO2 rhyolites with low Sr (1.3-0.3 ppm) is the Sierra La Primavera complex erupted in the Tepic-Zacoalco Rift (TZR) in western Mexico. For the last 600 kyrs, the TZR has been the site of calc-alkaline arc volcanism, including five andesite stratovolcanoes, owing to subduction of the Rivera plate. However, superimposed on this Quaternary arc is a longer history of extension and bimodal volcanism in the TZR that continues to the present. The predominant basement rocks in the TZR are high-SiO2 rhyolites (75-78 wt%) of three distinct age groups, which show a pattern of decreasing Sr concentration with decreasing age: (1) Paleocene-Eocene: 55-47 Ma, 110-73 ppm Sr; (2) Oligocene-Miocene: 37-18 Ma, 80-43 ppm Sr, and (3) Pliocene: 5-3 Ma; 77-2 ppm Sr. Rhyolite

  11. Composition of silicate partial melts of carbonated pelite at 3-5 GPa and genesis of arc magma

    NASA Astrophysics Data System (ADS)

    Tsuno, K.; Dasgupta, R.; Danielson, L. R.; Righter, K.

    2012-12-01

    The composition of arc magmas reflects a complex process of slab-modified mantle wedge melting and magma differentiation in the crust. The composition of arc magma is distinct among various subduction zones owing to the different thermal structures [1] and perhaps different subduction input. Partial melts of downgoing sediment generated at slab-top or in sedimentary diapir [2] may be key in metasomatizing the mantle wedge. However, the effect of carbonates on the silicate partial melt composition of pelitic sediments is less constrained under the deep sub-arc conditions (~5 GPa). Here we provide silicate partial melt composition of Al-poor carbonated pelite to 5 GPa and discuss whether such melts may be a potential metasomatizing agent for arc source, particularly in Central America, Sunda, and Vanuatu where low-alumina carbonated pelite subduct [3]. We performed piston cylinder (3 GPa) and multianvil (4 and 5 GPa) experiments at 800-1150 °C, using a synthetic pelite with 0.5 and 1.0 wt.% H2O and 5.0 wt.% CO2. The experimental procedures and the resulting melting phase relations of this study are described in ref. [4]. The rhyolitic partial melt at 3 GPa evolves to trachydacite at 4 GPa and tephriphonolite at 5 GPa. At 3 GPa silicate partial melt compositions of our study are similar to those derived from hydrous, CO2-free pelite [e.g., 5-7], and are lower in SiO2 (63-65 wt.%) and higher in TiO2 (1-2 wt.%), MnO (~0.6 wt.%) and CaO (2-9 wt.%) at 4 GPa. At 5 GPa and 1050-1100 °C immiscible silicate melts, in the presence of carbonatitic melt, are even more distinct in terms of SiO2 (51-55 wt.%), TiO2 (~2-3 wt.%), Al2O3 (~10-12 wt.%), FeO* (~5-9 wt.%), MnO (0.1-0.3 wt.%), and CaO (~11-14 wt.%) compared to pelite partial melts in the absence of CO2 (~69-74 wt.% SiO2, 0.5-1.0 wt.% TiO2, ~12-15 wt.% Al2O3, ~1 wt.% FeO*, ~0.1 wt.% MnO, and 0.3-0.9 wt.% CaO). The compositions of Central America, Sunda, and Vanuatu arc basalts, at 5-15 wt.% MgO, are richer in FeO*, Mn

  12. Evidence of melting, melt percolation and deformation in a supra-subduction zone (Marum ophiolite complex, Papua New Guinea)

    NASA Astrophysics Data System (ADS)

    Kaczmarek, Mary-Alix; Jonda, Leo; Davies, Hugh L.

    2015-08-01

    New geochemical and microstructural data are presented for a suite of ultramafic rocks from the Marum ophiolite in Papua New Guinea. Our results describe a piece of most depleted mantle made essentially of dunite and harzburgite showing compositions of supra-subduction zone peridotite. Strong olivine crystallographic preferred orientations (CPOs) in dunite and harzburgite inferred the activation of both (001)[100] and (010)[100] slip systems, which are activated at high-temperature and low-stress conditions. Clinopyroxene and orthopyroxene CPOs inferred the activation of (100)[001] and (010)[001] slip systems, which are common for pyroxenes deformed at high temperature. This plastic deformation is interpreted to have developed during the formation of the Marum ophiolite, prior to melt percolation. The orientation of the foliation and olivine [100] slip directions sub-parallel to the subduction zone indicates that mantle flow was parallel to the trench pointing a fast polarisation direction parallel to the arc. This provides new evidence that fast polarisation direction parallel to the arc could be caused by anisotropic peridotite and not by olivine [001] slip. After its formation, Marum ophiolite has been fertilised by diffuse crystallisation of a low proportion of clinopyroxene (1-2 %) (P1) and formation of cm-scale ol-clinopyroxenite and ol-websterite veins cross-cutting the foliation (P2). This percolating melt shows silica-rich magnesian affinities (boninite-like) related to supra-subduction zone in a young fore-arc environment. The peridotite has also been percolated by a melt with more tholeiite affinities precipitating plagioclase-rich wehrlite and thin gabbroic veins (P3); these are interpreted to form after the boninitic event. The small proportion of newly crystallised pyroxene in the dunite shows similar orientation of crystallographic axes to the host dunite (<100>ol parallel to <001>cpx-opx). In contrast, the pyroxenes in ol-clinopyroxenite, ol

  13. Water in Nominally Anhydrous Deep Crustal Minerals: Facilitators of Deformation and Partial Melting

    NASA Astrophysics Data System (ADS)

    Seaman, S. J.; Williams, M. L.; Koteas, G. C.

    2010-12-01

    Igneous rocks of the lowest crust are commonly dominated by anhydrous minerals such as plagioclase feldspar, alkali feldspar, and quartz. Hydrous minerals such as muscovite, biotite, and hornblende can facilitate melting through dehydration melting reactions. Eutectic melting is aided by the relatively high ambient temperature of the lowermost crust and by the tendency of partial melts of mantle rocks to heat the lower crust both as a result of underplating and by intrusion into the lower crust. Free water is the most typical flux for lowering the eutectic temperature of the crystalline rocks of the lowermost crust, and subduction is the most commonly cited mechanism for delivering water to this setting. However, water in nominally anhydrous minerals such as quartz and feldspar is an additional flux for partial melting of granitoid source rocks. Water occurs both in structural sites in the host minerals and in fluid inclusions. Although water occurs in low concentrations (300-5000 ppm is typical), the abundance of these minerals in granitoids makes the effect of the water significant in terms of slightly lowering the solidus and initiating partial melting. 500 ppm water in minerals that make up large volumes of crustal rocks (alkali feldspar, plagioclase feldspar, quartz) would lower the dry solidus of granite by 24oC at 1 GPa and, because of the small bulk distribution coefficient likely for water in these minerals, would produce a near-solidus melt with XH20 = 0.248, corresponding to 8.3 weight percent water in the partial melt. Water that is trapped in a single phase is not an effective flux. It is likely that deformation of lower crustal minerals by dislocation creep mobilizes water from mineral interiors and transporting it to sites of cotectic or eutectic mineral assemblages. Water in mineral structures is likely to weaken nominally anhydrous minerals, making them susceptible to deformation by dislocation creep. The positive feedback between structural

  14. Experimental derivation of nepheline syenite and phonolite liquids by partial melting of upper mantle peridotites

    NASA Astrophysics Data System (ADS)

    Laporte, Didier; Lambart, Sarah; Schiano, Pierre; Ottolini, Luisa

    2014-10-01

    Piston-cylinder experiments were performed to characterize the composition of liquids formed at very low degrees of melting of two fertile lherzolite compositions with 430 ppm and 910 ppm K2O at 1 and 1.3 GPa. We used the microdike technique (Laporte et al., 2004) to extract the liquid phase from the partially molten peridotite, allowing us to analyze liquid compositions at degrees of melting F down to 0.9%. At 1.3 GPa, the liquid is in equilibrium with olivine + orthopyroxene + clinopyroxene + spinel in all the experiments; at 1 GPa, plagioclase is present in addition to these four mineral phases up to about 5% of melting (T≈1240 °C). Important variations of liquid compositions are observed with decreasing temperature, including strong increases in SiO2, Na2O, K2O, and Al2O3 concentrations, and decreases in MgO, FeO, and CaO concentrations. The most extreme liquid compositions are phonolites with 57% SiO2, 20-22% Al2O3, Na2O + K2O up to 14%, and concentrations of MgO, FeO, and CaO as low as 2-3%. Reversal experiments confirm that low-degree melts of a fertile lherzolite have phonolitic compositions, and pMELTS calculations show that the amount of phonolite liquid generated at 1.2 GPa increases from 0.3% in a source with 100 ppm K2O to 3% in a source with 2000 ppm K2O. The enrichment in silica and alkalis with decreasing melt fraction is coupled with an increase of the degree of melt polymerization, which has important consequences for the partitioning of minor and trace elements. Thus Ti4+ in our experiments and, by analogy with Ti4+, other highly charged cations, and rare earth elements become less incompatible near the peridotite solidus. Our study brings a strong support to the hypothesis that phonolitic lavas or their plutonic equivalents (nepheline syenites) may be produced directly by partial melting of upper mantle rock-types at moderate pressures (1-1.5 GPa), especially where large domains of the subcontinental lithospheric mantle has been enriched in

  15. 49 CFR 222.42 - How does this rule affect Intermediate Quiet Zones and Intermediate Partial Quiet Zones?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... and Intermediate Partial Quiet Zones? 222.42 Section 222.42 Transportation Other Regulations Relating... Horns at Groups of Crossings-Quiet Zones § 222.42 How does this rule affect Intermediate Quiet Zones and..., if the public authority provides Notice of Quiet Zone Continuation, in accordance with § 222.43...

  16. Transport critical current density of melt textured YBa2Cu3O7 - x rods prepared by zone melting using a high temperature gradient

    NASA Astrophysics Data System (ADS)

    Brand, M.; Elschner, S.; Gauss, S.; Assmus, W.

    1994-04-01

    We have developed a quasicontinuous crucible free zone melting method for texturing YBCO bulk material. Dense sintered rods with a length of 10 cm were partially molten in the hot zone of a 5 zone furnace and recrystallized in the large temperature gradient (140 °C/cm) limiting this zone. Suitable additions of Y2BaCuO5 (20 mol %) and PtO2 (1 wt %) to the starting material and a growth rate of not more than 1 mm/h were necessary to obtain stable growth conditions. After natural grain selection we obtained 8-cm-long rods with a uniform orientation of the crystallographic axes within 2°. The angle between c direction and rod axis typically was 55°. The critical current density at 77 K measured with continuous current over a length of 4.5 cm was 1.3×104 A/cm2 in zero field and 8×103 A/cm2 in 0.5 T. These values confirm the absence of grain boundaries.

  17. Rapid submarine ice melting in the grounding zones of ice shelves in West Antarctica.

    PubMed

    Khazendar, Ala; Rignot, Eric; Schroeder, Dustin M; Seroussi, Helene; Schodlok, Michael P; Scheuchl, Bernd; Mouginot, Jeremie; Sutterley, Tyler C; Velicogna, Isabella

    2016-10-25

    Enhanced submarine ice-shelf melting strongly controls ice loss in the Amundsen Sea embayment (ASE) of West Antarctica, but its magnitude is not well known in the critical grounding zones of the ASE's major glaciers. Here we directly quantify bottom ice losses along tens of kilometres with airborne radar sounding of the Dotson and Crosson ice shelves, which buttress the rapidly changing Smith, Pope and Kohler glaciers. Melting in the grounding zones is found to be much higher than steady-state levels, removing 300-490 m of solid ice between 2002 and 2009 beneath the retreating Smith Glacier. The vigorous, unbalanced melting supports the hypothesis that a significant increase in ocean heat influx into ASE sub-ice-shelf cavities took place in the mid-2000s. The synchronous but diverse evolutions of these glaciers illustrate how combinations of oceanography and topography modulate rapid submarine melting to hasten mass loss and glacier retreat from West Antarctica.

  18. Rapid submarine ice melting in the grounding zones of ice shelves in West Antarctica

    NASA Astrophysics Data System (ADS)

    Khazendar, Ala; Rignot, Eric; Schroeder, Dustin M.; Seroussi, Helene; Schodlok, Michael P.; Scheuchl, Bernd; Mouginot, Jeremie; Sutterley, Tyler C.; Velicogna, Isabella

    2016-10-01

    Enhanced submarine ice-shelf melting strongly controls ice loss in the Amundsen Sea embayment (ASE) of West Antarctica, but its magnitude is not well known in the critical grounding zones of the ASE's major glaciers. Here we directly quantify bottom ice losses along tens of kilometres with airborne radar sounding of the Dotson and Crosson ice shelves, which buttress the rapidly changing Smith, Pope and Kohler glaciers. Melting in the grounding zones is found to be much higher than steady-state levels, removing 300-490 m of solid ice between 2002 and 2009 beneath the retreating Smith Glacier. The vigorous, unbalanced melting supports the hypothesis that a significant increase in ocean heat influx into ASE sub-ice-shelf cavities took place in the mid-2000s. The synchronous but diverse evolutions of these glaciers illustrate how combinations of oceanography and topography modulate rapid submarine melting to hasten mass loss and glacier retreat from West Antarctica.

  19. Rapid submarine ice melting in the grounding zones of ice shelves in West Antarctica

    PubMed Central

    Khazendar, Ala; Rignot, Eric; Schroeder, Dustin M.; Seroussi, Helene; Schodlok, Michael P.; Scheuchl, Bernd; Mouginot, Jeremie; Sutterley, Tyler C.; Velicogna, Isabella

    2016-01-01

    Enhanced submarine ice-shelf melting strongly controls ice loss in the Amundsen Sea embayment (ASE) of West Antarctica, but its magnitude is not well known in the critical grounding zones of the ASE's major glaciers. Here we directly quantify bottom ice losses along tens of kilometres with airborne radar sounding of the Dotson and Crosson ice shelves, which buttress the rapidly changing Smith, Pope and Kohler glaciers. Melting in the grounding zones is found to be much higher than steady-state levels, removing 300–490 m of solid ice between 2002 and 2009 beneath the retreating Smith Glacier. The vigorous, unbalanced melting supports the hypothesis that a significant increase in ocean heat influx into ASE sub-ice-shelf cavities took place in the mid-2000s. The synchronous but diverse evolutions of these glaciers illustrate how combinations of oceanography and topography modulate rapid submarine melting to hasten mass loss and glacier retreat from West Antarctica. PMID:27780191

  20. Formation of layered and schlieren migmatites by partial melting at Aspen Basin, New Mexico

    SciTech Connect

    Metcalf, R.V.

    1985-01-01

    Although several recent studies of layered migmatites have suggested that they originated by subsolidus differentiation, both layered and schlieren-type migmatites at Aspen Basin formed by partial melting. Proterozoic supracrustal rocks at Aspen Basin were intruded by a suite of calc-alkalic diorite, tonalite and granite, intensely deformed, then intruded by younger aplite and granite. The supra-crustal rocks consist of migmatitic, sillimanite-grade metagreywacke, felsic gneiss and amphibolite. Within the metagreywackes, concordant coarse-grained neosomes (leucosomes + melanosomes) are interlayered with fine-grained grey gneiss. These layered migmatites grade toward schlieren-type migamtites at deeper levels, where the proportions of leucocratic material and degree of discordance increase. Two pieces of evidence demonstrate that leucosomes crystallized from melts. Partial melting is favored over injection on the basis of major and trace element chemical analyses. None of the plutonic units have appropriate composition to serve as the migmatite source, and the chemical and mineralogical compositions of leucosomes and leucogranites correlate to their metamorphic host rock, implying local derivation. The transition from layered to schlieren migmatites is marked by an increase in Rb, Rb/Sr, and K/sub 2/O/Na/sub 2/O within the leucosomes and leucogranites, and apparently represents an increase in the degree of partial melting.

  1. Enhancement of Polycrystal Anelasticity Just Before Partial Melting: Experimental Details and Parameterization

    NASA Astrophysics Data System (ADS)

    Yamauchi, H.; Takei, Y.

    2016-12-01

    In order to investigate the effects of partial melting on polycrystal anelasticity, we measured modulus dispersion and attenuation of a rock analogue (polycrystalline aggregates of binary organic system: borneol + diphenylamine) at near-solidus temperatures, from below to above the solidus temperature. We also measured steady-state viscosity and ultrasonic velocity under the same temperature conditions, which are important to clarify the scaling law and underlying mechanism of anelasticity. The result shows that the effect of partial melting on anelasticity and viscosity appears both before and at the onset of melting. A high-frequency part of the attenuation spectra was significantly enhanced just below the solidus temperature (T/Tm ≃ 0.95, Tm = solidus). At the same temperature, reduction of diffusion creep viscosity by temperature was also accelerated. These changes are caused by a solid-state mechanism and were large even for the samples which generate very small amounts of melt (< 1%) at T = Tm. At the onset of melting, due to the direct effect of melt, further growth in attenuation spectra and further reductions of viscosity and elasticity occured. These direct effects were very small for the samples with very small melt fraction, but were non-negligible if φ > 1%. We performed a parameterization of these experimental results and obtained a new anelasticity model. The applicability of this new model to the mantle was shown by the fitting to the seismic velocity structure in the Pacific mantle [Priestley and McKenzie, 2013, EPSL]: the new model explains well the steep reduction of Vs just below the solidus temperature.

  2. The electrical conductivity during incipient melting in the oceanic low velocity zone

    NASA Astrophysics Data System (ADS)

    Gaillard, Fabrice; Sifre, David; Gardes, Emmanuel; Massuyeau, Malcolm; Hashim, Leila; Hier Majumder, Saswata

    2014-05-01

    A low viscosity layer at the Lithosphere-Asthenosphere Boundary (LAB) is certainly a requirement for plate tectonics but the nature of the rocks presents in this boundary remains controversial. The seismic low velocities and the high electrical conductivities of the LAB are attributed either to sub-solidus water-related defects in olivine minerals or to a few volume percents of partial melt but these two interpretations have shortcomings: (1) The amount of H2O stored in olivine is not expected to be high enough due to several mineralogical processes that have been sometimes ignored; (2) elevated melt volume fractions are impeded by the too cold temperatures prevailing in the LAB and by the high melt mobility that can lead to gravitational segregation. All this has in fact been partly settled 30 years ago, when a petrological LAB has been defined as a region of the upper mantle impregnated by incipient melts; that is small amounts of melt caused by small amount of CO2 and H2O. We show here that incipient melting is a melting regime that is allowed in the entire P-T-fO2 region of the LVZ. The top of the oceanic LVZ (LAB) is then best explained by a melt freezing layer due to a decarbonation reaction, whereas the bottom of the LVZ matches the depth at which redox melting defines the lower boundary of stability of incipient melts. Based on new laboratory measurements, we show here that incipient melts must be the cause of the high electrical conductivities in the oceanic LVZ. Considering relevant mantle abundances of H2O and CO2 and their effect on the petrology of incipient melting, we calculated conductivity profiles across the LAB for various ages. Several electrical discontinuities are predicted and match geophysical observations in a consistent petrological and geochemical framework. We conclude that incipient melts prevail in the LAB, what else?

  3. The electrical conductivity during incipient melting in the oceanic low velocity zone

    PubMed Central

    Sifré, David; Gardés, Emmanuel; Massuyeau, Malcolm; Hashim, Leila; Hier-Majumder, Saswata; Gaillard, Fabrice

    2014-01-01

    A low viscosity layer in the upper mantle, the Asthenosphere, is a requirement for plate tectonics1. The seismic low velocities and the high electrical conductivities of the Asthenosphere are attributed either to sub-solidus water-related defects in olivine minerals2-4 or to a few volume percents of partial melt5-8 but these two interpretations have shortcomings: (1) The amount of H2O stored in olivine is not expected to be higher than 50 ppm due to partitioning with other mantle phases9, including pargasite amphibole at moderate temperatures10, and partial melting at high temperatures9; (2) elevated melt volume fractions are impeded by the too cold temperatures prevailing in the Asthenosphere and by the high melt mobility that can lead to gravitational segregation11,12. Here we determined the electrical conductivity of CO2-H2O-rich melts, typically produced at the onset of mantle melting. Electrical conductivity modestly increases with moderate amounts of H2O and CO2 but it dramatically increases as CO2 content exceeds 6 wt% in the melt. Incipient melts, long-expected to prevail in the asthenosphere10,13-15, can therefore trigger its high electrical conductivities. Considering depleted and enriched mantle abundances in H2O and CO2 and their effect on the petrology of incipient melting, we calculated conductivity profiles across the Asthenosphere for various plate ages. Several electrical discontinuities are predicted and match geophysical observations in a consistent petrological and geochemical framework. In moderately aged plates (>5Ma), incipient melts most likely trigger both the seismic low velocities and the high electrical conductivities in the upper part of the asthenosphere, whereas for young plates4, where seamount volcanism occurs6, higher degree of melting is expected. PMID:24784219

  4. Electrical conductivity during incipient melting in the oceanic low-velocity zone.

    PubMed

    Sifré, David; Gardés, Emmanuel; Massuyeau, Malcolm; Hashim, Leila; Hier-Majumder, Saswata; Gaillard, Fabrice

    2014-05-01

    The low-viscosity layer in the upper mantle, the asthenosphere, is a requirement for plate tectonics. The seismic low velocities and the high electrical conductivities of the asthenosphere are attributed either to subsolidus, water-related defects in olivine minerals or to a few volume per cent of partial melt, but these two interpretations have two shortcomings. First, the amount of water stored in olivine is not expected to be higher than 50 parts per million owing to partitioning with other mantle phases (including pargasite amphibole at moderate temperatures) and partial melting at high temperatures. Second, elevated melt volume fractions are impeded by the temperatures prevailing in the asthenosphere, which are too low, and by the melt mobility, which is high and can lead to gravitational segregation. Here we determine the electrical conductivity of carbon-dioxide-rich and water-rich melts, typically produced at the onset of mantle melting. Electrical conductivity increases modestly with moderate amounts of water and carbon dioxide, but it increases drastically once the carbon dioxide content exceeds six weight per cent in the melt. Incipient melts, long-expected to prevail in the asthenosphere, can therefore produce high electrical conductivities there. Taking into account variable degrees of depletion of the mantle in water and carbon dioxide, and their effect on the petrology of incipient melting, we calculated conductivity profiles across the asthenosphere for various tectonic plate ages. Several electrical discontinuities are predicted and match geophysical observations in a consistent petrological and geochemical framework. In moderately aged plates (more than five million years old), incipient melts probably trigger both the seismic low velocities and the high electrical conductivities in the upper part of the asthenosphere, whereas in young plates, where seamount volcanism occurs, a higher degree of melting is expected.

  5. Magnesium isotopic variation of oceanic island basalts generated by partial melting and crustal recycling

    NASA Astrophysics Data System (ADS)

    Zhong, Yuan; Chen, Li-Hui; Wang, Xiao-Jun; Zhang, Guo-Liang; Xie, Lie-Wen; Zeng, Gang

    2017-04-01

    Ocean island basalts (OIBs) are geochemically diverse in radiogenic isotopes, a feature that is commonly ascribed to record the chemical heterogeneity of their deep-mantle source, where significant compositional variation relates to variable amounts of ancient recycled crustal material. Although Mg is a major constituent of the mantle, it is still unclear whether Mg isotopes of OIBs predominantly correspond to deep-mantle source heterogeneity or processes such as partial melting. Here, we present Mg isotopic and trace-element compositional data for OIBs from the Hawaii islands, the Louisville seamounts, and for altered oceanic crust samples from the South Pacific. The δ26Mg value range of these OIBs is - 0.29 ± 0.07 ‰ (2SD, n = 17), which is a variation approximately twice as large as the known compositional variation of the peridotitic mantle (- 0.23 ± 0.04 ‰, 2SD). Moreover, alkaline basalt (- 0.31 ± 0.04 ‰, 2SD, n = 12) is relatively enriched in light Mg isotopes compared to tholeiitic basalt (- 0.24 ± 0.02 ‰, 2SD, n = 5). In contrast, altered oceanic crust analyzed in this study has heavier Mg isotopic composition (- 0.18 ± 0.08 ‰, 2SD, n = 13) relative to the basalts and to the peridotitic mantle. An evaluation of our and published data shows that the δ26Mg values of most OIBs negatively correlate with melting-sensitive trace-element ratios, but that they are uncorrelated with source-sensitive elemental ratios. This implies that Mg isotopic variation in most OIBs is largely controlled by variable degrees of partial melting and not by source heterogeneity. Negative correlation between Nb/Zr (or La/Sm) versus δ26Mg suggests that altered oceanic crust with heavier Mg isotopic composition is a more suitable source candidate for common OIBs. However, for a given melting degree, Louisville basalts have lower δ26Mg values than other OIBs, suggesting a different source, e.g. a peridotitic mantle. Modeling calculations suggest that melting of both

  6. Evidence of melting, melt percolation and deformation in a supra-subduction zone (Marum ophiolite complex - Papua New Guinea)

    NASA Astrophysics Data System (ADS)

    Kaczmarek, M. A.; Jonda, L.; Davies, H. L.

    2015-12-01

    New geochemical and microstructural data from the Marum ophiolite in Papua New Guinea describe a piece of most depleted mantle made essentially of dunite and harzburgite showing compositions of supra-subduction zone (SSZ) peridotite. Strong olivine crystallographic preferred orientations (CPO) in dunite and harzburgite inferred the activation of both (001)[100] and (010)[100] slip systems. Clinopyroxene and orthopyroxene CPOs inferred the activation of (100)[001] and (010)[001] slip systems. This plastic deformation is interpreted to have developed at high temperature during the formation of the Marum ophiolite, prior to melt percolation. The orientation of the foliation and olivine [100] slip directions sub-parallel to the subduction zone indicates that mantle flow was parallel to the trench pointing a fast polarization direction parallel to the arc. Marum depleted mantle has been fertilised by diffuse crystallisation of a low proportion of clinopyroxene (1-2%) in the dunite and formation of cm-scale ol-clinopyroxenite and ol-websterite veins cross-cutting the foliation. This percolating melt shows silica-rich magnesian affinities (boninite-like) related to supra-subduction zone in a young fore-arc environment. The peridotite has also been percolated by a melt with more tholeiite affinities precipitating plagioclase-rich wehrlite and thin gabbroic veins; these are interpreted to form after the boninitic event. The small proportion of newly crystallized pyroxene distributed in the dunite shows similar orientation of crystallographic axes to the host dunite (<100>ol parallel to <001>cpx-opx). In contrast, the pyroxenes in ol-clinopyroxenite, ol-websterite and the thin gabbroic veins in the wehrlite, record their own orientation with <001> axes at 45 to 60˚ to olivine <100> axes. For low melt proportion, such as crystallization of pyroxenes in the dunite, the crystallization is governed by epitaxial growth, and when the proportion of melt is higher the newly formed

  7. Structure of the welding zone between titanium and orthorhombic titanium aluminide for explosion welding: II. Local melting zones

    NASA Astrophysics Data System (ADS)

    Grinberg, B. A.; Ivanov, M. A.; Rybin, V. V.; Kuz'min, S. V.; Lysak, V. I.; Elkina, O. A.; Patselov, A. M.; Antonova, O. V.; Inozemtsev, A. V.

    2011-10-01

    The structure and chemical composition of the local melting zones that form during explosion welding of orthorhombic titanium aluminide with commercial-purity titanium near a wavy interface between them are studied. The Rayleigh number is estimated to propose a possible mechanism for the formation of a concentric structure in these zones. Titanium aluminide fragments are detected near the zone boundaries. It is assumed that the fragmentation in the transition zone is caused by the division of a material into loosely coupled microvolumes under the action of a strong external action in a time comparable with the explosion time. Outside the transition zone, fragmentation occurs via a traditional way beginning from dislocation accumulation. Both processes occur in titanium aluminide and only one process (banded structure formation) takes place in titanium.

  8. Phosphorus Zoning Patterns and the Formation of Olivine-Hosted Melt Inclusions

    NASA Astrophysics Data System (ADS)

    Milman-Barris, M. S.; Baker, M.; Beckett, J.; Sobolev, A.; Vielzeuf, D.; Stolper, E.

    2006-12-01

    Melt inclusions, common in Hawaiian olivine (ol) phenocrysts, are used to infer compositional characteristics of parental magmas [1,2]. Here we describe textural associations of melt inclusions in Mauna Kea ol with zoning in phosphorus in the ol host. EMP X-ray maps show that Hawaiian ol phenocrysts are generally unzoned in Fe/Mg, Ca, and Ni, but most are prominently zoned in P (from ~0.006 wt% P2O5, the detection limit, to ~0.2 wt%). P zoning, often oscillatory, generally parallels crystal edges, is texturally variable, and can be present from core to rim. Al and Cr zoning, when present, correlates with P. P-rich zones sometimes outline skeletal, hopper shapes similar to ol morphologies grown in high-cooling rate experiments. Preservation of delicate P zonation in ol phenocrysts likely reflects slow diffusion of P in ol. We studied ol phenocrysts with multiple melt inclusions varying significantly in P2O5 (e.g., 0.3-0.4 to >1 wt% in one ol) to establish whether high-P inclusions are enclosed in high-P ol. Some grains contain inclusions spanning a K/P range (e.g., 0.14-1.86 in one grain), suggesting they are not related to each other by simple crystal fractionation. Although all of our melt-inclusion-bearing ol show melt inclusions to be spatially associated with high-P regions of the crystals, the ol in direct contact with melt inclusions is nearly always low in P. This observation holds true even where both high- and low-P inclusions are associated with the same P-rich ol zone. Moreover, low-P ol zones directly surrounding melt inclusions often cross-cut (and appear to replace) high-P features. In one case, a chevron-shaped wedge of low-P ol surrounding a melt inclusion crosscuts high-P, oscillatory zoned ol. Low-P regions directly around melt inclusions vary from <10 to many 10s of μm across; i.e., most are too large to represent simple crystallization on the inclusion wall. 1-atm cooling rate experiments (15-30°C/hr) on a primitive Mauna Kea basalt

  9. Radar measurements of melt zones on the Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

    Jezek, Kenneth C.; Gogineni, Prasad; Shanableh, M.

    1994-01-01

    Surface-based microwave radar measurements were performed at a location on the western flank of the Greenland Ice Sheet. Here, firn metamorphasis is dominated by seasonal melt, which leads to marked contrasts in the vertical structure of winter and summer firn. This snow regime is also one of the brightest radar targets on Earth with an average backscatter coefficient of 0 dB at 5.3 GHz and an incidence angle of 25 deg. By combining detailed observations of firn physical properties with ranging radar measurements we find that the glaciological mechanism associated with this strong electromagnetic response is summer ice lens formation within the previous winter's snow pack. This observation has important implications for monitoring and understanding changes in ice sheet volume using spaceborne microwave sensors.

  10. The effect of water on the partial melting of peridotite at 3 GPa.

    NASA Astrophysics Data System (ADS)

    Tenner, T. J.; Hirschmann, M. M.

    2008-12-01

    We have investigated the influence of water on partial melting of fertile garnet peridotite by performing experiments with a hydrated synthetic peridotite at 3 GPa. The starting material consists of a synthetic KLB-1 peridotite analog mixed in varying ratios with a synthetic hydrous olivine composition (Mg# of 83 + 10% H2O) to produce starting materials with 1, 1.5, and 2.5 wt.% H2O. Experiments were performed in a Walker-style multianvil apparatus in AuPd and Fe-presaturated AuPd capsules at 1250-1475 °C. Resulting charges consist of liquid+ol+opx±cpx±gt and all phase compositions were analyzed by electron microprobe. Though liquids quench to glass in some experiments, they are more commonly preserved as 20×20 to 100×300 micron pools of heterogeneous quench crystals. For these, extensive analyses are required to reconstruct partial melt compositions. Consequently, we perform ~150 individual microprobe analyses on the quench for each experiment and accept only those analyses (typically 10 to 40 analyses) that yield olivine-liquid Fe-Mg KD values between 0.30 and 0.35. Inferred equilibrium liquid compositions range from basaltic at high temperature to nephelinitic at low temperature. Melt fractions, F, are calculated by mass balance and range from 0.12 to 0.31. As an index of the influence of H2O on melting, we calculate ΔT, which is the difference between the temperature of the experiment and that required to generate that melt fraction under dry conditions, which are inferred from the experiments of Walter (1998) and from those of Davis and Hirschmann (in prep). For experiments in AuPd capsules, small corrections for iron loss are also required. Calculated values of ΔT as a function of dissolved H2O concentration are inferred by mass balance, and conservation of H2O during experiments can be investigated by FTIR on glassy quench products. The ΔT vs. H2O in the melt trend shows excellent agreement with previous determinations at lower pressure. This simple

  11. Experimental study of continental crust partial melting: rheological and microstructure effects.

    NASA Astrophysics Data System (ADS)

    Fauconnier, Julien; Stünitz, Holger; Rosenberg, Claudio; Labrousse, Loïc; Jolivet, Laurent

    2014-05-01

    Deformation on the orogen-scales involves localization due to weakening, and partial melting of the continental crust is one of the most important weakening agent. In order to understand the causes of melt-induced weakening and the way melt moves through an anisotropic medium (generally consisting of a foliation and/or layering) we conducted a series of high-pressure experiments to deform partially molten, crustal-like materials and compare the experimental microstructures with those of natural migmatites. Deformation experiments were performed in simple shear mode in a Griggs-type apparatus. The starting material consists of 90% quartz powder (crushed Fontainebleau sandstone; 10 to 20 µm grain size) and 10% biotite powder (50 to 100 µm grain size). In order to control the amount of melt, 5% to 10% of haplogranitic glass (HPG) were added to the starting material. Experiments were performed in the biotite stability field, but above the HPG transition temperature (1 GPa confining pressure, temperature between 700°C and 900°C). Deformation took place at a strain rate of 10-5 s-1,to a finite shear strain of up to γ ≡ 4. Our first results show the following features: (1) The presence of melt weakens the sample only during the first increments of deformation (below γ ≡ 2) compared to experiments without glass. (2) Small amounts of weak phase (5% HPG or 10% biotite) result in the nucleation of shear bands which localize deformation. (3) Larger amounts of melt (10% HPG) are associated with weakening by a factor of 3 compared to 5% melt samples, accompanied by a more homogeneously distributed deformation and absence of shear bands. The increase from 5 to 10% HPG changes the microstructures from dominant crystal plasticity of quartz to microstructures indicating grain boundary sliding. (4) Surprisingly, the weakening caused by 5% HPG in a pure quartz sample at 800°C (i.e. 5% melt) is very similar to the weakening effect of 10% biotite (after γ ≡ 2) without melt

  12. Melting of Bi-2212 under controlled oxygen partial pressures with silver

    NASA Astrophysics Data System (ADS)

    Lang, Th.; Buhl, D.; Gauckler, L. J.

    1997-02-01

    The solidus temperature Tsolidus of Bi 2Sr 2CaCu 2O x (Bi-2212) is decreased from 893°C to 880°C and further down to 834°C when the oxygen partial pressure of the atmosphere is changed from pO 2 = 1 atm to 0.21 atm and further to 0.001 atm. Silver additions to the superconductor exceeding 2 wt% lower Tsolidus by up to 25 K in a pure oxygen atmosphere. The weight loss during melting, which is related to oxygen release, is highest at low oxygen partial pressures and can be reduced by silver additions due to increased oxygen solubility of the Bi-2212 melt in presence of dissolved silver. The experimental results are compared with thermodynamic data of the BiSrCaCuO system.

  13. Phase-Change Characteristic Analysis of Partially Melted Sodium Acetate Trihydrate Using DSC

    NASA Astrophysics Data System (ADS)

    Jin, Xing; Medina, Mario A.; Zhang, Xiaosong; Zhang, Shuanglong

    2014-01-01

    Sodium acetate trihydrate (SAT), which is a kind of phase-change material, offers high potential for application in thermal energy storage. However, SAT has a natural tendency to supercool during its solidification process. Adding nucleating agents has been suggested as a possible solution. In this paper, the phase-change characteristics of the partially melted SAT were analyzed using a differential scanning calorimeter (DSC). A phenomenon related to SAT undergoing phase change was discovered and analyzed. The results showed that if SAT were cooled when it was partially melted, it would release heat and quickly solidify without adding any nucleating agents. Therefore, if the temperature range of SAT was controlled properly, supercooling could be significantly prevented.

  14. Experimental Measurement of Frozen and Partially Melted Water Droplet Impact Dynamics

    NASA Technical Reports Server (NTRS)

    Palacios, Jose; Yan, Sihong; Tan, Jason; Kreeger, Richard E.

    2014-01-01

    High-speed video of single frozen water droplets impacting a surface was acquired. The droplets diameter ranged from 0.4 mm to 0.9 mm and impacted at velocities ranging from 140 m/sec to 309 m/sec. The techniques used to freeze the droplets and launch the particles against the surfaces is described in this paper. High-speed video was used to quantify the ice accretion area to the surface for varying impact angles (30 deg, 45 deg, 60 deg), impacting velocities, and break-up angles. An oxygen /acetylene cross-flow flame used to ensure partial melting of the traveling frozen droplets is also discussed. A linear relationship between impact angle and ice accretion is identified for fully frozen particles. The slope of the relationship is affected by impact speed. Perpendicular impacts, i.e. 30 deg, exhibited small differences in ice accretion for varying velocities, while an increase of 60% in velocity from 161 m/sec to 259 m/sec, provided an increase on ice accretion area of 96% at an impact angle of 60 deg. The increase accretion area highlights the importance of impact angle and velocity on the ice accretion process of ice crystals. It was experimentally observed that partial melting was not required for ice accretion at the tested velocities when high impact angles were used (45 and 60 deg). Partially melted droplets doubled the ice accretion areas on the impacting surface when 0.0023 Joules were applied to the particle. The partially melted state of the droplets and a method to quantify the percentage increase in ice accretion area is also described in the paper.

  15. Smelting furnace melt zone wall modification to cope higher production rate operation

    NASA Astrophysics Data System (ADS)

    Prayoga, Antonius

    2017-01-01

    PT Smelting adopted the Mitsubishi Continuous Technology for its copper smelter plant which has been operating since 1998. Through a series of expansion projects, the plant annual production capacity increased gradually from 200,000 to 300,000 tons of copper. There were no significant modification works for smelter plant to reach the 50% additional capacity. It was mostly achieved by intensifying the furnaces operation by increasing oxygen content in the furnaces blowing-air. Intensive smelting furnace operation has caused shorter campaign life of some furnace refractory, especially the melt zone wall on the furnace outlet side. During each furnace relining, which is done once in every two years, severe wall erosion was found. The worst condition occurred in year 2007 when the smelting furnace experienced a melt leak through the eroded wall beneath the bath-line coolers. During the 2008 furnace relining, a modification was performed by installing vertical coolers behind the melt zone wall The additional vertical coolers were installed during the 2012 furnace relining to extend the coverage area. The modification improved melt zone wall healthiness significantly by keeping them safely within the two-year campaign life. Recently a modeling study was done to estimate the influences of molten waves on furnace wall erosion. The study was aimed to predict the impact of blowing parameters such as blowing air velocity, on the melt wave character and wall erosion.

  16. Experimental Constraints on CO2 Solubility in Rhyolitic Slab Melts - Implications for Carbon Flux in Subduction Zone

    NASA Astrophysics Data System (ADS)

    Duncan, M. S.; Dasgupta, R.

    2014-12-01

    Understanding the fate of carbon in subduction zones is critical to understand carbon cycle on a global scale. The amount of carbonate and reduced (organic) carbon that is subducted and the amount of CO2 that is released from arc volcanoes vary for subduction zones around the globe. If the agent of carbon transfer from slab to sub-arc mantle is a partial melt of either ocean-floor sediments [1] or hydrous basalt [2], we need to know the solubility of CO2 in rhyolitic slab melt to constrain the flux of carbon in subduction zones. Our previous experiments have constrained CO2 content in silicic slab melts as a function of P (1.5-3.0 GPa) and melt H2O content (0.5-3.0 wt.%) [3]. Here we extend our experiments to constrain the effect of temperature (1100-1400 °C) and fO2 (CO2 vapor-saturated [3] and graphite-saturated) on CO2 solubility and speciation in natural rhyolitic melts. From our data, we constructed empirical and thermodynamic models to calculate CO2 content in slab melts at P and T appropriate for the sub-arc region of the subducting slab at variable fO2 [4]. These experiments and models show that CO2 solubility increases with increasing P, fO2, and melt H2O contents to ~3.5 wt.%, while there is a only slight increase in CO2 solubility with increasing T though the effect is much smaller. Our study constrains the extent of C-cycling to the deep interior and to the arc source for graphite-saturated domains of the downgoing crust. Further, there is a general correspondence between CO2 solubility in slab-derived, rhyolitic melts at sub-arc depth with measured CO2 outflux at arcs [5]. For hotter slabs (T>800 °C) the calculated CO2 contents using our thermodynamic model, for example, are 1.5-3.4 wt.% for a low-H2O melt generated near the FMQ buffer and correspond to arc fluxes of 50-500 × 109 mol/yr. For colder slabs (T<800 °C) the calculated CO2 contents are 0.9-1.6 wt.% for a low-H2O melt generated near the FMQ buffer and correspond to arc fluxes of 0.1-15

  17. Partial melting and the efficiency of mantle outgasing in one-plate planets

    NASA Astrophysics Data System (ADS)

    Plesa, Ana-Catalina; Breuer, Doris

    2013-04-01

    The generation of partial melting can have a major impact on the thermo-chemical evolution of a terrestrial body by the depletion of the mantle material in incompatible elements such as radioactive elements and volatiles, crust formation and volcanic outgassing. During some period in the thermal history of a terrestrial planet, the temperature in regions of the upper mantle, either below tectonic plates or a stagnant lid, rises above the solidus - the temperature at which the mineral with the lowest melting temperature among those that form the silicate mantle mixture starts to melt. The melt than rises toward the surface, forms the crust, and releases volatiles into the atmosphere. In case of one-plate (stagnant lid) planets the thickness of the present-day crust can 'tell' us already about the efficiency of mantle melting and mantle degassing - the thicker the crust the more mantle material experienced melting and thus the more efficient can be the outgassing. However, it has been shown with parameterized convection models [1] but also 2-3D convection models [2] that crustal delamination is a common process in one-plate planets. Crustal delamination allows that possibly much more crust is produced during the entire evolution (and thus more mantle material experienced differentiation) than what is observed today, implying also more efficient outgassing than expected. Crustal delamination is therefore a process that may help to generate a substantial planetary atmosphere. In the present work we investigate the influence of partial melt on mantle dynamics and the volcanic outgassing of one-plate planets using the mantle convection code GAIA [3] in a 2D cylindrical geometry. We consider the depletion of the mantle, redistribution of radioactive heat sources between mantle and crust, as well as mantle dehydration and volcanic outgassing [4]. When melt is extracted to form the crust, the mantle material left behind is more buoyant than its parent material and depleted

  18. Deformation and melt transport in a highly depleted peridotite massif from the Canadian Cordillera: Implications to seismic anisotropy above subduction zones

    NASA Astrophysics Data System (ADS)

    Tommasi, Andréa; Vauchez, Alain; Godard, Marguerite; Belley, France

    2006-12-01

    Seismic anisotropy in subduction zones results from a combination of various processes. Although it depends primarily on the orientation of olivine in response to flow, the presence of water and melt in the wedge may modify the deformation of olivine. The melt distribution also influences anisotropy. Direct observations of the deformation and melt-rock interactions in a strongly depleted spinel-harzburgite massif from the Cache Creek terrane in the Canadian Cordillera allow evaluating the relative contribution of each process. Structural mapping shows that this massif has recorded high-temperature, low-stress deformation, high degrees of partial melting, and synkinematic melt-rock interaction at shallow depths (< 70 km) in the mantle, probably above an oblique subduction. Deformation, marked by shallow-dipping lineations and steep foliations, controlled melt distribution: reactive dunites and pyroxenite dykes are dominantly parallel to the foliation. Analysis of olivine crystal preferred orientations (CPO) indicates deformation by dislocation creep with dominant [100] glide. Glide planes are however different in harzburgites and dunites, suggesting that higher melt contents may favor glide on (001) relative to (010). Seismic properties, calculated by considering explicitly the large-scale structure of the massif, the olivine and pyroxene CPO, and possible melt distributions, show that the strain-induced olivine CPO results in up to 5% P- and S-wave anisotropy with fast seismic directions parallel to the lineation. Synkinematic melt transport by diffuse porous flow leading to melt pockets or dykes aligned in the foliation may significantly enhance this anisotropy, in particular for S-waves. In contrast, focused melt flow is not recorded by seismic anisotropy, unless associated with very high instantaneous melt fractions. Orientation of pyroxenite dykes suggests that the present orientation of the structures is representative of the pre-obduction situation, implying

  19. Chlorine and fluorine partition coefficients and abundances in sub-arc mantle xenoliths (Kamchatka, Russia): Implications for melt generation and volatile recycling processes in subduction zones

    NASA Astrophysics Data System (ADS)

    Bénard, A.; Koga, K. T.; Shimizu, N.; Kendrick, M. A.; Ionov, D. A.; Nebel, O.; Arculus, R. J.

    2017-02-01

    We report chlorine (Cl) and fluorine (F) abundances in minerals, interstitial glasses, and melt inclusions in 12 andesite-hosted, spinel harzburgite xenoliths and crosscutting pyroxenite veins exhumed from the sub-arc lithospheric mantle beneath Avacha volcano in the Kamchatka Arc (NE Russia). The data are used to calculate equilibrium mineral-melt partition coefficients (D mineral / melt) for Cl and F relevant to subduction-zone processes and unravel the history of volatile depletion and enrichment mechanisms in an arc setting. Chlorine is ∼100 times more incompatible in pyroxenes (DClmineral/melt = 0.005-0.008 [±0.002-0.003]) than F (DFmineral/melt = 0.50-0.57 [±0.21-0.24]), which indicates that partial melting of mantle sources leads to strong depletions in Cl relative to F in the residues. The data set in this study suggests a strong control of melt composition on DCl,Fpyroxene/melt, in particular H2O contents and Al/(Al + Si), which is in line with recent experiments. Fluorine is compatible in Ca-amphibole in the 'wet' sub-arc mantle (DFamphibole/melt = 3.5-3.7 [±1.5]) but not Cl (DClamphibole/melt = 0.03-0.05 [±0.01-0.03]), indicating that amphibole may fractionate F from Cl in the mantle wedge. The inter-mineral partition coefficients for Cl and F in this study are consistent amongst different harzburgite samples, whether they contain glass or not. In particular, disseminated amphibole hosts much of the Cl and F bulk rock budgets of spinel harzburgites (DClamphibole/pyroxene up to 14 and DFamphibole/pyroxene up to 40). Chlorine and fluorine are variably enriched (up to 1500 ppm Cl and 750 ppm F) in the parental arc picrite and boninite melts of primitive pyroxenite veins (and related melt inclusions) crosscutting spinel harzburgites.

  20. Steps in the transition of an entangled polymer melt to the partially crystalline state

    NASA Astrophysics Data System (ADS)

    Heck, B.; Hugel, T.; Iijima, M.; Sadiku, E.; Strobl, G.

    1999-11-01

    For s-polypropylene, three different s-poly(propene-co-octene)s, two poly(ethylene-co-octene)s and poly(ɛ-caprolactone) we determined the relationships between the crystallization temperature Tc, the crystal thickness dc and the melting peak temperature Tf by carrying out time- and temperature-dependent small-angle x-ray scattering experiments. As a general law, dc is found to be inversely proportional to the supercooling below a characteristic temperature, Tc∞, which is always located above the equilibrium melting point following from an application of the Gibbs-Thomson equation. Tc∞ is not (for the polypropylene-based copolymers) or only weakly (for the polyethylene-based copolymers) dependent on the co-unit content. The `crystallization line' Tc versus dc-1 and the Gibbs-Thomson melting line Tf versus dc-1 limit the range of the accessible partially crystalline states. The occurrence of two well defined independent boundary lines may be understood as indicating that the transformation from the melt into the partially crystalline state is generally, for homopolymers and copolymerized derivatives likewise, a two-step process, beginning with the building up of an initial form of lower order at the crystallization line which then becomes stabilized to end up in the state with layer-like morphology melting at Tf. Stabilization is achieved without a change in dc. AFM and TEM observations suggest that the initial structure could be composed of crystal blocks in planar assemblies. The stabilization then would result from their merging into a continuous lamella. It is proposed that the size of the blocks represents the minimum necessary to retain intrinsic stability. As a further result it was found that crystallinities reached at the end of isothermal crystallization processes remain invariant over larger ranges of Tc, in contrast to the changing length scales of the structure.

  1. Melting in the Mantle Wedge: Quantifying the Effects of Crustal Thickening and Viscous Decoupling on Melt Production with Application to the Cascadia Subduction Zone

    NASA Astrophysics Data System (ADS)

    Yang, J.; Rudolph, M. L.; Karlstrom, L.

    2016-12-01

    Arc magmatism is sustained by the complex interactions between the subducting slab, the overriding plate, and the mantle wedge. Partial melting of mantle peridotite is achieved by fluid induced flux melting and decompression melting due to upward flow. The distribution of melting is sensitive to temperature, the pattern of flow, and the pressure in the mantle wedge. The arc front is the surface manifestation of partial melting in the mantle wedge and is characterized by a narrow chain of active volcanoes that migrate in time. The conventional interpretation is that changes in slab dip angle lead to changes in the arc front position relative to the trench. We explore an alternative hypothesis: evolution of the overlying plate, specifically thickening of the arc root, causes arc front migration. We investigate the effects of crustal thickening and viscous decoupling of the shallow slab-mantle interface on melt production using 2D numerical models involving a stationary overriding plate, a subducting plate with prescribed motion, and a dynamic mantle wedge. Melt production is quantified using a hydrous melting parameterization. We conclude that crustal thickening beneath the arc front modifies the rate of melt production and induces a separation in fore-arc and back-arc mantle melt generation; and viscous decoupling limits the trenchward extent of melt production.

  2. Partial melting in one-plate planets: Implications for thermo-chemical and atmospheric evolution

    NASA Astrophysics Data System (ADS)

    Plesa, A.-C.; Breuer, D.

    2014-08-01

    In the present work, we investigate the influence of partial melting on mantle dynamics, crustal formation, and volcanic outgassing of a one-plate planet using a 2D mantle convection code. When melt is extracted to form crust, the mantle material left behind is more buoyant than its parent material and depleted in radioactive heat sources. The extracted heat-producing elements are then enriched in the crust, which also has an insulating effect due to its lower thermal conductivity compared to the mantle. In addition, partial melting can influence the mantle rheology through the dehydration (water depletion) of the mantle material by volcanic outgassing. As a consequence, the viscosity of water-depleted regions increases more than two orders of magnitude compared to water-saturated rocks resulting in slower cooling rates. The most important parameter influencing the thermo-chemical evolution is the assumed density difference between the primitive and the depleted mantle material (i.e., between peridotite and harzburgite). With small or negligible values of compositional buoyancy, crustal formation including crustal delamination is very efficient, also resulting in efficient processing and degassing of the mantle. The convecting mantle below the stagnant lid depletes continuously with time. In contrast, with increasing compositional buoyancy, crustal formation and mantle degassing are strongly suppressed although partial melting is substantially prolonged in the thermal evolution. The crust shows strong lateral variations in thickness, and crustal delamination is reduced and occurs only locally. Furthermore, two to four different mantle reservoirs can form depending on the initial temperature distribution. Two of these reservoirs can be sustained during the entire evolution - a scenario possibly valid for Mars as it may explain the isotope characteristic of the Martian meteorites.

  3. Silica-undersaturated reaction zones at a crust-mantle interface in the Highland Complex, Sri Lanka: Mass transfer and melt infiltration during high-temperature metasomatism

    NASA Astrophysics Data System (ADS)

    Fernando, G. W. A. R.; Dharmapriya, P. L.; Baumgartner, Lukas P.

    2017-07-01

    Sri Lanka is a crucial Gondwana fragment mostly composed of granulitic rocks in the Highland Complex surrounded by rocks with granulite to amphibolite grade in the Vijayan and Wanni Complex that were structurally juxtaposed during Pan-African orogeny. Fluids associated with granulite-facies metamorphism are thought to have controlled various lower crustal processes such as dehydration/hydration reactions, partial melting, and high-temperature metasomatism. Chemical disequilibrium in the hybrid contact zone between a near peak post-tectonic ultramafic enclave and siliceous granulitic gneiss at Rupaha within the Highland Complex produced metasomatic reaction zones under the presence of melt. Different reaction zones observed in the contact zone show the mineral assemblages phlogopite + spinel + sapphirine (zone A), spinel + sapphirine + corundum (zone B), corundum ( 30%) + biotite + plagioclase zone (zone C) and plagioclase + biotite + corundum ( 5%) zone (zone D). Chemical potential diagrams and mass balance reveal that the addition of Mg from ultramafic rocks and removal of Si from siliceous granulitic gneiss gave rise to residual enrichment of Al in the metasomatized mineral assemblages. We propose that contact metasomatism between the two units, promoted by melt influx, caused steady state diffusional transport across the profile. Corundum growth was promoted by the strong residual Al enrichment and Si depletion in reaction zone whereas sapphirine may have been formed under high Mg activity near the ultramafic rocks. Modelling also indicated that metasomatic alteration occurred at ca. 850 °C at 9 kbar, which is consistent with post-peak metamorphic conditions reached during the initial stage of exhumation in the lower crust and with temperature calculations based on conventional geothermometry.

  4. Mantle Partial Melting Beneath Gakkel Ridge Reflected in the Petrography of Spinel Lherzolites

    NASA Astrophysics Data System (ADS)

    Snow, J. E.; Dick, H.; Buechl, A.; Michael, P.; Hellebrand, E.; Ship Sc Parties HEALY 102-POLARSTERN 59,; Ship Sc Parties HEALY 102-POLARSTERN 59,; Ship Sc Parties HEALY 102-POLARSTERN 59,

    2001-12-01

    One of the main aims of the AMORE expedition to Gakkel Ridge was to investigate the nature of mantle residues of low-degree partial melting. Previous results from a single sample of highly serpentinized Gakkel peridotite were unable to conclusively resolve many of the issues of mantle melting and mantle veining involved (1). We have made a preliminary examination of 46 thin sections and hundreds of hand samples of mantle peridotites made on board PFS POLARSTERN and HEALY in the course of the expedition. Most of these peridotites are altered 60-90%, like most abyssal peridotites. Some however are stunningly fresh, containing no detectable serpentine in thin section. The distribution of mantle rock types is similar to that from other mid-ocean ridges. Dunites are present but rare, in contrast to the SW Indian Ridge oblique spreading center at 12° E, as are plagioclase peridotites, in contrast to their abundance at Molloy Ridge further south on the arctic ridge system. There are two differences between this sample set and those commonly observed on mid-ocean ridges that are of particular note. First is the relative abundance of clinopyroxene. The mean clinopyroxene content and size observed in thin section are both qualitatively greater than is commonly observed in abyssal peridotites. Second, the spinels are more nearly euhedral, more abundant and commonly very pale in color. The pale color is well known to be a sign of low Cr content (and thus high activity of Al) in the residual system. All of these observations suggest a low degree of partial melting in the Gakkel Ridge mantle, in accordance with theoretical predictions. What has not been observed to date in even the largest and freshest samples is any evidence of significant mantle veining. It may be that mantle veins have sufficiently low solidi that they melt out completely without a trace even at the lowest degrees of partial melting. The petrographic evidence however suggests that there never was significant

  5. Preservation of a nebular mg-Delta O-17 correlation during partial melting of ureilites

    NASA Astrophysics Data System (ADS)

    Goodrich, Cyrena A.

    1997-03-01

    Ureilites are a class of over 50 achondrites that display a bewildering mix of igneous and primitive characteristics. This work addresses the apparent incompatibility of the mineralogy and lithophile element chemistry of ureilites with their oxygen isotopic characteristics. One problem presented by the oxygen isotopic characteristics of ureilites is that ureilites show a correlation of the olivine and pyroxene mg ratio with delta O-17. Such correlations are otherwise observed only in very primitive materials such as among chondrules and their rims in Allende, and among the H-L-LL ordinary chondrite groups. The question is whether a nebular mg-delta O-17 correlation could survive the partial melting necessary to produce ureilites from chondritic material. Goodrich (1992) assumed that it could not, because ureilites would not be expected to have all undergone precisely the same degree of melting. Results of model calculations are presented here to test this assumption. From the results, it does appear that a nebular mg-delta O-17 correlation could survive the partial melting required to produce ureilites from chondritic material. Questions, however, still remain, and are posed at the conclusion of the paper.

  6. Petit-spot as definitive evidence for partial melting in the asthenosphere caused by CO2

    NASA Astrophysics Data System (ADS)

    Machida, Shiki; Kogiso, Tetsu; Hirano, Naoto

    2017-02-01

    The deep carbon cycle plays an important role on the chemical differentiation and physical properties of the Earth's mantle. Especially in the asthenosphere, seismic low-velocity and high electrical conductivity due to carbon dioxide (CO2)-induced partial melting are expected but not directly observed. Here we discuss the experimental results relevant to the genesis of primitive CO2-rich alkali magma forming petit-spot volcanoes at the deformation front of the outer rise of the northwestern Pacific plate. The results suggest that primitive melt last equilibrated with depleted peridotite at 1.8-2.1 GPa and 1,280-1,290 °C. Although the equilibration pressure corresponds to the pressure of the lower lithosphere, by considering an equilibration temperature higher than the solidus in the volatile-peridotite system along with the temperature of the lower lithosphere, we conclude that CO2-rich silicate melt is always produced in the asthenosphere. The melt subsequently ascends into and equilibrates with the lower lithosphere before eruption.

  7. Petit-spot as definitive evidence for partial melting in the asthenosphere caused by CO2.

    PubMed

    Machida, Shiki; Kogiso, Tetsu; Hirano, Naoto

    2017-02-02

    The deep carbon cycle plays an important role on the chemical differentiation and physical properties of the Earth's mantle. Especially in the asthenosphere, seismic low-velocity and high electrical conductivity due to carbon dioxide (CO2)-induced partial melting are expected but not directly observed. Here we discuss the experimental results relevant to the genesis of primitive CO2-rich alkali magma forming petit-spot volcanoes at the deformation front of the outer rise of the northwestern Pacific plate. The results suggest that primitive melt last equilibrated with depleted peridotite at 1.8-2.1 GPa and 1,280-1,290 °C. Although the equilibration pressure corresponds to the pressure of the lower lithosphere, by considering an equilibration temperature higher than the solidus in the volatile-peridotite system along with the temperature of the lower lithosphere, we conclude that CO2-rich silicate melt is always produced in the asthenosphere. The melt subsequently ascends into and equilibrates with the lower lithosphere before eruption.

  8. Petit-spot as definitive evidence for partial melting in the asthenosphere caused by CO2

    PubMed Central

    Machida, Shiki; Kogiso, Tetsu; Hirano, Naoto

    2017-01-01

    The deep carbon cycle plays an important role on the chemical differentiation and physical properties of the Earth's mantle. Especially in the asthenosphere, seismic low-velocity and high electrical conductivity due to carbon dioxide (CO2)-induced partial melting are expected but not directly observed. Here we discuss the experimental results relevant to the genesis of primitive CO2-rich alkali magma forming petit-spot volcanoes at the deformation front of the outer rise of the northwestern Pacific plate. The results suggest that primitive melt last equilibrated with depleted peridotite at 1.8–2.1 GPa and 1,280–1,290 °C. Although the equilibration pressure corresponds to the pressure of the lower lithosphere, by considering an equilibration temperature higher than the solidus in the volatile–peridotite system along with the temperature of the lower lithosphere, we conclude that CO2-rich silicate melt is always produced in the asthenosphere. The melt subsequently ascends into and equilibrates with the lower lithosphere before eruption. PMID:28148927

  9. The Behavior of Pyroxenes During Partial Melting of Pyroxenite and Lherzolite in the Mantle: An Experimental and Numerical Study

    NASA Astrophysics Data System (ADS)

    Lo Cascio, M.; Liang, Y.

    2004-12-01

    Pyroxenes are the primary phases involved in partial melting of peridotite and pyroxenite lithologies in the upper mantle. In order to better understand the grain-scale processes of pyroxene melting and their effects on major and trace element distributions during magma generation, we carried out a series of kinetic melting experiments using reaction couple method. Partial melting experiments were conducted at 1340° C and 1.5 GPa for 72 hrs using reaction couples formed by juxtaposing pre-synthesized rods of orthopyroxenite (90% opx, 5% olivine, 5% melt) against clinopyroxenite (90% cpx + 10% melt). These laboratory experiments were supplemented by numerical simulations of partial melting in binary and ternary systems. Reaction between orthopyroxenite and clinopyroxenite at 1340° C and 1.5GPa results in a reactive boundary layer (RBL, 240 μ m after 72 hrs) that consists of euhedral olivine (35%), cpx (45%), and melt (20%). The RBL is located on the orthopyroxenite side of the original interface. The grain sizes of ol and cpx in the RBL are significantly larger than those in the orthopyroxenite and the clinopyroxenite. Clinopyroxene compositions vary systematically across the RBL, for example the Na2O and TiO2 content decrease from 1.05% and 0.35%, respectively, in the clinopyroxenite to 0.83% and 0.14% at the orthopyroxenite-RBL interface. The melt is concentrated in the RBL and appears to localize in those areas where olivine grains are more densely accumulated. The average melt in the RBL is a ne-normative alkali basalt (10.6% MgO, 49.2% SiO2, 4.7% Na2O, 0.28% K2O) and has relatively high Al2O3 (15.5%) and CaO (10.7%). The characteristics of increasing grain size and varying cpx and melt compositions in the RBL are very similar to those observed in our clinopyroxenite-harzburgite partial melting experiments [1], consistent with the grain-scale melting processes that involve dissolution of opx at the orthopyroxenite-RBL interface, precipitation of ol and new

  10. Breeding bird response to partially harvested riparian management zones

    USGS Publications Warehouse

    Chizinski, Christopher J.; Peterson, Anna; Hanowski, JoAnn; Blinn, Charles R.; Vondracek, Bruce C.; Niemi, Gerald

    2011-01-01

    We compared avian communities among three timber harvesting treatments in 45-m wide even-age riparian management zones (RMZs) placed between upland clearcuts and along one side of first- or second-order streams in northern Minnesota, USA. The RMZs had three treatments: (1) unharvested, (2) intermediate residual basal area (RBA) (targeted goal 11.5 m2/ha, realized 16.0 m2/ha), and (3) low RBA (targeted goal 5.7 m2/ha, realized 8.7 m2/ha). Surveys were conducted one year pre-harvest and three consecutive years post-harvest. There was no change in species richness, diversity, or total abundance associated with harvest but there were shifts in the types of birds within the community. In particular, White-throated Sparrows (Zonotrichia albicollis) and Chestnut-sided Warblers (Dendroica pensylvanica) increased while Ovenbirds (Seiurus aurocapilla) and Red-eyed Vireos (Vireo olivaceus) decreased. The decline of avian species associated with mature forest in the partially harvested treatments relative to controls indicates that maintaining an unharvested RMZ adjacent to an upland harvest may aid in maintaining avian species associated mature forest in Minnesota for at least three years post-harvest. However, our observations do not reflect reproductive success, which is an area for future research.

  11. Subduction of fracture zones controls mantle melting and geochemical signature above slabs.

    PubMed

    Manea, Vlad C; Leeman, William P; Gerya, Taras; Manea, Marina; Zhu, Guizhi

    2014-10-24

    For some volcanic arcs, the geochemistry of volcanic rocks erupting above subducted oceanic fracture zones is consistent with higher than normal fluid inputs to arc magma sources. Here we use enrichment of boron (B/Zr) in volcanic arc lavas as a proxy to evaluate relative along-strike inputs of slab-derived fluids in the Aleutian, Andean, Cascades and Trans-Mexican arcs. Significant B/Zr spikes coincide with subduction of prominent fracture zones in the relatively cool Aleutian and Andean subduction zones where fracture zone subduction locally enhances fluid introduction beneath volcanic arcs. Geodynamic models of subduction have not previously considered how fracture zones may influence the melt and fluid distribution above slabs. Using high-resolution three-dimensional coupled petrological-thermomechanical numerical simulations of subduction, we show that enhanced production of slab-derived fluids and mantle wedge melts concentrate in areas where fracture zones are subducted, resulting in significant along-arc variability in magma source compositions and processes.

  12. Origins of ultralow velocity zones through slab-derived metallic melt

    DOE PAGES

    Liu, Jiachao; Li, Jie; Hrubiak, Rostislav; ...

    2016-05-03

    Understanding the ultralow velocity zones (ULVZs) places constraints on the chemical composition and thermal structure of deep Earth and provides critical information on the dynamics of large-scale mantle convection, but their origin has remained enigmatic for decades. Recent studies suggest that metallic iron and carbon are produced in subducted slabs when they sink beyond a depth of 250 km. Here we show that the eutectic melting curve of the iron-carbon system crosses the current geotherm near Earth’s core-mantle boundary, suggesting that dense metallic melt may form in the lowermost mantle. If concentrated into isolated patches, such melt could produce themore » seismically observed density and velocity features of ULVZs. Depending on the wetting behavior of the metallic melt, the resultant ULVZs may be short-lived domains that are replenished or regenerated through subduction, or long-lasting regions containing both metallic and silicate melts. Slab-derived metallic melt may produce another type of ULVZ that escapes core sequestration by reacting with the mantle to form iron-rich post-bridgmanite or ferropericlase. The hypotheses connect peculiar features near Earth’s core-mantle boundary to subduction of the oceanic lithosphere through the deep carbon cycle.« less

  13. Origins of ultralow velocity zones through slab-derived metallic melt

    PubMed Central

    Liu, Jiachao; Li, Jie; Smith, Jesse S.

    2016-01-01

    Understanding the ultralow velocity zones (ULVZs) places constraints on the chemical composition and thermal structure of deep Earth and provides critical information on the dynamics of large-scale mantle convection, but their origin has remained enigmatic for decades. Recent studies suggest that metallic iron and carbon are produced in subducted slabs when they sink beyond a depth of 250 km. Here we show that the eutectic melting curve of the iron−carbon system crosses the current geotherm near Earth’s core−mantle boundary, suggesting that dense metallic melt may form in the lowermost mantle. If concentrated into isolated patches, such melt could produce the seismically observed density and velocity features of ULVZs. Depending on the wetting behavior of the metallic melt, the resultant ULVZs may be short-lived domains that are replenished or regenerated through subduction, or long-lasting regions containing both metallic and silicate melts. Slab-derived metallic melt may produce another type of ULVZ that escapes core sequestration by reacting with the mantle to form iron-rich postbridgmanite or ferropericlase. The hypotheses connect peculiar features near Earth's core−mantle boundary to subduction of the oceanic lithosphere through the deep carbon cycle. PMID:27143719

  14. Origins of ultralow velocity zones through slab-derived metallic melt

    SciTech Connect

    Liu, Jiachao; Li, Jie; Hrubiak, Rostislav; Smith, Jesse S.

    2016-05-03

    Understanding the ultralow velocity zones (ULVZs) places constraints on the chemical composition and thermal structure of deep Earth and provides critical information on the dynamics of large-scale mantle convection, but their origin has remained enigmatic for decades. Recent studies suggest that metallic iron and carbon are produced in subducted slabs when they sink beyond a depth of 250 km. Here we show that the eutectic melting curve of the iron-carbon system crosses the current geotherm near Earth’s core-mantle boundary, suggesting that dense metallic melt may form in the lowermost mantle. If concentrated into isolated patches, such melt could produce the seismically observed density and velocity features of ULVZs. Depending on the wetting behavior of the metallic melt, the resultant ULVZs may be short-lived domains that are replenished or regenerated through subduction, or long-lasting regions containing both metallic and silicate melts. Slab-derived metallic melt may produce another type of ULVZ that escapes core sequestration by reacting with the mantle to form iron-rich post-bridgmanite or ferropericlase. The hypotheses connect peculiar features near Earth’s core-mantle boundary to subduction of the oceanic lithosphere through the deep carbon cycle.

  15. Origins of ultralow velocity zones through slab-derived metallic melt

    SciTech Connect

    Liu, Jiachao; Li, Jie; Hrubiak, Rostislav; Smith, Jesse S.

    2016-05-03

    Understanding the ultralow velocity zones (ULVZs) places constraints on the chemical composition and thermal structure of deep Earth and provides critical information on the dynamics of large-scale mantle convection, but their origin has remained enigmatic for decades. Recent studies suggest that metallic iron and carbon are produced in subducted slabs when they sink beyond a depth of 250 km. Here we show that the eutectic melting curve of the iron-carbon system crosses the current geotherm near Earth’s core-mantle boundary, suggesting that dense metallic melt may form in the lowermost mantle. If concentrated into isolated patches, such melt could produce the seismically observed density and velocity features of ULVZs. Depending on the wetting behavior of the metallic melt, the resultant ULVZs may be short-lived domains that are replenished or regenerated through subduction, or long-lasting regions containing both metallic and silicate melts. Slab-derived metallic melt may produce another type of ULVZ that escapes core sequestration by reacting with the mantle to form iron-rich post-bridgmanite or ferropericlase. The hypotheses connect peculiar features near Earth’s core-mantle boundary to subduction of the oceanic lithosphere through the deep carbon cycle.

  16. Origins of ultralow velocity zones through slab-derived metallic melt.

    PubMed

    Liu, Jiachao; Li, Jie; Hrubiak, Rostislav; Smith, Jesse S

    2016-05-17

    Understanding the ultralow velocity zones (ULVZs) places constraints on the chemical composition and thermal structure of deep Earth and provides critical information on the dynamics of large-scale mantle convection, but their origin has remained enigmatic for decades. Recent studies suggest that metallic iron and carbon are produced in subducted slabs when they sink beyond a depth of 250 km. Here we show that the eutectic melting curve of the iron-carbon system crosses the current geotherm near Earth's core-mantle boundary, suggesting that dense metallic melt may form in the lowermost mantle. If concentrated into isolated patches, such melt could produce the seismically observed density and velocity features of ULVZs. Depending on the wetting behavior of the metallic melt, the resultant ULVZs may be short-lived domains that are replenished or regenerated through subduction, or long-lasting regions containing both metallic and silicate melts. Slab-derived metallic melt may produce another type of ULVZ that escapes core sequestration by reacting with the mantle to form iron-rich postbridgmanite or ferropericlase. The hypotheses connect peculiar features near Earth's core-mantle boundary to subduction of the oceanic lithosphere through the deep carbon cycle.

  17. Origins of ultralow velocity zones through slab-derived metallic melt

    NASA Astrophysics Data System (ADS)

    Liu, Jiachao; Li, Jie; Hrubiak, Rostislav; Smith, Jesse S.

    2016-05-01

    Understanding the ultralow velocity zones (ULVZs) places constraints on the chemical composition and thermal structure of deep Earth and provides critical information on the dynamics of large-scale mantle convection, but their origin has remained enigmatic for decades. Recent studies suggest that metallic iron and carbon are produced in subducted slabs when they sink beyond a depth of 250 km. Here we show that the eutectic melting curve of the iron-carbon system crosses the current geotherm near Earth’s core-mantle boundary, suggesting that dense metallic melt may form in the lowermost mantle. If concentrated into isolated patches, such melt could produce the seismically observed density and velocity features of ULVZs. Depending on the wetting behavior of the metallic melt, the resultant ULVZs may be short-lived domains that are replenished or regenerated through subduction, or long-lasting regions containing both metallic and silicate melts. Slab-derived metallic melt may produce another type of ULVZ that escapes core sequestration by reacting with the mantle to form iron-rich postbridgmanite or ferropericlase. The hypotheses connect peculiar features near Earth's core-mantle boundary to subduction of the oceanic lithosphere through the deep carbon cycle.

  18. Post-collisional adakitic volcanism in the eastern part of the Sakarya Zone, Turkey: evidence for slab and crustal melting

    NASA Astrophysics Data System (ADS)

    Dokuz, Abdurrahman; Uysal, İbrahim; Siebel, Wolfgang; Turan, Mehmet; Duncan, Robert; Akçay, Miğraç

    2013-11-01

    New geochemical and isotopic data for post-collisional Early Eocene and Late Miocene adakitic rocks from the eastern part of the Sakarya Zone, Turkey, indicate that slab and lower crustal melting, respectively, played key roles in the petrogenesis of these rocks. The Early Eocene Yoncalık dacite (54.4 Ma) exhibits high Sr/Y and La/Yb ratios, low Y and HREE concentrations, moderate Mg# (44-65), and relatively high ɛNd and low ISr values, similar to adakites formed by slab melting associated with subduction. Geochemical composition of the Yoncalık dacite cannot be explained by simple crystal fractionation and/or crustal contamination of andesitic parent magma, but is consistent with the participation of different proportions of melts derived from subducted basalt and sediments. Sr/Y correlates horizontally with Rb/Y, and Pb/Nd correlates vertically with Nd isotopic composition, indicating that Sr and Pb budgets are strongly controlled by melt addition from the subducting slab, whereas positive correlations between Th/Nd and Pb/Nd, and Rb/Y and Nb/Y point to some contribution of sediment melt. In addition to low concentrations of heavy rare earth elements (~2-3 times chondrite), a systematic decrease in their concentrations and Nb/Ta ratios with increasing SiO2 contents suggests that slab partial melting occurred in the garnet stability field and that these elements were mobilized by fluid flux. These geochemical and isotopic signatures are best explained by slab breakoff and fusion shortly after the initiation of collision. Although the Late Micone Tavdağı rhyolite (8.75 Ma) has some geochemical features identical to adakites, such as high Sr/Y and La/Yb ratios, low Y and HREE concentrations, other requirements, such as sodic andesite and/or dacite with relatively high MgO and Mg# (>50), relatively high Ni and Cr, low K2O/Na2O (<0.4), high Sr (>400 ppm), for slab-derived adakites are not provided. It is sodic in composition and shows no traces of fractionation

  19. Partial melt in the upper-middle crust of the northwest Himalaya revealed by Rayleigh wave dispersion

    NASA Astrophysics Data System (ADS)

    Caldwell, Warren B.; Klemperer, Simon L.; Rai, Shyam S.; Lawrence, Jesse F.

    2009-11-01

    Seismic shear-wave velocities are sensitive to the partial melts that should be present in the Himalayan orogen if low-viscosity channel flow is active at the present day. We analyzed regional earthquakes in the western Himalaya and Tibet recorded on 16 broadband seismometers deployed across the NW Indian Himalaya, from the Indian platform to the Karakoram Range. We used a multiple filter technique to calculate the group velocity dispersion of fundamental-mode Rayleigh waves, and then inverted the dispersion records to obtain separate one-dimensional shear-wave velocity models for five geologic provinces: the Tibetan plateau, Ladakh arc complex, Indus Tsangpo suture zone, Tethyan Himalaya, and Himalayan thrust belt. Our velocity models show a low-velocity layer (LVL) with 7-17% velocity reduction centered at ~ 30 km depth and apparently continuous from the Tethyan Himalaya to the Tibetan plateau. This LVL shows good spatial correspondence with observations of low resistivity from magnetotelluric studies along the same profile. Of the possible explanations for low velocity and low resistivity in the mid-crust, only the presence of melts or aqueous fluids (or both) satisfactorily explains both sets of observations. Elevated heat flow observed in the NW Himalaya implies that if aqueous fluids are present in the mid-crust, then the mid-crust is well above its solidus. Comparison of our results with laboratory measurements and theoretical models suggests 3-7% melt is present in a channel in the upper-middle crust of the NW Himalaya at the present day, and the physical conditions to enable active channel flow may be present.

  20. Nanogranitoids in garnet clinopyroxenites of the Granulitgebirge (Bohemian Massif): evidence for metasomatism and partial melting?

    NASA Astrophysics Data System (ADS)

    Borghini, Alessia; Ferrero, Silvio; Wunder, Bernd; O'Brien, Patrick J.; Ziemann, Martin A.

    2017-04-01

    Primary nanogranitoids occur in garnet from the garnet clinopyroxenites of the Granulitgebirge, Bohemian Massif. They form clusters in the inner part of the garnet, and may occur both as polycrystalline and glassy inclusions with size from 5 to 20 µm. Because of their random distribution in garnet these inclusions are interpreted as primary inclusions, thus formed during the growth of the garnet. Garnet does not show any major element zoning. Nanogranitoids were identified in garnet clinopyroxenites from two different locations and show slightly different mineral assemblages. Kumdykolite or albite, phlogopite, osumilite, kokchetavite and a variable amount of quartz occur in both locations. However, osumilite is more abundant in one locality and kokchetavite in the other. All these phases are identified using Raman Spectroscopy. Both assemblages are consistent with the origin of these inclusions as former droplets of melt. Nanogranitoids from one locality have been re-homogenized at 1000°C and 22 kbar to a hydrous glass of granodioritic/quartz-monzonitic composition in a piston cylinder apparatus. The chosen experimental conditions correspond to the formation of the host garnet (O'Brien & Rötzler, 2003) and thus of melt entrapment. Nanogranitoid-bearing garnet clinopyroxenites occur in bodies of serpentinized peridotites, hosted in turn in felsic granulites. The garnet clinopyroxenites show granoblastic texture dominated by garnet and clinopyroxene porphyroblasts with a variable amount of interstitial plagioclase, biotite, two generations of amphiboles (brown and green) and rutile and opaque minerals as accessories. The bulk rock composition is basic to intermediate, and the garnet chemistry varies from 24% Alm, 65% Prp and 11% Grs to 38% Alm, 36% Prp and 26 % Grs between one outcrop and the other. The origin of the investigated inclusions could be due to different processes: localized melting of metasomatized mafic rocks with simultaneous production of garnet or

  1. Autochthonous inheritance of zircon through Cretaceous partial melting of Carboniferous plutons: the Arthur River Complex, Fiordland, New Zealand

    NASA Astrophysics Data System (ADS)

    Tulloch, Andrew J.; Ireland, Trevor R.; Kimbrough, David L.; Griffin, William L.; Ramezani, Jahandar

    2011-03-01

    TIMS and SHRIMP U-Pb analyses of zircons from Milford Orthogneiss metadiorite ( P = 1-1.4 GPa; T ≥ 750°C) of the Arthur River Complex of northern Fiordland reveal a bimodal age pattern. Zircons are predominantly either Paleozoic (357.0 ± 4.2 Ma) and prismatic with oscillatory zoning, or Cretaceous (133.9 ± 1.8 Ma) and ovoid with sector or patchy zoning. The younger age component is not observed overgrowing older grains. Most grains of both ages are overgrown by younger Cretaceous (~120 Ma) metamorphic zircon with very low U and Th/U (0.01). We interpret the bimodal ages as indicating initial igneous emplacement and crystallisation of a dioritic protolith pluton at ~357 Ma, followed by Early Cretaceous granulite-facies metamorphism at ~134 Ma, during which a significant fraction (~60%) of the zircon grains dissolved, and subsequently reprecipitated, effectively in situ, in partial melt pockets. The remaining ~40% of original Paleozoic grains were apparently not in contact with the partial melt, remained intact, and show only slight degrees of Pb loss. Sector zoning of the Cretaceous grains discounts their origin by solid state recrystallisation of Paleozoic grains. The alternative explanation—that the Paleozoic component represents a 40% inherited component in an Early Cretaceous transgressive dioritic magma—is considered less likely given the relatively high solubility of zircon in magma of this composition, the absence of 134 Ma overgrowths, the single discrete age of the older component, equivalent time-integrated 177Hf/176Hf compositions of both age groups, and the absence of the Cambrian-Proterozoic detrital zircon that dominates regional Cambro-Ordovician metasedimentary populations. Similar bimodal Carboniferous-Early Cretaceous age distributions are characteristic of the wider Arthur River Complex; 8 of 12 previously dated dioritic samples have a Paleozoic component averaging 51%. Furthermore, the age and chemical suite affinity of these and several

  2. Partial melting of a C-rich asteroid: Lithophile trace elements in ureilites

    NASA Astrophysics Data System (ADS)

    Barrat, Jean-Alix; Jambon, Albert; Yamaguchi, Akira; Bischoff, Addi; Rouget, Marie-Laure; Liorzou, Céline

    2016-12-01

    Ureilites are among the most common achondrites and are widely believed to sample the mantle of a single, now-disrupted, C-rich body. We analyzed 17 ureilite samples, mostly Antarctic finds, and determined their incompatible trace element abundances. In order to remove or reduce the terrestrial contamination, which is marked among Antarctic ureilites by light-REE enrichment, we leached the powdered samples with nitric acid. The residues display consistent abundances, which strongly resemble those of the pristine rocks. All the analyzed samples display light-REE depletions, negative Eu anomalies, low (Sr/Eu∗)n, and (Zr/Eu∗)n ratios which are correlated. Two groups of ureilites (groups A and B) are defined. Compared to group A, group B ureilites, which are the less numerous, tend to be richer in heavy REEs, more light-REE depleted, and display among the deepest Eu anomalies. In addition, olivine cores in group B ureilites tend to be more forsteritic (Mg# = 81.9-95.2) than in group A ureilites (Mg# = 74.7-86.1). Incompatible trace element systematics supports the view that ureilites are mantle restites. REE modeling suggests that their precursors were rather REE-rich (ca. 1.8-2 × CI) and contained a phosphate phase, possibly merrillite. The REE abundances in ureilites can be explained if at least two distinct types of magmas were removed successively from their precursors: aluminous and alkali-rich melts as exemplified by the Almahata Sitta trachyandesite (ALM-A), and Al and alkali-poor melts produced after the exhaustion of plagioclase from the source. Partial melting was near fractional (group B ureilites, which are probably among the least residual samples) to dynamic with melt porosities that did not exceed a couple of percent (group A ureilites). The ureilite parent body (UPB) was almost certainly covered by a crust formed chiefly from the extrusion products of the aluminous and alkali-rich magmas. It is currently uncertain whether the Al and alkali

  3. Probing the atomic structure of basaltic melts generated by partial melting of upper mantle peridotite (KLB-1): Insights from high-resolution solid-state NMR study

    NASA Astrophysics Data System (ADS)

    Park, S. Y.; Lee, S. K.

    2015-12-01

    Probing the structural disorder in multi-component silicate glasses and melts with varying composition is essential to reveal the change of macroscopic properties in natural silicate melts. While a number of NMR studies for the structure of multi-component silicate glasses and melts including basaltic and andesitic glasses have been reported (e.g., Park and Lee, Geochim. Cosmochim. Acta, 2012, 80, 125; Park and Lee, Geochim. Cosmochim. Acta, 2014, 26, 42), many challenges still remain. The composition of multi-component basaltic melts vary with temperature, pressure, and melt fraction (Kushiro, Annu. Rev. Earth Planet. Sci., 2001, 71, 107). Especially, the eutectic point (the composition of first melt) of nepheline-forsterite-quartz (the simplest model of basaltic melts) moves with pressure from silica-saturated to highly undersaturated and alkaline melts. The composition of basaltic melts generated by partial melting of upper mantle peridotite (KLB-1, the xenolith from Kilbourne Hole) also vary with pressure. In this study we report experimental results for the effects of composition on the atomic structure of Na2O-MgO-Al2O3-SiO2 (NMAS) glasses in nepheline (NaAlSiO4)-forsterite (Mg2SiO4)-quartz (SiO2) eutectic composition and basaltic glasses generated by partial melting of upper mantle peridotite (KLB-1) using high-resolution multi-nuclear solid-state NMR. The Al-27 3QMAS (triple quantum magic angle spinning) NMR spectra of NMAS glasses in nepheline-forsterite-quartz eutectic composition show only [4]Al. The Al-27 3QMAS NMR spectra of KLB-1 basaltic glasses show mostly [4]Al and a non-negligible fraction of [5]Al. The fraction of [5]Al, the degree of configurational disorder, increases from 0 at XMgO [MgO/(MgO+Al2O3)]=0.55 to ~3% at XMgO=0.79 in KLB-1 basaltic glasses while only [4]Al are observed in nepheline-forsterite-quartz eutectic composition. The current experimental results provide that the fraction of [5]Al abruptly increases by the effect of

  4. 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

  5. Subduction of Fracture Zones control mantle melting and geochemical signature above slabs

    NASA Astrophysics Data System (ADS)

    Constantin Manea, Vlad; Leeman, William; Gerya, Taras; Manea, Marina; Zhu, Guizhi

    2014-05-01

    The geochemistry of arc volcanics proximal to oceanic fracture zones (FZs) is consistent with higher than normal fluid inputs to arc magma sources. Here, enrichment of boron (B/Zr) in volcanic arc lavas is used to evaluate relative along-strike inputs of slab-derived fluids in the Aleutian, Andean, Cascades, and Trans-Mexican arcs. Significant B/Zr spikes coincide with subduction of prominent FZs in the relatively cool Aleutian and Andean subduction zones, but not in the relatively warm Cascadia and Mexican subduction zones, suggesting that FZ subduction locally enhances fluid introduction beneath volcanic arcs, and retention of fluids to sub-arc depths diminishes with subduction zone thermal gradient. Geodynamic treatments of lateral inhomogeneities in subducting plates have not previously considered how FZs may influence the melt and fluid distribution above the slab. Using high-resolution three-dimensional coupled petrological-thermomechanical numerical simulations of subduction, we show that fluids, including melts and water, concentrate in areas where fracture zones are subducted, resulting in along-arc variability in magma source compositions and processes.

  6. Secondary melting events in Semarkona chondrules revealed by compositional zoning in low-Ca pyroxene

    NASA Astrophysics Data System (ADS)

    Baecker, Bastian; Rubin, Alan E.; Wasson, John T.

    2017-08-01

    It is well established that many chondrules contain relict grains formed in previous generations of chondrules. We here describe evidence that chondrules experienced multiple mesostasis melting events while remaining closed systems. Spheroidal chondrule shapes resulted from surface-tension effects following a primary heating event that caused substantial melting (≳40%) of the precursor assemblages. In some high-FeO chondrules in LL3.00 Semarkona, low-Ca pyroxene phenocrysts show multiple overgrowth layers produced by secondary melting events. We characterized these layers with the electron microprobe in terms of Fe, Ca and Cr in two Semarkona chondrules. The first low-Ca pyroxene overgrowth that forms after a minor heating/melting event has low Ca and Fe; concentrations of these incompatibles gradually increase over the next 8 ± 4 μm until falling temperatures and slowing diffusion caused growth to stop. The next melting event remelts and mixes the local mesostasis; cooling causes growth of a normal igneously zoned layer. In the simplest cases, the Ca concentrations at the minima gradually increase towards the edge of the phenocryst. Heat deposition during heating events varied over a wide range; the weakest events produced recognizable changes in slopes (that we call "inflections" rather than minima). Large fractions of the individual phenocrysts were formed by the process that produced the overgrowth layers. It appears that overgrowth formation stopped when the Ca content of the mesostasis became high enough to make high-Ca pyroxene a liquidus phase. Both Semarkona chondrules include olivine phenocrysts similar in size and modal abundance to the low-Ca pyroxene phenocrysts. Olivine compositional profiles show symmetrical, apparently normal zoning except for asymmetries attributable to the presence of relict grains. Surface compositions of different olivine phenocrysts in the same chondrule are very similar to one another, consistent with growth from

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

    SciTech Connect

    Goldstein, N.E.; Flexser, S.

    1984-12-01

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

  8. Dynamics of partially faceted melt crystal interfaces III: Three-dimensional computational approach and calculations

    NASA Astrophysics Data System (ADS)

    Weinstein, Oleg; Brandon, Simon

    2005-10-01

    The modeling of partially faceted melt-crystal interfaces in bulk melt growth systems has been addressed in a number of recent publications. In particular, in Weinstein and Brandon [J. Crystal Growth 268(1-2) (2004) 299], a method for self-consistent two-dimensional dynamic analysis of such systems while accounting for both macro- and nano-scale phenomena, which result from the coupling between competing kinetic mechanisms and associated thermal fields, was presented. In this manuscript, we report on an extension of this approach to three-dimensional systems. The method is first described in detail after which it is applied to model processes involving the vertical gradient freeze growth both of silicon and of yttrium aluminum garnet. In axisymmetric situations, results are shown to successfully reproduce calculations obtained using the previous two-dimensional modeling approach. Additional results demonstrate a number of important three-dimensional nano- and macro-scale features of the melt-crystal interface. These include observations of the dominant role of the coldest dislocation step source in the case where more than one such dislocation line intersects an advancing facet, a demonstration of the effect of growth rate on the morphology of a multi-faceted interface, and a simple explicit analysis of step flow on an evolving facet.

  9. To the origin of Icelandic rhyolites: insights from partially melted leucocratic xenoliths

    NASA Astrophysics Data System (ADS)

    Gurenko, Andrey A.; Bindeman, Ilya N.; Sigurdsson, Ingvar A.

    2015-05-01

    We have studied glass-bearing leucocratic (granitic to Qz-monzonitic) crustal xenoliths from the Tindfjöll Pleistocene volcanic complex, SW Iceland. The xenoliths consist of strongly resorbed relicts of anorthitic plagioclase, K-rich feldspar and rounded quartz in colorless through pale to dark-brown interstitial glass. Spongy clinopyroxene and/or rounded or elongated crystals of orthopyroxene are in subordinate amount. Magnetite, ilmenite, zircon, apatite, allanite and/or chevkinite are accessory minerals. The xenoliths more likely are relicts of earlier-formed, partially melted Si-rich rocks or quartz-feldspar-rich crystal segregations, which suffered latter interaction with hotter and more primitive magma(s). Icelandic lavas are typically low in δ 18O compared to mantle-derived, "MORB"-like rocks (~5.6 ± 0.2 ‰), likely due to their interaction with, or contamination by, the upper-crustal rocks affected by rain and glacial melt waters. Surprisingly, many quartz and feldspar crystals and associated colorless to light-colored interstitial glasses of the studied xenoliths are not low but high in δ 18O (5.1-7.2 ‰, excluding three dark-brown glasses of 4-5 ‰). The xenoliths contain abundant, low- to high- δ 18O (2.4-6.3 ‰) young zircons (U-Pb age 0.2-0.27 ± 0.03 Ma; U-Th age 0.16 ± 0.07 Ma), most of them in oxygen isotope equilibrium with interstitial glasses. The δ 18O values >5.6 ‰ recorded in the coexisting zircon, quartz, feldspar and colorless interstitial glass suggest crystallization from melts produced by fusion of crustal rocks altered by seawater, also reflecting multiple melting and crystallization events. This suggests that "normal"- δ 18O silicic magmas may not be ultimately produced by crystallization of mafic, basaltic magmas. Instead, our new single-crystal laser fluorination and ion microprobe O-isotope data suggest addition of diverse partial crustal melts, probably originated from variously altered and preconditioned crust.

  10. Experimental Spinel Standards for Ferric Iron (Fe3+) Determination During Peridotite Partial Melting

    NASA Astrophysics Data System (ADS)

    Wenz, M. D.; Sorbadere, F.; Rosenthal, A.; Frost, D. J.; McCammon, C. A.

    2014-12-01

    The presence of ferric iron (Fe3+) in the mantle plays a significant role in the oxygen fugacity (fO2) of the Earth's interior. This has a wide range of implications for Earth related processes ranging from the composition of the atmosphere to magmatic phase relations during melting and crystallization processes [1]. A major source of Earth's mantle magmas is spinel peridotite. Despite its low abundance, spinel (Fe3+/ƩFe = 15-34%, [2]) is the main contributor of Fe3+to the melt upon partial melting. Analyses of Fe3+ on small areas of spinel and melt are required to study the Fe3+ behavior during partial melting of spinel peridotite. Fe K-edge X-ray Absorption Near Edge Structure (XANES) combines both high precision and small beam size, but requires standards with a wide range of Fe3+ content to obtain good calibration. Glasses with varying Fe3+ content are easily synthesized [3, 4]. Spinel, however, presents a challenge for experimental standards due to the low diffusion of Cr and Al preventing compositional homogeneity. Natural spinel standards are often used, but only cover a narrow Fe3+ range. Thus, there is a need for better experimental spinel standards over a wider range of fO2. Our study involves making experimental mantle spinels with variable Fe3+ content. We used a sol-gel auto-combustion method to synthesize our starting material [5]. FMQ-2, FMQ+0, and air fO2 conditions were established using a gas mixing furnace. Piston cylinder experiments were performed at 1.5GPa, and 1310 -1370°C to obtain solid material for XANES. To maintain distinct oxidizing conditions, three capsules were used: graphite for reduced, Re for intermediate and AuPd for oxidized conditions. The spinels were analyzed by Mössbauer spectroscopy. Fe3+/ƩFe ranged from 0.3 to 0.6. These values are consistent with the Fe edge position obtained using XANES analyses, between 7130 and 7132 eV, respectively. Our spinels are thus suitable standards for Fe3+ measurements in peridotite

  11. Partial melting during exhumation of Paleozoic retrograde eclogite in North Qaidam, western China

    NASA Astrophysics Data System (ADS)

    Cao, Yu-ting; Liu, Liang; Chen, Dan-ling; Wang, Chao; Yang, Wen-qiang; Kang, Lei; Zhu, Xiao-hui

    2017-10-01

    Ultrahigh pressure (UHP) rocks are often overprinted by high pressure (HP) granulite-facies metamorphism during exhumation. Here we investigate retrograde eclogite from the Lvliangshan area in North Qaidam which is associated with abundant felsic veins. The eclogite adjacent to the vein shows conversion to garnet amphibolite. Petrographic, mineralogical, geochemical, geochronological data suggest that the eclogite has been experienced peak eclogite facies metamorphism at c. 440 Ma, followed by granulite facies retrogression at c. 420 Ma, and amphibolite facies overprinting at <420 Ma. The retrograde eclogite has microstructural records for partial melting with elongated plagioclase grains occurring as veinlets along the garnet-ilmenite grain boundaries and interspersed in clinopyroxene. Moreover, highly cuspate, wedge-shaped and triangular plagioclase grains are distributed along the garnet boundaries, and banded felsic veins (Pl + Qz) occur along the boundaries of amphibole in garnet amphibolite. Whole-rock geochemistry suggests that the felsic veins have 438.1-1106 ppm Sr and 2.87-12.18 ppm Y with Sr/Y ratios from 81.98-166.2, exhibit pronounced positive Eu anomaly, and depletion of HREE, resembling those of adakitic rocks. Felsic veins contain zircon grains with an U-Pb age of ∼422 Ma, similar to the age of HP granulite-facies metamorphism (420 Ma) of retrograde eclogite. Combined with the identical Hf isotope compositions between the granulite-facies zircon grains from the host retrograde eclogite and those from the felsic vein, we infer closed system partial melting during HP granulite facies retrogression of the retrograde eclogite. The tonalitic (high Sr/Y ratio and enrichment of LREE) chemical feature, low Rb/Sr and high Ba/Rb ratios of the felsic veins suggest that zoisite and sodic amphibolite dehydration-melting together account for the formation of felsic veins during exhumation from the eclogite-facies to granulite-facies stages.

  12. Partially confined configuration for the growth of semiconductor crystals from the melt in zero-gravity environment

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Gatos, H. C.; Dabkowski, F. P.

    1985-01-01

    A novel partially confined configuration is proposed for the crystal growth of semiconductors from the melt, including those with volatile constituents. A triangular prism is employed to contain the growth melt. Due to surface tension, the melt will acquire a cylindrical-like shape and thus contact the prism along three parallel lines. The three empty spaces between the cylindrical melt and the edges of the prism will accommodate the expansion of the solidifying semiconductor, and in the case of semiconductor compounds with a volatile constituent, will permit the presence of the desired vapor phase in contact with the melt for controlling the melt stoichiometry. Theoretical and experimental evidence in support of this new type of confinement is presented.

  13. Magma transport and olivine crystallization depths in Kīlauea’s East Rift Zone inferred from experimentally rehomogenized melt inclusions

    USGS Publications Warehouse

    Tuohy, Robin M; Wallace, Paul J.; Loewen, Matthew W; Swanson, Don; Kent, Adam J R

    2016-01-01

    Concentrations of H2O and CO2 in olivine-hosted melt inclusions can be used to estimate crystallization depths for the olivine host. However, the original dissolved CO2concentration of melt inclusions at the time of trapping can be difficult to measure directly because in many cases substantial CO2 is transferred to shrinkage bubbles that form during post-entrapment cooling and crystallization. To investigate this problem, we heated olivine from the 1959 Kīlauea Iki and 1960 Kapoho (Hawai‘i) eruptions in a 1-atm furnace to temperatures above the melt inclusion trapping temperature to redissolve the CO2 in shrinkage bubbles. The measured CO2 concentrations of the experimentally rehomogenized inclusions (⩽590 ppm for Kīlauea Iki [n=10]; ⩽880 ppm for Kapoho, with one inclusion at 1863 ppm [n=38]) overlap with values for naturally quenched inclusions from the same samples, but experimentally rehomogenized inclusions have higher within-sample median CO2 values than naturally quenched inclusions, indicating at least partial dissolution of CO2 from the vapor bubble during heating. Comparison of our data with predictions from modeling of vapor bubble formation and published Raman data on the density of CO2 in the vapor bubbles suggests that 55-85% of the dissolved CO2 in the melt inclusions at the time of trapping was lost to post-entrapment shrinkage bubbles. Our results combined with the Raman data demonstrate that olivine from the early part of the Kīlauea Iki eruption crystallized at <6 km depth, with the majority of olivine in the 1-3 km depth range. These depths are consistent with the interpretation that the Kīlauea Iki magma was supplied from Kīlauea’s summit magma reservoir (∼2-5 km depth). In contrast, olivine from Kapoho, which was the rift zone extension of the Kīlauea Iki eruption, crystallized over a much wider range of depths (∼1-16 km). The wider depth range requires magma transport during the Kapoho eruption from deep beneath the

  14. Magma transport and olivine crystallization depths in Kīlauea's east rift zone inferred from experimentally rehomogenized melt inclusions

    NASA Astrophysics Data System (ADS)

    Tuohy, Robin M.; Wallace, Paul J.; Loewen, Matthew W.; Swanson, Donald A.; Kent, Adam J. R.

    2016-07-01

    Concentrations of H2O and CO2 in olivine-hosted melt inclusions can be used to estimate crystallization depths for the olivine host. However, the original dissolved CO2 concentration of melt inclusions at the time of trapping can be difficult to measure directly because in many cases substantial CO2 is transferred to shrinkage bubbles that form during post-entrapment cooling and crystallization. To investigate this problem, we heated olivine from the 1959 Kīlauea Iki and 1960 Kapoho (Hawai'i) eruptions in a 1-atm furnace to temperatures above the melt inclusion trapping temperature to redissolve the CO2 in shrinkage bubbles. The measured CO2 concentrations of the experimentally rehomogenized inclusions (⩽590 ppm for Kīlauea Iki [n = 10]; ⩽880 ppm for Kapoho, with one inclusion at 1863 ppm [n = 38]) overlap with values for naturally quenched inclusions from the same samples, but experimentally rehomogenized inclusions have higher within-sample median CO2 values than naturally quenched inclusions, indicating at least partial dissolution of CO2 from the vapor bubble during heating. Comparison of our data with predictions from modeling of vapor bubble formation and published Raman data on the density of CO2 in the vapor bubbles suggests that 55-85% of the dissolved CO2 in the melt inclusions at the time of trapping was lost to post-entrapment shrinkage bubbles. Our results combined with the Raman data demonstrate that olivine from the early part of the Kīlauea Iki eruption crystallized at <6 km depth, with the majority of olivine in the 1-3 km depth range. These depths are consistent with the interpretation that the Kīlauea Iki magma was supplied from Kīlauea's summit magma reservoir (∼2-5 km depth). In contrast, olivine from Kapoho, which was the rift zone extension of the Kīlauea Iki eruption, crystallized over a much wider range of depths (∼1-16 km). The wider depth range requires magma transport during the Kapoho eruption from deep beneath the summit

  15. Determination of calcium carbonate and sodium carbonate melting curves up to Earth's transition zone pressures with implications for the deep carbon cycle

    NASA Astrophysics Data System (ADS)

    Li, Zeyu; Li, Jie; Lange, Rebecca; Liu, Jiachao; Militzer, Burkhard

    2017-01-01

    Melting of carbonated eclogite or peridotite in the mantle influences the Earth's deep volatile cycles and bears on the long-term evolution of the atmosphere. Existing data on the melting curves of calcium carbonate (CaCO3) and sodium carbonate (Na2CO3) are limited to 7 GPa and therefore do not allow a full understanding of carbon storage and cycling in deep Earth. We determined the melting curves of CaCO3 and Na2CO3 to the pressures of Earth's transition zone using a multi-anvil apparatus. Melting was detected in situ by monitoring a steep and large increase in ionic conductivity, or inferred from sunken platinum markers in recovered samples. The melting point of CaCO3 rises from 1870 K at 3 GPa to ∼2000 K at 6 GPa and then stays within 50 K of 2000 K between 6 and 21 GPa. In contrast, the melting point of Na2CO3 increases continuously from ∼1123 K at 3 GPa to ∼1950 K at 17 GPa. A pre-melting peak in the alternating current through solid CaCO3 is attributed to the transition from aragonite to calcite V. Accordingly the calcite V-aragonite-liquid invariant point is placed at 13 ± 1 GPa and 1970 ± 40 K, with the Clapeyron slope of the calcite V to aragonite transition constrained at ∼70 K/GPa. The experiments on CaCO3 suggest a slight decrease in the melting temperature from 8 to 13 GPa, followed by a slight increase from 14 to 21 GPa. The negative melting slope is consistent with the prediction from our ab initio simulations that the liquid may be more compressible and become denser than calcite V at sufficiently high pressure. The positive melting slope at higher pressures is supported by the ab initio prediction that aragonite is denser than the liquid at pressures up to 30 GPa. At transition zone pressures the melting points of CaCO3 are comparable to that of Na2CO3 but nearly 400 K and 500 K lower than that of MgCO3. The fusible nature of compressed CaCO3 may be partially responsible for the majority of carbonatitic melts found on Earth's surface

  16. Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones

    DOE PAGES

    Khairallah, Saad A.; Anderson, Andrew T.; Rubenchik, Alexander; ...

    2016-02-23

    Our study demonstrates the significant effect of the recoil pressure and Marangoni convection in laser powder bed fusion (L-PBF) of 316L stainless steel. A three-dimensional high fidelity powder-scale model reveals how the strong dynamical melt flow generates pore defects, material spattering (sparking), and denudation zones. The melt track is divided into three sections: a topological depression, a transition and a tail region, each being the location of specific physical effects. The inclusion of laser ray-tracing energy deposition in the powder-scale model improves over traditional volumetric energy deposition. It enables partial particle melting, which impacts pore defects in the denudation zone.more » Different pore formation mechanisms are observed at the edge of a scan track, at the melt pool bottom (during collapse of the pool depression), and at the end of the melt track (during laser power ramp down). Finally, we discuss remedies to these undesirable pores are discussed. The results are validated against the experiments and the sensitivity to laser absorptivity.« less

  17. Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones

    SciTech Connect

    Khairallah, Saad A.; Anderson, Andrew T.; Rubenchik, Alexander; King, Wayne E.

    2016-02-23

    Our study demonstrates the significant effect of the recoil pressure and Marangoni convection in laser powder bed fusion (L-PBF) of 316L stainless steel. A three-dimensional high fidelity powder-scale model reveals how the strong dynamical melt flow generates pore defects, material spattering (sparking), and denudation zones. The melt track is divided into three sections: a topological depression, a transition and a tail region, each being the location of specific physical effects. The inclusion of laser ray-tracing energy deposition in the powder-scale model improves over traditional volumetric energy deposition. It enables partial particle melting, which impacts pore defects in the denudation zone. Different pore formation mechanisms are observed at the edge of a scan track, at the melt pool bottom (during collapse of the pool depression), and at the end of the melt track (during laser power ramp down). Finally, we discuss remedies to these undesirable pores are discussed. The results are validated against the experiments and the sensitivity to laser absorptivity.

  18. Partial melting on iron(II) oxide-rich asteroids: Insights to the first stage of planetary differentiation

    NASA Astrophysics Data System (ADS)

    Gardner-Vandy, Kathryn Gail

    2012-05-01

    The melting of planetesimals was a widespread geologic phenomenon taking place in the early inner solar system. Petrologic and geochemical evidence shows that this melting frequently resulted in full differentiation of planetary bodies into a core, mantle, and crust. The extent of this early planetary melting is evidenced in the breadth of achondrite meteorites. In the achondrite meteorite group, there exist meteorites that experienced low degrees of melting, such that the parent body underwent partial melting and did not fully differentiate. These meteorites, called the primitive achondrites, are a window to the first stage of melting in the early solar system. The primitive achondrites with FeO-poor silicate compositions have been well-studied, but little is known about the formation conditions and history of the FeO-rich primitive achondrites, which includes the brachinites and several ungrouped meteorites. The brachinites are olivine-dominated meteorites with a recrystallized texture that show evidence of partial melting and melt removal on their parent body. The ungrouped primitive achondrites are also olivine-dominated meteorites with a recrystallized texture, but they exhibit a larger range in mineralogy with most being essentially chondritic and containing relict chondrules. In this dissertation, I present a study of the petrology, geochemistry and formation conditions of the FeO-rich primitive achondrites. I analyze the petrology and bulk composition of the meteorites, and I conduct thermodynamic modelling of the mineral assemblages to determine oxidation conditions during their formation. Finally, I attempt to simulate the formation of the brachinite meteorites through 1-atmosphere, gas-mixing partial melting experiments of an FeO-rich chondritic meteorite. These meteorites represent a continuum of partial melting, akin to that seen in the acapulcoite-lodranite clan of primitive achondrites. Mineral compositions and oxygen fugacity formation conditions

  19. The composition of low-degree partial melts of garnet peridotite at 3 GPa by modified iterative sandwich experiments (MISE)

    NASA Astrophysics Data System (ADS)

    Davis, F. A.; Hirschmann, M. M.; Humayun, M.

    2009-12-01

    We have determined the composition of the incipient partial melt (F=0%) of garnet peridotite with composition similar to KLB-1 at 3 GPa through piston cylinder experiments using the modified iterative sandwich experiment (MISE) method (Hirschmann and Dasgupta, 2007). Sandwich experiments were performed iteratively, with new melt compositions for subsequent experiments determined by calculation from the bulk mineral/melt partition coefficients for each oxide from the previous experiment. Quenched melt in experimental charges does not form a glass but instead yields a heterogeneous region that proved difficult to analyze by electron microprobe (EMP) owing to under-sampling of certain components that are lost preferentially while polishing. To circumvent this problem, many microprobe spots were collected and then filtered by excluding analyses that were not close to Fe-Mg exchange equilibrium with coexisting olivine. Independent analyses of quenched melts by laser ablation ICP-MS, a volume measurement that is unaffected by difficulties in polishing, corroborate the accuracy of the filtering method. For LA-ICP-MS, major elements were analyzed using a New Wave UP193FX excimer (193 nm) laser system coupled to a Thermo Element XR (Humayun et al., 2007). A 20 µm beam spot was scanned over the melt region at 5 µm/s. The MPI-DING and USGS glasses were used as standards. Filtered EMP data and LA-ICP-MS data agreed within error for all elements. The final melt composition was calculated from partition coefficients derived from EMP data of the last iteration. This study represents the first determination of partial melt of garnet lherzolite at a melt fraction close to that actually forming in the source regions of ocean island basalts (OIB) and at a pressure corresponding to that at the base of the oceanic lithosphere (~100 km). This melt is useful for comparison with OIB believed to be derived from low-degree mantle partial melts. Comparing the 0% melt with alkalic OIB

  20. H2O storage capacity of olivine at 5-8 GPa and consequences for dehydration partial melting of the upper mantle

    NASA Astrophysics Data System (ADS)

    Ardia, P.; Hirschmann, M. M.; Withers, A. C.; Tenner, T. J.

    2012-09-01

    The H2O storage capacities of peridotitic minerals place crucial constraints on the onset of hydrous partial melting in the mantle. The storage capacities of minerals in equilibrium with a peridotite mineral assemblage (“peridotite-saturated” minerals) are lower than when the minerals coexist only with fluid because hydrous partial melt is stabilized at a lower activity of H2O. Here, we determine peridotite-saturated olivine H2O storage capacities from 5 to 8 GPa and 1400-1500 °C in layered experiments designed to grow large (∼100-150 μm) olivine crystals in equilibrium with the full hydrous peridotite assemblage (melt+ol+opx+gar+cpx). The peridotite-saturated H2O storage capacity of olivine at 1450 °C rises from 57±26 ppm (by wt.) at 5 GPa to 254±60 ppm at 8 GPa. Combining these with results of a parallel study at 10-13 GPa (Tenner et al., 2011, CMP) yields a linear relation applicable from 5 to 13 GPa for peridotite-saturated H2O storage capacity of olivine at 1450 °C, CH2Oolivine(ppm)=57.6(±16)×P(GPa)-169(±18). Storage capacity diminishes with increasing temperature, but is unaffected by variable total H2O concentration between 0.47 and 1.0 wt%. Both of these are as predicted for the condition in which the water activity in the melt is governed principally by the cryoscopic requirement of melt stability for a given temperature below the dry solidus. Measured olivine storage capacities are in agreement or slightly greater than those predicted by a model that combines data from experimental freezing point depression and olivine/melt partition coefficients of H2O (Hirschmann et al., 2009). Considering the temperature along the mantle geotherm, as well as available constraints on garnet/olivine and pyroxene/olivine partitioning of H2O (DH2Ogar/ol,DH2Opx/ol), we estimate the peridotite H2O storage capacity in the low velocity zone. The CH2O required to initiate melting between 150 and 250 km depth is between 270 and 855 ppm. We conclude that hydrous

  1. Partial Melting of Garnet Lherzolite with H2o and CO2 at 3 GPa: Implications for Intraplate Magmatism.

    NASA Astrophysics Data System (ADS)

    Baasner, A.; Medard, E.; Laporte, D.

    2014-12-01

    The origin and source rock of alkali-rich and SiO2-undersatured magmas in the Earth`s upper mantle have been under debate for a long time. The garnet signature in rare earth element patterns of such magmas suggest a garnet-bearing source rock, which could be garnet lherzolite or garnet pyroxenite. Partial melting experiments were performed at 3 GPa and 1345-1445 °C in a piston-cylinder apparatus using mixtures of natural lherzolite with 0.4-0.7 wt% H2O and 0.4-0.7 wt% CO2 as starting materials. Different designs of AuPd capsules were used for melt extraction. Mineral and melt phases were analysed with electron microprobe and laser ablation inductively coupled plasma mass spectrometry. The degree of partial melting in the experiments ranges from ~20% to ~4% and decreases with decreasing temperature and decreasing volatile content in the starting material. All samples contain olivine and orthopyroxene. Garnet is present in experiments performed below 1420 °C. The amount of clinopyroxene decreases with increasing degree of partial melting and volatile concentration in the starting material. Depending on the capsule design the melts quenched to glasses or to a mixture of quench crystals and residual glass. The composition of the partial melts ranges from basalts through picrobasalts to foidites. The alkali concentration increases and the SiO2 concentration decreases with decreasing degree of partial melting and increasing volatile concentration in the starting material. The partial melts are similar in many aspects to alkali intraplate magmas (basanites to melilitites), although they are richer in MgO. Compositions closer to natural basanites could be obtained either at lower degree of melting (and lower volatile contents) or through olivine fractionation. Our results strongly suggests that. SiO2-undersaturated intraplate magmas can be generated by mantle melting of garnet-lherzolite in the presence of H2O and CO2 in the Earth`s upper mantle at 3 GPa (~100 km depth).

  2. QUE 94204: A primitive enstatite achondrite produced by the partial melting of an E chondrite-like protolith

    NASA Astrophysics Data System (ADS)

    Izawa, Matthew R. M.; Flemming, Roberta L.; Banerjee, Neil R.; Matveev, Sergei

    2011-11-01

    Queen Alexandra Range (QUE) 94204, an enstatite achondrite, is a coarse-grained, highly recrystallized, chondrule-free and unbrecciated rock dominated (about 70 vol%) by anhedral, equigranular crystals of orthoenstatite of nearly endmember composition (Fs0.1-0.4, Wo0.3-0.4) with interstitial plagioclase, kamacite, and troilite. Abundance of approximately 120° triple junctions and the close association of metal-sulfide and plagioclase-rich melts indicate that QUE 94204 has undergone limited partial melting with inefficient melt extraction. Mineral chemistry indicates a high degree of thermal metamorphism. Kamacite in QUE 94204 contains between 2.09 and 2.55 wt% Si, similar to highly metamorphosed EL chondrites. Plagioclase has between 4.31 and 6.66 wt% CaO, higher than other E chondrites but closer in composition to plagioclase from metamorphosed EL chondrites. QUE 94204 troilite contains up to 2.55 wt% Ti, consistent with extensive thermal metamorphism of an E chondrite-like precursor. Results presented in this study indicate that QUE 94204 is the result of low degree, (about 5-20 vol%, probably toward the lower end of this range) partial melting of an E chondrite protolith. Textural and chemical evidence suggests that during the metamorphism of QUE 94204, melts formed first at the Fe,Ni-FeS cotectic near approximately 900 °C, followed by plagioclase-pyroxene silicate partial melts near approximately 1100 °C. Neither the Fe,Ni-FeS nor the plagioclase-pyroxene melts were efficiently segregated or extracted. QUE 94204 belongs to a grouplet of similar "primitive enstatite achondrites" that are analogous to the acapulcoites-lodranites, but that have resulted from the partial melting of an E chondrite-like protolith.

  3. Growth of GaAs crystals from the melt in a partially confined configuration

    NASA Technical Reports Server (NTRS)

    Gatos, Harry C.; Lagowski, Jacek

    1988-01-01

    The experimental approach was directed along two main goals: (1) the implementation of an approach to melt growth in a partially confined configuration; and (2) the investigation of point defect interaction and electronic characteristics as related to thermal treatment following solidification and stoichiometry. Significant progress was made along both fronts. Crystal growth of GaAs in triangular ampuls was already carried out successfully and consistent with the model. In fact, pronounced surface tension phenomena which cannot be observed in ordinary confinement system were identified and should premit the assessment of Maragoni effects prior to space processing. Regarding thermal treatment, it was discovered that the rate of cooling from elevated temperatures is primarily responsible for a whole class of defect interactions affecting the electronic characteristics of GaAs and that stoichiometry plays a critical role in the quality of GaAs.

  4. Experimental evidence for melt partitioning between olivine and orthopyroxene in partially molten harzburgite

    NASA Astrophysics Data System (ADS)

    Miller, Kevin J.; Zhu, Wen-lu; Montési, Laurent G. J.; Gaetani, Glenn A.; Le Roux, Véronique; Xiao, Xianghui

    2016-08-01

    Observations of dunite channels in ophiolites and uranium series disequilibria in mid-ocean ridge basalt suggest that melt transport in the upper mantle beneath mid-ocean ridges is strongly channelized. We present experimental evidence that spatial variations in mineralogy can also focus melt on the grain scale. This lithologic melt partitioning, which results from differences in the interfacial energies associated with olivine-melt and orthopyroxene-melt boundaries, may complement other melt focusing mechanisms in the upper mantle such as mechanical shear and pyroxene dissolution. We document here lithologic melt partitioning in olivine-/orthopyroxene-basaltic melt samples containing nominal olivine to orthopyroxene ratio of 3 to 2 and melt fractions of 0.02 to 0.20. Experimental samples were imaged using synchrotron-based X-ray microcomputed tomography at a resolution of 700 nm per voxel. By analyzing the local melt fraction distributions associated with olivine and orthopyroxene grains in each sample, we found that the melt partitioning coefficient, i.e., the ratio of melt fraction around olivine to that around orthopyroxene grains, varies between 1.1 and 1.6. The permeability and electrical conductivity of our digital samples were estimated using numerical models and compared to those of samples containing only olivine and basaltic melt. Our results suggest that lithologic melt partitioning and preferential localization of melt around olivine grains might play a role in melt focusing, potentially enhancing average melt ascent velocities.

  5. Origin and Constraints on Ilmenite-rich Partial Melt in the Lunar Lower Mantle

    NASA Astrophysics Data System (ADS)

    Mallik, A.; Fuqua, H.; Bremner, P. M.; Panovska, S.; Diamond, M. R.; Lock, S. J.; Nishikawa, Y.; Jiménez-Pérez, H.; Shahar, A.; Panero, W. R.; Lognonne, P. H.; Faul, U.

    2015-12-01

    Existence of a partially molten layer at the lunar core-mantle boundary has been proposed to explain the lack of observed far-side deep moonquakes, the observation of reflected seismic phases from deep moonquakes, and the dissipation of tidal energy within the lunar interior [1,2]. However, subsequent models explored the possibility that dissipation due to elevated temperatures alone can explain the observed dissipation factor (Q) and tidal love numbers [3]. Using thermo-chemical and dynamic modeling (including models of the early lunar mantle convection), we explore the hypothesis that an ilmenite-rich layer forms below crustal anorthosite during lunar magma ocean crystallization and may sink to the base of the mantle to create a partial melt layer at the lunar core-mantle boundary. Self-consistent physical parameters (including gravity, pressure, density, VP and Vs) are forward calculated for a well-mixed mantle with uniform bulk composition versus a mantle with preserved mineralogical stratigraphy from lunar magma ocean crystallization. These parameters are compared against observed mass, moment of inertia, real and imaginary parts of the Love numbers, and seismic travel times to further limit the acceptable models for the Moon. We have performed a multi-step grid search with over twenty thousand forward calculations varying thicknesses of chemically/mineralogically distinct layers within the Moon to evaluate if a partially molten layer at the base of the lunar mantle is well-constrained by the observed data. Furthermore, dynamic mantle modeling was employed on the best-fit model versions to determine the survivability of a partially molten layer at the core-mantle boundary. This work was originally initiated at the CIDER 2014 program. [1] Weber et al. (2011). Science 331(6015), 309-12. [2] Khan et al. (2014). JGR 119. [3] Nimmo et al. (2012). JGR 117, 1-11.

  6. High Melt Porosity in the Lower Oceanic Crust Inferred from Phosphorus Zoning in Olivine

    NASA Astrophysics Data System (ADS)

    Hellebrand, E.; Welsch, B. T.; Hammer, J. E.

    2013-12-01

    intrusion into overlying lithospheric mantle peridotites. Disintegration and partial dissolution of the peridotite minerals can provide the conditions for compositional (rather than thermal) undercooling and promote the rapid growth of new olivines inside the deep melt lens. [1] Lissenberg, C.J. & Dick, H.J.B. (2008) EPSL 271, 311-325. [2] Suhr, G. et al. (2008) G3, doi: 10.1029/2008GC002012. [3] Drouin, M. et al. (2009) Chem. Geol. 264, 71-88. [4] von der Handt, A. & Hellebrand, E. (2010) AGU Fall Meeting abstract.

  7. High-quality Silicon Films Prepared by Zone-melting Recrystallization

    NASA Technical Reports Server (NTRS)

    Chen, C. K.; Geis, M. W.; Tsaur, B. Y.; Fan, J. C. C.

    1984-01-01

    The graphite strip heater zone melting recrystallization (ZMR) technique is described. The material properties of the ZMR films, and SOI device results are reviewed. Although our ZMR work is primarily motivated by integrated circuit applications, this work evolved in part from earlier research on laser crystallization of thick amorphous GaAs and Si films, which was undertaken with the goal of producing low cost photovoltaic materials. The ZMR growth process and its effect on the properties of the recrystallized films may contribute some insight to a general understanding of the rapid recrystallization of Si for solar cells. Adaptation of ZMR for solar cell fabrication is considered.

  8. Residual stress and dislocations density in silicon ribbons grown via optical zone melting

    NASA Astrophysics Data System (ADS)

    Augusto, A.; Pera, D.; Choi, H. J.; Bellanger, P.; Brito, M. C.; Maia Alves, J.; Vallêra, A. M.; Buonassisi, T.; Serra, J. M.

    2013-02-01

    We investigate the relationships between growth rate, time-temperature profile, residual stress, dislocation density, and electrical performance of silicon ribbons grown via optical zone melting. The time-temperature profiles of ribbons grown at different velocities were investigated using direct measurements and computational fluid dynamics (CFD) modeling. Residual stresses up to 20 MPa were measured using infrared birefringence imaging. The effect of crystallization speed on dislocation density and residual stress is discussed from the context of thermal stresses during growth. More broadly, we demonstrate the usefulness of combining spatially resolved stress and microstructure measurements with CFD simulations toward optimizing kerfless silicon wafer quality.

  9. High-quality Silicon Films Prepared by Zone-melting Recrystallization

    NASA Technical Reports Server (NTRS)

    Chen, C. K.; Geis, M. W.; Tsaur, B. Y.; Fan, J. C. C.

    1984-01-01

    The graphite strip heater zone melting recrystallization (ZMR) technique is described. The material properties of the ZMR films, and SOI device results are reviewed. Although our ZMR work is primarily motivated by integrated circuit applications, this work evolved in part from earlier research on laser crystallization of thick amorphous GaAs and Si films, which was undertaken with the goal of producing low cost photovoltaic materials. The ZMR growth process and its effect on the properties of the recrystallized films may contribute some insight to a general understanding of the rapid recrystallization of Si for solar cells. Adaptation of ZMR for solar cell fabrication is considered.

  10. Shear-induced melt localization and the rheology of the partially molten mantle

    NASA Astrophysics Data System (ADS)

    Katz, R. F.; Spiegelman, M.; Holtzman, B. K.

    2005-12-01

    The emergence of patterns of melt distribution in experiments on partially molten aggregates undergoing simple shear [1,2] provide a rare opportunity to test magma migration theory [3,4,5] by directly comparing experiments and calculations. The fundamental observation is the emergence and persistence to large strains of bands of high porosity and concentrated deformation oriented at about 15-25° to the plane of shear [6]. We have extended the analysis of Spiegelman [7] and report results from new linear analysis and numerical solutions that suggest that band angle in experiments is controlled by a balance between porosity and strain rate-weakening mechanisms. Lower angles are predicted for stronger strain rate-weakening. For the specific model considered here, a power-law stress-dependent rheology, calculations with n~6 are consistent with the observations. These results suggest that partially molten aggregates deforming under shear may have a greater sensitivity to strain rate than previously believed [8]. [1] Zimmerman, M. et al., Geophys. Res. Lett., 26, 1999. [2]Holtzman, B. et al., Geochem. Geophys. Geosyst., 4, 2003. [3]Mc{K}enzie, D., J. Petrol., 25, 1984. [4]Fowler, A., Geophys. Astrophys. Fluid Dyn., 33, 1985. [5]Bercovici, D. et al., J. Geophys. Res.- Solid Earth, 106, 2001. [6]Spiegelman, M., Geochem. Geophys. Geosyst., 4, 2003. [7]Holtzman, B. et al., J. Petrol., 2005. [8]Hirth, G. and D. Kohlstedt, J. Geophys. Res., 100, 1995.

  11. Influence of partial melting on magnetic fabrics of migmatites: evidence from Paleoproterozoic terrains of Pointe Géologie, Terre Adélie (East Antarctica)

    NASA Astrophysics Data System (ADS)

    Bascou, Jérôme; Henry, Bernard; Ménot, René-Pierre; Funaki, Minoru; Barruol, Guilhem

    2014-05-01

    A magnetic structural mapping using Anisotropy of Magnetic Susceptibility (AMS) technique was carried out in Pointe Géologie archipelago (Terre Adélie, East Antarctica) that represents a deep crustal section affected by intensive anatectic processes during Paleoproterozoic times, 1.69 Ga ago. This generated different High Temperature rock types such as: migmatites including leucosomes and melanosomes, coarse-grained pink granites dyke and anatexites. Magnetic mineralogy study shows that oxide minerals are mainly large and solid state deformed grains of magnetite. In the leucosomes, oxides appear more scattered than in the melanosomes and their rounded isometric shape suggests rotations of the former elongated grain during melt segregation. This contrasted magnetite grains distribution will generate specific AMS signatures for melanocratic layers on the one hand and felsic leucosomes, dykes and anatexites on the other hand. The mean magnetic susceptibility (Km) and the anisotropy degree (P') are higher in the gneisses and much lower in granitic samples. Orientation of principal susceptibility axes also differs. In migmatitic gneisses, magnetic foliations are coherent with the local and regional structural pattern. Nevertheless AMS technique provides complementary information on the orientation of lineations when they are difficult to observe in the field. The magnetic lineations are dominantly sub-horizontal in the shear zone while they tend to be vertical in granitic dykes, anatexites and well-defined leucosomes. Such a changing of orientation is related to a rheological contrast between the solid-state deformation suffered by the oxide grains and their reorientation in a viscous flow during the aggregation of felsic melt. Increasing amounts of partial melting lead to a loss of the rock cohesion related to the migration of the melt trough a solid-state made of previously deformed minerals. Thus the former tectonic structures will be progressively erased. Melt

  12. Lithosphere and Asthenosphere Properties beneath Oceans and Continents and their Relationship with Domains of Partial Melt Stability in the Mantle

    NASA Astrophysics Data System (ADS)

    Dasgupta, R.

    2014-12-01

    The depth of the lithosphere-asthenosphere boundary (LAB) and the change in properties across the lithosphere, asthenosphere, and LAB in various tectonic settings are captured in a variety of geophysical data, including seismic velocities and electrical conductivity. A sharp drop in shear wave velocity and increase in electrical conductivity can potentially be caused by the appearance of partial melt at or below the LAB but the chemical and dynamic stability of partial melt across lithosphere and at LAB remain debated. Here I apply the recent models of mantle melting in the presence of water and carbon [1, 2] to evaluate the domains of stability of partial melt both beneath continents and oceans. The model allows prediction of the possible presence, the fraction, and composition of partial melt as a function of depth, bulk C and H2O content, and fO2 [3] in various geologic/tectonic settings. The results show that while a hydrous, carbonated melt is stable only beneath LAB and in the asthenospheric mantle beneath oceans, continental mantle can contain a carbonate-rich melt within the lithosphere. For geotherms corresponding to surface heat flux (SHF) of 40-50 mW m-2, which also match P-T estimates beneath cratons based on thermo-barometry of peridotite xenoliths [4], the solidus of fertile peridotite with trace amount of CO2 and H2O is crossed at depths as shallow as 80-120 km [5]. If elevated geotherms of the Proterozoic and Phanerozoic terrains are applied, carbonatitic melt becomes stable somewhat shallower. These depths are similar to those argued for a mid-lithospheric discontinuity (MLD) where a negative velocity gradient has been detected much shallower than the proposed depth of LAB in many places. With a drop in oxygen fugacity with depth, a freezing of carbonatitic melt may be expected at intermediate depths (~150-200 km). At 200-250 km a hydrous, carbonated silicate melt may reappear owing to the interplay of fO2 and freezing point depression effect of CO

  13. Uranium and minor-element partitioning in Fe-Ti oxides and zircon from partially melted granodiorite, Crater Lake, Oregon

    SciTech Connect

    La Tourrette, T.Z.; Burnett, D.S. ); Bacon C.R. )

    1991-02-01

    Crystal-liquid partitioning in Fe-Ti oxides and zircon was studied in partially melted granodiorite blocks ejected during the climactic eruption of Mt. Mazama (Crater Lake), Oregon. The blocks, which contain up to 33% rhyolite glass (75 wt% SiO{sub 2}), are interpreted to be portions of the magma chamber walls that were torn off during eruption. The glass is clear and well homogenized for all measured elements except Zr. Results for Fe-Ti oxides give D{sub U}{sup oxide/liq} {approx} 0.1. Partitioning of Mg, Mn, Al, Si, V, and Cr in Fe-Ti oxides indicates that grains surrounded by glass are modestly well equilibrated with the melt for many of the minor elements, while those that are inclusions in relict plagioclase are not. Uranium and ytterbium inhomogeneities in zircons indicate that the zircons have only partially equilibrated with the melt and that uranium appears to have been diffusing out of the zircons have only partially equilibrated with the melt and that uranium appears to have been diffusing out of the zircons faster that the zircons were dissolving. Based on the authors measurements and given their low abundances in most rocks, Fe-Ti oxides probably do not play a major role in U-Th fractional during partial melting. The partial melts were undersaturated with zircon and apatite, but both phases are present in the authors samples. This demonstrates an actual case of nonequilibrium source retention of accessory phases, which in general could be an important trace element fractionation mechanism. Their results do not support the hypothesis that liquid structure is the dominant factor controlling trace-element partitioning in high-silica rhyolites.

  14. CO2 Solubility in Rhyolitic Melts as a Function of P, T, and fO2 - Implications for Carbon Flux in Subduction Zones

    NASA Astrophysics Data System (ADS)

    Duncan, M. S.; Dasgupta, R.

    2013-12-01

    Understanding the balance between subduction inputs vs. arc output of carbon is critical for constraining the global carbon cycle. However, the agent of carbon transfer from slab to sub-arc mantle is not constrained [1]. Partial melt of ocean-floor sediments is thought to be a key agent of mass transfer in subduction zones, accounting for the trace element characteristics of arc magmas [2]. Yet the carbon carrying capacity of rhyolitic partial melts of sediments remains unknown at sub-arc depths. In our previous work [3], we constrained CO2 solubility of natural rhyolite from 1.5-3.0 GPa, 1300 °C and logfO2 at FMQ×1.0. However, the effects of T and fO2 on CO2 solubility remain unconstrained. In particular, for sediments with organic carbon, graphite stability is expected and the fO2 of C-dissolution can be lower, which may affect the solubility. Thus it is critical to constrain the CO2 solubility of sediment partial melts under graphite-saturated conditions. We determined CO2 solubility of a model rhyolite composition, similar to partial melt composition of natural metapelite [4], at graphite saturation, using Pt/Gr capsules and a piston cylinder device. Experiments were conducted at 1.5-3.0 GPa and 1100-1400 °C. FTIR was employed to measure the concentrations of CO2 and H2O in doubly polished experimental glasses. Raman and SIMS were used to determine the presence of reduced carbon species and total carbon, respectively. FTIR spectra reveal that CO2 is dissolved as both molecular CO2 (CO2mol.) and carbonates (CO32-). For graphite-saturated, hydrous melts with measured H2O ~2.0 wt.%, CO2tot. (CO2mol.+CO32-) values increase with increasing P from ~0.6 to 1.2 wt.% from 1.5 to 3.0 GPa at 1300 °C. These values are lower than more oxidized melts with the same water content, which were 0.85 to 1.99 wt.% CO2 as P increased. At 3 GPa, graphite-saturated experiments from 1100 to 1300 °C yield CO2tot. value of 1.18-1.20 wt.%, suggesting minor effect of temperature in

  15. Texture Development in Bi-Sr-Ca-Cu-O (BPSCCO) and Ag-BPSCCO Superconductor through Zone Melting-Refining

    NASA Astrophysics Data System (ADS)

    Mani, Themanam; Damodaran, Alathoor; Warrier, Krishna

    1995-02-01

    A horizontal sample holding novel zone melting refining technique for incorporating grain orientation in sintered Bi-based superconductor (BPSCCO) strips is presented. A three zone furnace having independent temperature controls and a rate of zone movement of 30 mm/h was used. While a-b plane oriented grains appear in BPSCCO samples, in Ag-BPSCCO composites the ductile silver is seen to flow along the intergranular boundaries of BPSCCO grains.

  16. Melt ponds and marginal ice zone from new algorithm of sea ice concentration retrieval

    NASA Astrophysics Data System (ADS)

    Repina, Irina; Tikhonov, Vasiliy; Komarova, Nataliia; Raev, Mikhail; Sharkov, Evgeniy

    2016-04-01

    Studies of spatial and temporal properties of sea ice distribution in polar regions help to monitor global environmental changes and reveal their natural and anthropogenic factors, as well as make forecasts of weather, marine transportation and fishing conditions, assess perspectives of mineral mining on the continental shelf, etc. Contact methods of observation are often insufficient to meet the goals, very complicated technically and organizationally and not always safe for people involved. Remote sensing techniques are believed to be the best alternative. Its include monitoring of polar regions by means of passive microwave sensing with the aim to determine spatial distribution, types, thickness and snow cover of ice. However, the algorithms employed today to retrieve sea ice characteristics from passive microwave sensing data for different reasons give significant errors, especially in summer period and also near ice edges and in cases of open ice. A new algorithm of sea ice concentration retrieval in polar regions from satellite microwave radiometry data is discussed. Beside estimating sea ice concentration, the algorithm makes it possible to indicate ice areas with melting snow and melt ponds. Melt ponds are an important element of the Arctic climate system. Covering up to 50% of the surface of drifting ice in summer, they are characterized by low albedo values and absorb several times more incident shortwave radiation than the rest of the snow and ice cover. The change of melt ponds area in summer period 1987-2015 is investigated. The marginal ice zone (MIZ) is defined as the area where open ocean processes, including specifically ocean waves, alter significantly the dynamical properties of the sea ice cover. Ocean wave fields comprise short waves generated locally and swell propagating from the large ocean basins. Depending on factors like wind direction and ocean currents, it may consist of anything from isolated, small and large ice floes drifting over a

  17. Partial Melting and Contact Metamorphism of Basic Dykes in the Aureole of an Ocean Island Pyroxenitic Intrusion; Fuerteventura, Canaries

    NASA Astrophysics Data System (ADS)

    Holloway, M. I.; Bussy, F.; Hernandez, J.; Epard, J.

    2004-12-01

    The hypabyssal root zone of an ocean island volcano can be directly observed in the uplifted Basal Complex of Fuerteventura (Canary Islands). This complex records a long-lasting magmatic activity characterised by the intrusion of numerous magma batches as small plutons, dykes, dyke swarms and ring-dyke complexes of alkali-gabbros, pyroxenites, syenites and carbonatites. The high heat flow generated by the successive magma pulses feeding the overlying subaerial volcanic centres induced remarkable metasomatic and metamorphic processes, culminating with the low-pressure partial melting of basic dykes within the heterogeneous Tierra Mala gabbro-pyroxenite-syenite formation, in a contact metamorphic aureole around a layered pyroxenite-gabbro intrusion (PX1). The migmatites are characterised by a dense, zebrated network of closely spaced millimetre-wide leucocratic veins with perfectly preserved igneous textures. Only limited partial melting over a small distance (15-20m) appears to have been generated around an apophysis of PX1 (250m wide), due to a presumably limited heat input. It is thus possible to follow the evolution of this phenomenon within particular dykes with increasing distance from the intrusion. Results show that lithologies are mineralogically and chemically highly variable and behave differently in the contact aureole. Dykes of mafic, foid-microgabbros with igneous intersertal textures show increasing alteration of diopside to kaersutite with increasing proximity to the PX1 apophysis, up to 16m from the contact. Subsequently diopside crystals begin to appear smaller and recrystallised, and within the first 4m the dykes almost completely lose their small leucocratic component, leaving a framework texture dominated by sub- to euhedral diopside, Fe-Ti oxides, poikiloblastic Ti-rich biotites and minor kaersutite. This is reflected by the whole-rock SiO2, alkali, and LILE concentrations, which decrease as you approach the intrusion. Trace element contents are

  18. The thermal effect of fluid circulation in the subducting crust on slab melting in the Chile subduction zone

    NASA Astrophysics Data System (ADS)

    Spinelli, Glenn A.; Wada, Ikuko; He, Jiangheng; Perry, Matthew

    2016-01-01

    Fluids released from subducting slabs affect geochemical recycling and melt generation in the mantle wedge. The distribution of slab dehydration and the potential for slab melting are controlled by the composition/hydration of the slab entering a subduction zone and the pressure-temperature path that the slab follows. We examine the potential for along-strike changes in temperatures, fluid release, and slab melting for the subduction zone beneath the southern portion of the Southern Volcanic Zone (SVZ) in south central Chile. Because the age of the Nazca Plate entering the subduction zone decreases from ∼14 Ma north of the Guafo Fracture Zone to ∼6 Ma to the south, a southward warming of the subduction zone has been hypothesized. However, both north and south of Guafo Fracture Zone the geochemical signatures of southern SVZ arc lavas are similar, indicating 3-5 wt.% sediment melt and little to no contribution from melt of subducted basalt or aqueous fluids from subducted crust. We model temperatures in the system, use results of the thermal models and the thermodynamic calculation code Perple_X to estimate the pattern of dehydration-derived fluid release, and examine the potential locations for the onset of melting of the subducting slab. Surface heat flux observations in the region are most consistent with fluid circulation in the high permeability upper oceanic crust redistributing heat. This hydrothermal circulation preferentially cools the hottest parts of the system (i.e. those with the youngest subducting lithosphere). Models including the thermal effects of fluid circulation in the oceanic crust predict melting of the subducting sediment but not the basalt, consistent with the geochemical observations. In contrast, models that do not account for fluid circulation predict melting of both subducting sediment and basalt below the volcanic arc south of Guafo Fracture Zone. In our simulations with the effects of fluid circulation, the onset of sediment

  19. The role of partial melting and syn-orogenic deformation in the pre-concentration of uranium and thorium. The example of the CAGE District (Northern Quebec).

    NASA Astrophysics Data System (ADS)

    Trap, Pierre; Goncalves, Philippe; Durand, Cyril; Marquer, Didier; Feybesse, Jean-Louis; Richard, Yoann; Lacroix, Brice; Caillet, Yoann; Paquette, Jean-Louis

    2015-04-01

    This contribution aims to discuss the relationships between metamorphism, deformation and U-Th mineralization within the orogenic crust, from millimeter to kilometer scale and during the whole P-T-t evolution. The study area is the CAGE district along the paleoproterozoic Torngat orogen (Northern Quebec) made of 2.1 Ga metasedimentary rocks, marbles and paragneisses, deposited upon a 2.5 Ga orthogneissic basement. Several types of U-Th mineralizations have been reported within the middle crust highly metamorphosed and deformed during the Torgnat orogeny (1.9-1.8 Ga). An integrated study with field, geophysical, structural, petrological, geochemical and thermochronological analyses enable a reconstitution of the tectono-metamorphic setting of these U-Th mineralizations and of the mechanism responsible for their pre-concentration into the orogenic crust. The petrological analysis allows us to build a clockwise P-T-t-D evolution with peak pressure conditions at 7.5 - 10 kbar and 725 - 750 ° C and peak temperature conditions at 5-6 kbar and 800-850°C. This high grade metamorphism and widespread partial melting developed within a single dextral transpressive regime. The structural analysis suggests strain partitioning responsible for a S-C-C' like architecture observed at all scales. Aeromagnetic, radiometric and field observations revealed that U-Th mineralizations are mainly focused along the kilometer scale C and C'-type shear zones. The age of crustal partial melting was constrained by U-Pb LA-ICP-MS analyses on zircon and monazite within migmatitic paragneiss and orthogneiss between 1841 ± 5 and 1828 ± 7 Ma. Younger U-Pb ages at around 1810-1750 Ma have been reported on monazite and titanites within the crustal scale shear bands (C and C' like). Results obtained on mylonitic metacarbonaceous and metapelites within kilometer scale shear zones suggest that late shearing formed during retrograde evolution at decreasing temperature after peak metamorphism. The δ13

  20. Evidence of partial melting in xenoliths from the Wooley Creek batholith, Klamath Mountains, California: implications for assimilation processes

    NASA Astrophysics Data System (ADS)

    Coint, N.; Barnes, C. G.; Yoshinobu, A. S.; Barnes, M. A.

    2010-12-01

    Host rocks assimilation has been described as a process allowing mafic magma to evolve toward more felsic compositions as well as a way to explain isotopic variations observed in igneous rock suites. Assimilation modalities were first modeled as assimilation coupled with fractional crystallization (De Paolo, 1981. EPSL, v.53, 189-202), assuming that assimilation of host rocks or xenoliths was instantaneous and left no residue. Spera and Bohrson (2001. J.Pet., v.42, 999-1018) introduced the concept of EC-AFC (Energy-Conserved Assimilation- Fractional Crystallization). In this model, assimilation is due to mixing of partial melts from host rocks into the magma, and energy required for partial melting is taken into account numerically. Partial melting of the contaminant need not be complete; therefore, evidence of partial melting of host rocks and xenoliths should be observed in the field. The Wooley Creek batholith, situated in the Klamath Mountains in northern California, was emplaced between 159 and 156 My ago (Coint et al, 2009. Eos Trans. AGU, v.90-52, 1777). Xenoliths have been observed along the contacts and several km inside the pluton. Xenolith sizes vary from ~100 meters long to the centimeter scale. Xenoliths further than 3 km from the contact tend to be refractory (quartz-rich or calc-silicate) and small (<40 cm). Metasedimentary and metavolcanic protoliths can be identified. In metavolcanic rocks, the texture is granoblastic with the mineral assemblage two pyroxenes + plagioclase ± biotite ± hornblende ± quartz. Compositional layering is preserved in some of the metasedimentary xenoliths, creating variations of texture and mineral assemblages within single xenoliths from two pyroxene + plagioclase ± quartz ± hornblende ± biotite ± rutile granofels to plagioclase, sillimanite, cordierite, muscovite, quartz, biotite ± orthoclase ± rutile ± kyanite schists. Calc-silicate rocks are scant. Evidence of partial melting is widespread in xenoliths both

  1. Mineralogy of Inclusions in the Campo Del Cielo and Mont Dieu Irons and Segregation of Partial Melts

    NASA Astrophysics Data System (ADS)

    Takeda, H.; Ishii, T.; Otsuki, M.

    2001-03-01

    To find partial melt segregation, we studied two new irons. Segregations of albite and chromite were found in Campo del Cielo and ameboidal FeS in Mont Dieu with the same shape as in IIE irons together with minor Cr diopside and Na,K-rich glass.

  2. Experimental and geochemical evidence for derivation of the El Capitan Granite, California, by partial melting of hydrous gabbroic lower crust

    USGS Publications Warehouse

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

    2005-01-01

    Partial melting of mafic intrusions recently emplaced into the lower crust can produce voluminous silicic magmas with isotopic ratios similar to their mafic sources. Low-temperature (825 and 850??C) partial melts synthesized at 700 MPa in biotite-hornblende gabbros from the central Sierra Nevada batholith (Sisson et al. in Contrib Mineral Petrol 148:635-661, 2005) have major-element and modeled trace-element (REE, Rb, Ba, Sr, Th, U) compositions matching those of the Cretaceous El Capitan Granite, a prominent granite and silicic granodiorite pluton in the central part of the Sierra Nevada batholith (Yosemite, CA, USA) locally mingled with coeval, isotopically similar quartz diorite through gabbro intrusions (Ratajeski et al. in Geol Soc Am Bull 113:1486-1502, 2001). These results are evidence that the El Capitan Granite, and perhaps similar intrusions in the Sierra Nevada batholith with lithospheric-mantle-like isotopic values, were extracted from LILE-enriched, hydrous (hornblende-bearing) gabbroic rocks in the Sierran lower crust. Granitic partial melts derived by this process may also be silicic end members for mixing events leading to large-volume intermediate composition Sierran plutons such as the Cretaceous Lamarck Granodiorite. Voluminous gabbroic residues of partial melting may be lost to the mantle by their conversion to garnet-pyroxene assemblages during batholithic magmatic crustal thickening. ?? Springer-Verlag 2005.

  3. Low HFSE Rhyolites from Oregon: Smoking Gun for an Origin Through Partial Melting of the Crust

    NASA Astrophysics Data System (ADS)

    Streck, M. J.; Steiner, A. R.; Jenkins, E. N.; Large, A.

    2014-12-01

    Rhyolites are a significant component of continental magmatism of Oregon for the last 40 million years. Rhyolites of all time slices are compositionally diverse ranging from low to high-silica rhyolites, from less fractionated rhyolites with high Ba concentrations (≥1300 ppm Ba) and weak Eu anomalies (>0.4 Eu/Eu*) to strongly fractionated rhyolites with very low Ba contents (≤100 ppm) but strong Eu anomalies (≤0.2 Eu/Eu*), and rhyolites range from Fe-rich, A-type rhyolites to calc-alkaline varieties. In this study, we focus on one compositional end member of rhyolites that is characterized by very low concentrations of high field strength elements (HFSE) designated here as low HFSE rhyolites. Such low HFSE rhyolites contain Nb and Ta contents of 8-13 ppm and 0.8-1.1 ppm, respectively, and Zr and Hf concentrations of 60-150 ppm and 2.5-4 ppm, respectively. The significance of these low HFSE concentrations is that they are consistent with partial melting of observed crustal rocks but not with fractionation of observed mafic magmas. Compilation of chemical data of Cenozoic mafic magmas across Oregon indicate that the vast majority of basaltic rocks contain Nb and Zr contents in excess of 5 and 100 ppm, respectively. Only the most primitive high-Al olivine basalts have concentrations as low as 1 and 40 ppm. Basaltic magmas generate rhyolitic liquids after ~90-95% crystallization (e.g., as seen in lava lakes). After such high amounts of crystallization using basaltic magmas from Oregon, Nb and Zr contents would be far in excess of what is observed in these low HFSE rhyolites as both elements will behave incompatibly (strongly to moderately) during fractionation to rhyolites. Also, there are chemical and petrographic arguments that neither late titanite nor zircon fractionation in rhyolites caused low HFSE contents. Although lesser amounts of fractionation would be needed starting with an andesitic composition, HFSE contents of most andesites are already on levels

  4. The effects of small amounts of H2O on partial melting of model spinel lherzolite in the system CMAS

    NASA Astrophysics Data System (ADS)

    Liu, X.; St. C. Oneill, H.

    2003-04-01

    Water (H_2O) is so effective at lowering the solidus temperatures of silicate systems that even small amounts of H_2O are suspected to be important in the genesis of basaltic magmas. The realization that petrologically significant amounts of H_2O can be stored in nominally anhydrous mantle minerals (olivine and pyroxenes) has fundamental implications for the understanding of partial melting in the mantle, for it implies that the role that H_2O plays in mantle melting may not be appropriately described by models in which the melting is controlled by hydrous phases such as amphibole. Although the effect of water in suppressing the liquidus during crystallization is quite well understood, such observations do not provide direct quantitative information on the solidus. This is because liquidus crystallization occurs at constant major-element composition of the system, but at unbuffered component activities (high thermodynamic variance). By contrast, for partial melting at the solidus the major-element component activities are buffered by the coexisting crystalline phases (low variance), but the major-element composition of the melt can change as a function of added H_2O. Accordingly we have determined both the solidus temperature and the melt composition in the system CMAS with small additions of H_2O, to 4 wt%, in equilibrium with the four-phase lherzolite assemblage of fo+opx+cpx+sp. Experiments were conducted at 1.1 GPa and temperatures from 1473 K to the dry solidus at 1593 K in a piston-cylinder apparatus. Starting materials were pre-synthesised assemblage of fo+opx+cpx+sp, plus an oxide/hydroxide mix of approximately the anticipated melt composition. H_2O was added as either Mg(OH)_2 or Al(OH)_3. The crystalline assemblage and melt starting mix were added as separate layers inside sealed Pt capsules, to ensure large volumes of crystal-free melt. After the run doubly polished sections were prepared in order to analyse the quenched melt by FTIR spectroscopy, to

  5. Surface Melt and Firn Density Evolution in the Western Greenland Percolation Zone Over the Past 50 Years

    NASA Astrophysics Data System (ADS)

    Graeter, K.; Osterberg, E. C.; Hawley, R. L.; Thundercloud, Z. R.; Marshall, H. P.; Ferris, D. G.; Lewis, G.

    2016-12-01

    Predictions of the Greenland Ice Sheet's (GIS) contribution to sea-level rise in a warming climate depend on our ability to model the surface mass balance (SMB) processes occurring across the ice sheet. These processes are poorly constrained in the percolation zone, the region of the ice sheet where surface melt refreezes in the firn, thus preventing that melt from directly contributing to GIS mass loss. In this way, the percolation zone serves as a buffer to higher temperatures increasing mass loss. However, it is unknown how the percolation zone is evolving in a changing climate and to what extent the region will continue to serve as a buffer to future runoff. We collected seven shallow ( 22-30 m) firn cores from the Western Greenland percolation zone in May-June 2016 as part of the Greenland Traverse for Accumulation and Climate Studies (GreenTrACS) project. Here we present data on melt layer stratigraphy, density, and annual accumulation for each core to determine: (1) the temporal and spatial accumulation and melt refreeze patterns in the percolation zone of W. Greenland over the past 40 - 55 years, and (2) the impacts of changing melt and refreeze patterns on the near-surface density profile of the percolation zone. Three of the GreenTrACS firn cores re-occupy firn core sites collected in the 1970's-1990's, allowing us to more accurately quantify the evolution of the percolation zone surface melt and firn density during the most recent decades of summertime warming. This work is the basis for broader investigations into how changes in W. Greenland summertime climate are impacting the SMB of the Greenland Ice Sheet.

  6. Uranium and minor-element partitioning in Fe-Ti oxides and zircon from partially melted granodiorite, Crater Lake, Oregon

    USGS Publications Warehouse

    Tourrette, T.Z.L.; Burnett, D.S.; Bacon, C.R.

    1991-01-01

    Crystal-liquid partitioning in Fe-Ti oxides and zircon was studied in partially melted granodiorite blocks ejected during the climactic eruption of Mt. Mazama (Crater Lake), Oregon. The blocks, which contain up to 33% rhyolite glass (75 wt% SiO2), are interpreted to be portions of the magma chamber walls that were torn off during eruption. The glass is clear and well homogenized for all measured elements except Zr. Results for Fe-Ti oxides give DUoxide/liq ??? 0.1. Partitioning of Mg, Mn, Al, Si, V, and Cr in Fe-Ti oxides indicates that grains surrounded by glass are moderately well equilibrated with the melt for many of the minor elements, while those that are inclusions in relict plagioclase are not. Uranium and ytterbium inhomogeneities in zircons indicate that the zircons have only partially equilibrated with the melt and that uranium appears to have been diffusing out of the zircons faster than the zircons were dissolving. Minimum U, Y, and P concentrations in zircons give maximum DUzrc/liq = 13,DYzrc/liq = 23, and DPzrc/liq = 1, but these are considerably lower than reported by other workers for U and Y. Based on our measurements and given their low abundances in most rocks, Fe-Ti oxides probably do not play a major role in U-Th fractionation during partial melting. The partial melts were undersaturated with zircon and apatite, but both phases are present in our samples. This demonstrates an actual case of non-equilibrium source retention of accessory phases, which in general could be an important trace-element fractionation mechanism. Our results do not support the hypothesis that liquid structure is the dominant factor controlling trace-element partitioning in high-silica rhyolites. Rough calculations based on Zr gradients in the glass indicate that the samples could have been partially molten for 800 to 8000 years. ?? 1991.

  7. Heat transfer and fluid flow in floating-zone crystal growth with a mostly covered melt surface

    NASA Technical Reports Server (NTRS)

    Lan, C. W.; Kou, Sindo

    1992-01-01

    Computer simulation was conducted to study a modified floating-zone crystal growth process, in which the melt surface is mostly covered with a heated ring. The growth of 6-mm diameter single crystals of NaNO3 was considered, and the effects of the following parameters were studied: (1) temperature of the ring, (2) growth rate, (3) surface tension-temperature coefficient of the melt, (4) thermal expansion coefficient of the melt, and (5) gravity. It was demonstrated that thermocapillary convection in the melt zone is reduced significantly in this modified process. The model was checked against the measured lengths of the meniscus near the growth front and axial temperature distribution in a growing crystal, and the agreement was good.

  8. Heat transfer and fluid flow in floating-zone crystal growth with a mostly covered melt surface

    NASA Technical Reports Server (NTRS)

    Lan, C. W.; Kou, Sindo

    1992-01-01

    Computer simulation was conducted to study a modified floating-zone crystal growth process, in which the melt surface is mostly covered with a heated ring. The growth of 6-mm diameter single crystals of NaNO3 was considered, and the effects of the following parameters were studied: (1) temperature of the ring, (2) growth rate, (3) surface tension-temperature coefficient of the melt, (4) thermal expansion coefficient of the melt, and (5) gravity. It was demonstrated that thermocapillary convection in the melt zone is reduced significantly in this modified process. The model was checked against the measured lengths of the meniscus near the growth front and axial temperature distribution in a growing crystal, and the agreement was good.

  9. Base-state stress-driven melt segregation in torsion and extrusion experiments on partially molten rocks

    NASA Astrophysics Data System (ADS)

    Qi, C.; Kohlstedt, D. L.; Katz, R. F.; Takei, Y.

    2013-12-01

    Partial melting in Earth mostly occurs at regions undergoing intense deformation. To understand the behavior of partially molten rocks exposed to differential stress, two-phase aggregates consisting of a solid and melt were deformed at high-temperature, high-pressure laboratory conditions. In these experiments, stress-driven melt segregation that leads to the formation of melt-enriched bands has been produced consistently. This segregation process has been successfully reproduced by a theory based on anisotropic viscosity of sheared two-phase aggregates. This theory also predicts a base-state (background), stress-driven melt segregation at the sample-scale. Here we present experimental results from torsion and extrusion experiments designed to test the theoretical predictions. Samples composed of fine-grained San Carlos olivine and uniformly distributed basalt melt were deformed in two different types of experiments at a temperature of 1200°C and a confining pressure of 300 MPa in a gas-medium apparatus. Samples were either sheared in torsion at constant strain rate to a maximum strain of γ ≈ 13 or extruded through a rigid tube at constant differential pressure in a Poiseuille flow geometry. Melt distribution maps obtained from reflected-light optical and backscattered electron micrographs demonstrate that melt migrates radially inward from the outer edge to the center of torsion samples and radially outward from the center to the wall of the tube in extrusion samples. This base-state melt segregation indicates that the partially molten aggregate decompacted (compacted) at the center (outer edge) of torsion samples and at the wall (center) of extrusion samples. Based on the observed melt distribution, we conclude that the compaction/decompaction rate increases with increasing stress, as predicted by the theory. These experimental observations qualitatively agree with the theoretical predictions, with some quantitative discrepancies remaining such as the

  10. Microstructural Evolution of Semisolid 6063 Aluminum Alloy Prepared by Recrystallization and Partial Melting Process

    NASA Astrophysics Data System (ADS)

    Wang, Yongfei; Zhao, Shengdun; Zhang, Chenyang

    2017-08-01

    Radial forging (RF) was proposed as a novel deformation method to prepare semisolid 6063 aluminum alloy in the recrystallization and partial melting (RAP) process. The effects of area reduction rate, isothermal holding temperature and time on the microstructural evolution of RF-deformed 6063 aluminum alloy were investigated. Results showed that RF can be successfully introduced in RAP process to prepare large semisolid 6063 aluminum alloy bar. With the increase of the area reduction rate, the average grain size firstly decreased and then no significant change occurred. Meanwhile, the spheroidization degree of solid grains firstly increased rapidly, and then increased slowly. The effects of isothermal holding temperature and time are similar, with the increase of the isothermal holding temperature or time, the average grain size initially decreased but then increased; and the spheroidization degree of solid grains gradually increased. High-quality semisolid 6063 aluminum alloy can be prepared with 70% area reduction rate and subsequent semisolid isothermal treatment (SSIT) at 630 °C for 10 min. The coarsening rate constant was 5185.2 µm3/s at 630 °C. Additionally, a strong deformation texture was created in the RF-deformed alloy with 70% area reduction rate, which was transformed to a weakened texture following the SSIT process.

  11. Development and characterization of zone melt growth GaAs for gamma-ray detectors

    SciTech Connect

    King, S.E.; Dietrich, H.B.; Henry, R.L.; Katzer, D.S.; Moore, W.J.; Phillips, G.W.; Mania, R.C.

    1996-06-01

    GaAs is a potentially attractive material for room temperature x-ray and {gamma}-ray spectrometers. To date, the only high resolution GaAs devices were produced by epitaxial growth. The usefulness of detectors made from bulk grown semi-insulating (SI) GaAs has been limited by low charge collection efficiency caused, it is believed, by the high density of EL2 deep donor defects. Vertical zone melt (VZM) growth of GaAs has recently been developed at the Naval Research Laboratory. Zone refining and zone leveling techniques were used with VZM to reduce the level of impurities and the EL2 defects in bulk SI-GaAs. Schottky barrier and PIN diodes have been fabricated from the newly grown material. These devices were characterized using {alpha} particles and {gamma}-rays. In this paper, the measurements and analysis of the first VZM GaAs devices are presented and compared with commercially available GaAs. The intent is to test the hypothesis that high purity, low defect GaAs material growth could lead to improved radiation detectors.

  12. Experimental investigation of the electrical behavior of olivine during partial melting under pressure and application to the lunar mantle

    NASA Astrophysics Data System (ADS)

    Pommier, A.; Leinenweber, K.; Tasaka, M.

    2015-09-01

    Electrical conductivity measurements were performed during melting experiments of olivine compacts (dry and hydrous Fo77 and Fo90) at 4 and 6 GPa in order to investigate melt transport properties and quantify the effect of partial melting on electrical properties. Experiments were performed in the multi-anvil apparatus and electrical measurements were conducted using the impedance spectroscopy technique with the two-electrode method. Changes in impedance spectra were used to identify the transition from an electrical response controlled by the solid matrix to an electrical response controlled by the melt phase. This transition occurs slightly above the solidus temperature and lasts until Tsolidus + 75 °C (±25). At higher temperature, a significant increase in conductivity (corresponding to an increase in conductivity values by a factor ranging from ∼30 to 100) is observed, consistent with the transition from a tube-dominated network to a structure in which melt films and pools become prominent features. This increase in conductivity corresponds to an abrupt jump for all dry samples and to a smoother increase for the hydrous sample. It is followed by a plateau at higher temperature, suggesting that the electrical response of the investigated samples lacks sensitivity to temperature at an advanced stage of partial melting. Electron microprobe analyses on quenched products indicated an increase in Mg# (molar Mg / (Mg +Fe)) of olivine during experiments (∼77-93 in the quenched samples with an initial Fo77 composition and ∼92-97 in the quenched samples with an initial Fo90 composition) due to the partitioning of iron to the melt phase. Assuming a respective melt fraction of 0.10 and 0.20 before and after the phase of significant increase in conductivity, in agreement with previous electrical and permeability studies, our results can be reproduced satisfactorily by two-phase electrical models (the Hashin and Shtrikman bounds and the modified brick layer model

  13. 49 CFR 222.41 - How does this rule affect Pre-Rule Quiet Zones and Pre-Rule Partial Quiet Zones?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Pre-Rule Partial Quiet Zones? 222.41 Section 222.41 Transportation Other Regulations Relating to... Groups of Crossings-Quiet Zones § 222.41 How does this rule affect Pre-Rule Quiet Zones and Pre-Rule...-Rule Quiet Zone may be established by automatic approval and remain in effect, subject to § 222.51,...

  14. The low magnetic field properties of superconducting bulk yttrium barium copper oxide - Sintered versus partially melted material

    NASA Technical Reports Server (NTRS)

    Hein, R. A.; Hojaji, H.; Barkatt, A.; Shafii, H.; Michael, K. A.; Thorpe, A. N.; Ware, M. F.; Alterescu, S.

    1989-01-01

    A comparison of the low magnetic field properties of sintered (990 C) and partially melted samples (1050 C) has been performed. Changes in the microstructure produced by recrystallization from the melt result in a significant increase in flux pinning at 77 K. Low-frequency (10-100 Hz), low-ac magnetic-field (0.01-9.0 Oe) ac susceptibility data show that gross changes in the loss component accompany the observed changes in microstructure. The effects of applied dc magnetic fields (10-220 Oe) on the ac responses of these microstructures have also been probed.

  15. The low magnetic field properties of superconducting bulk yttrium barium copper oxide - Sintered versus partially melted material

    NASA Technical Reports Server (NTRS)

    Hein, R. A.; Hojaji, H.; Barkatt, A.; Shafii, H.; Michael, K. A.; Thorpe, A. N.; Ware, M. F.; Alterescu, S.

    1989-01-01

    A comparison of the low magnetic field properties of sintered (990 C) and partially melted samples (1050 C) has been performed. Changes in the microstructure produced by recrystallization from the melt result in a significant increase in flux pinning at 77 K. Low-frequency (10-100 Hz), low-ac magnetic-field (0.01-9.0 Oe) ac susceptibility data show that gross changes in the loss component accompany the observed changes in microstructure. The effects of applied dc magnetic fields (10-220 Oe) on the ac responses of these microstructures have also been probed.

  16. Deeper Subduction Zone Melting Explains Enrichment of Upper Mantle and Resolves Dehydration Paradox

    NASA Astrophysics Data System (ADS)

    Dixon, Jacqueline; Bindeman, Ilya; Kingsley, Richard

    2017-04-01

    We present new volatile and stable isotope data on oceanic basaltic glasses with a range of enriched compositions. Basalt compositions studied here can be modeled by mixing between depleted mantle and various enriched (EM) and prevalent (PREMA) mantle components. We develop a multi-stage metasomatic and melting model for the origin of the enriched components, extending the subduction factory concept to involve melting of different components at different depths, down to the mantle transition zone (660 km), with slab temperature a key variable. EM components are heterogeneous, ranging from wet and heavy (Arctic Ridges) to dry and light (East Pacific Rise), and are derived from the subducted slab at depths of 150 to 250 km by addition of <1 % carbonated sediment-derived supercritical C-O-H fluids to depleted peridotite. PREMA mantle sources have a limited compositional range, and form at depths at and within the transition zone (410 to 660 km) by addition of <1 % carbonated eclogite ± sediment-derived supercritical fluids to depleted mantle. The model resolves several problems, including the "dehydration paradox," refering to the following conundrum. The enriched "prevalent mantle" (PREMA) end-member in mid-oceanic ridge and ocean island basalts requires involvement of a mostly dehydrated slab component to explain trace element ratios and radiogenic isotopic compositions, but a fully hydrated slab component to explain stable isotope compositions. In our model, thermal parameters of slabs control the timing and composition of subduction-derived components. This includes deep release of fluids from subcrustal hydrous phases that may rehydrate previously dehydrated slab, resolving the paradox.

  17. Timescales of partial melting in the Himalayan middle crust: insight from the Leo Pargil dome, northwest India

    NASA Astrophysics Data System (ADS)

    Lederer, Graham W.; Cottle, John M.; Jessup, Micah J.; Langille, Jackie M.; Ahmad, Talat

    2013-11-01

    The Leo Pargil dome (LPD) in northwest India exposes an interconnected network of pre-, syn-, and post-kinematic leucogranite dikes and sills that pervasively intrude amphibolite-facies metapelites of the mid-crustal Greater Himalayan sequence. Leucogranite bodies range from thin (5-cm-wide) locally derived sills to thick (2-m-wide) crosscutting dikes extending at least 100 m. Three-dimensional exposures elucidate crosscutting relations between different phases of melt injection and crystallization. Combined laser ablation inductively coupled plasma mass spectrometry U-Th/Pb geochronology and trace element analysis on well-characterized monazite grains from nineteen representative leucogranites yields a large, internally consistent data set of approximately 700 U-Th/Pb and 400 trace element analyses. Grain-scale variations in age correlate with trace element distributions and indicate semi-continuous crystallization of monazite from 30 to 18 Ma. The youngest U-Th/Pb ages in a given sample are consistent with the outcrop-scale crosscutting relations, whereas older ages within individual samples record inheritance from partially crystallized melt and source metapelites. U-Th/Pb isotopic and trace element data are incorporated into a model of melting within the LPD that involves (1) steady-state equilibrium batch melting of compositionally homogeneous metapelitic sources; (2) pulses of increased melt mobility lasting 1-2 m.y. resulting in segregation of melt from its source and amalgamation into mixed magmas; and (3) rapid emplacement and final crystallization of leucogranite bodies. Melt systems in the LPD evolved from locally derived, in situ melt in migmatitic source rocks into a vast network of dikes and sills in the overlying non-migmatitic host rocks.

  18. Generation of trondhjemite from partial melting of dacite under granulite facies conditions: an example from the New Jersey Highlands, USA

    USGS Publications Warehouse

    Puffer, J.H.; Volkert, R.A.

    1991-01-01

    New field and geochemical data place the Losee Metamorphic Suite (a tonalite/trondhjemite complex) of northern New Jersey into the context of a major Proterozoic continental are represented by a discontinuous belt of northern Appalachian metadacite. Samples of Losee rock range from extremely leucocratic trondhjemite locally associated with amphibolite, to banded biotite, hornblende, pyroxene, and garnet-bearing tonalites. The major element and REE composition of the tonalite closely resembles dacite from continental are settings and model melts extracted from an eclogite residue by partial melting at 15 kbar. The REE composition of most Losee trondhjemite is enriched in REE, particularly HREE, compared with Losee tonalite, and is interpreted as the product of local anatectic melting of Losee tonalite (metadacite) that occurred in a granulite facies environment during the Grenville orogeny. ?? 1991.

  19. Partial melting and refertilization of mantle peridotites in the Xigaze ophiolite: constraints from whole-rock and mineral geochemistry

    NASA Astrophysics Data System (ADS)

    Zhang, Chang; Liu, Chuan-Zhou; Wu, Fu-Yuan

    2016-04-01

    Ophiolites along the E-W trending Yarlung-Tsangpo Suture (YTS), which separates the Indian plate from the Eurasian plate, have been regarded as relics of the Neo-Tethyan Ocean. The Xigaze ophiolite in the central YTS has been extensively studied. One of the most intact crust-mantle sequences is preserved in the Luqu (or Beimarang) ophiolite. Mantle peridotites of the Luqu ophiolite are dominated by harzburgites, with 55-65% olivine, 30-40% orthopyroxene, 1-5% clinopyroxene and 1-3% spinel. Minor lherzolites and dunites are also outcropped, and the mode contents of clinopyroxene in lherzolite can be locally up to 10%. This contribution presented whole-rock major element and mineral chemistry including EMPA (Electronic MicroProbe Analysis) and clinopyroxene in situ trace elements. Whole rock Al2O3 (0.23-2.05%) and CaO (0.41-1.7%) contents are very low but show obviously inverse correlation with MgO (39.7-47.0%), indicating that the Luqu peridotites are residues of variable degrees of partial melting. This is supported by the Cr# (=molar Cr/(Cr+Al)) values of spinels which vary from 0.36 to 0.69. Meanwhile, the high Cr# values of spinels and homogenously high Mg# (= molar Mg/(Mg+Fe2+)) values of olivines, clustering at 0.91, indicate high degrees of partial melting. The low REE (rare earth elements) concentrations and chondrite-normalized distribution partterns of clinopyroxenes reflect ultra-depleted natures, with most showing LREE (light REEs) and MREE (medium REEs) depleted patterns and strong fractionations between MREEs and HREE (heavy REEs) ((Sm/Yb)N: 0.021-0.184). Based on the observations and analyses, a model of two-stage melting process was proposed that the primitive mantle underwent 2-8% melting in garnet stability field which was followed by 10-15% melting in spinel stability field. The clinopyroxenes in some peridotites exhibit obvious enrichment of somestrongly incompatible elements (such as sodium and LREE) that reveal later refertilization process for

  20. Feedbacks between deformation and melt distribution in the crust-mantle transition zone of the Oman ophiolite

    NASA Astrophysics Data System (ADS)

    Higgie, Katherine; Tommasi, Andréa

    2012-12-01

    This study presents microstructural evidence for deformation-controlled melt organization and for changes in olivine deformation associated with the presence of melt in an 80 m vertical section of the crust-mantle transition zone in the Oman ophiolite. This zone represents an ‘end member’ case for analyzing feedbacks between deformation and melt distribution in the upper mantle, since it experienced strong shear strains in presence of large melt fractions. It is characterized by a subhorizontal compositional layering at the mm to meter scale, from weakly impregnated dunites to olivine-rich gabbros, which parallels a pervasive foliation containing a strong stretching lineation. The parallelism between the compositional layering and the foliation, the diffuse limits of the layers, the alignment of elongated plagioclase-rich aggregates devoid of internal deformation structures with the elongation of olivine crystals in the dunitic layers, and the sharp compositional changes across some, but not all layer limits suggest deformation plays an essential role on the development of the layering. The variation on a mm-scale of the olivine crystal preferred orientation (CPO) symmetry as a function of the modal content: from axial-[100] symmetry in layers with <70% modal olivine to axial-[010] in more gabbroic levels (<40% olivine), which is repeated over the entire section, implies deformation in presence of variable melt fractions. Axial-[100] olivine CPO in olivine-rich layers is consistent with deformation by dislocation creep under high temperature, low pressure, dry conditions. Axial-[010] olivine CPO patterns imply additional sliding along preferentially wetted (010) grain boundaries, increase in the activity of [001] glide, or transpression localized in the melt-rich layers. Since the change in CPO symmetry is not accompanied by dispersion, instantaneous melt fractions must have remained <30-40% in all layers. The continuous variation in olivine CPO symmetry with

  1. A petrologic, thermodynamic and experimental study of brachinites: Partial melt residues of an R chondrite-like precursor

    NASA Astrophysics Data System (ADS)

    Gardner-Vandy, Kathryn G.; Lauretta, Dante S.; McCoy, Timothy J.

    2013-12-01

    The primitive achondrites provide a window into the initial melting of asteroids in the early solar system. The brachinites are olivine-dominated meteorites with a recrystallized texture that we and others interpret as evidence of partial melting and melt removal on the brachinite parent body. We present a petrologic, thermodynamic and experimental study of the brachinites to evaluate the conditions under which they formed and test our hypothesis that the precursor material to the brachinites was FeO-rich compared to the precursors of other primitive achondrites. Petrologic analysis of six brachinites (Brachina, Allan Hills (ALH) 84025, Hughes 026, Elephant Moraine (EET) 99402, Northwest Africa (NWA) 3151, and NWA 4969) and one brachinite-like achondrite (NWA 5400) shows that they are meteorites with recrystallized texture that are enriched in olivine (⩾80 vol.%) and depleted in other minerals with respect to a chondritic mineralogy. Silicates in the brachinites are FeO-rich (Fa32-36). Brachinite-like achondrite Northwest Africa 5400 is similar in mineralogy and texture to the brachinites but with a slightly lower FeO-content (Fa30). Thermodynamic calculations yield equilibration temperatures above the Fe,Ni-FeS cotectic temperature (∼950 °C) for all meteorites studied here and temperatures above the silicate eutectic (∼1050 °C) for all but two. Brachina formed at an fO2 of ∼IW, and the other brachinites and NWA 5400 formed at ∼IW - 1. All the meteorites show great evidence of formation by partial melting having approximately chondritic to depleted chondritic mineralogies, equilibrated mineral compositions, and recrystallized textures, and having reached temperatures above that required for melt generation. In an attempt to simulate the formation of the brachinite meteorites, we performed one-atmosphere, gas-mixing partial melting experiments of R4 chondrite LaPaz Ice Field 03639. Experiments at 1250 °C and an oxygen fugacity of IW - 1 produce residual

  2. Magnetic and elastic wave anisotropy in partially molten rocks: insight from experimental melting of synthetic quartz-mica schist (Invited)

    NASA Astrophysics Data System (ADS)

    Almqvist, B.; Misra, S.; Biedermann, A. R.; Mainprice, D.

    2013-12-01

    We studied the magnetic and elastic wave speed anisotropy of a synthetically prepared quartz-mica schist, prior to, during and after experimental melting. The synthetic rock was manufactured from a mixture of powders with equal volumes of quartz and muscovite. The powders were initially compacted with 200 MPa uniaxial stress at room temperature and sealed in a stainless steel canister. Subsequently the sealed canister was isostatically pressed at 180 MPa and 580 °C for 24 hours. This produced a solid medium with ~25 % porosity. Mica developed a preferred grain-shape alignment due to the initial compaction with differential load, where mica flakes tend to orient perpendicular to the applied stress and hence define a synthetic foliation plane. In the last stage we used a Paterson gas-medium apparatus, to pressurize and heat the specimens up to 300 MPa and 750 °C for a six hour duration. This stage initially compacted the rock, followed by generation of melt, and finally crystallization of new minerals from the melt. Elastic wave speed measurements were performed in situ at pressure and temperature, with a transducer assembly mounted next to the sample. Magnetic measurements were performed before and after the partial melt experiments. Anisotropy was measured in low- and high-field, using a susceptibility bridge and torsion magnetometer, respectively. Additionally we performed measurements of hysteresis, isothermal remanent magnetization (IRM) and susceptibility as a function of temperature, to investigate the magnetic properties of the rock. The elastic wave speed, before the melting-stage of the experiment, exhibits a distinct anisotropy with velocities parallel to the foliation being about 15 % higher than normal to the foliation plane. Measurements of the magnetic anisotropy in the bulk sample show that anisotropy is originating from the preferred orientation of muscovite, with a prominent flattening fabric. In contrast, specimens that underwent partial melting

  3. A New Approach for Studying Softening and Melting Behavior of Particles in a Blast Furnace Cohesive Zone

    NASA Astrophysics Data System (ADS)

    Yang, Wenjing; Zhou, Zongyan; Pinson, David; Yu, Aibing

    2015-04-01

    The cohesive zone where ferrous burden materials soften and melt plays a critical role in determining the performance and stability of a blast furnace. The softening and melting behavior of ore particles significantly affects the layer permeability and structure, and subsequently changes the gas/liquid distribution and heat transfer in the cohesive zone. Wax balls are often used in physical experiments to study the ore softening and melting behavior because of their low melting temperature. In this work, a new approach on the basis of discrete element method is established. The relationship between Young's modulus ( E) and temperature ( T) of wax balls is first proposed based on the experimental data, and then implemented into a DEM model. The particle deformation, temperature, coordination number, and gas pressure drop under conditions relevant to blast furnace operations are then examined. The results show that the proposed approach can capture the main features of softening and melting behavior of particles. On this basis, the effects of a few variables are investigated. The approach and results should be useful to the establishment of a comprehensive picture about softening and melting behavior, and its effect on blast furnace operations.

  4. Snow distribution, melt and surface water inputs to the soil in the mountain rain-snow transition zone

    USDA-ARS?s Scientific Manuscript database

    The timing, magnitude, and spatial distribution of snow cover and the resulting surface water inputs (SWI) are quantified for a catchment in the rain-snow transition zone. Although the timing of melt events are similar across the basin, southwest facing slopes receive smaller and more frequent SWI ...

  5. Vegetative growth and cluster development in Shiraz grapevines subjected to partial root-zone cooling.

    PubMed

    Rogiers, Suzy Y; Clarke, Simon J

    2013-01-01

    Heterogeneity in root-zone temperature both vertically and horizontally may contribute to the uneven vegetative and reproductive growth often observed across vineyards. An experiment was designed to assess whether the warmed half of a grapevine root zone could compensate for the cooled half in terms of vegetative growth and reproductive development. We divided the root system of potted Shiraz grapevines bilaterally and applied either a cool or a warm treatment to each half from budburst to fruit set. Shoot growth and inflorescence development were monitored over the season. Simultaneous cooling and warming of parts of the root system decreased shoot elongation, leaf emergence and leaf expansion below that of plants with a fully warmed root zone, but not to the same extent as those with a fully cooled root zone. Inflorescence rachis length, flower number and berry number after fertilization were smaller only in those vines exposed to fully cooled root zones. After terminating the treatments, berry enlargement and the onset of veraison were slowed in those vines that had been exposed to complete or partial root-zone cooling. Grapevines exposed to partial root-zone cooling were thus delayed in vegetative and reproductive development, but the inhibition was greater in those plants whose entire root system had been cooled.

  6. Vegetative growth and cluster development in Shiraz grapevines subjected to partial root-zone cooling

    PubMed Central

    Rogiers, Suzy Y.; Clarke, Simon J.

    2013-01-01

    Heterogeneity in root-zone temperature both vertically and horizontally may contribute to the uneven vegetative and reproductive growth often observed across vineyards. An experiment was designed to assess whether the warmed half of a grapevine root zone could compensate for the cooled half in terms of vegetative growth and reproductive development. We divided the root system of potted Shiraz grapevines bilaterally and applied either a cool or a warm treatment to each half from budburst to fruit set. Shoot growth and inflorescence development were monitored over the season. Simultaneous cooling and warming of parts of the root system decreased shoot elongation, leaf emergence and leaf expansion below that of plants with a fully warmed root zone, but not to the same extent as those with a fully cooled root zone. Inflorescence rachis length, flower number and berry number after fertilization were smaller only in those vines exposed to fully cooled root zones. After terminating the treatments, berry enlargement and the onset of veraison were slowed in those vines that had been exposed to complete or partial root-zone cooling. Grapevines exposed to partial root-zone cooling were thus delayed in vegetative and reproductive development, but the inhibition was greater in those plants whose entire root system had been cooled. PMID:24244839

  7. Coherent x-ray wavefront reconstruction of a partially illuminated Fresnel zone plate.

    PubMed

    Mastropietro, F; Carbone, D; Diaz, A; Eymery, J; Sentenac, A; Metzger, T H; Chamard, V; Favre-Nicolin, V

    2011-09-26

    A detailed characterization of the coherent x-ray wavefront produced by a partially illuminated Fresnel zone plate is presented. We show, by numerical and experimental approaches, how the beam size and the focal depth are strongly influenced by the illumination conditions, while the phase of the focal spot remains constant. These results confirm that the partial illumination can be used for coherent diffraction experiments. Finally, we demonstrate the possibility of reconstructing the complex-valued illumination function by simple measurement of the far field intensity in the specific case of partial illumination.

  8. [Effect of water stress in partial root zone on response of photosynthesis of Aconitum barbatum].

    PubMed

    Li, Jie; Zhou, Chune; Liang, Zhiying; Miao, Qing

    2012-05-01

    To study the effect of different water stress mode on photosynthesis characteristics of Aconitum barbaturnm, aimed at providing the theoretical basis for cultivating this kind of plant for the arid area. The transplanted seedlings of A. barbatum were processed with fixed partial root zone drying(TI) ,alternate partial root zone drying(T2) and both partial root zone irrigation (T3) for three cycles,and relative parameters were measured. The net photosynthetic rate (Pn) in the treatment of T2 gradually increased and was higher than that in the treatment of T3 about 6.53%, mainly effected by non-stomatal factors. The water use efficiency (WUE) was higher than that in the treatments of T3 about 25.21%, while the transpiration rate (Tr) and the stomatal conductance was lower than those in the treatment of T1 and T3 separately. The maximum net photosynthesis rate (Pmax),the apparent quantum yield (AQY) and the dark respiration rate (Rd) were higher than those in comparison condition slightly. The alternate partial root zone drying is worth promoting vigorously, and it shall be a rational way to cultivate the A. barbatum under woodland.

  9. A meteorological experiment in the melting zone of the Greenland ice sheet

    SciTech Connect

    Oerlemans, J. ); Vugts, H.F. )

    1993-03-01

    Preliminary results are described from a glaciometeorological experiment carried out in the margin (melting zone) of the Greenland ice sheet in the summers of 1990 and 1991. This work was initiated within the framework of a Dutch research program on land ice and sea level change. Seven meteostations were operated along a transect running from the tundra well onto the ice sheet. At the ice edge, humidity, temperature, and wind profiles were obtained with a tethered balloon. On the ice sheet, 90 km from the edge, a boundary-layer research unit, including a sound detecting and ranging system (SODAR) and a radio acoustic sounding system (RASS), was established. Although focusing on the relation between surface energy balance, glacier mass balance, and ice flow, the experiment has also delivered a unique dataset on the dynamics of the atmospheric boundary layer around the warm tundra-cold ice sheet transition. Unexpected behavior was found for the surface albedo during the melt season. Lowest values are not found close to the ice edge, which is usual for glaciers, but higher on the ice sheet. Meltwater accumulation due to inefficient surface drainage was found to be the cause for this. The wind regime is dominated by katabatic flow from the ice sheet. The katabatic layer is typically 100-200 m thick. Close to the ice edge, the flow exhibits a very regular daily rhythm, with maximum wind speed in the afternoon. Farther on the ice sheet, the regime changes, and wind speed reaches maximum values in late night/early morning.

  10. Why Archaean TTG cannot be generated by MORB melting in subduction zones

    NASA Astrophysics Data System (ADS)

    Martin, Hervé; Moyen, Jean-François; Guitreau, Martin; Blichert-Toft, Janne; Le Pennec, Jean-Luc

    2014-06-01

    Until recently it was assumed that the Archaean continental crust (made of TTGs: tonalites, trondhjemites, and granodiorites) was generated through partial melting of MORB-like basalts in hot subduction environments, where the subducted oceanic crust melted at high pressure, leaving a garnet-bearing amphibolitic or eclogitic residue. However, recent geochemical models as well as basalt melting experiments have precluded MORB as a plausible source for TTGs. Rather, geochemical and experimental evidences indicate that formation of TTG required a LILE-enriched source, similar to oceanic plateau basalts. Moreover, subduction is a continuous process, while continental growth is episodic. Several “super-growth events” have been identified at ~ 4.2, ~ 3.8, ~ 3.2, ~ 2.7, ~ 1.8, ~ 1.1, and ~ 0.5 Ga, which is inconsistent with the regular pattern that would be expected from a subduction-driven process. In order to account for this periodicity, it has been proposed that, as subduction proceeds, descending residual slabs accumulate at the 660-km seismic discontinuity. When stored oceanic crust exceeds a certain mass threshold, it rapidly sinks into the mantle as a cold avalanche, which induces the ascent of mantle plumes that in turn produce large amounts of magmas resulting in oceanic plateaus. However, melting at the base of thick oceanic plateaus does not appear to be a realistic process that can account for TTG genesis. Modern oceanic plateaus contain only small volumes (≤ 5%) of felsic magmas generally formed by high degrees of fractional crystallization of basaltic magmas. The composition of these felsic magmas drastically differs from that of TTGs. In Iceland, the interaction between a mantle plume and the mid-Atlantic ridge gives rise to an anomalously (Archaean-like) high geothermal gradient resulting in thick basaltic crust able to melt at shallow depth. Even in this favorable context though, the characteristic Archaean TTG trace element signature is not being

  11. Modeling composition of partial melts in mantle upwellings through Earth history: an example of a 2D poster

    NASA Astrophysics Data System (ADS)

    Sparks, D. W.; Cheadle, M.

    2004-12-01

    The composition of magmas created by partial melting of the mantle depend on the interplay of several processes: the mantle phase diagram, the physics of magma migration through the mantle and crust, the patterns of solid-state mantle and fluid circulation and heat transfer, to name a few. This modeling study attempts a self-consistent combination of these physical and chemical processes, to predict the composition of magma created in upwelling mantle over a very broad range of mantle conditions, with particular emphasis on the deep past in a hot Archean mantle. We utilize 1) high P-T melting experiments to constrain the composition of melts formed at different depths in the mantle, 2) thermal and compositional solid-state convection models to constrain the temperature and melting rate and the three-dimensional distribution of these melts, and 3) simplified models of magma migration to predict the accumulation and mixing of these magmas, for comparison with mantle-derived primitive melts over time. An explanation of this study requires a description of details from a number of varied disciplines (Archean geology, trace element geochemistry, experimental petrology, solid-state convection, magma migration). While most interested poster readers will want to know the details of one or two aspects of the calculations, few will want to wade through them all. This goal of this poster design is to present the outline of the story in way that can be scanned quickly at a distance, but with several independent offshoots containing explanation of parts of the story that can be either read or skipped, and yet another level containing details for the experts on a particular topic.

  12. Partial melting of the St. Severin (LL) and Lost City (H) ordinary chondrites: One step backwards and two steps forward

    NASA Technical Reports Server (NTRS)

    Jurewicz, A. J. G.; Jones, J. H.; Mittlefehldt, D. W.

    1994-01-01

    This study looks at partial melting in H and LL chondrites at nearly one atmosphere of total pressure as part of a continuing study of the origins of basaltic achondrites. Previously, melting experiments on anhydrous CM and CV chondrites showed that, near its solidus, the CM chondrite produced melts having major element chemistries similar to the Sioux County eucrite; but, the pyroxenes in the residuum were too iron-rich to form diogenites. Our preliminary results from melting experiments on ordinary (H, LL) chondrites suggested that, although the melts did not look like any known eucrites, pyroxenes from these charges bracketed the compositional range of pyroxenes found in diogenites. We had used the Fe/Mg exchange coefficients calculated for olivine, pyroxene, and melt in these charges to evaluate the approach to equilibrium, which appeared to be excellent. Unfortunately, mass balance calculations later indicated to us that, unlike our CM and CV charges, the LL and H experimental charges had lost significant amounts of iron to their (Pt or PtRh) supports. Apparently, pyroxene stability in chondritic systems is quite sensitive to the amount of FeO, and it was this unrecognized change in the bulk iron content which had stabilized the high temperature, highly magnesian pyroxenes. Accordingly, this work reinvestigates the phase equilibria of ordinary chondrites, eliminating iron and nickel loss, and reports significant differences. It also looks closely at how the iron and sodium in the bulk charge affect the stability of pyroxene, and it comments on how these new results apply to the problems of diogenite and eucrite petrogenesis.

  13. Trace element signature of subduction-zone fluids, melts and supercritical liquids at 120-180 km depth.

    PubMed

    Kessel, Ronit; Schmidt, Max W; Ulmer, Peter; Pettke, Thomas

    2005-09-29

    Fluids and melts liberated from subducting oceanic crust recycle lithophile elements back into the mantle wedge, facilitate melting and ultimately lead to prolific subduction-zone arc volcanism. The nature and composition of the mobile phases generated in the subducting slab at high pressures have, however, remained largely unknown. Here we report direct LA-ICPMS measurements of the composition of fluids and melts equilibrated with a basaltic eclogite at pressures equivalent to depths in the Earth of 120-180 km and temperatures of 700-1,200 degrees C. The resultant liquid/mineral partition coefficients constrain the recycling rates of key elements. The dichotomy of dehydration versus melting at 120 km depth is expressed through contrasting behaviour of many trace elements (U/Th, Sr, Ba, Be and the light rare-earth elements). At pressures equivalent to 180 km depth, however, a supercritical liquid with melt-like solubilities for the investigated trace elements is observed, even at low temperatures. This mobilizes most of the key trace elements (except the heavy rare-earth elements, Y and Sc) and thus limits fluid-phase transfer of geochemical signatures in subduction zones to pressures less than 6 GPa.

  14. A geochemical study of the winonaites: Evidence for limited partial melting and constraints on the precursor composition

    NASA Astrophysics Data System (ADS)

    Hunt, Alison C.; Benedix, Gretchen K.; Hammond, Samantha J.; Bland, Philip A.; Rehkämper, Mark; Kreissig, Katharina; Strekopytov, Stanislav

    2017-02-01

    The winonaites are primitive achondrites which are associated with the IAB iron meteorites. Textural evidence implies heating to at least the Fe, Ni-FeS cotectic, but previous geochemical studies are ambiguous about the extent of silicate melting in these samples. Oxygen isotope evidence indicates that the precursor material may be related to the carbonaceous chondrites. Here we analysed a suite of winonaites for modal mineralogy and bulk major- and trace-element chemistry in order to assess the extent of thermal processing as well as constrain the precursor composition of the winonaite-IAB parent asteroid. Modal mineralogy and geochemical data are presented for eight winonaites. Textural analysis reveals that, for our sub-set of samples, all except the most primitive winonaite (Northwest Africa 1463) reached the Fe, Ni-FeS cotectic. However, only one (Tierra Blanca) shows geochemical evidence for silicate melting processes. Tierra Blanca is interpreted as a residue of small-degree silicate melting. Our sample of Winona shows geochemical evidence for extensive terrestrial weathering. All other winonaites studied here (Fortuna, Queen Alexander Range 94535, Hammadah al Hamra 193, Pontlyfni and NWA 1463) have chondritic major-element ratios and flat CI-normalised bulk rare-earth element patterns, suggesting that most of the winonaites did not reach the silicate melting temperature. The majority of winonaites were therefore heated to a narrow temperature range of between ∼1220 (the Fe, Ni-FeS cotectic temperature) and ∼1370 K (the basaltic partial melting temperature). Silicate inclusions in the IAB irons demonstrate partial melting did occur in some parts of the parent body (Ruzicka and Hutson, 2010), thereby implying heterogeneous heat distribution within this asteroid. Together, this indicates that melting was the result of internal heating by short-lived radionuclides. The brecciated nature of the winonaites suggests that the parent body was later disrupted by

  15. Low-Degree Partial Melting Experiments of CR and H Chondrite Compositions: Implications for Asteroidal Magmatism Recorded in GRA 06128 and GRA 06129 T

    NASA Technical Reports Server (NTRS)

    Usui, T.; Jones, John H.; Mittlefehldt, D. W.

    2010-01-01

    Studies of differentiated meteorites have revealed a diversity of differentiation processes on their parental asteroids; these differentiation mechanisms range from whole-scale melting to partial melting without the core formation [e.g., 1]. Recently discovered paired achondrites GRA 06128 and GRA 06129 (hereafter referred to as GRA) represent unique asteroidal magmatic processes. These meteorites are characterized by high abundances of sodic plagioclase and alkali-rich whole-rock compositions, implying that they could originate from a low-degree partial melt from a volatile-rich oxidized asteroid [e.g., 2, 3, 4]. These conditions are consistent with the high abundances of highly siderophile elements, suggesting that their parent asteroid did not segregate a metallic core [2]. In this study, we test the hypothesis that low-degree partial melts of chondritic precursors under oxidizing conditions can explain the whole-rock and mineral chemistry of GRA based on melting experiments of synthesized CR- and H-chondrite compositions.

  16. Quantifying the Evolution of Melt Ponds in the Marginal Ice Zone Using High Resolution Optical Imagery and Neural Networks

    NASA Astrophysics Data System (ADS)

    Ortiz, M.; Pinales, J. C.; Graber, H. C.; Wilkinson, J.; Lund, B.

    2016-02-01

    Melt ponds on sea ice play a significant and complex role on the thermodynamics in the Marginal Ice Zone (MIZ). Ponding reduces the sea ice's ability to reflect sunlight, and in consequence, exacerbates the albedo positive feedback cycle. In order to understand how melt ponds work and their effect on the heat uptake of sea ice, we must quantify ponds through their seasonal evolution first. A semi-supervised neural network three-class learning scheme using a gradient descent with momentum and adaptive learning rate backpropagation function is applied to classify melt ponds/melt areas in the Beaufort Sea region. The network uses high resolution panchromatic satellite images from the MEDEA program, which are collocated with autonomous platform arrays from the Marginal Ice Zone Program, including ice mass-balance buoys, arctic weather stations and wave buoys. The goal of the study is to capture the spatial variation of melt onset and freeze-up of the ponds within the MIZ, and gather ponding statistics such as size and concentration. The innovation of this work comes from training the neural network as the melt ponds evolve over time; making the machine learning algorithm time-dependent, which has not been previously done. We will achieve this by analyzing the image histograms through quantification of the minima and maxima intensity changes as well as linking textural variation information of the imagery. We will compare the evolution of the melt ponds against several different array sites on the sea ice to explore if there are spatial differences among the separated platforms in the MIZ.

  17. Transport Property Measurements in Doped Bi2Te3 Single Crystals Obtained via Zone Melting Method

    NASA Astrophysics Data System (ADS)

    Jariwala, Bhakti; Shah, Dimple; Ravindra, N. M.

    2015-06-01

    Single crystals of Se- and Fe-doped Bi2Te3 have been synthesized via the zone melting method. Energy-dispersive x-ray and x-ray powder diffraction analyses have been carried out to identify the constituent elements and determine the lattice parameters of the grown crystals. Surface topological features of the as-grown single crystals have been studied. The transport properties of doped stoichiometric Bi2Te3 single crystals have been studied by measuring the thermoelectric power and electrical conductivity in the temperature range from 303 K to 473 K. The thermoelectric power, S, effective mass, scattering parameter, and Fermi energy have been calculated from thermoelectric power measurements. The temperature dependence of the electrical conductivity, σ, shows that the dopants in the crystals are thermally activated. All the crystals exhibit semiconducting behavior as confirmed by the temperature dependence of σ and S. The effective mass of electrons and the effective density of states have been determined and are reported for Bi2Te3- x Se x (0 ≤ x ≤ 0.3) and Bi2- y Fe y Te3 (0 ≤ y ≤ 0.3).

  18. Analysis of the molten/solidified zone in selective laser melted parts

    NASA Astrophysics Data System (ADS)

    Campanelli, Sabina Luisa; Casalino, Giuseppe; Contuzzi, Nicola; Angelastro, Andrea; Ludovico, Antonio D.

    2014-02-01

    The process of Selective Laser Melting (SLM) is an innovative technology for rapid prototyping that can be included among the SFF (Solid Freeform Fabrication) techniques, which are characterized by "free-form" manufacturing of solid parts. SLM is an additive technology that operates starting from the data encoded in the three-dimensional computer aided design (CAD) file of the component to be built. After the slicing operation made on the 3D model of the component, the consequent data file is sent to a computer-controlled laser device that fuses successive layers of metal powder to create the three-dimensional product. The SLM is a technological process which involves optical, thermal and solidification phenomena; thus the analysis of the process is rather complex. This work aims to study the molten/solidified zone in SLM samples through the experimental analysis of the shape and the size of laser tracks. The functional relationships between dimensional parameter of the molten/solidified track and the main parameters used to control the process was identified.

  19. The dynamics of melt and shear localization in partially molten aggregates.

    PubMed

    Katz, Richard F; Spiegelman, Marc; Holtzman, Benjamin

    2006-08-10

    The volcanoes that lie along the Earth's tectonic boundaries are fed by melt generated in the mantle. How this melt is extracted and focused to the volcanoes, however, remains an unresolved question. Here we present new theoretical results with implications for melt focusing beneath mid-ocean ridges. By modelling laboratory experiments, we test a formulation for magma dynamics and provide an explanation for localized bands of high-porosity and concentrated shear deformation observed in experiments. These bands emerge and persist at 15 degrees-25 degrees to the plane of shear. Past theoretical work on this system predicted the emergence of melt bands but at an angle inconsistent with experiments. Our results suggest that the observed band angle results from a balance of porosity-weakening and strain-rate-weakening deformation mechanisms. Lower band angles are predicted for greater strain-rate weakening. From these lower band angles, we estimate the orientation of melt bands beneath mid-ocean ridges and show that they may enhance magma focusing toward the ridge axis.

  20. Garnet Sm-Nd and Zircon U-Pb Ages Track Pluton Emplacement, Granulite Facies Metamorphism, Partial Melting, and Extension in the Lower Crust, Fiordland New Zealand

    NASA Astrophysics Data System (ADS)

    Stowell, H. H.; Klepeis, K. A.; Odom Parker, K.

    2011-12-01

    Resolution Island. New ages, and metamorphic and structural studies link periods of magmatism and metamorphism to specific spatial and temporal patterns of extensional deformation. The Malaspina pluton in central Fiordland underwent garnet granulite metamorphism <3.5 Myr after emplacement and then in part cooled to amphibolite facies conditions ca. 110 Ma. Fabrics record a progression from magmatic flow to high-T extensional deformation at garnet granulite & eclogite (700-800°C, 1.2-1.8 GPa) facies to lower-T extensional deformation at upper amphibolite facies (550-650°C, 0.7-0.9 GPa). Locally, the lower crust cooled thru 550-650°C without significant exhumation by 111 Ma. Elsewhere garnet ages indicate hot lower crust at 111 Ma. Within a 3.5 Myr timeframe the pluton cooled & crystallized, and extensional shear zones underwent a rapid (<3 Ma) transition from distributed melt-assisted deformation to cooler, localized upper amphibolite facies deformation at pluton margins. These results indicate that rheological variations and structural transitions linked to magmatism and partial melting may be more spatially heterogeneous and short-lived than previously believed.

  1. Iron isotope fractionation during sulfide-rich felsic partial melting in early planetesimals

    NASA Astrophysics Data System (ADS)

    Wang, Kun; Day, James M. D.; Korotev, Randy L.; Zeigler, Ryan A.; Moynier, Frédéric

    2014-04-01

    New Fe isotope data of feldspar-rich meteorites Graves Nunataks 06128 and 06129 (GRA 06128/9) reveal that they are the only known examples of crustal materials with isotopically light Fe isotope compositions (δFe56=-0.08±0.06‰; δ56Fe is defined as the per mille deviation of a sample's 56Fe/54Fe ratio from the IRMM-014 standard) in the Solar System. In contrast, associated brachinites, as well as brachinite-like achondrites, have Fe isotope compositions (δFe56=+0.01±0.02‰) that are isotopically similar to carbonaceous chondrites and the bulk terrestrial mantle. In order to understand the cause of Fe isotope variations in the GRA 06128/9 and brachinite parent body, we also report the Fe isotope compositions of metal, silicate and sulfide fractions from three ordinary chondrites (Semarkona, Kernouve, Saint-Séverin). Metals from ordinary chondrites are enriched in the heavier isotopes of Fe (average δFe56=0.15‰), sulfide fractions are enriched in the lighter isotopes of Fe (average δFe56=-0.14‰), and the δ56Fe values of the silicates are coincident with that of the bulk rock (average δFe56=0.03‰). The enrichment of light isotopes of Fe isotopes in GRA 06128/9 is consistent with preferential melting of sulfides in precursor chondritic source materials leading to the formation of Fe-S-rich felsic melts. Conceptual models show that melt generation to form a GRA 06128/9 parental melt occurred prior to the onset of higher-temperature basaltic melting (<1200 °C) in a volatile-rich precursor and led to the generation of buoyant felsic melt with a strong Fe-S signature. These models not only reveal the origin of enrichment in light isotopes of Fe for GRA 06128/9, but are also consistent with petrological and geochemical observations, experimental studies for the origin of Fe-S-rich felsic melts, and for the cessation of early melting on some asteroidal parent bodies because of the effective removal of the major radioactive heat-source, 26Al. The mode of

  2. Trace element evidence for anatexis at oceanic magma chamber roofs and the role of partial melts for contamination of fresh MORB

    NASA Astrophysics Data System (ADS)

    Fischer, Lennart A.; Erdmann, Martin; France, Lydéric; Wolff, Paul E.; Deloule, Etienne; Zhang, Chao; Godard, Marguerite; Koepke, Jürgen

    2016-09-01

    At oceanic spreading centers, interactions between magma and hydrothermal convecting systems trigger major physical, thermal, and chemical exchanges. The two-pyroxene hornfels recovered from the base of the sheeted dike sequence at Integrated Ocean Drilling Program (IODP) Site 1256 (equatorial Eastern Pacific) are interpreted as a conducting boundary layer between the underlying axial melt lens and the hydrothermally cooled sheeted dikes. They are cut by numerous small, felsic veins, which were recently interpreted as a product of hydrous partial melting of sheeted dikes. Here, we present trace element compositions of products (melts and residues) of hydrous partial melting experiments using basalts and hornfels from IODP Site 1256 as starting material. The experimental products generated between 910 °C and 970 °C match the natural lithologies from Site 1256 in terms of major and trace element compositions. The compositions of the anatectic melts correspond to the compositions of the felsic veins, while the residual minerals match the compositions of the two-pyroxene hornfels, evidencing that hydrous partial melting is an important magmatic process in the gabbro/dike transition of fast-spreading mid-oceanic ridges. Our results complement previous experimental studies on anatectic processes occurring at the roof of the magma chambers from fast-spreading mid-ocean ridges. Moreover, calculations of mixing and assimilation fractional crystallization using the experimental partial melts as contaminant/assimilant showed that anatectic melts can only be a minor contributor to the contamination process.

  3. Growth of GaAs from a free surface melt under controlled arsenic pressure in a partially confined configuration

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.; Wu, Y.

    1988-01-01

    A partially confined configuration for the growth of GaAs from melt in space was developed, consisting of a triangular prism containing the seed crystal and source material in the form of a rod. It is suggested that the configuration overcomes two obstacles in the growth of GaAs in space: total confinement in a quartz crucible and lack of arsenic pressure control. Ground tests of the configuration show that it is capable of crystal growth in space and is useful for studying the growth of GaAs from a free-surface melt on earth. The resulting chemical composition, electrical property variations, and phenomenological models to account for the results are presented.

  4. Partial melt growth process of Bi2Sr2Ca1Cu2O(x) textured tapes on silver

    NASA Astrophysics Data System (ADS)

    Kase, Jun-Ichiro; Irisawa, Naoshi; Togano, Kazumasa; Kumakura, Hiroaki; Dietderich, Daniel R.

    1990-07-01

    Bi2Sr2Ca1Cu2O(x) textured tapes with an excellent J(c) were synthesized by doctor-blade casting and a melt process. Green tape was laid on a silver foil and oxide/silver composite tape was heat treated. A highly textured microstructure was formed by slow cooling from 890 C to 870 C with the oxide in a partially melted state. The highest T(c) and J(c) (77 K, 0 T), 89 K and 13,000 A/sq cm, respectively, were obtained by quenching from 870 C. However, J(c) at 4.2 K was higher for the sample slowly cooled to room temperature and reached 140,000 A/sq cm at 25 T. These results indicate the potential for the practical application of Bi-based oxide superconductors at both 77 K and 4.2 K.

  5. Growth of GaAs from a free surface melt under controlled arsenic pressure in a partially confined configuration

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.; Wu, Y.

    1988-01-01

    A partially confined configuration for the growth of GaAs from melt in space was developed, consisting of a triangular prism containing the seed crystal and source material in the form of a rod. It is suggested that the configuration overcomes two obstacles in the growth of GaAs in space: total confinement in a quartz crucible and lack of arsenic pressure control. Ground tests of the configuration show that it is capable of crystal growth in space and is useful for studying the growth of GaAs from a free-surface melt on earth. The resulting chemical composition, electrical property variations, and phenomenological models to account for the results are presented.

  6. Temperature and Time Constraints on Dissolution, Fe-Mg Exchange and Zoning between Relict Forsterite and Chondrule Melt - Implications for Thermal History of Chondrules

    NASA Astrophysics Data System (ADS)

    Ustunisik, G. K.; Ebel, D. S. S.; Walker, D.

    2016-12-01

    The chemical and textural characteristics of different generations of relict olivine grains in chondrules record the fact that chondrules were re-melted. Mineral dissolution, Fe-Mg exchange, and zoning within the relict crystals constrain the T-t aspects of this re-melting process. Here, we performed isothermal and dynamic cooling experiments at LDEO of Columbia University. For each run, a cubic crystal of known dimensions of Mogok forsterite (Fo99) was placed in synthetic Type IIA chondrule mesostasis with 4.92 wt% FeO (TLiq 1315ºC). Pressed pellets of this mixture were hung on Pt-wire loops and inserted in vertical Deltech furnace where CO-CO2 gas mixtures kept fO2 IW-1. For isothermal experiments, each charge was heated to 1428ºC, 1350ºC, 1250ºC, and 1150ºC and was held there from 20 mins to several days (>3 days) before drop-quenching into cold water. The dynamic crystallization experiments were held at 1428ºC for 20 mins, cooled at rates of 75ºC, 722ºC, and 1444ºC/hr to 1000ºC and then water quenched. X-ray-CT and EMPA at AMNH were used to image the partially resorbed/zoned olivines in 3-D before and after each run to observe textural evolution of the crystal shapes and volumes and to determine chemical changes. The isothermal experiments at 1150 and 1250ºC for 20 mins, produced no bulk FeO diffusion into the Mogok forsterite. Very minor Fe-Mg exchange at the crystal rims gives slight MgO zoning within the nearby melt. With increasing duration (1 hr and 22 hrs), at 1250ºC, embayments of melt form into the rims of the crystal (amplified at 22 hrs) with significant Fe-Mg exchange. FeO content of Mogok increased with major MgO zonation within nearby melt. At 1150ºC, the same increase in FeO in Mogok and zonation in nearby glass could only be achieved in >3 days experiment. At high Ts (1428ºC) in 20 min run, 75 volume % of Mogok forsterite has been dissolved into the melt. Resorption erodes the Fe-Mg exchange at the rims of the crystal. At longer

  7. Controlled alternate partial root-zone irrigation: its physiological consequences and impact on water use efficiency.

    PubMed

    Kang, Shaozhong; Zhang, Jianhua

    2004-11-01

    Controlled alternate partial root-zone irrigation (CAPRI), also called partial root-zone drying (PRD) in other literature, is a new irrigation technique and may improve the water use efficiency of crop production without significant yield reduction. It involves part of the root system being exposed to drying soil while the remaining part is irrigated normally. The wetted and dried sides of the root system are alternated with a frequency according to soil drying rate and crop water requirement. The irrigation system is developed on the basis of two theoretical backgrounds. (i) Fully irrigated plants usually have widely opened stomata. A small narrowing of the stomatal opening may reduce water loss substantially with little effect on photosynthesis. (ii) Part of the root system in drying soil can respond to the drying by sending a root-sourced signal to the shoots where stomata may be inhibited so that water loss is reduced. In the field, however, the prediction that reduced stomatal opening may reduce water consumption may not materialize because stomatal control only constitutes part of the total transpirational resistance. The boundary resistance from the leaf surface to the outside of the canopy may be so substantial that reduction in stomatal conductance is small and may be partially compensated by the increase in leaf temperature. It is likely that densely populated field crops, such as wheat and maize, may have a different stomatal control over transpiration from that of fruit trees which are more sparsely separated. It was discussed how long the stomata can keep 'partially' closed when a prolonged and repeated 'partial' soil drying is applied and what role the rewatering-stimulated new root growth may play in sensing the repeated soil drying. The physiological and morphological alternation of plants under partial root-zone irrigation may bring more benefits to crops than improved water use efficiency where carbon redistribution among organs is crucial to the

  8. The effect of bulk composition on the solidus of carbonated eclogite from partial melting experiments at 3 GPa

    NASA Astrophysics Data System (ADS)

    Dasgupta, Rajdeep; Hirschmann, Marc M.; Dellas, Nikki

    2005-05-01

    To explore the effect of bulk composition on the solidus of carbonated eclogite, we determined near-solidus phase relations at 3 GPa for four different nominally anhydrous, carbonated eclogites. Starting materials (SLEC1, SLEC2, SLEC3, and SLEC4) were prepared by adding variable proportions and compositions of carbonate to a natural eclogite xenolith (66039B) from Salt Lake crater, Hawaii. Near-solidus partial melts for all bulk compositions are Fe Na calcio-dolomitic and coexist with garnet + clinopyroxene + ilmenite ± calcio-dolomitic solid solution. The solidus for SLEC1 (Ca#=100 × molar Ca/(Ca + Mg + FeT)=32, 1.63 wt% Na2O, and 5 wt% CO2) is bracketed between 1,050°C and 1,075°C (Dasgupta et al. in Earth Planet Sci Lett 227:73 85, 2004), whereas initial melting for SLEC3 (Ca# 41, 1.4 wt% Na2O, and 4.4 wt% CO2) is between 1,175°C and 1,200°C. The solidus for SLEC2 (Ca# 33, 1.75 wt% Na2O, and 15 wt% CO2) is estimated to be near 1,100°C and the solidus for SLEC3 (Ca# 37, 1.47 wt% Na2O, and 2.2 wt% CO2) is between 1,100°C and 1,125°C. Solidus temperatures increase with increasing Ca# of the bulk, owing to the strong influence of the calcite magnesite binary solidus-minimum on the solidus of carbonate bearing eclogite. Bulk compositions that produce near-solidus crystalline carbonate closer in composition to the minimum along the CaCO3-MgCO3 join have lower solidus temperatures. Variations in total CO2 have significant effect on the solidus if CO2 is added as CaCO3, but not if CO2 is added as a complex mixture that maintains the cationic ratios of the bulk-rock. Thus, as partial melting experiments necessarily have more CO2 than that likely to be found in natural carbonated eclogites, care must be taken to assure that the compositional shifts associated with excess CO2 do not unduly influence melting behavior. Near-solidus dolomite and calcite solid solutions have higher Ca/(Ca + Mg) than bulk eclogite compositions, owing to Ca Mg exchange equilibrium

  9. Experimental Study of Dehydration and Partial Melting of Biotite-Amphibole Gneiss Under Influence of the H2O-CO2-(K, Na)cl Fluids at 5.5 Kbar and 750 and 800 C

    NASA Astrophysics Data System (ADS)

    Safonov, O.; Kosova, S.

    2012-12-01

    by dacitic melt and Ti-magnetite. Newly formed assemblages regularly change with an increase of the KCl content in the fluid: Opx+Ti-Mt+melt, Opx+Amp+Ilm+Ti-Mt + melt, Opx+Cpx+Ilm+melt, Cpx+ Ilm+melt. In this sequence, the melt evolves toward potassic rhyolitic composition. Orthopyroxene appears in assemblage with sodic amphibole in equilibrium with NaCl-rich fluids, as well. Present experiments allow conclusion that the interaction of the biotite-amphibole gneiss with the H2O-CO2-(K, Na)Cl fluids can be accompanied by a partial melting at 750-800 C. Melting progress is vitally depends on the NaCl/KCl ratio in a fluid. NaCl intensifies melting because of higher solubility of Cl and CO2 in the sodic melts in comparison to the potassic varieties. Charnockitic and mangeritic assemblages (Opx+Cpx+Kfs+Pl) form in presence of the partial melts at temperature 800 C and are stable in presence of KCl-bearing fluids with relatively low salt concentrations (H2O/(KCl+H2O) < 0.015). Fluids of higher salinity result in formation syenitic and monzonitic assemblages (Cpx+Amp+Kfs+Pl). Applicability of the experimental data is demonstrated by mineral assemblages of local-scale dehydration zones in the high-grade terrains.

  10. Coupled thermodynamic and two-phase flow modelling of partially melting crust

    NASA Astrophysics Data System (ADS)

    Riel, Nicolas; Bouilhol, Pierre; Magni, Valentina; van Hunen, Jeroen; Velic, Mirko

    2016-04-01

    How magmas are formed, transferred and interact in the lower crust to form mid-crust plutonic belts remain a fundamental question to understand the chemical and mechanical evolution of continents. To assess this question we developed a 2-D two-phase flow code using finite volume method. Our formulation takes into account: (i) an extended Darcy's law for fluid flow with first order temperature- and fluid-content dependency for the host-rock viscosity and silica-dependent viscosity for the fluid, (ii) the heat equation assuming thermal equilibrium for both solid and liquid and temperature-dependent diffusivity, (iii) thermodynamic modelling of stable phases via a dynamic coupling with Perple_X, and (iv) chemical advection of both the solid and liquid composition. To model chemical interactions with the host rock during magma transport, the melt is assumed to be either in thermodynamic equilibrium or in thermodynamic disequilibrium, or as function of these two endmembers. We applied our modelling approach to investigate the behaviour and composition of magma during lower crust melting. Our goal is to better understand the formation of felsic crust through melting, segregation and assimilation of lower crustal lithologies, applied to Archaean systems. Our preliminary results show the ascend of silica-rich magmas is slow, occurring on the timescale of millions of years, and is highly controlled by (i) the melting curve of the protolith and (ii) by its chemical degree of interaction with the host rock. The resulting transferred magmas are in good accordance with observed composition forming the grey gneisses of Archean terranes (i.e SiO2-rich > 62%, Mg# = 40-50, Na2O ~6%, MgO = 0.5-1%).

  11. Melting experiments on anhydrous peridotite KLB-1: Compositions of magmas in the upper mantle and transition zone

    NASA Astrophysics Data System (ADS)

    Herzberg, Claude; Zhang, Jianzhong

    1996-04-01

    Electron microprobe results are reported for liquid and crystalline phases that were synthesized at 5-22.5 GPa in multianvil experiments on anhydrous peridotite KLB-1 [Zhang and Herzberg, 1994]. The results provide information on the partitioning of TiO2, Al2O3, Cr2O3, FeO, MnO, MgO, Na2O, and NiO among liquid and the crystalline phases olivine, modified spinel, garnet, magnesiowustite, and magnesium perovskite. Uncertainties in these partition coefficients stem from quenching problems and from the effects of thermal migration of liquid in a temperature gradient. We have, however, exploited the temperature gradients by determining how the crystalline phase chemistry varies throughout the melting interval from the liquidus to the solidus. This has permitted new constraints to be obtained on the compositions of liquids along the anhydrous peridotite solidus at low melt fractions and at pressures in the 5-18 GPa range. It is demonstrated that the wide range of Al2O3 and CaO/Al2O3 contents in picrites and komatiites can be explained by melt segregation at upper mantle pressures that ranged from 3 to ˜10 GPa. These magmas could have formed by anhydrous melting in plumes with temperatures that were only 100°-200°C higher than ambient mantle below ridges, demonstrating that unusually hot conditions are not required to form komatiites. Primary igneous MgO contents in excess of 26% should be rare, and those that do exist in some komatiites can be explained by advanced melting during adiabatic or superadiabatic ascent, by low Na2O in the source, or by melting in hot plumes from the transition zone and lower mantle. Evidence for deep melting in hot plumes is rather conjectural, but it may be contained in some 2700 Myr komatiites that have high MgO and mantle-like CaO/Al2O3.

  12. Partial melting of oxidized planetesimals: An experimental study to test the formation of oligoclase-rich achondrites Graves Nunataks 06128 and 06129

    NASA Astrophysics Data System (ADS)

    Lunning, Nicole G.; Gardner-Vandy, Kathryn G.; Sosa, Emma S.; McCoy, Timothy J.; Bullock, Emma S.; Corrigan, Catherine M.

    2017-10-01

    The meteorites Graves Nunataks (GRA) 06128 and 06129 are igneous meteorites dominated by oligoclase feldspar and have basaltic trachyandesite-like whole rock compositions. Formation of the GRA 06128/9 meteorites as primary melts on an oxidized planetesimal has been previously proposed (Day et al. 2009a, 2012a; Gardner-Vandy et al., 2013; Wang et al., 2014). We show experimentally that anhydrous partial melting of an oxidized R chondrite at IW to IW+1 between 1120-1140 °C produces melts of GRA 06128/9-like compositions: intermediate SiO2 and FeO concentrations that are enriched in volatile sodium. From a process perspective, GRA 06128/9-like magmas are complementary to partial melt residues such as olivine-rich brachinite and FeO-rich brachinite-like meteorites. Magmas of GRA 06128/9's composition can be generated under equilibrium conditions, as demonstrated by MELTS modeling, but only at temperatures ∼1140 °C. At lower degrees of partial melting liquids formed under equilibrium and non-equilibrium conditions follow distinct compositional pathways to reach GRA 06128/9-like melts. For lower degrees of melting, the non-equilibrium trend more closely resembles GRA 06128/9's composition. Phase abundance modeling indicates that GRA 06128/9-composition magmas form by 14-22% silicate melting of an oxidized R-chondrite. We conclude that GRA 06128/9-composition magmas can be generated at ∼1140 °C from partial melting of an oxidized chondritic precursor under both non-equilibrium and equilibrium conditions.

  13. Partial reactive crystallization of variable CO2-bearing siliceous MORB-eclogite-derived melt in fertile peridotite and genesis of alkalic basalts with signatures of crustal recycling

    NASA Astrophysics Data System (ADS)

    Mallik, A.; Dasgupta, R.

    2013-12-01

    The presence of heterogeneity in the form of recycled altered oceanic crust (MORB-eclogite) has been proposed in the source of HIMU ocean island basalts (OIBs) [1]. Partial melts of recycled oceanic crust, however, are siliceous and Mg-poor and thus do not resemble the major element compositions of alkalic OIBs that are silica-poor and Mg-rich. In an upwelling heterogenous mantle, MORB-eclogite undergoes melting deeper than volatile-free peridotite, hence, andesitic partial melt derived from eclogite will react with subsolidus peridotite. We have examined the effect of such a melt-rock reaction under volatile-free conditions at 1375 °C, 3 GPa by varying the melt-rock ratio from 8 to 50 wt.% [2]. We concluded that the reacted melts reproduce certain major element characteristics of oceanic basanites, but not nephelinites. Also, the melt-rock reaction produces olivine and garnet-bearing websteritic residue. Because presence of CO2 has been invoked in the source of many HIMU ocean islands, the effect of CO2 on such a melt-rock reaction needs to be evaluated. Accordingly, we performed reaction experiments on mixtures of 25% and 33% CO2-bearing andesitic partial melt and peridotite at 1375 °C, 3 GPa by varying the dissolved CO2 content of the reacting melts from 1 to 5 wt.% (bulk CO2 from 0.25 to 1.6 wt.%) [3, this study]. Owing to melt-rock reaction, with increasing CO2 in the bulk mixture, (a) modes of olivine and cpx decrease while melt, opx and garnet increase, (b) reacted melts evolve to greater degree of Si-undersaturation (from andesite through basanite to nephelinite), (c) enhanced crystallization of garnet take place with higher CO2 in the melt, reducing alumina content of the reacted melts, and (d) CaO and MgO content of the reacted melts increase, without affecting FeO* and Na2O contents (indicating greater propensity of Ca2+ and Mg2+ over Fe2+ and Na+ to enter silicate melt as carbonate). For a given melt-MgO, the CO2-bearing reacted melts are a better

  14. Phase-equilibrium geobarometers for silicic rocks based on rhyolite-MELTS. Part 2: application to Taupo Volcanic Zone rhyolites

    NASA Astrophysics Data System (ADS)

    Bégué, Florence; Gualda, Guilherme A. R.; Ghiorso, Mark S.; Pamukcu, Ayla S.; Kennedy, Ben M.; Gravley, Darren M.; Deering, Chad D.; Chambefort, Isabelle

    2014-11-01

    Constraining the pressure of crystallisation of large silicic magma bodies gives important insight into the depth and vertical extent of magmatic plumbing systems; however, it is notably difficult to constrain pressure at the level of detail necessary to understand shallow magmatic systems. In this study, we use the recently developed rhyolite-MELTS geobarometer to constrain the crystallisation pressures of rhyolites from the Taupo Volcanic Zone (TVZ). As sanidine is absent from the studied deposits, we calculate the pressures at which quartz and feldspar are found to be in equilibrium with melt now preserved as glass (the quartz +1 feldspar constraint of Gualda and Ghiorso, Contrib Mineral Petrol 168:1033. doi:10.1007/s00410-014-1033-3. 2014). We use glass compositions (matrix glass and melt inclusions) from seven eruptive deposits dated between ~320 and 0.7 ka from four distinct calderas in the central TVZ, and we discuss advantages and limitations of the rhyolite-MELTS geobarometer in comparison with other geobarometers applied to the same eruptive deposits. Overall, there is good agreement with other pressure estimates from the literature (amphibole geobarometry and H2O-CO2 solubility models). One of the main advantages of this new geobarometer is that it can be applied to both matrix glass and melt inclusions—regardless of volatile saturation. The examples presented also emphasise the utility of this method to filter out spurious glass compositions. Pressure estimates obtained with the new rhyolite-MELTS geobarometer range between ~250 to ~50 MPa, with a large majority at ~100 MPa. These results confirm that the TVZ hosts some of the shallowest rhyolitic magma bodies on the planet, resulting from the extensional tectonic regime and thinning of the crust. Distinct populations with different equilibration pressures are also recognised, which is consistent with the idea that multiple batches of eruptible magma can be present in the crust at the same time and

  15. A partial melting study of an ordinary (H) chondrite composition with application to the unique achondrite Graves Nunataks 06128 and 06129

    NASA Astrophysics Data System (ADS)

    Usui, Tomohiro; Jones, John H.; Mittlefehldt, David W.

    2015-04-01

    Melting experiments of a synthesized, alkali-bearing, H-chondrite composition were conducted at ambient pressure with three distinct oxygen fugacity conditions (IW-1, IW, and IW+2). Oxygen fugacity conditions significantly influence the compositions of partial melts. Partial melts at IW-1 are distinctly enriched in SiO2 relative to those of IW and IW+2 melts. The silica-enriched, reduced (IW-1) melts are characterized by high alkali contents and have silica-oversaturated compositions. In contrast, the silica-depleted, oxidized (≥IW) melts, which are also enriched in alkali contents, have distinctly silica-undersaturated compositions. These experimental results suggest that alkali-rich, felsic, asteroidal crusts as represented by paired achondrites Graves Nunataks 06128 and 06129 should originate from a low-degree, relatively reduced partial melt from a parent body having near-chondritic compositions. Based on recent chronological constraints and numerical considerations as well as our experimental results, we propose that such felsic magmatism should have occurred in a parent body that is smaller in size and commenced accreting later than those highly differentiated asteroids having basaltic crusts and metallic cores.

  16. Numerical models of transient partial melting of the lower crust during repeated emplacement of basalt sills and subsequent cooling due to advection of melt out of the lower crust

    NASA Astrophysics Data System (ADS)

    Lim, S.; Hetland, E. A.; Lange, R. A.

    2012-12-01

    The thermal evolution of arc crust can be modeled as a consequence of repeated emplacement of basaltic sills in the lower crust, along with subsequent advection of melt up the crustal column or erupted to the surface. Melt that advects from the lower to the upper crust might be either residual melt from the solidifying basaltic intrusion or partial melt of the crust surrounding the intrusion. Considering only emplacement of basaltic sills, after 100's of sill emplacements (assuming 1285°C sills at a rate of 50 m per 10 kyr), temperatures are >900°C for a significant fraction of the lower crustal column. In this view, much of the lower crust may be partially molten after 3 Myr, with sustained melt fractions >20%. At such high melt fractions, melt can segregate and migrate over large distances (Vigneress and Tikoff, 1999), and it is therefore expected that a significant amount of this melt will be emplaced into the upper crust as granitoids or erupted on the surface as andesite/dacite. Numerically modeling the thermal evolution of the crust in response to repeated sill emplacement and vertical migration of melt is a challenge due to the large range in spatial and temporal scales, where sills are 10-50 m thick vs. a 20-40 km thick crust and where solidification/melting occurs over hundreds of years vs. the 1-3 million years to capture the full thermal evolution of the crust. We have developed two numerical techniques with adaptive spatial and temporal resolution (a 1D finite-difference method and a 2D finite-element method) in order to explore the various phases of the thermal evolution of arc crust. We focus the 1D models on the thermal evolution of the entire crust due to repeated emplacement of basaltic sills over several million years, and we achieve meter level resolution. Thus far we have only considered secondary advection of residual melt from the solidifying basaltic sills. After 100's of emplacements advection of this melt results in cooling, with

  17. Multiple episodes of partial melting, depletion, metasomatism and enrichment processes recorded in the heterogeneous upper mantle sequence of the Neotethyan Eldivan ophiolite, Turkey

    NASA Astrophysics Data System (ADS)

    Uysal, Ibrahim; Ersoy, E. Yalçın; Dilek, Yildirim; Kapsiotis, Argyrios; Sarıfakıoğlu, Ender

    2016-03-01

    The Eldivan ophiolite along the Izmir-Ankara-Erzincan suture zone in north-central Anatolia represents a remnant of the Neotethyan oceanic lithosphere. Its upper mantle peridotites include three lithologically and compositionally distinct units: clinopyroxene (cpx)-harzburgite and lherzolite (Group-1), depleted harzburgite (Group-2), and dunite (Group-3). Relics of primary olivine and pyroxene occur in the less refractory harzburgites, and fresh chromian spinel (Cr-spinel) is ubiquitous in all peridotites. The Eldivan peridotites reflect a petrogenetic history evolving from relatively fertile (lherzolite and cpx-harzburgite) toward more depleted (dunite) compositions through time, as indicated by (i) a progressive decrease in the modal cpx distribution, (ii) a progressive increase in the Cr#s [Cr / (Cr + Al)] of Cr-spinel (0.15-0.78), and (iii) an increased depletion in the whole-rock abundances of some magmaphile major oxides (Al2O3, CaO, SiO2 and TiO2) and incompatible trace elements (Zn, Sc, V and Y). The primitive mantle-normalized REE patterns of the Group-1 and some of the Group-2 peridotites display LREE depletions. Higher YbN and lower SmN/YbN ratios of these rocks are compatible with their formation after relatively low degrees (9-25%) of open-system dynamic melting (OSDM) of a Depleted Mid-ocean ridge Mantle (DMM) source, which was then fluxed with small volumes of oceanic mantle-derived melt [fluxing ratio (β): 0.7-1.2%]. Accessory Cr-spinel compositions (Cr# = 015-0.53) of these rocks are consistent with their origin as residual peridotites beneath a mid-ocean ridge axis. Part of the Group-2 harzburgites exhibit lower YbN and higher SmN/YbN ratios, LREE-enriched REE patterns, and higher Cr-spinel Cr#s ranging between 0.54 and 0.61. Trace element compositions of these peridotites can be modeled by approximately 15% OSDM of a previously 17% depleted DMM, which was then fluxed (β: 0.4%) with subduction-influenced melt. The Group-3 dunite samples contain

  18. Melt extraction in mush zones: The case of crystal-rich enclaves at the Sabatini Volcanic District (central Italy)

    NASA Astrophysics Data System (ADS)

    Masotta, M.; Mollo, S.; Gaeta, M.; Freda, C.

    2016-04-01

    A peculiar feature of the Sabatini Volcanic District (SVD, central Italy) is the occurrence of crystal-poor pumices and crystal-rich enclaves within the same eruptive host-deposit. The stratigraphic sequence of pumices and enclaves indicates the tapping of a stratified magma chamber, where a crystal-poor phonolitic magma lay on top of a more primitive crystal-rich magma. The crystal-rich enclaves are genetically related to the pumices and record the evolution of a solidification front, in which a more differentiated melt was produced, extracted and eventually erupted. We collected and analyzed crystal-rich enclaves from one of the largest phonolitic eruptions at the SVD and used their petrological and geochemical features to reconstruct magma differentiation and crystal-melt separation in the solidification front. On this basis, three groups of enclaves have been identified: porphyritic enclaves, holocrystalline enclaves and sanidinites. The mineralogical variability faithfully reproduces the spatial and temporal evolution expected of a solidification front, from early-to-intermediate crystallization conditions (porphyritic and holocrystalline type) to the late stage of solidification (sanidinites), in which the percolation of a more differentiated melt through the crystal mush triggered the instability of the solidification front. Results from numerical models indicate that gravitational instability is the most efficient mechanism to explain melt extraction in mush zones of medium-sized (~ 10 km3), short-lived (~ 104 years) magma chambers.

  19. Improvements to the snow melting process in a partially double moment microphysics parameterization

    NASA Astrophysics Data System (ADS)

    Brown, Bonnie R.; Bell, Michael M.; Thompson, Gregory

    2017-06-01

    Polarimetric upgrades to the U.S. radar network have allowed new insight into the precipitation processes of tropical cyclones. Previous work by the authors compared the reflectivity at horizontal polarization and differential reflectivity observations from two hurricanes to simulated radar observations from the WRF model, and found that the aerosol-aware Thompson-Eidhammer microphysical scheme performed the best of several commonly used bulk microphysical parameterizations. Here we expand our investigation of the Thompson-Eidhammer scheme, and find that though it provided the most accurate forecast in terms of wind speed and simulated radar signatures, the scheme produces areas in which the differential reflectivity was much higher than observed. We conclude that the Thompson-Eidhammer scheme produces drop size distributions that have a larger median drop size than observed in regions of light stratiform precipitation. Examination of the vertical structure of simulated differential reflectivity indicates that the source of the discrepancy between the model and radar observations likely originates within the melting layer. The treatment of number production of rain drops from melting snow in the microphysical scheme is shown to be the ultimate source of the enhancement of differential reflectivity. A modification to the scheme is shown to result in better fidelity of the radar variables with the observations without degrading the short-term intensity forecast. Additional tests with an idealized squall line simulation are consistent with the hurricane results, suggesting the modification is generally applicable. The modifications to the Thompson-Eidhammer scheme shown here have been incorporated into updates of the WRF model starting with version 3.8.1.

  20. Mantle Melting in the Plagioclase-Spinel Transition Zone; Reconciling Experiments and Thermodynamic Models

    NASA Astrophysics Data System (ADS)

    Smith, P. M.; Asimow, P. D.

    2003-12-01

    The slope of the solidus of plagioclase and spinel bearing lherzolite is important as it controls mantle melting behaviour during isentropic decompression. The invariant point in CaO-MgO-Al2}O{3}-SiO_{2 (CMAS), where the reaction of plagioclase lherzolite to spinel lherzolite intersects the solidus, expands to form a divariant surface in CaO-MgO-Al2}O{3}-SiO_{2}-Na_{2O-FeO (CMASNF). Experimental results in two five component systems, CMASN and CMASF, suggest that the temperature of the surface increases slightly with pressure, so that the plagioclase-spinel transition interval could be the site of enhanced melting consistent with seismic observations (Presnall et al., 2000 and references therein). In contrast, calculations using the MELTS (Ghiorso & Sack, 1995) and pMELTS (Ghiorso, 1998) algorithms predict a strong or weak temperature drop respectively as pressure is increased, giving a pronounced cusp in the solidus where melts would freeze (Asimow et al., 1995). We are currently using an integrated experimental and theoretical approach to explore the equilibrium between plagioclase, spinel, olivine, orthopyroxene, clinopyroxene and liquid to see if these results may be reconciled. Piston-cylinder experiments are being carried out in CMASNF and sub-systems. Using the parameterisation of Walter & Presnall (1994) we have chosen a suitable bulk composition in CMASN that should intersect the univariant melting reaction over a range of pressures (11-15 kbar) whilst maximizing the modal proportion of each phase above and below the reaction. To account for interlaboratory differences in pressure-calibration we are redetermining the CMAS invariant point. We are also developing calibration software suitable for a new thermodynamic model of peridotite melting. The CMASNF system is outside the calibrated composition ranges of MELTS and pMELTS, which were constructed exclusively from natural system data. By using experiments from CMAS, CMASN and CMASF in our calibration

  1. Hypereutectic Al2O3/YAG/ZrO2 In Situ Composite Prepared by Horizontal Laser Zone Melting

    NASA Astrophysics Data System (ADS)

    Song, Kan; Zhang, Jun; Liu, Lin

    2017-01-01

    Al2O3/YAG/ZrO2 eutectic in situ composite has now been considered as the new generation of high-temperature structural material due to its excellent performance even close to its melting point. In this work, hypereutectic Al2O3/YAG/ZrO2 in situ composite is manufactured by the horizontal laser zone melting technique. The relationship between the solidification microstructure and the solidification parameters is studied. The minimum lamellar spacing is as finer as 0.20 μm when the laser scanning rate is 800 μm/s. Compared with eutectic Al2O3/YAG/ZrO2, hypereutectic exhibits more regular and finer microstructure at the similar conditions. Meanwhile, it is found that the lamellar spacing remains almost as constant at a certain high solidification velocity. The maximum hardness and fracture toughness are 15.9 GPa and 4.2 MPa · m1/2, respectively.

  2. Carbon dioxide partial pressure and 13C content of north temperate and boreal lakes at spring ice melt

    USGS Publications Warehouse

    Striegl, R.G.; Kortelainen, Pirkko; Chanton, J.P.; Wickland, K.P.; Bugna, G.C.; Rantakari, M.

    2001-01-01

    Carbon dioxide (CO2) accumulates under lake ice in winter and degasses to the atmosphere after ice melt. This large springtime CO2 pulse is not typically considered in surface-atmosphere flux estimates, because most field studies have not sampled through ice during late winter. Measured CO2 partial pressure (pCO2) of lake surface water ranged from 8.6 to 4,290 Pa (85-4,230 ??atm) in 234 north temperate and boreal lakes prior to ice melt during 1998 and 1999. Only four lakes had surface pCO2 less than or equal to atmospheric pCO2, whereas 75% had pCO2 >5 times atmospheric. The ??13CDIC (DIC = ??CO2) of 142 of the lakes ranged from -26.28??? to +0.95.???. Lakes with the greatest pCO2 also had the lightest ??13CDIC, which indicates respiration as their primary CO2 source. Finnish lakes that received large amounts of dissolved organic carbon from surrounding peatlands had the greatest pCO2. Lakes set in noncarbonate till and bedrock in Minnesota and Wisconsin had the smallest pCO2 and the heaviest ??13CDIC, which indicates atmospheric and/or mineral sources of C for those lakes. Potential emissions for the period after ice melt were 2.36 ?? 1.44 mol CO2 m-2 for lakes with average pCO2 values and were as large as 13.7 ?? 8.4 mol CO2 m-2 for lakes with high pCO2 values.

  3. Contrasting MORB-Boninite melt reaction trends in IBM forearc moho transition zone

    NASA Astrophysics Data System (ADS)

    Loocke, M. P.; Snow, J. E.; Ishizuka, O.

    2013-12-01

    Models of arc crust formation prior to subduction initiation are hampered by a paucity of observations from present-day arc lower crust. Here we report petrographic analysis and mineral chemistry of spinel from 35 lower crustal peridotites and gabbros recovered from the inner trench slope of the Bonin Ridge (BR). Two groups of these gabbroic samples appear to have reacted with distinct melt compositions. Group M consists of peridotite (a single cpx-harzburgite), wehrlites, and gabbroic rocks with medium Cr# (100 x Cr / Cr + Al) spinels ranging from 45 to 60 and high TiO2 and Al2O3 spanning ~0.1-2.25 and ~12-30 wt. % respectively. Group B consists of only dunites and cpx-free peridotites with high Cr# spinels ranging from 65 to 94 and low TiO2 and Al2O3 spanning ~0-0.12 and ~3-21 wt. % respectively. The group M and group B samples appear to be the result of melt-rock reaction with a MORB-like melt and a more depleted boninitic melt respectively. MORB-like forearc basalts (FAB) (~50-52 Ma) and younger boninites (~44-48 Ma) recovered from the BR have been interpreted to represent a change from decompression melting at subduction initiation to flux melting and boninitic volcanism after establishment of the arc. The gabbroic samples of group M and group B similarly represent a lower crustal record of the change from MORB-like melts created by decompression melting at or soon after subduction initiation to arc-type flux melting and boninite volcanism thereafter. The presence of lower crustal peridotites and gabbroic rocks with spinels belonging to group M and not group B suggests that the lower crust of the BR may be dominated by gabbroic rocks and material genetically related to the FABs. This would imply that a large portion of the lower crust in the fore-arc was formed during or shortly after subduction initiation and is similar in composition to MOR lower crust.

  4. Evidence for partial melt in the crust beneath Mt. Paektu (Changbaishan), Democratic People's Republic of Korea and China.

    PubMed

    Kyong-Song, Ri; Hammond, James O S; Chol-Nam, Ko; Hyok, Kim; Yong-Gun, Yun; Gil-Jong, Pak; Chong-Song, Ri; Oppenheimer, Clive; Liu, Kosima W; Iacovino, Kayla; Kum-Ran, Ryu

    2016-04-01

    Mt. Paektu (also known as Changbaishan) is an enigmatic volcano on the border between the Democratic People's Republic of Korea (DPRK) and China. Despite being responsible for one of the largest eruptions in history, comparatively little is known about its magmatic evolution, geochronology, or underlying structure. We present receiver function results from an unprecedented seismic deployment in the DPRK. These are the first estimates of the crustal structure on the DPRK side of the volcano and, indeed, for anywhere beneath the DPRK. The crust 60 km from the volcano has a thickness of 35 km and a bulk V P/V S of 1.76, similar to that of the Sino-Korean craton. The V P/V S ratio increases ~20 km from the volcano, rising to >1.87 directly beneath the volcano. This shows that a large region of the crust has been modified by magmatism associated with the volcanism. Such high values of V P/V S suggest that partial melt is present in the crust beneath Mt. Paektu. This region of melt represents a potential source for magmas erupted in the last few thousand years and may be associated with an episode of volcanic unrest observed between 2002 and 2005.

  5. Evidence for partial melt in the crust beneath Mt. Paektu (Changbaishan), Democratic People’s Republic of Korea and China

    PubMed Central

    Kyong-Song, Ri; Hammond, James O. S.; Chol-Nam, Ko; Hyok, Kim; Yong-Gun, Yun; Gil-Jong, Pak; Chong-Song, Ri; Oppenheimer, Clive; Liu, Kosima W.; Iacovino, Kayla; Kum-Ran, Ryu

    2016-01-01

    Mt. Paektu (also known as Changbaishan) is an enigmatic volcano on the border between the Democratic People’s Republic of Korea (DPRK) and China. Despite being responsible for one of the largest eruptions in history, comparatively little is known about its magmatic evolution, geochronology, or underlying structure. We present receiver function results from an unprecedented seismic deployment in the DPRK. These are the first estimates of the crustal structure on the DPRK side of the volcano and, indeed, for anywhere beneath the DPRK. The crust 60 km from the volcano has a thickness of 35 km and a bulk VP/VS of 1.76, similar to that of the Sino-Korean craton. The VP/VS ratio increases ~20 km from the volcano, rising to >1.87 directly beneath the volcano. This shows that a large region of the crust has been modified by magmatism associated with the volcanism. Such high values of VP/VS suggest that partial melt is present in the crust beneath Mt. Paektu. This region of melt represents a potential source for magmas erupted in the last few thousand years and may be associated with an episode of volcanic unrest observed between 2002 and 2005. PMID:27152343

  6. Evidence for partial melt in the crust beneath Mt. Paektu (Changbaishan), Democratic People’s Republic of Korea and China

    USGS Publications Warehouse

    Kyong-Song, Ri; Hammond, James O. S.; Chol-Nam, Ko; Hyok, Kim; Yong-Gun, Yun; Gil-Jong, Pak; Chong-Song, Ri; Oppenheimer, Clive; Liu, Kosima W.; Iacovino, Kayla D.; Kum-Ran, Ryu

    2016-01-01

    Mt. Paektu (also known as Changbaishan) is an enigmatic volcano on the border between the Democratic People’s Republic of Korea (DPRK) and China. Despite being responsible for one of the largest eruptions in history, comparatively little is known about its magmatic evolution, geochronology, or underlying structure. We present receiver function results from an unprecedented seismic deployment in the DPRK. These are the first estimates of the crustal structure on the DPRK side of the volcano and, indeed, for anywhere beneath the DPRK. The crust 60 km from the volcano has a thickness of 35 km and a bulk VP/VS of 1.76, similar to that of the Sino-Korean craton. The VP/VS ratio increases ~20 km from the volcano, rising to >1.87 directly beneath the volcano. This shows that a large region of the crust has been modified by magmatism associated with the volcanism. Such high values of VP/VS suggest that partial melt is present in the crust beneath Mt. Paektu. This region of melt represents a potential source for magmas erupted in the last few thousand years and may be associated with an episode of volcanic unrest observed between 2002 and 2005.

  7. Pseudotachylyte in the Bench Canyon Shear Zone, central Sierra Nevada, California: Frictional melting in the brittle and semi-brittle fields

    SciTech Connect

    McNulty, B.A. )

    1993-04-01

    Many aspects of pseudotachylyte are controversial, particularly whether it is the product of intense comminution (e.g. ultracataclasite'') or frictional melting. Ubiquitous exposures of pseudotachylyte in the Bench Canyon shear Zone (BCSZ), central Sierra Nevada, California, provide an excellent opportunity for further study. Scanning electron microscopy (SEM) reveals vesicles, amygdules, crystallites and embayments of microxenocrysts, textures which are supportive of a melt origin for pseudotachylyte in the BCAZ. EDS and microprobe analyses indicate strong compositional contrasts between pseudotachylyte and granodiorite host; one explanation for this is preferential melting in order of individual mineral melting points.

  8. Geochemistry and petrology of spinel lherzolite xenoliths from Xalapasco de La Joya, San Luis Potosi, Mexico: Partial melting and mantle metasomatism

    NASA Astrophysics Data System (ADS)

    Liang, Yan; Elthon, Don

    1990-09-01

    Spinel Iherzolite xenoliths from Xalapasco de La Joya, San Luis Potosi, Mexico, are divided into two distinct groups according to their major element and trace element characteristics. Group Ia xenoliths are characterized by light rare earth element (LREE) depletion ((La/Lu)N = 0.10-0.77 in clinopyroxene) and linear major and compatible trace element relationships. Group Ib xenoliths are characterized by FeO and Na2O enrichment and higher (La/Lu)N ratios (0.80-4.1 in clinopyroxene) and complex major element relationships. These samples, which have a range of equilibrium temperatures of 910°-1070°C, exhibit protogranular textures and typical orthopyroxene+clinopyroxene+spinel clusters. Modal abundances and chemical compositions of the group Ia xenoliths vary from primitive (15.2% clinopyroxene, 38.5% MgO, 1824 ppm Ni) to moderately depleted (6.4-8.7% clinopyroxene, 43.8-44.1% MgO, 2192 ppm Ni). Systematic variations of major elements and compatible trace elements in the group Ia xenoliths are interpreted to result from various degrees (<25%) of partial melting and melt extraction, followed by subsolidus equilibration and annealing. The extracted melts have a range of compositions similar to picritic basalts. Abundances of moderately incompatible trace elements, Sc and Cr, in the group Ia minerals have been substantially redistributed during subsolidus equilibration. In a few of these xenoliths there appears to be vestiges of incipient metasomatism, but metasomatism has not substantially influenced the group as a whole. Group Ib xenoliths have been substantially influenced by metasomatic processes. The ∑FeO and Na2O contents of the cores of clinopyroxenes in group Ib xenoliths are higher than clinopyroxenes in group Ia samples. The higher La contents and La/Lu ratios in group Ib clinopyroxenes (compared to group Ia), together with this FeO and Na2O enrichment, suggest that equilibration of basanites with residual mantle has been a major process in the evolution

  9. H2O storage capacity of olivine and low-Ca pyroxene from 10 to 13 GPa: consequences for dehydration melting above the transition zone

    NASA Astrophysics Data System (ADS)

    Tenner, Travis J.; Hirschmann, Marc M.; Withers, Anthony C.; Ardia, Paola

    2012-02-01

    The onset of hydrous partial melting in the mantle above the transition zone is dictated by the H2O storage capacity of peridotite, which is defined as the maximum concentration that the solid assemblage can store at P and T without stabilizing a hydrous fluid or melt. H2O storage capacities of minerals in simple systems do not adequately constrain the peridotite water storage capacity because simpler systems do not account for enhanced hydrous melt stability and reduced H2O activity facilitated by the additional components of multiply saturated peridotite. In this study, we determine peridotite-saturated olivine and pyroxene water storage capacities at 10-13 GPa and 1,350-1,450°C by employing layered experiments, in which the bottom 2/3 of the capsule consists of hydrated KLB-1 oxide analog peridotite and the top 1/3 of the capsule is a nearly monomineralic layer of hydrated Mg# 89.6 olivine. This method facilitates the growth of 200-μm olivine crystals, as well as accessory low-Ca pyroxenes up to 50 μm in diameter. The presence of small amounts of hydrous melt ensures that crystalline phases have maximal H2O contents possible, while in equilibrium with the full peridotite assemblage (melt + ol + pyx + gt). At 12 GPa, olivine and pyroxene water storage capacities decrease from 1,000 to 650 ppm, and 1,400 to 1,100 ppm, respectively, as temperature increases from 1,350 to 1,450°C. Combining our results with those from a companion study at 5-8 GPa (Ardia et al., in prep.) at 1,450°C, the olivine water storage capacity increases linearly with increasing pressure and is defined by the relation C_{{{{H}}2 {{O}}}}^{{olivine}} ( {{ppm}} ) = 57.6( { ± 16} ) × P( {{GPa}} ) - 169( { ± 18} ). Adjustment of this trend for small increases in temperature along the mantle geotherm, combined with experimental determinations of D_{{{{H}}2 {{O}}}}^{{pyx/olivine}} from this study and estimates of D_{{{{H}}2 {{O}}}}^{{{{gt}}/{{olivine}}}} , allows for estimation of peridotite

  10. Ca(Ti,Si)O3 Diamond Inclusions Crystallized From Carbonate Melts in the Transition Zone: Experimental Constraints

    NASA Astrophysics Data System (ADS)

    Armstrong, L. S.; Walter, M. J.; Keshav, S.; Bulanova, G.; Pickles, J.; Lord, O. T.; Lennie, A.

    2007-12-01

    Composite diamond inclusions consisting of coexisting endmember CaSiO3 and CaTiO3 are rare but occur in diamond populations from Juina, Brazil1-2. Phase relations show that above ~9 GPa (at 1500 K) a perovskite-structured solid solution exists between these endmembers, while at lower pressures intermediate compositions produce coexisting CaTiO3-perovskite and CaSiO3 in the walstromite structure3. Inclusions with `perovskite' stoichiometry are commonly interpreted as fragments of solid mantle from the transition zone or lower mantle4-6. Here we report on two composite diamond inclusions from Juina kimberlite, and can effectively eliminate a subsolidus origin on the basis of experimental mineral phase relations. Instead, based on new melting experiments we find that the inclusions most likely crystallized directly from Ca-rich carbonate melts. Like other workers1-2 we interpret the composite inclusions as exsolution products of a high-pressure Ca(Ti,Si)O3 perovskite stable in the transition zone. Our bulk inclusion compositions are estimated to contain 50- 65 mol% CaTiO3, and are remarkably low in MgSiO3 component at less than 0.2 mol%. Experiments have shown that in peridotite or eclogite lithologies, Ca-rich perovskite in equilibrium with an MgSiO3-phase (majorite or Mg-perovskite) have about 3 to 7 mol% MgSiO37-8. Here we report on new subsolidus laser-heated diamond anvil cell experiments at 20-50 GPa in the ternary system CaSiO3-CaTiO3-MgSiO3 that bracket the CaTi-rich limb of the solvus between Ca- and Mg-rich perovskites. All experiments were made at 2000 (±200) K for 45-75 min, and were analysed using synchrotron micro-focus X-ray diffraction. We find that the solubility of MgSiO3 in CaTi-perovskite solid solutions increases significantly with increasing CaTiO3 component. Thus, Ti-rich calcium perovskite in peridotite or eclogite lithologies should have very high, not exceptionally low, MgSiO3 component. Accordingly, a subsolidus paragenesis is unlikely for

  11. The Relationship Between Partial Contaminant Source Zone Remediation and Groundwater Plume Attenuation

    NASA Astrophysics Data System (ADS)

    Falta, R. W.

    2004-05-01

    Analytical solutions are developed that relate changes in the contaminant mass in a source area to the behavior of biologically reactive dissolved contaminant groundwater plumes. Based on data from field experiments, laboratory experiments, numerical streamtube models, and numerical multiphase flow models, the chemical discharge from a source region is assumed to be a nonlinear power function of the fraction of contaminant mass removed from the source zone. This function can approximately represent source zone mass discharge behavior over a wide range of site conditions ranging from simple homogeneous systems, to complex heterogeneous systems. A mass balance on the source zone with advective transport and first order decay leads to a nonlinear differential equation that is solved analytically to provide a prediction of the time-dependent contaminant mass discharge leaving the source zone. The solution for source zone mass discharge is coupled semi-analytically with a modified version of the Domenico (1987) analytical solution for three-dimensional reactive advective and dispersive transport in groundwater. The semi-analytical model then employs the BIOCHLOR (Aziz et al., 2000; Sun et al., 1999) transformations to model sequential first order parent-daughter biological decay reactions of chlorinated ethenes and ethanes in the groundwater plume. The resulting semi-analytic model thus allows for transient simulation of complex source zone behavior that is fully coupled to a dissolved contaminant plume undergoing sequential biological reactions. Analyses of several realistic scenarios show that substantial changes in the ground water plume can result from the partial removal of contaminant mass from the source zone. These results, however, are sensitive to the nature of the source mass reduction-source discharge reduction curve, and to the rates of degradation of the primary contaminant and its daughter products in the ground water plume. Aziz, C.E., C.J. Newell, J

  12. Low-Velocity Zone of the Earth's Mantle: Incipient Melting Caused by Water.

    PubMed

    Lambert, I B; Wyllie, P J

    1970-08-21

    Experimental phase diagrams for the systems gabbro-water and peridotite-water indicate that, if there is any water in the upper mantle, then traces of hydrous interstitial silicate magma will be produced at depths corresponding to the beginning of the low-velocity zone. This explanation for the zone is more satisfactory than others proposed.

  13. Pine Island Glacier melt rates, grounding zone evolution, and dynamic response from 2008-2015

    NASA Astrophysics Data System (ADS)

    Shean, D. E.; Joughin, I.; Smith, B.; Berthier, E.

    2015-12-01

    Significant grounding line retreat, acceleration, and thinning have occurred along the Amundsen Sea sector of West Antarctica in recent decades. These changes are directly linked to ice-ocean interaction beneath ice shelves, but existing observations of the spatial distribution, timing, and magnitude of ice shelf basal melt are very limited. We generated ~2 m/px DEMs for all available 2010-2015 high-resolution stereo satellite imagery (WorldView-1/2/3 and GeoEye-1) of the West Antarctic coast (excluding the Ross and Ronne-Filchner ice shelves). Annual and sub-annual DEM mosaics were produced for the Amundsen Sea sector, with focus on the Pine Island Glacier (PIG). We integrated SPIRIT ~40 m/px DEMs to extend the PIG time series to 2007/2008, and incorporated surface velocity maps from TerraSAR-X/TanDEM-X from 2009-2015. We use these products to compute ice thickness, Eulerian dH/dt, and Lagrangian DH/Dt, which capture evolving grounding line position, shelf thickening/thinning, and upstream ice dynamics. Ice shelf basal melt rate estimates are derived from both lagrangian DH/Dt and dense flux gate mass budget analysis. We document the spatial and temporal evolution of melt rates for the 2008-2015 period, and compare with existing ICESat (2003-2008) melt estimates and oceanographic observations. Finally, we compare observed melt vs. depth relationships with existing ice flow model parameterizations. Estimated basal melt rates are >100-150 m/yr within the PIG inner cavity, with significantly lower rates of <50 m/yr beneath the outer shelf. Eulerian dh/dt observations show significant thinning (>5-10 m/yr) upstream of the PIG grounding line following the ~2008-2009 ungrounding of the PIG "ice plain," with additional thinning along lateral margins in subsequent years. A combination of reduced melt rates and increased flux resulted in ice shelf regrounding on a large transverse seabed ridge and significant ice shelf thickening. These new data provide critical

  14. Two-stage partial melting during the Variscan extensional tectonics (Montagne Noire, France)

    NASA Astrophysics Data System (ADS)

    Poujol, Marc; Pitra, Pavel; Van Den Driessche, Jean; Tartèse, Romain; Ruffet, Gilles; Paquette, Jean-Louis; Poilvet, Jean-Charles

    2017-03-01

    One of the striking features that characterise the late stages of the Variscan orogeny is the development of gneiss and migmatite domes, as well as extensional Late Carboniferous and Permian sedimentary basins. It remains a matter of debate whether the formation of domes was related to the well-documented late orogenic extension or to the contractional tectonics that preceded. Migmatization and magmatism are expected to predate extension if the domes are compression-related regional anticlines, but they must both precede and be contemporaneous with extension if they are extensional core complexes. In the Montagne Noire area (southern French Massif Central), where migmatization, magmatism and the deformation framework are well documented, the age of the extensional event was unequivocally constrained to 300-290 Ma. Therefore, dating migmatization in this area is a key point for discriminating between the two hypotheses and understanding the Late Palaeozoic evolution of this part of the Variscan belt. For this purpose, a migmatite and an associated anatectic granite from the Montagne Noire dome were dated by LA-ICP-MS (U-Th-Pb on zircon and monazite) and laser probe 40Ar-39Ar (K-Ar on muscovite). Although zircon did not record any Variscan age unequivocally related to compression (380-330 Ma), two age groups were identified from the monazite crystals. A first event, at ca. 319 Ma (U-Th-Pb on monazite), is interpreted as a first stage of migmatization and as the emplacement age of the granite, respectively. A second event at ca. 298-295 Ma, recorded by monazite (U-Th-Pb) and by the muscovite 40Ar-39Ar system in the migmatite and in the granite, could be interpreted as a fluid-induced event, probably related to a second melting event identified through the syn-extensional emplacement of the nearby Montalet leucogranite ca. 295 Ma ago. The ages of these two events post-date the Variscan compression and agree with an overall extensional context for the development of the

  15. Partial melting of a phlogopite-clinopyroxenite nodule from south-west Uganda: an experimental study bearing on the origin of highly potassic continental rift volcanics

    NASA Astrophysics Data System (ADS)

    Lloyd, F. E.; Arima, M.; Edgar, A. D.

    1985-12-01

    Melting experiments on a mantle-derived nodule assemblage consisting of clinopyroxene, phlogopite and minor titanomagnetite, sphene and apatite have been done at 20 and 30 kbar between 1,175 and 1,300° C. The nodule composition was selected on the basis of modal and chemical analyses of 84 mantle derived nodules with metasomatic textures from the Katwe-Kikorongo and Bunyaruguru volcanic fields of south-west Uganda. At 30 kbar, 1,225 and 1,250° C, representing 20 30% partial melting, the compositions of glasses compare favourably to those of the average composition of 26 high potassic mafic lavas from the same region. Glasses produced by sufficiently low degrees of partial melting at 20 kbar could not be analysed. Glass compositions obtained for 20 30% melting at 30 kbar have high K2O (3.07 5.05 wt.%), low SiO2 (35.0 39.2 wt.%), high K/K + Na (0.54 0.71), K + Na/Al (0.99 1.08) and Mg/ Mg + FeT of 0.59 0.62. These results support the suggestion of Lloyd and Bailey (1975) that the nodules represent the source material for the high K-rich lavas of south-west Uganda. If this conclusion is correct it implies that anomalous mantle source of phlogopite clinopyroxenite composition could produced the Ugandan lavas by relatively higher degrees of partial melting than that normally considered for highly alkaline mafic magmas derived from a pyrolitic mantle source. Higher degrees of melting are considered likely from such a different source region, rich in alkalis, water and radioactive elements. Steeper geotherms and increased fluxing of sub-rift mantle by degassing would also produce higher degrees of partial melting.

  16. Viscosity determinations of some frictionally generated silicate melts: Implications for slip zone rheology during impact-induced faulting

    NASA Technical Reports Server (NTRS)

    Spray, John G.

    1992-01-01

    Analytical scanning electron microscopy, using combined energy dispersive and wavelength dispersive spectrometry, was used to determine the major-element compositions of some natural and artificial glasses and their crystalline equivalents derived by the frictional melting of acid to intermediate protoliths. The major-element compositions are used to calculate the viscosities of their melt precursors using the model of Shaw at temperatures of 800-1400 C, with Fe(2+)/Fe(tot) = 0.5 and for 1-3 wt percent H2O. These results are then modified to account for suspension effects in order to determine viscosities. The results have implications for the generation of pseudotachylitic breccias as seen in the basement lithologies of the Sudbury and Vredefort structures and possibly certain dimict lunar breccias. Many of these breccias show similarities with the more commonly developed pseudotachylite fault and injection veins seen in endogenic fault zones that typically occur in thicknesses of a few centimeters or less. The main difference is one of scale: Impact-induced pseudotachylite breccias can attain several meters in thickness. This would suggest that they were generated under exceptionally high slip rates and hence high strain rates and that the friction melts generated possessed extremely low viscosities.

  17. Depths and Temperatures of Mantle Melt Extraction in the Southern Cascadia Subduction Zone (Invited)

    NASA Astrophysics Data System (ADS)

    Till, C.; Grove, T. L.; Donnelly-Nolan, J. M.; Carlson, R. W.

    2013-12-01

    Plagioclase and spinel lherzolite thermometry and barometry applied to an extensive suite of <10.5 Ma primitive basaltic lavas (most Mg#>0.70) containing variable H2O contents (<<1 to ~4 wt%) suggests these melts were extracted from the mantle at 40-58 km below Oregon's High Lava Plains, 41-51 km below California's Modoc Plateau, and 37-60 km below the central-southern Cascades volcanic arc. Of the 155 basalt samples investigated, 33 are calc-alkaline basalts (CAB) and the remainder are high alumina olivine tholeiites (HAOT) or mildly alkaline basalts (MAB). All 33 of the CAB are from the subduction-influenced volcanic centers of Lassen, Mt. Shasta, Three Sisters, Medicine Lake, and Newberry in the present-day Cascades arc or rear arc. All of these volcanic centers also erupted HAOT or MAB. Olivine-plagioclase hygrometry for a representative subset of the 20 CAB from Newberry indicates they contained ~4 wt% H2O prior to eruption. Water contents for the remaining CAB were approximated using the H2O-melt composition scaling relationship developed by Ruscitto et al. [2010, EPSL 298(1-2), 153-161] yielding ≤1-3 wt% H2O. The calculated pressures and temperatures of last equilibration with mantle lherzolite for all 33 CAB were adjusted for the effects of H2O following Till et al. [2012, JGR 117(B06206)] and are on average 50×15°C (1s) cooler and 1.65×0.27 km deeper than their calculated temperatures and depths for anhydrous conditions. The minimum depths of melt extraction calculated for all basalts considered (including the CAB) are close to the Moho, as determined by regional geophysical studies. Thus, our results suggest that the geophysical Moho and lithosphere-asthenosphere boundary are located in close proximity to one another (within 5-10 km). The basalts originated at 1185-1383°C and the presence of both wet and dry basalts that were generated at such different temperatures at similar times, depths, and geographic locations in the Cascades arc and rear arc

  18. Frictional melting experiments investigate coseismic behaviour of pseudotachylyte-bearing faults in the Outer Hebrides Fault Zone, UK.

    NASA Astrophysics Data System (ADS)

    Campbell, L.; De Paola, N.; Nielsen, S. B.; Holdsworth, R.; Lloyd, G. E. E.; Phillips, R. J.; Walcott, R.

    2015-12-01

    Recent experimental studies, performed at seismic slip rates (≥ 1 m/s), suggest that the friction coefficient of seismic faults is significantly lower than at sub-seismic (< 1 mm/s) speeds. Microstructural observations, integrated with theoretical studies, suggest that the weakening of seismic faults could be due to a range of thermally-activated mechanisms (e.g. gel, nanopowder and melt lubrication, thermal pressurization, viscous flow), triggered by frictional heating in the slip zone. The presence of pseudotachylyte within both exhumed fault zones and experimental slip zones in crystalline rocks suggests that lubrication plays a key role in controlling dynamic weakening during rupture propagation. The Outer Hebrides Fault Zone (OHFZ), UK contains abundant pseudotachylyte along faults cutting varying gneissic lithologies. Our field observations suggest that the mineralogy of the protolith determines volume, composition and viscosity of the frictional melt, which then affects the coseismic weakening behaviour of the fault and has important implications for the magnitudes and distribution of stress drops during slip episodes. High velocity friction experiments at 18 MPa axial load, 1.3 ms-1 and up to 10 m slip were run on quartzo-feldspathic, metabasic and mylonitic samples, taken from the OHFZ in an attempt to replicate its coseismic frictional behaviour. These were configured in cores of a single lithology, or in mixed cores with two rock types juxtaposed. All lithologies produce a general trend of frictional evolution, where an initial peak followed by transient weakening precedes a second peak which then decays to a steady state. Metabasic and felsic single-lithology samples both produce sharper frictional peaks, at values of μ = 0.19 and μ= 0.37 respectively, than the broader and smaller (μ= 0.15) peak produced by a mixed basic-felsic sample. In addition, both single-lithology peaks occur within 0.2 m slip, whereas the combined-lithology sample displays a

  19. A dearth of intermediate melts at subduction zone volcanoes and the petrogenesis of arc andesites.

    PubMed

    Reubi, Olivier; Blundy, Jon

    2009-10-29

    Andesites represent a large proportion of the magmas erupted at continental arc volcanoes and are regarded as a major component in the formation of continental crust. Andesite petrogenesis is therefore fundamental in terms of both volcanic hazard and differentiation of the Earth. Andesites typically contain a significant proportion of crystals showing disequilibrium petrographic characteristics indicative of mixing or mingling between silicic and mafic magmas, which fuels a long-standing debate regarding the significance of these processes in andesite petrogenesis and ultimately questions the abundance of true liquids with andesitic composition. Central to this debate is the distinction between liquids (or melts) and magmas, mixtures of liquids with crystals, which may or may not be co-genetic. With this distinction comes the realization that bulk-rock chemical analyses of petrologically complex andesites can lead to a blurred picture of the fundamental processes behind arc magmatism. Here we present an alternative view of andesite petrogenesis, based on a review of quenched glassy melt inclusions trapped in phenocrysts, whole-rock chemistry, and high-pressure and high-temperature experiments. We argue that true liquids of intermediate composition (59 to 66 wt% SiO(2)) are far less common in the sub-volcanic reservoirs of arc volcanoes than is suggested by the abundance of erupted magma within this compositional range. Effective mingling within upper crustal magmatic reservoirs obscures a compositional bimodality of melts ascending from the lower crust, and masks the fundamental role of silicic melts (>/=66 wt% SiO(2)) beneath intermediate arc volcanoes. This alternative view resolves several puzzling aspects of arc volcanism and provides important clues to the integration of plutonic and volcanic records.

  20. Three-dimensional electrical conductivity structure beneath Australia from inversion of geomagnetic observatory data: evidence for lateral variations in transition-zone temperature, water content and melt

    NASA Astrophysics Data System (ADS)

    Koyama, Takao; Khan, Amir; Kuvshinov, Alexey

    2014-03-01

    In this paper, we report the 3-D electrical conductivity distribution beneath the Australian continent in the depth range 410-1600 km, which we have imaged by inverting C-response estimates from a regional network of geomagnetic observatories. The inversion scheme is based on a quasi-Newton optimization method while the forward algorithm relies on an integral-equation approach. To properly account for the ocean effect in responses at coastal observatories we included a high-resolution (1° × 1°) fixed thin laterally varying surface conductance layer. As starting model in the inversion we considered a laboratory-based 3-D conductivity model of the region obtained from seismic surface wave data and thermodynamic modelling. This model provides a good fit to observed C-response estimates supporting its choice as initial model. The most striking feature of the obtained 3-D model is a high-conductivity anomaly in the lower part of the mantle transition zone (MTZ; 520-660 km depth) beneath southeastern Australia implying considerable lateral as radial heterogeneity in the conductivity structure. The high-conductivity region appears to be 0.5-1 log units more conductive than previous global and other regionalized 1-D models. Further analysis using laboratory-based conductivity models combined with thermochemical phase equilibrium computations shows that the strong conductivity anomaly implies water contents of around 0.1 wt per cent in the upper part and >0.4 wt per cent in the lower part of the MTZ. This implies a large MTZ water reservoir that likely totals one to three times that which currently resides in the oceans. The amount of water in the lower MTZ appears to exceed the experimentally determined water storage capacity of the main lower MTZ mineral ringwoodite, which, as a result, undergoes dehydration-induced partial melting. Including contributions to conductivity from a thin melt layer (20 km thick) located in the mid-MTZ increases conductivity locally in the

  1. Relation Between Glacier Velocity, SAR Glacier Zones, and the Timing of Melting in the Southern Patagonia Icefield

    NASA Astrophysics Data System (ADS)

    Berti, C.; Ramage, J. M.; Willis, M. J.; Semmens, K. A.; Melkonian, A. K.; Pritchard, M. E.

    2012-12-01

    outlet glaciers. The analysis of a subset of the processed scenes, favorable to the observation of the slow moving part of the icefield, highlight a velocity field compatible with the presence of icestreams, draining the high ground of the main basins. On a regional scale, the definition of the velocity field for the SPI helps in better defining the extent and variation of glacier zones in this inaccessible and dynamic region. The results of this integrated study, conducted on a rich dataset that spans a relatively short time, demonstrate the correlation between velocity field and melt dynamics on the SPI, reinforcing the common belief of extreme sensitivity of such environments to even small temperature fluctuations. The clear picture of the icefield behavior for the mid '90 provides a baseline from which to assess future change and stands as a reference for similar study over a longer or more recent time span.

  2. The petrogenesis of felsic calc-alkaline magmas from the southernmost Cascades, California: origin by partial melting of basaltic lower crust

    USGS Publications Warehouse

    Borg, L.E.; Clynne, M.A.

    1998-01-01

    The majority offelsic rocks from composite centers in teh southernmost Cascades have geochemical and Sr, Nd and Pb isotopic ratios that suggest derivation by partial melting of lower crust that is compositionally similar to cale-alkaline basalts observed in the region. Only a few felsic rocks have ???18O and Pb isotopic compositions that indicate interaction with the upper crust. Mineralogical and geochemical differences among the felsic magmas results primarily from melting under variable f(H2O) and lower temperature conditions leaves an amphibole-rich residuum, and produced magmas that have amphibole ?? biotite phenocrysts, relatively high silica contents, and pronounced middle rare earch element depletions. These conclusions are consistent with published thermal models that suggest that reasonable volumes of basaltic magma emplaced beneath large composite centers in the southernmost Cascades can serve as the eat source for melting of the lower crust. Melting of the lower crust under varible f(H2O contents of these basaltic magmas.

  3. Experimental determination of dissolved CO2 content in nominally anhydrous andesitic melts at graphite/diamond saturation - Remobilization of deeply subducted reduced carbon via partial melts of MORB-like eclogite

    NASA Astrophysics Data System (ADS)

    Eguchi, J.; Dasgupta, R.

    2015-12-01

    Experimental phase relations of carbonated lithologies [1] and geochemistry of deep diamonds [2] suggest that deep recycling of carbon has likely been efficient for a significant portion of Earth's history. Both carbonates and organic carbon subduct into the mantle, but with gradual decrease of fO2 with depth [3] most carbon in deep mantle rocks including eclogite could be diamond/graphite [4]. Previous studies investigated the transfer of CO2 from subducted eclogite to the ambient mantle by partial melting in the presence of carbonates, i.e., by generation of carbonate-rich melts [5]. However, the transfer of carbon from subducted eclogite to the mantle can also happen, perhaps more commonly, by extraction of silicate partial melt in the presence of reduced carbon; yet, CO2 solubility in eclogite-derived andesitic melt at graphite/diamond saturation remains unconstrained. CO2content of eclogite melts is also critical as geochemistry of many ocean island basalts suggest the presence of C and eclogite in their source regions [6]. In the present study we determine CO2 concentration in a model andesitic melt [7] at graphite/diamond saturation at conditions relevant for partial melting of eclogite in the convecting upper mantle. Piston cylinder and multi anvil experiments were conducted at 1-6 GPa and 1375-1550 °C using Pt/Gr double capsules. Oxygen fugacity was monitored with Pt-Fe sensors in the starting mix. Completed experiments at 1-3 GPa show that CO2 concentration increases with increasing P, T, and fO2 up to ~0.3 wt%. Results were used to develop empirical and thermodynamic models to predict CO2 concentration in partial melts of graphite saturated eclogite. This allowed us to quantify the extent to which CO2 can mobilize from eclogitic heterogeneities at graphite/diamond saturated conditions. With estimates of eclogite contribution to erupted basaltic lavas, the models developed here allow us to put constraints on the flux of CO2 to mantle source regions

  4. Subduction of fracture zones

    NASA Astrophysics Data System (ADS)

    Constantin Manea, Vlad; Gerya, Taras; Manea, Marina; Zhu, Guizhi; Leeman, William

    2013-04-01

    Since Wilson proposed in 1965 the existence of a new class of faults on the ocean floor, namely transform faults, the geodynamic effects and importance of fracture zone subduction is still little studied. It is known that oceanic plates are characterized by numerous fracture zones, and some of them have the potential to transport into subduction zones large volumes of water-rich serpentinite, providing a fertile water source for magma generated in subduction-related arc volcanoes. In most previous geodynamic studies, subducting plates are considered to be homogeneous, and there is no clear indication how the subduction of a fracture zone influences the melting pattern in the mantle wedge and the slab-derived fluids distribution in the subarc mantle. Here we show that subduction of serpentinized fracture zones plays a significant role in distribution of melt and fluids in the mantle wedge above the slab. Using high-resolution tree-dimensional coupled petrological-termomechanical simulations of subduction, we show that fluids, including melts and water, vary dramatically in the region where a serpentinized fracture zone enters into subduction. Our models show that substantial hydration and partial melting tend to concentrate where fracture zones are being subducted, creating favorable conditions for partially molten hydrous plumes to develop. These results are consistent with the along-arc variability in magma source compositions and processes in several regions, as the Aleutian Arc, the Cascades, the Southern Mexican Volcanic Arc, and the Andean Southern Volcanic Zone.

  5. Occurrence and characterization of carbon nanoparticles below the soot laden zone of a partially premixed flame

    SciTech Connect

    Paul, Bireswar; Datta, Amitava; Datta, Aparna; Saha, Abhijit

    2009-12-15

    An experimental study has been performed to detect the occurrence of nanosized carbon particulates below the soot laden zone of a co-flowing partially premixed flame. Samples have been extracted from different points across the flame and passed through DI water. Absorption and fluorescence spectroscopies have been performed with the collected water suspensions. The occurrence of carbon nanoparticles is evident across the inner flame front. In addition, evidence of naphthalene has also been found inside the inner rich premixed flame. The concentration of naphthalene decreases while that of the carbon nanoparticles increases as the inner flame front is reached. The stability of the nanoparticles in the sample has been ensured by observing that the change in fluorescence quantum yield from the sample over a long duration is small. The band gap energy has been evaluated using the absorption data to characterize the likely structures of the particles in the collected suspension. Two kinds of particles having different zones of band gap energy are found in the flame. Dynamic light scattering measurements show that the particle size grows with the increase in height in the lower part of the flame. While, at 3 and 6 mm elevations the particles are observed to be below 2.5 nm in diameter, the particles at 10 mm elevation are found in the size range of 2.5-5.5 nm. (author)

  6. The Growth of Melt Inclusion- and Water-Rich Zones in Clinopyroxene Phenocrysts of the Powai Ankaramite Flow, Deccan Traps, India: Rapid Closed System Oscillatory Mineral Growth

    NASA Astrophysics Data System (ADS)

    Seaman, S. J.

    2015-12-01

    Water concentrations were measured and mapped using FTIR spectroscopy in clinopyroxene phenocrysts of the Powai ankaramite flow, located near Mumbai, west of the Western Ghats escarpment of the Deccan province, India. Samples were provided by Dr. Hetu Sheth of the Indian Institute of Technology, Mumbai. Chatterjee and Sheth (2015) showed that phenocrysts in the flow were part of a cumulate layer intruded by high-temperature basaltic melt at ~ 6 kb and ~1230oC. Cpx phenocrysts are euhedral and have concentric bands (100 to 200 microns thick) of fine (10-20 micron diameter) melt inclusions. Cpx bands that host melt inclusions have higher concentrations of water than inclusion-free bands. Water concentrations of cpx and ol were used to calculate water concentrations in the melt from which the crystals formed. Water concentrations in the parent magma were between 4.35 and 8.26 wt. % based on water concentrations in cpx, and between 8.24 and 9.41 wt. % based on those in ol. Both Mg and Fe are relatively depleted in the water- and melt inclusion-rich zones in cpx, and Ca is enriched in these zones. We suggest that oscillatory zoning in cpx is a result of repeated growth of cpx in water-richer and water-poorer boundary layers in which water lowered melt viscosity and enhanced diffusion and crystal growth rates. Water-enhanced growth rates may have resulted in preferential capture of melt inclusions preserved in water-rich cpx zones. Mg was preferentially incorporated into the cpx, causing Ca and water to build up in the boundary layer, and Mg and Fe to become relatively depleted in the boundary layer, as discussed for oscillatorially-zoned minerals by Wang and Merino (1993). Application of the equations for growth of oscillatory zones in crystals given by Wang and Merino (1993) to the growth of cpx crystals in the Powai ankaramite indicate that crystal growth occurred relatively quickly, on the order of days, although the width of the boundary zone, which is uncertain

  7. The investigation of custom grown vertical zone melt semi-insulating bulk gallium arsenide as a radiation spectrometer

    SciTech Connect

    McGregor, D.S.; Antolak, A.J.; Chui, H.C.

    1996-06-01

    Vertical zone melt (VZM) bulk GaAs boules have been zone refined (ZR) and zone leveled (ZL) to reduce EL2 deep donor levels and impurity concentrations with the intent of improving properties for gamma ray detectors. Zr and Zl GaAs boules had background impurity levels and deep donor EL2 concentrations near or below detectable limits. The crystal mosaic of the material at locations near the seed end was slightly superior to commercial liquid encapsulated Czochralski (LEC) material, and nearly equivalent to commercial vertical gradient freeze (VGF) material. The crystal mosaic in ZL material degraded towards the tail end. The homogeneity of the electrical properties for the ZL and ZR VZM material was inferior compared to commercially available bulk GaAs material. Post growth annealing may help to homogenize some electrical properties of the material. The charge collection efficiency of the ZR GaAs detectors was only 30% maximum, and only 25% maximum for the ZL GaAs detectors. Resulting gamma ray spectra was poor from detectors fabricated with the ZL or ZR VZM material. Detectors fabricated from material that was both ZR and ZL did not demonstrate gamma ray resolution, and operated mainly as counters. The poor spectroscopic performance is presently attributed to the inhomogeneity of the electrical properties of the ZR and ZL GaAs materials. Comparisons are made with detectors fabricated from VGF SI bulk GaAs.

  8. EBSD and DTA Characterization of A356 Alloy Deformed by ECAP During Reheating and Partial Re-melting

    NASA Astrophysics Data System (ADS)

    Moradi, Marzyeh; Nili-Ahmadabadi, Mahmoud; Poorganji, Behrang; Heidarian, Bashir; Furuhara, Tadashi

    2013-11-01

    Recrystallization and partial re-melting processes have been developed for producing semi-solid feedstock in a solid state in which a globular microstructure is obtained by plastic deformation followed by reheating. In this research, to induce strain, a cast- and solution-treated Aluminum A356 (7 wt pct Si) alloy was subjected to a repetitive equal channel angular pressing process using a 90 deg die, up to a total accumulated strain of approximately 8 in route A (increasing strain through a sequence of passes with no rotation of the sample after each pass) at ambient temperature. The microstructural evolutions of deformed and reheated materials were studied by optical microscopy, scanning electron microscopy, and electron back-scattered diffraction analysis. In addition, the influences of pre-deformation on the recrystallization mechanism and liquid formation of A356 alloy were presented and discussed. The results are also supported by differential thermal analysis experiments. Evaluation of the observations indicated that the average cell boundary misorientation increased with increasing strain, so this increased misorientation accelerated the mobility of boundaries and recrystallization kinetics. Therefore, the recrystallization mechanism and kinetics affected by deformation, reheating condition, and intrinsic material properties determined the particle size in the semi-solid state.

  9. Partial Melting of Subducted Sediments Produced Early Mesozoic Calc-alkaline Lamprophyres from Northern Guangxi Province, South China.

    PubMed

    Su, Hui-Min; Jiang, Shao-Yong; Zhang, Dong-Yang; Wu, Xiang-Ke

    2017-07-07

    There is growing agreement that subducted sediments recycled into the deep mantle could make a significant contribution to the generation of various mantle-derived rocks. However, solid evidence and examples to support this view are few, and whether or not the subducted sediments can act as the dominating material source for the magma is unclear. Here, we report a comprehensive geochemical study that demonstrates that the newly identified Early Mesozoic calc-alkaline lamprophyres in the northern Guangxi Province, southeastern Yangtze Block in South China were likely derived in large part from the partial melting of the subducted terrigenous sediments in the deep mantle. The investigated lamprophyres are SiO2-rich minettes, characterized by moderate TFeO and MgO and high Mg(#) (>70). The multi-element pattern shows a typical crustal-like signature, such as enrichments in large-ion lithophile elements (LILE) and light rare earth elements (LREE) with troughs in Nb-Ta, Ti and Eu and peaks in Th-U and Pb. These rocks also show sediment-like ratios of Nb/U, Nb/Th and Ce/Pb, together with extremely radiogenic (87)Sr/(86)Sr (0.71499-0.71919), unradiogenic (143)Nd/(144)Nd (0.51188-0.51195) and radiogenic (207)Pb/(204)Pb (15.701-15.718) isotopic compositions.

  10. Trace element analyses of spheres from the melt zone of the Greenland ice cap using synchrotron X ray fluorescence

    NASA Technical Reports Server (NTRS)

    Chevallier, P.; Wang, J.; Jehanno, C.; Maurette, M.; Sutton, S. R.

    1986-01-01

    Synchrotron X-ray fluorescence spectra of unpolished iron and chondritic spheres extracted from sediments collected on the melt zone of the Greenland ice cap allow the analysis of Ni, Cu, Zn, Ga, Ge, Pb, and Se with minimum detection limits on the order of several parts per million. All detected elements are depleted relative to chondritic abundance with the exception of Pb, which shows enrichments up to a factor of 500. An apparent anticorrelation between the Ni-content and trace element concentration was observed in both types of spherules. The fractionation patterns of the iron and chondritic spheres are not complementary and consequently the two iron spheres examined in this study are unlikely to result from ejection of globules of Fe/Ni from parent chondritic micrometeoroids.

  11. Trace element analyses of spheres from the melt zone of the Greenland ice cap using synchrotron X ray fluorescence

    NASA Technical Reports Server (NTRS)

    Chevallier, P.; Wang, J.; Jehanno, C.; Maurette, M.; Sutton, S. R.

    1986-01-01

    Synchrotron X-ray fluorescence spectra of unpolished iron and chondritic spheres extracted from sediments collected on the melt zone of the Greenland ice cap allow the analysis of Ni, Cu, Zn, Ga, Ge, Pb, and Se with minimum detection limits on the order of several parts per million. All detected elements are depleted relative to chondritic abundance with the exception of Pb, which shows enrichments up to a factor of 500. An apparent anticorrelation between the Ni-content and trace element concentration was observed in both types of spherules. The fractionation patterns of the iron and chondritic spheres are not complementary and consequently the two iron spheres examined in this study are unlikely to result from ejection of globules of Fe/Ni from parent chondritic micrometeoroids.

  12. Large and rapid melt-induced velocity changes in the ablation zone of the Greenland Ice Sheet.

    PubMed

    van de Wal, R S W; Boot, W; van den Broeke, M R; Smeets, C J P P; Reijmer, C H; Donker, J J A; Oerlemans, J

    2008-07-04

    Continuous Global Positioning System observations reveal rapid and large ice velocity fluctuations in the western ablation zone of the Greenland Ice Sheet. Within days, ice velocity reacts to increased meltwater production and increases by a factor of 4. Such a response is much stronger and much faster than previously reported. Over a longer period of 17 years, annual ice velocities have decreased slightly, which suggests that the englacial hydraulic system adjusts constantly to the variable meltwater input, which results in a more or less constant ice flux over the years. The positive-feedback mechanism between melt rate and ice velocity appears to be a seasonal process that may have only a limited effect on the response of the ice sheet to climate warming over the next decades.

  13. Partial melting to produce high-silica rhyolites of a young bimodal suite: compositional constraints among rhyolites, basalts, and metamorphic xenoliths from the Harney Basin, Oregon

    NASA Astrophysics Data System (ADS)

    Streck, Martin J.

    2002-08-01

    The Rattlesnake Ash Flow Tuff from eastern Oregon includes lithic fragments (xenoliths) of which metasedimentary or metavolcanic lithologies around the vent area in the Harney Basin are samples of the concealed crust. Metasedimentary xenoliths are volcanic lithic to feldspathic graywackes that could be sampling lithologies similar to arc-related terranes to the north that have accreted during Mesozoic time along the Oregon Pacific margin. The importance of finding metaxenoliths in the Rattlesnake Tuff is that they are the first basement samples of southeastern Oregon possibly representative of larger portions of the concealed crust from which voluminous Rattlesnake Tuff and other rhyolites were initially generated during partial melting with subsequent evolution through fractional crystallization. High Ba/Rb ratios of ~30 and La/Yb of ~6.5 of least-evolved Rattlesnake Tuff high-silica rhyolites in combination with other low concentrations of some incompatible trace elements preclude the derivation of least-evolved Rattlesnake Tuff high-silica rhyolite from local low-silica rhyolites through fractionation, which suggests instead that some chemical characteristics could be nearly unmodified signatures derived from partial melting. Rattlesnake metamorphic xenoliths and primitive basalt lavas (HAOT) have the most compatible chemistries as source rock for partial melting among a large range of other local rock compositions. Compositional evidence, comparison with literature data of experimental melts derived from laboratory experiments, and modeling of required effective partition coefficients indicate that least-evolved Rattlesnake Tuff rhyolite was likely generated during dehydration melting of mafic crust at melt percentage ranging from ~5 to 10% with residues as observed in experiments with abundant pyroxene and plagioclase.

  14. Geochemical signatures of metasedimentary rocks of high-pressure granulite facies and their relation with partial melting: Carvalhos Klippe, Southern Brasília Belt, Brazil

    NASA Astrophysics Data System (ADS)

    Cioffi, Caue Rodrigues; Campos Neto, Mario da Costa; da Rocha, Brenda Chung; Moraes, Renato; Henrique-Pinto, Renato

    2012-12-01

    High-grade metasedimentary rocks can preserve geochemical signatures of their sedimentary protolith if significant melt extraction did not occur. Retrograde reaction textures provide the main evidence for trapped melt in the rock fabrics. Carvalhos Klippe rocks in Southern Brasília Orogen, Brazil, present a typical high-pressure granulite assemblage with evidence of mica breakdown partial melting (Ky + Grt + Kfs ± Bt ± Rt). The metamorphic peak temperatures obtained by Zr-in-Rt and ternary feldspar geothermometers are between 850 °C and 900 °C. The GASP baric peak pressure obtained using grossular rich garnet core is 16 kbar. Retrograde reaction textures in which the garnet crystals are partially to totally replaced by Bt + Qtz ± Fsp intergrowths are very common in the Carvalhos Klippe rocks. These reactions are interpreted as a result of interactions between residual phases and trapped melt during the retrograde path. In the present study the geochemical signatures of three groups of Carvalhos Klippe metasedimentary rocks are analysed. Despite the high metamorphic grade these three groups show well-defined geochemical features and their REE patterns are similar to average compositions of post-Archean sedimentary rocks (PAAS, NASC). The high-pressure granulite facies Grt-Bt-Pl gneisses with immature arenite (wacke, arkose or lithic-arenite) geochemical signatures present in the Carvalhos Klippe are compared to similar rocks in amphibolite facies from the same tectonic framework (Andrelândia Nappe System). The similar geochemical signatures between Grt-Bt-Pl gneisses metamorphosed in high-pressure granulite facies and Grt-Bt-Pl-Qtz schists from the Andrelândia and Liberdade Nappes, with minimal to absent melting conditions, are suggestive of low rates of melt extraction in these high-grade rocks. The rocks with pelitic compositions most likely had higher melt extraction and even under such circumstances nevertheless tend to show REE patterns similar to

  15. Petrology, geochemistry, zircon U-Pb dating and Lu-Hf isotope of granitic leucosomes within felsic gneiss from the North Qaidam UHP terrane: Constraints on the timing and nature of partial melting

    NASA Astrophysics Data System (ADS)

    Shengyao, Yu; Jianxin, Zhang; Deyou, Sun; del Real, Pablo García; Yunshuai, Li; Xilin, Zhao; Kejun, Hou

    2015-03-01

    Granitic leucosomes are widely distributed within felsic gneiss in the North Qaidam ultrahigh-pressure (UHP) metamorphic terrane in western China, which is crucial to understanding the relationships between partial melting, metamorphic evolution and orogenic processes. We have applied petrology, whole-rock geochemistry and Sr-Nd isotope, zircon U-Pb geochronology, trace element composition and Lu-Hf isotope of these granitic leucosomes to determine the nature and timing of partial melting of these rocks. Anatexis of the felsic gneiss is evidenced by (1) highly cuspate, elongated feldspar grains along quartz-quartz and quartz-feldspar boundaries, (2) cuspate wedge-shaped pockets of K-feldspar + quartz + plagioclase ± muscovite along the boundaries of quartz and/or plagioclase, and (3) felsic veinlets of K-feldspar + quartz ± plagioclase ± muscovite along grain boundaries. Major elements (FeOT, MnO, MgO and TiO2) as well as LREEs, HREEs and HFSEs are mainly retained in the melanosomes, whereas the large-ion lithophile elements (LILEs, e.g., Rb, Ba, K, Sr, Pb) are preferentially partitioned into the granitic leucosomes. Three discrete U-Pb ages are recorded in the zoned zircons from the melanosomes and granitic leucosomes. The inherited magmatic (pre-metamorphic) zircon cores from melanosomes and granitic leucosomes contain quartz + feldspar inclusions and record a Neoproterozoic protolith age of approximately ~ 950 Ma. The unzoned zircon mantles in the melanosomes and granitic leucosomes show characteristics similar to metamorphic zircons, in terms of such as remarkably flat heavy rare earth element (HREE) patterns, an absence of obviously negative Eu anomalies, and low Th/U ratios. These zircon mantles record an eclogite-facies metamorphic age of 444-449 Ma. The last discrete age at 433-435 Ma is preserved in anatectic zircon rims, which display pronounced oscillatory zoning, and contain felsic mineral inclusions of K-feldspar + plagioclase + quartz. The

  16. Concept of the exhumed partial annealing (retention) zone in thermochronology: An appraisal

    NASA Astrophysics Data System (ADS)

    Fitzgerald, P. G.

    2013-12-01

    The concept of an exhumed partial annealing zone (PAZ) in fission track (FT) thermochronology has been a widely used and successful interpretative tool since the 1980s. This 1D-interpretative approach is typically applied to samples collected over significant relief, with best results if the sampling is undertaken in steep short-wavelength topography and samples collected parallel to topography (perpendicular to curved isotherms), and for samples following a vertical exhumation path. While annealing of fission tracks occurs even at low ambient temperatures the PAZ is defined as the zone between where tracks are annealed 'geologically' instantaneously and where the rate of annealing slows dramatically; between ~60 and ~110°C for tracks in apatite depending on composition. The shape and average slope of a PAZ varies depending on the paleogeothermal gradient and its stability, and the length of time over which a PAZ forms. PAZs and partial retention zones (PRZ) are now known for different minerals for various techniques. Single grain age dispersion can be significantly magnified in a PAZ/PRZ depending on composition, grain size, [eU], radiation damage and zoning for the FT and (U-Th)/He methods. An exhumed PAZ/PRZ may be revealed in an age-elevation ('vertical') profile when, following a period of uplift/exhumation, the form of the PAZ/PRZ is retained with a 'sharp' convex inflexion (the 'break in slope') marking the base of the exhumed PAZ/PRZ with reset samples structurally beneath. The break in slope represents a minimal age for the transition from 'relative thermal stability' to rapid cooling, as the rock column has to cool through the PAZ/PRZ, with the underestimate greater if the change in cooling rate is not significant. The base of an exhumed PAZ/PRZ is a curve, but we approximate it with straight lines, with less precision with fewer samples. The break in slope may not be distinguishable if the cooling/exhumation was long ago and/or of low magnitude. The

  17. Effects of partial root-zone irrigation on hydraulic conductivity in the soil–root system of maize plants

    PubMed Central

    Hu, Tiantian; Kang, Shaozhong; Li, Fusheng; Zhang, Jianhua

    2011-01-01

    Effects of partial root-zone irrigation (PRI) on the hydraulic conductivity in the soil–root system (Lsr) in different root zones were investigated using a pot experiment. Maize plants were raised in split-root containers and irrigated on both halves of the container (conventional irrigation, CI), on one side only (fixed PRI, FPRI), or alternately on one of two sides (alternate PRI, APRI). Results show that crop water consumption was significantly correlated with Lsr in both the whole and irrigated root zones for all three irrigation methods but not with Lsr in the non-irrigated root zone of FPRI. The total Lsr in the irrigated root zone of two PRIs was increased by 49.0–92.0% compared with that in a half root zone of CI, suggesting that PRI has a significant compensatory effect of root water uptake. For CI, the contribution of Lsr in a half root zone to Lsr in the whole root zone was ∼50%. For FPRI, the Lsr in the irrigated root zone was close to that of the whole root zone. As for APRI, the Lsr in the irrigated root zone was greater than that of the non-irrigated root zone. In comparison, the Lsr in the non-irrigated root zone of APRI was much higher than that in the dried zone of FPRI. The Lsr in both the whole and irrigated root zones was linearly correlated with soil moisture in the irrigated root zone for all three irrigation methods. For the two PRI treatments, total water uptake by plants was largely determined by the soil water in the irrigated root zone. Nevertheless, the non-irrigated root zone under APRI also contributed to part of the total crop water uptake, but the continuously non-irrigated root zone under FPRI gradually ceased to contribute to crop water uptake, suggesting that it is the APRI that can make use of all the root system for water uptake, resulting in higher water use efficiency. PMID:21527627

  18. Effects of partial root-zone irrigation on hydraulic conductivity in the soil-root system of maize plants.

    PubMed

    Hu, Tiantian; Kang, Shaozhong; Li, Fusheng; Zhang, Jianhua

    2011-08-01

    Effects of partial root-zone irrigation (PRI) on the hydraulic conductivity in the soil-root system (L(sr)) in different root zones were investigated using a pot experiment. Maize plants were raised in split-root containers and irrigated on both halves of the container (conventional irrigation, CI), on one side only (fixed PRI, FPRI), or alternately on one of two sides (alternate PRI, APRI). Results show that crop water consumption was significantly correlated with L(sr) in both the whole and irrigated root zones for all three irrigation methods but not with L(sr) in the non-irrigated root zone of FPRI. The total L(sr) in the irrigated root zone of two PRIs was increased by 49.0-92.0% compared with that in a half root zone of CI, suggesting that PRI has a significant compensatory effect of root water uptake. For CI, the contribution of L(sr) in a half root zone to L(sr) in the whole root zone was ∼50%. For FPRI, the L(sr) in the irrigated root zone was close to that of the whole root zone. As for APRI, the L(sr) in the irrigated root zone was greater than that of the non-irrigated root zone. In comparison, the L(sr) in the non-irrigated root zone of APRI was much higher than that in the dried zone of FPRI. The L(sr) in both the whole and irrigated root zones was linearly correlated with soil moisture in the irrigated root zone for all three irrigation methods. For the two PRI treatments, total water uptake by plants was largely determined by the soil water in the irrigated root zone. Nevertheless, the non-irrigated root zone under APRI also contributed to part of the total crop water uptake, but the continuously non-irrigated root zone under FPRI gradually ceased to contribute to crop water uptake, suggesting that it is the APRI that can make use of all the root system for water uptake, resulting in higher water use efficiency.

  19. [Effects of controlled alternate partial root-zone drip irrigation on apple seedling morphological characteristics and root hydraulic conductivity].

    PubMed

    Yang, Qi-Liang; Zhang, Fu-Cang; Liu, Xiao-Gang; Ge, Zhen-Yang

    2012-05-01

    To investigate the effects of alternate partial root-zone drip irrigation (ADI) on the morphological characteristics and root hydraulic conductivity of apple seedlings, three irrigation modes, i.e., fixed partial root-zone drip irrigation (FDI, fixed watering on one side of the seedling root zone), controlled alternate partial root-zone drip irrigation (ADI, alternate watering on both sides of the seedling root zone), and conventional drip irrigation (CDI, watering cling to the seedling base), and three irrigation quotas, i. e., each irrigation amount of FDI and ADI was 10, 20 and 30 mm, and that of CDI was 20, 30 and 40 mm, respectively, were designed. In treatment ADI, the soil moisture content on the both sides of the root zone appeared a repeated alternation of dry and wet process; while in treatment CDI, the soil moisture content had less difference. At the same irrigation quotas, the soil moisture content at the watering sides had no significant difference under the three drip irrigation modes. At irrigation quota 30 mm, the root-shoot ratio, healthy index of seedlings, and root hydraulic conductivity in treatment ADI increased by 31.6% and 47.1%, 34.2% and 53.6%, and 9.0% and 11.0%, respectively, as compared with those in treatments CDI and FDI. The root dry mass and leaf area had a positive linear correlation with root hydraulic conductivity. It was suggested that controlled alternate partial root-zone drip irrigation had obvious compensatory effects on the root hydraulic conductivity of apple seedlings, improved the soil water use by the roots, benefited the equilibrated dry matter allocation in seedling organs, and markedly enhanced the root-shoot ratio and healthy index of the seedlings.

  20. Record of Fluctuating Magmatic Environments, Melt Fractionation, and Mixing of Crystals: Elemental Compositions of Zircon Zones, Spirit Mountain Batholith, Nevada

    NASA Astrophysics Data System (ADS)

    Miller, C. F.; Claiborne, L. L.; Wooden, J. L.; Mazdab, F. K.; Walker, B. A.

    2006-12-01

    Spirit Mountain batholith is a large, tilted, subvolcanic intrusion in southernmost Nevada (Walker et al., in press; Lowery Claiborne et al., in press). Field relations and elemental chemistry of rocks ranging from felsic cumulates to leucogranites demonstrate both fractionation and frequent recharging. SHRIMP U-Pb analysis of zircon reveals a 2 m.y. history (17.4-15.3 Ma) for the batholith; almost all of the samples record multiple age populations. Elemental concentrations and zoning patterns document the utility of zircon in tracking magmatic environments and crystal transfer processes and provide important insights into the complex and protracted history of the batholith. The data lend strong support to the Watson et al. (2006) Ti-in-zircon thermometer. At reasonable a(TiO2) between 0.5 and 0.9, all calculated T's are consistent with petrological constraints and granite phase equilibria; using a(TiO2) = 0.7, T ranges from 675-900 C. Over this apparent T interval, which reflects a range in Ti from 3.2-34 ppm, concentrations of Hf (6000-18000 ppm), U (20-5000 ppm), and Th (50-13,000 ppm), and REE patterns all vary dramatically and systematically. Hf, U, Th, and Ce/Ce* are negatively correlated with T; LREE/MREE, MREE/HREE, and Eu/Eu* are positively correlated with T. These variations indicate that zircon preferentially incorporated Zr over Hf (hence falling Zr/Hf); U and Th behaved as strongly incompatible elements in the crystallizing assemblage as a whole; compatibility of REE increased with decreasing atomic number (effect of LREE accessories?); Eu+2 was more compatible (feldspars) and Ce+4 less compatible than equivalent +3 REE. All of these trends are consistent with the observed crystallizing assemblage and with general trends in whole rocks. More striking, however, is intrasample and intragrain variability. Although leucogranite samples have a larger proportion of zircon with compositions indicating low T and growth from fractionated melt, all samples have

  1. Evaluating the Extent of C Cycling Through a Cold Subduction Zone: New Clues from Izu- Bonin Melt Inclusions

    NASA Astrophysics Data System (ADS)

    Shaw, A. M.; Hauri, E. H.; Fischer, T. P.; Hilton, D. R.

    2006-05-01

    Subduction zones provide our best window into C cycling processes between Earth's surface reservoirs and the mantle. The efficiency of this process can be constrained through volatile studies of melt inclusions, where measured pre-eruptive CO2 contents are combined with magma production rates to obtain an output CO2 flux. These outputs can then be compared to C inputs from the subducting slab (sedimentary, organic and altered oceanic crust) to evaluate budgets through a given arc system. Decarbonation of the various C components within a slab are strongly controlled by temperature, pressure and fluid availability. The Izu-Bonin subduction zone system is a cold subduction zone and modeled CO2 behaviour for low temperature geotherms suggest that little decarbonation would occur at subarc depths 1. However, fluids can effectively promote decarbonation. Trace element ratios of Izu arc rocks 2 predict that a significant amount of fluid is fluxed through the Izu-Bonin arc system. This study aims to evaluate the extent of C recycling through a cold, yet fluid-rich arc system. Here we report new CO2 melt inclusions abundance data from 4 volcanoes in the Izu-Bonin arc: Nijima, Oshima, Hachijojima and Aogashima. Concentrations of CO2, along with other volatiles (H2O, F, SO2, Cl), were determined using SIMS techniques at the Carnegie Institution of Washington. Various processes can modify intrinsic volatile contents such as degassing, fractional crystallization, crustal contamination and extent of melting, thereby masking true source values. CO2 contents of Izu-Bonin melt inclusions show positive trends with other volatiles (H2O and SO2) and with MgO contents (with the exception of Nijima). This indicates that differentiation and degassing have occurred simultaneously. In this case, we assume that the highest CO2 concentration samples (up to 1200 ppm CO2 from Nijima volcano) best represent pre-eruptive magma compositions. Comparing a total CO2 input of 10.35 Mmol/yr3 to our

  2. Critical porosity of melt segregation during crustal melting: Constraints from zonation of peritectic garnets in a dacite volcano

    NASA Astrophysics Data System (ADS)

    Yu, Xun; Lee, Cin-Ty A.

    2016-09-01

    The presence of leucogranitic dikes in orogenic belts suggests that partial melting may be an important process in the lower crust of active orogenies. Low seismic velocity and low electrical resistivity zones have been observed in the lower crust of active mountain belts and have been argued to reflect the presence of partial melt in the deep crust, but volcanoes are rare or absent above many of these inferred melt zones. Understanding whether these low velocity zones are melt-bearing, and if so, why they do not commonly erupt, is essential for understanding the thermal and rheologic structure of the crust and its dynamic evolution. Central to this problem is an understanding of how much melt can be stored before it can escape from the crust via compaction and eventually erupt. Experimental and theoretical studies predict trapped melt fractions anywhere from <5% to >30%. Here, we examine Mn growth-zoning in peritectic garnets in a Miocene dacite volcano from the ongoing Betic-Rif orogeny in southern Spain to estimate the melt fraction at the time of large-scale melt extraction that subsequently led to eruption. We show that the melt fraction at segregation, corresponding approximately to the critical melt porosity, was ∼30%, implying significant amounts of melt can be stored in the lower crust without draining or erupting. However, seismic velocities in the lower crust beneath active orogenic belts (southern Spain and Tibet) as well as beneath active magmatic zones (e.g., Yellowstone hotspot) correspond to average melt porosities of <10%, suggesting that melt porosities approaching critical values are short-lived or that high melt porosity regions are localized into heterogeneously distributed sills or dikes, which individually cannot be resolved by seismic studies.

  3. Growth and proteomic analysis of tomato fruit under partial root-zone drying.

    PubMed

    Marjanović, Milena; Stikić, Radmila; Vucelić-Radović, Biljana; Savić, Sladjana; Jovanović, Zorica; Bertin, Nadia; Faurobert, Mireille

    2012-06-01

    The effects of partial root-zone drying (PRD) on tomato fruit growth and proteome in the pericarp of cultivar Ailsa Craig were investigated. The PRD treatment was 70% of water applied to fully irrigated (FI) plants. PRD reduced the fruit number and slightly increased the fruit diameter, whereas the total fruit fresh weight (FW) and dry weight (DW) per plant did not change. Although the growth rate was higher in FI than in PRD fruits, the longer period of cell expansion resulted in bigger PRD fruits. Proteins were extracted from pericarp tissue at two fruit growth stages (15 and 30 days post-anthesis [dpa]), and submitted to proteomic analysis including two-dimensional gel electrophoresis and mass spectrometry for identification. Proteins related to carbon and amino acid metabolism indicated that slower metabolic flux in PRD fruits may be the cause of a slower growth rate compared to FI fruits. The increase in expression of the proteins related to cell wall, energy, and stress defense could allow PRD fruits to increase the duration of fruit growth compared to FI fruits. Upregulation of some of the antioxidative enzymes during the cell expansion phase of PRD fruits appears to be related to their role in protecting fruits against the mild stress induced by PRD.

  4. Partial primary structure of human pregnancy zone protein: extensive sequence homology with human alpha 2-macroglobulin.

    PubMed Central

    Sottrup-Jensen, L; Folkersen, J; Kristensen, T; Tack, B F

    1984-01-01

    Human pregnancy zone protein (PZP) is a major pregnancy-associated protein. Its quaternary structure (two covalently bound 180-kDa subunits, which are further non-covalently assembled into a tetramer of 720 kDa) is similar to that of human alpha 2-macroglobulin (alpha 2M). Here we show, from the results of complete or partial sequence determination of a random selection of 38 tryptic peptides covering 685 residues of the subunit of PZP, that PZP and alpha 2M indeed are extensively homologous. In the stretches of PZP sequenced so far, the degree of identically placed residues in the two proteins is 68%, indicating a close evolutionary relationship between PZP and alpha 2M. Although the function of PZP in pregnancy is largely unknown, its close structural relationship to alpha 2M suggests analogous proteinase binding properties and a potential for being taken up in cells by receptor-mediated endocytosis. In this regard our studies indicate a bait region in PZP significantly different from that present in alpha 2M. PZP could be the human equivalent of the acute-phase alpha-macroglobulins (e.g., rat alpha 2M and rabbit alpha 1M) described earlier. PMID:6209714

  5. Mantle ingredients for making the fingerprint of Etna alkaline magmas: implications for shallow partial melting within the complex geodynamic framework of Eastern Sicily

    NASA Astrophysics Data System (ADS)

    Viccaro, Marco; Zuccarello, Francesco

    2017-09-01

    Mantle ingredients responsible for the signature of Etnean Na- and K-alkaline magmas and their relationships with short-term geochemical changes of the erupted volcanic rocks have been constrained through a partial melting model that considers major, trace elements and water contents in the produced liquids. Characteristics of the Etnean source for alkaline magmas have been supposed similar to those of the mantle accessible at a regional scale, namely below the Hyblean Plateau. The assumption that the Etnean mantle resembles the one beneath the Hyblean Plateau is justified by the large geochemical affinities of the Etnean hawaiites/K-trachybasalts and the Hyblean hawaiites/alkali basalts for what concerns both trace elements and isotope systematics. We have modeled partial melting of a composite source constituted by two rock types, inferred by lithological and geochemical features of the Hyblean xenoliths: 1) a spinel lherzolite bearing metasomatic, hydrous phases and 2) a garnet pyroxenite in form of veins intruded into the spinel lherzolite. The partial melting modeling has been applied to each rock type and the resulting primary liquids have been then mixed in various proportions. These compositions have been compared with some Etnean alkaline magmas of the post ∼60 ka activity, which were firstly re-equilibrated to mantle conditions through mass balance calculations. Our results put into evidence that concentrations of major and trace elements along with the water obtained from the modeling are remarkably comparable with those of Etnean melts re-equilibrated at primary conditions. Different proportions of the spinel lherzolite with variable modal contents of metasomatic phases and of the garnet pyroxenite can therefore account for the signature of a large spectrum of Etnean alkaline magmas and for their geochemical variability through time, emphasizing the crucial role played by compositional small-scale heterogeneity of the source. These heterogeneities are

  6. Partial melting of fertile peridotite fluxed by hydrous rhyolitic melt at 2-3 GPa: implications for mantle wedge hybridization by sediment melt and generation of ultrapotassic magmas in convergent margins

    NASA Astrophysics Data System (ADS)

    Mallik, Ananya; Nelson, Jared; Dasgupta, Rajdeep

    2015-05-01

    We investigated the melting behavior of peridotite fluxed with 25 wt% of H2O-bearing rhyolitic sediment melt (1.8 wt% bulk H2O), by performing experiments from 1100 to 1300 °C at 2 GPa and 1050-1350 °C at 3 GPa. The apparent solidus of our bulk composition lies between 1100 and 1150 °C at both pressures, which is at a higher temperature than the vapor-saturated solidus and close to the pargasite dehydration solidus of peridotite. With increasing temperature, reacted melt fraction increases from 20 to 36 wt% from 1200 to 1300 °C at 2 GPa and 7 to 24 wt% from 1225 to 1350 °C at 3 GPa. Orthopyroxene is present as a residual phase in all the experiments, while olivine is present as a residual phase in all the experiments at 2 GPa only. Amphibole is absent above 1100 °C at both pressures, clinopyroxene disappears above 1200 and 1300 °C at 2 and 3 GPa, respectively, and garnet (only present at 3 GPa) melts out above 1300 °C. Upon reaction with the mantle wedge and subsequent melting of the hybrid rock, subducted sediment-derived rhyolites evolve in composition to a nepheline-normative ultrapotassic leucitite, similar in major element composition to ultrapotassic lavas from active arcs such as Sunda and inactive arcs such as in the Roman Magmatic Province. Fluxing peridotite with H2O versus H2O-bearing sediment melt at similar pressures does not appear to have an effect on isobaric melt productivity, but does have significant effect on melting reactions and resultant melt composition, with influx of sediment melt adding K2O to the system, thereby stabilizing phlogopite, which in turn buffers the reacted melt to ultrapotassic compositions. Previous experimental studies, along with this study, find that phlogopite can be stable near the hotter core of the mantle wedge and, hence, is likely to be subducted to deeper mantle, thereby influencing deeper cycling of volatiles and large ion lithophile elements. Also, because D {Rb/phl/melt} ≫ D {Sr/phl/melt} and D {Nd/phl/melt

  7. Partial melting of granitoids under eclogite-facies conditions: nanogranites from felsic granulites from Orlica-Śnieżnik Dome (Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Ferrero, Silvio; O'Brien, Patrick; Walczak, Katarzyna; Wunder, Bernd; Hecht, Lutz

    2014-05-01

    Melt inclusions (MI) study in migmatites is a powerful tool to retrieve the original composition of the anatectic melt, both as major elements (Ferrero et al., 2012) and fluid contents (Bartoli et al., 2013). Crystallized MI, or "nanogranites" (Cesare et al., 2009), were identified within HP felsic granulites from Orlica-Śnieżnik Dome, NE Bohemian Massif (Walczak, 2011). The investigated samples are Grt+Ky leucogranulites originated from a granitic protolith, with assemblage Qtz+Pl+Kfs+Grt+Ky+Ttn+Rt+Ilm. Nanogranites occur in garnet as primary inclusions, and consist of Qtz+Ab+Bt+Kfs±Ep±Ap. Such assemblage results from the crystallization of a melt generated during a partial melting reaction; the same reaction is also responsible for the production of the host garnet, interpreted therefore as a peritectic phase. Besides nanogranites, former presence of melt is supported by the occurrence of tiny pseudomorphs of melt-filled pores (Holness & Sawyer, 2008) and euhedral faces in garnet. Garnet composition, with Grs =0.28-0.31, phase assemblage (kyanite, ternary feldspar) and classic thermobarometry suggest that partial melting took place at T≥875°C and P~2.2-2.6 GPa, under eclogite-facies conditions. Although other authors reported palisade quartz after coesite in this area (see e.g. Bakun-Czubarow, 1992), no clear evidence of UHP conditions have been identified during this study. Piston cylinder re-homogenization experiments were performed on MI-bearing garnet chips to obtain the composition of the pristine anatectic melt. The first data from experiments in the range 850-950°C and 2-2.2 GPa show that nanogranites can be re-melted at T≥875°. However, homogenization has not been reached yet since new Grt, with lower CaO and higher MgO, crystallizes on the walls of the inclusion. As P increases, the modal amount of new phase decreases, while its composition evolves closer to those of the host garnet. Further experiments at higher pressure are in underway, with

  8. The effect of the melt thermal gradient on the size of the constitutionally supercooled zone

    NASA Astrophysics Data System (ADS)

    Prasad, A.; Yuan, L.; Lee, P. D.; Easton, M.; StJohn, D.

    2016-03-01

    Recent verification of the analytical Interdependence model by a numerical solidification model (µMatIC) confirmed the critical role of constitutional supercooling (CS) in achieving sufficient undercooling to trigger successful nucleation events. The location of the maximum amount of CS (ΔTCSmax) is some distance from the interface of the previously growing grain and this distance contributes to the final as-cast grain size. The effect of the thermal gradient, G, on the size of the CS zone (CSZ) was neglected in that work. However, G is expected to affect the size of the CSZ (i.e. the length of the CSZ, x’ CSZ , and the location of ΔTCSmax, x’ CSmax ). This investigation assesses the effect of G on x’csz and x' CSmax . A range of G values is introduced into both the analytical and the numerical models to obtain a correlation between the value of G and the dimensions of the CSZ. The result of a test case from the analytical model shows that x’ CSmax initially decreases rapidly and then decreases gradually approaching zero at very high values of G. Independent of the analytical model, the results from the numerical model replicate the trend obtained from the analytical model.

  9. Radiologically hyperdense zones of the patella seem to be partial osteonecroses subsequent to fracture treatment.

    PubMed

    Schüttrumpf, Jan Philipp; Behzadi, Cyrus; Balcarek, Peter; Walde, Tim Alexander; Frosch, Stephan; Wachowski, Martin Michael; Stürmer, Klaus Michael; Frosch, Karl-Heinz

    2013-10-01

    assessment, respectively. The clinical outcome of these patients with a hyperdense area on the patella, in this small series, was not shown to be worse than those who demonstrated normal healing. Radiologically hyperdense areas subsequent to patella fracture may represent partial osteonecrosis caused by localized vascular compromise. This was confirmed by MRI and histological examinations in two patients with persistent hyperdense lesions. The clinical outcome of patients with hyperdense zones seems to be poorer than that of patients without such findings, but no statistical difference was shown in this small series. It is possible that earlier surgical treatment and thus a shorter ischemic period as well as tissue-conserving operative techniques could prevent the occurrence of partial necroses. This hypothesis would require further study. Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.

  10. Influence of gravitational and vibrational convection on the heat- and mass transfer in the melt during crystal growing by Bridgman and floating zone methods

    NASA Astrophysics Data System (ADS)

    Fedorov, Oleg

    2016-07-01

    Space materials science is one of the priorities of different national and international space programs. The physical processes of heat and mass transfer in microgravity (including effect of g-jitter) is far from complete clarity, especially for important practical technology for producing crystals from the melt. The idea of the impact on crystallizing melt by low frequency vibration includes not only the possibility to suppress unwanted microaccelerations, but also to actively influence the structure of the crystallization front. This approach is one of the most effective ways to influence the quality of materials produced in flight conditions. The subject of this work is the effect of vibrations on the thermal and hydrodynamic processes during crystal growth using Bridgman and floating zone techniques, which have the greatest prospect of practical application in space. In the present approach we consider the gravitational convection, Marangoni convection, as well as the effect of vibration on the melt for some special cases. The results of simulation were compared with some experimental data obtained by the authors using a transparent model substance - succinonitrile (Bridgman method), and silicon (floating zone method). Substances used, process parameters and characteristics of the experimental units correspond the equipment developed for onboard research and serve as a basis for selecting optimum conditions vibration exposure as a factor affecting the solidification pattern. The direction of imposing vibrations coincides with the axis of the crystal, the frequency is presented by the harmonic law, and the force of gravity was varied by changing its absolute value. Mathematical model considered axisymmetric approximation of joint convective-conductive energy transfer in the system crystal - melt. Upon application of low-frequency oscillations of small amplitude along the axis of growing it was found the suppression of the secondary vortex flows near the

  11. Hydrous melting and partitioning in and above the mantle transition zone: Insights from water-rich MgO-SiO2-H2O experiments

    NASA Astrophysics Data System (ADS)

    Myhill, R.; Frost, D. J.; Novella, D.

    2017-03-01

    Hydrous melting at high pressures affects the physical properties, dynamics and chemical differentiation of the Earth. However, probing the compositions of hydrous melts at the conditions of the deeper mantle such as the transition zone has traditionally been challenging. In this study, we conducted high pressure multianvil experiments at 13 GPa between 1200 and 1900 °C to investigate the liquidus in the system MgO-SiO2-H2O. Water-rich starting compositions were created using platinic acid (H2Pt(OH)6) as a novel water source. As MgO:SiO2 ratios decrease, the T -XH2O liquidus curve develops an increasingly pronounced concave-up topology. The melting point reduction of enstatite and stishovite at low water contents exceeds that predicted by simple ideal models of hydrogen speciation. We discuss the implications of these results with respect to the behaviour of melts in the deep upper mantle and transition zone, and present new models describing the partitioning of water between the olivine polymorphs and associated hydrous melts.

  12. [Determination of N-nitrosodimethylamine in beer by frozen zone melting liquid-liquid extraction/gas chromatography].

    PubMed

    Peng, Qiaorong; Tang, Tao; Yu, Shuxin; Sun, Yuanshe; Lei, Wu; Wang, Fengyun; Zhang, Weibing; Li, Tong

    2014-04-01

    A simple and effective sample enrichment method of frozen zone melting liquid-liquid extraction was optimized and validated for the analysis of trace N-nitrosodimethylamine (NDMA) in beer samples. The method was based on high pressure liquid-liquid extraction with a low temperature frozen step. The 90 mL beer was placed in a container with 10 mL dichloromethane. After agitation, the sample was kept in a freezer for 16 h at -19 degrees C. The organic extract was analyzed by gas chromatography with a flame ionization detector (GC-FID). The accuracy, precision, detection and quantification limits and linearity of the method were evaluated. The results showed that the calibration curve of NDMA was linear in the range of 5-200 mg/L with a good correlation coefficient (r2) of 0.999 6. The recoveries at the spiked levels of 5, 10 and 20 mg/L were 84.94%, 83.24%, 85.14% with the relative standard deviations (n = 7) of 3.06%, 3.19%, 2.63%, respectively. The ordinary extraction method of N-nitrosodimethylamine in beer includes the four steps of low-temperature distillation, liquid-liquid extraction, rotary evaporation and nitrogen blowing concentration. With the extremely low volume of solvent used, the proposed extraction method proved to be easy and simple, and adequate for high-throughput analysis at low cost.

  13. Subpixel variability of MODIS albedo retrievals and its importance for ice sheet surface melting in southwestern Greenland's ablation zone

    NASA Astrophysics Data System (ADS)

    Moustafa, S.; Rennermalm, A. K.; Roman, M. O.; Koenig, L.; Smith, L. C.; Schaaf, C.; Wang, Z.; Mioduszewski, J.

    2013-12-01

    On the Greenland ice sheet, albedo declined across 70% of its surface since 2000, with the greatest reduction in the lower 600 m of the southwestern ablation zone. Because albedo plays a prominent role in the ice sheet surface energy balance, its decline has resulted in near doubling of meltwater production. To characterize ice sheet albedo, Moderate Imaging Spectrometer (MODIS) surface albedo products are typically used. However, it is unclear how the spatial variability of albedo within a MODIS pixel influences surface melting and whether it can be considered a linear function of albedo. In this study, high spatiotemporal resolution measurements of spectral albedo and ice sheet surface ablation were collected along a ~ 1.3 km transect during June 2013 within the Akuliarusiarsuup Kuua (AK) River watershed in southwest Greenland. Spectral measurements were made at 325-1075 nm using a Analytical Spectral Devices (ASD) spectroradiometer, fitted with a Remote Cosine Receptor (RCR). In situ albedo measurements are compared with the daily MODIS albedo product (MCD43A) to analyze how space, time, surface heterogeneity, atmospheric conditions, and solar zenith angle geometry govern albedo at different scales. Finally, analysis of sub-pixel albedo and ablation reveal its importance on meltwater production in the lower parts of the ice sheet margin.

  14. Partial Melt Systems in Plate-Driven Corner Flow: Evaluating the Formation of Porosity Bands as a Mechanism for Magma Focusing at Mid-Ocean Ridges

    NASA Astrophysics Data System (ADS)

    Gebhardt, D.; Butler, S. L.

    2015-12-01

    The imposition of an external shear on a system of partial melt will result in compaction of the solid matrix and concentration of the interstitial liquid melt leading to the formation of regions of contrasting high and low porosity. In experiments, direct and torsional shear geometries have demonstrated that these regions of varying porosity form in bands orientated at low angles relative to the shear plane. A variety of numerical models have been employed to recreate these experimental results. Simple shear, pure shear and torsional shear geometries have been used in both linear and nonlinear numerical settings to model the formation of the porosity bands. In this contribution the numerical models utilize a shear geometry derived from the velocity field of the plate-driven corner flow of a mid-ocean ridge. Motivation for using the velocity field of a mid-ocean ridge comes from evidence that suggests the existence of lateral melt channeling from either side of the ridge axis. Imposing the shear from a mid-ocean ridge corner flow allows for the evaluation of the resulting porosity bands in terms of suitability for channeling melt laterally toward the ridge axis. This is done using both slow and fast spreading ridge geometries. The degree of similarity between previous numerical and experimental results has been found to be greatly influenced by the imposed viscosity law of the solid matrix phase. In order to keep this in mind, the numerical models in this contribution use three different matrix viscosity laws: strain-rate independent, strain-rate dependent and anisotropic. Of these rheologies, strain-rate independence results in the poorest orientation for channeling melt directly to the ridge axis. The strain-rate dependent and anisotropic viscosities present more favorable direct-channeling orientations for the fastest growing porosity bands, but in both cases the background flow will rotate bands to less ideal orientations over time. However, these less

  15. Zr complexation in high pressure fluids and silicate melts and implications for the mobilization of HFSE in subduction zones

    NASA Astrophysics Data System (ADS)

    Louvel, Marion; Sanchez-Valle, Carmen; Malfait, Wim J.; Testemale, Denis; Hazemann, Jean-Louis

    2013-03-01

    Field observations and solubility experiments show evidence for the efficient mobilization of nominally insoluble HFSE (i.e., Ti, Zr, Nb and Hf) by high pressure fluids, probably via complexation with polymerized alkali-silica dissolved species and halogens (F and Cl). Here we investigate the complexation of Zr in subduction-related fluids (aqueous fluids and hydrous haplogranite melts) up to 800 °C and 2.4 GPa using X-ray absorption spectroscopy (XANES and EXAFS) in a hydrothermal diamond anvil cell and provide evidence for the formation of Zr-O-Si/Na polymeric species in alkali-(alumino)silicate fluids at high pressure. Zr4+ speciation in dilute fluids (2.5 wt% HCl) is dominated by 8-fold-coordinated [Zr(H2O)8]4+ hydrated complexes at room conditions and no evidence for extensive Zr-Cl complexation in the fluid was found up to 420 °C, as confirmed by ab initio XANES calculations of various ZrO8-xClx clusters. The addition of Na and Si dissolved species (from 35 to 60 wt% dissolved Na2Si2O5, NS2) into the fluid favors the formation of alkali-zirconosilicate clusters Zr-O-Si/Na similar to those found in vlasovite (Na2ZrSi4O11), with Zr4+ in octahedral coordination with oxygen (Zr-O distance = 2.09 ± 0.04 Å) and ˜6 Si (Na) second neighbors (Zr-Si/Na distance = 3.66 ± 0.06 Å). This coordination environment also dominates Zr speciation in F-free and F-bearing NS2 and haplogranite glasses and high pressure hydrous haplogranite melts (15.5-33 wt% dissolved H2O) in the investigated pressure-temperature range. The XAS analyses, assisted by ab initio XANES calculations, are not conclusive concerning the extent of Zr-F complexation in hydrous granitic melts. Alkali-zirconosilicate Zr-O-Si/Na clusters such as those identified in this study may explain the enhanced solubility of zircon ZrSiO4 (and other HFSE-bearing minerals) in alkali-aluminosilicate-bearing aqueous fluids produced by dehydration and melting of the slab and provide a favorable mechanism for the

  16. Maine Pseudotachylyte Localities and the Role of Host Rock Anisotropy in Fault Zone Development and Frictional Melting

    NASA Astrophysics Data System (ADS)

    Swanson, M. T.

    2004-12-01

    Three brittle strike-slip fault localities in coastal Maine have developed pseudotachylyte fault veins, injection veins and other reservoir structures in a variety of host rocks where the pre-existing layering can serve as a controlling fabric for brittle strike-slip reactivation. Host rocks with a poorly-oriented planar anisotropy at high angles to the shear direction will favor the development of R-shears in initial en echelon arrays as seen in the Two Lights and Richmond Island Fault Zones of Cape Elizabeth that cut gently-dipping phyllitic quartzites. These en echelon R-shears grow to through-going faults with the development of P-shear linkages across the dominantly contractional stepovers in the initial arrays. Pseudotachylyte on these faults is very localized, typically up to 1-2 mm in thickness and is restricted to through-going fault segments, P-shear linkages and some sidewall ripouts. Overall melt production is limited by the complex geometry of the multi-fault array. Host rocks with a favorably-oriented planar anisotropy for reactivation in brittle shear, however, preferentially develop a multitude of longer, non-coplanar layer-parallel fault segments. Pseudotachylyte in the newly-discovered Harbor Island Fault Zone in Muscongus Bay is developed within vertical bedding on regional upright folds with over 50 individual layer-parallel single-slip fault veins, some of which can be traced for over 40 meters along strike. Many faults show clear crosscuts of pre-existing quartz veins that indicate a range of coseismic displacements of 0.23-0.53 meters yielding fault vein widths of a few mm and dilatant reservoirs up to 2 cm thick. Both vertical and rare horizontal lateral injection veins can be found in the adjoining wall rock up to 0.7 cm thick and 80 cm in length. The structure of these faults is simple with minor development of splay faults, sidewall ripouts and strike-slip duplexes. The prominent vertical flow layering within the mylonite gneisses of

  17. Decrease in water activity due to fluid absent partial melting monitored with water content in biotite in the Western Adamello contact aureole (Italy)

    NASA Astrophysics Data System (ADS)

    Siron, Guillaume; Baumgartner, Lukas; Bouvier, Anne-Sophie; Vennemann, Torsten

    2016-04-01

    The fluorine and chlorine exchange on the hydroxyl site in micas is used to monitor changes in fluid composition (Munoz 1984). Most studies assume that the OH-site does not contain vaccancies, since the vast majority of studies use analytical techniques that does not allow to directly measure the OH- content of the mica. Nevertheless, studies have shown that significant amounts of O2- are present, and its concentration increases with temperature and titanium content. This feature was intrepreted as the consequence of a Ti-oxygen exchange in amphibolite and granulite facies rocks (Dyar et al. 1993, Cesare et al. 2008). Here, we present OH, F, Cl data for biotite from contact aureoles from biotite-schist to partially molten sillimanite-cordierite schists. OH-F-Cl content of biotites were analyzed using Secondary Ion Mass Spectrometry (SIMS), and major elements were analyzed by EMP. Samples were collected in the mid-crustal Western Adamello contact aureole (Italian Alps, Floess and Baumgartner, 2013). For that purpose we used biotite standards with water content constrained by Thermal Conversion Elemental Analyzer (TC/EA) see Bauer and Vennemann 2014, at a level of precision of 0.1-0.2 wt% (2SD). SIMS measurements typically have a precision of 0.1wt% (2SD), corresponding to the homogeneity of the internal standard at the SwissSIMS laboratory. OH- content decreases in samples with increasing peak temperature and Ti content (Ti range for biotites of 0.15-0.42 p.f.u for all samples). Nevertheless, within each individual sample, OH- is not a function of Ti. Ti variations are about 0.4 p.f.u., which is ten times the analytical uncertainty of the EMP analysis (0.004 p.f.u., 1SD). Water content is constant within analytical precision for each sample. The mean of OH- measurements is 3.41 p.f.u. in biotite and garnet grade samples, whereas those of samples in the partially molten zone have values of 3.27 p.f.u. We do not see any correlation with XMg or F and Cl. Hence, we

  18. Melting in super-earths.

    PubMed

    Stixrude, Lars

    2014-04-28

    We examine the possible extent of melting in rock-iron super-earths, focusing on those in the habitable zone. We consider the energetics of accretion and core formation, the timescale of cooling and its dependence on viscosity and partial melting, thermal regulation via the temperature dependence of viscosity, and the melting curves of rock and iron components at the ultra-high pressures characteristic of super-earths. We find that the efficiency of kinetic energy deposition during accretion increases with planetary mass; considering the likely role of giant impacts and core formation, we find that super-earths probably complete their accretionary phase in an entirely molten state. Considerations of thermal regulation lead us to propose model temperature profiles of super-earths that are controlled by silicate melting. We estimate melting curves of iron and rock components up to the extreme pressures characteristic of super-earth interiors based on existing experimental and ab initio results and scaling laws. We construct super-earth thermal models by solving the equations of mass conservation and hydrostatic equilibrium, together with equations of state of rock and iron components. We set the potential temperature at the core-mantle boundary and at the surface to the local silicate melting temperature. We find that ancient (∼4 Gyr) super-earths may be partially molten at the top and bottom of their mantles, and that mantle convection is sufficiently vigorous to sustain dynamo action over the whole range of super-earth masses.

  19. Melting relations of hydrous pyrolite in CaO-MgO-Al2O3-SiO2-H2O System at the transition zone pressures

    NASA Astrophysics Data System (ADS)

    Litasov, Konstantin; Ohtani, Eiji; Taniguchi, Hiromitsu

    Phase relations and melt compositions in CaO-MgO-Al2O3-SiO2-pyrolite under hydrous (+2% of H2O) and anhydrous conditions have been determined at 13-20 GPa and 1600-2220°C. Liquidus and solidus temperatures for the hydrous system are about 50-100°C and 180-240°C lower than those for the dry system, respectively. Majorite is a liquidus phase of the hydrous pyrolite from 13 to 20 GPa. Olivine is a liquidus phase at 13 GPa and both periclase and majorite are the liquidus phases at 20 GPa in the dry pyrolite. We observed expansion of the stability field of anhydrous phase B in hydrous experiments. Compositions of partial melts at 13-20 GPa are generally similar in dry and hydrous systems, but hydrous melts contain more SiO2 at 13-17 GPa. The melts formed by low degree of melting have Al2O3-depleted and CaO-rich compositions. Trends of hydrous melt compositions are generally consistent with those of aluminum-depleted komatiite magmas.

  20. Melt densities in the CaO-FeO-Fe 2O 3-SiO 2 system and the compositional dependence of the partial molar volume of ferric iron in silicate melts

    NASA Astrophysics Data System (ADS)

    Dingwell, Donald B.; Brearley, Mark

    1988-12-01

    The densities of 10 melts in the CaO-FeO-Fe 2O 3-SiO 2 system were determined in equilibrium with air, in the temperature range of 1200 to 1550°C, using the double-bob Archimedean technique. Melt compositions range from 6 to 58 wt% SiO 2, 14 to 76 wt% Fe 2O 3 and 10 to 46 wt% CaO. The ferric-ferrous ratios of glasses drop-quenched from loop fusion equilibration experiments were determined by 57Fe Mössbauer spectroscopy. Melt densities range from 2.689 to 3.618 gm/cm 3 with a mean standard deviation from replicate experiments of 0.15%. Least-squares regressions of molar volume versus molar composition have been performed and the root mean squared deviation shows that a linear combination of partial molar volumes for the oxide components (CaO, FeO, Fe 2O 3 and SiO 2) cannot describe the data set within experimental error. Instead, the inclusion of excess terms in CaFe 3+ and CaSi (product terms using the oxides) is required to yield a fit that describes the experimental data within error. The nonlinear compositional-dependence of the molar volumes of melts in this system can be explained by structural considerations of the roles of Ca and Fe 3+. The volume behavior of melts in this system is significantly different from that in the Na 2O-FeO-Fe 2O 3-SiO 2 system, consistent with the proposal that a proportion of Fe 3+ in melts in the CaO-FeO-Fe 2O 3-SiO 2 system is not tetrahedrally-coordinated by oxygen, which is supported by differences in 57Fe Mössbauer spectra of glasses. Specifically, this study confirms that the 57Fe Mössbauer spectra exhibit an area asymmetry and higher values of isomer shift of the ferric doublet that vary systematically with composition and temperature (this study; Dingwell and Virgo, 1987, 1988). These observations are consistent with a number of other lines of evidence ( e.g., homogeneous redox equilibria, Dickenson and Hess, 1986; viscosity, Dingwell and Virgo, 1987,1988). Two species of ferric iron, varying in proportions with

  1. Tularosa Basin Play Fairway Analysis: Partial Basin and Range Heat and Zones of Critical Stress Maps

    DOE Data Explorer

    Adam Brandt

    2015-11-15

    Interpolated maps of heat flow, temperature gradient, and quartz geothermometers are included as TIF files. Zones of critical stress map is also included as a TIF file. The zones are given a 5km diameter buffer. The study area is only a part of the Basin and Range, but it does includes the Tularosa Basin.

  2. Effect of partial melting on Vp and Vs in crustal enclaves from Mazarrón (SE Spain)

    NASA Astrophysics Data System (ADS)

    Ferri, Fabio; Burlini, Luigi; Cesare, Bernardo

    2016-03-01

    The combination of compressional and shear wave velocity is an important tool in discriminating rock types and identifying residing melts within the continental crust. Here we report the laboratory measurements for Vp and Vs obtained in varying conditions up to those exceeding the beginning of melting (950 °C at 500 MPa confining pressure) on two residual garnet-biotite-sillimanite-cordierite-spinel metapelitic enclaves recovered from the Neogene dacites of Mazarrón (SE Spain). The enclaves preserve widespread interstitial rhyolitic glass as evidence of primary melt extraction. At 500 MPa, the experimental Vp ranges from 7.21 ÷ 7.46 km s- 1 at room temperature to 5.44 km/s at 950 °C. The mean Vs is 4.5 km/s at room temperature with shear-wave splitting of 0.25 ÷ 0.3 km/s, measured along three mutually orthogonal directions. When temperature increases, the Vs evidences a reversible slope change at about 650 °C, and the shear-wave splitting reduces to zero (isotropic material) at 850-950 °C, where the sample Vs is ~ 3.0 km/s. The Vp anisotropy is 7-10% up to 700 °C increasing to ~ 20% at 950 °C, while the Vs anisotropy continuously decreases with temperature from 5% to 7% at room temperature to zero at 950 °C. No mineral reactions are observed up to 650-700 °C; however, microstructure equilibrates due to the relaxation of the primary glass at the glass transition temperature. Between 850 °C and 950 °C, a new melting reaction is observed producing biotite + spinel + ilmenite + plagioclase + melt. At melting, the rock becomes isotropic for Vs, and Poisson's ratio increases to 0.30. Our seismic data show that the seismic signature of high grade metapelitic rocks is similar to that of mafic materials. The evolution of Vp and Vs at melting conditions is compatible with the geophysical data of the area, supporting the hypothesis of the current existence of anatectic melts at intermediate depths of the Alborán domain.

  3. Magnetocaloric effect in a dual-phase coupled LaFe11Si2 crystal prepared by a modified high-pressure zone-melting technique

    NASA Astrophysics Data System (ADS)

    Feng, Shutong; Fang, Yue; Zhai, Qijie; Luo, Zhiping; Zheng, Hongxing

    2016-10-01

    A modified high-pressure optical zone-melting technique was adopted to grow a rare-earth-based LaFe11Si2 crystal in the present work. Dual-phase coupled microstructure was obtained where aligned α(Fe) phase distributed in the La(Fe,Si)13 matrix. Magnetic measurements showed that the produced crystal underwent a second-order magnetic transition in the vicinity of 250 K. Under a magnetic field change of 30 kOe, the refrigeration capacity (RC) of the produced crystal reached up to 162 J/kg. It was confirmed that zone-melting crystal growth technique is an effective approach to strikingly enhance the magnetocaloric effect of La-Fe-Si refrigeration materials.

  4. Origin of felsic achondrites Graves Nunataks 06128 and 06129, and ultramafic brachinites and brachinite-like achondrites by partial melting of volatile-rich primitive parent bodies

    NASA Astrophysics Data System (ADS)

    Day, James M. D.; Walker, Richard J.; Ash, Richard D.; Liu, Yang; Rumble, Douglas; Irving, Anthony J.; Goodrich, Cyrena A.; Tait, Kimberly; McDonough, William F.; Taylor, Lawrence A.

    2012-03-01

    New major- and trace-element abundances, highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundances, and oxygen and rhenium-osmium isotope data are reported for oligoclase-rich meteorites Graves Nunataks 06128 and 06129 (GRA 06128/9), six brachinites (Brachina; Elephant Morraine 99402/7; Northwest Africa (NWA) 1500; NWA 3151; NWA 4872; NWA 4882) and three olivine-rich achondrites, which are referred to here as brachinite-like achondrites (NWA 5400; NWA 6077; Zag (b)). GRA 06128/9 represent examples of felsic and highly-sodic melt products from an asteroid that may provide a differentiation complement to brachinites and/or brachinite-like achondrites. The new data, together with our petrological observations, are consistent with derivation of GRA 06128/9, brachinites and the three brachinite-like achondrites from nominally volatile-rich and oxidised 'chondritic' precursor sources within their respective parent bodies. Furthermore, the range of Δ17O values (˜0‰ to -0.3‰) among the meteorites indicates generation from isotopically heterogeneous sources that never completely melted, or isotopically homogenised. It is possible to generate major- and trace-element compositions similar to brachinites and the three studied brachinite-like achondrites as residues of moderate degrees (13-30%) of partial melting of primitive chondritic sources. This process was coupled with inefficient removal of silica-saturated, high Fe/Mg felsic melts with compositions similar to GRA 06128/9. Melting of the parent bodies of GRA 06128/9, brachinites and brachinite-like achondrites halted well before extensive differentiation, possibly due to the exhaustion of the short-lived radionuclide 26Al by felsic melt segregation. This mechanism provides a potential explanation for the cessation of run-away melting in asteroids to preserve achondrites such as GRA 06128/9, brachinites, brachinite-like achondrites, acapulcoite-lodranites, ureilites and aubrites. Moderate degrees of

  5. Seismological detection of low-velocity anomalies surrounding the mantle transition zone in Japan subduction zone

    NASA Astrophysics Data System (ADS)

    Liu, Zhen; Park, Jeffrey; Karato, Shun-ichiro

    2016-03-01

    In the Japan subduction zone, a locally depressed 660 discontinuity has been observed beneath northeast Asia, suggesting downwelling of materials from the mantle transition zone (MTZ). Vertical transport of water-rich MTZ materials across the major mineral phase changes could lead to water release and to partial melting in surrounding mantle regions, causing seismic low-velocity anomalies. Melt layers implied by low-velocity zones (LVZs) above the 410 discontinuity have been detected in many regions, but seismic evidence for partial melting below the 660 discontinuity has been limited. High-frequency migrated Ps receiver functions indicate LVZs below the depressed 660 discontinuity and above the 410 discontinuity in the deep Japan subduction zone, suggesting dehydration melting induced by water transport out of the MTZ. Our results provide insights into water circulation associated with dynamic interactions between the subducted slab and surrounding mantle.

  6. Atmospheric constraints for the CO2 partial pressure on terrestrial planets near the outer edge of the habitable zone

    NASA Astrophysics Data System (ADS)

    von Paris, P.; Grenfell, J. L.; Hedelt, P.; Rauer, H.; Selsis, F.; Stracke, B.

    2013-01-01

    Context. In recent years, several potentially habitable, probably terrestrial exoplanets and exoplanet candidates have been discovered. The amount of CO2 in their atmosphere is of great importance for surface conditions and habitability. In the absence of detailed information on the geochemistry of the planet, this amount could be considered as a free parameter. Aims: Up to now, CO2 partial pressures for terrestrial planets have been obtained assuming an available volatile reservoir and outgassing scenarios. This study aims at calculating the allowed maximum CO2 pressure at the surface of terrestrial exoplanets orbiting near the outer boundary of the habitable zone by coupling the radiative effects of the CO2 and its condensation at the surface. These constraints might limit the permitted amount of atmospheric CO2, independent of the planetary reservoir. Methods: A 1D radiative-convective cloud-free atmospheric model was used to calculate surface conditions for hypothetical terrestrial exoplanets. CO2 partial pressures are fixed according to surface temperature and vapor pressure curve. Considered scenarios cover a wide range of parameters, such as gravity, central star type and orbital distance, atmospheric N2 content and surface albedo. Results: Results show that for planets in the habitable zone around K-, G-, and F-type stars the allowed CO2 pressure is limited by the vapor pressure curve and not by the planetary reservoir. The maximum CO2 pressure lies below the CO2 vapor pressure at the critical point of pcrit = 73.8 bar. For M-type stars, due to the stellar spectrum being shifted to the near-IR, CO2 pressures above pcrit are possible for almost all scenarios considered across the habitable zone. This implies that determining CO2 partial pressures for terrestrial planets by using only geological models is probably too simplified and might over-estimate atmospheric CO2 towards the outer edge of the habitable zone.

  7. Thermal characteristics of the Main Himalaya Thrust and the Indian lower crust with implications for crustal rheology and partial melting in the Himalaya orogen

    NASA Astrophysics Data System (ADS)

    Nábělek, Peter I.; Nábělek, John L.

    2014-06-01

    The Main Himalaya Thrust (MHT) is the current tectonic boundary between the subducting Indian lithosphere and the overlying Himalayan orogenic prism and the Tibetan crust. We present thermo-kinematic calculations and metamorphic P-T-t paths of the Indian lower crust (ILC) that constrain the thermal structure of the MHT and the southern Tibetan crust (Lhasa Block) and explain the origin of a thin, seismic low velocity zone that was revealed by the recent Hi-CLIMB experiment from receiver functions of teleseismic waves. Northward of the Himalayas, the low velocity zone occurs within the ductile regime of the crust and is thought to extend along the MHT into the Lhasa Block. In the Lhasa Block, the low velocity zone occurs directly above the ILC. Predicted evolution of mineralogy of the ILC along its subduction P-T-t path shows that its dehydration can potentially induce wet melting within the orogenic prism above the inclined portion of the MHT. However, north of the Yarlung Tsangpo Suture (YTS) below the southern Lhasa Block, where subduction of the ILC is flat, the ILC is predicted to be anhydrous eclogite and therefore, it cannot supply H2O to the overlying crust. The seismic low velocity zone above this portion of the ILC is best explained by dehydration melting due to strain heating. The MHT there appears to be localized by the rheological contrast between the ductile lower Lhasa Block and the strong eclogitic ILC. Southward thrusting of the Himalaya orogenic prism, which contains accreted Indian upper crust, causes advection of hot middle-crustal rocks to shallower levels, thereby producing a shallow ductile regime between the Himalayas and the YTS. The shallow ductile regime is evident in the limit of upper crustal earthquake foci to shallow depths in this region.

  8. Silicate diffusion in alkali-carbonatite and hydrous melts at 16.5 and 24 GPa: Implication for the melt transport by dissolution-precipitation in the transition zone and uppermost lower mantle

    NASA Astrophysics Data System (ADS)

    Shatskiy, Anton; Litasov, Konstantin D.; Borzdov, Yuriy M.; Katsura, Tomoo; Yamazaki, Daisuke; Ohtani, Eiji

    2013-12-01

    The diffusivity of dissolved Mg2SiO4 in wadsleyite saturated KMC melt (K2Mg(CO3)2 + 25.7 wt.% MgSiO3) at 16.5 GPa and 1700 °C, MgSiO3 diffusivity in perovskite saturated KMCH (K2Mg(CO3)2 × 2H2O + 31.7 wt.% MgSiO3) and HM (H2O + 75.7 wt.% MgSiO3) melts at 24 GPa and 1500 °C were determined experimentally using a scaled-up version of a Kawai-type multi-anvil apparatus. During a diffusion experiment, silicate saturation was maintained at different levels in the two temperature regions by placing the diffusion cell in the thermal gradient of 20 °C/mm. The diffusivity was computed from the total mass of silicate transported from “hot” to the “cold” region during the course of an experiment. At given conditions silicate diffusivities were estimated to be DKMCMg2SiO4=2×10-9 m/s, DKMCHMgSiO3=4×10-9 m/s, and DHMMgSiO3=5×10-8 m/s. Using obtained diffusivities we estimated possible migration rates of dispersed melt inclusion in the deep mantle by means of dissolution-precipitation considering different driving forces. The rates of melt migration driven by the lateral thermal gradient of 1 °C/km in the mantle plume range from 4 × 10-8 to 8 × 10-7 m/year. This means that during plume ascent time of about 50 Ma, the melt can be moved by 2-40 m. These values clearly demonstrate that the thermal gradient is very weak driving force in terms of melt segregation in the deep mantle. On the other hand, at typical mantle stress of 1 MPa and droplet size of 100 μm the migration rates of the HM, KMCH and KMC melts are estimated to be 22.5, 0.9 and 0.2 m/year, respectively, which are 2-3 orders of magnitude faster than ascent rate of the mantle plume. This implies that all melt droplets on the way of ascending plume would be entrapped by the stressed zone in front of plume and accumulated in the plume head. This mechanism may explain segregation of mantle magmas with the source regions deeper than 150-250 km, such as kimberlites.

  9. The limited depth range of a metallic-Fe-bearing layer in the lower mantle and its implications for partial melting

    NASA Astrophysics Data System (ADS)

    Girard, J.; Karato, S. I.

    2014-12-01

    Partial melting in (most of) the lower mantle occurs only by the presence of volatile elements such as hydrogen (and/or carbon). The experimental studies by [Kawamoto, 2004] showed that partial melting is possible even at temperature of 1673 K in the shallow lower mantle if there is sufficient water. However, if metallic Fe is present in the lower mantle as suggested by [Frost et al., 2004]). most of hydrogen will be dissolved in metallic Fe, and thus melting will be prevented, making it difficult to explain a seismic velocity drop in the shallow lower mantle [Schmandt et al., 2014]. In this study we conducted high pressure experiments using the Rotational Drickamer Apparatus (RDA), on bridgmanite (Mg,Fe)SiO3 + (Mg,Fe)O mixture at pressure up to 23-29 GPa and temperature of about 2000-2200K. Using the advantage of the new RDA cell design which provide a larger pressure gradient (~6 GPa across the sample), we report experimental observations showing that metallic Fe is formed only in the low pressure conditions, 24-26.5 GPa (corresponding to the depth range of 660-730 km), leaving the shallow lower mantle minerals "dry". Our results are also consistent with the published results by [Irifune et al., 2010; Sinmyo and Hirose, 2013] where they did not find any metallic Fe above 27 GPa. Therefore we conclude that metallic Fe is present only in the narrow depth range in the lower mantle. In such a case partial melt would be impossible and only occur at depth greater than 730 km. Our results explain why a velocity drop is observed at ~730 km not at 660 km [Schmandt et al., 2014]. The present results also have important implications for other geochemical issues including the behaviors of siderohpile elements during core formation. Frost, D. J., et al., (2004), Nature, 428, 409-412. Irifune, T., et al., (2010), Science, 327, 193-195. Kawamoto, T. (2004), Physics of Earth and Planetary Interiors, 143/144, 387-395. Schmandt, B., et al., (2014), Science, 344(6189), 1265

  10. Magma formation in hot-slab subduction zones: Insights from hydrogen isotopes in Cascade Arc melt inclusions

    NASA Astrophysics Data System (ADS)

    Walowski, K. J.; Wallace, P. J.; Hauri, E. H.; Clynne, M. A.; Rea, J.; Rasmussen, D. J.

    2013-12-01

    In a comparison of arcs globally, primitive basaltic magmas in the Cascades have slightly lower H2O concentrations, consistent with the hotter nature of the young subducted plate [Ruscitto et al., 2012]. In addition, geodynamic models [Syracuse et al., 2010] and geochemical studies [Cooper et al., 2012] agree that slab surface temperatures beneath the Cascade arc axis are hotter, on average, than in many other arcs. Data on volatiles and their relationships to fluid mobile trace elements are key to understanding volatile recycling and the formation of arc magmas. Here, we present the first data on hydrogen isotopes (D/H) in basaltic melt inclusions (MI) from the Cascades, as measured by NanoSIMS, in conjunction with a complete dataset on volatile, major, and trace elements in the MI. Recent work on MI from the Marianas [Shaw et al., 2012] has shown the potential for using δD to understand the cycling of hydrous fluids through subduction zones. Our samples were collected from cinder cones in the Lassen region of the southern Cascades (6 calc-alkaline basalts [CAB] and 2 transitional between CAB and low-K tholeiite [LKT]), and 2 basaltic tephra units from Mount St. Helens (MSH) that have OIB-like trace element characteristics, which is common in the central part of the arc. Using the maximum volatile contents at each cone to represent the undegassed magma, we find values of 2.1-3.4 wt% H2O and 500-1200 ppm CO2 for CABs and 1.15-1.30 wt% H2O and 750-850 ppm CO2 for transitional LKTs (all corrected to be in eq. with Fo90 olivine) in the Lassen Region. At MSH, we find 1.7 wt% H2O and <300 ppm CO2 for the OIB samples. For CABs from the Lassen Region, (Sr/P)N correlates with slab fluid tracers such as H2O/Ce and Cl/Nb, indicating a link between volatile and trace element enrichment of the mantle wedge, but transitional LKTs deviate slightly from the overall pattern. At MSH, values of (Sr/P)N, H2O/Ce, and Cl/Nb are lower than those in the Lassen Region, and are more

  11. The role of partial melting on superplasticity of Si{sub 3}N{sub 4}p/Al-Cu-Mg composite

    SciTech Connect

    Jeong, H.G.; Hiraga, K.; Mabuchi, M.; Higashi, K.

    2000-02-14

    For metal matrix composites containing ceramic reinforcements, stress concentration during tensile deformation occurs at interfaces between the matrix and ceramic, so that, cavitation is excessively developed at interfaces, resulting in premature fracture. In a previous paper, it was suggested that the dominant deformation process of high-strain-rate superplasticity for metal matrix composites if grain boundary sliding (GBS), and that liquid phases in high-strain-rate superplasticity serve both to relax the stress concentration and to limit the appearance of internal cavitation and subsequent failure. In their experimental observation, it has been observed that a large elongation is obtained at the temperature, that is close to the onset temperature for partial melting in the superplastic composites, but the elongation significantly decreases at slightly higher temperatures, which are close to the end temperature for partial melting. This indicates that there is an optimum amount of the liquid phase for obtaining high-strain-rate superplasticity in these materials. Thus, it is important to examine the nature of ceramic-matrix interfaces of superplastic composites in order to understand the origin of superplastic flow related to liquid grain boundaries during high-strain-rate superplastic deformation. The aim of this work is to study the nature of the interfaces and surfaces of the deformed specimens in Si{sub 3}N{sub 4}p/A;-Cu-Mg composites to understand GBS related with liquid phases at interfaces during superplastic flow.

  12. Negligible sulfur isotope fractionation during partial melting: Evidence from Garrett transform fault basalts, implications for the late-veneer and the hadean matte

    NASA Astrophysics Data System (ADS)

    Labidi, J.; Cartigny, P.

    2016-10-01

    We report the quadruple sulfur isotope compositions, sulfur contents and speciation major and trace elements (including copper and chlorine abundances) of eleven basalts collected in the Garrett transform fault. We combine these data to discuss the absence of S isotopic fractionation along both partial melting and low-pressure fractional crystallization. The variations of K2O/TiO2 and La/SmN-ratios (respectively between 0.017 and 0.067, and between 0.31 and 0.59) suggest a range of depletion in Garrett lavas that includes ultra depleted samples (K2O/TiO2 < 0.03). The remarkable level of incompatible element depletion is consistent with re-melting of a depleted source. Contrasting with incompatible element depletion, all samples display similar S and Cu abundance (at a given major-element composition) to mid-ocean ridge basalts (MORB). This indicates that Garrett Intra Transform Lavas (ITL) are sulfide saturated as MORB are. Copper content for Garrett parental melts (MgO >8%) are ∼80 ppm, indistinguishable from MORBs. This requires their mantle sources, variably depleted in incompatible element, to host residual sulfide buffering the Cu content of all erupted melts. We calculate a minimum S content for the source of ultra-depleted Garrett lavas of 100 ± 40ppmS, i.e. roughly a factor of 2 below the MORB mantle source. After exclusion of a single sample with Cl/K ratio >0.1 that likely experienced hydrothermal sulfide assimilation, Garrett ITLs display homogeneous δ34 S, Δ33 S and Δ36 S values with averages of - 0.68 ± 0.08 ‰, + 0.010 ± 0.005 ‰ and - 0.04 ± 0.04 ‰, respectively (all 1σ, n = 10). The δ34 S values display no relationship with either K2O/TiO2 variations or extent sulfide fractionation. From these observations, we derive a 34S/32S fractionation factor between exsolved sulfides and sulfide dissolved in silicate melts of 1.0000 ± 0.0003. The S isotopic fractionation during partial melting can thus be considered as negligible, and both

  13. Andesitic crustal growth via mélange partial melting: Evidence from Early Cretaceous arc dioritic/andesitic 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; Yang, Jin-Hui; Li, Jie; Long, Xiao-Ping

    2016-05-01

    Deciphering the petrogenesis of andesitic/dioritic rocks is fundamental to understanding the formation of the continental crust. Here we present detailed petrology, geochronology, major and trace element, Sr-Nd-Hf-O isotope data for the Early Cretaceous (˜122 Ma) dioritic rocks in the Bizha area in southern Qiangtang, Tibet. The dioritic rocks are characterized by large ion lithophile elements, Pb, and light rare earth elements but depletion of high field strength elements with slightly enriched and variable ɛNd(t) values of -0.01 to -3.31 and initial 87Sr/86Sr isotopic ratios of 0.7053-0.7062. They also have variable magmatic zircon Hf-O isotope compositions (ɛHf(t) = -5.3 to +3.6 and δ18O = +7.3 to +9.5 ‰). Combined with contemporary andesitic lavas in southern Qiangtang, we suggest that the intermediate magmatic rocks in this area were most probably derived by partial melting of a subduction mélange, which is a mixture of mid-oceanic ridge basalts (MORBs), sediments, and mantle wedge peridotites, formed along the interface between the subducted slab and the overlying mantle wedge in a subduction channel before ˜124 Ma. The mélange diapir melting was triggered by the asthenospheric upwelling and hot corner flow caused by roll-back of the northward subducted Bangong-Nujiang oceanic slab during the Early Cretaceous. The Early Cretaceous intermediate magmatic rocks in southern Qiangtang have an overall continental crust-like andesitic composition. Therefore, partial melting of mélange provides an important support for the generation of andesitic magmas in continental arcs and the "andesite model" for crustal growth.

  14. ANALYTICAL ASSESSMENT OF THE IMPACTS OF PARTIAL MASS DEPLETION IN DNAPL SOURCE ZONES (SAN FRANCISCO, CA)

    EPA Science Inventory

    Analytical solutions describing the time-dependent DNAPL source-zone mass and contaminant discharge rate are used as a flux-boundary condition in a semi-analytical contaminant transport model. These analytical solutions assume a power relationship between the flow-averaged sourc...

  15. ANALYTICAL ASSESSMENT OF THE IMPACTS OF PARTIAL MASS DEPLETION IN DNAPL SOURCE ZONES (SAN FRANCISCO, CA)

    EPA Science Inventory

    Analytical solutions describing the time-dependent DNAPL source-zone mass and contaminant discharge rate are used as a flux-boundary condition in a semi-analytical contaminant transport model. These analytical solutions assume a power relationship between the flow-averaged sourc...

  16. Partial Root-Zone Drying of Olive (Olea europaea var. 'Chetoui') Induces Reduced Yield under Field Conditions.

    PubMed

    Dbara, Soumaya; Haworth, Matthew; Emiliani, Giovani; Ben Mimoun, Mehdi; Gómez-Cadenas, Aurelio; Centritto, Mauro

    2016-01-01

    The productivity of olive trees in arid and semi-arid environments is closely linked to irrigation. It is necessary to improve the efficiency of irrigation techniques to optimise the amount of olive fruit produced in relation to the volume of water used. Partial root-zone drying (PRD) is a water saving irrigation technique that theoretically allows the production of a root-to-shoot signal that modifies the physiology of the above-ground parts of the plant; specifically reducing stomatal conductance (gs) and improving water use efficiency (WUE). Partial root-zone drying has been successfully applied under field conditions to woody and non-woody crops; yet the few previous trials with olive trees have produced contrasting results. Thirty year-old olive trees (Olea europaea 'var. Chetoui') in a Tunisian grove were exposed to four treatments from May to October for three-years: 'control' plants received 100% of the potential evapotranspirative demand (ETc) applied to the whole root-zone; 'PRD100' were supplied with an identical volume of water to the control plants alternated between halves of the root-zone every ten-days; 'PRD50' were given 50% of ETc to half of the root-system, and; 'rain-fed' plants received no supplementary irrigation. Allowing part of the root-zone to dry resulted in reduced vegetative growth and lower yield: PRD100 decreased yield by ~47% during productive years. During the less productive years of the alternate bearing cycle, irrigation had no effect on yield; this suggests that withholding of water during 'off-years' may enhance the effectiveness of irrigation over a two-year cycle. The amount and quality of oil within the olive fruit was unaffected by the irrigation treatment. Photosynthesis declined in the PRD50 and rain-fed trees due to greater diffusive limitations and reduced biochemical uptake of CO2. Stomatal conductance and the foliar concentration of abscisic acid (ABA) were not altered by PRD100 irrigation, which may indicate the

  17. The density, compressibility and seismic velocity of hydrous melts at crustal and upper mantle conditions

    NASA Astrophysics Data System (ADS)

    Ueki, K.; Iwamori, H.

    2015-12-01

    Various processes of subduction zone magmatism, such as upward migration of partial melts and fractional crystallization depend on the density of the hydrous silicate melt. The density and the compressibility of the hydrous melt are key factors for the thermodynamic calculation of phase relation of the hydrous melt, and the geophysical inversion to predict physicochemical conditions of the melting region based on the seismic velocity. This study presents a new model for the calculations of the density of the hydrous silicate melts as a function of T, P, H2O content and melt composition. The Birch-Murnaghan equation is used for the equation of state. We compile the experimentally determined densities of various hydrous melts, and optimize the partial molar volume, compressibility, thermal expansibility and its pressure derivative, and K' of the H2O component in the silicate melt. P-T ranges of the calibration database are 0.48-4.29 GPa and 1033-2073 K. As such, this model covers the P-T ranges of the entire melting region of the subduction zone. Parameter set provided by Lange and Carmichael [1990] is used for the partial molar volume and KT value of the anhydrous silicate melt. K' of anhydrous melt is newly parameterized as a function of SiO2 content. The new model accurately reproduces the experimentally determined density variations of various hydrous melts from basalt to rhyolite. Our result shows that the hydrous melt is more compressive and less dense than the anhydrous melt; with the 5 wt% of H2O in melt, density and KT decrease by ~10% and ~30% from those of the anhydrous melt, respectively. For the application of the model, we calculated the P-wave velocity of the hydrous melt. With the 5 wt% of H2O, P-wave velocity of the silicate melt decreases by >10%. Based on the melt P-wave velocity, we demonstrate the effect of the melt H2O content on the seismic velocity of the partially molten zone of the subduction zone.

  18. Partial melting and rapid exhumation of a Pliocene UHP terrane: CA-TIMS zircon results from Normanby Island, Papau New Guinea

    NASA Astrophysics Data System (ADS)

    DesOrmeau, J. W.; Gordon, S. M.; Little, T. A.; Bowring, S. A.

    2012-12-01

    Some ultra-high pressure (UHP) terranes contain eclogite embedded within migmatitic gneisses that preserve evidence for multiple episodes of partial melting. Understanding the mechanisms by which crustal rocks are subducted to mantle depths and subsequently exhumed requires understanding the timing of metamorphism and the timing and role of partial melting. The D'Entrecasteaux Islands of southeastern Papua New Guinea (PNG) expose Pliocene UHP eclogites contained within migmatitic host gneisses. Garnet-whole rock Lu-Hf geochronology suggests UHP metamorphism may have begun by ca. 7 Ma, and Ar-Ar thermochronology indicates that the rocks were exhumed to the surface by ca. 2 Ma; the history between 7 and 2 Ma is crucial for tectonic models of PNG. We have applied U-Pb chemical-abrasion thermal-ionization mass spectrometry (CA-TIMS) geochronology to zircons separated from granitoid intrusions within the host gneisses to better understand the timing and role of melting in the exhumation of the PNG UHP rocks. Three granodiorite intrusions were collected from Normanby Island as it has received far less study in previous investigations than the other D'Entrecasteaux Islands (Goodenough and Fergusson) and exposes the contact of the UHP-HP rocks against the structurally overlying, weakly metamorphosed rocks of the Papuan ultramafic belt (PUB). From the west side of Normanby dome in contact with the PUB, zircons from a foliated protomylonitic granodiorite sill yielded 206Pb/238U dates of ca. 4.1 Ma. In comparison, on the eastern side of Normanby dome, zircons from a weakly foliated, discordant pegmatitic dike yielded a complex array of zircon analyses and the youngest dates are ca. 4.1 Ma. The zircons extracted from these deformed intrusions are interpreted to date melt emplacement, crystallization, and zircon growth, which may be coeval with amphibolite facies (570-730 °C and ~7-12 Kbar) metamorphism recorded from Goodenough and Fergusson Islands. Zircons from a non

  19. Two-stage partial melting and contrasting cooling history within the Higher Himalayan Crystalline Sequence in the far-eastern Nepal Himalaya

    NASA Astrophysics Data System (ADS)

    Imayama, Takeshi; Takeshita, Toru; Yi, Keewook; Cho, Deung-Lyong; Kitajima, Kouki; Tsutsumi, Yukiyasu; Kayama, Masahiro; Nishido, Hirotsugu; Okumura, Tasuku; Yagi, Koshi; Itaya, Tetsumaru; Sano, Yuji

    2012-03-01

    The timing of partial melting and the pressure-temperature (P-T) paths in the High Himalayan Crystalline Sequence (HHCS) in far-eastern Nepal has been investigated using zircon chronology, rare earth element (REE) compositions, and P-T pseudosection analysis. Zircon from migmatites formed during Himalayan thermal events displays inherited magmatic core overgrown by two generations of metamorphic rims. The new rims are distinguished on the basis of their Tertiary ages, low MREE contents, and low Th/U ratios. The inner zircon rims from Sil + Grt + Bt + Kfs + Pl + Qtz and Ky + Sil + Grt + Bt + Ms + Pl + Qtz migmatites at different structural level of the HHCS display ages of c. 33-28 Ma (Early Oligocene) and c. 21-18 Ma (Early Miocene): these rims are characterized by flat MREE to HREE patterns and were overgrown by partial melt through muscovite dehydration melting under the stability of garnet, which occurred at P = c. 7-10 kbar and T = c. 730-780 °C, and at P = c. 8-14 kbar and T = c. 720-770 °C, respectively. The outer zircon rims are relatively enriched in HREE with respect to the inner rims and were overgrown at c. 27-23 Ma (Late Oligocene) and at c. 18-16 Ma (Early Miocene) during melt crystallization accompanying breakdown of garnet at P = c. 4-7 kbar and T = c. 650-725 °C. Early Miocene Ms-Bt leucogranites with two successively overgrown zircon rims at c. 18.3 ± 0.3 Ma and c. 16.3 ± 0.2 Ma were intruded into Early Oligocene migmatite hosts. Microstructural observations and the corresponding P-T conditions associated with the two generations of zircon rims indicate that the Early Oligocene and Early Miocene migmatites show relatively isobaric and nearly isothermal P-T paths during exhumation, respectively. The inferences are consistent with higher average cooling rates for the Early Miocene (c. 30-40 °C/My) than the Early Oligocene (c. 15-25 °C/My) migmatites, inferred from peak-T conditions and FT (c. 6 Ma for both migmatites) and U-Pb zircon ages. The

  20. Two-stage partial melting and contrasting cooing histories within the Higher Himalayan Crystalline Sequence in the far-eastern Nepal

    NASA Astrophysics Data System (ADS)

    Imayama, T.; Takeshita, T.; Keewook, Y.

    2011-12-01

    The timing of partial melting and the pressure-temperature paths in the High Himalayan Crystalline Sequence (HHCS) in far-eastern Nepal has been investigated using zircon chronology, trace element compositions, and P-T pseudosection analysis. Two metamorphic rims in zircon from the migmatites formed during Himalayan thermal events can be distinguished from the inherited magmatic cores, based on their Tertiary ages, low MREE content, and low Th/U ratio. The inner rim zircons with the ages of c. 30 Ma and c. 20 Ma obtained from two migmatites at different structural level of the HHCS were overgrown by muscovite dehydration melting under the stability field of garnet, which occurred during Early Oligocene at P = c. 7-10 kbar and T = c. 725-750 °C, and during Early Miocene at P = c. 8-14 kbar and T = c. 720-770 °C, respectively. A subsequent growth of the outer zircon rims occurred at c. 25 Ma (Late Oligocene) and at c. 17 Ma (Early Miocene) during melt crystallization accompanying breakdown of garnet at P = c. 4-7 kbar and T = c. 650-725 °C. The Early Oligocene migmatites were intruded by the Early Miocene leucogranite sill that has two zircon rims overgrown by anatectic melting at c. 18 Ma and by melt crystallization at c. 16 Ma, correlated with the growth of zircon rims in the Early Miocene migmatites. Microstructural observations combined with P-T pseudosections indicate that the P-T paths of Early Miocene and Early Oligocene migmatites are nearly isothermal paths and the relatively isobaric paths, respectively. Based on the U-Pb ages of the two zircon rims and the corresponding P-T conditions, it is likely that the Early Miocene migmatites had been buried, when the Early Oligocene had been exhumed. The different P-T-t paths for the two migmatites could have been caused by multiple channel flows within the HHCS, where the return flow of the previously buried rocks at the upper structural level caused tectonic loading on those at the lower structural level by

  1. Microtextural characterisation of the Lower Zone in the western limb of the Bushveld Complex, South Africa: evidence for extensive melt migration within a sill complex

    NASA Astrophysics Data System (ADS)

    Karykowski, Bartosz T.; Maier, Wolfgang D.

    2017-08-01

    The Lower Zone of the Bushveld Complex comprises an up to 2-km-thick package of different ultramafic rock types with an approx. 90-cm-thick, sulphide-bearing noritic interval that occurs in the western and eastern limbs. The distribution and geometry of the zone are highly variable across the Complex, showing pronounced, yet laterally discontinuous layering on different scales. Together with the ubiquitous lack of large-scale fractionation in the Mg# of orthopyroxene, variable Sr isotope compositions and erratic Pt/Pd ratios, these observations strongly suggest an emplacement of the Lower Zone as a sill complex, as these contrasting geochemical characteristics are difficult to account for in a large Bushveld magma chamber, as previously suggested. It is more likely that these sills were episodically fed from a sub-Bushveld staging chamber, and variably contaminated, while passing through the crust before their final emplacement in the Lower Zone. Detailed mineralogical and microtextural work based on high-resolution elemental mapping of a set of samples, covering the entire Lower Zone stratigraphy of the western Bushveld shows that the variations in the late crystallising interstitial mineral mode are different from what would be expect, if all phases crystallised from a fixed initial mass of interstitial liquid. The interstitial mineral mode, represented by plagioclase, clinopyroxene and other late stage phases, shows variable ratios of these minerals ranging from ca. 21:15:64 to 75:17:8. In comparison to modelled expected ratios, most of the analysed rocks have higher amounts of early crystallising interstitial phases (e.g. plagioclase, clinopyroxene), relative to late crystallising phases (e.g. quartz, alkali feldspar). Therefore, interstitial melt must have migrated at different stages of fractionation during cumulate solidification, as a consequence of either compaction or displacement by convecting interstitial liquids. Two samples, however, show the opposite

  2. Multi-zone modelling of partially premixed low-temperature combustion in pilot-ignited natural-gas engines

    SciTech Connect

    Krishnan, S. R.; inivasan, K. K.

    2010-09-14

    Detailed results from a multi-zone phenomenological simulation of partially premixed advanced-injection low-pilot-ignited natural-gas low-temperature combustion are presented with a focus on early injection timings (the beginning of (pilot) injection (BOI)) and very small diesel quantities (2-3 per cent of total fuel energy). Combining several aspects of diesel and spark ignition engine combustion models, the closed-cycle simulation accounted for diesel autoignition, diesel spray combustion, and natural-gas combustion by premixed turbulent flame propagation. The cylinder contents were divided into an unburned zone, several pilot fuel zones (or 'packets') that modelled diesel evaporation and ignition, a flame zone for natural-gas combustion, and a burned zone. The simulation predicted the onset of ignition, cylinder pressures, and heat release rate profiles satisfactorily over a wide range of BOIs (20-60° before top dead centre (before TDC)) but especially well at early BOIs. Strong coupling was observed between pilot spray combustion in the packets and premixed turbulent combustion in the flame zone and, therefore, the number of ignition centres (packets) profoundly affected flame combustion. The highest local peak temperatures (greater than 2000 K) were observed in the packets, while the flame zone was much cooler (about 1650 K), indicating that pilot diesel spray combustion is probably the dominant source of engine-out emissions of nitrogen oxide (NOx). Further, the 60° before TDC BOI yielded the lowest average peak packet temperatures (about 1720 K) compared with the 20° before TDC BOI (about 2480 K) and 40° before TDC BOI (about 2700 K). These trends support experimental NOx trends, which showed the lowest NOx emissions for the 60°, 20°, and 40° before TDC BOIs in that order. Parametric studies showed that increasing the intake charge temperature, pilot quantity, and natural-gas equivalence ratio all led to higher peak

  3. Evaporative cooling of air in an adiabatic channel with partially wetted zones

    NASA Astrophysics Data System (ADS)

    Terekhov, V. I.; Gorbachev, M. V.; Khafaji, H. Q.

    2016-03-01

    The paper deals with the numerical study of heat and mass transfer in the process of direct evaporation air cooling in the laminar flow of forced convection in a channel between two parallel insulated plates with alternating wet and dry zones along the length. The system of Navier-Stokes equations and equations of energy and steam diffusion are being solved in two-dimensional approximation. At the channel inlet, all thermal gas-dynamic parameters are constant over the cross section, and the channel walls are adiabatic. The studies were carried out with varying number of dry zones ( n = 0-16), their relative length ( s/l = 0-1) and Reynolds number Re = 50-1000 in the flow of dry air (φ0 = 0) with a constant temperature at the inlet (T 0 = 30 °C). The main attention is paid to optimization analysis of evaporation cell characteristics. It is shown that an increase in the number of alternating steps leads to an increase in the parameters of thermal and humid efficiency. With an increase in Re number and a decrease in the extent of wet areas, the efficiency parameter reduces.

  4. Probing depth dependencies of melt emplacement on time dependent quantities in a continental rift scenario with melting and melt extraction

    NASA Astrophysics Data System (ADS)

    Wallner, Herbert; Schmeling, Harro

    2014-05-01

    Since some years seismological observations provide increasing evidence of a discontinuity near the mid of older mantle lithosphere. Explanation may be a melt infiltration front (MIF) as upper margin of an evolving network of veins. These are formed by crystallized melt supplied by episodic melting events in the asthenosphere. To test this concept geodynamically we performed numerical modelling applying melting, extraction of melt and emplacement in a viscous matrix. Thereupon, we were faced to the problem defining an intrusion level for the melt. Findings of prior studies led to the need of movable, process dependent boundaries of the emplacement zone additionally making the process probably more self-consistent. Here we present a preliminary study exploring several empirical attempts to relate time dependent states to an upward moving boundary for intrusion. Modeled physics is based on thermo-mechanics of visco-plastic flow. The equations of conservation of mass, momentum and energy are solved for a multi component (crust-mantle) and two phase (melt-matrix) system. Rheology is temperature-, pressure-, and stress-dependent. In consideration of depletion and enrichment melting and solidification are controlled by a simplified linear binary solid solution model. The Compaction Boussinesq Approximation and the high Prandtl number approximation are used, elasticity is neglected and geometry is restricted to 2D. Approximation is done with the Finite Difference Method with markers in an Eulerian formulation (FDCON). Model guiding scenario is a extending thick lithosphere associated to by updoming asthenosphere probably additionally heated by a plume nearby. As the P-T conditions in the asthenosphere are near the solidus caused changes may increase melting and generate partial melt. Against conventional expectations on permeability at lithosphere-asthenosphere boundary (LAB) depth a fast melt transport into and sometimes through the lithosphere often is observed. The

  5. Effects of water-saturation on strength and ductility of three igneous rocks at effective pressures to 50 MPA and temperatures to partial melting

    SciTech Connect

    Bauer, S.J.; Friedman, M.; Handin, J.

    1981-01-01

    The short-term failure strengths and strains at failure of room-dry and water-saturated, cylindrical specimens (2 by 4 cm) of Charcoal Granodiorite (CG), Mt. Hood Andesite (MHA), and Cuerbio Basalt (CB) at a strain rate of 10/sup -4/s/sup -1/, at effective confining pressures of 0, 50, and 100 MPa and at temperatures to partial melting were investigated. Data from water-saturated specimens of the granodiorite and andesite, compared to room-dry counterparts, indicate (1) the pore pressures are essentially communicated throughout each test specimen so that they are fully effective; (2) at P/sub e/ = 0 and 50 MPa the granodiorite does not water-weaken; (3) at these same effective pressures the more porous and finer-grained andesite begins to exhibit water-weakening at about 600/sup 0/C; (4) at P/sub e/ = 0 and 870 to 900/sup 0/C the andesite's strength averages 20 MPa while the strength of dry specimens at the same P and T exhibit a strength of 100 MPa; (5) at P/sub e/ = 50 MPa compared to 160 MPa dry; (6) the basalt at P/sub e/ = 0, appears to be water-weakened at 800/sup 0/C; (7) water saturated specimens deformed at temperatures less than that of melting exhibit ultimate strengths at less than 2% shortening and then work-soften along faults; (8) again as do the dry counterparts, the wet specimens deform primarily by microscopic fracturing that coalesces into one or more macroscopic faults; and (9) the temperature for incipient melting of the andesite is decreased >150/sup 0/C in the water-saturated tests.

  6. A refined method for trace element modelling of nonmodal batch partial melting processes: The Cenozoic continental volcanism of Calatrava, central Spain

    NASA Astrophysics Data System (ADS)

    Cebriá, José-María; López-Ruiz, José

    1996-04-01

    A refined method for quantitative trace element modelling of partial melting processes is proposed here. This method is based on a two-part approach: (1) From binary diagrams and a minimal number of assumptions, a set of constrained values of the parameters ( F, D0i, PLi, C0i) are constrained for selected trace elements; (2) A simultaneous best-fit solution is obtained for those elements, which is then used to calculate the parameters for the remaining trace elements. This approach eliminates much of the mathematical complexity of other inversion techniques as well as the necessity of assuming values for poorly constrained parameters (e.g., mineral/liquid distribution coefficients). This method was succesfully applied to the primary melilitites, nephelinites, and olivine basalts from Calatrava, central Spain. The results of this calculation suggest that this basaltic suite was generated from a homogeneous garnet lherzolite with phlogopite that was enriched relative to chondrites up to 18 times for the highly incompatible elements and about 3 times for the moderately incompatible. This source underwent progressively higher melting degrees between 5% (melilitites) and 17% (olivine basalts).

  7. Direct Observations of Rapid Basal Melting and Bed Topography in the Grounding Zones of the Dotson and Crosson Ice Shelves, West Antarctica

    NASA Astrophysics Data System (ADS)

    Khazendar, A.; Rignot, E. J.; Schroeder, D. M.; Seroussi, H. L.; Schodlok, M.; Scheuchl, B.; Sutterley, T. C.; Velicogna, I.

    2015-12-01

    Glaciological changes of the Dotson and Crosson ice shelves and their tributary glaciers of Smith, Pope and Kohler are among the most noticeable in the Amundsen Sea Embayment region of West Antarctica. Here, we present sounding radar and laser altimetry observations of two aspects that are indispensable for understanding those changes: basal melting and bedrock topography in the grounding zones. We find that Smith Glacier in particular thinned by a remarkably fast 300-490 m between the years 2002 and 2009. Its grounding line has retreated far enough to be now at 2000 m below sea level in a previously identified trench. All three glacier grounding lines have already retreated down steeper parts of their bedrocks to flatter terrains, plausibly contributing to the reported slowing down in the acceleration of their ice volume discharges. The wider implications of the work emphasize the unprecedented perspectives that direct observation can offer of diverse grounding zone structures and evolution scenarios.

  8. Effects of water-saturation on strength and ductility of three igneous rocks at effective pressures to 50 MPa and temperatures to partial melting

    SciTech Connect

    Bauer, S.J.; Friedman, M.; Handin, J.

    1981-01-01

    Instantaneous-failure strengths and ductilities of water-saturated cylindrical specimens of Charcoal Granodiorite, Mount Hood Andesite, and Cuerbio Basalt are determined at a strain rate of 10{sup -4}s{sup -1} and at effective confining pressures (Pe) of 0 and 50 MPa and at temperatures to partial melting. The data indicate: (1) at Pe = 0 and 50 MPa (Pc and Pp of 50 MPa and of 100 and 50 MPa, respectively) the granodiorite does not water-weaken; (2) at these same Pe the more porous and finer-grained andesite begins to exhibit water-weakening at about 600/sup 0/C; (3) at Pe = 0 and 870-900{sup 0}C the andesite's wet strength averages 20 MPa compared to 100 MPa, dry; (4) at Pe = 50 MPa and 920{sup 0}C its wet strength is 45 MPa compared to 160 MPa dry; (5) at Pe = 0, the basalt appears to be water-weakened above 800{sup 0}C; (6) water-saturated specimens deformed at temperatures less than T{sub m} exhibit ultimate strengths at less than 2 percent shortening and then work-soften along faults; and (7) both dry and wet specimens deform primarily by brittle fracture. Extrapolations indicate: (1) crystalline rocks should be drillable because they remain brittle until partial melting occurs, and penetration rates should increase with temperature because there is a corresponding decrease in brittle fracture strength; (2) boreholes in ''water-filled'' holes will be stable to >10 km at temperatures 10 km; and (4) open boreholes in the andesite are apt to be much less stable, and at similar temperatures would fail at 2 to 5-km depth.

  9. Use of IR pyrometry to measure free-surface temperatures of partially melted tin as a function of shock pressure

    SciTech Connect

    Seifter, A.; Furlanetto, M. R.; Holtkamp, D. B.; Obst, A. W.; Payton, J. R.; Stone, J. B.; Tabaka, L. J.; Grover, M.; Macrum, G. S.; Stevens, G. D.; Turley, W. D.; Swift, D. C.; Veeser, L. R.

    2009-06-15

    Equilibrium equation of state theory predicts that the free-surface release temperature of shock-loaded tin will show a plateau at 505 K in the stress range from 19.5 to 33.0 GPa, corresponding to the solid-liquid, mixed-phase region of tin. In this paper we report free-surface temperature measurements on shock-loaded tin from 15 to 31 GPa using multiwavelength optical pyrometry. The shock waves were generated by direct contact of detonating high explosive with a tin sample, and the stress in the sample was determined by free-surface velocity measurements using photon Doppler velocimetry. We measured the emitted thermal radiance in the near IR region at four wavelengths from 1.5 to 5.0 mum. Above 25 GPa the measured free-surface temperatures were higher than the predicted 505 K, and they increased with increasing stress. This deviation may be explained by hot spots and/or variations in surface emissivity, and it may indicate a weakness in the use of a simple analysis of multiwavelength pyrometry data for conditions, such as above the melt threshold, where hot spots or emissivity variations may be significant. We are continuing to study the discrepancy to determine its cause.

  10. The low-temperature endotherm in poly(ethylene terephthalate): partial melting and rigid amorphous fraction mobilization.

    PubMed

    Righetti, Maria Cristina; Lorenzo, Maria Laura Di; Tombari, Elpidio; Angiuli, Marco

    2008-04-10

    A detailed investigation of the low-temperature endotherm of poly(ethylene terephthalate) (PET) performed by temperature-modulated differential scanning calorimetry is presented. The origin of the small endotherm, generally observed a few degrees above the crystallization temperature in PET and in many other polymers, is a widely discussed matter. The most frequent interpretation considers it the result of partial fusion with superposition of a recrystallization process even if it has also been proposed that it can originate from enthalpic recovery connected to mobilization of the rigid amorphous fraction. In an attempt to resolve the question, a new method for the interpretation of the modulated heat-flow-rate curve resulting from a temperature modulation program is proposed. The procedure consists of the analysis of the initial points of the steady-state heat-flow-rate signals in the heating and cooling semiperiods with the temperature modulation being performed with a sawtooth profile. The study conducted in parallel on the reversing specific heat capacity and the heat-flow-rate curves, observed on heating after isothermal crystallization at various temperatures, showed that multiple processes, involving both the crystalline and the rigid amorphous fraction, overlap in the temperature range in which the low-temperature endotherm is observed. The origin of the endotherm under investigation is therefore connected with both partial fusion of the crystalline portions and enthalpy recovery subsequent to structural relaxation of the rigid amorphous fraction. An estimation of the relative percentages of the two different processes is presented and discussed.

  11. Thermal Conductive Heat Transfer and Partial Melting of Volatiles in Icy Moons, Asteroids, and Kuiper Belt Objects (Invited)

    NASA Astrophysics Data System (ADS)

    Kargel, J. S.; Furfaro, R.

    2013-12-01

    Thermal gradients within conductive layers of icy satellite and asteroids depend partly on heat flow, which is related to the secular decay of radioactive isotopes, to heat released by chemical phase changes, by conversion of gravitational potential energy to heat during differentiation, tidal energy dissipation, and to release of heat stored from prior periods. Thermal gradients are also dependent on the thermal conductivity of materials, which in turn depends on their composition, crystallinity, porosity, crystal fabric anisotropy, and details of their mixture with other materials. Small impurities can produce lattice defects and changes in polymerization, and thereby have a huge influence on thermal conductivity, as can cage-inclusion (clathrate) compounds. Heat flow and thermal gradients can be affected by fluid phase advection of mass and heat (in oceans or sublimating upper crusts), by refraction related to heterogeneities of thermal conductivity due to lateral variations and composition or porosity. Thermal profiles depend also on the surface temperature controlled by albedo and climate, surface relief, and latitude, orbital obliquity and surface insolation, solid state greenhouses, and endogenic heating of the surface. The thermal state of icy moon interiors and thermal gradients can be limited at depth by fluid phase advection of heat (e.g., percolating meteoric methane or gas emission), by the latent heat of phase transitions (melting, solid-state transitions, and sublimation), by solid-state convective or diapiric heat transfer, and by foundering. Rapid burial of thick volatile deposits can also affect thermal gradients. For geologically inactive or simple icy objects, most of these controls on heat flow and thermal gradients are irrelevant, but for many other icy objects they can be important, in some cases causing large lateral and depth variations in thermal gradients, large variations in heat flow, and dynamically evolving thermal states. Many of

  12. Preparation of a non-woven poly(ε-caprolactone) fabric with partially embedded apatite surface for bone tissue engineering applications by partial surface melting of poly(ε-caprolactone) fibers.

    PubMed

    Kim, In Ae; Rhee, Sang-Hoon

    2017-03-21

    This article describes a novel method for the preparation of a biodegradable non-woven poly(ε-caprolactone) fabric with a partially embedded apatite surface designed for application as a scaffold material for bone tissue engineering. The non-woven poly(ε-caprolactone) fabric was generated by the electro-spinning technique and then apatite was coated in simulated body fluid after coating the PVA solution containing CaCl2 ·2H2 O. The apatite crystals were partially embedded or fully embedded into the thermoplastic poly(ε-caprolactone) fibers by controlling the degree of poly(ε-caprolactone) fiber surface melting in a convection oven. Identical apatite-coated poly(ε-caprolactone) fabric that did not undergo heat-treatment was used as a control. The features of the embedded apatite crystals were evaluated by FE-SEM, AFM, EDS, and XRD. The adhesion strengths of the coated apatite layers and the tensile strengths of the apatite coated fabrics with and without heat-treatment were assessed by the tape-test and a universal testing machine, respectively. The degree of water absorbance was assessed by adding a DMEM droplet onto the fabrics. Moreover, cell penetrability was assessed by seeding preosteoblastic MC3T3-E1 cells onto the fabrics and observing the degrees of cell penetration after 1 and 4 weeks by staining nuclei with DAPI. The non-woven poly(ε-caprolactone) fabric with a partially embedded apatite surface showed good water absorbance, cell penetrability, higher apatite adhesion strength, and higher tensile strength compared with the control fabric. These results show that the non-woven poly(ε-caprolactone) fabric with a partially embedded apatite surface is a potential candidate scaffold for bone tissue engineering due to its strong apatite adhesion strength and excellent cell penetrability. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2017.

  13. [Effects of alternate partial root-zone subsurface drip irrigation on potato yield and water use efficiency].

    PubMed

    Huang, Zhong-Dong; Qi, Xue-Bin; Fan, Xiang-Yang; Hu, Chao; Zhu, Dong-Hai; Li, Ping; Qiao, Dong-Mei

    2010-01-01

    Field experiment was conducted to investigate the effects of alternate partial root-zone subsurface drip irrigation (APRSDI) on the physiological responses, yield, and water use efficiency of potato. Compared with conventional drip irrigation (CDI), APRSDI had less negative effects on the potato leaf photosynthesis rate (P(n)), but decreased the transpiration rate and stomatal conductance significantly. The slightly higher P(n) under CDI was at the expense of consuming more water. No significant difference was observed in the potato yield under APRSDI and CDI, but APRSDI saved the irrigation amount by 25.8% and increased the irrigation water use efficiency and total water use efficiency by 27.5% and 15.3%, respectively, suggesting that APRSDI would be a feasible water-saving irrigation technique for the planting of potato.

  14. Alteration of chaotic advection in blood flow around partial blockage zone: Role of hematocrit concentration

    NASA Astrophysics Data System (ADS)

    Maiti, Soumyabrata; Chaudhury, Kaustav; DasGupta, Debabrata; Chakraborty, Suman

    2013-01-01

    Spatial distributions of particles carried by blood exhibit complex filamentary pattern under the combined effects of geometrical irregularities of the blood vessels and pulsating pumping by the heart. This signifies the existence of so called chaotic advection. In the present article, we argue that the understanding of such pathologically triggered chaotic advection is incomplete without giving due consideration to a major constituent of blood: abundant presence of red blood cells quantified by the hematocrit (HCT) concentration. We show that the hematocrit concentration in blood cells can alter the filamentary structures of the spatial distribution of advected particles in an intriguing manner. Our results reveal that there primarily are two major impacts of HCT concentrations towards dictating the chaotic dynamics of blood flow: changing the zone of influence of chaotic mixing and determining the enhancement of residence time of the advected particles away from the wall. This, in turn, may alter the extent of activation of platelets or other reactive biological entities, bearing immense consequence towards dictating the biophysical mechanisms behind possible life-threatening diseases originating in the circulatory system.

  15. Partial Root-Zone Drying of Olive (Olea europaea var. 'Chetoui') Induces Reduced Yield under Field Conditions

    PubMed Central

    Dbara, Soumaya; Haworth, Matthew; Emiliani, Giovani; Ben Mimoun, Mehdi; Gómez-Cadenas, Aurelio; Centritto, Mauro

    2016-01-01

    The productivity of olive trees in arid and semi-arid environments is closely linked to irrigation. It is necessary to improve the efficiency of irrigation techniques to optimise the amount of olive fruit produced in relation to the volume of water used. Partial root-zone drying (PRD) is a water saving irrigation technique that theoretically allows the production of a root-to-shoot signal that modifies the physiology of the above-ground parts of the plant; specifically reducing stomatal conductance (gs) and improving water use efficiency (WUE). Partial root-zone drying has been successfully applied under field conditions to woody and non-woody crops; yet the few previous trials with olive trees have produced contrasting results. Thirty year-old olive trees (Olea europaea ‘var. Chetoui’) in a Tunisian grove were exposed to four treatments from May to October for three-years: ‘control’ plants received 100% of the potential evapotranspirative demand (ETc) applied to the whole root-zone; ‘PRD100’ were supplied with an identical volume of water to the control plants alternated between halves of the root-zone every ten-days; ‘PRD50’ were given 50% of ETc to half of the root-system, and; ‘rain-fed’ plants received no supplementary irrigation. Allowing part of the root-zone to dry resulted in reduced vegetative growth and lower yield: PRD100 decreased yield by ~47% during productive years. During the less productive years of the alternate bearing cycle, irrigation had no effect on yield; this suggests that withholding of water during ‘off-years’ may enhance the effectiveness of irrigation over a two-year cycle. The amount and quality of oil within the olive fruit was unaffected by the irrigation treatment. Photosynthesis declined in the PRD50 and rain-fed trees due to greater diffusive limitations and reduced biochemical uptake of CO2. Stomatal conductance and the foliar concentration of abscisic acid (ABA) were not altered by PRD100 irrigation

  16. Melt layer statistic of two firn cores recently drilled at Dye3 and South dome in the dry snow zone of Southern Greenland

    NASA Astrophysics Data System (ADS)

    Freitag, Johannes; Kipfstsuhl, Sepp; Hoerz, Sebastian; Eling, Lukas; Vinther, Bo; Popp, Trevor

    2014-05-01

    In the last couple of years remote sensing data have shown large areas of wet snow in the Southern part of the Greenland ice sheet. These melt features are attributed to the overall warming trend. Persistent warming implies changes in the firn layer as well. Even in areas of the dry snow zone one can observe sporadically a few ice lenses within the firn column indicating refrozen meltwater from warm events in the past. In our contribution we want to close the gap between investigations of firn cores drilled in the 70's and the observational record of remote sensing data over the last decade in South Greenland. The focus lies on firn of the dry snow zone which is sensitive against changes in a warming atmosphere and cold enough to prevent a longway percolation path of meltwater to several firn layers. To this end we had drilled two 45m-long firn cores at the former drilling sites of DYE3 (65°11'N, 43°49'W) and South Dome (SD) (63°32'N, 44°34'W) during a aircraft-supported field campaign 2012. The retrieved 3inch-firn core segments of 1m length are measured by a X-ray-scanning routine with the means of the core-scale AWI-ICE-CT. The 2d-density fields are calculated and allow to distinguish between refreezing meltwater and compacted firn. The depth-scales are converted to time-scales by using DEP (dielectric profiling) and (in case of DYE3) discrete sampled d18O measurements. Number density of melt layers and relative amount of melt show an synchronized behavior with an general increase over the last 30 years. Local maxima are observed in both sites at around 6-9m and 25m at DYE3 and 5-8m, 22m and 40m at SD.

  17. Predicting the width and average fracture frequency of damage zones using a partial least squares statistical analysis: Implications for fault zone development

    NASA Astrophysics Data System (ADS)

    O'Hara, Alex P.; Jacobi, Robert D.; Sheets, H. David

    2017-05-01

    We introduce the partial least squares (PLS) statistical analysis that quantifies and predicts the observed relationships among normal fault slip, fracturing associated with the fault, and lithology. We describe the systematic process for constructing a multivariate PLS model that predicts the average fracture frequency and the width of fracture-dominated fault damage zones from fault, lithologic and fracture data. Conversely, the model can also predict normal fault net slip for a defined lithology given the average fracture frequency and width of a fracture-dominated fault damage zone, hereafter defined as a fracture intensification domain (FID). Fracture, fault and lithologic data were collected in the Mohawk Valley of New York State from outcrops in the Upper Ordovician Utica Group and Lorraine Group. Data collection was focused on faults with observable slip, associated FIDs, and no observable lateral restriction. Our statistical analysis used three variables to describe the geometry of the FID: FID width (FIDw), average fracture frequency within the FID (FIDƒ), and the power law regression exponent (FIDR) of the least squares trend line. We incorporated additional data from literature and tested multiple PLS models in order to refine the analysis using quality indicators provided by the PLS summary statistics output. Variables included in the final predictive model included FIDw, FIDƒ, fault slip, grain size and clay percent. Fault slip and grain size were found to have a positive covariance with FIDw while clay percent had a negative covariance. Fault slip, grain size and clay percent all showed a negative covariance with FIDƒ. Results from this research indicate that increasing fault slip leads to wider FIDs and lower average fracture frequency within the FID. The lower average fracture frequency in wider FIDs is primarily attributed to an increase in the length of the low-frequency FID tail away from the associated fault. A possible secondary influence

  18. San Andreas Fault dip, Peninsular Ranges mafic lower crust and partial melt in the Salton Trough, Southern California, from ambient-noise tomography

    NASA Astrophysics Data System (ADS)

    Barak, Shahar; Klemperer, Simon L.; Lawrence, Jesse F.

    2015-11-01

    We use ambient-noise tomography to improve CVM-H11.9, a community velocity model of southern California. Our new 3-D shear-velocity model with 0.05° x 0.05° lateral and 1 km vertical blocks reveals new structure beneath the San Andreas Fault (SAF), Peninsular Ranges batholith (PRB), southern Sierra Nevada batholith (SNB), and the Salton Trough (ST). We use 4 years of data recorded on 849 broadband stations, vastly more than previous studies and including our own broadband Salton Seismic Imaging Project, a 40 station transect across the ST, as well as other campaign stations in both Mexico and the United States. Mean lower crust and upper mantle wave speeds (3.6 km/s at 20 km, 4.2 km/s at 40 km) are low by global standards. Across the SAF, southeast of San Gorgonio Pass, we observe vertical to steeply dipping lateral velocity contrasts that extend beneath the Moho. Beneath the western PRB and westernmost southern SNB, we observe relatively high shear velocities (≥3.8 km/s) in the lower crust that we interpret as the mafic roots of the overlying arc. Relatively high-velocity upper mantle (up to ˜4.5 km/s) may be part of the intact arc, or possibly a remnant of the Farallon plate. Beneath the ST, we observe zones of low shear-velocity in the lower crust and upper mantle which permit up to ˜4.5% melt in the lower crust and up to ˜6% melt in the upper mantle, depending on the assumed composition and pore geometry. Our results preclude the existence of older continental crust beneath the ST and support the creation of new crust beneath the ST.

  19. Crustal structure off Kong Oscar Fjord, East Greenland: Evidence for focused melt supply along the Jan Mayen Fracture Zone

    NASA Astrophysics Data System (ADS)

    Hermann, Tobias; Jokat, Wilfried

    2016-11-01

    The complex structure of the North-East Greenland margin is the consequence of two rifting events: the initial separation of Greenland and Scandinavia around 56 Ma, and the breaking off of the Jan Mayen microcontinent from Greenland around 33 Ma likely driven by the arrival of the Iceland Plume beneath the east coast of Greenland. The boundary between these two rifting events is the Jan Mayen Fracture Zone. While seismic lines north of this pronounced topographic structure document the presence of a high velocity lower crust, existing data south of the fracture zone show no indications that the lower crust consists of a large, high velocity body. This gap is closed by a 500 km long seismic transect, which starts in Kong Oscar Fjord and extends out beyond the Kolbeinsey Ridge. It provides a detailed view of the crustal structure just south of the Jan Mayen Fracture Zone. The transect includes parts of the Caledonian crust of Greenland, crosses the present-day shelf and the oceanic crust formed since the separation of the Jan Mayen microcontinent. The seismic refraction line shows a constant 9 km thick oceanic crust between the extended continental margin and the mid-ocean ridge. Evidence for an only 3 km thick high-velocity lower crustal body is observed within the continent-ocean transition zone. While such high velocity crust is ubiquitous beneath the shelf to the north of the fracture zone, to the south it only occurs beneath Mesozoic basins that have been attributed to extensional collapse of the Caledonian orogeny. Inline with earlier interpretations of high velocities in the lower crust of extended continental margins, we suggest that Kong Oscar Fjord is underlain by the products of excess magma production that were focused along the Jan Mayen Fracture Zone during the breakup of the Jan Mayen microcontinent from Greenland.

  20. Growth of Mushy Zone during Solidification of Supercooled Alloy Melts: Experiment for primary arm spacing selection during two-dimensional solidification

    NASA Astrophysics Data System (ADS)

    Yoshioka, Hideaki; Yanagitani, Ryuto; Tada, Yukio; Hayashi, Yujiro

    The growth of mushy zone during solidification of supercooled melt is studied experimentally using Pb-Sn alloys casted in a cylinder mold. From the viewpoint of macro-micro link, changes of primary cell⁄dendrite arm spacing in the alloy are observed by varying supercooling degree. From the experiment, it is shown that the change of number of crystals in the mushy zone consists of a stage of quasi-stable growth, in which the number of crystals is maintained constantly, and a development stage of overgrowth, where the number of crystals decreases by competing⁄interfering with each other. Comparison of the experimentally measured primary spacing and the analytically predicted temperature and concentration fields suggests that the primary spacing is controlled by thermal diffusion during the free growth. The change of frequency distribution of the primary spacing is also investigated to discuss the history dependence of crystal growth. In conclusion, the mechanism of primary arm spacing selection in centripetal solidification is clarified in relation to temperature and concentration fi