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Sample records for partially melted zone

  1. Partially melted zone in aluminum welds

    NASA Astrophysics Data System (ADS)

    Huang, Chen-Che

    The partially melted zone (PMZ) is a region immediately outside the weld metal where grain boundary (GB) liquation can occur and cause intergranular cracking. Aluminum alloys are known to be susceptible to liquation and liquation cracking. The PMZ of alloy 2219 (essentially Al-6.3Cu) was studied. Liquation is initiated eutectically. Solidification of the GB liquid was directional---upward and toward the weld as a result of the temperature gradients across the PMZ. The liquated material solidifies with severe segregation into a low-strength, low-ductility structure consisting of a solute-depleted ductile phase and a solute-rich brittle eutectic. In tensile testing the maximum load and displacement before failure were both far below those of the base metal. The GB eutectic fractured while the adjacent Cu-depleted a deformed readily under tension. The solidification mode of the grain boundary liquid was mostly planar. However, cellular solidification was also observed near the bottom of partial-penetration welds, where temperature gradients were lowest. The liquation mechanisms in wrought multicomponent aluminum alloys during welding were also studied. Three mechanisms were identified. They cover most, if not all, wrought aluminum alloys. Liquation cracking in the PMZ was investigated in full-penetration aluminum welds. Liquation cracking occurs because the solidifying PMZ is pulled by a solidifying and thus contracting weld metal that is stronger than the PMZ. Liquation cracking can occur if there is significant liquation in the PMZ, if there is no solidification cracking in the adjacent weld metal, and if the PMZ becomes lower in solid fraction (and hence strength) during its terminal solidification than the solidifying weld metal. Liquation cracking in the PMZ was also investigated in partial-penetration aluminum welds. The papillary (nipple) type penetration common in welding with spray transfer of the filler wire actually oscillates along the weld and promotes

  2. Early Oligocene partial melting in the Main Central Thrust Zone (Arun valley, eastern Nepal Himalaya)

    NASA Astrophysics Data System (ADS)

    Groppo, Chiara; Rubatto, Daniela; Rolfo, Franco; Lombardo, Bruno

    2010-08-01

    The Main Central Thrust Zone (MCTZ) is a key tectonic feature in the architecture of the Himalayan chain. In the Arun valley of the eastern Nepal Himalaya, the MCTZ is a strongly deformed package of amphibolite- to granulite-facies metapelitic schist and granitic orthogneiss. This package is tectonically interposed between the underlying, low-grade, Lesser Himalaya sequences and the overlying, high-grade and locally anatectic, Higher Himalayan Crystallines (HHC). The MCTZ is characterized by a well documented inverted metamorphism from the Grt-Bt zone, across the Ky-in, St-in and -out, Kfs-in, Ms-out and Sil-in isograds. Partial melting with local occurrence of migmatitic segregations has been rarely reported from the highest structural levels of the MCTZ. While it is widely accepted that thrusting along the MCT occurred during the Miocene, geochronological data constraining the timing of crustal anatexis in the upper portion of the MCTZ are still lacking. In order to understand the link between partial melting in the MCTZ and the Miocene activation of the MCT, we present the P- T-time evolution of a kyanite-bearing anatectic gneiss occurring at the highest structural levels of the MCTZ, along the Arun-Makalu transect (eastern Nepal). Microstructural observations combined with P- T pseudosection analysis show that dehydration partial melting occurred in the kyanite-field. After reaching peak conditions at about 820 °C, 13 kbar, the studied sample experienced decompression accompanied by cooling down to 805 °C, 10 kbar, which caused in situ melt crystallization. SHRIMP monazite and zircon geochronology provides evidence that the anatexis affecting the upper portion of the MCTZ occurred during Early Oligocene (˜ 31 Ma). These results demonstrate that in the upper MCTZ, at least in the eastern Himalaya, crustal anatexis was earlier than, and not a consequence of, decompression linked to exhumation along the MCT.

  3. Experimental Hydrous Partial Melting of Natural Pristine and Altered MORB Beneath Subduction Zones

    NASA Astrophysics Data System (ADS)

    Carter, L. B.; Skora, S. E.; Blundy, J.

    2012-12-01

    ). Textural evidence further suggests that the K-composition of the starting material likely contributes to the location of the elusive second critical endpoint. Textural evidence implies the presence of 2 immiscible fluids at 850°C in the pristine MORB sample (in agreement with the location of the second critical endpoint of Kessel et al. 2005, using K-free MORB). This is in contrast to AOC which appears to have had only a single fluid phase (in agreement with the conclusion of Klimm et al. 2008, simulating a synthetic AOC composition). Accessory phases, apart from rutile, were not yet positively identified in our run products. Instead, we will use trace element data combined with a mass balance approach and fractionation of key trace element ratios (e.g. U/Th; La/Th, etc.) to evaluate whether accessory phases are present or not. Our study suggests that subducted MORB may behave heterogeneously during partial melting in subduction zone environments, owing to significant chemical variations in the K2O content of pristine versus altered oceanic crust. Geochemical analysis of the resulting mineralogy and melt composition of this study will further assist in the understanding of element transfer from the subducted slab to the overriding mantle wedge.

  4. Detection of partial melt in continental collision zones using different magnetotelluric tensor relationships: Results from synthetic models and real data

    NASA Astrophysics Data System (ADS)

    LLovet, Joan Campanya i.; Ledo, Juanjo; Jones, Alan G.; Queralt, Pilar; Marcuello, Alex; Liesa, Montserrat; Antón Muñoz, Josep

    2014-05-01

    Three magnetotelluric (MT) tensor relationships - the single-station MT impedance tensor (Z), the single-station vertical geomagnetic transfer function (GTF) and the multiple-station horizontal geomagnetic transfer function (HGTF) - were investigated for their effectiveness in detecting the presence of partial melt in continental collision zones. Realistic synthetic models, based on prior field studies, were used to characterize the sensitivity of each tensor relationship constraining the presence of partial melt at lower-crustal and upper-mantle depths. From the MT response of the synthetic models, each type of data was inverted separately and jointly with the others, thus determining the properties and advantages of each when modeling the subsurface. Non-linear sensitivity tests were carried out to determine the resolution that can be expected in constraining electrical resistivity anomalies associated with the presence of partial melt. Results obtained show which configuration of the HGTF is more sensitive to partial melt. The analysis of partial melt sensitivity was also performed using real data from a MT survey carried out in the Pyrenees. The data comprise a total of 82 broadband MT sites and 29 long period MT sites distributed along four profiles across the Pyrenean mountain range between the Atlantic Ocean and the Mediterranean Sea. Using the results from the synthetic models, real MT data in the Eastern Pyrenees were used to constrain if the partial melting area associated with the Iberian subducted lower crust observed below the Western, the West-central and the Central Pyrenees continues to the East. A non-linear sensitivity test was undertaken to determine the boundary to the east of this geoelectrical anomaly associated with partial melt.

  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. 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.

  7. CO2 Solubility in Natural Rhyolitic Melts at High Pressures - Implications for Carbon Flux in Subduction Zones by Sediment Partial Melts

    NASA Astrophysics Data System (ADS)

    Duncan, M. S.; Dasgupta, R.

    2011-12-01

    Partial melts of subducting sediments is thought to be a critical agent in carrying trace elements and water to arc basalt source regions. For subduction zones that contain significant amount of carbonates in ocean-floor sediments, sediment melts likely also act as a carrier of CO2. However, the CO2 carrying capacity of natural rhyolitic melts at sub-arc depths remains unconstrained. We conducted experiments on a synthetic composition, similar to average, low-degree experimental partial melt of pelitic sediments. The composition was constructed with reagent grade oxides and carbonates, the source of excess CO2. Experiments were conducted between 1 and 3 GPa at 1200 °C in Au80Pd20 capsules using a piston cylinder apparatus with a half-inch BaCO3 assembly at Rice University. Quench products showed glasses with bubbles, the latter suggesting saturation of the melt with a CO2-rich vapor phase. Oxygen fugacity during the experiments was not strictly controlled but the presence of CO2 bubbles and absence of graphite indicates fO2 above the CCO buffer. Major element concentrations of glasses were measured using EPMA. The CO2 and H2O contents of experimental doubly polished (50-110 μm), bubble-free portions of the glass chips were determined using a Thermo Nicolet Fourier Transform Infrared Spectrometer. Spectra were recorded with a resolution of 4 cm-1, 512 scans, from 650 to 4000 cm-1, under a nitrogen purge to eliminate atmospheric gases. Dissolved volatile concentrations were quantified using the Beer-Lambert law and linear molar absorption coefficients from previous studies [1, 2]. Total dissolved carbon dioxide of experimental glasses was determined from the intensity of the ν3 antisymmetric stretch bands of CO32- at 1430 cm-1 and CO2mol at 2348 cm-1. Dissolved water content of experimental glasses was determined from the intensity of O-H stretching at 3520 cm-1. Estimated total CO2 concentrations at 3 GPa are in the range of 1-2 wt%, for melts with H2O contents

  8. Partial melting of subducting oceanic crust

    NASA Astrophysics Data System (ADS)

    Peacock, Simon M.; Rushmer, Tracy; Thompson, Alan Bruce

    1994-01-01

    The conditions under which partial melting of subducting oceanic crust occurs can be determined by combining a partial melting model for basaltic compositions with two-dimensional thermal models of subduction zones. For porosities of approximately 1% containing H2O the amount of partial melt generated at the wet basaltic solidus is limited to less than 5 vol%. At higher temperatures (approximately 1000 C at 1.5 GPa) large amounts of partial melt, up to 50 vol%, form by the breakdown of amphibole and the release of structurally bound H2O. In most subduction zones, substantial partial melting of subducting oceanic crust will only occur if high shear stresses (greater than approximately 100 MPa) can be maintained by rocks close to, or above, their melting temperatures. In the absence of high shear stresses, substantial melting of the oceanic crust will only occur during subduction of very young (less than 5 Ma) oceanic lithosphere. Partial melting of hydrated basalt (amphibolites) derived from the mid-ocean ridge has been proposed as being responsible for the generation of certain recent high-Al andesitic to dacitic volcanic rocks (adakites). Three of these volcanic suites (Mount St. Helens, southern Chile, and Panama) occur in volcanic arcs where oceanic crust less than 25 Ma is being subducted at rates of 1 - 3 cm/yr and the calculated thermal regime is several hundreds of degrees hotter than more typical subduction zone environments. However, oceanic lithosphere is not currently being subducted beneath Baja and New Guinea, where recent adakites are also present, suggesting that some adakite magmas may form by water-undersaturated partial melting of underplated mafic lower crust or previously subducted oceanic crust. Further experimental work on compositions representative of oceanic crust is required to define the depth of possible adakite source regions more accurately.

  9. The role of different magnetotelluric tensor relationships in detecting partial melt in continental collision zones: Results from synthetic models and real data

    NASA Astrophysics Data System (ADS)

    Campanya i Llovet, J.; Ledo, J.; Jones, A. G.; Queralt, P.; Marcuello, A.; Liesa, M.; Muñoz, J.

    2013-12-01

    Three magnetotelluric (MT) tensor relationships - the single-station MT impedance tensor, the single-station vertical geomagnetic transfer function (GTF) and the multiple-station horizontal geomagnetic transfer function (HGTF) - were investigated for their role in detecting the presence of partial melting in continental collision zones. Synthetic models based on previous studies were used to characterize the sensitivity of each tensor relationship constraining the presence of partial melt at lower-crustal and upper-mantle depths. From the MT response of the synthetic models, each type of data has been inverted separately and jointly with the others, thus determining the properties and advantages of each when modeling the subsurface. Non-linear sensitivity tests have been carried out to determine the resolution that can be expected when constraining electrical resistivity anomalies associated with the presence of partial melt. The electrical resistivity anomalies associated with different amounts of partial melt were calculated using the two phases of Archie's law and Hashin Shtrikman extremal bounds. The results have been compared with the sensitivity of the MT tensor relationships, thus determining the resolution that can be expected in the detection of partial melt at lower-crustal and upper-mantle depths. Equivalent analyses have been performed using real MT data from a survey carried out in the Pyrenees. The data comprise a total of 82 broadband MT sites and 29 long period MT sites distributed along four profiles across the Pyrenean mountain range between the Atlantic Ocean and the Mediterranean Sea. The results show the presence of a low-electrical-resistivity structure that has been associated with partial melting of the Iberian subducted lower crust. This anomaly has been constrained below three of the MT profiles but seems to be absent below the Eastern Pyrenees MT profile. A non-linear sensitivity tests was undertaken to ensure that the absence of this

  10. SHRIMP U-Pb dating of zircons related to the partial melting in deep subduction zone -case study from the Sanbagawa quartz bearing eclogite-

    NASA Astrophysics Data System (ADS)

    Arakawa, M.; Okamoto, K.; Keewook, Y.; Tsutsumi, Y.

    2011-12-01

    Subducting oceanic plate is dehydrated due to metamorphic reaction in increase of pressure and temperature. The dehydrated fluid is considered to cause deep focused earthquake and Island Arc volcanism. Recently we have discovered an eclogite outcrop exhibiting partial melting texture from the Sanbagawa high P/T metamorphic belt, characterized as subducted Pacific plate. The discovery is significantly important because the melt may play an important role in deep focused earthquake and the melt itself directly may contribute to the origin of Island Arc magma. However, the melting feature is hardly recognized in thin sections from the eclogite because of extensive retrograde hydration and deformation. Zircon is the best tool to reconstruct melting process at eclogite faces condition because it preserves 1) high P minerals, 2) melt and fluid as inclusion and 3) the zircon growth history can be traced from its zonal texture. In order to confirm the age of partial melting of Sanbagawa metamorphic rocks, we had separated zircons from the melted portion(quartz-bearing eclogite) and dated using the SHRIMP at the Korean Basic Science Institute(KBSI). We collected the melting portion (SHT16&75) in the eclogite (SHT15&76) that is characterized as quartz-rich domain from the outcrop. The zircons from the melted portion (SHT16&75) are rounded and have sector zoning. Geochronological data demonstrates that the core and mantle yield U-Pb age in the 130-113 (120 in average) Ma range, and the rim ages are in the 115-104 Ma range. The zircons from the eclogite (SHT15&76) have homogenous core with thin mantle and rims. The U-Pb ages are concentrated to 123 - 112Ma. The ages are identical to the zircon U-Pb ages (120-110 Ma) reported by Okamoto et al (2004). Above these evidences suggest that eclogite metamorphism was occurred at 120Ma. Subsequent partial melting was happened at 110Ma. REE concentrations of the studied zircon were determined also using SHRIMP. REE pattern of the

  11. Phase relations in the partial melting of the Baldissero spinel-lherzolite (Ivrea-Verbano zone, Western Alps, Italy)

    NASA Astrophysics Data System (ADS)

    Sinigoi, Silvano; Comin-Chiaramonti, Piero; Alberti, Antonio A.

    1980-12-01

    The occurrence of various types of mobilizates in the Baldissero spinel lherzolite is due to partial melting of the same body. The study of the relationships between the peridotite and its mobilizates demonstrates that olivine did not take an active part in the fusion. Estimates of the degree of partial melting vary from 10% for the average composition, to 20% for the most depleted samples. These values refer to an initial pyrolitic composition, and thus are relative, as they can vary depending on the actual primary composition. The calculated composition of the liquid generated by partial melting is quite similar to that of a picritic basalt, and is practically the same irrespective of the 10% and 20% fusion. This fact provides strong evidence that melting took place at a unique invariant point of the natural system, producing a liquid with a remarkably constant composition. Projection of the liquid in the fo-an-di-si diagram is fairly well aligned with the modal compositions of the solid residua, but does not coincide with the minimum of the simplified system. The proposed solution is based on the enlargement of the spinel field (at constant pressure), due to the Cr content in this phase. Therefore, the position of the invariant minimum is not fixed, but rather controlled by the Cr content of the spinel. Is is suggested that, by an increase in the Cr content, spinel might at a given moment become refractory. Thus, saturated or over-saturated magmas are produced depending on the phase relations between olivine, orthopyroxene and clinopyroxene. This would happen in the case of very advanced fusions or in the case of fusion of already depleted peridotites. The relationships between mobilizates of different generations suggest a non adiabatic mantle upwelling.

  12. 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

  13. Commercial Zone Melting Ingots

    NASA Astrophysics Data System (ADS)

    Zheng, Yun; Xie, Hongyao; Shu, Shengcheng; Yan, Yonggao; Li, Han; Tang, Xinfeng

    2014-06-01

    Bismuth telluride-based compounds have been extensively utilized for commercial application. However, thermoelectric materials must suffer numerous mechanical vibrations and thermal stresses while in service, making it equally important to discuss the mechanical properties, especially at high temperature. In this study, the compressive and bending strengths of Bi0.5Sb1.5Te3 commercial zone melting (ZM) ingots were investigated at 25, 100, and 200 °C, respectively. Due to the obvious anisotropy of materials prepared by ZM method, the effect of anisotropy on the strengths was also explored. Two-parameter Weibull distribution was employed to fit a series of values acquired by a universal testing machine. And digital speckle photography was applied to record the strain field evolution, providing visual observation of surface strain. The compressive and bending strengths along ZM direction were approximately three times as large as those perpendicular to the ZM direction independent of the temperature, indicating a weak van der Waals bond along the c axis.

  14. Melt migration modeling in partially molten upper mantle

    NASA Astrophysics Data System (ADS)

    Ghods, Abdolreza

    The objective of this thesis is to investigate the importance of melt migration in shaping major characteristics of geological features associated with the partial melting of the upper mantle, such as sea-floor spreading, continental flood basalts and rifting. The partial melting produces permeable partially molten rocks and a buoyant low viscosity melt. Melt migrates through the partially molten rocks, and transfers mass and heat. Due to its much faster velocity and appreciable buoyancy, melt migration has the potential to modify dynamics of the upwelling partially molten plumes. I develop a 2-D, two-phase flow model and apply it to investigate effects of melt migration on the dynamics and melt generation of upwelling mantle plumes and focusing of melt migration beneath mid-ocean ridges. Melt migration changes distribution of the melt-retention buoyancy force and therefore affects the dynamics of the upwelling plume. This is investigated by modeling a plume with a constant initial melt of 10% where no further melting is considered. Melt migration polarizes melt-retention buoyancy force into high and low melt fraction regions at the top and bottom portions of the plume and therefore results in formation of a more slender and faster upwelling plume. Allowing the plume to melt as it ascends through the upper mantle also produces a slender and faster plume. It is shown that melt produced by decompressional melting of the plume migrates to the upper horizons of the plume, increases the upwelling velocity and thus, the volume of melt generated by the plume. Melt migration produces a plume which lacks the mushroom shape observed for the plume models without melt migration. Melt migration forms a high melt fraction layer beneath the sloping base of the impermeable oceanic lithosphere. Using realistic conditions of melting, freezing and melt extraction, I examine whether the high melt fraction layer is able to focus melt from a wide partial melting zone to a narrow region

  15. Partial Melting in the Inner Core

    NASA Astrophysics Data System (ADS)

    Hernlund, J. W.

    2014-12-01

    The inner core boundary (ICB) is often considered to be permeable to flow, because solid iron could melt as it upwells across the ICB. Such a mechanism has been proposed to accompany inner core convective processes (including translation from a freezing to melting hemisphere), and has also been invoked to explain the formation of a dense Fe-rich liquid F-layer above the ICB. However, the conceptions of ICB melting invoked thus far are extremely simplistic, and neglect the many lessons learned from melting in other geological contexts. Owing to some degree of solid solution in relatively incompatible light alloys in solid iron, the onset of melting in the inner core will likely occur as a partial melt, with the liquid being enriched in these light alloys relative to the co-existing solid. Such a partial melt is then subject to upward migration/percolation out of the solid matrix owing to the buoyancy of melt relative to solid. Removal of melt and viscous compaction of the pore space results in an iron-enriched dense solid, whose negative buoyancy will oppose whatever buoyancy forces initially gave rise to upwelling. Either the negative buoyancy will balance these other forces and cause upwelling to cease, or else the solid will become so depleted in light alloys that it is unable to undergo further melting. Thus a proper accounting of partial melting results in a very different melting regime in the inner core, and suppression of upwelling across the ICB. Any fluid that is able to escape into the outer core from inner core partial melting will likely be buoyant because in order to be a melt it should be enriched in incompatiable alloys relative to whatever is freezing at the ICB. Therefore inner core melting is unlikely to contribute to the formation of an F-layer, but instead will tend to de-stabilize it. I will present models that illustrate these processes, and propose that the F-layer is a relic of incomplete mixing of the core during Earth's final stages of

  16. 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

  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. 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. PMID:27386548

  19. 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

  20. 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

  1. 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.

  2. Generation of felsic melts within fast-spreading oceanic crust: Experimental partial melting of hydrothermally altered sheeted dike

    NASA Astrophysics Data System (ADS)

    Fischer, L. A.; Erdmann, M.; France, L.; Deloule, E.; Koepke, J.

    2013-12-01

    In recent oceanic crust and in ophiolites, felsic lithologies are observed. Different processes, like fractional crystallization of MORB and partial melting of mafic rocks are discussed to form these lithologies. Partial melting is expected as a major process in forming felsic lithologies at the base of the sheeted dike complex of fast-spreading ridges, where the axial melt lens is assumed to be located directly beneath the sheeted dikes.It is widely accepted that this melt lens has the potential to trigger partial melting of mafic lithologies at the gabbro/dike transition zone. In this experimental study, the influence of partial melting on the generation of felsic lithologies is examined. Therefore, partial melting experiments at a pressure of 100 MPa were performed. As starting material, a natural basalt from the IODP (Integrated Ocean Drilling Program) drilling at Site 1256 (equatorial East Pacific Rise) was chosen, which is representative for the lower sheeted dike complex. It is characterized as a moderately altered dolerite containing plagioclase (An50-57), clinopyroxene (Mg# 0.55-0.60) and quartz, with chlorite as secondary phase; sulfides and Fe-Ti-oxides are present as accessory minerals. The partial melting experiments were conducted in an H2-controlled IHPV at the Institute of Mineralogy in Hanover, Germany. To investigate the evolution of the partial melts, different experiments were performed at temperatures between 1030°C and 910°C and a constant pressure of 100 MPa. All experiments were water saturated leading to a fO2 corresponding to QFM +1 (QFM = quartz-fayalite-magnetite oxygen buffer). This is slightly more oxidized than MORB crystallization due to the influence of a hydrous fluid which generally increases the oxygen activity. The experimental products were analyzed using electron microprobe for major elements, and a SIMS (CRPG Nancy, France) for trace elements. We present here our first results on phase relations and mineral compositions

  3. 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.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  6. Olivine-FeS Partial-Melt

    SciTech Connect

    Roberts, J; Siebert, J; Ryerson, F J; Kinney, J

    2006-10-02

    The figure shows Fe-S-filled melt channels in olivine created at high temperature and pressure. The 3D image was obtained on Beamline 8.3.2 at the Advanced Light Source, Lawrence Berkeley Laboratory, with a spatial resolution of better than two microns (bar is 10 microns). Permeability of Fe-S melts in olivine at high temperatures and pressures provides an important constraint on models of planetary core formation. Permeability must be inferred from empirical relationships based on microstructure. To date, estimates of permeability have varied by more than five orders of magnitude. To provide more accurate constraints, we used high-resolution synchrotron radiation computed tomography to image the three-dimensional network of melt-containing pores in an olivine matrix, and calculated the permeability directly by solving the equations of Stokes flow through the actual pore network using a lattice-Boltzmann approach. These calculations provide an independent constraint on models of planetary core formation.

  7. Partial melting, fluid supercriticality and element mobility in ultrahigh-pressure metamorphic rocks during continental collision

    NASA Astrophysics Data System (ADS)

    Zheng, Yong-Fei; Xia, Qiong-Xia; Chen, Ren-Xu; Gao, Xiao-Ying

    2011-08-01

    Partial melting at continental lithosphere depths plays an important role in generating geochemical variations in igneous rocks. In particular, dehydration melting of ultrahigh-pressure (UHP) metamorphic rocks during continental collision provides a petrological link to intracrustal differentiation with respect to the compositional evolution of continental crust. While island arc magmatism represents one end-member of fluid-induced large-scale melting in the mantle wedge during subduction of the oceanic crust, the partial melting of UHP rocks can be viewed as the other end-member of fluid-induced small-scale anatexis during exhumation of the deeply subducted continental crust. This latter type of melting is also triggered by metamorphic dehydration in response to P-T changes during the continental collision. It results in local occurrences of hydrous melts (even supercritical fluids) as felsic veinlets between boundaries of and multiphase solid inclusions in UHP metamorphic minerals as well as local accumulation of veinlet-like felsic leucosomes in foliated UHP metamorphic rocks and metamorphically grown zircons in orogenic peridotites. Thus, very low-degree melts of UHP rocks provide a window into magmatic processes that operated in continental subduction zones. This article presents a review on available results from experimental petrology concerning the possibility of partial melting under conditions of continental subduction-zone metamorphism, and petrological evidence for the occurrence of dehydration-driven in-situ partial melting in natural UHP rocks during the continental collision. Although the deeply subducted continental crust is characterized by a relative lack of aqueous fluids, the partial melting in UHP rocks commonly takes place during decompression exhumation to result in local in-situ occurrences of felsic melts at small scales. This is caused by the local accumulation of aqueous fluids due to the breakdown of hydrous minerals and the exsolution

  8. Silicic Melt Generation, Segregation, and Injection by Dolerite Partial Melting of Granitic Wall Rock, McMurdo Dry Valleys, Antarctica

    NASA Astrophysics Data System (ADS)

    Hersum, T. G.; Simon, A. C.; Marsh, B. D.

    2005-12-01

    within the partially melted zone that initiated crack formation at and parallel to the contact, into which, interstitial melts flowed in response to a pore pressure gradient. Excess pore pressure within this granitic melt reservoir along the contact subsequently tore open the brittle dolerite chilled margin like a trap door and emplaced, essentially by evacuation, granitic dikes into the (nearly?) solidified dolerite. Granite partial melting, segregation, and dike emplacement likely occurred within a period of several years as suggested by corroborative evidence from thermal modeling and the time estimated to produce, by interdiffusion between the granitic melt and dolerite, a thin (2 mm) distinctive planar orthopyroxenite zone within the dolerite chilled margin. Reactivation of similarly injected basaltic feeders deeper in the crust, with dikelet stretching and absorption by simultaneous diffusion, presents a viable and efficient means of extensive and subtle crustal contamination of basaltic magma.

  9. Partial melting of TTG gneisses: crustal contamination and the production of granitic melts

    NASA Astrophysics Data System (ADS)

    Meade, F. C.; Masotta, M.; Troll, V. R.; Freda, C.; Johnson, T. E.; Dahren, B.

    2011-12-01

    Understanding partial melting of ancient TTG gneiss terranes is crucial when considering crustal contamination in volcanic systems, as these rocks are unlikely to melt completely at magmatic temperatures (1000-1200 °C) and crustal pressures (<500 MPa). Variations in the bulk composition of the gneiss, magma temperature, pressure (depth) and the composition and abundance of any fluids present will produce a variety of melt compositions, from partial melts enriched in incompatible elements to more complete melts, nearing the bulk chemistry of the parent gneiss. We have used piston cylinder experiments to simulate partial melting in a suite of 12 gneisses from NW Scotland (Lewisian) and Eastern Greenland (Ammassalik, Liverpool Land) under magma chamber temperature and pressure conditions (P=200 MPa, T=975 °C). These gneisses form the basement to much of the North Atlantic Igneous Province, where crustal contamination of magmas was commonplace but the composition of the crustal partial melts are poorly constrained [1]. The experiments produced partial melts in all samples (e.g. Fig 1). Electron microprobe analyses of glasses indicate they are compositionally heterogeneous and are significantly different from the whole rock chemistry of the parent gneisses. The melts have variably evolved compositions but are typically trachy-dacitic to rhyolitic (granitic). This integrated petrological, experimental and in-situ geochemical approach allows quantification of the processes of partial melting of TTG gneiss in a volcanic context, providing accurate major/trace element and isotopic (Sr, Pb) end-members for modeling crustal contamination. The experimental melts and restites will be compared geochemically with a suite of natural TTG gneisses, providing constraints on the extent to which the gneisses have produced and subsequently lost melt. [1] Geldmacher et al. (2002) Scottish Journal of Geology, v.38, p.55-61.

  10. 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

  11. 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

  12. 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

  13. 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.

  14. Evidence From a Crystal-Poor, Zoned (Rhyolite-Andesite) Pyroclastic Deposit From Volcan Tepetiltic, Western Mexico for Rapid Generation of Silicic Melt by Partial Melting of Granitoid and not by Segregation From a Long-Lived Crystal-Rich Mush

    NASA Astrophysics Data System (ADS)

    Lange, R. A.; Frey, H.; Hall, C.; Delgado-Granados, H.

    2007-12-01

    %), intermediate (56-66 wt% SiO2), hornblende- free lavas of V. Tepetiltic and the explosive, caldera-forming eruption that produced the crystal-poor (0-3 vol%), zoned (60-75 wt% SiO2), hornblende-bearing pyroclastic deposit. Most models for the formation of high- silica rhyolite, especially when part of an eruption that zones to andesite/dacite, is that it forms by melt segregation from the andesite/dacite crystalline mush. In the case of the erupted products from V. Tepetiltic, however, this oft-cited model is not viable. The crystal-poor andesite cannot be the parent for the rhyolite as too few crystals have formed. Instead, the most plausible scenario is that the magma chamber that fed construction of the main edifice of V. Tepetiltic solidified below its solidus by ~350 ka. Then, at ~214 ± 64 ka, a pulse of basaltic andesite magma was emplaced into the upper crust, which drove partial melting of granitoid beneath V. Tepetiltic, by the transfer of heat and volatiles. The partial melt (ranging from voluminous rhyolite to minor andesite) segregated, ascended, and erupted quickly (at ~190 ka) before extensive degassing- induced crystallization could occur. This model for the formation of rhyolite (by partial melting of granitoid) may be more widespread than currently recognized.

  15. Partial melt and seismic properties: A case study from the Seiland Igneous Province

    NASA Astrophysics Data System (ADS)

    Lee, Amicia; Walker, Andrew; Lloyd, Geoff; Torvela, Taija

    2016-04-01

    The geological evolution of orogenies is partly controlled by partial melting in the middle and/or lower crust. However, seismic methods cannot reliably quantify the amount of melting at depth in tectonically active mountain belts. We have developed a numerical modelling method to assess the impact of melt on seismic properties and applied this to samples from a transect across a migmatitic shear zone in the Seiland Igneous Province, Northern Norway. These rocks represent an analogue to lower crustal shear zones undergoing orogenic collapse. Compressional and shear waves reduce when melt is introduced but the effect on seismic anisotropy is unclear and recent evidence suggests the melt-seismic property relationship is not simple. We have measured crystallographic preferred orientations in sheared migmatites using EBSD and use this data as input for multiple numerical models designed to quantify the variation of seismic properties with melt volume. Three 'end member' models have been developed: a reference 'isotropic model' consisting of a rock matrix comprising randomly oriented grains with distributed spherical melt pockets, the 'shape fabric model' an isotropic matrix with ellipsoidal melt inclusions, and the 'CPO model' consisting of a textured mineralogical matrix with randomly distributed spherical melt pockets. The isotropic and matrix dominated models give end member seismic properties for the isotropic and anisotropic dominated regimes. Importantly, these models do not consider the shape of the melt fractions, and instead the melt is averaged over the whole rock. The shape fabric model calculates the seismic properties of an isotropic inclusion within an isotropic matrix. The results of this modelling show that an oblate ellipsoid has the greatest effect on seismic properties. It is also the most likely shape for melt pockets as it is an analogue shape for extensional melting during orogenic collapse; a large oblate ellipsoid produces a high S

  16. 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

  17. Fault Zone Drainage, Heating and Melting During Earthquake Slip

    NASA Astrophysics Data System (ADS)

    Rempel, A. W.; Rice, J. R.; Jacques, L. M.

    2003-12-01

    The expansion of pore water caused by frictional heating during large crustal events provides a powerful weakening mechanism (Sibson, 1973; Lachenbruch, 1980). It may explain the magnitude of seismically inferred fracture energy and aspects of its variation with increased slip (Abercrombie and Rice, 2003; Rice et al., 2003; Rice, this section, 2003). The weakening is mediated by the effects of fluid transport, which are sensitive to the permeability structure of the fault zone and its modification by damage induced by the passing rupture front (Poliakov et al., 2002), as well as by the increase in pore pressure itself. Higher permeabilities allow partial drainage to occur, so that enough strength remains for the heat generated to cause partial melting of the fault gouge at large enough slip. We use recent field and laboratory data for fluid transport through pressurized fault gouge (e.g. Lockner et al., 2000; Wibberley and Shimamoto, 2003) to motivate models for drainage and melting during earthquake slip. A dramatic illustration of the role of drainage is provided by an idealized model in which we assume that a freshly damaged, highly permeable region extends right up to a localized shear zone of thickness ho=5 mm, with fixed porosity n and much lower permeability k. At 7 km depth, for n=0.02 and k=10-19 m2, the slip distance required to reach the onset of melting at 750oC is approximately 0.4 m for a constant friction coefficient of f=0.6. At 14 km depth, for n=0.01 and k=10-20 m2, the same temperature is reached after only 0.1 m of slip. Yet more efficient drainage might occur due to the permeability increases that accompany reductions in the effective stress, so that even more rapid temperature increases would be predicted. For example, with ten times higher k, melting begins after 0.1 m slip at 7 km depth and just 0.05 m at 14 km. At onset of melting the high melt viscosity impedes further drainage and, with increasing melt fraction, inter-particle contact is

  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. Magnetotelluric imaging of upper crustal partial melt at Tendaho graben in Afar, Ethiopia

    NASA Astrophysics Data System (ADS)

    Didana, Yohannes Lemma; Thiel, Stephan; Heinson, Graham

    2014-05-01

    We report on a recent magnetotelluric (MT) survey across the Manda Hararo magmatic segment (MHMS) within the Tendaho graben in the Afar Depression in northeastern Ethiopia. Twenty-two broadband MT sites with ˜1 km station spacing were deployed along a profile with the recorded data covering a period range from 0.003 s to 1000 s. A two-dimensional (2-D) resistivity model reveals an upper crustal fracture zone (fault) and partial melt with resistivity of 1-10Ωm at a depth of >1 km. The partial melt has a maximum horizontal width of 15 km and extends to a depth of 15 km within the Afar Stratoid Series basalts. We estimate a melt fraction of about 13% based on geochemical and borehole data, and bulk resistivity from the 2-D MT inversion model. The interpreted upper crustal partial melt may have been formed by either a magma intrusion from mantle sources or a large volume of continental crust that has been fluxed by a small amount of mantle melt and heat. Within the MHMS and Tendaho graben, a magma intrusion is a plausible explanation for the upper crustal conductor. The inferred presence of a conductive fracture zone or fault with hydrothermal fluid and shallow heat sourcing magma reservoir also makes the Tendaho graben a promising prospect for the development of conventional hydrothermal geothermal energy.

  20. Reactive Melt Migration and Channelization in Partially Molten Rocks

    NASA Astrophysics Data System (ADS)

    Pec, M.; Kohlstedt, D. L.; Zimmerman, M. E.; Holtzman, B. K.

    2014-12-01

    Several lines of evidence suggest that melt from partially molten regions of the mantle moves rapidly along chemically isolated pathways toward Earth's surface. In some previous experiments, reactive melt infiltration led to channelization; in others, it did not. To better understand the conditions required for channel formation, we developed an experimental set-up that allows flow of a reactive melt through a rock under a controlled pressure gradient by sandwiching a partially molten rock between a melt reservoir and porous sink. Hot-pressed 50:50 mixtures of olivine (Ol) and clinopyroxene (Cpx) with either 4 or 20 vol% alkali basalt formed ~4 mm long cylinders of partially molten rock. Source and sink are disks of alkali basalt and porous alumina. A melt reservoir-to-rock volume ratio of 2:1 ensured chemical disequilibrium. We anneal melt:rock:sink triplets for up to 5 h at a confining pressure of Pc=300 MPa with effective pressure Pe=0 to 299.9 MPa (Pe = Pc - Pp) , at T = 1200° & 1250°C. Two distinct melt migration features form, 1) a planar reaction layer and 2) finger-shaped channels. Both the reaction layer and the fingers contain Ol + melt with little to no Cpx. Planar reaction layers develop at the melt-rock interface in all experiments. Finger-shaped channels form only in experiments in which a fluid pressure gradient exists from source to sink, i.e. Pe>0 The thickness of the planar reaction layer increases with increasing T and with the square root of time, indicating that diffusion controls the growth rate, reaching thicknesses of ~70 μm at 1200°C and ~200 μm at 1250°C in 5 h, though layer thickness is independent of Peand initial melt content. The finger-shaped channels are more closely spaced and thicker in the experiments at higher temperature and higher initial melt content. To conclude, under our laboratory conditions, channelization of a reactive melt required application of a fluid pressure gradient; scaling conditions for channel formation

  1. 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.

  2. Differentiation of partial melts in the mantle: Evidence from the Balmuccia peridotite, Italy

    NASA Astrophysics Data System (ADS)

    Sinigoi, S.; Comin-Chiaramonti, P.; Demarchi, G.; Siena, F.

    1983-06-01

    The Balmuccia peridotite shows evidence, in the form of a network of dykes, of partial melting and flow crystallization processes. The partial melting processes probably occurred over a fairly long time interval, and seem to have been related to different “melting pulses”. Resultant liquids were broadly picritic. Melting occurred incongruently according to the scheme cpx+opx+(ol+sp)=Mg-richer ol+Cr-richer sp+L. Partial melts tended at first to accumulate in horizontal layers; then, as the critical melting threshold was exceeded, liquids were able to filter slowly towards lower pressure zones. In doing so liquids fractionated initially in situ, via crystallisation of websteritic dykes of the Cr-diopside suite, and later, in the overlying mantle, via crystallisation of transitional dykes and those of the Al-augite suite. This filter-pressing stage, when flow velocities were very low and discontinuous, probably corresponded to the period of maximum deformability of the peridotite. The type of differentiation testified by the dykes of the Balmuccia peridotite, is characterized by a decrease in SiO2, a rapid enrichment in Al2O3 and a mild increase in FeO, and is substantially in accordance with experimental trends from the fo-an-di-SiO2 system in the spinel-peridotite stability field. A close relationship between type of differentiation, flow velocity and mechanical behaviour of the mantle peridotite is a feature of the proposed model.

  3. 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.

  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. PMID:12075348

  6. Partial Melting of Ordinary Chondrite Under Reducing Conditions

    NASA Astrophysics Data System (ADS)

    Ford, R.; Rushmer, T.; Benedix, G.; McCoy, T.

    2004-12-01

    A critical parameter in determining the nature and processes of differentiation of planetary materials in the early solar system is oxygen fugacity. Chondrites record a range of oxygen fugacities from approximately 5 log units below the iron-wustite (Fe-FeO) buffer (enstatite chondrites) to close to QFM (some carbonaceous chondrites). Among the equilibrated chondrites, an "oxidation gap" appears to exist between ordinary chondrites and enstatite chondrites, although several groups of unequilibrated carbonaceous chondrites appear to occupy this "gap". Some primitive achondrites fill this gap (e.g. pallasites, acapulcoites, lodranites, winonaites, and silicate-bearing IAB and IIE irons), although the precursors to these groups are poorly known. In this experimental study, we have determined the modification in mineral compositions during partial melting under reducing conditions and explore the idea that the primitive achondrites may be formed through differentiation under reducing conditions of a more oxidized precursor. Partial melting experiments were conducted on an H6 chondrite (Kernouve) under reducing conditions at 1 atm and at 1.3 GPa pressure in a solid media deformation apparatus. In the 1 atm experiments, fO2 was buffered by gas mixing and sealed silica tube techniques to values determined from thermodynamic calculations of primitive achondrites; in the deformation experiments, aluminum jackets were used. The experiments suggest that partial melting of an oxidized precursor under reducing conditions can produce some of the reduced features observed in primitive achondrites such as magnesian olivine, pyroxene and chromite compositions typical of primitive achondrites at temperatures of 1200-1300 ° C, as well as chalcophilic behavior of previously lithophillic ions (e.g., Cr in sulfide) at temperatures at 1000° C. Some features of primitive achondrites (e.g. oxygen isotopic compositions and Cr/(Cr+Al) ratios of chromites) appear to be intrinsic to the

  7. 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.

  8. Can slabs melt beneath forearcs in hot subduction zones?

    NASA Astrophysics Data System (ADS)

    Ribeiro, J.; Maury, R.; Gregoire, M.

    2015-12-01

    At subduction zones, thermal modeling predict that the shallow part of the downgoing oceanic crust (< 80 - 100 km depth to the slab) is usually too cold to cross the water-rich solidus and melts beneath the forearc. Yet, the occasional occurrence of adakites, commonly considered as slab melts, in the forearc region challenges our understanding of the shallow subduction processes. Adakites are unusual felsic rocks commonly associated with asthenospheric slab window opening or fast subduction of young (< 25 Ma) oceanic plate that enable slab melting at shallow depths; but their genesis has remained controversial. Here, we present a new approach that provides new constraints on adakite petrogenesis in hot subduction zones (the Philippines) and above an asthenospheric window (Baja California, Mexico). We use amphibole compositions to estimate the magma storage depths and the composition of the parental melts to test the hypothesis that adakites are pristine slab melts. We find that adakites from Baja California and Philippines formed by two distinct petrogenetic scenarios. In Baja California, hydrous mantle melts mixed/mingled with high-pressure (HP) adakite-type, slab melts within a lower crustal (~30 km depth) magma storage region before stalling into the upper arc crust (~7-15 km depth). In contrast, in the Philippines, primitive mantle melts stalled and crystallized within lower and upper crustal magma storage regions to produce silica-rich melts with an adakitic signature. Thereby, slab melting is not required to produce an adakitic geochemical fingerprint in hot subduction zones. However, our results also suggest that the downgoing crust potentially melted beneath Baja California.

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

    PubMed

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

    2003-10-01

    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. PMID:14534583

  10. 3D Model of Melt Distribution in Partially Molten Dunite

    NASA Astrophysics Data System (ADS)

    Garapic, G.; Faul, U.; Brisson, E.

    2010-12-01

    The currently existing model of grain-scale melt geometry in the Earth’s upper mantle is derived from theoretical considerations that stem from material science research, combined with relatively low-resolution observations of polished two-dimensional surfaces. This model predicts a simple, interconnected network of melt along three-grain edges in static surface energy equilibrium. However, due to a continuous rearrangements of neighboring grains caused by grain growth, melt forms complex shapes among the grains. As a result, it is impossible to construct a 3D image of the pore space from 2D surfaces, which makes it particularly challenging to resolve the current controversy on whether all two-grain boundaries are wetted or melt-free. We present a new method for reconstruction of the 3D pore space in partially molten rocks. The method consists of serial sectioning and high resolution imaging (Field Emission SEM) of polished surfaces, followed by image alignment and rendering. The ablation rate during serial sectioning is determined by measuring the depth of a laser hole by interferometry. We removed a total of 25 layers with a spacing of of 1.3.microns between layers. Each layer consists of a mosaic of images approximately 300 x 320 microns in size. Melt regions are identified within each layer by hand-digitizing SEM images. We obtain a 3D model by stacking the slices, registering each slice, and using alpha shapes as a surface reconstruction technique. The sample we investigated is a partially molten dunite consisting of Fo90 olivine with a mean grain size of 33 microns and 4% melt. It was run in a piston cylinder at 1350°C and 1 GPa for 432 hours to achieve steady state grain growth. Rendering of the 3D pore space shows that the larger melt pockets at multi-grain junctions change within only a few microns in depth, whereas thin inclusions along two-grain boundaries persist over the entire depth of the imaged volume, which is similar to the mean grain size

  11. 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

  12. Isotopic equilibration during partial melting: an experimental test of the behaviour of Sr

    NASA Astrophysics Data System (ADS)

    Hammouda, T.; Pichavant, M.; Chaussidon, M.

    1996-10-01

    Experiments using isotopically enriched, Sr doped minerals designed to test for isotopic equilibrium between source and melt during partial melting reveal that 87Sr/ 86Sr ratios of the liquids are primarily determined by the proportions of minerals consumed and vary with the advancement of the melting reaction. The experiments were performed at 1 atm on model crustal assemblages composed of pairs of natural plagioclase (An 68; 87Sr/ 86Sr= 0.701 ) and synthetic fluorphlogopite doped with 90 ppm Sr having 87Sr/ 86Sr= 4.2 . SIMS traverses showed that during the initial stages of the reaction, liquids are isotopically zoned. All the analyzed melts have 87Sr/ 86Sr markedly higher than that of the bulk starting assemblage (i.e. the source), because of the faster melting rate of fluorphlogopite. At 1200°C and 1250°C melting occurs above a critical temperature, wherein the dissolution rates of the crystals are controlled by diffusion of species in the melt, and reactants and reaction products are out of isotopic equilibrium. This is due to faster melt-crystal boundary migration when compared to Sr diffusion in the crystals. Equilibration is possible only if melting stops. Calculations show that total equilibration between melt and residue by Sr tracer diffusion in the crystals takes 10 4-10 6 yr (for temperature and grain size ranging, respectively, from 800°C to 1000°C, and 0.1 to 1 cm). When compared to the proposed residence time of crustal magmas at their sources, this result strongly suggests that magmas that do not reflect the bulk isotopic characteristics of their source regions can be produced.

  13. 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.

  14. 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.

  15. Partial Melting and Liquefaction of Granular Fault Gouge During Earthquake Slip

    NASA Astrophysics Data System (ADS)

    Jacques, L. M.; Rice, J. R.

    2002-12-01

    Gouge particles interact by friction and must heat significantly in large earthquake slip (> 1 m) accommodated by a narrow fault core. For very impermeable border zones of a water-infiltrated core, and when gouge dilation is small compared to differential thermal expansion, pore pressure p rises towards the ambient fault-normal stress σ n and the frictional resistance drops, reducing strength, and hence the rate of continuing temperature rise, to negligible values before the onset of melting (Sibson, Lachenbruch, Mase and Smith). However, those border zones will have just experienced the high stress fluctuations associated with passage of the rupture front and will be extensively cracked with renewed, high permeability k. (k measured by Lockner et al. for the Nojima fault zone, active in the 1995 Kobe earthquake, is of order 500 times higher for the damage zones than for the sheared ultracataclastic core within them.) In presence of such high k border zones, the time tr to relax away thermally elevated p scales as h2/α where h is core thickness and α is its poroelastic diffusivity. Using core permeability k = 10-19 m2 like for Nojima, we roughly estimate tr < 0.1 s for h < 10 mm. Thus thermal pressurization of water will sometimes be insufficient to eliminate frictional strength, and temperature will continue to rise so that the gouge begins to melt. We must then confront the problem of describing the rheology of a gouge with particles that are in frictional contact, at least in the earliest stages of melting, but with a pore fluid (mixture of melt and residual water) that sustains large shear stress. The Terzaghi effective stress procedure treats the fluid as if under hydrostatic pressure and is then not fully applicable. Within it, p is predicted to rapidly rise towards σ n in the early stages of partial melting because α scales inversely with the then very large viscosity of the pore fluid, so tr is large and the pressure increase, due to differential

  16. 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

  17. Paradoxical pseudotachylyte - Fault melt outside the seismogenic zone

    NASA Astrophysics Data System (ADS)

    White, Joseph Clancy

    2012-05-01

    Fault generated melt, pseudotachylyte, is an established indicator of palaeoseismic faulting. The existing consensus that frictionally induced melting occurs within the classic seismogenic zone contrast the contention over how pseudotachylyte forms within the ductile regime. Central to this issue is whether all pseudotachylyte originates as pressure-dependent frictional melt along slip surfaces, or if pressure-independent processes have roles in its formation. Propagation of high-velocity slip into deeper crustal levels provides a satisfactory explanation for pseudotachylyte at depth, but does not of itself rationalize earthquake nucleation outside the classic seismogenic zone. Pseudotachylyte from the Minas Fault Zone, Nova Scotia, Canada is used to demonstrate the formation and preservation of fault-related melt under lower crustal conditions. Microstructures retain evidence of intense dislocation glide with minimal climb, and ductile disaggregation of the host; the latter are consistent with intracrystalline deformation in the Peierls stress-controlled glide regime. It remains unclear whether the crystal plasticity serves only as a precursory stage to rupture and high-velocity slip or is itself responsible for both instability and the thermal transient. There are similarities between accelerating plastic slip leading to rupture and aseismic creep bursts (tremor) that emphasize the mechanistic complexity of deep faulting, and the need to extend consideration beyond that of a simple brittle-ductile response. The occurrence of tremor bursts fall within the depth range of "paradoxical" pseudotachylyte and provides a circumstantial link between active tectonics and the geologic record that merits examination.

  18. 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.

  19. 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

  20. Lithium and magnesium isotopes fractionation by zone melting

    NASA Astrophysics Data System (ADS)

    Akimov, D. V.; Egorov, N. B.; Dyachenko, A. N.; Pustovalova, M. P.; Podoinikov, I. R.

    2016-06-01

    The process of changing isotopic composition of the lithium and magnesium salts was studied by using the process of zone melting. It was founded in the paper that the process of separation of the lithium isotopes is more effective than for magnesium isotopes when the conditions of process were the same. The coefficients of isotopes separation were calculated and have the next value: α = 1.006 for 26Mg isotope and α = 1.0022 for 6Li isotope.

  1. 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).

  2. 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).

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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. PMID:21454786

  8. 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.

  9. 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.

  10. 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

    2013-08-01

    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. PMID:23841755

  11. 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.

  12. 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.

  13. Partial Melting and Assimilation of the Roof of Melt Lens, and New Perspectives of Hydrothermal Systems Beneath Fast-Spread Ocean Ridges

    NASA Astrophysics Data System (ADS)

    Miyashita, S.; Adachi, Y.

    2014-12-01

    Numerous anatectic blocks derived from a sheeted dike complex appear in a block-rich zone between the foliated gabbro and a large plagiogranite complex in the Oman ophiolite. Five blocks from blocks 1 to 5 in a descending stratigraphic order are studied. Host rocks are quart diorite (block 1), diorite (block 2), massive gabbronorite (block 3), and foliated gabbronorite and olivine gabbronorite (blocks 4 and 5). The textural and petrographical features vary depending on the depths of the blocks. Block 1 preserves a doleritic texture despite of the presence of a granulite facies mineral assemblage. Abundant mafic and quartz globules in blocks 2 and 3 suggest processes of in-situ partial melting and melt accumulation. Hornblende occurs in the globules but is absent from the matrix. Hornblendes and quartz decrease with increasing depth, suggesting the progressive extraction of partial melts from the blocks. Assimilation of the host gabbro by the expelled silicic melts is shown by the co-existence of quartz and olivine. The SiO2 and trace element contents of the blocks decrease with increasing depths. With decreasing REE contents, there is an increase in positive Eu anomalies, and the REE patterns vary from flat to patterns that are depleted in light REEs. The rates of partial meting evaluated by a mass balance equation and trace element contents increase with depths. Inverted pigeonite appears in the blocks 3 to 5, and is absent at a shallower level of the blocks 1 and 2. The thermal gradient in the block-rich zone, ~100 m thick, was very high more than ~1°C/1m. At the shallower level of the block-rich zone, the temperatures do not attain the minimum stability limit of pigeonites, ~ 965 °C. Elevating temperatures with depth result in the appearance of pigeonites. However, they are limited inside the blocks due to varying Mg# values within the blocks. Efficient extraction of partial melts, and/or intensive effects of assimilation with gabbroic magmas at the margin of

  14. 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. PMID:21536910

  15. 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

  16. Wide-angle seismic reflections as direct indictors of partial melt beneath an andesite arc

    NASA Astrophysics Data System (ADS)

    Stern, T. A.; Benson, A.; Stratford, W. R.; Gamble, J. A.

    2011-12-01

    ~ 80% drop in the S-wave seismic velocity (Vs) and a modest (10%) drop in Vp. Such a change in wave-speeds is consistent with R3 representing the upper surface of a volume where the partial melt content may be as high as 12%. We propose this volume to be primitive basaltic melt from the mantle wedge that has penetrated under the arc into a relatively narrow zone and has become stalled at a thermal boundary layer in the upper mantle. Fractionation of the mantle melt is proposed to occur at this level.

  17. 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.

  18. Evidence in Support of Sulfide Partial Melting at Broken Hill Australia and Broken Hill, South Africa

    NASA Astrophysics Data System (ADS)

    Sparks, H. A.; Mavrogenes, J. A.

    2004-05-01

    In the past there has been much debate over the genesis of Broken Hill, Australia and Broken Hill, South Africa since many of the original characteristics have been obscured by high-grade metamorphism and intense deformation. The idea that a sulfide melt can form from partial melting of pre-existing ore during metamorphism was first proposed by Brett and Kullerud (1967 Economic Geology) and Lawrence (1967 Mineral Deposita), but was largely ignored due to a lack of direct field and experimental evidence. However, recent experimental support in the system PbS-Fe0.96S-ZnS-(1% Ag2S) determined a quaternary eutectic melt at 795 700° C at 5 kbar (Mavrogenes et al., 2001 Economic Geology), clear indirect evidence that at least some of the Broken Hill lodes partially melted during metamorphism. Features at both Broken Hill, Australia and Broken Hill, South Africa are consistent with the formation of a sulfide partial melt. At Broken Hill, Australia, abundant polyphase sulfide melt inclusions (SMINCs) have been identified within garnetite and quartz surrounding remobilised ore. Preliminary examination of garnetites associated with remobilised ore from Broken Hill, South Africa also reveals SMINCs similar to those documented at Broken Hill, Australia. This establishes that sulfide partial melting occurred, at least in the higher metamorphic grade portion of Broken Hill, South Africa. Development of a high temperature heating stage allows reflected light monitoring of submerged SMINCs during heating. The results indicate that quartz-hosted SMINCs from Broken Hill, Australia partially melt at temperatures as low as 420 700° C with total homogenisation occurring at temperatures well below peak metamorphic temperatures (810 700° C). Low melting point chalcophile elements (LMCE) increase in abundance as homogenisation temperatures decrease. This observation along with analysed bulk sulfide melt composition fractionation trends of Pb, Cu, Sb, Ag and Au similar to those observed

  19. 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.

  20. 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. PMID:9092469

  1. 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

  2. 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.

  3. Trace element behavior and P-T-t evolution during partial melting of exhumed eclogite in the North Qaidam UHPM belt (NW China): Implications for adakite genesis

    NASA Astrophysics Data System (ADS)

    Zhang, Guibin; Niu, Yaoling; Song, Shuguang; Zhang, Lifei; Tian, Zuolin; Christy, Andrew G.; Han, Lei

    2015-06-01

    We have studied trace element behavior and timing of decompression melting of UHP rocks during exhumation recorded in the magmatic products, i.e., the melt phase (leucosomes), cumulate (garnetite) and residue (amphibolitized eclogite) from a single outcrop in the south Dulan area, North Qaidam UHPM belt, NW China. Two distinct episodes of partial melting are recognized. First, Grt-free tonalitic-trondhjemitic leucosome melts with higher silica crystallized at 424.0 ± 2.7 Ma. Garnets grew in the leucosome melt but fractionated out to form garnetite cumulates along with Ti-rich phases (rutile and titanite), strengthening the adakitic signature of the leucosome. Later Grt-bearing leucosome melts with an age of 412.4 ± 2.9 Ma cross-cut boudins and layers of amphibolitized eclogite. Geochemical investigation of bulk-rocks and in situ minerals verifies the genetic relationship between the amphibolitized eclogite and the tonalitic-trondhjemitic melts. Zircons from the amphibolitized eclogite have older (> 700 Ma) protolith ages, with subsequent eclogite-facies metamorphism, retrograde granulite-facies overprinting and partial melting. Phase modeling and Zr-in-rutile thermometry calculations in combination with zircon geochronology reveal the evolution P-T-t path for the exhumation and the partial melting of the deeply subducted continental crust at the North Qaidam subduction zone in the Early Paleozoic.

  4. Influence of melt viscosity of basaltic and andesitic composition on seismic attenuation in partially molten gabbronorite

    NASA Astrophysics Data System (ADS)

    Fontaine, Fabrice R.; Neuville, Daniel R.; Ildefonse, Benoit; Mainprice, David

    2008-04-01

    The characteristic frequencies at which two different melt-related attenuation mechanisms occur in partially molten gabbronorite are computed as a function of aspect ratios of the melt-filled cracks, and the melt viscosity. The computations were done for basaltic and andesitic melts. The melt viscosity is constrained by (i) laboratory measurements performed in the range 10 8-10 14 Pa s with a creep apparatus and in the range 10 -1 to 10 5 Pa s with a rotational Couette viscometer, and (ii) modeling of viscosity at high temperatures. The results of the characteristic frequency calculations suggest that melt squirt flow is a viable attenuation mechanism at seismic frequencies for aspect ratio of melt inclusions in the range 10 -3 to 10 -2 for the andesite, and 10 -4 to 10 -3 for the two basalts.

  5. 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.

  6. H2O-fluid-saturated melting of subducted continental crust facilitates exhumation of ultrahigh-pressure rocks in continental subduction zones

    NASA Astrophysics Data System (ADS)

    Labrousse, L.; Duretz, T.; Gerya, T.

    2015-10-01

    We present two-dimensional numerical models of plate subduction and collision inspired by the Scandinavian Caledonian orogeny to investigate the possible impact of continental crust partial melting on the exhumation of ultra-high pressure metamorphic rocks. Three possible reactions were tested: low temperature solidus representing H2O-fluid-saturated partial melting, and two end-member reaction curves for dehydration melting. Thermo-mechanical effects of partial melting were implemented as (1) a viscosity decrease as a determined rheologically critical melt percentage was reached (here 0.1), (2) a change in effective heat capacity and adiabatic heating/cooling accounting for a latent heat term in the heat equation. Among the 3 tested reactions, only H2O-fluid-saturated partial melting drastically modifies the collision dynamics from the non-melting reference model holding all other parameters constant. A substantially low general viscosity truncation (here 1017 Pa s) is needed to properly resolve the effect of partial melting on deep collision processes. Low temperature melting indeed induces the development of a low viscosity buoyant plume prior to slab detachment, where migmatites exhume from UHP conditions at rates and with pressure-temperature paths similar to the natural values acknowledged for the Norwegian Caledonides. High temperature melting has no drastic influence on early collision dynamics. While positive buoyancy remains the first order driver for the exhumation of buried continental rocks, exhumation initiates in these cases with eduction subsequent to slab detachment. Melting and formation of a migmatite plume can later occur along decompression path while continental crust undergoes thermal reequilibration at temperatures above 900 °C. Some of the partially molten material can also relaminate in the overriding plate rather than exhume within the collision zone. Even if minor in terms of amount of magma produced, H2O-fluid-saturated partial melting

  7. 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

  8. 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.

  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. 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.

  11. Chloride-bearing liquids and partial melting of mantle eclogites: experimental study and application to the diamond-forming processes.

    NASA Astrophysics Data System (ADS)

    Safonov, Oleg

    2010-05-01

    -13000C [8] produces CO2-depleted aluminosilicate melts with up to 46 wt. % of SiO2, 9-10 wt. % of K2O, 2-5 wt. % of Cl, whose SiO2 and K2O contents resemble the silica-poor varieties of melt relics in the eclogite xenoliths [1, 2]. Presence of KCl in the fluid intensifies melting, that is related both to high Cl content in the melt and its enrichment in K2O via K-Na exchange reactions with the immiscible chloride melt. The ratio K2O/Cl in the melts increases with the increase of the KCl content in the system and reaches 2.5-3.5 in the melts coexisting with immiscible chloride liquids. No additional crystalline phases, except Grt, Cpx, and Phl, were observed in the above experiments. However, experiments in the model system jadeite-diopside-KCl(±H2O) at 4-5 GPa shows, that KCl liquids provoke formation of ultrapotassic Cl-bearing silica-rich (i.e. 63-65 wt. % of SiO2) melt, which is able to produce sanidine and Al-celadonite-phlogopite mica, which are observed in partially molten eclogites [2]. Dissolution of pyrope in KCl-rich liquids results in formation of spinel and olivine, which are also common products of garnet breakdown within the zones of partial melting in eclogite xenoliths [1, 2]. Thus, the reviewed experiments imply that the KCl-bearing liquids could serve as triggers for formation of the wide varieties of K-rich aluminosilicate and carbonate-silicate melts during the eclogite melting in the mantle. Nevertheless, compositional variability of the produced melts, as well as formation of some crystalline phases (sanidine, mica, spinel, olivine) during this process could be a result of highly localized action of these liquids. The study is supported by the RFBR (10-05-00040), Russian President Grant (MD-130.2008.5) and Russian Science Support Foundation. References: [1] Misra et al. (2004) Contrib. Mineral. Petrol., V. 146, P. 696-714; [2] Shatsky et al. (2008) Lithos, 105, 289-300; [3] Izraeli et al. (2001) Earth Planet. Sci. Lett., 5807, 1-10; [3] Zedgenizov

  12. Partial melting of the Allende (CV3) meteorite - Implications for origins of basaltic meteorites

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    Eucrites and angrites are distinct types of basaltic meteorites whose origins are poorly known. Experiments in which samples of the Allende (CV3) carbonaceous chondrite were partially melted indicate that partial melts can resemble either eucrites or angrites, depending only on the oxygen fugacity. Melts are eucritic if this variable is below that of the iron-wuestite buffer or angritic if above it. With changing pressure, the graphite-oxygen redox reaction can produce oxygen fugacities that are above or below those of the iron-wuestite buffer. Therefore, a single, homogeneous, carbonaceous planetoid greater than 110 kilometers in radius could produce melts of drastically different composition, depending on the depth of melting.

  13. 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

  14. Electrical conductivity of partially-molten olivine aggregate and melt interconnectivity in the oceanic upper mantle

    NASA Astrophysics Data System (ADS)

    Laumonier, Mickael; Frost, Dan; Farla, Robert; Katsura, Tomoo; Marquardt, Katharina

    2016-04-01

    A consistent explanation for mantle geophysical anomalies such as the Lithosphere-Astenosphere Boundary (LAB) relies on the existence of little amount of melt trapped in the solid peridotite. Mathematical models have been used to assess the melt fraction possibly lying at mantle depths, but they have not been experimentally checked at low melt fraction (< 2 vol. %). To fill this gap, we performed in situ electrical conductivity (EC) measurement on a partially-molten olivine aggregate (Fo92-olivine from a natural peridotite of Lanzarote, Canary Islands, Spain) containing various amount of basaltic (MORB-like composition) melt (0 to 100%) at upper mantle conditions. We used the MAVO 6-ram press (BGI) combined with a Solartron gain phase analyser to acquire the electrical resistance of the sample at pressure of 1.5 GPa and temperature up to 1400°C. The results show the increase of the electrical conductivity with the temperature following an Arrhenius law, and with the melt fraction, but the effect of pressure between 1.5 and 3.0 GPa was found negligible at a melt fraction of 0.5 vol.%. The conductivity of a partially molten aggregate fits the modified Archie's law from 0.5 to 100 vol.%. At melt fractions of 0.25, 0.15 and 0.0 vol.%, the EC value deviates from the trend previously defined, suggesting that the melt is no longer fully interconnected through the sample, also supported by chemical mapping. Our results extend the previous results obtained on mixed system between 1 and 10% of melt. Since the melt appears fully interconnected down to very low melt fraction (0.5 vol.%), we conclude that (i) only 0.5 to 1 vol.% of melt is enough to explain the LAB EC anomaly, lower than previously determined; and (ii) deformation is not mandatory to enhance electrical conductivity of melt-bearing mantle rocks.

  15. 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

  16. 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

  17. Receiver function constraints on crustal seismic velocities and partial melting beneath the Red Sea rift and adjacent regions, Afar Depression

    NASA Astrophysics Data System (ADS)

    Reed, Cory A.; Almadani, Sattam; Gao, Stephen S.; Elsheikh, Ahmed A.; Cherie, Solomon; Abdelsalam, Mohamed G.; Thurmond, Allison K.; Liu, Kelly H.

    2014-03-01

    The Afar Depression is an ideal locale for the investigation of crustal processes involved in the transition from continental rifting to oceanic spreading. To provide relatively high resolution images of the crust beneath the Red Sea rift (RSR) represented by the Tendaho graben in the Afar Depression, we deployed an array of 18 broadband seismic stations in 2010 and 2011. Stacking of about 2300 receiver functions from the 18 and several nearby stations along the ~200 km long array reveals an average crustal thickness of 22±4 km, ranging from ~17 km near the RSR axis to 30 km within the overlap zone between the Red Sea and Gulf of Aden rifts. The resulting anomalously high Vp/Vs ratios decrease from 2.40 in the southwest to 1.85 within the overlap zone. We utilize theoretical Vp and melt fraction relationships to obtain an overall highly reduced average crustal Vp of ~5.1 km/s. The melt percentage is about 10% beneath the RSR while the overlap zone contains minor quantities of partial melt. The observed high Vp/Vs values beneath most of the study area indicate widespread partial melting beneath the southwest half of the profile, probably as a result of gradual eastward migration of the RSR axis. Our results also suggest that the current extensional strain in the lower crust beneath the region is diffuse, while the strain field in the upper crust is localized along narrow volcanic segments. These disparate styles of deformation imply a high degree of decoupling between the upper and lower crust.

  18. 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

  19. 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

    2014-01-01

    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

  20. 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

  1. 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

  2. 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.

  3. 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

  4. 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

  5. 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

  6. Melting curve of CaCO3 with implications for the presence of melt in the transition zone

    NASA Astrophysics Data System (ADS)

    Li, Z.; Li, J.

    2014-12-01

    Carbonates are important carriers for carbon exchange between the surface and interior of the Earth and therefore their melting behavior bears directly on the deep carbon cycle. Previous studies showed that the solidus temperature of carbonated silicate spans a wide range of temperature due to composition variations in the starting materials. In order to provide fundamental data for thermodynamic calculations, the melting curve of pure CaCO3 was measured up to 22 GPa using an in-situ electrical method in this study. The measurement was realized by monitoring abrupt changes in electrical conductivity upon melting. The results showed that the melting temperature of CaCO3 increases rapidly from 2 to 8 GPa, consistent with the existing data (Irving and Wyllie, 1975; Suito et al., 2001). Our new data at high pressures reveal that the CaCO3 melting curve flattens around 8GPa, starts to decrease until 15 GPa, and then increases again from 15 to 22 GPa. The changes in the melting slope reflect the evolution of the melt compressibility with pressure and the sub-solidus structural phase transformations. The inferred CaCO3 melt density from melting curve slope is slightly smaller than basaltic melt at same pressureand temperature. The unusual negative slope melting curve between 8 and 15 GPa likely indicates the presence of melt around 400-500 Km depth, which may explain some of observed low-velocity zones in the transition zone (Vinnik & Farra, 2006). Reference: Irving AJ, Wyllie PJ (1975) Subsolidus and melting relationshipsfor calcite, magnesite and the join CaCO3-MgCO3 to 36 kb. GeochimCosmochimActa 39: 35-53. Suito K, Namba J, Horikawa T, Taniguchi Y, Sakurai N, Kobayashi M, Onodera A, Shimomura O, Kikegawa T (2001) Phase relations of CaCO3 at high pressure and high temperature. Am Mineral 86(9):997-1002. Vinnik L. & Farra V. (2006) S velocity reversal in the mantle Transition Zone. Geophysical Research Letters 33, L18316.

  7. 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.

  8. Partial and integral enthalpies of mixing of Cu-Fe-Ti melts at 1873 K

    NASA Astrophysics Data System (ADS)

    Abdulov, A. R.; Dreval', L. A.; Agraval, P. G.; Turchanin, M. A.

    2009-10-01

    The partial enthalpy of mixing of titanium in Cu-Fe-Ti melts are studied by high-temperature isoperibolic calorimetry at 1873 K in the composition range x Ti = 0-0.6 along three sections with a ratio x Fe / x Cu = 1/3, 1, and 3. The integral enthalpy of mixing of the ternary melts is calculated by integrating the Gibbs-Duhem equation and is described in terms of the Redlich-Kister-Muggianu model. Function Δ H demonstrates negative values over a wide concentration range. The contribution of a ternary interaction to the enthalpy of mixing of Cu-Fe-Ti melts is mainly positive. The first partial enthalpies of mixing of Al, Sn, Si, Y, Zr, Hf, and Ni with Cu-Fe-Ti melts are negative and indicate an increase of the thermodynamic stability of the liquid phase upon the dissolution of these additions.

  9. 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

  10. 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. PMID:23112158

  11. 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.

  12. Results of partial melting experiments on chondritic precursors of basaltic achondrites. [Abstract only

    NASA Technical Reports Server (NTRS)

    Boesenberg, J. S.; Delaney, J. S.

    1994-01-01

    Recent partial melting experiments on Murchison produced eucrite like glasses at reducing conditions. Although the glasses were remarkably similar to eucrites, the Fe/Mn ratio of the glasses was too high and the O isotopes cannot match eucrites. Mixing 70% H chondrite with 30% CM chondrite makes a potential precursor that satisfies the O isotope constraint on the eucrites. From experiments on both synthetic Murchison and a simplified version of the H70-CM30 mixture, simple partial melting of any individual or combination of known chondritic meteorites is incapable of producing eucritic glasses that have the appropriate Fe/Mn, Fe/(Fe + Mg), and O isotope ratios. In order to satisfy the Fe-Mn-Mg constraints imposed by the eucrites, both reduction of FeO to Fe-metal and olivine fractionation must occur in the precursor before partial melting is allowed to occur and produce the eucritic glass. To test this hypothesis, partial melting experiments on both Murchison and a mixture of 70% Allegan (H6)-30% Murchison (CM2) were conducted. The results of these new experiments show that to satisfy the O isotopes, Fe/Mn ratio, and Fe/(Fe + Mg) ratio, approximately 12% reduction of FeO to Fe-metal (in the silicate portion) and 20% olivine fractionation is required within the H-CM precursor to permit the formation of eucrites by partial melting. The sequence of FeO reduction and mantle fractionation permits very eucritic glasses to be produced. The problem that many remain with the H-CM precursor, however, is an overabundance of alkali elements. Correlations between temperature, O fugacity, and composition have also been found within our experiments. A basaltic achondrite precursor formed by mixing H and CM chondrites and constrained by O isotopes and Fe-Mn-Mg is compatible with a model of natural eucrites having formed by partial melting after metal and olivine fractionation in that precursor.

  13. 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).

  14. An experimental study of partial melting and fractional crystallization on the HED parent body

    NASA Astrophysics Data System (ADS)

    Ashcroft, Helen O.; Wood, Bernard J.

    2015-11-01

    We have performed an experimental and modeling study of the partial melting behavior of the HED parent body and of the fractional crystallization of liquids derived from its mantle. We estimated the mantle composition by assuming chondritic ratios of refractory lithophile elements, adjusting the Mg# and core size to match the density and moment of inertia of Vesta, and the compositions of Mg-rich olivines found in diogenites. The liquidus of a mantle with Mg# (=100*[Mg/(Mg+Fe)]) 80 is ~1625 °C and, under equilibrium conditions, the melt crystallizes olivine alone until it is joined by orthopyroxene at 1350 °C. We synthesized the melt from our 1350 °C experiment and simulated its fractional crystallization path. Orthopyroxene crystallizes until it is replaced by pigeonite at 1200 °C. Liquids become eucritic and crystal assemblages resemble diogenites below 1250 °C. MELTS correctly predicts the olivine liquidus but overestimates the orthopyroxene liquidus by ~70 °C. Predicted melt compositions are in reasonable agreement with those generated experimentally. We used MELTS to determine that the range of mantle compositions that can produce eucritic liquids and diogenitic solids in a magma ocean model is Mg# 75-80 (with chondritic ratios of refractory elements). A mantle with Mg# ~ 70 can produce eucrites and diogenites through sequential partial melting.

  15. Evidence of partial melting beneath a continental margin: case of Dhofar, in the Northeast Gulf of Aden (Sultanate of Oman)

    NASA Astrophysics Data System (ADS)

    Basuyau, C.; Tiberi, C.; Leroy, S.; Stuart, G.; Al-Lazki, A.; Al-Toubi, K.; Ebinger, C.

    2010-02-01

    Gravity data and P-wave teleseismic traveltime residuals from 29 temporary broad-band stations spread over the northern margin of the Gulf of Aden (Dhofar region, Oman) were used to image lithospheric structure. We apply a linear relationship between density and velocity to provide consistent density and velocity models from mid-crust down to about 250 km depth. The accuracy of the resulting models is investigated through a series of synthetic tests. The analysis of our resulting models shows: (1) crustal heterogeneities that match the main geological features at the surface; (2) the gravity edge effect and disparity in anomaly depth locations for layers at 20 and 50 km; (3) two low-velocity anomalies along the continuation of Socotra-Hadbeen and Alula-Fartak fracture zones between 60 and 200 km depth; and (4) evidence for partial melting (3-6 per cent) within these two negative anomalies. We discuss the presence of partial melting in terms of interaction between the Sheba ridge melts and its along-axis segmentation.

  16. 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.

  17. 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.

  18. 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

  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. Are seismic wave velocities and anisotropies reliable proxies for partial melts?

    NASA Astrophysics Data System (ADS)

    Lee, Amicia; Torvela, Taija; Lloyd, Geoffrey; Walker, Andrew

    2015-04-01

    Partial melts and their segregation weaken mineral crystallographic alignment, resulting in a decrease in seismic anisotropy (AV). Furthermore, introduction of melt induces a drop in seismic wave velocities, especially for shear (Vs) but also compressional (Vp) waves, although some solid-state processes can also lead to velocity drops. Thus, decreases in AV and/or V are often used to infer the presence and even the amount of melt in both the crust and mantle, for example via the Vp/Vs ratio. However, evidence is accumulating that the relationship between melt fraction and seismic properties is not straight-forward. We consider how varying melt fraction (f) might affect crustal seismic properties. Our modelling approach is based on electron backscattered diffraction (EBSD) analysis of crystallographic preferred orientation (CPO) patterns from granulite facies sheared migmatites. The CPO data are used to model the seismic properties of rocks with different solid/melt proportions. Subsequently, melt was simulated via an isotropic elastic stiffness matrix and combined mathematically with the CPO-derived seismic properties, and seismic properties then recalculated to take into account the presence of melt. These melt models, therefore, predict changes in seismic properties at different f. The models show that low (c. f < 0.15) and high (0.7 < f < 1) values affect seismic properties much more than the 'crystal mush' part (0.1 < f < 0.7): velocities (V) and anisotropies (AV) for both low and high f drop rapidly but 'plateau' at intermediate f. Our results imply that V and, especially, AV may not be reliable proxies for the amount of crustal melt present. Seismic wave behaviour in crystal-supported (0.1 < f < 0.7) material may be controlled by the solid rather than the melt phase.

  1. 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

  2. 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

  3. Reaction between MORB-Pyroxenite-derived Partial Melts and Subsolidus Peridotite at 3 GPa and Generation of Alkalic Ocean Island Basalts

    NASA Astrophysics Data System (ADS)

    Mallik, A.; Dasgupta, R.

    2010-12-01

    Major element characteristics of ocean island basalts (OIBs) source heterogeneities are a subject of major debate that primarily stems from the fact that neither volatile-free fertile peridotite nor subducted oceanic crust (silica-excess MORB-pyroxenite at mantle depths) produce partial melts that match the major element chemistry of alkalic OIBs [1]. This has led to exploring many exotic lithologies as OIB sources. No studies, however, have systematically explored the evolution of MORB-pyroxenite partial melts owing to reaction with peridotite. Because the solidus of subducted crust intersects with mantle adiabat deeper than the peridotite solidus [2,3], partial melt extracted from MORB-pyroxenite will react with subsolidus peridotite and form secondary pyroxenite [4,5]. Here we explore whether such a melt-rock reaction between pyroxenite partial melt and peridotite can produce alkalic OIBs. We performed reaction experiments between partial melt of the anhydrous MORB-like pyroxenite [3] and fertile peridotite KLB-1. Experiments were performed using a piston-cylinder apparatus and Pt/Gr capsules at 1375°C and 3 GPa, a condition where volatile-free MORB-pyroxenite is ~10% melted [4]. The added fraction of andesitic melt varied from ~8-33%. Melt was introduced either in a layered geometry or mixed homogeneously with peridotite to simulate channelized and porous flow, respectively. All the experiments produced a residual assemblage of olivine+opx+cpx±garnet coexisting with reacted partial melts. Layered experiments produced a zone of (± garnet-)websterite separating the pool of melt from four-phase lherzolite. With increasing opx mode from ~16 to 35 wt.% in the residue, reacted melts in the layered experiments show a systematic decrease in SiO2 (~55 to 45 wt%) and Al2O3 (~15 to 13 wt%), and increase in MgO (~5.4 to 14.9 wt%) and CaO (~7 to 14 wt%). TiO2 varies from ~2.4 to 5.6 wt%, Na2O from ~2.2 to 4.2 wt% and FeO* from ~ 6.8 to 8.1 wt%. Experiments with

  4. Tracing partial melting and subduction-related metasomatism in the Kamchatkan mantle wedge using noble gas compositions

    NASA Astrophysics Data System (ADS)

    Hopp, Jens; Ionov, Dmitri A.

    2011-02-01

    We determined noble gas composition of minerals separated from mantle-derived xenoliths hosted by andesites in the active Avacha volcano, Kamchatka peninsula, Russia in order to better constrain the provenance and nature of fluids involved in partial melting and metasomatism in the mantle wedge. The lithospheric mantle beneath Avacha mainly consists of spinel harzburgites produced by high degrees of melt extraction. Data on coarse olivine separated from seven harzburgite xenoliths constrain fluid regime during flux melting in arc settings. Pyroxenes from two websterite veins cross-cutting the harzburgites characterize post-melting metasomatism by subduction-related melts or fluids. 3He/4He-ratios of 5.2 ± 0.6 to 8.1 ± 0.3 RA obtained on both olivines and pyroxenes overlap the highest values reported for volcanic rocks from Kamchatka and fall into the typical range of continental lithospheric mantle worldwide. This rules out significant contributions of slab-derived radiogenic 4He*. The highest 40Ar/36Ar ratios are 400; Ne and Xe isotope ratios are indistinguishable from those in the air. We consider the slab as the initial source of a major portion of these ‘atmospheric’ gases. Element composition of noble gases in olivine differs markedly from that in vein pyroxene indicating that the composition of the fluid phase involved in partial melting was distinct from that during metasomatism. In particular, the harzburgites and veins define distinct linear trends on plots of 3He/36Ar vs. 40Ar/36Ar and of 132Xe/36Ar vs. 40Ar/36Ar. Estimates of ‘mantle’ 132Xe/36Ar values by extrapolating 40Ar/36Ar to 40 000 yield unrealistically high values of 0.5-0.8 (olivine) and 4-5 (vein pyroxene) ruling out a simple two-component mixing of mantle and atmospheric noble gases. Rather a two-stage mixing process applies: (1) Changes in relative proportions of slab-derived element-fractionated atmospheric gases and ‘mantle’ produce two hybrid mixtures dominated by atmospheric

  5. 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

  6. Thermocapillary flow and melt/solid interfaces in floating-zone crystal growth under microgravity

    NASA Technical Reports Server (NTRS)

    Lan, C. W.; Kou, Sindo

    1990-01-01

    Computer simulation of steady-state axisymmetrical heat transfer and fluid flow was conducted to study thermocapillary flow and melt/solid interfaces in floating-zone crystal growth under microgravity. The effects of key variables on the extent of thermocapillary flow in the melt zone, the shapes of melt/solid interfaces and the length of the melt zone were discussed. These variables are: (1) the temperature coefficient of surface tension (or the Marangoni number), (2) the pulling speed (or the Peclet number), (3) the feed rod radius, (4) the ambient temperature distribution, (5) the heat transfer coefficient (or the Biot number), and (6) the thermal diffusivity of the material (or the Prandtl number).

  7. Receiver function constraints on crustal seismic velocities and partial melting in the Red Sea Rift, Central Afar

    NASA Astrophysics Data System (ADS)

    Reed, C. A.; Almadani, S.; Gao, S. S.; Elsheikh, A. A.; Cherie, S.; Thurmond, A. K.; Liu, K. H.

    2013-12-01

    The Afar Depression is currently a unique locale for the investigation of crustal and mantle processes involved in the transition from continental to oceanic rifting. To provide high-quality images of the crust and upper mantle beneath the Red Sea Rift in Central Afar, we deployed an array of 18 broadband seismic stations in 2010 and 2011. Here we report receiver function stacking results to investigate crustal properties of this presumably incipient oceanic rift. Stacking of approximately 2200 radial receiver functions along the ~200 km long array reveals an average crustal thickness of 22 km, ranging from nearly 18 km within the Red Sea Rift axis to approximately 30 km within the overlap zone between the Red Sea and Gulf of Aden rift axes. The resulting anomalously high Vp/Vs ratios systematically decrease toward the northeast, ranging from 2.40 southwest of the Tendaho Graben to 1.85 within the overlap zone. We utilize theoretical Vp and melt fraction relationships to constrain a highly reduced average crustal P-velocity of 5.0 km/s within the rift axis, which is characterized by a melt percentage of ~11% confined primarily to the lower crust while the overlap zone contains relatively minor quantities of partial melt. An observed asymmetric distribution of high Vp/Vs values within the Tendaho Graben, as well as regionally maximum values on the southwestern rift flank, suggest crustal magmas either delivered from off-axis subcrustal magma chambers or as material present as residuum from the Red Sea Rift axis migration. Comparisons of these crustal properties beneath the Red Sea Rift and those found beneath mature mid-ocean ridges suggest the locus of extensional strain within the Central Afar is currently diffuse and in the process of localizing toward the Tendaho Graben accompanying the northeastward migration of the Afar Triple Junction.

  8. Experimental partial melting of the Allende (CV) and Murchison (CM) chondrites and the origin of asteroidal basalt

    NASA Astrophysics Data System (ADS)

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

    1993-05-01

    Following the investigation of Jurewicz et al. (1991) on the composition of partial melts of eucrites and angrites, this study investigates partial melts of the Allende and Murchison chondrites and details the anhydrous phase relations of both chondrites at 1 atm, under temperatures and oxygen fugacities plausigle for the formation of basaltic meteorites. It was found that, in general, ambient oxygen fugacity exerts a strong influence on the compositions of partial melts of chondrites by controlling the amount of FeO available to the silicate system. At high f(O2), angritic magmas are produced, whereas eucritic melts are produced at low levels of f(O2).

  9. Experimental partial melting of the Allende (CV) and Murchison (CM) chondrites and the origin of asteroidal basalt

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    Following the investigation of Jurewicz et al. (1991) on the composition of partial melts of eucrites and angrites, this study investigates partial melts of the Allende and Murchison chondrites and details the anhydrous phase relations of both chondrites at 1 atm, under temperatures and oxygen fugacities plausigle for the formation of basaltic meteorites. It was found that, in general, ambient oxygen fugacity exerts a strong influence on the compositions of partial melts of chondrites by controlling the amount of FeO available to the silicate system. At high f(O2), angritic magmas are produced, whereas eucritic melts are produced at low levels of f(O2).

  10. 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

  11. Mineral Physics-Based Interpretation of the LAB: Partial Melting or Sub-Solidus Processes?

    NASA Astrophysics Data System (ADS)

    Olugboji, T. M.; Karato, S.; Park, J. J.

    2012-12-01

    Recent seismological studies using high-frequency body waves show relatively sharp and large velocity reduction at the oceanic lithosphere-asthenosphere boundary (LAB). We explore possible models for such seismological signature of the LAB using the latest mineral-physics observations. The key features that need to be explained by any viable model include (1) a sharp (<20 km width) and a large (5-10%) velocity drop, (2) at ~70 km depth in the old oceanic upper mantle and (3) the age-dependent LAB depth in the young oceanic upper mantle. We examine the plausibility of both partial melt and sub-solidus models. Because many of the LABs in the old oceanic regions are located in areas where temperature is ~1000-1200 K, significant partial melting is difficult, and some mechanisms of melt accumulation are required to explain a large velocity reduction. We examine the layered melt model and a model of melt accumulation at the LAB and show that both models are difficult to reconcile with seismological observations. We present a detailed analysis of a new version of sub-solidus model where the role of grain-boundary sliding is included. A broad range of parameter space is explored based on the statistical analysis of the experimental data. In contrast to the old model where only the absorption-band behavior was assumed, the new model predicts an age-dependent LAB structure including the age-dependent LAB depth and its sharpness.

  12. 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.

  13. Influence of melt motion on the shape of molten zone in the FZ crystal growth process

    NASA Astrophysics Data System (ADS)

    Dadzis, K.; Muiznieks, A.; Rudevics, A.; Riemann, H.; Ludge, A.

    2007-06-01

    In numerical simulations of the floating-zone crystal growth process, the shape of phase boundaries is unknown beforehand and must be obtained as a part of the solution. One of the factors, which may influence the shape of phase boundaries significantly, is convective heat transfer in the molten zone. The present paper offers an analysis based on mathematical modelling of the influence of the melt motion on the shape of phase boundaries by investigating a specific 2" floating zone growth system and compares the modelling results with experiment. A needle-eye inductor is used in the growth system leading to curved boundaries of the molten zone and to strong high-frequency electromagnetic forces in the melt. The influence of the melt motion on the crystallization interface is also estimated analytically. Figs 12, Refs 8.

  14. 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

  15. Partial melting of lower crust at 10-15 kbar: constraints on adakite and TTG formation

    NASA Astrophysics Data System (ADS)

    Qian, Qing; Hermann, Jörg

    2013-06-01

    The pressure-temperature ( P- T) conditions for producing adakite/tonalite-trondhjemite-granodiorite (TTG) magmas from lower crust compositions are still open to debate. We have carried out partial melting experiments of mafic lower crust in the piston-cylinder apparatus at 10-15 kbar and 800-1,050 °C to investigate the major and trace elements of melts and residual minerals and further constrain the P- T range appropriate for adakite/TTG formation. The experimental residues include the following: amphibolite (plagioclase + amphibole ± garnet) at 10-15 kbar and 800 °C, garnet granulite (plagioclase + amphibole + garnet + clinopyroxene + orthopyroxene) at 12.5 kbar and 900 °C, two-pyroxene granulite (plagioclase + clinopyroxene + orthopyroxene ± amphibole) at 10 kbar and 900 °C and 10-12.5 kbar and 1,000 °C, garnet pyroxenite (garnet + clinopyroxene ± amphibole) at 13.5-15 kbar and 900-1,000 °C, and pyroxenite (clinopyroxene + orthopyroxene) at 15 kbar and 1,050 °C. The partial melts change from granodiorite to tonalite with increasing melt proportions. Sr enrichment occurs in partial melts in equilibrium with <20 wt% plagioclase, whereas depletions of Ti, Sr, and heavy rare earth elements (HREE) occur relative to the starting material when the amounts of residual amphibole, plagioclase, and garnet are >20 wt%, respectively. Major elements and trace element patterns of partial melts produced by 10-40 wt% melting of lower crust composition at 10-12.5 kbar and 800-900 °C and 15 kbar and 800 °C closely resemble adakite/TTG rocks. TiO2 contents of the 1,000-1,050 °C melts are higher than that of pristine adakite/TTG. In comparison with natural adakite/TTG, partial melts produced at 10-12.5 kbar and 1,000 °C and 15 kbar and 1,050 °C have elevated HREE, whereas partial melts at 13.5-15 kbar and 900-1,000 °C in equilibrium with >20 wt% garnet have depressed Yb and elevated La/Yb and Gd/Yb. It is suggested that the most appropriate P- T conditions for

  16. U-Th-Ba elemental fractionation during partial melting of crustal xenoliths and implications for U-series disequilibria in continental arc rocks

    NASA Astrophysics Data System (ADS)

    Brens, R.; Hickey-Vargas, R.

    2010-12-01

    Understanding U-series isotopic disequilibria of partially melted crust is integral in determining the effect that crustal assimilation has on the U-series signature of magmas. Unfortunately, U-series isotopes are too low in abundance to determine by any micro-beam technique. In this work U, Th and Ba (as a proxy for Ra) abundances were measured in quenched glass in partially melted crustal xenoliths of granitic (71-73% SiO2) composition from the Mirador volcano in the Chilean Southern Volcanic Zone using micro-beam techniques (EPMA and LA-ICP-MS). Since the crustal xenoliths are old (Miocene) they can be assumed to be at secular equilibrium. The eruption of Mirador occurred in 1979, and partial melting/quenching of the xenoliths accompanied the eruption. Any recent fractionation of U from Th or Th from Ra by partial melting will result in isotopic disequilibrium. A comparison of the ratios of the elements (Ba/Th & U/Th) in the quenched glasses with those of the whole rock reveals how much fractionation has occurred during partial melting. An EPMA was used to locate (through BSE images) and analyze glass pockets in the samples for major elements establishing a baseline idea for the composition of the potential assimilates with SiO2 contents between 54% and 75%, Al2O3 (13% - 27%) and K2O (0.2% - 7%). Laser ablation ICP-MS was used to analyze U, Th and Ba elements in the quenched partial melts, and ICP-MS was used for the whole rocks. Measured (Ba/Th glass)/(Ba/Th whole rock) are between 0.2 to 51 and (Th/U glass)/(Th/U whole rock) range from 0.3 to 7. The vast majority of analyses show barium and uranium excesses relative to Th in the glasses. Different ratios of U, Th and Ba (Ra) compared to the whole rock substantiate fractionation of these elements via partial melting. The results suggest that assimilation of partial melts of crustal rocks can play a role in producing U-series isotopic disequilibria, which is commonly observed in continental arc magmas.

  17. Subduction zone Hf-anomalies: Mantle messenger, melting artefact or crustal process?

    NASA Astrophysics Data System (ADS)

    Woodhead, Jon; Hergt, Janet; Greig, Alan; Edwards, Louise

    2011-04-01

    The origin of Hf elemental depletions in subduction zone magmas is investigated using new major- and trace-element data for cumulate xenoliths from the Mariana arc, and deep sea sediments recovered by the DSDP and ODP drilling programmes. Results indicate that most of the rare earth element (REE) and Hf inventory in the xenoliths is contained within two minerals—clinopyroxene and titanomagnetite—and that removal of a typical gabbroic fractionating assemblage reduces the depletion in Hf relative to neighbouring REE on a mantle normalised trace element diagram (commonly denoted Hf/Hf*) in the evolving magmas. Confirmation of this observation is provided by a variety of literature data from different subduction zones in which bulk-rock samples also define a positive correlation between Hf/Hf* and the silica content of the magmas. In agreement with experimental studies on REE-HFSE partitioning, we observe that the ability of clinopyroxene to influence the Hf/Hf* of fractionating magmas is associated with its aluminium content. This decoupling of Hf from the REE in differentiating arc magmas suggests that bulk rock Hf/Hf* values, when used in isolation, are unlikely to provide a robust measure of source REE-Hf characteristics, even when suites are filtered to exclude all but the most mafic samples. It may be possible to normalise data to a constant degree of fractionation, and in this way distinguish subtle changes in source Hf/Hf* but most existing datasets are of neither the size nor quality to attempt such calculations. Modification of Hf/Hf* is also seen when modelling mantle melting processes and there are strong suggestions that source variations are influenced by not only subducted sediment, which exhibits a remarkably wide range in Hf/Hf*, but also subduction zone fluids. These observations remove some of the constraints imposed on recent models that attempt to reconcile Hf isotope data with Hf-REE abundance data in some arc suites. Although a case may be

  18. 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.

  19. 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. PMID:24784219

  20. 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

  1. 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?

  2. Laboratory Measurements of Seismic Wave Attenuation in Upper-mantle Materials: the Effect of Partial Melting

    NASA Astrophysics Data System (ADS)

    Jackson, I.; Faul, U. H.; Fitz Gerald, J. D.

    2001-12-01

    The frequency-dependent mechanical behaviour expected of Earth materials at high temperature places a special premium on laboratory measurements of wave speeds and attenuation at seismic frequencies. The symposium in honour of Mervyn Paterson provides a welcome opportunity to acknowledge his vital role in the design of the specialised equipment for this purpose described by Jackson and Paterson (PEPI 45: 349-367, 1987; Pageoph 141: 445-466, 1993). This instrument allows the study of low-strain high-temperature viscoelastic behaviour through the application of torsional forced oscillation/ microcreep techniques within the P-T environment (200 MPa, 1600 K) provided by an internally heated gas apparatus. Application of these techniques to fine-grained synthetic olivine polycrystals is beginning to provide a robust basis for the understanding of seismic wave attenuation (and dispersion) in the upper mantle under sub-solidus conditions. More recently, we have begun to explore the effects of partial melting through the fabrication, characterisation and mechanical testing of a suite of fine-grained olivine polycrystals containing up to 4% basaltic melt. The most striking effect of the added melt is the appearance of a melt-related dissipation peak superimposed upon the dissipation background characteristic of melt-free materials - which varies monotonically with period and temperature. The melt-related dissipation peak is adequately modelled as a Gaussian in log X, where X = To exp(E/RT). The melt-related dissipation peak sweeps across the seismic band from period To > 100 s to To < 1 s as temperature increases across the range 1300 - 1600 K producing pronounced systematic changes in the frequency dependence of 1/Q, that may be seismologically observable. >http://rses.anu.adu.au/petrophysics/PetroHome.html

  3. 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

  4. 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

  5. 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.

  6. Measuring kinetic coefficients by molecular dynamics simulation of zone melting

    NASA Astrophysics Data System (ADS)

    Celestini, Franck; Debierre, Jean-Marc

    2002-04-01

    Molecular dynamics simulations are performed to measure the kinetic coefficient at the solid-liquid interface in pure gold. Results are obtained for the (111), (100), and (110) orientations. Both Au(100) and Au(110) are in reasonable agreement with the law proposed for collision-limited growth. For Au(111), stacking fault domains form, as first reported by Burke, Broughton, and Gilmer [J. Chem. Phys. 89, 1030 (1988)]. The consequence on the kinetics of this interface is dramatic: the measured kinetic coefficient is three times smaller than that predicted by collision-limited growth. Finally, crystallization and melting are found to be always asymmetrical and here again the effect is much more pronounced for the (111) orientation.

  7. Modeling the exhumation path of partially melted ultrahigh-pressure metapelites, North-East Greenland Caledonides

    NASA Astrophysics Data System (ADS)

    Lang, Helen M.; Gilotti, Jane A.

    2015-06-01

    Pseudosection modeling constrains the pressure-temperature (P-T) exhumation path of partially melted ultrahigh-pressure (UHP) metapelites exposed in the North-East Greenland UHP terrane. A robust peak P and T estimate of 3.6 GPa and 970 °C based on mineral assemblages in nearby kyanite eclogites is the starting point for the P-T path. Although the peak assemblage for the metapelite is not preserved, the calculated modeled peak assemblage contained substantial clinopyroxene, garnet, phengite, K-feldspar and coesite with minor kyanite and rutile. Combining the pseudosection and observed textures, the decompression path crosses the coesite-quartz transition before reaching the dry phengite dehydration melting reaction where phengite is abruptly consumed. In the range of 2.5 to 2.2 GPa, clinopyroxene is completely consumed and garnet grows to its maximum volume and grossular content, matching the high grossular rims of relict megacrysts. Plagioclase joins the assemblage and the pseudosection predicts up to 12-13 vol.% melt in the supersolidus assemblage, which contained garnet, liquid, K-feldspar, plagioclase, kyanite, quartz and rutile. At this stage, the steep decompression path flattened out and became nearly isobaric. The melt crystallization assemblage that formed when the path crossed the solidus with decreasing temperature contains phengite, garnet, biotite, 2 feldspars, kyanite, quartz and rutile. Therefore, the path must have intersected the solidus at approximately 1.2 GPa, 825 °C. The pseudosection predicts that garnet is consumed on the cooling path, but little evidence of late garnet consumption or other retrograde effects is observed. This may be due to partial melt loss from the rock. Isochemical PT-n and PT-X sections calculated along the P-T path display changes in mineral assemblage and composition that are consistent with preserved assemblages.

  8. A partial molar volume for ZnO in silicate melts.

    NASA Astrophysics Data System (ADS)

    Ledda, B.; Potuzak, M.; Dingwell, D. B.; Courtial, P.

    2004-12-01

    Trace elements in igneous petrology have, in comparison with major elements, a relevance in the petrogenetic modelling of magmatic differentiation that far outweighs their relative abundance. Optimal use of the information contained in trace element variations within igneous phases requires an accurate description of their partitioning behaviour as a function of phase composition and structure, as well as temperature and pressure. In this manner, the partial molar thermodynamic properties of trace elements in silicate melts may contribute to the petrogenetic modelling of such systems. With this in mind, a series of investigations into the partial molar properties of trace elements in silicate melts have been carried out in recent years. Here we extend this work to the analysis of the volumetric properties of ZnO in silicate melts. Densities of 8 Zn-bearing silicate melts have been determined in air in the temperature range of 1363 to 1850 K. The compositional joins investigated (sodium disilicate (NS2) - ZnO; anorthite-diopside 1 bar eutectic (AnDi) - ZnO; and diopside - petedunnite) were chosen based on the pre-existing experimental density data set, their petrological relevance and to provide a test for significant compositionally induced variations in the structural role of ZnO. The ZnO concentrations investigated range up to 25 mol% for sodium disilicate, 20 mol% for the anorthite-diopside 1 atm eutectic and 100 mol% petedunnite. Molar volumes and expansivities of all melts have been derived. The molar volumes of the present liquids all decrease with increasing ZnO content. The partial molar volume of ZnO derived here from the volumetric measurements for each binary system is the same within error. A multicomponent fit to the volumetric data for all compositions yields a value of 14.141(0.730) cm3.mol-1 at 1300 K. We find, herewith, no volumetric evidence for compositionally-induced coordination number variations for ZnO in alkali-bearing versus alkali

  9. The formation of komatiites by melt accumulation and segregation in the transition zone

    NASA Astrophysics Data System (ADS)

    Arndt, Nicholas T.; Schmeling, Harro; Kohl, Svenja

    2014-05-01

    Komatiites are highly magnesian volcanic rocks characteristic of the Archean. There are three types: Al-depleted komatiites, which have low Al/Ti, relatively high concentrations of incompatible elements and depleted HREE; Al-undepleted komatiites, with chondritic Al/Ti and slightly depleted LREE; and Al-enriched komatiites, with high Al/Ti, low concentrations of incompatible elements and extremely depleted LREE. Petrological and geochemical information indicates that these rocks formed by melting in hot mantle plumes at pressures greater than about 13GPa. In a model developed by Robin-Popieul et al (2010 J Petrol 53: 2191), Al-depleted komatiites form by batch melting and segregate at 13GPa leaving a garnet-rich residue while Al-enriched komatiites form by advanced fractional melting at shallower depth. Two aspects of the model posed problems. First, at the depths where the Al-depleted komatiite is generated, the melt is denser than mantle olivine, and it is unclear how this melt separated from its source. Second, the compositions of melts produced by fractional melting are extremely variable, depending delicately on the degree of partial melting, yet the compositions of packages of erupted Al-enriched komatiites are relatively uniform. A solution to these problems is provided by the investigation of the physics of melting and melt segregation within hot upwelling mantle described in the companion abstract by Schmeling et al. These studies showed that when the level of neutral buoyancy lies above the depth of onset of melting, the dense melt accumulates behind the solid phases within the rising plume, only to escape as high-degree melt once the plume rises above the neutral buoyancy level. This pattern of melting explains the formation of Al-depleted komatiites. Under other conditions, the melt accumulates within the plume as a series of standing waves that escape upwards as they reach the level of neutral buoyancy. This process progressively depletes the source in

  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. 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

  12. Partitioning of Ni between olivine and siliceous eclogite partial melt: experimental constraints on the mantle source of Hawaiian basalts

    NASA Astrophysics Data System (ADS)

    Wang, Zhengrong; Gaetani, Glenn A.

    2008-05-01

    Olivine is abundant in Earth’s upper mantle and ubiquitous in basaltic lavas, but rarely occurs in eclogite. Partial melts of eclogite are, therefore, not in equilibrium with olivine, and will react with peridotite as they migrate through the upper mantle. If such melts erupt at Earth’s surface, their compositions will be highly modified and they may be olivine-saturated. We investigated experimentally the reaction between olivine and siliceous eclogite partial melt, and determined element partitioning between olivine and the melt produced by this reaction. Our results demonstrate that mixing of reacted eclogite partial melt with primitive basalt is capable of producing the positive correlation between melt SiO2 content and olivine Ni content observed in some Hawaiian lavas. Experiments were carried out by equilibrating eclogite partial melt or basalt with San Carlos olivine at 1 bar and 1,201 1,350°C. Our results show that eclogite partial melts equilibrated with mantle olivine retain their high SiO2, low FeO and MgO characteristics. Further, olivine-melt partition coefficients for Ni measured in these experiments are significantly larger than for basalt. Mixing of these melts with primitive Hawaiian tholeiitic lavas results in crystallization of high-Ni olivines similar to those in Makapuu-stage Koolau lavas, even though the mixed magmas have only moderate Ni contents. This results from a hyperbolic increase of the Ni partition coefficient with increasing polymerization of the mixed melt. Note that while eclogite partial melt in contact with peridotite will equilibrate with pyroxene as well as olivine, this will have the effect of buffering the activity of SiO2 in the reacted melt at a higher level. Therefore, an eclogite partial melt equilibrated with harzburgite will have higher SiO2 than one equilibrated with dunite, enhancing the effects observed in our experiments. Our results demonstrate that an olivine-free “hybrid” pyroxenite source is not

  13. Impact of melt segregation on chemical composition with application to deep crustal hot zones

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Models of heat transfer during the emplacement of mantle-derived basaltic sills in the mid- to lower crust demonstrate that large volumes of evolved melt may be generated in deep crustal hot zones (DCHZ). These models consider only the thermal evolution of a DCHZ, yet melt must also segregate from along the grain boundaries where it initially resides to form a magma which leaves the DCHZ. However, models which include melt migration describe phase change using simple melt fraction-temperature relations, which do not capture the impact of melt segregation on the chemical evolution of melt and residual solid. We present a model of melting and buoyancy-driven melt segregation in which phase change is described using a phase diagram and the chemical evolution of the melt and residual solid is properly captured. Melt migration is assumed to occur along grain boundaries so local thermodynamic equilibrium is maintained. We begin by using a simple binary phase diagram and model a 1-D column with several different initial compositions and thermal boundary conditions. We investigate this simple case because it could be closely replicated in the laboratory, and allows aspects of the physics which hitherto have been poorly understood to be clearly observed and explained. It is trivial to extend our model to more complex systems. For an initially homogenous column, in which the fraction of component A is less than the eutectic composition, we find that the melt fraction at the base decreases and the bulk composition becomes enriched in component A, while the melt fraction at the top increases and the bulk composition tends towards the eutectic composition. Melt segregation provides a mechanism for accumulating melt of (or close to) the eutectic composition, but at much higher melt fractions than predicted by purely thermal models; for example, static melting to 10% may yield the eutectic composition, but melt segregation allows that composition to accumulate to 100%. For a

  14. Permeability-porosity relationship in a stochastic model of partial melting

    NASA Astrophysics Data System (ADS)

    Riedel, M. R.; Lammers, P.

    2005-12-01

    We present a model for calculating permeability of a porous solid-melt polycrystal during melting. Unlike to previous two-phase models, a solid framework is used that does not have a regular geometry nor a typical grainsize. Instead, we use a polycrystal that is created on the basis of a stochastic nucleation and growth process for first-order phase transformations as the starting state for partial melting. It is a polycrystal with continuously distributed grainsizes and random grain locations. Permeability is then estimated through flow simulation on the constructed 3D porous two-phase body using the Lattice-Boltzmann (LB) technique. The LB method describes fluid motion with the interaction of a massive number of particles following simple local rules, rules that recover the Navier-Stokes equation at the macroscopic scale [Rothman and Zaleski, 1997]. It is known that the LB flow simulation is able to handle successfully very complex 3D pore geometries [Keehm et al., 2004]. Here, the investigated porous framework shows a fractal-like geometry near to percolation of either melt or solid phase. The flow simulation is done with an assigned pressure gradient ∇ P across opposite faces of cubes. From the local flux, the volume-averaged flux < q > is then calculated using Darcy's relationship < q > = - κ η̅ ∇ P where κ is the (wanted) macroscopic permeability and η is the dynamic viscosity of the melt. References: Keehm Y., T. Mukerji T. and A. Nur. Permeability prediction from thin sections: 3D reconstruction and Lattice-Boltzmann flow simulation. GRL, 31, L04606, doi: 10.1029/2003GL018761, 2004. Rothman D.H. and S. Zaleski. Lattice-Gas Cellular Automata. Cambridge University Press, Cambridge, 1997.

  15. Equivalence of equations describing trace element distribution during equilibrium partial melting

    NASA Technical Reports Server (NTRS)

    Consolmagno, G. J.; Drake, M. J.

    1976-01-01

    It is shown that four equations used for calculating the evolution of trace-element abundances during equilibrium partial melting are mathematically equivalent. The equations include those of Hertogen and Gijbels (1976), Shaw (1970), Schilling (1971), and O'Nions and Clarke (1972). The general form to which all these equations reduce is presented, and an analysis is performed to demonstrate their mathematical equivalence. It is noted that the utility of the general equation flows from the nature of equilibrium (i.e., the final state is independent of the path by which that state is attained).

  16. 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

  17. Partial Melting in the Iron-Sulfur System at High Pressures

    NASA Astrophysics Data System (ADS)

    Campbell, A. J.; Seagle, C. T.; Heinz, D. L.; Shen, G.; Prakapenka, V. B.

    2005-12-01

    Melting in the Fe-rich portion of the Fe-S system was investigated to pressures of 80 GPa, using in situ synchrotron x-ray diffraction through a laser-heated diamond anvil cell at the GSECARS sector of APS. Intimately mixed Fe-FeS powders were compressed between insulating layers of NaCl in the diamond anvil cell. Double-sided laser heating was used to reduce axial temperature gradients, and temperatures were measured spectroradiometrically on both sides of the cell. Only the central, hottest part of the laser-heated region was probed with the 5x7 micron x-ray beam. At high pressures, Fe3S was formed by reaction between Fe and FeS upon laser heating, with excess Fe remaining. The Fe was used as an internal, high-temperature pressure standard based on existing equation of state data. Diffraction data were collected during laser heating and also from the quenched sample following each heating episode. The use of an image plate area detector greatly improved our ability to verify the presence of both metal and sulfide during heating. The eutectic temperature was bracketed by the absence of one phase above the melting point and the presence of both phases at lower temperature. The reappearance of the absent component (sulfide or metal) upon rapid quenching was taken as confirmation that partial melting had been achieved. Our results using this method are in broad agreement with earlier data that were based on textural criteria.

  18. 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

  19. 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.

  20. 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

  1. 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

    2014-01-01

    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. PMID:25342158

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

  3. The role of synmetamorphic igneous rocks in the metamorphism and partial melting of metasediments, Northwest Adirondacks

    NASA Astrophysics Data System (ADS)

    Powers, Roger E.; Bohlen, Steven R.

    1985-08-01

    Field and petrologic studies along the Adirondack Lowlands — Highlands boundary near Harrisville, NY, indicate that heat from the synmetamorphic intrusion of the Diana syenite complex (intrusion temperature of ˜1,050° C) played a major role in the local metamorphic thermal regime and was responsible for extensive partial melting of adjacent metasedimentary units (Major Paragneiss of Engel and Engel). Metamorphic temperatures inferred from two — feldspar and spinel — quartz assemblages decrease from 850 950° C along the Diana — metasediment contact to 650 700° C, 2 3 km away from the contact. Metamorphic pressures are 7±0.5 kb as determined from coexisting plagioclase — garnet — sillimanite — quartz, kyanite — sillimanite, and garnet — rutile — ilmenite — sillimanite — quartz (GRAIL). In the paragneiss, migmatites consisting of quartz — microcline perthite — sodic plagioclase leucosomes are generally concordant with the melanosome consisting of biotite — sillimanite — garnet — spinel — plagioclase ±corundum±cordierite. Qualitatively the amount of partial melt and occurrences of corundum-bearing assemblages decrease away from the Diana contact. Activity of H2O inferred from coexisting biotite — sillimanite — quartz — garnet — K-feldspar ranges from 0.01 to 0.17 and is five to ten times lower in corundum-bearing rocks. Melting proceeded via vapor-absent reactions involving biotite in response to localized heating by synmetamorphic intrusion of magma. This unusually preserved, synmetamorphic contact aureole in a regional granulite terrane supports the concept that granulites owe their origin to magma intrusion and/or the ponding of magmas at the base of the crust.

  4. 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. PMID:27143719

  5. 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.

  6. The structure of melting mushy zones, with implications for Earth's inner core (Invited)

    NASA Astrophysics Data System (ADS)

    Bergman, M. I.; Huguet, L.; Alboussiere, T.

    2013-12-01

    Seismologists have inferred hemispherical differences in the isotropic wavespeed, the elastic anisotropy, the attenuation, and the attenuation anisotropy of Earth's inner core. One hypothesis for these hemispherical differences involves an east-west translation of the inner core, with enhanced solidification on one side and melting on the other. Another hypothesis is that long term mantle control over outer core convection can lead to hemispherical variations in solidification that could even result in melting in some regions of the inner core boundary. It has also been hypothesized that the inner core is growing dendritically, resulting in an inner core that has the structure of a mushy zone (albeit one with a high solid fraction). It would therefore be helpful to understand how the structure of a melting mushy zone might look in comparison with one that is solidifying, in an effort to help interpret the seismic inferences. We have carried out experiments on the solidification of ammonium chloride from an aqueous solution, yielding a mushy zone. The experiments run in a centrifuge, in order to reach a more realistic ratio of convective velocity to phase change rate, expected to be very large at the boundary of the inner core. Hypergravity thus increases the experimental solid fraction of the mush. So far the maximum gravity we have achieved is 200 g. A Peltier cell provides cooling at one end of the cell, and after the mushy zone has grown we turn on a heater at the other end. Probes monitor the temperature along the height of the cell. As ammonium chloride in the mushy zone melts it produces more dense fluid, which results in convection in the mushy zone, a greater ammonium chloride concentration deeper in the mushy zone, and hence enhanced solidification there. This thus changes the solid fraction profile from that during solidification, which may be observable in the lab experiments using ultrasonic transducers and post-mortem under a microscope. The melting

  7. 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

  8. Partial Melting of Ordinary Chondrite: Implications for Siderophile Behavior During Early Differentiation

    NASA Astrophysics Data System (ADS)

    Rushmer, T.

    2002-12-01

    Core formation scenarios in growing planetesimals include a variety of possible physical mechanisms such as segregation in a solid or partially molten silicate body or whether or not the body was actively deforming. The resulting geochemical composition of the metal and silicate phases will also be a function of bulk composition, percent of metal melted and oxygen fugacity. To explore the relationship between physical core formation scenarios and geochemistry, deformation experiments have been conducted on a H6 ordinary chondrite at different stages of melting. Deformation experiments provide a dynamic component that allows liquid metal to segregate from solid silicate, or from matrices containing various amounts of silicate melt. Geochemical analyses of metal quench in several experimental charges and on metal grains in the Kernouve H6 starting material have been performed by LA-ICP-MS (Hummayun &\\ Campbell, EPSL, 2002; Rushmer et.al., Geochem. Cosmochem. Acta, Goldschmidt Conf. Abs,, 2002). Below the silicate solidus (KM-10, 1.0 GPa, 925°C, 1x10-5 s-1), analyses of compatible (Re, Os) and incompatible (Pd, Au) siderophiles in residual, strained Fe-Ni metal and unmodified metal show little variation. These data suggest even though metamorphosed, siderophile abundances are not strongly modified by shearing. At higher temperatures, (KM-17, 1.2 GPa, 940°C, 10-6 s-1) data from metal quench representing early formed liquid (S-rich and possibly O-rich) and of residual Fe-Ni metal have been plotted on a Fe, H-chondrite normalized plot with starting Kernouve metal and bulk H4-6 metal compositions. The quench metal resembles liquid, being depleted in compatible siderophiles, e.g., Re, Os, Ir, and enriched in Ni, Pd. Residual metal mirrors the quench metal and is enriched in compatible elements and depleted in the incompatibles when compared with bulk H metal. Ga and Ge show slight fractionation. Ga, Ge, Co and Ir vs. Ni plots show quench metal compositions are similar

  9. 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.

  10. 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.

  11. 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).

  12. 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

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

    DOE PAGESBeta

    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.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

  16. Melt Impregnation, Strain Localization, and Deformation Mechanisms in a Fossil Oceanic Fracture Zone (Ingalls Ophiolite)

    NASA Astrophysics Data System (ADS)

    Miller, R. B.; Gordon, S. M.

    2010-12-01

    A steep mantle shear zone that deforms ultramafic rocks of the Jurassic Ingalls ophiolite is inferred to preserve a record of the interplay of melt impregnation, strain localization, and switching deformation mechanisms in a fossil oceanic fracture zone. This ~2-km-wide, E-W-striking shear zone separates harzburgite and dunite on the south from lherzolite and cpx-rich harzburgite on the north. Geochemical data from the lherzolite, which contains veinlets of plagioclase and cpx, suggest impregnation by infiltrating basaltic melt. The shear zone reworks the lherzolite unit, but also contains widespread plagioclase peridotite and hornblende peridotite, and shear-zone mylonites are less depleted than the adjacent units. Olivine is reduced in average grain size from 1.5-3.0 mm in the lherzolites to 50 µm in some mylonites. In the mylonites, opx and cpx porphyroclasts are set in a mosaic of olivine, cpx, opx +/- hornblende +/- plagioclase. Lattice preferred orientations (LPO) determined by EBSD indicate that olivine in the dunite-harzburgite and lherzolite units deformed by glide on [100] (010), a common mechanism for dislocation creep in the upper mantle. In contrast, olivine in the mylonites has much weaker, poorly defined LPOs. This weakening of the LPO and the microstructures are compatible with dynamic recrystallization and grain-size reduction resulting from dislocation creep leading to a change to a grain-size-sensitive deformation mechanism. We suggest that impregnation by infiltrating melts may have helped localize strain, and the formation of multiple phases, in part as a result of impregnation, may have stabilized the small olivine grain size.

  17. 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.

  18. Attenuation and Velocity Structure in Spain and Morocco: Distinguishing Between Water, Temperature, and Partial Melt

    NASA Astrophysics Data System (ADS)

    Bezada, M. J.; Humphreys, E.

    2014-12-01

    Temperature, melt fraction, and water content affect seismic velocity and attenuation differently. Both are sensitive to temperature, but velocity is more sensitive to melt fraction and attenuation is thought to be more sensitive to water content. For these reasons, combining attenuation measurements with tomographic imaging of velocity structure can help untangle these fields and better resolve lithospheric structure and physical state. We map variations in attenuation beneath Spain and northern Morocco using teleseismic data generated by more than a dozen teleseismic deep-focus earthquakes recorded on a dense array of stations. For each event, we first estimate the source from the best quality recordings. We then apply an attenuation operator to the source estimate, using a range of t* values, to match the record at each station. We invert for a smooth map of t* from the ensemble of measurements. The spatial patterns in t* correlate very well with the tectonic domains in Spain and Morocco. In particular, areas in Spain that resisted deformation during the Variscan and Alpine orogenies produce very little attenuation. Comparing the attenuation map with seismic velocity structure we find that, in Morocco, some areas with strong low-velocity anomalies and recent volcanism do not cause high attenuation. These observations suggest that water content is a more likely cause for seismic attenuation in the study area than temperature, and that the non-attenuative low-velocity anomalies in Morocco are produced by partial mel.

  19. 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.

  20. Early Earth Felsic Crust Formation: Insights from Numerical Modelling of High-MgO Archaean Basalt Partial Melting

    NASA Astrophysics Data System (ADS)

    Riel, N., Jr.

    2015-12-01

    The Tonalite-Trondhjemite-Granodiorite series (TTGs) represent the bulk of the felsic continental crust that formed between 4.4 and 2.5 Ga and is preserved in Archaean craton (3.8-2.5 Ga). It is now recognized that the petrogenesis of TTG series derives from an hydrous mafic system at high pressure. However, the source of the early TTGs (3.5-3.2 Ga) have not been preserved and its characteristics are still debated. In this study we use thermodynamical modelling coupled with two-phase flow to investigate the products of partial melting of high-MgO primary mafic crust. Our model setup is made of a 45-km thick hydrated mafic crust and is heated above the solidus from 50 to 200°C. To explore the effects of melt-rock interactions during melt transfer (via two-phase flow), the melt composition is modelled either in thermodynamic equilibrium with the rock or in thermodynamic disequilibrium. Our modelling results show that partial melting of hydrous high-MgO metabasalt crust can produce significant volumes of felsic melt. The average composition of these melts is SiO2-rich > 62%, Mg# = 40-50, Na2O ~6%, MgO = 0.5-1% which is consistent with the composition of TTGs. The residual rock after melt segregation is composed of olivine + garnet + pyroxene which is in agreement with Archaean eclogites found in mantle xenoliths of Archaean cratons. Moreover, the depleted residual rock is denser than the mantle and is likely to be recycled in the mantle. We show that the early felsic crust with a TTGs signature could have been formed by partial melting of high-MgO hydrated metabasaltic crust, and propose that plume-related activity and/or rapid burial due to high volcanic activity are likely geodynamic conditions to generate an early felsic crust.

  1. Imaging melt and thermal structure in subduction zones: what does seismic attenuation tell us?

    NASA Astrophysics Data System (ADS)

    Abers, G. A.; Fischer, K. M.; Hirth, G.; Holtzman, B. K.; McCarthy, C.; Plank, T. A.; Wiens, D. A.

    2013-12-01

    Subduction zones provide opportunities for observation of the mantle melting region not easily available elsewhere. Earthquakes within subducting plates can be recorded in the overlying plate. These paths sample the volumes where melting occurs with high resolution and short ray paths, and produce simple signals with much higher frequency content than available elsewhere. Also, arc volcanoes provide a direct sample of mantle melting products, and magmas record H2O concentrations, temperature, and pressure in their geochemical compositions. Beneath both volcanic arcs and back-arc basins, seismic waves exhibit very high attenuation (1/Q) for both P and S waves. Several recent field experiments have shown that the region of high 1/Q is localized and more than an order of magnitude more attenuating than adjacent regions in the forearc or slab. We have systematically re-analyzed data from two sets of these experiments, from Central America and the Marianas, where 1/Q anomalies are well defined and where arc or backarc lavas provide independent constraints on mantle properties. These analyses show strong attenuation anomalies, with Qs at 1 Hz no lower than 60-80 beneath Costa Rica but lower beneath other arcs and back-arc basins, to Qs<40. The systematic decrease in Qs (increase in attenuation) correlates well with temperature from geothermometers based on major-element chemistry. However, these Qs values are a factor of 2-4 lower than predicted from temperature by current laboratory-based calibrations in olivine-dominated rocks, at relevant conditions. We refine the Qs predictions using a grain size evolution model and estimates of mantle water content from olivine-hosted melt inclusions, effects which decrease but do not eliminate the discrepancy. We conclude that melt must have a significant impact on Q, bigger than predicted by models of grain-boundary dissipation with equilibrium grain geometries. One possibility is that in these very high 1/Q regions additional

  2. 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

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. Paramagnetic resonance of LaGaO3: Mn single crystals grown by floating zone melting

    NASA Astrophysics Data System (ADS)

    Vazhenin, V. A.; Potapov, A. P.; Artyomov, M. Yu.; Salosin, M. A.; Fokin, A. V.; Gil'mutdinov, I. F.; Mukhamedshin, I. R.

    2016-02-01

    The EPR spectrum of Mn-doped lanthanum gallate single crystals grown by floating zone melting with optical heating has been studied. In contrast to the crystals grown according to the Czochralski method, no manganese is found in these crystals even after high-temperature annealing in air. The spectral characteristics of Fe3+ and Gd3+ centers in crystals prepared by various methods have been compared in the rhombohedral phase, and the fourth-rank nondiagonal parameters of the Fe3+ trigonal centers have been determined, as well.

  10. 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.

  11. Influences of the buoyancy of partially molten rock on 3-D plume patterns and melt productivity above retreating slabs

    NASA Astrophysics Data System (ADS)

    Zhu, Guizhi; Gerya, Taras V.; Honda, Satoru; Tackley, Paul J.; Yuen, David A.

    2011-04-01

    Using 3-D petrological-thermo-mechanical subduction models, we investigate how the buoyancy of partially molten rock affects the development of thermal-chemical plumes and melt productivity in the mantle wedge. As a first order approximation we limit the positive buoyancy of partially molten rock (compared to non-molten rock), which can be decreased due to rapid melt extraction and removal to the surface. Our simulations show that a large to moderate density contrast (Δ ρ) of >200 kg/m 3 between non-molten ( ηn-m) and partially molten rock ( ηp-m). (i.e. low to moderate degree of melt removal from rock) promotes the development of three distinct patterns of plumes (finger-like, ridge-like and wave-like). In contrast, a low density contrast (Δ ρ) of 0-50 kg/m 3 (i.e. high to complete melt removal) suppresses pronounced plumes and is associated with low-amplitude (50-100 km wide and 10-15 km high) domal structures developing atop the slab due to the chemical buoyancy of subducted hydrated non-molten rock types (oceanic crust, sediments, serpentinites). Variation in partially molten rock viscosity ( ηp-m) also notably affects plume patterns and lateral dimensions: wave-like plumes are most pronounced at higher ( ηp-m = 10 19 Pa s) viscosity, which also favors the development of larger plumes compared to models with lower ( ηp-m = 10 18 Pa s) viscosity. Integrated melt productivity above the slab is notably higher for cases with pronounced hydrated thermal-chemical plumes developed in the mantle wedge. Indeed, all models are characterized by periodic (5-10 Myr long episodes of enhanced productivity), spatially clustered (30-50 km distance between productivity maxima) melt production, which may explain the periodicity and clustering of volcanic activity observed in magmatic arcs such as in North-East Japan and New Zealand.

  12. 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

  13. Producing Ni-rich olivine phenocrysts by mixing partial melts of eclogite and peridotite: an alternative to an olivine-free source for Hawaiian shield basalts

    NASA Astrophysics Data System (ADS)

    Wang, Z.; Gaetani, G.

    2007-12-01

    It has been posited that presence of unusually Ni-rich (2500-4000 ppm) magnesian olivine phenocrysts in SiO2-enriched Hawaiian shield-building basalts, most notably the Koolau lavas, is inconsistent with a deep, olivine-bearing source rock. Instead, Sobolev et al. (2005) proposed that these lavas are generated by a multi- stage process in which partial melts of eclogite react with peridotite within the plume to form an olivine-free source rock with high Ni concentration. As the plume continues to ascend, partial melts of this "hybrid" pyroxenite mix with peridotite melts to produce SiO2- enriched Hawaiian shield-building lavas that crystallize high-Ni olivine. This model has also been used to argue for significant amounts of "hybrid" pyroxenite in the source regions of lavas from other ocean islands, continental basalts, and even MORB, implying that the upper mantle is highly heterogeneous (Sobolev et al., 2007). New experimental results demonstrate that Ni-rich magnesian olivine crystallizes from mixtures of peridotite partial melt and Ni-poor eclogite partial melt that have equilibrated with mantle olivine. This occurs because the concentration of Ni decreases linearly as eclogite partial melt is added to peridotite partial melt, whereas changing major element composition of the mixed melts causes DNi to increase hyperbolically. Experiments were conducted in which either (1) siliceous partial melt of eclogite or (2) primitive basalt was equilibrated with San Carlos olivines at 1 bar and 1201-1350°C. Experimental results demonstrate that eclogite partial melts in equilibrium with mantle olivine retain their high SiO2, low FeO and MgO characteristics. Theoretical modeling calibrated from these experimental results suggest that reaction of siliceous eclogite melt with mantle olivine at low pressure produces a melt containing ~300 ppm Ni. Despite its low Ni content, mixing of this melt with peridotite partial melt produces a high SiO2 melt that crystallizes Ni

  14. 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.

  15. 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

  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. 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

  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. Thermochronology of the South Cyclades Shear Zone, Ios, Greece: Effects of ductile shear in the argon partial retention zone

    NASA Astrophysics Data System (ADS)

    Baldwin, Suzanne L.; Lister, Gordon S.

    1998-04-01

    Micas and potassium feldspars from the South Cyclades Shear Zone, Ios, Cyclades, Greece, yield varied and complex 40Ar/39Ar apparent age spectra. A correlation exists between 40Ar/39Ar apparent ages and the relative timing of different episodes of recrystallization and grain growth, as indicated by fabric and microstructural analysis. The 40Ar/39Ar apparent age spectra record the effects of variation in the degree of recrystallization and grain growth, and partial to complete resetting of argon systematics in potassium-bearing minerals during Hercynian (M0), Alpine (M1) and late Oligocene - early Miocene (M2) metamorphism. Deformation was strongly partitioned within the shear zone and this led to localized recrystallization and heterogeneous resetting of argon systematics within preexisting minerals. Modeling suggests the Oligo-Miocène thermal events were of insufficient magnitude and/or duration to completely reset the isotopic systematics in these samples. Our data lead to the concept of the argon partial retention and resetting zone (PRZ), defined as that portion of the crust where temperatures are insufficient to completely reset argon systematics within preexisting potassium-bearing minerals. Within the PRZ, some radiogenic argon in preexisting potassium bearing minerals will be outgassed and only partially retained. Tectonic exhumation of the PRZ involves movement on crustal-scale ductile shear zones, accompanied by strongly partitioned deformation and localized recrystallization. Recrystallization leads to resetting of argon systematics, and thus will result in heterogeneous 40Ar/39Ar age distributions within these ductile shear zones (e.g., in the South Cyclades Shear Zone).

  20. Cr-Spinel as an Indicator of Cumulates Partial Melting and Liquid Hybridization

    NASA Astrophysics Data System (ADS)

    Leuthold, J.; Blundy, J. D.

    2014-12-01

    The Rum Layered Intrusion (Scotland) was emplaced 60.53 ± 0.08 Ma ago [1], in response to the proto-Iceland plume [2]. The Unit 9 gabbro cumulates were successively intruded by olivine-phyric picritic sills. Reactive liquid flow produced clinopyroxene-poor gabbro, troctolite and dunite restite, and expelled melt crystallized to form gabbro with poikilitic clinopyroxene and Cr-spinel-rich anorthosite [3]. The Cr-spinel origin is strongly debated (e.g. [4]). We have run one atmosphere, fO2-controlled equilibrium experiments of the Rum parental picritic parental liquid [5]. At NNO-0.8 conditions, Cr- spinel saturates from 1360°C, olivine from ~1330°C, plagioclase from 1240°C and clinopyroxene from 1220°C, systematically ~40°C above MELTS calculations. Natural Cr- spinel grains have a higher Cr/(Cr+Al+Fe3+) ratio (~0.51 to 0.03) than grains crystallized along the picrite NNO-0.8 liquid line of descent (0.38 to 0.06). Fe3+-rich spinel is abundant (~1 vol%) at NNO+1, and Al-rich spinel occurs as trace at NNO-3. In picrite-troctolite hybrid experiments, plagioclase (~An86) saturates from 1280°C and clinopyroxene from 1200°C. Al- spinel crystallizes at high temperature, and gets more Cr-rich upon cooling, reaching the highest measured Cr/(Cr+Al+Fe3+) ratio of ~0.44 at 1225°C, falling to 0.09 at 1200°C. Plagioclase and clinopyroxene stability plays a major role in spinel composition. Increasing the pressure or the parental magma water content would delay plagioclase saturation and result in spinel with lower Cr/Al ratio. We deduce that Unit 9 peridotite, troctolite, anorthosite and also gabbro and poikilitic gabbro Cr-rich spinel did not crystallize from the Rum parental picritic liquid. Instead, they crystallized from a hybrid liquid produced by the mixing of invading picritic liquid with a partially molten plagioclase ± clinopyroxene -rich cumulate, leaving an olivine-rich residue/cumulate. [1] Hamilton et al. (1998) Nature 394: 260-263 [2] Saunders et al

  1. 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.

  2. Experimental study of the partitioning of Cu during partial melting of Earth's mantle

    NASA Astrophysics Data System (ADS)

    Fellows, Steve A.; Canil, Dante

    2012-07-01

    Primitive basaltic glasses from mid-ocean ridges (MORB), ocean islands (OIB) and arcs contain three to five times the Cu as the currently accepted primitive upper mantle (PUM) value, suggesting a bulk partition coefficient DCumantle/melt of ˜0.20. Sulfide, with a DCusulfide/melt of 250-960 is presumed to be ubiquitous in the mantle. The Cu abundances in basalts are unable to be achieved if Cu behaves compatibly, or if a high enough modal abundance of sulfide exists during the onset of melting to sequester significant Cu. To address this conundrum we determined DCu in olivine and orthopyroxene at 1250-1525 °C and 1.0 GPa in a hydrous basalt and KLB1 peridotite, at ƒO2 of FMQ-1, near to melting conditions of the upper mantle. The measured DCuol/liq of 0.06-0.21 and DCuopx/liq 0.15-0.82 do not vary with melt fraction, or significantly with ƒO2, and can be combined with estimates for DCu for clinopyroxene into melting models to examine the Cu contents of mantle-derived melts. The Cu abundances for MORB, OIB, and arc glasses are all explicable by up to 15% melting of the silicate—only portion of the mantle in which Cu behaves as a mildly incompatible element (DCumantle/melt˜0.26). For Cu to be enriched in basaltic melts in the presence of sulfide, the melt/sulfide ratio, or the oxidation state of the mantle during melting, must be significantly high to diminish the potential of sulfide to sequester any Cu. Our results suggest the role of sulfide during mantle melting may be insignificant with regards to controlling the concentration of moderately chalcophile elements like Cu, and confirm that the previously estimated Cu content for PUM of 20 ppm is correct.

  3. Partial crustal melting beneath the Betic Cordillera (SE Spain): The case study of Mar Menor volcanic suite

    NASA Astrophysics Data System (ADS)

    Álvarez-Valero, A. M.; Kriegsman, L. M.

    2008-03-01

    The Neogene Volcanic Province (NVP) within the Betic Cordillera (SE Spain) consists of three main metapelitic enclave suites (from SW to NE: El Hoyazo, Mazarrón and Mar Menor). Since the NVP represents a singular place in the world where crustal enclaves were immediately quenched after melting, their microstructures provide a "photograph" of the conditions at depth just after the moment of the melting. The thermobarometric information provided by the different microstructural assemblages has been integrated with the geophysical and geodynamical published data into a model of the petrologic evolution of the Mar Menor enclaves. They were equilibrated at 2-3 kbar, 850-900 °C, and followed a sequence of heating melt producing reactions. A local cooling event evidenced by minor melt crystallization preceded the eruption. The lower crustal studies presented in this work contribute to the knowledge of: (i) the partial melting event beneath the Mar Menor volcanic suite through a petrologic detailed study of the enclaves; (ii) how the microstructures of fast cooled anatectic rocks play an important role in tracing the magma evolution in a chamber up to the eruption, and how they can be used as pseudothermobarometers; (iii) the past and current evolution of the Alborán Domain (Betic Cordillera) and Mediterranean Sea, and how the base of a metapelitic crust has melted within an active geodynamic setting.

  4. Generation of incompatible element depleted high-Al melts: Constraints from melt inclusions from the FAMOUS zone, mid-Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    Laubier, M.; Gale, A.; Langmuir, C. H.

    2009-12-01

    High-Al, low-Si and high-Mg melts have been reported for various mid-ocean ridges (Eason and Sinton, EPSL, 2006; le Roux et al., Contrib. Min. Pet., 2002; Lissenberg and Dick, EPSL, 2008) and seem to occur preferentially at slow spreading ridges or close to fracture zones and ridge ends. Two hypotheses have been suggested to explain their chemistry: (1) high-pressure fractionation of clinopyroxene (Eason and Sinton, EPSL, 2006) and (2) a reaction between primitive cumulates and migrating melts in the lower crust (Lissenberg and Dick, EPSL, 2008). Our study of numerous lavas (>100) and melt inclusions (>335) along the FAMOUS segment (Northern mid-Atlantic Ridge) shows that high-Al melts occur both as melt inclusions and lavas, mostly found in the FAMOUS area near the center of the segment. The high-Al lavas studied for their melt inclusions host both high-Al and normal inclusions. No high-Al inclusion has been found in non-high Al basalts. High-Al melts are characterized by high Al2O3 (up to 18.4 wt%), high MgO (>8.3 wt% in the lavas; >10.3 wt% in the inclusions), low SiO2 (48.4-50.5 wt% in the lavas; 46.6-49.0 wt% in the inclusions) and low TiO2 (< 1 wt% in the lavas, < 0.73 wt% in the inclusions) contents. High-Al melt compositions are distinctively lower in highly incompatible elements (Ba as low as 18 ppm in the lavas and 1 ppm in the inclusions). With such low incompatible element concentrations, the high-Al melt inclusions constitute ultra-depleted melts (UDM). High-Al inclusions and lavas also display a relative enrichment in the HREE/MREE ratios compared to normal melts. Similarly, olivine phenocrysts that host high-Al melt inclusions present relatively higher Al2O3, NiO contents and Y/MREE and HREE/MREE than those with normal inclusions. High-pressure clinopyroxene fractionation is inconsistent with the relatively high Sc and very low SiO2 contents in High-Al inclusions. Reaction between a MORB and a plagioclase-rich cumulate results in trace element

  5. 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.

  6. 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.

  7. 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

  8. 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

  9. 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

  10. Czochralski growth techniques of germanium crystals grown from a melt covered partially or fully by liquid B2O3

    NASA Astrophysics Data System (ADS)

    Taishi, Toshinori; Hashimoto, Yoshio; Ise, Hideaki; Murao, Yu; Ohsawa, Takayuki; Yonenaga, Ichiro

    2012-12-01

    We propose two unique Czochralski (CZ) techniques for growing germanium (Ge) crystals with an extremely low dislocation density and high interstitial oxygen concentration ([Oi]) using boron oxide (B2O3) and a silica crucible. When a Ge melt is partially covered with liquid B2O3, but only on the outer region of the melt surface, germanium-oxide (GeO2)-related particles forming naturally in the melt are effectively dissolved by the liquid B2O3. The clean central portion of the melt produces dislocation-free undoped or Ga-doped Ge crystals. In addition, Ge crystals with [Oi] up to 6×1017 cm-3 can be grown from a melt fully covered by liquid B2O3 with added GeO2 powder. The reaction and transportation of oxygen atoms during the growth process using B2O3 was investigated, revealing that liquid B2O3 acts like a catalyst without heavy contamination of the growing Ge crystal by B and Si atoms.

  11. Permafrost Melt in the Wetland-Dominated Zone of Discontinuous Permafrost - Implications for Basin Runoff

    NASA Astrophysics Data System (ADS)

    Quinton, W. L.; Hayashi, M.; Chasmer, L.; Hopkinson, C.

    2009-05-01

    Field studies were initiated in 1999 at Scotty Creek in the lower Liard River basin, NWT, Canada, to improve the understanding and model-representation of the major water flux and storage processes within this wetland- dominated zone of discontinuous permafrost. Over this period, permafrost melt has led to appreciable landscpae change. As a result, permafrost plateaus have been replaced by flat bogs and channel fens. Because these three peatland types have very different functions in the overall cycling and storage of water in the basins of this region, there is good reason to suspect that permafrost melt will lead to changes in basin runoff production. This paper documents the rates and patterns of permafrost loss in this region using a variety of ground-based and remotely sensed measurements. A mechanistic-based conceptual model of landscape evolution is presented that offers insights for water scientists and managers into how the on-going landscape change in this region resulting from climate and human disturbances may influence the basin hydrograph.

  12. Microstructures, Chemical Composition, and Viscosities of Fault-generated Friction Melts in the Shimanto Accretionary Complex, Southwest Japan: Implication for Dynamics of Earthquake Faulting in Subduction Zones

    NASA Astrophysics Data System (ADS)

    Ujiie, K.; Yamaguchi, H.

    2004-12-01

    The pseudotachylytes (PT) were recently found in the Cretaceous Shimanto accretionary complex of eastern and western Shikoku, southwest Japan, but their microstructures under a backscattered electron image, chemical composition, and effects of frictional melting on co-seismic slip in the accretionary prism remains poorly understood. The PT bearing fault is the 1-2 m thick roof thrust of a duplex structure, which bounds the off-scraped coherent turbidites above from the imbricated melange below without a thermal inversion across the fault. The fault zone consists of foliated cataclasite of sandstone-shale melange in origin and dark veins. The PT commonly occurs as brecciated fragments in dark veins. The PT matrix is transparent under plane-polarized light and is optically homogeneous under cross-polarized light, similar to glass matrix. Under a backscattered electron image, the PT clearly shows the evidences for frictional melting and subsequent rapid cooling: rounded and irregularly shaped grains and vesicles in matrix and fracturing associated with grain margins. These textural features of the PT are very similar to those of experimentally generated PT. The EPMA analysis indicates that chemical composition of the PT matrix corresponds to illite with 5.7-9.9 wt% H2O and that partially melted grains are dominated by orthoclase and quartz. This indicates that the temperatures of the PT melt could reach the breakdown temperatures of orthoclase (1150 C) and quartz (1730 C), greater than the maximum temperature recorded in host rocks (170-200 C). We calculated the viscosity of friction melt, based on the chemical composition of the PT matrix and the volume fraction and aspect ratio of grains in the PT. We considered both Arrhenian and non-Arrhenian models for viscosity calculation. Our result demonstrates that the melt viscosity is much lower than PT in continental plutonic and metamorphic rocks: 10^3 Pa s (Arrhenian model) and 10^2 Pa s (non-Arrhenian model) even at

  13. Partial crystallization of picritic melt and its applications for the genesis of high-Ti and low-Ti basalts

    NASA Astrophysics Data System (ADS)

    Yang, J.; WANG, C.; Jin, Z.; Jin, S.; Yan, S.

    2015-12-01

    Geochemical and petrological studies have revealed the existence of high-Ti and low-Ti basalts in large igneous provinces (LIPs). However the originate of these high-Ti and low-Ti magmas are still under debate. Several different mechanisms have been proposed: (1) the high-Ti basalts are formed by the melting of mantle plume containing recycled oceanic crust (Spandler et al., 2008) while low-Ti basalts are formed by the melting of subcontinental lithospheric mantle (Xiao et al., 2004); (2) both high-Ti and low-Ti basalts are from mantle plume source, but the production of high-Ti basalts are associated with the thick lithosphere while the low-Ti basalts are controlled by the thin lithosphere (Arndt et al., 1993); (3) they are derived from the different degrees of melting, with high-Ti basalts representing low degree of partial melting of mantle plume (Xu et al., 2004). The low Mg# (below 0.7) of high-Ti and low-Ti basalts provides that they are far away from direct melting of mantle peridotite. In addition, seismic data indicate unusually high seismic velocities bodies beneath the LIPs which explained by the fractionated cumulates from picritic magmas (Farnetani et al., 1996). Therefore, we believed that the crystallization differentiation process might play a more significant role in the genesis of high-Ti and low-Ti basalts.In order to investigate the generation of high-Ti and low-Ti basalts, a series of high pressure and high temperature partial crystallization experiments were performed at pressures of 1.5, 3.0 and 5.0 GPa and a temperature range of 1200-1700℃. The starting material is picrate glass with relative high TiO2 (2.7 wt %), which is synthesized according to the chemical composition of primary magmas of Emeishan LIP (Xu et al., 2001). The experimental results show that: (1) At a given pressure, the TiO2 content is decreased with increasing melt fraction; (2) At a given melt fraction, the TiO2 content of melts is increased with increasing pressure. On

  14. Migmatites formed by water-fluxed partial melting of a leucogranodiorite protolith: Microstructures in the residual rocks and source of the fluid

    NASA Astrophysics Data System (ADS)

    Sawyer, E. W.

    2010-05-01

    The Opatica Subprovince in the Canadian Shield is a late Archaean (2761-2702 Ma) plutonic arc formed above a north-dipping subduction zone. Anatexis (2690-2677 Ma) of leucogranodiorite and leucotonalite orthogneisses in the Opatica generated migmatites in an area of north-vergent back thrusts visible at the surface and in L ITHOPROBE seismic profile 48. Schollen diatexite migmatites occur in the thrusts and metatexite migmatites between them. The modal mineralogy, microstructure, and whole rock major, trace and oxygen isotope compositions of the protolith and migmatites were investigated to; 1) determine the melting reaction, 2) find microstructural criteria for identifying residual rocks in leucocratic systems where there is no melanosome, and 3) to determine the source of the fluid involved in anatexis. Partial melting of the protolith did not change the mineral assemblage, but the abundance of quartz and microcline both declined and plagioclase and biotite increased in the residual rocks. Quartz, plagioclase and microcline show evidence for dissolution and biotite does not. Thus, water-fluxed melting of quartz + plagioclase + microcline occurred. A mass balance indicates 25-30% partial melting. The melting reaction consumed the microcline and created essentially monomineralic domains of plagioclase. Extraction of 80-90% of the melt left a thin film of melt on the grain boundaries, and crystallization of these in the plagioclase domains created diagnostic microstructures. Microcline fills the last remaining pore space and forms high-aspect ratio crystals between plagioclases or triangular crystals at grain junctions. Quartz shows a range of morphologies, from high-aspect ratio films through the "string of beads" to isolated rounded grains, as the microstructure progressively equilibrated after crystallisation. Most accessory phases, including zircon, remained in the residuum. However, almost all the schollen migmatites have high contents of Th, U, Nb, Ta and REE

  15. Melt Extraction Zones in Shallow Arc Plutons: Insights from Fisher Lake Orbicules and Comb Layers, Northern Sierra Nevada

    NASA Astrophysics Data System (ADS)

    McCarthy, A. J.; Muntener, O.

    2015-12-01

    Identifying the processes behind magma flow structures and complex sheeted zones within otherwise near-homogeneous shallow plutons is fundamental in order to understand the mechanisms of melt transport, magma differentiation, crustal recycling and growth of mid-upper crustal plutons. The Cretaceous gabbro-diorite pluton of Fisher Lake, Northern Sierra Nevada (USA), contains multiple m-sized orbicule and magma-breccia bodies as well as orbicule- and comb layer-bearing dikes. Olivine-bearing norites, hornblende diorites and gabbros which have crystallized at low pressure (2kbar) from hydrous basaltic-andesite melts form texturally diverse orbicule cores which act as nuclei for comb layers. Rising hydrous mafic melts remobilizing low pressure cumulates and/or crystal mushes are injected at the contact between cooling plutons prior to the initiation of comb layer growth. Multiple generations of melt injections are attested by the presence of magma-breccia bodies which incorporate fractured, disaggregated fragments of pre-existing orbicule and comb layer bodies. The cumulate signature of the orbicule-bearing matrix indicates that interstitial melt was extracted towards shallower depth. Though orbicule and comb layer bodies have been variously ascribed to melt migration within cooling plutons, magma mixing or fluid flow, we propose an alternative interpretation where these m-scale features represent localized subvertical channels formed during the extraction of multiple batches of hydrous melts within a volcanic plumbing system or shallow plutonic feeder zone. These features thus preserve unique evidence of upper-crustal melt migration processes during the transfer of hydrous mafic melts towards shallower depth. Geochemical gradients between decompressing liquids and crystallizing cumulates are the main driving force for crystallization. We will illustrate examples of this process on the basis of field observations, textural data, whole rock and mineral geochemistry.

  16. 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.

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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 ...

  18. 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.

  19. 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.

  20. Geochemical characterization of migmatized orthogneiss from Porto Ottiolu (NE Sardinia, Italy) and its inferences on partial melting process

    NASA Astrophysics Data System (ADS)

    Cruciani, Gabriele; Fancello, Dario; Franceschelli, Marcello; Columbu, Stefano

    2015-04-01

    by the occurrence of myrmekitic miscrostructures between quartz and feldspar, quartz films at the feldspar interface and by albite rims around plagioclase. Some selected samples were analysed for major, minor and trace element content. The leucosomes are characterized by the following major elements content: SiO2: 72.9-76.2; Al2O3: 14.7-15.4; Fe2O3tot: 0.1-0.7; MgO: 0.1-0.3; CaO: 0.5-3.2; Na2O: 2.4-3.5; K2O: 4.0-8.6 wt%. The noticeable wide range in CaO and K2O is related to the high variability of the plagioclase/K-feldspar ratio. Most leucosomes have granitic composition, except for those occurring along shear zones that have tonalitic composition. Mesosomes major elements contents are SiO2 ca. 70; Al2O3: 14.4-15.1; Fe2O3tot: 2.1-3.4; MgO ca. 1.0; CaO ca. 3.0; Na2O ca. 3.5; K2O ca. 2.6 wt.%. They have granodioritic compositions. All leucosome and mesosome samples are corundum normative. Chondrite-normalized REE patterns of leucosomes are characterized by a marked positive Eu anomaly and by LREE enrichment. Mesosomes are characterized by marked negative Eu anomalies, as well as by LREE and HREE enrichment. ∑REE is higher in mesosomes (153 ppm) than in leucosomes (20-63 ppm). Field relationships, microstructural and geochemical data support the hypothesis that migmatization was generated by partial melting of a probaby Ordovician granitoid. The origin of the various types of leucosome has been discussed.

  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. 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.

  3. 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.

  4. Seismic Evidence of Localized Distribution of Fluids or Melts in the Mantle Transition Zone

    NASA Astrophysics Data System (ADS)

    Tajima, F.; Nakagawa, T.

    2009-04-01

    waveforms did not show such anomaly. The waveform modeling was carried out up to 1 Hz using a finite difference code. Results indicate that a highly localized LVA zone (about -10% anomaly) is responsible for broadening the P waveforms. The LVA zones may indicate fluids dehydrated from hydrous mineral compositions or melts through the phase transformation at the bottom of the MTZ. A number of studies propose that a certain amount of water can be transported through the subduction process, and stored in the MTZ as the lower mantle minerals may not include much water (e.g., Ohtani et al., 2004). However, the distribution or fate of "water" dehydrated from minerals which are descending further into the lower mantle has been known little. On the other hand a recent study suggests that the MTZ may be dry based on the electrical conductivity modeling (Yoshino et al., 2008). We suggest that if the distribution of transported water is very localized in the MTZ, then the debates do not have to be contradictory to each other.

  5. Field and Geochronological Evidence of Partial Melting, Melt Mobilisation and - in a 2.7 GA Metatexite-Diatexite Complex in Troms, Northern Norway

    NASA Astrophysics Data System (ADS)

    Slagstad, T.

    2013-12-01

    diatexite host, and suggest that the latter had a melt-dominated rheology. Abundant pegmatite collected in the spaces between and around the blocks demonstrating that copious melt was available in the system and that ongoing deformation led to pressure differences facilitating melt mobility. The granites are heterogeneous, displaying a diffusely to sharply defined compositional, dm-thick layering. The darker layers can locally be identified as metatexite, and where strain is relatively low, several-dm-long, biotite-rich schlieren are observed. In one place, two enclaves of amphibolite are connected by a 3-4 m-long irregular string of amphibolite. Although field relationships do not exist to demonstrate a genetic relationship between meta-/diatexite and the granitic gneisses, these relationships along with the geochronological data suggest that such a link is likely. Ongoing work aims to demonstrate and characterise the link between partial melting and granite formation in this Neoarchean, Fennoscandian terrain.

  6. 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. PMID:16193050

  7. A new method to investigate the dynamic properties of hydrous minerals and melts pertaining to subduction zones (Invited)

    NASA Astrophysics Data System (ADS)

    Jackson, J. M.

    2013-12-01

    Hydrous phases and melts play an important role in the geochemical and geodynamical evolution of the Earth's interior, and in particular subduction zones. Melts form an important basis for understanding the current state of our planet, as they are responsible for forming the crust of our planet and may likely play a role in understanding low-velocity regions deep within our planet. In an effort to obtain a more detailed understanding of minerals under high-pressure temperature conditions, we have developed a novel metric for detecting the solid-liquid phase boundary of iron-bearing materials at high-pressures using synchrotron Mössbauer spectroscopy (SMS), also known as nuclear forward scattering. Focused synchrotron radiation with 1 meV bandwidth passes through a laser-heated Fe-bearing sample inside a diamond anvil cell. The characteristic SMS time signature vanishes when melting occurs. This process is described by the Lamb-Mössbauer factor, a quantity that is directly related to the mean-square displacement of the iron atoms. Therefore, we measure the dynamics of the atoms in the material, in contrast to a static diffraction measurement. As this method monitors the dynamics of the atoms, the SMS technique provides a new and independent means of melting point determination for materials under high-pressure, as well as access to vibrational properties of the solid near its melting point (Jackson et al. EPSL 2013). In this presentation, we will discuss the applications to phases relevant to subduction zones.

  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. Structural defects and microindentation analysis of zone melted Bi2Te3-xSex whiskers

    NASA Astrophysics Data System (ADS)

    Jariwala, Bhakti; Shah, Dimple V.

    2012-08-01

    The dislocation density and microhardness of Bi2Te3-xSex (x=0-0.3 at% Se) grown by the zone melting method have been investigated. We also have got the whiskers of Bi2Te3-xSex at the end of ampoule during the growth process. SEM was characterized for surface analysis of the grown whisker. The length of the grown whiskers was around 10 mm in the direction of the crystallographic c-axis. Concentric pairs of dislocation triangle were observed on the as-grown surfaces of short hexagonal prisms. A systematic study of dislocations in these crystals was carried out by the chemical etching technique. Dislocation etching was achieved on all crystal planes examined using a saturated solution of citric acid and nitric acid as the etchant. The dislocation etchant has been found to give reproducible etch-pits on the cleavage surface. The use of citric acid and nitric acid proved to be especially advantageous for the basal plane, producing etched pits suitable for dislocation etch pit counting. The effects of Se doping, annealing and quenching on the mechanical properties have also been studied on the (001) faces of Bi2Te3-xSex.

  10. 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.

  11. 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%).

  12. Partial re-equilibration of highly siderophile elements and the chalcogens in the mantle: A case study on the Baldissero and Balmuccia peridotite massifs (Ivrea Zone, Italian Alps)

    NASA Astrophysics Data System (ADS)

    Wang, Zaicong; Becker, Harry; Gawronski, Timo

    2013-05-01

    The conditions at which melt percolation and reactive infiltration of depleted mantle peridotites fractionate highly siderophile elements (HSE) and cause re-equilibration of 187Os/188Os in mantle rocks are still poorly constrained. In a comparative study of the Paleozoic Balmuccia (BM) and Baldissero (BD) peridotite tectonites (Ivrea-Verbano Zone, Northern Italy), the influence of partial melting and melt infiltration on abundances of HSE, chalcogens (S, Se and Te) and 187Os/188Os have been studied. At BM, Re depletion ages (TRD) of lherzolites and replacive dunites display a uniform distribution with a maximum near 400-500 Ma. BD peridotites also display a Paleozoic distribution peak but a significant number of samples yielded Proterozoic TRD. The predominance of Paleozoic Re depletion ages in both bodies is consistent with Sm-Nd ages and the late Paleozoic magmatic and geodynamic evolution of the Ivrea-Verbano Zone. The different extents of preservation of ancient 187Os/188Os in BM and BD peridotites are interpreted to reflect different degrees of isotopic homogenization and chemical re-equilibration with incompatible element-depleted infiltrating melt during the Paleozoic. The differences between the two bodies are also reflected by differences in HSE and chalcogen abundances, with BD displaying large scatter among HSE patterns, slight re-enrichment of Re relative to Au, and linear trends of Pd, Se and Te with Al2O3. The differences in distributions of model ages and heterogeneity in HSE abundances support the view that the lithophile element, HSE and chalcogen variations of different suites of lherzolites likely reflect different extents of reactive melt infiltration in mantle peridotites, with partial re-equilibration and melt extraction in open system environments. However, the variable re-equilibration of BM and BD lherzolites apparently did not produce significant differences in HSE ratios such as Os/Ir, Ru/Ir, Rh/Ir, and Pd/Pt, which are in the range of

  13. Reductions in contaminant mass discharge following partial mass removal from DNAPL source zones.

    PubMed

    Suchomel, Eric J; Pennell, Kurt D

    2006-10-01

    Although in situ remediation technologies have been used to aggressively treat dense nonaqueous phase liquid (DNAPL) source zones, complete contaminant removal or destruction is rarely achieved. To evaluate the effects of partial source zone mass removal on dissolved-phase contaminant flux, four experiments were conducted in a two-dimensional aquifer cell that contained a tetrachloroethene (PCE) source zone and down-gradient plume region. Initial source zone PCE saturation distributions, quantified using a light transmission system, were expressed in terms of a ganglia-to-pool ratio (GTP), which ranged from 0.16 (13.8% ganglia) to 1.6 (61.5% ganglia). The cells were flushed sequentially with a 4% (wt.) Tween 80 surfactant solution to achieve incremental PCE mass removal, followed by water flooding until steady-state mass discharge and plume concentrations were established. In all cases, the GTP ratio decreased with increasing mass removal, consistent with the observed preferential dissolution of PCE ganglia and persistence of high-saturation pools. In the ganglia-dominated system (GTP = 1.6), greater than 70% mass removal was required before measurable reductions in plume concentrations and mass discharge were observed. For pool-dominated source zones (GTP < 0.3), substantial reductions (>50%) in mass discharge were realized after only 50% mass removal. PMID:17051808

  14. 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.

  15. Partial melting of thickened continental crust in central Tibet: Evidence from geochemistry and geochronology of Eocene adakitic rhyolites in the northern Qiangtang Terrane

    NASA Astrophysics Data System (ADS)

    Long, Xiaoping; Wilde, Simon A.; Wang, Qiang; Yuan, Chao; Wang, Xuan-Ce; Li, Jie; Jiang, Ziqi; Dan, Wei

    2015-03-01

    The composition of the deep crust is a key to understanding the formation of the low-velocity zone in the middle to lower crust of the Tibetan Plateau. The Suyingdi rhyolites exposed in the northern Qiangtang Terrane have high Sr (296-384 ppm) and low Y (5.81-7.93 ppm), with therefore high Sr/Y ratios (42-56), showing geochemical features of adakitic rocks. Zircon U-Pb dating yields an eruption age of 38.2 ± 0.8 Ma (MSWD = 0.78). These adakitic rhyolites are high-K calc-alkaline in composition, displaying a weakly peraluminous character. They have low MgO content (0.20-0.70 wt.%) and Mg# values (24-39), as well as low Sc (2.25-2.76 ppm), Cr (8-14 ppm), Co (1.6-3.5 ppm) and Ni (2-3 ppm) concentrations. The rocks are LREE-enriched ((La/Yb)N = 50-62) and display weakly negative Eu anomalies (Eu/Eu* = 0.82-0.95) and pronounced negative Nb and Ta anomalies. They have low initial (87Sr/86Sr)i ratios (0.707860 to 0.708342) and enriched Nd isotopic compositions with εNd (t) values ranging from -8.4 to -5.0, which are indistinguishable from those of Cenozoic potassic and ultra-potassic lavas exposed in northern Tibet. Their much higher SiO2 and lower Fe2O3 contents, yet similar MgO, Cr, Co, Ni, and Mg# values to the potassic and ultra-potassic lavas, however, indicate that the rhyolites are unlikely to have formed by fractional crystallization of these lavas. Because of their low Nb/Ta ratios and similar Sr-Nd isotopic compositions to granulite xenoliths within the Cenozoic potassic rocks, we infer that the Suyingdi adakitic rhyolites were most likely produced by partial melting of a thickened lower crust in the garnet stability field. The magma source is most likely dominated by granulite facies metabasalts and clay-poor metamorphosed sedimentary rocks which indicate that the lower crust of northern Tibet is heterogeneous. In combination with data from previously-reported peraluminous and metaluminous adakitic rocks in the same region, the age and petrogenesis of the

  16. The Melt Segregation During Ascent of Buoyant Diapirs in Subduction Zones

    NASA Astrophysics Data System (ADS)

    Zhang, N.; Behn, M. D.; Parmentier, E. M.; Kincaid, C. R.

    2014-12-01

    Cold, low-density diapirs arising from hydrated mantle and/or subducted sediments on the top of subducting slabs may transport key chemical signatures from the slab to the shallow source region for arc magmas. These chemical signatures are strongly influenced by melting of this buoyant material during its ascent. However, to date there have been relatively few quantitative models to constrain melting and melt segregation in an ascending diapir, as well as the induced geochemical signature. Here, we use a two-phase Darcy-Stokes-energy model to investigate thermal evolution, melting, and melt segregation in buoyant diapirs as they ascend through the mantle wedge. Using a simplified 2-D axi-symmetric circular geometry we investigate diapir evolution in three scenarios with increasing complexity. First, we consider a case without melting in which the thermal evolution of the diapir is controlled solely by thermal diffusion during ascent. Our results show that for most cases (e.g., diapir radius ≤ 3.7 km and diapir generation depths of ~ 75 km) thermal diffusion times are smaller than the ascent time—implying that the diapir will thermal equilibrate with the mantle wedge. Secondly, we parameterize melting within the diapir, but without melt segregation, and add the effect of latent heat to the thermal evolution of the diapir. Latent heat significantly buffers heating of the diapir. For the diapir with radius ~3.7 km, the heating from the outside is slowed down ~30%. Finally, we include melt segregation within the diapir in the model. Melting initiates at the boundaries of the diapir as the cold interior warms in response to thermal equilibration with the hot mantle wedge. This forms a high porosity, high permeability rim around the margin of the diapir. As the diapir continues to warm and ascend, new melts migrate into this rim and are focused upward, accumulating at the top of the diapir. The rim thus acts like an annulus melt channel isolating the central part of

  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. 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.

  19. 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

  20. 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. PMID:27152343

  1. Partial melting and fractionation in the Mesa Chivato alkali basalt-trachyte series, Mount Taylor Volcanic Field, New Mexico

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Mesa Chivato comprises a series of alkaline cones, flows, and domes within the Mount Taylor Volcanic Field (MTVF) in northwest New Mexico. Compositions range from alkali basalt to trachyte. Intermediate magmas are less well represented than mafic and felsic rocks, but benmoreites and transitional benmoreite-trachytes provide a window into the differentiation processes. Major element, trace element, and isotopic data suggest that petrogenesis of benmoreite proceeded by fractional crystallization of mafic liquids and magma mixing with partially melted mafic rocks. Major element mass balance models permit the derivation of transitional benmoreite/trachyte from the benmoreite by 20-25% crystallization of microphenocryst phases (olivine, plagioclase, Ti-magnetite, and apatite) and further fractionation to trachyte by 10-15% crystallization of olivine, plagioclase and alkali feldspar, Fe-Ti oxide, and apatite. These models are supported by SiO2-Sr and -Ba systematics. However, the hawaiite to benmoreite gap cannot be crossed by fractional crystallization alone. While major element models permit the mafic lavas to yield the benmoreite, they require extensive fractionation of clinopyroxene and plagioclase - this is unsupported by petrography (clinopyroxene phenocrysts are rare in the mafic rocks and lacking in the intermediate rocks) and cannot explain the benmoreite's very high Sr contents (>1800 ppm), which would have been depleted by plagioclase fractionation. From LA-ICPMS analysis of plagioclase: 87Sr/86Sr of early alkali basalt (0.70285-0.70300) and late hawaiite (0.70406-0.70421) bracket the 87Sr/86Sr of the benmoreite (0.70361-0.70406). Thus, either could represent the fractionated liquid parental to the benmoreite and the other the partially melted source.

  2. 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

  3. Modified Iterative Sandwich Experiments (MISE) for determination of small-degree partial melt compositions: An example for carbonated peridotite at 6.6 GPa

    NASA Astrophysics Data System (ADS)

    Hirschmann, M. M.; Dasgupta, R.

    2006-12-01

    Small degree partial melts may play a significant role in the geochemical and geodynamical evolution of the mantle at a spectrum of depths ranging from the source regions of erupted basalts down to the lower mantle. However, because small-degree partial melts reside in small pockets along grain edges or triple junctions, they are not easily analyzed and so direct experimental determination of their compositions is challenging. Melt trap methods overcome some of these problems, but for various reasons such methods are best employed chiefly at modest pressures (<3 GPa). Sandwich experiments, in which a layer of melt is added to a whole-rock to produce large melt pools, have significant promise. Applied iteratively, with the melt composition resulting from one experiment added as the "meat" of the subsequent experimental sandwich, the method converges to the composition of the partial melt at the solidus (melt fraction approaching zero) of the "bread" composition. However, iterative sandwich experiments converge very slowly, possibly requiring dozens of iterations to yield a meaningful result for some elements. To circumvent this problem, we have developed a modified iterative sandwich experiment (MISE) technique that employs measured partition coefficients, D, and mass balance to estimate the equilibrium solidus melt composition. Monte Carlo simulations show that the method is robust and converges rapidly even when estimates of D have considerable random and systematic uncertainties. The MISE method can also be adapted to investigate small finite (0-10%) melt fractions above the solidus. We applied the MISE method to determine the composition of near-solidus partial melt of carbonated peridotite at 6.6 GPa and 1200°-1260° C using a Walker-style multi-anvil apparatus. We performed 6 iterations, but melt compositions changed little after the third iteration, demonstrating that rapid convergence can be achieved with this method. The near solidus liquid, estimated from

  4. The partial molar sound speed of TiO2 in sodium silicate melts: Evidence for an exceptionally compressible component

    NASA Astrophysics Data System (ADS)

    Liu, Q.; Ai, Y.; Lange, R. A.

    2005-12-01

    Longitudinal acoustic velocities were measured at one bar by an ultrasonic frequency sweep acoustic interferometer for ten Na2O-TiO2-SiO2 (NTS) liquids for which previous density and thermal expansion measurements were made (Liu and Lange, 2001). This previous study showed that the partial molar volume of the TiO2 component varied systematically with composition and reflected changes in the average coordination of Ti4+ from values of ~4.6 to ~5.4. Sound speed data were collected at frequencies of 4.5, 5, and 6 MHz between 1233 and 1896 K; in all cases, the sound speeds decrease with increasing temperature. Six of the liquids share a similar (~25 mol%) TiO2 concentration, so that the effect of varying Na:Si ratio on the partial molar sound speed of the TiO2 component can be evaluated. The results for these ten NTS liquids were combined with sound speed data on Na2O-SiO2 liquids from the literature to derive the partial molar sound speed of the TiO2 component in these liquids. The results show that, at 1573 K, it is inversely correlated with SiO2 concentration, from values as low as 571±56 m/s to those as high as 1235±54 m/s, a variation of more than 100%. Fitted values for the partial molar sound speeds of the SiO2 and Na2O components at 1573 K are constants at 2538±52 and 2713±52 m/s, respectively. When the sound speed data are combined with density data to calculate melt compressibility, the results show that the TiO2 component is 3-15 more compressible than either the Na2O or SiO2 component. The partial molar compressibility of the TiO2 component is also strongly correlated to its partial molar thermal expansivity. It is shown that the TiO2 component is most compressible and most expansive when the average Ti4+ coordination in these sodium silicate liquids is near five, which strongly suggests that the abundance of five-coordinated Ti4+ enhances topological mechanisms of both compression and thermal expansion.

  5. 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

  6. Evidence of partial melting beneath the passive margin of the Gulf of Aden from a joint analysis of gravity and seismology

    NASA Astrophysics Data System (ADS)

    Basuyau, C.; Tiberi, C.; Leroy, S.; Ebinger, C.; Al-Lazki, A.; Al-Tobi, K.

    2007-12-01

    Rifting processes though extensively studied are still not well known. Nevertheless geophysical studies can provide new insight into the mechanisms of continental opening. The Gulf of Aden is a young narrow and obliquely opening oceanic basin formed during the Olig-Miocene. Its conjugate margins are well preserved beneath a thin post-rift sedimentary cover.It thus makes it an ideal region to study the processes of rifting and continental lithospheric break-up. In 2003 and 2005, numerous teleseismic earthquakes were recorded at twenty-nine broadband seismic stations in Dhofar (Oman) in order to study the northern margin of the Gulf of Aden. In this work, we used a joint inversion of teleseismic P-wave delay times and Bouguer anomaly. We obtain velocity ans density models that shows (1) crustal heterogeneities that match to the main geological features at the surface, (2) the presence of two low velocity anomalies in the continuation of Socotra and Alula Fartak fracture zones that appear at 60 km depth and may extend to at least 200 km, (3) gravity edge effect on the margin. The S wave tomography results are consistent with the joint inversion ones, and evidence partial melting within the two deep velocity anomalies. These results which suggest that the Afar hotspot has an influence up to the Dhofar will be discussed.

  7. Experimental investigation of low temperature garnet-melt partitioning in CMASH, with application to subduction zone processes.

    NASA Astrophysics Data System (ADS)

    Morizet, Y.; Blundy, J.; McDade, P.

    2003-04-01

    During subduction, the slab undergoes several processes such as dehydration and partial melting at pressures of 2-3 GPa and temperatures of 600-900^oC. Under these conditions, there is little or no distinction between melt and fluid phases (Bureau &Keppler, 1999, EPSL 165, 187-196). To investigate the behaviour of trace elements under these conditions we have carried out partitioning experiments in the system CMASH at 2.2 GPa, 700-920^oC. CMAS starting compositions were doped with trace elements, and loaded together with quartz and water into a Pt capsule, which was in turn contained within a Ni-lined Ti capsule. Run durations were 3-7 days. A run at 810^oC produced euhedral calcic garnet, zoisite, quartz, hydrous melt and tiny clinopyroxene interpreted as quench crystals. LA-ICPMS and SIMS were used to quantify trace element concentrations of the phases. Garnet-melt D's for the HREE decrease from ˜300 for Lu to less than 0.2 for La. DSc and D_V are less than 5, consistent with the large X-site dimension in the garnet. DLi DSr and DBa are considerably less than the adjacent REE. There is a very slight negative partitioning anomaly for Zr and Hf relative to Nd and Sm; DHf is slightly greater than DZr. D_U < DTh, due largely to the oxidizing conditions of the experiment (NNO). The most striking result is very high D's for Nb and Ta: 18±10 and 5.4±1.9 (LA-ICPMS), 25.8±11.9 and 6.6±1.3 (SIMS) for Nb and Ta respectively. These are considerably larger than any previously measured (at much higher temperatures). The observed partitioning behaviour is consistent with the large temperature dependence for DREE proposed by Van Westrenen et al. (2001, Contrib Min Pet, 142, 219-234), and an even larger temperature dependence for DNb and DTa. These preliminary results suggest that garnet (rather than rutile) may play the key role in controlling the Nb and Ta budget of arc magmas and the Nb/Ta ratio of residual eclogites. For example, modelling of eclogite melting, using a N

  8. 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.

  9. Ascent and emplacement of pegmatitic melts in a major reverse shear zone (Sierras de Córdoba, Argentina)

    NASA Astrophysics Data System (ADS)

    Demartis, Manuel; Pinotti, Lucio Pedro; Coniglio, Jorge Enrique; D'Eramo, Fernando Javier; Tubía, José María; Aragón, Eugenio; Agulleiro Insúa, Leonardo Alfredo

    2011-09-01

    Ordovician to Devonian aged crustal-scale Guacha Corral shear zone (GCSZ), central Argentina, hosts rare element pegmatites of the Comechingones pegmatitic field (CPF). In the CPF an eastwards decreasing strain gradient related to the GCSZ deformation is defined, with a high strain domain (HSD) to the west and a low strain domain (LSD) to the east. Pegmatites of the CPF were emplaced in both HSD and LSD synkinematically during ductile GCSZ deformation. Two main mechanisms for pegmatitic melt ascent and emplacement are recognized: "fracture-controlled" and "magma pumping" mechanisms. The former implies fracturing generated due to simple shear deformation not related to any previous heterogeneity. With further deformation, pegmatites were emplaced in low-dip surfaces of anisotropy (C'-planes or T-fractures), that might behave as releasing bends connecting adjacent high-dip conduits or shear zones. Displacements along staggered shear zones with releasing bends induce the local development of domains with negative pressure gradients, where open spaces could form transiently attracting for the collection of buoyant melts, a mechanism similar to "magma pumping". With ongoing deformation pegmatites were progressively rotated, sheared and transposed to the mylonitic foliation. Late pegmatites emplaced by either of the two mechanisms in the HSD and the TZ have retained their original orientations.

  10. Experimental Constraints on Pelite Melting in Subduction Zones: a New Approach Using HP Metapelites

    NASA Astrophysics Data System (ADS)

    Levay, B.; Kerrick, D.; Eggler, D.

    2004-12-01

    During subduction, sea-floor pelites melt and enrich the mantle wedge with many of the elements that give arc magmas their unique chemistry. This melt allows us to constrain subduction thermal models; e.g., the plate must be hotter than the experimentally determined pelite solidus. Previous melting experiments used marine red clays, but we know from high pressure and ultra-high pressure terrains that prograde metamorphism changes the composition of sediments before they reach sub-arc depths. A prime example of this alteration comes from the Gåsetjorn unit in the Norwegian Caledonides. Here, 400-410 million years ago, ocean sediments were subducted beyond 50 km and heated to 600° C. These minimally retrograded metapelites have a higher aluminum to silica ratio than any modern sea-floor sediment and they are depleted in potassium, sodium, magnesium, and calcium. Thus, the Gåsetjorn metapelite is a more appropriate starting material than marine clay for deep melting experiments. We performed high pressure melting experiments on a sample from the Gåsetjorn unit and we found a 20 kb fluid-saturated solidus between 625° C and 650° C. This is the lowest pelite solidus yet obtained at these depths.

  11. 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

  12. 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.

  13. 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. PMID:17820306

  14. 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)

  15. 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.

  16. Drastic shift in lava geochemistry in the volcanic-front to rear-arc region of the Southern Kamchatkan subduction zone: Evidence for the transition from slab surface dehydration to sediment melting

    NASA Astrophysics Data System (ADS)

    Duggen, Svend; Portnyagin, Maxim; Baker, Joel; Ulfbeck, David; Hoernle, Kaj; Garbe-Schönberg, Dieter; Grassineau, Nathalie

    2007-01-01

    The shift of lava geochemistry between volcanic front to rear-arc volcanoes in active subduction zones is a widespread phenomenon. It is somehow linked to an increase of the slab surface depth of the subducting oceanic lithosphere and increasing thickness of the mantle wedge and new constraints for its causes may improve our understanding of magma generation and element recycling in subduction zones in general. As a case study, this paper focuses on the geochemical composition of lavas from two adjacent volcanic centres from the volcanic front (VF) to rear-arc (RA) transition of the Southern Kamchatkan subduction zone, with the aim to examine whether the shift in lava geochemistry is associated with processes in the mantle wedge or in the subducted oceanic lithosphere or both. The trace element and O-Sr-Nd-Hf-Pb (double-spike)-isotopic composition of the mafic Mutnovsky (VF) and Gorely (RA) lavas in conjunction with geochemical modelling provides constraints for the degree of partial melting in the mantle wedge and the nature of their slab components. Degrees of partial melting are inferred to be significantly higher beneath Mutnovsky (˜18%) than Gorely (˜10%). The Mutnovsky (VF) slab component is dominated by hydrous fluids, derived from subducted sediments and altered oceanic crust, eventually containing minor but variable amounts of sediment melts. The composition of the Gorely slab component strongly points to a hydrous silicate melt, most likely mainly stemming from subducted sediments, although additional fluid-contribution from the underlying altered oceanic crust (AOC) is likely. Moreover, the Hf-Nd-isotope data combined with geochemical modelling suggest progressive break-down of accessory zircon in the melting metasediments. Therefore, the drastic VF to RA shift in basalt chemistry mainly arises from the transition of the nature of the slab component (from hydrous fluid to melt) in conjunction with decreasing degrees of partial melting within ˜15 km

  17. 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.

  18. How do Hyporheic Zones Mediate Stream Solute Loads? Using Antarctic Glacial Melt Streams to Simplify the Problem.

    NASA Astrophysics Data System (ADS)

    Wlostowski, A. N.; Gooseff, M. N.; McKnight, D. M.

    2014-12-01

    The McMurdo Dry Valleys of Antarctica are one of the coldest and driest places on earth. This polar desert provides a simple hydrologic system, where seasonally intermittent streams convey glacier melt water into closed basin lakes. Streams are underlain by continuous permafrost, but during the flow season a thawed hyporheic zone (<1m) develops around the open channel. The exchange of relatively dilute glacier water with hyporheic sediments facilitates weathering processes that control stream solute loads. This study uses several end-member mixing models to simulate concentration - discharge relationships observed in 14 streams, using over 20 years of hydro chemical data. Results show that (1) streams exhibit chemostatic behavior across daily and annual timescales, indicating a temporally variable flux of solutes from the hyporheic zone; (2) the chemical budgets of longer streams are more influenced by hyporheic zone reactions than shorter streams; and (3) end-member mixing models and naturally occurring tracers allow for the passive modeling of hyporheic exchange processes. This work provides insight into how weathering contributions from hyporheic zones affect catchment ionic budgets in diverse temperate and polar catchments with dilute snow and glacial meltwater sources of streamflow.

  19. 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

  20. 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

  1. Rebound of a coal tar creosote plume following partial source zone treatment with permanganate

    NASA Astrophysics Data System (ADS)

    Thomson, N. R.; Fraser, M. J.; Lamarche, C.; Barker, J. F.; Forsey, S. P.

    2008-11-01

    The long-term management of dissolved plumes originating from a coal tar creosote source is a technical challenge. For some sites stabilization of the source may be the best practical solution to decrease the contaminant mass loading to the plume and associated off-site migration. At the bench-scale, the deposition of manganese oxides, a permanganate reaction byproduct, has been shown to cause pore plugging and the formation of a manganese oxide layer adjacent to the non-aqueous phase liquid creosote which reduces post-treatment mass transfer and hence mass loading from the source. The objective of this study was to investigate the potential of partial permanganate treatment to reduce the ability of a coal tar creosote source zone to generate a multi-component plume at the pilot-scale over both the short-term (weeks to months) and the long-term (years) at a site where there is > 10 years of comprehensive synoptic plume baseline data available. A series of preliminary bench-scale experiments were conducted to support this pilot-scale investigation. The results from the bench-scale experiments indicated that if sufficient mass removal of the reactive compounds is achieved then the effective solubility, aqueous concentration and rate of mass removal of the more abundant non-reactive coal tar creosote compounds such as biphenyl and dibenzofuran can be increased. Manganese oxide formation and deposition caused an order-of-magnitude decrease in hydraulic conductivity. Approximately 125 kg of permanganate were delivered into the pilot-scale source zone over 35 days, and based on mass balance estimates < 10% of the initial reactive coal tar creosote mass in the source zone was oxidized. Mass discharge estimated at a down-gradient fence line indicated > 35% reduction for all monitored compounds except for biphenyl, dibenzofuran and fluoranthene 150 days after treatment, which is consistent with the bench-scale experimental results. Pre- and post-treatment soil core data

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

    NASA Astrophysics Data System (ADS)

    Akasaki, Eri; Owada, Masaaki; Kamei, Atsushi

    2015-08-01

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

  3. 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

  4. 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. PMID:19865169

  5. 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.

  6. 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

  7. 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

  8. Impact of gneissic layering and localized incipient melting upon melt flow during experimental deformation of migmatites

    NASA Astrophysics Data System (ADS)

    Ganzhorn, A. C.; Trap, P.; Arbaret, L.; Champallier, R.; Fauconnier, J.; Labrousse, L.; Prouteau, G.

    2016-04-01

    In this study, we test experimentally the role of compositional layering as a key parameter for controlling melt flow in a natural migmatite during coaxial deformation. We performed in - situ pure-shear experiments on two natural gneisses. The first gneiss is weakly foliated with minerals homogenously distributed. The second gneiss shows a pronounced compositional layering of alternating quartz - feldspar - rich and biotite - muscovite - rich layers. Experimental conditions were selected to obtain homogeneous melt distribution in the homogeneous gneiss and heterogeneous melt distribution in the layered gneiss. Initial melt distribution is not modified by deformation in experiments on the homogeneous gneiss, implying that melting products did not migrate from their initiation sites. In contrast, melt flowed in shear zones or in inter-boudin positions during experimental deformation of the heterogeneous gneiss. These experiments attest to the strong influence of initial gneissic layering on melting pattern, melt segregation and flow during deformation of partially molten rocks.

  9. 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. PMID:21527627

  10. 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

  11. 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

  12. Experimentally determined distribution of fluorine and chlorine upon hydrous slab melting, and implications for F-Cl cycling through subduction zones

    NASA Astrophysics Data System (ADS)

    Van den Bleeken, Greg; Koga, Kenneth T.

    2015-12-01

    Fluorine and chlorine are volatile elements known to be enriched in primitive arc magmas, and variations of F/Cl ratios can carry information about slab devolatilization processes. Recent experiments on the fractionations of these elements suggest that aqueous fluid has limited capacity to enrich the magma source region in F. Hence, it is difficult to explain observations of primitive arc magmas particularly rich in F. To complement previous experimental studies, we examined the fractionation of fluorine and chlorine during hydrous partial melting of subducting slab. Element-doped phase equilibria experiments were carried out in a complex chemical system at conditions equivalent to potential slab melting temperatures (750-1000 °C) across the amphibolite to eclogite facies transition (1.3-3 GPa). Partition coefficients of F and Cl between hydrous silicic melts and minerals were determined by electron microprobe and/or ion probe. Fluorine is compatible in amphibole (DFamp/glass = 1.18-1.85), and incompatible in garnet (0.034-0.140), clinopyroxene (0.059-0.505), and allanite (0.205-0.504). Hence, amphibole is an important F host, and can retain significant quantities of F in the solid residue of partial melting. On the contrary, Cl is incompatible, with DClmineral/glass generally decreasing from amphibole (0.079-0.625; one outlier at 1.87) to allanite (0.163), clinopyroxene (0.066-0.158), and garnet (0.031-0.153; outlier at 0.492). As a result, Cl is easily mobilized during partial melting. Fluorine and chlorine release during slab melting have been quantified by applying our partition coefficients to a non-modal batch melting model. The model shows that amphibole plays a key role in F/Cl fractionation during partial melting, while F/Cl is close to that of source for the melting of amphibole free eclogite. Moreover, the results from a flux-melting model employing several source compositions are compared to F and Cl abundances in primitive arc magmas. The observed

  13. 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.

  14. Trace element analyses of spheres from the melt zone of the Greenland ice CAP using synchrotron X ray fluorescence

    NASA Astrophysics Data System (ADS)

    Chevallier, P.; Wang, J.; Jehanno, C.; Maurette, M.; Sutton, S. R.

    1987-03-01

    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 the 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 the ejection of globules of Fe/Ni from parent chondritic micrometeoroids.

  15. Trace element analyses of spheres from the melt zone of the Greenland Ice Cap using synchrotron X ray fluorescence

    NASA Astrophysics Data System (ADS)

    Chevallier, P.; Jehanno, C.; Maurette, M.; Sutton, S. R.; Wang, J.

    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 the ejection of globules of Fe/Ni from parent chondritic micrometeoroids.

  16. Trace element analyses of spheres from the melt zone of the Greenland ice cap using synchrotron X ray fluorescence

    NASA Astrophysics Data System (ADS)

    Chevallier, P.; Jehanno, C.; Maurette, M.; Sutton, S. R.; Wang, J.

    1987-09-01

    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 chondrite spheres are not complementary and consequently the two iron spheres examined in this study are unlikely to result from the ejection of globules of Fe/Ni from parent chondritic micrometeroids. © American Geophyscial Union 1987

  17. Purification of Cu by hydrogen plasma-arc zone melting and characterization of trace impurities by secondary ion mass spectrometry

    SciTech Connect

    Lalev, G.M.; Lim, J.-W. Munirathnam, N.R. Choi, G.-S.; Uchikoshi, M.; Mimura, K.; Isshiki, M.

    2009-01-15

    Purification of 4N (99.99%) and 6N (99.9999%) purity Cu rods by hydrogen plasma-arc zone melting was carried out. Weight loss in the 4N and 6N Cu rods as a function of number of zone refined passes revealed a higher rate of impurity removal by vaporization in 4N Cu when compared to 6N Cu. Purification effect was studied by analyzing major impurities like Mg, Si, Ca, Ti, Cr, Ni and Fe by O{sub 2}{sup +} ions and C, O, As, Cl, P and S by Cs{sup +} ion sources using secondary ion mass spectrometry. A remarkable decrease of Si, Ti and Fe impurity concentrations in Cu at x/L = 0.03 after 10 zone passes was observed, but no similar purification effect along the remaining length of the zone refined copper rod was observed. Mg, Se and Ca in the Cu rods were reduced faster by a high evaporation effect due to P{sub i}/P{sub Cu} > 10{sup 2}. On the other hand, removal of O, C, S and Se was expectedly dominated by vaporization in the form of H{sub 2}O, CH{sub 4,} H{sub 2}S, and H{sub 2}Se through thermodynamically favored reactions. The overall segregation rate of the individual impurity elements was decreased with an increase in the purity from 4N to 6N of Cu rods. SIMS analysis of trace impurities was successfully carried out on HPZM Cu for quantitative estimation.

  18. Zircon U-Pb ages and Hf-O isotopic composition of migmatites from the Zanjan-Takab complex, NW Iran: Constraints on partial melting of metasediments

    NASA Astrophysics Data System (ADS)

    Moghadam, Hadi Shafaii; Li, Xian-Hua; Stern, Robert J.; Ghorbani, Ghasem; Bakhshizad, Farzaneh

    2016-01-01

    We study migmatites and other metamorphic rocks in the Zanjan-Takab region of NW Iran and use these results to report the first evidence of Oligocene core complex formation in Iran. Four samples of migmatites associated with paragneisses, including leucosomes and associated para-amphibolite melanosomes were selected for U-Pb dating and Hf-O isotopic analysis. Zircon cores - interpreted as originally detrital zircons - have variable ages that peak at ca. 100-110 Ma, but their sedimentation age - indicated by the youngest 206Pb/238U ages - is ca. 35-40 Ma. New zircons associated with incipient melting occur as overgrowths around zircon cores and/or as newly grown grains. Morphologies and internal structures suggest that rim growth and formation of new zircons were associated with partial melting. All four samples contain zircons with rims that yield 206Pb/238U ages of 28-25 Ma, indicating that partial melting occurred in Late Oligocene time. δ18O values for zircon rims vary between 8.2 and 12.3‰, significantly higher than expected for mantle inputs (δ18O ~ 6‰) and consistent with equilibrium with surface materials. Zircon rims yield εHf(t) between 2.2 and 12.4 and two-stage Hf model ages of ~ 448-562 Ma, indicating that the region is underlain by Cadomian-Caledonian crust. According to the Hf-O isotopic values, the main mechanism forming zircon rims was dissolution of pre-existing detrital zircons with reprecipitation of new zircon shortly thereafter. Oligocene ages indicate that partial melting accompanied core complex formation in the Zanjan-Takab region. Extension, melting, and core complex formation in south-central Iran are Eocene in age, but younger ages of Oligocene-Miocene in NW Iran and Turkey indicate that extension was distributed throughout the region during Cenozoic time.

  19. 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

  20. Unusual Presentations of Focal Periphyseal Edema Zones: A Report of Bilateral Symmetric Presentation and Partial Physeal Closure

    PubMed Central

    Beckmann, Nicholas; Spence, Susanna

    2015-01-01

    Focal periphyseal edema (FOPE) zones are areas of periphyseal edema seen near the time of physeal closure which are believed to be a physiologic phenomenon related to changes in distribution of forces around the physis as it closes. Since the original case series describing these areas of periphyseal edema, there has been little published in regard to FOPE zone outside of review articles. We present a set of three patients identified with focal periphyseal edema zones around the knee and compare our findings with the initial case series. We include a patient presenting with bilateral, nearly symmetric, focal periphyseal edema zones of the proximal tibia physis and a patient with partial closure of the physis at time of presentation, which were not reported in the original case series. PMID:26640734

  1. 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.

  2. Primitive Subduction Zone Magmatism at Mt. Shasta, California: Geochemical and Petrologic Characteristics of Hydrous Mantle Derived Melts

    NASA Astrophysics Data System (ADS)

    Barr, J. A.; Grove, T. L.; Carlson, R. W.

    2008-12-01

    peridotite to the dacite will lower its Os isotopic composition and raise its Os content to values similar to the PMA. However, this very small amount of peridotite has negligible effect on the major element content of the mixture. Hence, contamination with basement peridotite cannot simultaneously explain the high-Mg character and Os isotope characteristics of the andesite. Thus, the geochemical and petrologic evidence preclude the derivation of PMA magma from being mixtures of other Mt. Shasta lavas and ultramafic materials. Therefore, the PMA lavas can provide clues to the geochemical signature, HFSE and isotopic, of subduction zone fluids and primitive mantle melts. Overall, the difference in major elemental compositions of the flow and vent PMA samples is so little that the experimental results from previous studies of the Grove et al. (2003), on PMA sample 85-41c of Mt. Shasta, are applicable to the conditions of hydrous mantle melting that produced the PMA magma, and the PMA flow samples provide the most uncontaminated look at the primitive inputs into Mt. Shasta.

  3. 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.

  4. 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

  5. Responses of canopy transpiration and canopy conductance of peach (Prunus persica) trees to alternate partial root zone drip irrigation

    NASA Astrophysics Data System (ADS)

    Gong, Daozhi; Kang, Shaozhong; Zhang, Jianhua

    2005-08-01

    We investigated canopy transpiration and canopy conductance of peach trees under three irrigation patterns: fixed 1/2 partial root zone drip irrigation (FPRDI), alternate 1/2 partial root zone drip irrigation (APRDI) and full root zone drip irrigation (FDI). Canopy transpiration was measured using heat pulse sensors, and canopy conductance was calculated using the Jarvis model and the inversion of the Penman-Monteith equation. Results showed that the transpiration rate and canopy conductance in FPRDI and APRDI were smaller than those in FDI. More significantly, the total irrigation amount was greatly reduced, by 34.7% and 39.6%, respectively for APRDI and FPRDI in the PRDI (partial root zone drip irrigation) treatment period. The daily transpiration was linearly related to the reference evapotranspiration in the three treatments, but daily transpiration of FDI is more than that of APRDI and FPRDI under the same evaporation demand, suggesting a restriction of transpiration water loss in the APRDI and FPRDI trees. FDI needed a higher soil water content to carry the same amount of transpiration as the APRDI and FPRDI trees, suggesting the hydraulic conductance of roots of APRDI and FPRDI trees was enhanced, and the roots had a greater water uptake than in FDI when the average soil water content in the root zone was the same. By a comparison between the transpiration rates predicted by the Penman-Monteith equation and the measured canopy transpiration rates for 60 days during the experimental period, an excellent correlation along the 1:1 line was found for all the treatments (R2 > 0.80), proving the reliability of the methodology.

  6. 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

  7. Tularosa Basin Play Fairway Analysis: Partial Basin and Range Heat and Zones of Critical Stress Maps

    SciTech Connect

    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.

  8. Effect of subduction components on production of basalts from Tateshina volcano, central Japan: geochemical calculation of dehydration of subducting oceanic crust and partial melting of overlying sediments, and subsequent fluid-mantle interaction

    NASA Astrophysics Data System (ADS)

    Katoh, Masayasu; Shuto, Kenji

    Effect of subduction components on production of basalts from Tateshina volcano, central Japan: geochemical calculation of dehydration of subducting oceanic crust and partial melting of overlying sediments, and subsequent fluid-mantle interaction

  9. 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.

  10. Do melt-rich shear zones lubricate rift flanks? 3-D spatial gradients in anisotropy beneath the East African Rift in Ethiopia

    NASA Astrophysics Data System (ADS)

    Holtzman, B. K.; Gaherty, J. B.; Kendall, J.; Stuart, G.

    2006-12-01

    Melt-enhanced weakening of the mantle may be essential for a continent to break apart and rift. A primary means of understanding this aspect of the dynamics of rifting (and other geodynamic settings) is the interpretation of seismic anisotropy in terms of melt distribution and/or mantle flow direction. In recent rock- deformation experiments, the relationships between flow direction and seismic fast direction are complicated by the presence of water (e.g. Katayama et al., 2004) and segregated melt (Holtzman et al. 2003). In the latter, deviatoric stress drives melt to organize into networks of melt-rich shear zones. Scaling from laboratory to upper mantle conditions predicts characteristic network spacings of <1 km, less than wavelengths of measured seismic waves; thus they should cause significant seismic anisotropy. Measurable gradients in anisotropy may be diagnostic indicators of gradients in melt segregation. Because melt-rich shear zones will weaken the mantle on a large scale, the presence of such anisotropy gradients would map to gradients in viscosity. To map melt distribution beneath the rift and test for the presence or absence of this process, we combine measurements of seismic velocities beneath the East African Rift in Ethiopia with modeling of elastic properties of aligned, segregated melt and olivine fabric. Analysis of SKS phases has shown that fast directions parallel magmatic centers in the rift and splitting magnitudes are largest near the rift flanks, consistent with the hypothesis above (e.g. Kendall et al., 2006). Preliminary analysis of Love-Rayleigh differential times across the rift are consistent with a vertical fast axis, suggesting the presence of a vertically aligned, rift parallel melt phase down to the solidus (Pilidou et al., 2005). We expand on these results by applying a cross-correlation procedure to precisely estimate relative amplitude and phase of surface waves traversing the rift. Data are derived from the EAGLE and Ethiopia

  11. [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. PMID:25069335

  12. 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.

  13. 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

  14. 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

  15. Mineralogy of silicate inclusions of the Colomera IIE iron and crystallization of Cr-diopside and alkali feldspar from a partial melt

    NASA Astrophysics Data System (ADS)

    Takeda, Hiroshi; Hsu, Weibiao; Huss, Gary R.

    2003-06-01

    We studied the mineralogy, mineral chemistry, and compositions of 48 interior silicate inclusions and a large K-rich surface inclusion from the Colomera IIE iron meteorite. Common minerals in the interior silicate inclusions are Cr diopside and Na plagioclase (albite). They are often enclosed by or coexist with albitic glasses with excess silica and minor Fe-Mg components. This mineral assemblage is similar to the "andesitic" material found in the Caddo County IAB iron meteorite for which a partial melt origin has been proposed. The fairly uniform compositions of Cr diopside (Ca 44Mg 46Fe 10) and Na plagioclase (Or 2.5Ab 90.0An 7.5 to Or 3.5Ab 96.1An 0.4) in Colomera interior inclusions and the angular boundaries between minerals and metal suggest that diopside and plagioclase partially crystallized under near-equilibrium conditions from a common melt before emplacement into molten metal. The melt-crystal assemblage has been called "crystal mush." The bulk compositions of the individual composite inclusions form an array between the most diopside-rich inclusion and plagioclase. This is consistent only with a simple mechanical mixing relationship, not a magmatic evolution series. We propose a model in which partly molten metal and crystal mush were mixed together by impact on the IIE parent body. Other models involving impact melting of the chondritic source material followed by growth of diopside and plagioclase do not easily explain near equilibrium growth of diopside and Na plagioclase, followed by rapid cooling. In the K-rich surface inclusion, K feldspar, orthopyroxene, and olivine were found together with diopside for the first time. K feldspar (sanidine, Or 92.7Ab 7.2An 0.1 to Or 87.3Ab 11.0An 1.7) occurs in an irregular veinlike region in contact with large orthopyroxene crystals of nearly uniform composition (Ca 1.3Mg 80.5Fe 17.8 to Ca 3.1Mg 78.1Fe 18.9) and intruding into a relict olivine with deformed-oval shape. Silica and subrounded Cr diopside are

  16. 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.

  17. Experimental determination of electrical conductivity during deformation of melt-bearing olivine aggregates: Implications for electrical anisotropy in the oceanic low velocity zone

    NASA Astrophysics Data System (ADS)

    Caricchi, Luca; Gaillard, Fabrice; Mecklenburgh, Julian; Le Trong, Emmanuel

    2011-02-01

    A novel experimental setup was used to measure in-situ variations of electrical conductivity (EC) during deformation in torsion (simple shear) at 300 MPa confining pressure and temperatures between 873 and 1473 K. This setup is designed to test if deformation of partially molten systems can produce electrical anisotropy. The motivation for this study comes from the observation that the Lithosphere-Asthenosphere Boundary (LAB) at mid-ocean ridges and in particular at the East Pacific Rise is strongly electrically anisotropic. In an initial set of calibration experiments, the variation of EC with temperature (873-1473 K) was determined for Carrara marble, Åheim dunite and basalt-bearing olivine aggregates. EC was then monitored during deformation experiments at 1473 K and measured in the frequency range between 6 MHz and 1 Hz. The electrical response of the different materials tested as a function of frequency, changes significantly depending on the presence, absence, proportion and distribution of melt contained in the specimen. Melt-free samples show a single conduction mechanism whereas melt-bearing samples display two conduction mechanisms linked in series, reflecting the contribution of isolated and connected melt. Impedance was measured along the sample radius, in a direction parallel to the shear gradient inherent in torsion experiments. During the tests, increasing values of the impedance measured suggest that the long range melt connectivity decreases radially, and melt drains from low to high shear stress regions. The conductivity, calculated from impedance measurements, is low and comparable to values measured along mid-ocean ridges. We suggest that electrical anisotropy of the LAB reflects an alternation of melt-enriched and melt-depleted channels elongated in the spreading direction possibly induced by spreading velocity gradients along the ridge. This implies that the observed electrical anisotropy reveals larger scale processes than strain

  18. Dependence of the Tidal Response on the Internal Structure of the Moon: Geodetic Implication to the Partial Melt Layer at the Lower-Most Part of the Lunar Mantle

    NASA Astrophysics Data System (ADS)

    Harada, Y.; Goossens, S. J.; Matsumoto, K.; Yan, J.; Ping, J.; Noda, H.

    2012-12-01

    viscosity in this part is probably lower than that in the upper portion because the knowledge of seismology also indicates the presence of a high attenuation zone. On the other hand, the viscosity of the upper portion is regarded to be uniform in here, and fixed to the maximum value of the above parameter range. As a result, it is clarified that the viscosity solution consistent with geodetic observations of both rotation and gravity field exists if the interior structure includes the specific low viscosity zone. There is just one narrow range of allowable viscosity with the observed Q, which can only be explained by this low viscosity zone. This viscosity range determines a numerical k2 which is consistent with the observed values. As a conclusion, the strong seismic attenuation zone inside the lunar interior is probably equivalent to the low viscosity zone. Particularly, it is the remarkable point that the value of the viscosity inferred here is too low considering solid rock whereas it is too high considering complete melt. Therefore, as has formerly been pointed out, the partial melting would occur in this lower-most part like that of the ultra-low velocity zone on the Earth. Moreover, this zone is expected to include the fluid phase with a ratio corresponding to the rheologically critical melt fraction.

  19. 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.

  20. Trace element partitioning in Earth's lower mantle and implications for geochemical consequences of partial melting at the core-mantle boundary

    NASA Astrophysics Data System (ADS)

    Hirose, Kei; Shimizu, Nobumichi; van Westrenen, Wim; Fei, Yingwei

    2004-08-01

    Trace element partitioning data between CaSiO 3-perovskite (CaPv), MgSiO 3-perovskite (MgPv), calcium-aluminum silicate (CAS-phase), and coexisting melts in peridotite and mid-ocean ridge basalt (MORB) compositions were obtained at 25-27 GPa and 2400-2530 °C using multi-anvil apparatus and ion microprobe. Results clearly show that CaPv is the predominant host for large ion lithophile elements (LILE) in the lower mantle. Because of the overwhelmingly high CaPv/melt partition coefficients (>10 for many of the LILE), partial melting in the lower mantle causes strong enrichment of LILE in the CaPv-bearing solid phase residue. CaPv has the following partitioning characteristics: (1) uniformly high partition coefficients for heavy rare earth elements (HREE) (e.g. 15 for Yb), decreasing toward light REE (e.g. 7 for La), (2) systematically lower partition coefficients for high field strength elements (Nb, Zr, Ti) and Sr relative to neighboring REE, (3) high Th and U, and systematically low Pb partition coefficients. Previous high-pressure studies have shown that the stability field of CaPv above solidus temperature is much wider in basaltic composition than in peridotite, indicating that melting of subducted oceanic crust in the lower mantle could produce significant geochemical CaPv signatures. Strong enrichment in Th and U relative to Pb in CaPv would result in radiogenic Pb isotopic compositions of the CaPv-bearing solid residue. Some clinopyroxenes in plume mantle peridotite xenoliths possess trace element patterns closely resembling those of natural CaPv found in diamonds and CaPv from the present experiments, suggesting that they were inherited from the CaPv-bearing precursor. In contrast, CaPv is the first phase to disappear during partial melting of peridotite above 24 GPa, and its geochemical signature may not be observable in nature. (MgPv + CaPv) fractional crystallization from a magma ocean has previously been put forward as a mechanism for Si depletion of the

  1. Fractal analysis and thermal-elastic modeling of a subvolcanic magmatic breccia: The role of post-fragmentation partial melting and thermal fracture in clast size distributions

    NASA Astrophysics Data System (ADS)

    Roy, Samuel G.; Johnson, Scott E.; Koons, Peter O.; Jin, Zhihe

    2012-05-01

    This paper examines the development of a subvolcanic magmatic breccia located along the contact of a granitic intrusion using fractal analysis and thermal-elastic modeling. The breccia grades from clast-supported, angular clasts adjacent to unfractured host rock to isolated, rounded clasts supported by the granitic matrix adjacent to the intrusion. Field observations point to an explosive breccia mechanism, and clast size distribution analysis yields fractal dimensions (Ds > 3) that exceed the minimum value known to result from explosion (Ds > 2.5). Field observations, clast size distribution data, clast circularity data, and boundary roughness fractal dimension data suggest that the clast sizes and shapes reflect post-brecciation modification by partial melting and thermal fracture. Numerical modeling is employed to explore the possible thermal-elastic effects on the size distribution of clasts. Instantaneous immersion is assumed for metasedimentary clasts of a fractal size distribution in a superheated granitic matrix for different matrix volume percentages. Thermal analysis is restricted to conductive heat transfer corrected for latent heat. Partial melting of metasedimentary clasts is an effective secondary modification process that was probably responsible for markedly altering the clast size distribution for clast populations adjacent to the intrusion. Diabase clasts experienced late-stage fracture due to the instantaneous thermal pulse in which angular clasts with high surface area to volume ratios were preferentially fractured, although this process does not appear to have markedly influenced the clast size distribution.

  2. Petrogenesis of adakite and high-Nb basalt association in the SW of Sabzevar Zone, NE of Iran: Evidence for slab melt-mantle interaction

    NASA Astrophysics Data System (ADS)

    Mazhari, Seyed Ali

    2016-04-01

    Adakitic rocks appear in close association with high Nb basaltic (HNB) rocks in the SW of Sabzevar ophiolitic belt. Adakites are calc-alkaline and include trachy-andesite, teachy-dacite and dacite. These rocks are rich in Na2O, Al2O3 and Sr and show depletion in MgO, Y and Yb. Adakitic samples are defined by high Sr/Y (88-128) and La/Yb (20-45) ratios; as well as a lack of Eu anomaly (Eu/Eu∗ = 0.92-0.99) in REE patterns. Geochemical composition indicates that adakites were generated from slab melting in a high pressure-high heat flow subducting setting. Different adakitic rocks have been formed by various slab partial melting degrees and reaction of adakitic magma with heterogeneous mantle wedge rocks. HNB rocks are alkaline, nepheline normative and sodic (Na2O/K2O = 2.7-3.4) with high concentration of Al2O3, TiO2, MgO, P2O5, LILE and HFSE, especially Nb (30-56 ppm). These basalts show fractionated REE patterns with elevated LREE/HREE (LaN/YbN = 20-25) and trace elements contents suggest their generation by low partial melting degrees (<2%) from garnet-peridotite origin which have already metasomatized by adakitic melts.

  3. 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...

  4. 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

  5. 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.

  6. Trace element compositions of apatite from the middle zone of the Panzhihua layered intrusion, SW China: Insights into the differentiation of a P- and Si-rich melt

    NASA Astrophysics Data System (ADS)

    Xing, Chang-Ming; Wang, Christina Yan; Li, Congying

    2014-09-01

    The Panzhihua layered intrusion in the ~ 260 Ma Emeishan large igneous province is composed of melagabbro and Fe-Ti oxide ore bodies in the lower zone (LZ) and the lower part of the middle zone (MZa), and Fe-Ti oxide-poor leucogabbro in the upper part of the middle zone (MZb) and upper zone (UZ). Cumulus apatite grains occur in the ~ 500- to 600-m-thick MZb, which makes up 25-30% of the ~ 2-km-thick intrusion. Apatite grains from the MZb show two compositional reversals in the composition of Sr, which divide the MZb into three sub-units from the base upwards, MZb1, MZb2 and MZb3. There is 1-3 vol.% apatite in the MZb1 and MZb2 and 2-5 vol.% apatite in the MZb3. Both apatite and plagioclase have an overall trend of decreasing Sr in each sub-unit. Most apatite grains from the MZb1 and MZb2 have negative Eu anomalies (Eu/Eu* = 0.70-0.98) on chondrite-normalized REE plots and some at the top of the MZb2 have positive Eu anomalies (Eu/Eu* = 1.09-1.18), whereas all grains from the MZb3 have positive Eu anomalies (Eu/Eu* = 1.11-1.25). We consider that the Panzhihua intrusion formed due to immiscibility of ferrobasaltic magmas in a large convection cell at high temperatures. The immiscible Fe-rich melt tended to move towards the base of the chamber, whereas the Si-rich melt moved upwards due to density differences. Crystallization of Fe-Ti oxides from the Fe-rich melt at high temperatures may result in the enrichment of P in the residual magmas. The upward moving residual P-rich magmas may have mixed with Si-rich melt to form a P- and Si-rich melt in the upper part of the chamber, from which the MZb formed. Double-diffusive convection circulated in the P- and Si-rich melt to form stratified magma layers. Magma mixing between the stratified magma layers resulted in the compositional reversals of apatite along the boundaries. Negative Eu anomaly of apatite in the MZb1 and MZb2 is attributed to prior crystallization of plagioclase, whereas replenishment of a syenitic magma to

  7. 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

  8. 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

  9. Melting Phase Relation of Nominally Anhydrous, Carbonated Pelite at Sub-arc Depths and Cycling of Sedimentary Carbon in Subduction Zones

    NASA Astrophysics Data System (ADS)

    Tsuno, K.; Dasgupta, R.

    2009-12-01

    An important mass transfer process for subduction zone magmatism is the cycling of C-O-H volatiles from subducting slab to arc volcanoes. However, CO2 is known to remain stable in subducting lithologies in the form crystalline carbonates. Mass balance of chemical tracers between slab input and arc output1 and stable isotopic compositions of arc fluids2, on the other hand, suggest that subducting sediments contribute to arc volcanism and arc-flux of CO2 derives primarily from subducting sediments. Therefore, it is important to explore the possible link between sediment contributions to arc volcanism and CO2 release from subducting sediments to mantle wedge. We have investigated, using an end-loaded piston cylinder device, melting relation of a carbonate-bearing, nominally anhydrous pelagic sediment composition at a single pressure of 3 GPa and at temperatures of 900-1350 °C. The starting material (HPLC1) has ~5 wt.% CO2 and corresponds (in H2O-free basis) to a mixture of 10 wt.% pelagic carbonate unit and 90 wt.% overlying hemipelagic mud unit that enter the Central American trench3. The subsolidus assemblage at 900 °C consists of garnet+cpx+K-feldspar+coesite+rutile+ankeritess, whereas just above the solidus (900-1000 °C), carbonatitic melt appears and ankeritess disappears (1000-1100 °C). The appearance of CO2-bearing silicate melt at 1100 °C coincides with the disappearance of K-feldspar and rutile, and the melt coexists with garnet+cpx+coesite/quartz from 1100 to 1300 °C. The liquidus is located >1350 °C, and the sole liquidus phase is quartz. Silicate melt composition evolves systematically from 1100 to 1350 °C with a decrease in SiO2 (65.7 to 59.1 wt.%), Al2O3 (13.5 to 12.4 wt.%), K2O (~5.5 to 2.1 wt.%), and CO2 (~8.5 to 5.2 wt.%), whereas MgO, FeO*, and CaO contents of the melt increase from 0.4 to 2.6 wt.%, 1.5 to 6.7 wt.%, and 2.4 to 8.7 wt.%, respectively. The Na2O content increases from 2.3 to 3.6 wt.% between 1100 and 1200 °C and decreases to 2

  10. 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.

  11. 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.

  12. Numerical simulation of Marangoni flow in partially confined half-zone liquid bridge of low-Prandtl-number fluids

    NASA Astrophysics Data System (ADS)

    Shiratori, Suguru; Yasuhiro, Shouichi; Hibiya, Taketoshi

    2004-05-01

    Direct numerical simulation using a finite difference method was done to reveal the fundamental characteristics of the flow in a half-zone liquid bridge of low Prandtl number fluids with the free surface partially confined by oxide films (non-slip adiabatic rigid walls). The critical Marangoni number Mac1 was calculated for several geometries, which are determined by the free surface ratio ( ξ= Lw/ L, Lw: length of the free surface, L: height of the whole liquid bridge) and the axial position of the free surface. When the oxide film exists between the free surface and the cold disc, the flow separates from the oxide film, and a weak cell with a counter flow arises near the cold disc. An axisymmetric flow exhibits a direct transition to an oscillatory flow, when the free surface ratio ξ is sufficiently small and free surface was located away from the cold disc.

  13. 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

  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. 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

  16. 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

    ...-Rule Quiet Zone may be established by automatic approval and remain in effect, subject to § 222.51, if the Pre-Rule Quiet Zone is in compliance with §§ 222.35 (minimum requirements for quiet zones) and 222... Zone may be established by automatic approval and remain in effect, subject to § 222.51, if the...

  17. 49 CFR 222.41 - How does this rule affect Pre-Rule Quiet Zones and Pre-Rule Partial Quiet Zones?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ...-Rule Quiet Zone may be established by automatic approval and remain in effect, subject to § 222.51, if the Pre-Rule Quiet Zone is in compliance with §§ 222.35 (minimum requirements for quiet zones) and 222... Zone may be established by automatic approval and remain in effect, subject to § 222.51, if the...

  18. 49 CFR 222.41 - How does this rule affect Pre-Rule Quiet Zones and Pre-Rule Partial Quiet Zones?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ...-Rule Quiet Zone may be established by automatic approval and remain in effect, subject to § 222.51, if the Pre-Rule Quiet Zone is in compliance with §§ 222.35 (minimum requirements for quiet zones) and 222... Zone may be established by automatic approval and remain in effect, subject to § 222.51, if the...

  19. 49 CFR 222.41 - How does this rule affect Pre-Rule Quiet Zones and Pre-Rule Partial Quiet Zones?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ...-Rule Quiet Zone may be established by automatic approval and remain in effect, subject to § 222.51, if the Pre-Rule Quiet Zone is in compliance with §§ 222.35 (minimum requirements for quiet zones) and 222... Zone may be established by automatic approval and remain in effect, subject to § 222.51, if the...

  20. 49 CFR 222.41 - How does this rule affect Pre-Rule Quiet Zones and Pre-Rule Partial Quiet Zones?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ...-Rule Quiet Zone may be established by automatic approval and remain in effect, subject to § 222.51, if the Pre-Rule Quiet Zone is in compliance with §§ 222.35 (minimum requirements for quiet zones) and 222... Zone may be established by automatic approval and remain in effect, subject to § 222.51, if the...

  1. Network of off-axis melt bodies at the East Pacific Rise

    NASA Astrophysics Data System (ADS)

    Canales, J. P.; Carton, H.; Carbotte, S. M.; Mutter, J. C.; Nedimović, M. R.; Xu, M.; Aghaei, O.; Marjanović, M.; Newman, K.

    2012-04-01

    Magmatic accretion of new oceanic crust at intermediate- to fast-spreading mid-ocean ridges occurs along a narrow axial zone. This zone is characterized by molten sills in the crust that are emplaced within about 3km of the ridge axis and overlie a zone of elevated temperatures and partial melt. There are disparate indications of off-axis magmatism and lavas erupted in the near-axis region are more compositionally variable than in the axial zone. Here we present three-dimensional seismic reflection images from the fast-spreading East Pacific Rise that reveal a network of sills 4 to 8km east of the ridge axis. Our crustal model, constrained using seismic velocity and attenuation data, shows that the sills are located outside of the main axial zone of crustal accretion, and above a region containing partial melt. We infer that the sills represent sites of sustained off-axis magmatism. Pockets of melt extend from the off-axis sills to the axial zone and may represent melt migration pathways. These pathways could promote mixing between enriched off-axis melts and normal on-axis melts, contributing to the compositional variability of the near-axis lavas. We suggest that off-axis magmatism occurs preferentially, but not exclusively, where pre-existing fractures inherited from offsets of the spreading axis promote melt transport from the mantle into the crust.

  2. Quantifying melting and mobilistaion of interstitial melts in crystal mushes

    NASA Astrophysics Data System (ADS)

    Veksler, Ilya; Dobson, Katherine; Hess, Kai-Uwe; Ertel-Ingrisch, Werner; Humphreys, Madeleine

    2015-04-01

    The deformation of crystals mushes and separation of melts and crystals in is critical to understanding the development of physical and chemical heterogeneity in magma chambers and has been invoked as an eruption trigger mechanism. Here we investigate the behaviour of the melt in the well characterised, classic crystal mush system of the Skaergaard intrusion by combining experimental petrology and the non-destructive 3D imaging methods. Starting materials for partial melting experiments were four samples from the upper Middle Zone of the Layered Series. Cylinders, 15 mm in diameter and 20 mm in length, were drilled out of the rock samples, placed in alumina crucibles and held for 5 days in electric furnaces at atmospheric pressure and 1050-1100 °C. Redox conditions set by the CO-CO2 gas mixture were kept close to those of the FMQ buffer. We then use spatially registered 3D x-ray computed tomography images, collected before and after the experiment, to determine the volume and distribution of the crystal framework and interstitial phases, and the volume, distribution and connectivity the interstitial phases that undergo melting and extraction while at elevated temperature. Image analysis has allowed us to quantify these physical changes with high spatial resolution. Our work is a first step towards quantitative understanding of the melt mobilisation and migration processes operating in notionally locked crystal rich magmatic systems.

  3. 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.

  4. Carbonatite melt infiltration in mantle xenoliths from the Eurasian plate - North American modern plate collision zone (Ruditch, Yakutia)

    NASA Astrophysics Data System (ADS)

    Tschegg, Cornelius; Ntaflos, Theodoros; Akinin, Viacheslav; Hauzenberger, Christoph

    2010-05-01

    Within the seismic active Chersky belt, the modern border between North American and Eurasian plates (Indigirka River area, Sakha-Yakutia Republic), mantle xenoliths were found in eroded alkaline basalt dike remnants.The peridotite xenoliths are represented by mainly anhydrous spinel lherzolites that appear together with subordinate orthpyroxene, clinopyroxene and feldspar megacrysts. Spinel lherzolites have protogranular textures and are well equilibrated, lacking any mineral zonation. The constituent minerals have minor compositional variations whithin and between different samples. Olivine compositions range from Fo 89-90.5, with CaO contents between 0.04 and 0.06 wt.%. Orthopyroxenes indicate a very narrow composititional variance (Wo1En63Fs36, Mg# 90-91 and Al2O3 from 4 to 4.7 wt.%), just like clinopyroxene phases that are represented by Wo38En40Fs22, with Mg#s from 90 to 91 and Al2O3 between 6.8 and 7.6 wt.%. Spinels also show a fertile composition with Cr#s ranging between 26 and 29 and Mg#s between 77 and 78 respectively. Equlibration temperature estimations gives approx. 1000 °C at 15 kbar pressure for all studied samples. In one xenolith, a round melt pocket with 200 microns in diameter consisting of well crystallized dolomite (25 wt.% CaO, 31 wt.% MgO) in perfect contact with homogeneous glass (16 wt.% Na2O, 51 wt.% SiO2, 20 wt.% Al2O3), apparently an immiscibility of carbonatite and silicate melt, was found at the triple point of olivine, orthopyroxene and clinopyroxene. Mineral chemistries show that the lithospheric mantle underneath the study area is a fertile lherzolith. Clinopyroxene LA-ICP-MS trace element analyses confirm the fertile nature of the xenoliths. The primitive mantle normalized REE patterns show a slight depletion of LREE with respect to HREE. The majority of the analyzed cpx have (La/Yb)N that vary between 0.1 and 0.5 and (Tb/Yb)N from 1.0 to 1.1 indicating the overal absense and metasomatic processes and low degree of melt

  5. Alpine-type sensu strictu(ophiolitic) peridotites: Refractory residues from partial melting or igneous sediments? A contribution to the discussion of the paper: "The origin of ultramafic and ultrabasic rocks" by P.J. Wyllie

    USGS Publications Warehouse

    Thayer, T.P.

    1969-01-01

    Although Alpine peridotites and basaltic lavas are widely associated in eugeosynclines and oceanic areas, their genetic ties are obscure. Three major characteristics of olivine-rich Alpine peridotite and dunite-relict cumulus textures, aggregated masses of chromitite, and intimate association with magnesium-rich gabbro - cannot be explained by partial melting of garnet peridotite to form tholeiite. Association of magnesium-rich gabbro with the chromite-bearing and so-called high-temperature Alpine peridotites is believed to present problems that have not been considered by advocates of the partial-melting hypothesis. The chromite-bearing Alpine peridotites and related feldspathic rocks are believed to have formed near the top of the mantle by gravitational differentiation processes which are largely independent of the melting processes that produce basaltic magma at depths of 50 km or more. ?? 1969.

  6. Early Cretaceous low-Mg# adakitic rocks in the southern margin of the central North China Craton: Partial melting of thickened lower continental crust and tectonic implications

    NASA Astrophysics Data System (ADS)

    Yang, D.

    2015-12-01

    This paper reports new whole-rock geochemical, Sr-Nd-Pb isotopic, and zircon U-Pb and Hf isotopic data for Early Cretaceous intrusive rocks in the Sanmenxia-Houma area of central China, and uses these data to constrain the petrogenesis of low-Mg adakitic rocks (LMAR) and the spatial extent of the influence of the deeply subducted Yangtze slab during the Triassic evolution of this region. New zircon LA-ICP-MS U-Pb data indicate that the early- and late-stage southern Quli, Qiligou, and Gaomiao porphyritic quartz diorites, the Canfang granodiorite, and the northern Wangmao porphyritic quartz monzodiorite were emplaced during the Early Cretaceous (~130 Ma) and the late Early Cretaceous (116 Ma). These rocks are characterized by high Na2O/K2O, Sr/Y, and (La/Yb)n ratios as well as high Sr concentrations, low Mg# values, and low heavy rare earth element and Y concentrations, all of which indicate an LMAR affinity. The samples have relatively high initial 87Sr/86Sr ratios (0.7054-0.7095), and low eNd(t) (-11.90 to -22.20) and eHf(t) (-16.7 to -32.7) values, indicative of a lower continental crust origin. The presence of Neoproterozoic (754-542 Ma) and inherited Late Triassic (220 Ma) metamorphic zircons within the late Early Cretaceous LMAR and the relatively high 206Pb/204Pb ratios of these rocks suggest that they formed from primary magmas derived from partial melting of Yangtze Craton (YC) basement material that had undergone ultrahigh-pressure metamorphism. In contrast, the presence of Paleoproterozoic and Archean inherited zircons within early Early Cretaceous LMAR in this area and the relatively low 206Pb/204Pb ratios of these rocks are indicative of derivation from primary magmas generated by partial melting of the thickened lower continental crust of the North China Craton (NCC). These rocks may have formed in an extensional environment associated with the upwelling of asthenospheric mantle material. The presence of YC basement material within the NCC in the

  7. Technical Note: Approximate solution of transient drawdown for constant-flux pumping at a partially penetrating well in a radial two-zone confined aquifer

    NASA Astrophysics Data System (ADS)

    Huang, C.-S.; Yang, S.-Y.; Yeh, H.-D.

    2015-06-01

    An aquifer consisting of a skin zone and a formation zone is considered as a two-zone aquifer. Existing solutions for the problem of constant-flux pumping in a two-zone confined aquifer involve laborious calculation. This study develops a new approximate solution for the problem based on a mathematical model describing steady-state radial and vertical flows in a two-zone aquifer. Hydraulic parameters in these two zones can be different but are assumed homogeneous in each zone. A partially penetrating well may be treated as the Neumann condition with a known flux along the screened part and zero flux along the unscreened part. The aquifer domain is finite with an outer circle boundary treated as the Dirichlet condition. The steady-state drawdown solution of the model is derived by the finite Fourier cosine transform. Then, an approximate transient solution is developed by replacing the radius of the aquifer domain in the steady-state solution with an analytical expression for a dimensionless time-dependent radius of influence. The approximate solution is capable of predicting good temporal drawdown distributions over the whole pumping period except at the early stage. A quantitative criterion for the validity of neglecting the vertical flow due to a partially penetrating well is also provided. Conventional models considering radial flow without the vertical component for the constant-flux pumping have good accuracy if satisfying the criterion.

  8. Melt Inclusions from Volcán Llaima (38.7°S, Andean Southern Volcanic Zone, Chile): Insights into Shallow Magma Storage and Crystallization

    NASA Astrophysics Data System (ADS)

    Bouvet de Maisonneuve, C.; Dungan, M. A.; Bachmann, O.; Burgisser, A.

    2009-12-01

    Olivine-hosted melt inclusions in scoria from four large historic eruptions of Llaima are used to elucidate processes of magma differentiation, recharge, mixing, and eruption triggering. These deposits were produced as violent Strombolian eruptions of crystal-rich mafic magma (<6 wt% MgO; 25-45% plag+oliv±cpx) associated with voluminous lava flows. Major element melt inclusion compositions are highly diverse in single samples (50-58 wt% SiO2; 6-3 wt% MgO). These overlap with the whole-rock data trend defined by the entire volcano up to 53-55% SiO2, but more evolved compositions form a divergent, linear trend up to >2 wt% TiO2 with Al2O3 as low as 12.5 wt% at 57-58 wt% SiO2, compared to 1.2-1.4 wt% TiO2 and 16-17 wt% Al2O3 at 58 wt% SiO2 in most Llaima andesitic magmas. The evolved extension of the melt inclusion trend is inferred to be the product of shallow evolution of interstitial melt during the formation of crystal mush as a consequence of degassing and decompression crystallization following magma stagnation. The suppression of FeTi-oxide stability and the dominance of plagioclase crystallization are consistent with low-P dry conditions. These observations are in accord with relatively low H2O (dominantly 1-3.5 wt%) and CO2 (dominantly 0-300 ppm) contents in melt inclusions (SIMS-ASU), which yield saturation pressures of ~300-500 bars (<2 km). H2O and CO2 contents do not correlate with major element melt composition, and melt inclusion fluid-saturation pressures do not correlate systematically with fractionation indices such as K2O or Mg#. Corollaries to these observations are that degassed matrix glasses attached to many of these olivines are commonly less evolved than corresponding melt inclusions (generally in equilibrium with host olivines), olivine core compositions in single samples are diverse (Fo69-83), and many of these olivines are reversely zoned to rims of Fo77-79. The absence of correlated degassing and magma evolution trends in historic Llaima

  9. Petrogenesis of magmatic albite granites associated to cogenetic A-type granites: Na-rich residual melt extraction from a partially crystallized A-type granite mush

    NASA Astrophysics Data System (ADS)

    Barboni, Mélanie; Bussy, François

    2013-09-01

    from the pure melting of an immature biotite-bearing quartz-feldspathic crustal protolith induced by early mafic injections at low crustal levels. Strong field evidences coupled to mineral chemistry and elemental geochemistry strongly support a magmatic origin for the albite granite. Sr, Nd, Hf zircon isotope data, U-Pb zircon ages, as well as data on petrography, mineral chemistry and elemental geochemistry attest that A-type and albite granites are closely related. Our preferred petrogenetic model is to consider the albite granite magma as a compositionally extreme melt that was extracted from a partially crystallized A-type granite mush at a late stage of crystallization. Alternatively, albite granites could form by melting of plagioclase-rich layers formed during A-type granite differentiation.

  10. Silurian/Ordovician asymmetrical sill-like bodies from La Codosera syncline, W Spain: A case of tholeiitic partial melts emplaced in a single magma pulse and derived from a metasomatized mantle source

    NASA Astrophysics Data System (ADS)

    López-Moro, F. J.; Murciego, A.; López-Plaza, M.

    2007-07-01

    between the country rock and the magma itself. The compositional characteristics of chilled margins enable them to be ruled out as primary melts in equilibrium with mantle olivine (Fo 91), a certain amount of olivine fractionation being required, which might have occurred in magma conduits en route to shallow emplacement levels in the crust. Spinel lherzolitic xenoliths from the European Cenozoic alkaline magmatism appear to be unsuitable protoliths to account for the chilled margin compositions. Instead, a hybrid mantle source consisting of a small amount of OIB-mantle component (5 wt.%) and a depleted end-member mantle component seems to be a plausible protolith, resulting in a good fit with the fractionation-corrected chilled margin trends for 10% of partial melting.

  11. Fluid processes in subduction zones.

    PubMed

    Peacock, S A

    1990-04-20

    Fluids play a critical role in subduction zones and arc magmatism. At shallow levels in subduction zones (<40 kilometers depth), expulsion of large volumes of pore waters and CH(4)-H(2)O fluids produced by diagenetic and low-grade metamorphic reactions affect the thermal and rheological evolution of the accretionary prism and provide nutrients for deep-sea biological communities. At greater depths, H(2)O and CO(2) released by metamorphic reactions in the subducting oceanic crust may alter the bulk composition in the overlying mantle wedge and trigger partial melting reactions. The location and conse-quences of fluid production in subduction zones can be constrained by consideration of phase diagrams for relevant bulk compositions in conjunction with fluid and rock pressure-temperature-time paths predicted by numerical heat-transfer models. Partial melting of subducting, amphibole-bearing oceanic crust is predicted only within several tens of million years of the initiation of subduction in young oceanic lithosphere. In cooler subduction zones, partial melting appears to occur primarily in the overlying mantle wedge as a result of fluid infiltration. PMID:17784486

  12. Techniques for Elastic Properties Measurements of Partial Molten Rocks, Hydrous Minerals and Melts in Gas Pressure Vessels and Multi-Anvil Devices

    NASA Astrophysics Data System (ADS)

    Mueller, H. J.; Roetzler, K.; Schilling, F. R.; Wehber, M.; Lathe, C.

    2008-12-01

    The interpretation of highly resolved seismic data from Earth's deep interior require measurements of the physical properties of Earth materials under experimental simulated mantle conditions. For deep crustal to uppermost mantle conditions high performance gas pressure vessels enable a virtually unrestricted optimization of the measuring configurations for high p-T-conditions [1]. Exhumed high pressure rocks can be used as representative samples. The paper presents transient measurements of elastic wave velocities for granulite facies rocks under partial melting conditions. Despite the compact natural rock samples as a result of long-term experiments exceeding pressures of 1.5 GPa and temperatures of 1,000°C newly-formed garnets, orthopyroxenes and potash feldspars could be found in the samples after the experiments. Discovering the huge water storage capacity of nominally anhydrous minerals (NAMs) under high pressure conditions dramatically changed our image of state and dynamics of Earth's deep interior [2]. The simulation of these in situ conditions require using of diamond anvil cells (DAC) and multi-anvil devices (MAD) as well as mostly synthetical samples. MADs are more limited in pressure, but provide sample volumes 3 to 7 orders of magnitude bigger. They offer small and even adjustable temperature gradients over the whole sample. The bigger samples make anisotropy and structural effects in complex systems accessible for measurements in principle. Using ultrasonic interferometry the measurement of both elastic wave velocities have no limits for opaque and encapsulated samples. Using the 6 to 8 anvils of a MAD as buffers allow the simultaneous recording of acoustic emissions from different directions of space and consequently the localization of the spikes during ongoing phase transitions and dehydration. The recent development of deformation-DIA MADs (D-DIA) make not only deformation measurements under simulated mantle conditions possible, but also the

  13. Mantle migration of K-LILE-enriched melts/fluids in supra-subduction settings: evidence from the Finero Complex (Ivrea-Verbano Zone, Southern Alps)

    NASA Astrophysics Data System (ADS)

    Zanetti, A.; Mazzucchelli, M.; Giovanardi, T.; Tiepolo, M.; Vannucci, R.

    2011-12-01

    The Finero Complex is located in the northern sector of the Ivrea-Verbano Zone (Southern Alps). It is placed in contact with the Austro-Alpine terrains of the Sesia-Lanzo Zone by the Insubric line and consists of a dunitic-harzburgitic mantle unit, surrounded by a layered mafic-ultramafic intrusion. Unlike the central and southern sectors of the Ivrea-Verbano Zone, recent geochronological data suggest that metasomatic events of the Finero mantle unit, as well as the emplacement of the layered intrusion, occurred over a time span covering Middle Triassic to Lower Jurassic. A number of different geodynamic scenarios, among which aborted rifting processes and/or mantle plume activity, have been proposed to account for Lower Mesozoic melt-related events. However, the trace element and isotopic evidence points to the occurrence of large amount of crustal component in melts migrating through the mantle unit, which, consistently with regional structural features, has been proposed to be related to the development of roll-back subduction(s) during the early Mesozoic. New field, petrochemical and geochronological work has allowed to place further constraints on the geochemical affinity and evolution of the metasomatic melts/fluids affecting the mantle unit. Particular emphasis has been placed on the reconstruction of different migration stages recorded by decameter-wide dunites. In these bodies, an early migration stage produced dm-wide chromitite layers formed by chromite and orthopyroxene (Opx), with subordinate clinopyroxene (Cpx) and accessory amounts of amphibole (Amph), zircon and zirconolite. Successive migration events produced a lithologic series formed by, in order of crystallization: i) straight, cm-large websterites formed by Cpx-Opx-Amph-Phlogopite (Phl); ii) cm- to dm-wide bands with curved strike, characterized by segregation of Cpx-Phl-Amph-Opx; iii) dm-scale pockets filled by pegmatoidal Amph and Phlog; iv) finally, mm-thick veins with random strike and

  14. Earth's interior. Dehydration melting at the top of the lower mantle.

    PubMed

    Schmandt, Brandon; Jacobsen, Steven D; Becker, Thorsten W; Liu, Zhenxian; Dueker, Kenneth G

    2014-06-13

    The high water storage capacity of minerals in Earth's mantle transition zone (410- to 660-kilometer depth) implies the possibility of a deep H2O reservoir, which could cause dehydration melting of vertically flowing mantle. We examined the effects of downwelling from the transition zone into the lower mantle with high-pressure laboratory experiments, numerical modeling, and seismic P-to-S conversions recorded by a dense seismic array in North America. In experiments, the transition of hydrous ringwoodite to perovskite and (Mg,Fe)O produces intergranular melt. Detections of abrupt decreases in seismic velocity where downwelling mantle is inferred are consistent with partial melt below 660 kilometers. These results suggest hydration of a large region of the transition zone and that dehydration melting may act to trap H2O in the transition zone. PMID:24926016

  15. Gravitational Sensitivity of Melts at the Growth of InSb:Te Crystals by the Bridgman and Floating Zone Methods under the Conditions of Microgravity

    NASA Astrophysics Data System (ADS)

    Zemskov, V. S.; Raukhman, M. R.; Shalimov, V. P.

    2001-07-01

    The comparative analysis of the results of space and ground-based experiments IMET RAS on the growth of InSb:Te crystals by the Bridgman method and floating zone method (FZM) is made for the purpose of studying the influence of microgravity on the growth, structure, and properties of grown crystals, and thus the gravity sensitivity of InSb melt is demonstrated. It is shown that, under microgravity conditions, the Bridgman method makes it possible to grow InSb:Te crystals without contact with the ampoule walls, which provides for the single crystal structure, the absence of striations, and a low dislocation density. For the first time, InSb:Te monocrystals were grown with the FZM under microgravity. The anomalous behavior of the impurity core (facet effect) in these crystals correlates with the changed magnitude and direction of the quasi-stationary (residual) microaccelerations.

  16. Experimental determination of C, F, and H partitioning between mantle minerals and carbonated basalt, CO2/Ba and CO2/Nb systematics of partial melting, and the CO2 contents of basaltic source regions

    NASA Astrophysics Data System (ADS)

    Rosenthal, A.; Hauri, E. H.; Hirschmann, M. M.

    2015-02-01

    To determine partitioning of C between upper mantle silicate minerals and basaltic melts, we executed 26 experiments between 0.8 and 3 GPa and 1250-1500 °C which yielded 37 mineral/glass pairs suitable for C analysis by secondary ion mass spectrometry (SIMS). To enhance detection limits, experiments were conducted with 13C-enriched bulk compositions. Independent measurements of 13C and 12C in coexisting phases produced two C partition coefficients for each mineral pair and allowed assessment of the approach to equilibrium during each experiment. Concentrations of C in olivine (ol), orthopyroxene (opx), clinopyroxene (cpx) and garnet (gt) range from 0.2 to 3.5 ppm, and resulting C partition coefficients for ol/melt, opx/melt, cpx/melt and gt/melt are, respectively, 0.0007 ± 0.0004 (n = 2), 0.0003 ± 0.0002 (n = 45), 0.0005 ± 0.0004 (n = 17) and 0.0001 ± 0.00007 (n = 5). The effective partition coefficient of C during partial melting of peridotite is 0.00055 ± 0.00025, and therefore C is significantly more incompatible than Nb, slightly more compatible than Ba, and, among refractory trace elements, most similar in behavior to U or Th. Experiments also yielded partition coefficients for F and H between minerals and melts. Combining new and previous values of DFmineral/melt yields bulk DFperidotite/melt = 0.011 ± 0.002, which suggests that F behaves similarly to La during partial melting of peridotite. Values of DHpyx/melt correlate with tetrahedral Al along a trend consistent with previously published determinations. Small-degree partial melting of the mantle results in considerable CO2/Nb fractionation, which is likely the cause of high CO2/Nb evident in some Nb-rich oceanic basalts. CO2/Ba is much less easily fractionated, with incompatible-element-enriched partial melts having lower CO2/Ba than less enriched basalts. Comparison of calculated behavior of CO2, Nb, and Ba to systematics of oceanic basalts suggests that depleted (DMM-like) sources have 75 ± 25

  17. Primary carbonatite melt from deeply subducted oceanic crust

    SciTech Connect

    Walter, M.J.; Bulanova, G.P.; Armstrong, L.S.; Keshav, S.; Blundy, J.D.; Gudfinnesson, G.; Lord, O.T.; Lennie, A.R.; Clark, S.M.; Smith, C.B.; Gobbo, L.

    2008-07-01

    Partial melting in the Earth's mantle plays an important part in generating the geochemical and isotopic diversity observed in volcanic rocks at the surface. Identifying the composition of these primary melts in the mantle is crucial for establishing links between mantle geochemical 'reservoirs' and fundamental geodynamic processes. Mineral inclusions in natural diamonds have provided a unique window into such deep mantle processes. Here they provide exper8imental and geochemical evidence that silicate mineral inclusions in diamonds from Juina, Brazil, crystallized from primary and evolved carbonatite melts in the mantle transition zone and deep upper mantle. The incompatible trace element abundances calculated for a melt coexisting with a calcium-titanium-silicate perovskite inclusion indicate deep melting of carbonated oceanic crust, probably at transition-zone depths. Further to perovskite, calcic-majorite garnet inclusions record crystallization in the deep upper mantle from an evolved melt that closely resembles estimates of primitive carbonatite on the basis of volcanic rocks. Small-degree melts of subducted crust can be viewed as agents of chemical mass-transfer in the upper mantle and transition zone, leaving a chemical imprint of ocean crust that can possibly endure for billions of years.

  18. Primary carbonatite melt from deeply subducted oceanic crust.

    PubMed

    Walter, M J; Bulanova, G P; Armstrong, L S; Keshav, S; Blundy, J D; Gudfinnsson, G; Lord, O T; Lennie, A R; Clark, S M; Smith, C B; Gobbo, L

    2008-07-31

    Partial melting in the Earth's mantle plays an important part in generating the geochemical and isotopic diversity observed in volcanic rocks at the surface. Identifying the composition of these primary melts in the mantle is crucial for establishing links between mantle geochemical 'reservoirs' and fundamental geodynamic processes. Mineral inclusions in natural diamonds have provided a unique window into such deep mantle processes. Here we provide experimental and geochemical evidence that silicate mineral inclusions in diamonds from Juina, Brazil, crystallized from primary and evolved carbonatite melts in the mantle transition zone and deep upper mantle. The incompatible trace element abundances calculated for a melt coexisting with a calcium-titanium-silicate perovskite inclusion indicate deep melting of carbonated oceanic crust, probably at transition-zone depths. Further to perovskite, calcic-majorite garnet inclusions record crystallization in the deep upper mantle from an evolved melt that closely resembles estimates of primitive carbonatite on the basis of volcanic rocks. Small-degree melts of subducted crust can be viewed as agents of chemical mass-transfer in the upper mantle and transition zone, leaving a chemical imprint of ocean crust that can possibly endure for billions of years. PMID:18668105

  19. A melt-focusing zone in the lithospheric mantle preserved in the Santa Elena Ophiolite, Costa Rica

    NASA Astrophysics Data System (ADS)

    Madrigal, Pilar; Gazel, Esteban; Denyer, Percy; Smith, Ian; Jicha, Brian; Flores, Kennet E.; Coleman, Drew; Snow, Jonathan

    2015-08-01

    The Santa Elena Ophiolite in Costa Rica is composed of a well-preserved fragment of the lithospheric mantle that formed along a paleo-spreading center. Within its exposed architecture, this ophiolite records a deep section of the melt transport system of a slow/ultra-slow spreading environment, featuring a well-developed melt-focusing system of coalescent diabase dikes that intrude the peridotite in a sub-vertical and sub-parallel arrangement. Here we present an integrated analysis of new structural data, 40Ar/39Ar geochronology, major and trace element geochemistry and radiogenic isotope data from the diabase dikes in order to elucidate the tectonic setting of the Santa Elena Ophiolite. The dikes are basaltic and tholeiitic in composition. Petrological models of fractional crystallization suggest deep pressures of crystallization of > 0.4 GPa for most of the samples, which is in good agreement with similar calculations from slow/ultra-slow spreading ridges and require a relatively hydrated (~ 0.5 wt.% H2O) MORB-like source composition. The diabase dikes share geochemical and isotope signatures with both slow/ultra-slow spreading ridges and back-arc basins and indicate mixing of a DMM source and an enriched mantle end-member like EMII. The 40Ar/39Ar geochronology yielded an age of ~ 131 Ma for a previous pegmatitic gabbroic magmatic event that intruded the peridotite when it was hot and plastic and an age of ~ 121 Ma for the diabase intrusions, constraining the cooling from near asthenospheric conditions to lithospheric mantle conditions to ~ 10 Ma. Our findings suggest a complex interplay between oceanic basin and back-arc extension environments during the Santa Elena Ophiolite formation. We propose an alternative hypothesis for the origin of Santa Elena as an obducted fragment of an oceanic core complex (OCC).

  20. The basalt-high magnesium andesite association formed by multi-stage partial melting of a heterogeneous source mantle: Evidence from Hirado-Seto, Northwest Kyushu, Southwest Japan

    NASA Astrophysics Data System (ADS)

    Mashima, Hidehisa

    2009-10-01

    An association of basalts and high magnesium andesites (HMAs), erupted at 7 Ma after the opening of the Sea of Japan, exposed at Hirado-Seto in northwest Kyushu, southwest Japan. The rocks are aphyric and are characterized by enrichments in incompatible trace elements similar to those seen for oceanic island basalts, although the HMAs show a weak negative Nb anomaly. High MgO, Ni and low FeO*/MgO indicate that the Hirado-Seto rocks were originally primitive magmas. They do not show a positive correlation between K 2O/La and SiO 2, or between Pb/La and SiO 2, indicating that hydrous components derived from a subducting slab did not play a significant role in the genesis of the Hirado-Seto basalt-HMA magmas. Alternatively, the normative olivine-quartz-[Jd + CaTs] compositions indicate that the Hirado-Seto basalt-HMA magmas were formed by multi-stage partial melting of the source mantle at pressures ranging from 1 to 0.5 GPa along the 1300 °C mantle adiabat, assuming anhydrous conditions. Basalt magmas separated from the source mantle at 1 GPa. HMA magmas separated at 0.5 GPa. A weak negative anomaly for Nb in HMAs can be explained by precipitation of Ti-P oxides during their ascent under high fO 2 condition. Thinning of the Hirado-Seto lithosphere caused by transtensional strain during the opening of the Sea of Japan would have enabled separation of HMA magmas at unusually low pressures.

  1. Late Carboniferous adakitic granodiorites in the Qiongkusitai area, western Tianshan, NW China: Implications for partial melting of lower crust in the southern Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Yin, Jiyuan; Chen, Wen; Xiao, Wenjiao; Yuan, Chao; Long, Xiaoping; Cai, Keda; Zhang, Bin

    2016-07-01

    Carboniferous granitic rocks are wide spread in the western Tianshan, but their tectonic contexts remain controversial. We present zircon U-Pb age, major element, trace element, and in situ zircon Hf isotopic data for the Qiongkusitai granodiorites from the southern part of the Yili block in the western Tianshan. The granodiorites were emplaced in the Late Carboniferous (ca. 314 Ma) and are characterized by high SiO2 (62.1-65.7 wt.%), high Sr (376-485 ppm), low Y (13.7-17.7 ppm) and low Yb (1.34-1.81 ppm) with Sr/Y ratios of 23-34. Such characteristics imply adakitic affinities. Their low concentrations of Cr (3.85-6.75 ppm), Co (7.63-10.7 ppm) and Ni (2.94-6.80 ppm) suggest little, if any, interaction with a mantle source. Compared to the thickened lower crustal-derived adakitic rocks, the relatively low Nb/Ta ratios of the Qiongkusitai adakitic granodiorites indicate that they were probably generated by partial melting of amphibolite facies rocks, but not eclogite facies rocks. The Qiongkusitai adakitic granodiorites have positive zircon εHf(t) values of +0.7 to +5.1 and TDM2 of 1.28-1.68 Ga, and they are interpreted as being derived from remelting of amphibolite facies Mesoproterozoic basement with an input of juvenile material. Late Carboniferous magmatism in the western Tianshan was possibly triggered by asthenospheric upwelling as a result of the roll-back of the subducted southern Tianshan oceanic lithosphere.

  2. Dynamics of Melting and Melt Migration as Inferred from Incompatible Trace Element Abundance in Abyssal Peridotites

    NASA Astrophysics Data System (ADS)

    Peng, Q.; Liang, Y.

    2008-12-01

    To better understand the melting processes beneath the mid-ocean ridge, we developed a simple model for trace element fractionation during concurrent melting and melt migration in an upwelling steady-state mantle column. Based on petrologic considerations, we divided the upwelling mantle into two regions: a double- lithology upper region where high permeability dunite channels are embedded in a lherzolite/harzburgite matrix, and a single-lithology lower region that consists of partially molten lherzolite. Melt generated in the single lithology region migrates upward through grain-scale diffuse porous flow, whereas melt in the lherzolite/harzburgite matrix in the double-lithology region is allowed to flow both vertically through the overlying matrix and horizontally into its neighboring dunite channels. There are three key dynamic parameters in our model: degree of melting experienced by the single lithology column (Fd), degree of melting experienced by the double lithology column (F), and a dimensionless melt suction rate (R) that measures the accumulated rate of melt extraction from the matrix to the channel relative to the accumulated rate of matrix melting. In terms of trace element fractionation, upwelling and melting in the single lithology column is equivalent to non-modal batch melting (R = 0), whereas melting and melt migration in the double lithology region is equivalent to a nonlinear combination of non-modal batch and fractional melting (0 < R < 1). Given the nonlinear nature of the melting model and uncertainties in trace element data for the abyssal peridotite, we showed, with the help of Monte Carlo simulations, that it is difficult to invert for all three dynamic parameters from a set of incompatible trace element data with confidence. However, given Fd, it is quite possible to constrain F and R from incompatible trace element abundances in residual peridotite. As an illustrative example, we used the simple melting model developed in this study and

  3. Technical Note: Approximate solution of transient drawdown for constant-flux pumping at a partially penetrating well in a radial two-zone confined aquifer

    NASA Astrophysics Data System (ADS)

    Huang, C.-S.; Yang, S.-Y.; Yeh, H.-D.

    2015-03-01

    An aquifer consisting of a skin zone and a formation zone is considered as a two-zone aquifer. Existing solutions for the problem of constant-flux pumping (CFP) in a two-zone confined aquifer involve laborious calculation. This study develops a new approximate solution for the problem based on a mathematical model including two steady-state flow equations with different hydraulic parameters for the skin and formation zones. A partially penetrating well may be treated as the Neumann condition with a known flux along the screened part and zero flux along the unscreened part. The aquifer domain is finite with an outer circle boundary treated as the Dirichlet condition. The steady-state drawdown solution of the model is derived by the finite Fourier cosine transform. Then, an approximate transient solution is developed by replacing the radius of the boundary in the steady-state solution with an analytical expression for a dimensionless time-dependent radius of influence. The approximate solution is capable of predicting good temporal drawdown distributions over the whole pumping period except at the early stage. A quantitative criterion for the validity of neglecting the vertical flow component due to a partially penetrating well is also provided. Conventional models considering radial flow without the vertical component for the CFP have good accuracy if satisfying the criterion.

  4. Fluid mechanics and mass transfer in melt crystal growth: Analysis of the floating zone and vertical Bridgman processes

    NASA Technical Reports Server (NTRS)

    Brown, R. A.

    1986-01-01

    This research program focuses on analysis of the transport mechanisms in solidification processes, especially one of interest to the Microgravity Sciences and Applications Program of NASA. Research during the last year has focused on analysis of the dynamics of the floating zone process for growth of small-scale crystals, on studies of the effect of applied magnetic fields on convection and solute segregation in directional solidification, and on the dynamics of microscopic cell formation in two-dimensional solidification of binary alloys. Significant findings are given.

  5. Late Cretaceous dacitic dykes swarm from Central Iran, a trace for amphibolite melting in a subduction zone

    NASA Astrophysics Data System (ADS)

    Nosouhian, N.; Torabi, G.; Arai, S.

    2016-05-01

    Late Cretaceous Bayazeh dyke swarm is situated in the western part of the Central-East Iranian Microcontinent (CEIM). These dykes with a dominant northeast-southwest trend occur in the Eastern margin of the Yazd block. They cross cut the Lower Cretaceous sedimentary rocks. The length of the Bayazeh dykes occasionally reaches up to the 2 km. Rock forming minerals of these dykes are plagioclase (andesine and oligoclase), amphibole (magnesio-hastingsitic hornblende, magnesio-hornblende and tschermakitic hornblende), quartz, K-feldspar (orthoclase), zircon and apatite. Secondary minerals are chlorite (pycnochlorite), albite, magnetite and calcite. The main textures are porphyritic, glomeroporphyritic and poikilitic. The felsic character of the Bayazeh dacitic dykes is shown by their high SiO2 (62.70 to 64.60 wt %) and low [Fe2O3* + MgO + MnO + TiO2] (average 4.64 wt %) contents. These dykes represent the peraluminous to metaluminous nature and their Na2O and K2O values are 5.20-7.14 and 1.51-2.59 wt %, respectively, which reveal their sodic chemistry. The trace element characteristics are the LREE enrichment relative to HREE, [La/Yb]CN = 13.27-22.99, and slightly negative or positive Eu anomaly. These geochemical characteristics associated with low Nb/La (0.16-0.25), Yb/Nd (0.04-0.05) and high Zr/Sm (37.60-58.25) ratios indicate that the melting of a metamorphosed subducted oceanic crust is occurred where the residual mineral assemblage is dominated by garnet amphibolite. The chemical compositions of the Bayazeh dykes resemble those of slab-derived tonalite-trondhjemite-granodiorite (TTG) series. They were formed by subduction of Mesozoic Neo-Tethys -related Nain and Ashin oceanic crusts.

  6. Constraints on melt migration in the Earth's upper mantle

    NASA Astrophysics Data System (ADS)

    Garapic, Gordana

    Melting and melt segregation are key processes in the geochemical evolution of the Earth. However, mechanism and time scale of melt transport from the source to the surface are still not well understood and are dependent on the grain-scale distribution of melt. A related question is the retention of melt in partially molten regions of the Earth's upper mantle. Seismic observations from mid-ocean ridges (MOR) and subduction zones are interpreted to show in-situ melt contents up to 3%, while geochemical observations from MOR basalts are inferred to indicate very efficient extraction of melt (porosities of order of 0.1%). Earlier theoretical models of the melt distribution were based on the balance of surface tension between melt and uniform crystalline grains, predicting a simple network of melt along three-grain edges. Analyses of experimentally produced samples of olivine and basaltic melt show that the melt geometry is much more complex, and includes wetted two-grain boundaries. I reconstructed the 3-D model of melt geometry of two experimentally produced samples by serial sectioning and rendering of the pore space which demonstrates for the first time that melt exists in thin layers on two-grain boundaries. This confirms the inferences from previous 2-D observations and has significant implications for physical properties of partially molten regions, for example seismic velocities and attenuation. The wetted two-grain boundaries are inferred to be a consequence of continuous grain growth. Due to the complexity of the 3-D melt geometry the permeability of partially molten rocks can not be predicted from simple models. I therefore investigated the permeability as a function of porosity for both synthetic and experimentally determined pore geometries using a lattice-Boltzmann method. The calculated permeability is not a simple function of porosity, but increases rapidly at a critical fraction of wetted two-grain boundaries. To extrapolate the experimentally based

  7. Experimental Phase Relations of Hydrous, Primitive Melts: Implications for variably depleted mantle melting in arcs and the generation of primitive high-SiO2 melts

    NASA Astrophysics Data System (ADS)

    Weaver, S.; Wallace, P. J.; Johnston, A.

    2010-12-01

    There has been considerable experimental and theoretical work on how the introduction of H2O-rich fluids into the mantle wedge affects partial melting in arcs and chemical evolution of mantle melts as they migrate through the mantle. Studies aimed at describing these processes have become largely quantitative, with an emphasis on creating models that suitably predict the production and evolution of melts and describe the thermal state of arcs worldwide. A complete experimental data set that explores the P-T conditions of melt generation and subsequent melt extraction is crucial to the development, calibration, and testing of these models. This work adds to that data set by constraining the P-T-H2O conditions of primary melt extraction from two end-member subduction zones, a continental arc (Mexico) and an intraoceanic arc (Aleutians). We present our data in context with primitive melts found worldwide and with other experimental studies of melts produced from fertile and variably depleted mantle sources. Additionally, we compare our experimental results to melt compositions predicted by empirical and thermodynamic models. We used a piston-cylinder apparatus and employed an inverse approach in our experiments, constraining the permissible mantle residues with which our melts could be in equilibrium. We confirmed our inverse approach with forced saturation experiments at the P-T-H2O conditions of melt-mantle equilibration. Our experimental results show that a primitive, basaltic andesite melt (JR-28) from monogenetic cinder cone Volcan Jorullo (Central Mexico) last equilibrated with a harzburgite mantle residue at 1.2-1.4 GPa and 1150-1175°C with H2O contents in the range of 5.5-7 wt% H2O prior to ascent and eruption. Phase relations of a tholeiitic high-MgO basaltic melt (ID-16) from the Central Aleutians (Okmok) show the conditions of last equilibration with a fertile lherzolite mantle residue at shallower (1.2 GPa) but hotter (1275°C) conditions with

  8. Partial port-closing strategy for obtaining high throughput or high purities in a four-zone simulated moving bed chromatography for binary separation.

    PubMed

    Mun, Sungyong

    2010-10-15

    The "partial port-closing" operation strategy for a four-zone simulated moving bed (SMB) chromatographic process for binary separation was developed to improve the SMB performance. This strategy included the partial extract-closing (PEC) and the partial raffinate-closing (PRC) operations. In case of the PEC operation, the extract port is made to be closed during the first-half stage of a switching period. During the latter-half stage, the extract port is made to be open. In case of the PRC operation, the raffinate port is made to be open during the first-half stage of a switching period. During the latter-half stage, the raffinate port is made to be closed. If the operating conditions are chosen properly in each operation using a highly efficient optimization tool, the product stream can be collected during only the period that the product is almost separated from impurity. During the other period that the product is contaminated with impurity, the collection of the product stream can be stopped by closing the product port. The uncollected product stream is then allowed to keep migrating through the adjacent zone within the SMB process. Such a partial port-closing operation including PEC and PRC was found to surpass a conventional SMB operation remarkably in throughput and product purity. PMID:20837353

  9. The Effect of Temperature and Carbon to Hematite Ratio on the Formation of Cementite During the Couple of STMA and Partial Melting Processes

    NASA Astrophysics Data System (ADS)

    Soleymani, Amir Peyman; Panjepour, Masoud; Meratian, Mahmood

    2016-04-01

    In this research, the role of the couple of simultaneous thermal-mechanical activation (STMA) and partial melting (PM) processes in the carbothermic reduction of hematite and cementite formation was studied. For this purpose, the STMA process was performed for 6 hours at 1073 K (800 °C) on the mixture of hematite and graphite with stoichiometry ratio (22 wt pct C) in argon atmosphere in the first stage, and then this process was coupled to the PM process at 1453 K (1180 °C) for 25 minutes. The results obtained showed that the percentage of cementite phase in the product of the STMA process was only about 24 wt pct and after carrying out the PM process, this value reached 77 wt pct in the final product. In the second stage, the effect of the ratio of the parameters of carbon to hematite on the initial mixture (1:1, 1:25, and 1:5 times the stoichiometry ratio) and STMA process temperature [1073 K, 1123 K, and 1173 K (800 °C, 850 °C, and 900 °C)] was studied. The results were indicative of the fact that by an increase in the ratio of carbon to hematite and at STMA temperature, the percentage of cementite in the final product obtained from the PM process significantly increased. In fact, the specimens obtained from the couple of the STMA and PM processes with a carbon to hematite ratio of 1.5:1 at 1073 K (800 °C) and that of 1.25:1 at 1173 K (900 °C) showed the greatest percentage of cementite. The mechanism regarding the processes showed that by controlling the amount and manner of free carbon distribution in the STMA product based on the parameters of the ratio of carbon to hematite and temperature, it was possible to obtain pure cementite. Therefore, the couple of STMA and PM processes can also be brought up as a new method in the production of pure cementite.

  10. Trapping control of phase development in zone melting of Bi-Sr-Ca-Cu-O superconducting fibres

    NASA Astrophysics Data System (ADS)

    Costa, F. M.; Carrasco, M. F.; Silva, R. F.; Vieira, J. M.

    2003-03-01

    Highly-texturized polycrystalline fibres of the Bi-Sr-Ca-Cu-O system have been grown by the laser floating zone technique at seven different pulling rates: (1.1, 2.2, 4.17, 8.3, 16.7, 33.3, 60.5) × 10-6 m s-1. The assessment of the cation segregation at the solid/liquid interface allowed us to calculate their equilibrium and effective distribution coefficients. The equilibrium distribution coefficients (k0,Bi = 0.55, k0,Sr = 0.97, k0,Ca = 1.67, k0,Cu = 1.10) were estimated using the Burton, Primm and Slichter (BPS) theory by taking into account the determined effective values. The effective distribution coefficients tend to unity as long as the pulling rate increases. The composition profiles along the initial transient region of the solidified fibres show a fast approach to the nominal composition as the pulling rate increases. The outstanding effect of the growth speed on superconducting phase type development is explained based on the solute trapping phenomena. The sequence of crystallization for superconducting phases ('2212' rightarrow '4413' rightarrow '2201') with pulling rate is a spontaneous effect of the system thermodynamics in order to balance the Bi trapping. This phase sequence corresponds to the smallest change of Bi chemical potential from the liquid phase to the solid phase. A diagram of free energy curves of the interdendritic superconducting phases illustrates the partitionless solidification phenomena at the highest growth speed.

  11. Quantification of the CO2 budget and H2O-CO2 systematics in subduction-zone magmas through the experimental hydration of melt inclusions in olivine at high H2O pressure

    NASA Astrophysics Data System (ADS)

    Mironov, Nikita; Portnyagin, Maxim; Botcharnikov, Roman; Gurenko, Andrey; Hoernle, Kaj; Holtz, François

    2015-09-01

    Reliable evaluation of CO2 contents in parental arc magmas, which can be preserved in melt inclusions in phenocrysts, is required to verify the proposed efficiency of CO2 recycling at convergent margins. Quantification of bulk CO2 concentration in melt inclusions requires their complete homogenization. Using samples from lavas from the Bulochka vent of Klyuchevskoy Volcano (Kamchatka), we applied a novel experimental approach to homogenize and re-equilibrate naturally dehydrated (<1 wt.% H2O) melt inclusions from high-Fo (85-91 mol.%) olivine. The experiments were performed at temperatures of 1150-1400 °C, pressures of up to 500 MPa, under dry to H2O-saturated conditions and with oxygen fugacity ranging from CCO to QFM+3.3. No homogenization was achieved at dry conditions. Complete dissolution of fluid bubbles (homogenization) in the melt inclusions was achieved at H2O pressures of 500 MPa and temperature of 1150 °C, when water content in the melt inclusions reached 4-5 wt.% H2O. The CO2 content in the homogenized inclusions is 3800 ± 140 ppm and CO2/Nb = 3000 ± 420, which are the highest values reported so far for the typical middle-K primitive arc melts and fall within the range of values inferred from the magmatic flux and volcanic gas data for primary arc magma compositions. About 83% of the CO2 in Klyuchevskoy magmas is likely to be derived from the subducting slab and can be attributed to flux melting with a fluid having a CO2/H2O ratio of ∼0.06. The H2O and CO2 contents in the melt inclusions after hydrous experiments were found to correlate positively with each other and negatively with the volume of fluid bubble, reflecting increasing internal pressure in melt inclusions with increasing melt hydration. Therefore, similar trends observed in some natural sets of melt inclusions can be attributed to a partial dehydration of melts after entrapment, operating simultaneously with or following post-entrapment crystallization. Our study implies that the

  12. Neutral buoyancy of titanium-rich melts in the deep lunar interior

    NASA Astrophysics Data System (ADS)

    van Kan Parker, Mirjam; Sanloup, Chrystèle; Sator, Nicolas; Guillot, Bertrand; Tronche, Elodie J.; Perrillat, Jean-Philippe; Mezouar, Mohamed; Rai, Nachiketa; van Westrenen, Wim

    2012-03-01

    The absence of moonquakes originating deeper than about 1,100km (ref. ) implies that the lower mantle of the Moon could be partially molten. Up to 30% melt by volume has been estimated to exist between about 1,200 and 1,350km depth. However, the absence of recent volcanic activity at the Moon's surface implies that such deep partial melts must be at least as dense as their surroundings. Here we use a combination of in situ synchrotron X-ray absorption techniques and molecular dynamics simulations to determine the density range of primitive lunar melts at pressures equivalent to those in the lunar interior. We find that only melts that contain about 16 wt% titanium dioxide are neutrally buoyant at depths corresponding to the top of the proposed partial melt zone. These titanium-rich melts are formed by deep partial melting of titanium-rich rocks. As such rocks are thought to have formed at shallow levels during crystallization of the lunar magma ocean, we infer that a significant vertical transport of mass occurred before melt formation. Our measurements therefore provide evidence for a large-scale overturn of the lunar mantle shortly after crystallization of the magma ocean and point to the continuing influence of a dense, titanium-rich reservoir on lunar interior evolution.

  13. Microstructural characterization of laser surface melted AISI M2 tool steel.

    PubMed

    Arias, J; Cabeza, M; Castro, G; Feijoo, I; Merino, P; Pena, G

    2010-09-01

    We describe the microstructure of Nd:YAG continuous wave laser surface melted high-speed steel, namely AISI M2, treated with different laser scanning speeds and beam diameters on its surface. Microstructural characterization of the remelted surface layer was performed using light optical and scanning electron microscopy and X-ray diffraction. The combination of the three techniques provided new insights into the substantial changes induced by laser surface melting of the steel surface layer. The advantage of the method is that it avoids the difficult and tedious work of preparing samples of this hard material for transmission electron microscopy, which is the technique normally used to study these fine microstructures. A melted zone with a dendritic structure and a partially melted zone with a heterogeneous cellular structure were observed. M(2)C carbides with different morphologies were identified in the resolidified surface layer after laser melting. PMID:20701656

  14. Rapid Ascent of Aphyric Mantle Melts through the Overriding Crust in Subduction Zones: Evidence from Variable Uranium-Series Disequilibria, Amorphous Hydrous Alteration Microtextures in Crystal Rims, and Two-Pyroxene Pseudo-Decompression Paths

    NASA Astrophysics Data System (ADS)

    Zellmer, G. F.; Freymuth, H.; Hsieh, H. H.; Hwang, S. L.; Iizuka, Y.; Miller, C. A.; Rubin, K. H.; Sakamoto, N.; Yurimoto, H.

    2014-12-01

    Volcanic hazard mitigation at subduction zones critically depends on knowledge of magma generation and ascent processes and timescales. Two diametrically opposite scenarios are presently debated: One paradigm is the generation of low-silica (basaltic) melts in the mantle wedge, followed by protracted sub-liquidus magma ascent and evolution through crystal growth and fractionation in crustal reservoirs, which are tapped during volcanic eruptions. In contrast, a diametrically opposite model favours the generation of higher silica melts in the mantle or in a lower crustal hot zone, followed by rapid decompression to the surface under super-liquidus conditions. In the latter case, crystals are picked up during magma ascent, and are in the process of dissolving. We present multiple lines of evidence that point to crystal uptake as the principal processes by which arc melts acquire their crystal cargo: (i) variable 234U-238U disequilibria in mineral separates; (ii) hydrous mineral rims with amorphous alteration textures; and (iii) two-pyroxene pseudo-decompression paths; cf. Zellmer et al. (2014a,b,c), doi: 10.1144/SP385.3 and 10.1144/SP385.9 and 10.1144/SP410.1. These observations point to a scarcity of true phenocrysts in many arc magmas, and thus to decompression of aphyric melts that take up their crystal cargo during ascent. The data imply that many hydrous wedge melts are more silica-rich than basalts and achieve super-liquidus conditions during rapid ascent from great depth.

  15. Paradise Lost: Uncertainties in melting and melt extraction processes beneath oceanic spreading ridges

    NASA Astrophysics Data System (ADS)

    Kelemen, P. B.

    2014-12-01

    In many ways, decompression melting and focused melt transport beneath oceanic spreading ridges is the best understood igneous process on Earth. However, there are remaining - increasing - uncertainties in interpreting residual mantle peridotites. Indicators of degree of melting in residual peridotite are questionable. Yb concentration and spinel Cr# are affected by (a) small scale variations in reactive melt transport, (b) variable extents of melt extraction, and (c) "impregnation", i.e. partial crystallization of cooling melt in pore space. Roughly 75% of abyssal peridotites have undergone major element refertilization. Many may have undergone several melting events. The following three statements are inconsistent: (1) Peridotite melt productivity beyond cpx exhaustion is > 0.1%/GPa. (2) Crustal thickness is independent of spreading rate at rates > 2 cm/yr full rate (excluding ultra-slow spreading ridges). (3) Thermal models predict, and observations confirm, thick thermal boundary layers beneath slow spreading ridges. If (a) melt productivity is << 0.1%/GPa beyond cpx-out, and (b) cpx-out occurs > 15 km below the seafloor beneath most ridges, then the independence of crustal thickness with spreading rate can be understood. Most sampled peridotites from ridges melted beyond cpx-out. Cpx in these rocks formed via impregnation and/or exsolution during cooling. Most peridotites beneath ridges may undergo cpx exhaustion during decompression melting. This would entail an upward modification of potential temperature estimates. Alternatively, perhaps oceanic crustal thickness does vary with spreading rate but this is masked by complicated tectonics and serpentinization at slow-spreading ridges. Dissolution channels (dunites) are predicted to coalesce downstream, but numerical models of these have not shown why > 95% of oceanic crust forms in a zone < 5 km wide. There may be permeability barriers guiding deeper melt toward the ridge, but field studies have not identified

  16. The Asthenosphere Melting Regimes Alteration due to Changing Conditions of Upper Mantle

    NASA Astrophysics Data System (ADS)

    Perepechko, Y. V.; Sharapov, V. N.; Sorokin, K., Jr.

    2014-12-01

    Analyzed in the article are different asthenosphere magma generation regimes above the upper mantle hot spots as thermodynamic and geometric parameters of the upper mantle and the conditions on its boundaries vary. The two-layer mantle model is applied to consider the formation of decompression melting areas. The thickness of metasomatically altered lithospheric mantle is determined by the mantle substance rheology and the location of the upper boundary of asthenosphere. We also take into consideration the principal solid state phase transitions by using the mantle substance state equation. The sizes and distribution of hot spots as well as their maximal temperature were defined by the thermodynamic conditions of the perovskite transition existence. The numerical analysis results demonstrate the manifestation of three main mantle dynamics modes; the conditions necessary to form the partial melting zones are not reached; some melting areas with the 30 to 65 Ma existence time do occur; the melting areas that are formed exist permanently. The permanently existing asthenosphere zones are marked by quasiperiodical variation in thickness and the degree of melting. The typical temperatures of a hot spot sharing these modes are the 1740°С and 2020°С correspondingly. The originally presupposed heating degree and the temperature ratio of the upper mantle do influence the decompression melting degree substantially and - to a lesser extent - they influence the size of melting zones. The primary evolution of the second mode is described by the development of a complex system of asthenosphere zones that lead to the occurrence of additional convectional cells dividing the partial melting zone. The variation in the rheological properties of the mantle substance also contributes to the manifestation of the complex structure of asthenosphere zone. The work was made with support of the Russian Foundation for Basic Research grant #12-05-00625.

  17. Porosity of the melting zone and variations in the solid mantle upwelling rate beneath Hawaii: Inferences from {sup 238}U-{sup 230}Th-{sup 226}Ra and {sup 235}U-{sup 231}Pa disequilibria

    SciTech Connect

    Sims, K.W.W.; DePaolo, D.J.; Murrell, M.T.; Baldridge, W.S.; Goldstein, S.; Clague, D.; Jull, M.

    1999-12-01

    Measurements of {sup 238}U-{sup 230}Th-{sup 226}Ra and {sup 235}U-{sup 231}Pa disequilibria in a suite of tholeiitic-to-basanitic lavas provide estimates of porosity, solid mantle upwelling rate and melt transport times beneath Hawaii. The observation that ({sup 230}Th/{sup 238}U) {gt} 1 indicates that garnet is required as a residual phase in the magma sources for all of the lavas. Both chromatographic porous flow and dynamic melting of a garnet peridotite source can adequately explain the combined U-Th-Ra and U-Pa data for these Hawaiian basalts. For chromatographic porous flow, the calculated maximum porosity in the melting zone ranges from 0.3--3% for tholeiites and 0.1--1% for alkali basalts and basanites, and solid mantle upwelling rates range from 40 to 100 cm/yr for tholeiites and from 1 to 3 cm/yr for basanites. For dynamic melting, the escape or threshold porosity is 0.5--2% for tholeiites and 0.1--0.8% for alkali basalts and basanites, and solid mantle upwelling rates range from 10 to 30 cm/yr for tholeiites and from 0.1 to 1 cm/yr for basanites. Assuming a constant melt productivity, calculated total melt fractions range from 15% for the tholeiitic basalts to 3% for alkali basalts and basanites.

  18. Adakitic (tonalitic-trondhjemitic) magmas resulting from eclogite decompression and dehydration melting during exhumation in response to continental collision

    NASA Astrophysics Data System (ADS)

    Song, Shuguang; Niu, Yaoling; Su, Li; Wei, Chunjing; Zhang, Lifei

    2014-04-01

    Modern adakite or adakitic rocks are thought to result from partial melting of younger and thus warmer subducting ocean crust in subduction zones, with the melt interacting with or without mantle wedge peridotite during ascent, or from melting of thickened mafic lower crust. Here we show that adakitic (tonalitic-trondhjemitic) melts can also be produced by eclogite decompression during exhumation of subducted and metamorphosed oceanic/continental crust in response to continental collision, as exemplified by the adakitic rocks genetically associated with the early Paleozoic North Qaidam ultra-high pressure metamorphic (UHPM) belt on the northern margin of the Greater Tibetan Plateau. We present field evidence for partial melting of eclogite and its products, including adakitic melt, volumetrically significant plutons evolved from the melt, cumulate rocks precipitated from the melt, and associated granulitic residues. This “adakitic assemblage” records a clear progression from eclogite decompression and heating to partial melting, to melt fractionation and ascent/percolation in response to exhumation of the UHPM package. The garnetite and garnet-rich layers in the adakitic assemblage are of cumulate origin from the adakitic melt at high pressure, and accommodate much of the Nb-Ta-Ti. Zircon SHRIMP U-Pb dating shows that partial melting of the eclogite took place at ∼435-410 Ma, which postdates the seafloor subduction (>440 Ma) and temporally overlaps the UHPM (∼440-425 Ma). While the geological context and the timing of adakite melt formation we observe differ from the prevailing models, our observations and documentations demonstrate that eclogite melting during UHPM exhumation may be important in contributing to crustal growth.

  19. Slab melting and magma generation beneath the southern Cascade Arc

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Magma formation in subduction zones is interpreted to be caused by flux melting of the mantle wedge by fluids derived from dehydration of the downgoing oceanic lithosphere. In the Cascade Arc and other hot-slab subduction zones, however, most dehydration reactions occur beneath the forearc, necessitating a closer investigation of magma generation processes in this setting. Recent work combining 2-D steady state thermal models and the hydrogen isotope composition of olivine-hosted melt inclusions from the Lassen segment of the Cascades (Walowski et al., 2014; in review) has shown that partial melting of the subducted basaltic crust may be a key part of the subduction component in hot arcs. In this model, fluids from the slab interior (hydrated upper mantle) rise through the slab and cause flux-melting of the already dehydrated MORB volcanics in the upper oceanic crust. In the Shasta and Lassen segments of the southern Cascades, support for this interpretation comes from primitive magmas that have MORB-like Sr isotope compositions that correlate with subduction component tracers (H2O/Ce, Sr/P) (Grove et al. 2002, Borg et al. 2002). In addition, mass balance calculations of the composition of subduction components show ratios of trace elements to H2O that are at the high end of the global arc array (Ruscitto et al. 2012), consistent with the role of a slab-derived melt. Melting of the subducted basaltic crust should contribute a hydrous dacitic or rhyolitic melt (e.g. Jego and Dasgupta, 2013) to the mantle wedge rather than an H2O-rich aqueous fluid. We are using pHMELTS and pMELTS to model the reaction of hydrous slab melts with mantle peridotite as the melts rise through the inverted thermal gradient in the mantle wedge. The results of the modeling will be useful for understanding magma generation processes in arcs that are associated with subduction of relatively young oceanic lithosphere.

  20. Partial root-zone drying and conventional deficit irrigation applied during the whole berry growth maintain yield and berry quality in 'Crimson Seedless' table grapes

    NASA Astrophysics Data System (ADS)

    Pérez-Pastor, Alejandro; Domingo, Rafael; De la Rosa, Jose M.°; Rosario Conesa Saura, M.°

    2016-04-01

    To compare the effects of partial root-zone drying and conventional deficit irrigation applied during post-veraison and the whole berry growth on water relations, yield and berry quality, one experiment was conducted in a commercial vineyard of 'Crimson Seedless' table grapes. Five irrigation treatments were imposed: (i) Control (CTL) irrigated to 110% of crop evapotranspiration (ETc), (ii) regulated deficit irrigation (RDI) irrigated at 50% of CTL during the non- critical period of post-verasion, (iii) continuous deficit irrigation (DIc), irrigated at 50% of CTL throughout the whole berry growing season, (iv) partial root-zone drying (PRD), irrigated similar to RDI, but alternating the irrigation applied in the dry side every 10-14 days; and (v) continuous partial root-zone drying (PRDc), irrigated as DIc but alternating the irrigation in the dry side every 10-14 days. RDI and PRD received 24% and 28% less water than CTL, respectively. These reductions were higher in DIc and PRDc (65% and 53%, respectively). Total yield was not affected by any DI strategy. Only significantly lower values were observed in the weight and height's berries in respect to CTL. However, the colour parameters evaluated increased in all DI treatments, being slightly higher in DIc and PRDc compared with RDI and PRD. In addition, total soluble solids (TSS) were significantly higher in DIc, compared to other irrigated counterparts. Our findings showed that the application of water deficit during the whole berry growth through the use of DIc and PRDc, can be considered for irrigation scheduling in 'Crimson Seedless' table grapes. Acknowledgements This work has been funded by the European Union LIFE+ project IRRIMAN (LIFE13 ENV/ES/000539).

  1. Melt-rock reaction an melt impregnation in oceanic peridotites: insights from the Ligurian-Piemontese ophiolites

    NASA Astrophysics Data System (ADS)

    Piccardo, G. B.

    2011-12-01

    Mantle peridotites from Alpine-Apennine ophiolites, deriving from the Jurassic Ligurian Tethys, record signatures of the complex petrogenetic evolution, other than partial melting, that the lithospheric mantle suffered during pre-oceanic extension and melt percolation, melt-rock interaction and refertilization of early melts from decompression melting of the almost adiabatically upwelling asthenosphere (Piccardo et al., 2008). Lithosphere extension by far field tectonic forces lead to thinning of the lithospheric mantle and its progressive exhumation. Field and petrographic-structural data indicate that lithosphere extension was driven by extensional shear zones during the whole evolution of the mantle lithosphere, from garnet- to plagioclase-facies conditions. The pristine sub-continental lithospheric mantle is still preserved in ophiolites deriving from the passive margins (ocean-continent transition zones) of the basin, whereas melt-reacted and refertilized peridotites are dominant in more internal oceanic domains. OCT peridotites maintain structural-paragenetic features indicating their provenance from the deep lithosphere (P > 2.5 GPa) (Piccardo et al., 2009). Km-scale extensional shear zones in spinel peridotites (e.g., Vissers et al., 1991; Hoogerduijn Strating et al., 1993) have been dated to 220 Ma (Lu-Hf age) (Montanini et al., 2006) and 225 Ma (40Ar/39Ar amphibole age) (Müntener & Hermann, 2001) indicating that significant lithosphere extension and mantle exhumation was already active during Triassic times. Passive upwelling asthenosphere underwent fractional melting under spinel-facies conditions forming MORB-type depleted single melt increments that were injected into the lithospheric spinel-facies shear zones. Porous flow percolation of the silica-undersaturated melt fractions and melt-peridotite interaction (pyroxene dissolution and olivine precipitation) formed reactive spinel harzburgites and dunites. Melt-peridotite interaction led to silica

  2. Temperature and melt fraction distributions in a mantle wedge determined from the electrical conductivity structure: Application to one nonvolcanic and two volcanic regions in the Kyushu subduction zone, Japan

    NASA Astrophysics Data System (ADS)

    Hata, Maki; Uyeshima, Makoto

    2015-04-01

    We propose a new method for estimating the temperatures and melt fractions of the upper mantle. Our method is based on connecting the electrical conductivity structure from geophysical observations with laboratory-determined relationships between the electrical conductivity and temperature of four nominally anhydrous minerals (olivine, orthopyroxene, clinopyroxene, and garnet) and basaltic melt. The temperatures are expressed as the upper limit temperatures using the Hashin-Shtrikman lower bound in solid phases and using the Hashin-Shtrikman upper bound in solid-liquid mixed phases. We apply the method to a nonvolcanic and two volcanic regions in the Kyushu subduction zone, southwest Japan. Our results suggest that the temperatures of the upper mantle are 1100-1450°C for dry mantle and 900-1350°C for wet mantle and that the melt fractions of the upper mantle are <20% beneath the two volcanic regions and <5% beneath the nonvolcanic region for both dry and wet mantle.

  3. Formation of harzburgite by pervasive melt/rock reaction in the upper mantle

    USGS Publications Warehouse

    Kelemen, P.B.; Dick, H.J.B.; Quick, J.E.

    1992-01-01

    Many mantle peridotite samples are too rich in SiO2 (in the form of orthopyroxene) and have ratios of light to heavy rare earth elements that are too high to be consistent with an origin as the residuum of partial melting of the primitive mantle. Trace element studies of melt/rock reaction zones in the Trinity peridotite provide evidence for reaction of the mantle lithosphere with ascending melts, which dissolved calcium-pyroxene and precipitated orthopyroxene as magma mass decreased. This process can account for the observed major and trace element compositions of lithospheric mantle samples, and may accordingly be prevalent in the upper mantle.

  4. Melt segregation and strain partitioning: implications for seismic anisotropy and mantle flow.

    PubMed

    Holtzman, B K; Kohlstedt, D L; Zimmerman, M E; Heidelbach, F; Hiraga, T; Hustoft, J

    2003-08-29

    One of the principal means of understanding upper mantle dynamics involves inferring mantle flow directions from seismic anisotropy under the assumption that the seismic fast direction (olivine a axis) parallels the regional flow direction. We demonstrate that (i) the presence of melt weakens the alignment of a axes and (ii) when melt segregates and forms networks of weak shear zones, strain partitions between weak and strong zones, resulting in an alignment of a axes 90 degrees from the shear direction in three-dimensional deformation. This orientation of a axes provides a new means of interpreting mantle flow from seismic anisotropy in partially molten deforming regions of Earth. PMID:12947196

  5. The evolution and storage of primitive melts in the Eastern Volcanic Zone of Iceland: the 10 ka Grímsvötn tephra series (i.e. the Saksunarvatn ash)

    NASA Astrophysics Data System (ADS)

    Neave, David A.; Maclennan, John; Thordarson, Thorvaldur; Hartley, Margaret E.

    2015-08-01

    Major, trace and volatile elements were measured in a suite of primitive macrocrysts and melt inclusions from the thickest layer of the 10 ka Grímsvötn tephra series (i.e. Saksunarvatn ash) at Lake Hvítárvatn in central Iceland. In the absence of primitive tholeiitic eruptions (MgO > 7 wt%) within the Eastern Volcanic Zone (EVZ) of Iceland, these crystal and inclusion compositions provide an important insight into magmatic processes in this volcanically productive region. Matrix glass compositions show strong similarities with glass compositions from the AD 1783-1784 Laki eruption, confirming the affinity of the tephra series with the Grímsvötn volcanic system. Macrocrysts can be divided into a primitive assemblage of zoned macrocryst cores (An78-An92, Mg#cpx = 82-87, Fo79.5-Fo87) and an evolved assemblage consisting of unzoned macrocrysts and the rims of zoned macrocrysts (An60-An68, Mg#cpx = 71-78, Fo70-Fo76). Although the evolved assemblage is close to being in equilibrium with the matrix glass, trace element disequilibrium between primitive and evolved assemblages indicates that they were derived from different distributions of mantle melt compositions. Juxtaposition of disequilibrium assemblages probably occurred during disaggregation of incompatible trace element-depleted mushes (mean La/Ybmelt = 2.1) into aphyric and incompatible trace element-enriched liquids (La/Ybmelt = 3.6) shortly before the growth of the evolved macrocryst assemblage. Post-entrapment modification of plagioclase-hosted melt inclusions has been minimal and high-Mg# inclusions record differentiation and mixing of compositionally variable mantle melts that are amongst the most primitive liquids known from the EVZ. Coupled high-field strength element (HFSE) depletion and incompatible trace element enrichment in a subset of primitive plagioclase-hosted melt inclusions can be accounted for by inclusion formation following plagioclase dissolution driven by interaction with plagioclase

  6. Granodiorites of the South Mountain Batholith (Nova Scotia, Canada) derived by partial melting of Avalonia granulite rocks beneath the Meguma terrane: Implications for the heat source of the Late Devonian granites of the Northern Appalachians

    NASA Astrophysics Data System (ADS)

    Shellnutt, J. Gregory; Dostal, Jaroslav

    2015-08-01

    The Late Devonian South Mountain Batholith (SMB) of Nova Scotia is the largest batholith of the northern Appalachians. The peraluminous granitic rocks range from biotite granodiorite to leucogranite. Samples collected from a drill core of the Scrag Lake granodioritic pluton of the western SMB are chemically homogeneous from the surface to a depth of ~ 1425 m. The homogeneous composition implies that the granodiorite was derived from a relatively homogeneous source and that country rock assimilation was not an important source for the parental magma. Equilibrium partial melt modeling of underlying sub-Meguma granulite rocks indicates that they are the primary source rocks of the granodiorites. We suggest that mantle-derived magmas intruded the lower crust and induce large-scale melting of the granulite basement rocks to produce the granodiorites. Fractional crystallization of the granodiorites plus assimilation of Meguma Supergroup metasediments likely produces the silica-rich rocks of the SMB. The cause of mantle melting is uncertain however it may be related to the transitioning of the northern Appalachians from a position above the deep mantle Pacific large low shear velocity province (LLSVP) to a higher shear velocity region of the mantle.

  7. Contrasting physiological effects of partial root zone drying in field-grown grapevine (Vitis vinifera L. cv. Monastrell) according to total soil water availability

    PubMed Central

    Romero, Pascual; Dodd, Ian C.; Martinez-Cutillas, Adrian

    2012-01-01

    Different spatial distributions of soil moisture were imposed on field-grown grapevines by applying the same irrigation volumes to the entire (DI; deficit irrigation) or part of the (PRD; partial root zone drying) root zone. Five treatments were applied: controls irrigated at 60% ETc (crop evapotranspiration) for the whole season (308 mm year−1); DI-1 and PRD-1 that received the same irrigation as controls before fruit set, 30% ETc from fruit set to harvest and 45% ETc post-harvest (192 mm year−1); and DI-2 and PRD-2 that were the same, except that 15% ETc was applied from fruit set to harvest (142 mm year−1). Compared with DI-1, PRD-1 maintained higher leaf area post-veraison and increased root water uptake, whole-plant hydraulic conductance, leaf transpiration, stomatal conductance, and photosynthesis, but decreased intrinsic gas exchange efficiency without causing differences in leaf xylem abscisic acid (ABA) concentration. Compared with DI-2, PRD-2 increased leaf xylem ABA concentration and decreased root water uptake, whole-plant hydraulic conductance, leaf transpiration, stomatal conductance, and photosynthesis, mainly at the beginning of PRD cycles. Distinctive PRD effects (e.g. greater stomatal closure) depended on the volumetric soil water content of the wet root zone, as predicted from a model of root-to-shoot ABA signalling. PMID:22451721

  8. Study of the Ionospheric D Layer using Partial Reflections at the Middle Latitudes and in the Auroral Zone

    NASA Astrophysics Data System (ADS)

    Belikovich, V. V.; Vyakhirev, V. D.; Kalinina, E. E.; Tereshshenko, V. D.; Ogloblina, O. F.; Tereshshenko, V. A.

    2003-03-01

    Using the measuring facilities located in different latitudinal regions: in Vasil'sursk near Nizhny Novgorod (56.1° N and 46.1° E) and in Tumanny (Murmansk region, 69.0° N and 35.7° E), we study the ionospheric D layer by the partial-reflection technique. Quantitative estimates are obtained for the electron density in the polar and mid-latitude D layer, distinctions of these values are revealed, and the possible reasons for latitudinal variations in the electron density at the D-layer altitudes are discussed.

  9. Tectonic impact of anatexis on collision zones dynamics : insights from numerical modelling

    NASA Astrophysics Data System (ADS)

    Labrousse, Loic; Duretz, Thibault; Gerya, Taras

    2013-04-01

    Partial melting reactions constitute a first order weakening process in the continental crust involed in collision zones. It can act as a possible decoupling mechanism within the lithosphere and therefore influence the dynamics of continental subduction-collision. The Western Gneiss Region, Norwegian Caledonides, exhibits a direct relationship between eclogites occurrences and partial melting textures in the surrounding gneiss. This fact implies that partial melting is associated with part of the exhumation of High Pressure (HP) rocks. Several metamorphic reactions produce silicate melts at different PT conditions, depending mainly on the availability of aqueous fluids. Even if most of the partial melting textures observed in hot orogens relate to water-absent dehydration melting, evidences of water-present partial melting of gneiss and eclogites at HP in the Western Gneiss Region, suggest that water-present melting reactions may play a role in fostering HP metamorphic rocks exhumation. Another question arising from experimental rheological studies relies in quantifying the amount of liquid phase necessary to trigger strength drops of migmatites (i.e. the Rheologically Critical Melt Percentage, RCMP). Proposed values span from very low percentages close to 1% up to 20-30%, when migmatites turn to diatexites. In this study, we employ lithospheric scale numerical experiments, to compare the effects of water-present or dehydration partial melting reactions on continental collision systems. The two-dimensional thermo-mechanical experiments explore the extent of melt-weakening by allowing a wide range viscosity variations (9 orders of magnitude). The model set-up is representative of the Scandian collision and its sensitivity to the initial Moho temperature, the value of RCMP, and the buoyancy of the extracted melts, was investigated.

  10. Partial melting of the mélange for the growth of andesitic crust indicated by the Early Cretaceous arc dioritic/andesitic rocks in southern Qiangtang, central Tibet

    NASA Astrophysics Data System (ADS)

    Hao, LuLu; Wang, Qiang; Wyman, Derek; Ou, Quan; Dan, Wei; Jiang, ZiQi; Yang, JinHui; Long, XiaoPing; Li, Jie

    2016-04-01

    Deciphering the petrogenesis of andesitic/dioritic rocks is fundamental to understanding the formation of the continental crust. Here we present the detailed petrology, geochronology, major and trace element, Sr-Nd-Hf-O isotope data for the Early Cretaceous (ca. 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 to 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 the mélange, which is a mixture of the middle 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 the mélange provides an important support for the generation of andesitic magmas in continental arcs and the "andesite model" for crustal growth.

  11. Diffusive fractionation of U-series radionuclides during mantle melting and shallow-level melt cumulate interaction

    NASA Astrophysics Data System (ADS)

    Van Orman, James A.; Saal, Alberto E.; Bourdon, Bernard; Hauri, Erik H.

    2006-09-01

    U-series radioactive disequilibria in basaltic lavas have been used to infer many important aspects of melt generation and extraction processes in Earth's mantle and crust, including the porosity of the melting zone, the solid mantle upwelling rate, and the melt transport rate. Most of these inferences have been based on simplified theoretical treatments of the fractionation process, which assume equilibrium partitioning of U-series nuclides among minerals and melt. We have developed a numerical model in which solid-state diffusion controls the exchange of U-series nuclides among multiple minerals and melt. First the initial steady-state distribution of nuclides among the phases, which represents a balance between diffusive fluxes and radioactive production and decay, is calculated. Next, partial melting begins, or a foreign melt is introduced into the system, and nuclides are again redistributed among the phases via diffusion. U-series nuclides can be separated during this stage due to differences in their diffusivity; radium in particular, and possibly protactinium as well, can be strongly fractionated from slower-diffusing thorium and uranium. We show that two distinct processes are not required for the generation of 226Ra and 230Th excesses in mid-ocean ridge basalts, as has been argued previously; instead the observed negative correlations of the ( 226Ra/ 230Th) activity ratio with ( 230Th/ 238U) and with the extent of trace element enrichment may result from diffusive fractionation of Ra from Th during partial melting of the mantle. Alternatively, the ( 226Ra/ 230Th) disequilibrium in mid-ocean ridge basalts may result from diffusive fractionation during shallow-level interaction of mantle melts with gabbroic cumulates, and we show that the results of the interaction have a weak dependence on the age of the cumulate if both plagioclase and clinopyroxene are present.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

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

    PubMed

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

    2016-01-01

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

  14. Density and seismic velocity of hydrous melts under crustal and upper mantle conditions

    NASA Astrophysics Data System (ADS)

    Ueki, Kenta; Iwamori, Hikaru

    2016-05-01

    We present a new model for calculating the density of hydrous silicate melts as a function of P, T, H2O concentration, and melt composition. We optimize VPr,Tr, ∂V/∂T, ∂V/∂P, ∂V2/∂T∂P, and K' of H2O end-member components in hydrous silicate melts, as well as K' of anhydrous silicate melts, using previously reported experimental results. The parameter set for H2O end-member component in silicate melt optimized in this study is internally consistent with the parameter values for the properties of anhydrous silicate melt reported by Lange and Carmichael (1987, 1990). The model calculation developed in this study reproduces the experimentally determined densities of various hydrous melts, and can be used to calculate the relationships between pressures, temperatures, and H2O concentrations of various hydrous melts from ultramafic to felsic compositions at pressures of 0-4.29 GPa. Using the new parameter set, we investigate the effects of H2O content on the seismic velocity of hydrous melts, as well as seismic velocities in partially molten regions of subduction zones. The results show that water content in silicate melt plays a key role in determining seismic velocity structure, and therefore must be taken into account when interpreting seismic tomography.

  15. The jumbo squid, Dosidicus gigas (Ommastrephidae), living in oxygen minimum zones I: Oxygen consumption rates and critical oxygen partial pressures

    NASA Astrophysics Data System (ADS)

    Trueblood, Lloyd A.; Seibel, Brad A.

    2013-10-01

    Dosidicus gigas is a large, metabolically active, epipelagic squid known to undertake diel vertical migrations across a large temperature and oxygen gradient in the Eastern Pacific. Hypoxia is known to cause metabolic suppression in D. gigas. However, the precise oxygen level at which metabolic suppression sets in is unknown. Here we describe a novel ship-board swim tunnel respirometer that was used to measure metabolic rates and critical oxygen partial pressures (Pcrit) for adult squids (2-7kg). Metabolic rate measurements were validated by comparison to the activity of the Krebs cycle enzyme, citrate synthase, in mantle muscle tissue (2-17kg). We recorded a mean routine metabolic rate of 5.91μmolg-1h-1 at 10°C and 12.62μmolg-1h-1 at 20°C. A temperature coefficient, Q10, of 2.1 was calculated. D. gigas had Pcrits of 1.6 and 3.8kPa at 10 and 20°C, respectively. Oxygen consumption rate (MO2) varied with body mass (M) according to MO2=11.57M-0.12±0.03 at 10°C. Citrate synthase activity varied with body mass according to Y=9.32M-0.19±0.02.

  16. Seismic evidence of effects of water on melt transport in the Lau back-arc mantle.

    PubMed

    Wei, S Shawn; Wiens, Douglas A; Zha, Yang; Plank, Terry; Webb, Spahr C; Blackman, Donna K; Dunn, Robert A; Conder, James A

    2015-02-19

    Processes of melt generation and transport beneath back-arc spreading centres are controlled by two endmember mechanisms: decompression melting similar to that at mid-ocean ridges and flux melting resembling that beneath arcs. The Lau Basin, with an abundance of spreading ridges at different distances from the subduction zone, provides an opportunity to distinguish the effects of these two different melting processes on magma production and crust formation. Here we present constraints on the three-dimensional distribution of partial melt inferred from seismic velocities obtained from Rayleigh wave tomography using land and ocean-bottom seismographs. Low seismic velocities beneath the Central Lau Spreading Centre and the northern Eastern Lau Spreading Centre extend deeper and westwards into the back-arc, suggesting that these spreading centres are fed by melting along upwelling zones from the west, and helping to explain geochemical differences with the Valu Fa Ridge to the south, which has no distinct deep low-seismic-velocity anomalies. A region of low S-wave velocity, interpreted as resulting from high melt content, is imaged in the mantle wedge beneath the Central Lau Spreading Centre and the northeastern Lau Basin, even where no active spreading centre currently exists. This low-seismic-velocity anomaly becomes weaker with distance southward along the Eastern Lau Spreading Centre and the Valu Fa Ridge, in contrast to the inferred increase in magmatic productivity. We propose that the anomaly variations result from changes in the efficiency of melt extraction, with the decrease in melt to the south correlating with increased fractional melting and higher water content in the magma. Water released from the slab may greatly reduce the melt viscosity or increase grain size, or both, thereby facilitating melt transport. PMID:25642964

  17. Seismic evidence of effects of water on melt transport in the Lau back-arc mantle

    NASA Astrophysics Data System (ADS)

    Wei, S. Shawn; Wiens, Douglas A.; Zha, Yang; Plank, Terry; Webb, Spahr C.; Blackman, Donna K.; Dunn, Robert A.; Conder, James A.

    2015-02-01

    Processes of melt generation and transport beneath back-arc spreading centres are controlled by two endmember mechanisms: decompression melting similar to that at mid-ocean ridges and flux melting resembling that beneath arcs. The Lau Basin, with an abundance of spreading ridges at different distances from the subduction zone, provides an opportunity to distinguish the effects of these two different melting processes on magma production and crust formation. Here we present constraints on the three-dimensional distribution of partial melt inferred from seismic velocities obtained from Rayleigh wave tomography using land and ocean-bottom seismographs. Low seismic velocities beneath the Central Lau Spreading Centre and the northern Eastern Lau Spreading Centre extend deeper and westwards into the back-arc, suggesting that these spreading centres are fed by melting along upwelling zones from the west, and helping to explain geochemical differences with the Valu Fa Ridge to the south, which has no distinct deep low-seismic-velocity anomalies. A region of low S-wave velocity, interpreted as resulting from high melt content, is imaged in the mantle wedge beneath the Central Lau Spreading Centre and the northeastern Lau Basin, even where no active spreading centre currently exists. This low-seismic-velocity anomaly becomes weaker with distance southward along the Eastern Lau Spreading Centre and the Valu Fa Ridge, in contrast to the inferred increase in magmatic productivity. We propose that the anomaly variations result from changes in the efficiency of melt extraction, with the decrease in melt to the south correlating with increased fractional melting and higher water content in the magma. Water released from the slab may greatly reduce the melt viscosity or increase grain size, or both, thereby facilitating melt transport.

  18. Serpentinization, element transfer, and the progressive development of zoning in veins: evidence from a partially serpentinized harzburgite

    NASA Astrophysics Data System (ADS)

    Schwarzenbach, Esther M.; Caddick, Mark J.; Beard, James S.; Bodnar, Robert J.

    2016-01-01

    Serpentinization is an important geochemical process that affects the chemistry and petrophysical properties of the oceanic lithosphere and supports life through abiogenic formation of hydrogen. Here, we document through detailed mineralogical evidence and equilibrium thermodynamic models the importance of water (H2O) and silica (SiO2) activities on mineral assemblages produced during progressive serpentinization of a harzburgite. We describe a harzburgite from the Santa Elena Ophiolite in Costa Rica that is ~30 % serpentinized. Serpentine + brucite ± magnetite veins occur in olivine, Al-rich serpentine + talc veins occur in orthopyroxene, and Al-rich serpentine ± talc ± brucite veins occur at the boundary of orthopyroxene and olivine. Bulk vein chemistry and element distribution maps demonstrate distinct chemical zonations within veins and chemical gradients between orthopyroxene- and olivine-dominated areas. Specifically, the sample records (1) varying brucite composition depending on whether or not it is associated with magnetite, (2) formation of magnetite from Fe-rich brucite (±Fe-rich serpentine) during olivine hydration, where magnetite coexists with brucite Mg#96 and serpentine Mg#99, (3) chemical gradients in Si, Al, Cr, and Ca within and between orthopyroxene- and olivine-hosted veins, and 4) local (different) equilibrium assemblages within different zones of veins. The studied sample preserves rarely observed textures documenting continuous replacement of olivine, rather than individual vein generations and overprinting that is typically observed in more intensely serpentinized peridotites. Furthermore, the presence of a discrete sequence of vein textures and mineralogy allows direct comparison between mineral textures and equilibrium thermodynamic models and permits new insights into mineral reactions during serpentinization.

  19. Comparative effects of deficit irrigation and alternate partial root-zone irrigation on xylem pH, ABA and ionic concentrations in tomatoes

    PubMed Central

    Wang, Yaosheng; Liu, Fulai; Jensen, Christian Richardt

    2012-01-01

    Comparative effects of partial root-zone irrigation (PRI) and deficit irrigation (DI) on xylem pH, ABA, and ionic concentrations of tomato (Lycopersicon esculentum L.) plants were investigated in two split-root pot experiments. Results showed that PRI plants had similar or significantly higher xylem pH, which was increased by 0.2 units relative to DI plants. Nitrate and total ionic concentrations (cations+anions), and the proportion of cations influenced xylem pH such that xylem pH increases as nitrate and total ionic concentrations decrease, and the proportion of cations increases. In most cases, the xylem ABA concentration was similar for PRI and DI plants, and a clear association between increases in xylem pH with increasing xylem ABA concentration was only found when the soil water content was relatively low. The concentrations of anions, cations, and the sum of anions and cations in PRI were higher than in the DI treatment when soil water content was relatively high in the wetted soil compartment. However, when water content in both soil compartments of the PRI pots were very low before the next irrigation, the acquisition of nutrients by roots was reduced, resulting in lower concentrations of anions and cations in the PRI than in the DI treatment. It is therefore essential that the soil water content in the wet zone should be maintained relatively high while that in the drying soil zone should not be very low, both conditions are crucial to maintain high soil and plant water status while sustaining ABA signalling of the plants. PMID:22162869

  20. The influence of partial timber harvest in riparian management zones on macroinvertebrate and fish communities on first- and second-order streams in northern Minnesota

    USGS Publications Warehouse

    Chizinski, Christopher J.; Vondracek, Bruce C.; Blinn, Charles R.; Newman, Raymond M.; Atuke, Dickson M.; Fredricks, Keith; Hemstad, Nathaniel A.; Merten, Eric; Schlesser, Nicholas

    2010-01-01

    Relatively few evaluations of aquatic macroinvertebrate and fish communities have been published in peer-reviewed literature detailing the effect of varying residual basal area (RBA) after timber harvesting in riparian buffers. Our analysis investigated the effects of partial harvesting within riparian buffers on aquatic macroinvertebrate and fish communities in small streams from two experiments in northern Minnesota northern hardwood-aspen forests. Each experiment evaluated partial harvesting within riparian buffers. In both experiments, benthic macroinvertebrates and fish were collected 1 year prior to harvest and in each of 3 years after harvest. We observed interannual variation for the macroinvertebrate abundance, diversity and taxon richness in the single-basin study and abundance and diversity in the multiple-basin study, but few effects related to harvest treatments in either study. However, interannual variation was not evident in the fish communities and we detected no significant changes in the stream fish communities associated with partially harvested riparian buffers in either study. This would suggest that timber harvesting in riparian management zones along reaches ≤200 m in length on both sides of the stream that retains RBA ≥ 12.4 ± 1.3 m2 ha−1 or on a single side of the stream that retains RBA ≥ 8.7 ± 1.6 m2 ha−1 may be adequate to protect macroinvertebrate and fish communities in our Minnesota study systems given these specific timber harvesting techniques.

  1. Melting of subducted basalt at the core-mantle boundary.

    PubMed

    Andrault, Denis; Pesce, Giacomo; Bouhifd, Mohamed Ali; Bolfan-Casanova, Nathalie; Hénot, Jean-Marc; Mezouar, Mohamed

    2014-05-23

    The geological materials in Earth's lowermost mantle control the characteristics and interpretation of seismic ultra-low velocity zones at the base of the core-mantle boundary. Partial melting of the bulk lower mantle is often advocated as the cause, but this does not explain the nonubiquitous character of these regional seismic features. We explored the melting properties of mid-oceanic ridge basalt (MORB), which can reach the lowermost mantle after subduction of oceanic crust. At a pressure representative of the core-mantle boundary (135 gigapascals), the onset of melting occurs at ~3800 kelvin, which is ~350 kelvin below the mantle solidus. The SiO2-rich liquid generated either remains trapped in the MORB material or solidifies after reacting with the surrounding MgO-rich mantle, remixing subducted MORB with the lowermost mantle. PMID:24855266

  2. Partial root zone drying: regulation of photosynthetic limitations and antioxidant enzymatic activities in young olive (Olea europaea) saplings.

    PubMed

    Aganchich, Badia; Wahbi, Said; Loreto, Francesco; Centritto, Mauro

    2009-05-01

    The effect of partial root drying (PRD) irrigation on split-root olive (Olea europaea L. cv Picholine marocaine) saplings was investigated. An irrigated control and two PRD regimes were applied (control: irrigation applied on both sides of the root system to keep the soil water content close to field capacity; PRD(50): irrigation applied at 50% of the control amount on one side of the root system and irrigation withheld from the other side, with irrigation regimes switched between the sides of the root system every 2 weeks; and PRD(100): irrigation applied at 100% of the control amount on one side and irrigation withheld on the other side, with irrigation regimes switched between the sides of the root system every 2 weeks. Only saplings in the PRD(50) regime were subjected to water-deficit irrigation. The PRD treatments significantly affected water relations and vegetative growth throughout the growing season. Predawn leaf water potential and relative water content differed significantly between the PRD(50) and PRD(100) saplings, leading to reduced stomatal conductance, carbon assimilation, shoot length and leaf number in PRD(50) saplings. However, the PRD(50) water-deficit treatment did not affect the capacity of the saplings to assimilate CO(2). Activities of superoxide dismutase, soluble and insoluble peroxidase (POX) and polyphenol oxidase were up-regulated by the PRD(50) and PRD(100) treatments compared with control values. The higher activities of both soluble and insoluble POX observed in PRD(50) saplings may reflect the greater inhibitory effect of this treatment on vegetative growth. Up-regulation of the detoxifying systems in the PRD(100) and PRD(50) saplings may have provided protection mechanisms against irreversible damage to the photosynthetic machinery, thereby allowing the photosynthetic apparatus to function and preventing the development of severe water stress. We also measured CO(2) assimilation rate/internal leaf CO(2) concentration (A

  3. Role of magmatic and fluid concentrating in formation of platinum mineralization in the Lower Zone and Platreef as follows from composition of phlogopite, cumulus silicates, and sulfide melt, the northern limb of Bushveld Complex

    NASA Astrophysics Data System (ADS)

    Yudovskaya, M. A.; Kinnaird, J. A.; Udachina, L. V.; Distler, V. V.; Kuz'min, D. V.

    2014-11-01

    As follows from the results of new geological exploration, the thick sequence of primitive cumulates of the Lower Zone underlies Platreef in separate magmatic depressions of the northern limb of the Bushveld Complex. In the Turfspruit area, the Lower Zone is separated from the overlying Platreef by an interval of contact metasedimentary rocks with sills of fine-grained norite and plagioclase orthopyroxenite of the Marginal Zone. The magmatic stratigraphy of Platreef in Turfspruit and its western plunge, where it is slightly contaminated with sedimentary rocks, is close to the section of Critical Zone in the Bushveld. The Lower Zone and Platreef contain sulfide mineralization enriched in PGE in particular units-reefs-throughout the section. The main reef can be correlated with the Merensky Reef. The objective of this study was to estimate the relationships between fluid and magmatic PGE concentrating in the reefs localized in the upper part of Platreef near its unconformable contact with the Main Zone. It is shown that Ni partitioning between cumulus olivine and orthopyroxene, on the one hand, and coexisting sulfide liquid, on the other, indicates their equilibrium crystallization in the Lower Zone and Platreef at close redox conditions. The composition of sulfide liquid was recalculated as sulfide tenor on the basis of bulk Ni, Cu, and S concentrations in rock. In contrast, Ni partitioning between phlogopite and sulfide melt does not provide evidence in favor of their equilibrium crystallization, although Mg # of phlogopite from the intercumulus assemblage is correlated with Mg # of cumulus mineral throughout the section. The results of phlogopite microprobing throughout the section show that the highest F and Cl contents are characteristic of highly evolved rocks, including both the PGE-bearing plagioclase pyroxenite from reefs and barren norite from the Marginal Zone. We have arrived at the conclusion that enrichment in volatile components is the attendant rather

  4. Sulfur and chalcophile elements in subduction zones: constraints from a laser ablation ICP-MS study of melt inclusions from Galunggung Volcano, Indonesia

    NASA Astrophysics Data System (ADS)

    de Hoog, J. C. M.; Mason, P. R. D.; van Bergen, M. J.

    2001-09-01

    Mafic melt inclusions hosted in olivine phenocrysts (Fo 89-78) in high-Mg basalts of Galunggung volcano (Java, Indonesia) were analyzed in situ by laser ablation ICP-MS to determine concentrations of chalcophile and associated trace elements. Our results indicate that sulfur in the mantle beneath Galunggung is significantly enriched relative to MORB source mantle, suggesting large-scale fluxing of sulfur into the mantle wedge during slab dehydration. Melt-inclusion compositions range from strongly undersaturated to transitional basaltic and are characterized by a wide range of sulfur contents (350-2900 ppm). Chalcophile element concentrations are not affected by exsolution of immiscible sulfide liquids and generally fall within the range of whole-rock samples from other arcs. We infer that primary Galunggung melts contain approximately 290 ppm Ni, 60 ppm Co, 190 ppm Cu, and 3 ppm Pb. Patterns of refractory trace elements point to ˜15% melting of a MORB-source mantle below Galunggung, which was enriched in LILE and LREE by slab-derived fluids before melting. Based on this value, we use melting model calculations to investigate whether slab-derived contributions to a MORB-source mantle are required to balance the budgets of sulfur and associated chalcophile elements, assuming that all Cu and S originally resided in sulfides and adopting a Cu concentration of 28 ppm in the presubduction mantle, similar to that in MORB-type mantle. Modeling results predict at least 256 to 465 ppm S in the magma source of Galunggung, which is up to twice the amount commonly assumed for MORB sources. A slab-derived origin of the excess sulfur is consistent with 34S enrichments that commonly characterize arc magmas and gases. Although modeling suggests that elevated copper concentrations relative to MORB can be the consequence of the higher solubility of sulfur in Galunggung melts, the results do not rule out that the subarc mantle was enriched by slab-derived Cu. Lead must have been

  5. Seismic evidence for silicate melt atop the 410-km mantle discontinuity

    USGS Publications Warehouse

    Revenaugh, Justin; Sipkin, S.A.

    1994-01-01

    LABORATORY results demonstrating that basic to ultrabasic melts become denser than olivine-rich mantle at pressures above 6 GPa (refs 1-3) have important implications for basalt petrogenesis, mantle differentiation and the storage of volatiles deep in the Earth. A density cross-over between melt and solid in the extensively molten Archaean mantle has been inferred from komatiitic volcanism and major-element mass balances, but present-day evidence of dense melt below the seismic low-velocity zone is lacking. Here we present mantle shear-wave impedance profiles obtained from multiple-ScS reverberation mapping for corridors connecting western Pacific subduction zone earthquakes with digital seismograph stations in eastern China, imaging a ~5.8% impedance decrease roughly 330 km beneath the Sea of Japan, Yellow Sea and easternmost Asia. We propose that this represents the upper surface of a layer of negatively buoyant melt lying on top of the olivine ??? ??- phase transition (the 410-km seismic discontinuity). Volatile-rich fluids expelled from the partial melt zone as it freezes may migrate upwards, acting as metasomatic agents and perhaps as the deep 'proto-source' of kimberlites. The remaining, dense, crystalline fraction would then concentrate above 410 km, producing a garnet-rich layer that may flush into the transition zone.

  6. Effect of Mantle Wedge Hybridization by Sediment Melt on Geochemistry of Arc Magma and Arc Mantle Source - Insights from Laboratory Experiments at High Pressures and Temperatures

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Generation of arc magmas involves metasomatism of the mantle wedge by slab-derived H2O-rich fluids and/or melts and subsequent melting of the modified source. The chemistry of arc magmas and the residual mantle wedge are not only regulated by the chemistry of the slab input, but also by the phase relations of metasomatism or hybridization process in the wedge. The sediment-derived silica-rich fluids and hydrous partial melts create orthopyroxene-rich zones in the mantle wedge, due to reaction of mantle olivine with silica in the fluid/melt [1,2]. Geochemical evidence for such a reaction comes from pyroxenitic lithologies coexisting with peridotite in supra-subduction zones. In this study, we have simulated the partial melting of a parcel of mantle wedge modified by bulk addition of sediment-derived melt with variable H2O contents to investigate the major and trace element chemistry of the magmas and the residues formed by this process. Experiments at 2-3 GPa and 1150-1300 °C were conducted on mixtures of 25% sediment-derived melt and 75% lherzolite, with bulk H2O contents varying from 2 to 6 wt.%. Partial reactive crystallization of the rhyolitic slab-derived melt and partial melting of the mixed source produced a range of melt compositions from ultra-K basanites to basaltic andesites, in equilibrium with an orthopyroxene ± phlogopite ± clinopyroxene ± garnet bearing residue, depending on P and bulk H2O content. Model calculations using partition coefficients (from literature) of trace elements between experimental minerals and silicate melt suggest that the geochemical signatures of the slab-derived melt, such as low Ce/Pb and depletion in Nb and Ta (characteristic slab signatures) are not erased from the resulting melt owing to reactive crystallization. The residual mineral assemblage is also found to be similar to the supra-subduction zone lithologies, such as those found in Dabie Shan (China) and Sanbagawa Belt (Japan). In this presentation, we will also

  7. Laboratory investigations of the effects of nitrification-induced acidification on Cr cycling in vadose zone material partially derived from ultramafic rocks.

    PubMed

    Mills, Christopher T; Goldhaber, Martin B

    2012-10-01

    Sacramento Valley (California, USA) soils and sediments have high concentrations of Cr(III) because they are partially derived from ultramafic material. Some Cr(III) is oxidized to more toxic and mobile Cr(VI) by soil Mn oxides. Valley soils typically have neutral to alkaline pH at which Cr(III) is highly immobile. Much of the valley is under cultivation and is both fertilized and irrigated. A series of laboratory incubation experiments were conducted to assess how cultivation might impact Cr cycling in shallow vadose zone material from the valley. The first experiments employed low (7.1 mmol N per kg soil) and high (35 mmol Nkg(-1)) concentrations of applied (NH(4))(2)SO(4). Initially, Cr(VI) concentrations were up to 45 and 60% greater than controls in low and high incubations, respectively. After microbially-mediated oxidation of all NH(4)(+), Cr(VI) concentrations dropped below control values. Increased nitrifying bacterial populations (estimated by measurement of phospholipid fatty acids) may have increased the Cr(VI) reduction capacity of the vadose zone material resulting in the observed decreases in Cr(VI). Another series of incubations employed vadose zone material from a different location to which low (45 meq kg(-1)) and high (128 meq kg(-1)) amounts of NH(4)Cl, KCl, and CaCl(2) were applied. All treatments, except high concentration KCl, resulted in mean soil Cr(VI) concentrations that were greater than the control. High concentrations of water-leachable Ba(2+) (mean 38 μmol kg(-1)) in this treatment may have limited Cr(VI) solubility. A final set of incubations were amended with low (7.1 mmol Nkg(-1)) and high (35 mmol Nkg(-1)) concentrations of commercial liquid ammonium polyphosphate (APP) fertilizer which contained high concentrations of Cr(III). Soil Cr(VI) in the low APP incubations increased to a concentration of 1.8 μmol kg(-1) (5× control) over 109 days suggesting that Cr(III) added with the APP fertilizer was more reactive than naturally

  8. Melt Migration in the Mantle Lithosphere: Evidence From Ophiolitic Peridotites

    NASA Astrophysics Data System (ADS)

    Spagnolo, G.; Piccardo, G. B.; Poggi, E.

    2006-12-01

    Records of diffuse porous flow migration of asthenospheric melts through the lithospheric mantle are evident in mantle peridotites deriving from the oceanic lithosphere of the Jurassic Ligurian Tethys, exposed in the Alpine- Apennine orogenic system of Northern Italy. The migrating melts caused structural and chemical modifications, as a consequence of melt/peridotite interaction. Microstructures indicating pyroxene(Px)-dissolving/olivine(Ol)-forming reactions suggest that early percolating melts were Px(-silica)-undersaturated and their intergranular flow through the peridotite enhanced melt/peridotite interaction. Px dissolution modified: 1) the peridotite composition: in fact, the reacted peridotites changed their bulk rock characteristics to significantly SiO2-depleted, MgO-enriched compositions, and their mineral modal contents to significantly Ol-enriched compositions, with respect to any refractory residua after any kink of mantle partial melting; 2) the melt composition: in fact, the melt composition progressively attained Px(-silica)-saturation at the end of the reactive percolation, as evidenced by late Px interstitial crystallization. Depending on the degree of Px dissolution, the reacted peridotites from the same peridotite body have highly variable Px contents but their clinopyroxenes(Cpx) have closely similar trace element contents. This decoupling between mineral modal content and geochemical composition strongly suggests that these peridotites cannot have been originated by partial melting but it supports the evidence of melt/peridotite interaction. Thus, Cpx trace element composition depends on the geochemical equilibration with the percolating melt; it indicates, moreover, the MORB affinity of the percolating melt. Significant evidences of melt migration through lithospheric peridotites are represented by the plagioclase(Plg)- enriched peridotites, which are frequently present within the ophiolitic peridotites and particularly abundant in those

  9. Comparative effect of partial root-zone drying and deficit irrigation on incidence of blossom-end rot in tomato under varied calcium rates

    PubMed Central

    Sun, Yanqi; Feng, Hao; Liu, Fulai

    2013-01-01

    This study investigated the comparative effects of reduced irrigation regimes—partial root-zone drying (PRD) and conventional deficit irrigation (DI)—on the incidence of blossom-end rot (BER) in tomato (Solanum lycopersicum L.) under three Ca-fertilization rates: 0, 100, and 200mg Ca kg–1 soil (denoted Ca0, Ca1, and Ca2, respectively). The plants were grown in split-root pots in a climate-controlled glasshouse and treated with PRD and DI during early flowering to the fruit maturity stage. The results showed that, in comparison with DI treatment, PRD significantly reduced BER incidence. A greater xylem sap abscisic acid concentration, lower stomatal conductance, and higher plant water status in the PRD in relation to the DI plants might have contributed to the increased fruit Ca uptake, and could have reduced BER development in tomato fruits. Therefore, under conditions with limited freshwater resources, application of PRD irrigation could be a promising approach for saving water and for preventing BER development in tomatoes. PMID:23530128

  10. Comparative effect of partial root-zone drying and deficit irrigation on incidence of blossom-end rot in tomato under varied calcium rates.

    PubMed

    Sun, Yanqi; Feng, Hao; Liu, Fulai

    2013-04-01

    This study investigated the comparative effects of reduced irrigation regimes--partial root-zone drying (PRD) and conventional deficit irrigation (DI)--on the incidence of blossom-end rot (BER) in tomato (Solanum lycopersicum L.) under three Ca-fertilization rates: 0, 100, and 200mg Ca kg(-1) soil (denoted Ca0, Ca1, and Ca2, respectively). The plants were grown in split-root pots in a climate-controlled glasshouse and treated with PRD and DI during early flowering to the fruit maturity stage. The results showed that, in comparison with DI treatment, PRD significantly reduced BER incidence. A greater xylem sap abscisic acid concentration, lower stomatal conductance, and higher plant water status in the PRD in relation to the DI plants might have contributed to the increased fruit Ca uptake, and could have reduced BER development in tomato fruits. Therefore, under conditions with limited freshwater resources, application of PRD irrigation could be a promising approach for saving water and for preventing BER development in tomatoes. PMID:23530128

  11. Effects of tilt angle of mirror-lamp system on shape of solid-liquid interface of silicon melt during floating zone growth using infrared convergent heating

    NASA Astrophysics Data System (ADS)

    Hossain, Md. Mukter; Watauchi, Satoshi; Nagao, Masanori; Tanaka, Isao

    2016-01-01

    The tilt effects of the mirror-lamp (M-L) system on the shape of the interface of the silicon molten zone formed during growth using the infrared convergent heating floating zone method were studied at various positions of the M-L system. The stability and the interfaces of the molten zone formed in the tilted condition were compared with those in the no tilt condition. The molten zone appeared to be more stabilized in the tilted condition than in the no tilt condition. However, the conventional parameters characterizing the interface shape such as convexities (h/r), gap and zone length (L) were almost independent of the tilt angle (θ) of the M-L system and insufficient to discuss the tilting effects on the molten zone shape. The curvature of the solid-liquid interface was affected by the θ. New characterizing parameters such as the growth interface and triple point angles (δ and TPA, respectively) were effective to quantitatively describe the tilting effects on the interface shape. With increase of the θ, the δ was decreased and the TPA was increased in both the feed and crystal sides. A silicon crystal of 45 mm in diameter was grown successfully in the tilted condition.

  12. Distribution of melt beneath Mount St Helens and Mount Adams inferred from magnetotelluric data

    USGS Publications Warehouse

    Hill, G.J.; Caldwell, T.G.; Heise, W.; Chertkoff, D.G.; Bibby, H.M.; Burgess, M.K.; Cull, J.P.; Cas, Ray A.F.

    2009-01-01

    Three prominent volcanoes that form part of the Cascade mountain range in Washington State (USA)Mounts StHelens, Adams and Rainierare located on the margins of a mid-crustal zone of high electrical conductivity1,5. Interconnected melt can increase the bulk conductivity of the region containing the melt6,7, which leads us to propose that the anomalous conductivity in this region is due to partial melt associated with the volcanism. Here we test this hypothesis by using magnetotelluric data recorded at a network of 85 locations in the area of the high-conductivity anomaly. Our data reveal that a localized zone of high conductivity beneath thisvolcano extends downwards to join the mid-crustal conductor. As our measurements were made during the recent period of lava extrusion at Mount St Helens, we infer that the conductivity anomaly associated with the localized zone, and by extension with the mid-crustal conductor, is caused by the presence of partial melt. Our interpretation is consistent with the crustal origin of silicic magmas erupting from Mount St Helens8, and explains the distribution of seismicity observed at the time of the catastrophic eruption in 1980 (refs9, 10). ?? 2009 Macmillan Publishers Limited. All rights reserved.

  13. Alternate partial root-zone irrigation reduces bundle-sheath cell leakage to CO2 and enhances photosynthetic capacity in maize leaves

    PubMed Central

    Wang, Zhenchang; Kang, Shaozhong; Jensen, Christian R.; Liu, Fulai

    2012-01-01

    The physiological basis for the advantage of alternate partial root-zone irrigation (PRI) over common deficit irrigation (DI) in improving crop water use efficiency (WUE) remains largely elusive. Here leaf gas exchange characteristics and photosynthetic CO2–response and light–response curves for maize (Zea mays L.) leaves exposed to PRI and DI were analysed under three N-fertilization rates, namely 75, 150, and 300 mg N kg−1 soil. Measurements of net photosynthetic rate (An) and stomatal conductance (gs) showed that, across the three N-fertilization rates, the intrinsic WUE was significantly higher in PRI than in DI leaves. Analysis of the CO2–response curve revealed that both carboxylation efficiency (CE) and the CO2-saturated photosynthetic rate (Asat) were significantly higher in PRI than in DI leaves across the three N-fertilization rates; whereas the N-fertilization rates did not influence the shape of the curves. The enhanced CE and Asat in the PRI leaves was accompanied by significant decreases in carbon isotope discrimination (Δ13C) and bundle-sheath cell leakiness to CO2 (Φ). Analysis of the light–response curve indicated that, across the three N-fertilization rates, the quantum yield (α) and light-saturated gross photosynthetic rate (Amax) were identical for the two irrigation treatments; whilst the convexity (κ) of the curve was significantly greater in PRI than in DI leaves, which coincided with the greater CE and Asat derived from the CO2–response curve at a photosynthetic photon flux density of 1500 μmol m−2 s−1. Collectively, the results suggest that, in comparison with the DI treatment, PRI improves photosynthetic capacity parameters CE, Asat, and κ of maize leaves and that contributes to the greater intrinsic WUE in those plants. PMID:22121199

  14. Constraints on the Nature of Terrestrial Core-Forming Melts: Ultra-High Pressure Transport Property Measurements and X-Ray Computed Tomography Final Report

    SciTech Connect

    Roberts, J J; Kinney, J H; Ryerson, F J

    2006-01-20

    A key issue in models of planetary core formation is the interconnectness and potential percolation of iron-sulfide melts in contact with silicates at high temperature and pressure. To address this issue an integrated study of the electrical conductivity-texture-permeability relationships of olivine-sulfide partial-melt samples was performed. This work has application to the interpretation of high conductivity zones in the Earth as revealed by electromagnetic studies and to the origin and development of the Earth's core. The project consisted of three main tasks. (1) Synthesis and characterization of olivine-sulfide partial-melts. (2) Electrical conductivity measurements of the partial-melt and the individual melt and crystalline phases. (3) X-ray microtomographic determination of the 3-D structure and interconnectedness of the melt phase. The results are used to determine a model of permeability of a partially molten solid that incorporates the melt distribution, a goal that has never before been achieved. Material synthesis was accomplished in the piston cylinder apparatus and electrical conductivity measurements were performed at one atmosphere. X-ray computed tomography was performed on recovered samples at the ALS. This work makes use of and further enhances LLNL's strengths in high-pressure material properties, x-ray micro- and nanoscale imaging and development of transport theory.

  15. On the occurrence and implications of Jurassic primary continental boninite-like melts in the Zagros orogen

    NASA Astrophysics Data System (ADS)

    Esna-Ashari, A.; Tiepolo, M.; Hassanzadeh, J.

    2016-08-01

    Ultramafic rocks, ranging from pyroxenites to hornblendites, are associated with granitoids of the Aligoodarz intrusive complex in the central Sanandaj-Sirjan Zone, representing the Mesozoic continental arc segment of the Zagros orogen. As inferred from the ultramafic whole rock composition and the most primitive clinopyroxene composition in pyroxenites, the geochemical signature of primary melt is significantly different from that of the continental arc basalts. In particular, primary melt is characterized by extremely low concentrations of incompatible elements and high concentrations of Mg and refractory elements typical of boninites. Amphibole is a late crystallizing mineral in these rocks and is in textural and chemical disequilibrium with olivine + orthopyroxene + clinopyroxene. Amphibole crystallized from a liquid underwent differentiation through a process of melt-rock reaction. In particular, early differentiated boninitic cumulates reacted with later melts with a strong crustal signature similar to Aligoodarz granodiorite. Usbnd Pb zircon geochronology from ultramafic rocks and surrounding quartz-diorite yield similar ages and indicate that they are coeval with Aligoodarz granitoids (ca. 165-170 Ma). However, the occurrence of a marked negative Eu anomaly in zircon from the ultramafic rocks, which is absent in the boninitic primary melt, indicates that zircons crystallized from the infiltrating melt and in turn date the timing of melt infiltration. The interaction between ultramafic cumulates and infiltrated melt has generated a new liquid compositionally similar to high-Mg andesites and to the quartz-diorites hosting the ultramafic cumulates. The scenario that better account for the genesis of boninitic melts in the Sanandaj-Sirjan Zone is partial melting of a depleted mantle wedge in response to the onset of NeoTethys subduction. According to this hypothesis, middle Jurassic calc-alkaline magmatism in the Sanandaj-Sirjan Zone represents the mature stage

  16. Melting processes under microgravity conditions

    NASA Astrophysics Data System (ADS)

    Glicksman, M.; Lupulescu, A.; Koss, M.

    The Rensselaer Isothermal Dendritic Growth Experiment (RIDGE) uses the large data archive amassed through a series of three NASA-supported microgravity experiments (IDGE/USMP-2, -3, and -4), all of which flew aboard the space shuttle Columbia. The IDGE instruments aboard USMP-2 and -3 provided in-flight CCD images, and 35-mm films (postflight). USMP-4 also allowed streaming of near-real-time video. Using 30 fps video data, it became possible for the first time to study both freezing and melting sequences for high-purity pivalic acid (PVA). We report on the melting process observed for PVA crystal fragments, observed under nearly ideal convection-free conditions. Conduction-limited melting processes are of importance in orbital melting of materials, meteoritic genesis, mushy-zone evolution, and in fusion weld pools where length scales for thermal buoyancy are restricted. Microgravity video show clearly that PVA dendrites melt into fragments that shrink at accelerating rates to extinction. The melting paths of individual fragments follow characteristic time dependences derived from theory. The theoretical melting kinetics against which the experimental observations are carefully compared is based on conduction-limited quasi-static melting under shape-preserving conditions. Good agreement between theory and experiment is found for the stable melting of needle-shaped prolate spheroidal PVA crystal fragments with aspect ratios near C /A = 12.

  17. Thermocapillary flow and natural convection in a melt column with an unknown melt/solid interface

    NASA Technical Reports Server (NTRS)

    Lan, C. W.; Kou, Sindo

    1991-01-01

    A vertical melt column set up between an upper heating rod and a lower sample rod, i.e., the so-called half-zone system, is a convenient experimental tool for studying convection in the melt in floating-zone crystal growth. In order to help understand the convection observed in the melt column, a computer model has been developed to describe steady state, axisymmetrical thermocapillary flow and natural convection in the melt. The governing equations and boundary conditions are expressed in general non-orthogonal curvilinear coordinates in order to accurately treat the unknown melt/solid interface as well as all other physical boundaries in the system. The effects of key dimensionless variables on the following items are discussed: (1) convection and temperature distribution in the melt; (2) the shape of the melt/solid interface; (3) the height of the melt column. These dimensionless variables are the Grashof, Marangoni and Prandtl numbers.

  18. Mineralogy, Petrology, Chemistry, and Ar-39 - Ar-40 and Ages of the Caddo County IAB Iron: Evidence for Early Partial Melt Segregation of a Gabbro Area Rich in Plagioclase-Diopside

    NASA Technical Reports Server (NTRS)

    Takeda, Hiroshi; Bogard, Donald D.; Mittlefehldt, David W.; Garrison, Daniel H.

    2000-01-01

    We found coarse-grained gabbroic material rich in plagioclase and diopside in the Caddo County IAB iron meteorite. The polished thin sections studied were made from areas rich in Al and Ca detected by a micro-focus X-ray fluorescence (XRF) mapping technique. The gabbro is not a clast within a breccia, but rather this area is located mainly at silicate-metal boundaries only a few cm away from an area with fine-grained, ultramafic silicate similar to winonaites. Medium-grained orthopyroxene and olivine are found in transitional areas showing no disturbance of their crystalline textures. A vein-like region, starting at the area rich in fine-grained mafic silicate, extends towards the gabbroic area with a gradual increase in abundance of plagioclase and diopside. This texture and our accumulated knowledge of the formation mechanism of IAB/winonaltes meteorites, suggest that the gabbroic materials were formed by inhomogeneous segregation of partial melts of chondritic source materials. Compositional data on two mineralogically distinct samples of the gabbro-rich portion of the inclusion were obtained by INAA. Compared to an average of LAB silicate inclusions or winonaites, the Caddo County gabbro is enriched in the incompatible lithophile elements Na, Ca, Sc, REE and Hf, which is consistent with a melt origin for the gabbro. The cosmogenic space exposure age of Caddo County (511 Ma) is significantly younger than exposure ages of some other IAB meteorites, An 39Ar-40Ar age determination of the gabbroic material indicates a series of upward steps in age from 4.516 Ga to 4.523 Ga, with a few high temperature ages up to 4.54 Ga. The older age could approximate the primary recrystallization age of silicates. The stepped Ar age spectrum may indicate differences in Ar closure temperatures during slow cooling of -2-20'C/Myr in the parent body. Alternatively, the younger Ar-Ar ages may date a shock event which occurred while Caddo County was hot and which also created textures

  19. Composition and origin of rhyolite melt intersected by drilling in the Krafla geothermal field, Iceland

    USGS Publications Warehouse

    Zierenberg, R.A.; Schiffman, P.; Barfod, G.H.; Lesher, C.E.; Marks, N.E.; Lowenstern, Jacob B.; Mortensen, A.K.; Pope, E.C.; Bird, D.K.; Reed, M.H.; Friðleifsson, G.O.; Elders, W.A.

    2013-01-01

    The Iceland Deep Drilling Project Well 1 was designed as a 4- to 5-km-deep exploration well with the goal of intercepting supercritical hydrothermal fluids in the Krafla geothermal field, Iceland. The well unexpectedly drilled into a high-silica (76.5 % SiO2) rhyolite melt at approximately 2.1 km. Some of the melt vesiculated while extruding into the drill hole, but most of the recovered cuttings are quenched sparsely phyric, vesicle-poor glass. The phenocryst assemblage is comprised of titanomagnetite, plagioclase, augite, and pigeonite. Compositional zoning in plagioclase and exsolution lamellae in augite and pigeonite record changing crystallization conditions as the melt migrated to its present depth of emplacement. The in situ temperature of the melt is estimated to be between 850 and 920 °C based on two-pyroxene geothermometry and modeling of the crystallization sequence. Volatile content of the glass indicated partial degassing at an in situ pressure that is above hydrostatic (~16 MPa) and below lithostatic (~55 MPa). The major element and minor element composition of the melt are consistent with an origin by partial melting of hydrothermally altered basaltic crust at depth, similar to rhyolite erupted within the Krafla Caldera. Chondrite-normalized REE concentrations show strong light REE enrichment and relative flat patterns with negative Eu anomaly. Strontium isotope values (0.70328) are consistent with mantle-derived melt, but oxygen and hydrogen isotope values are depleted (3.1 and −118 ‰, respectively) relative to mantle values. The hydrogen isotope values overlap those of hydrothermal epidote from rocks altered by the meteoric-water-recharged Krafla geothermal system. The rhyolite melt was emplaced into and has reacted with a felsic intrusive suite that has nearly identical composition. The felsite is composed of quartz, alkali feldspar, plagioclase, titanomagnetite, and augite. Emplacement of the rhyolite magma has resulted in partial melting of

  20. Growth of Si Bulk Crystals with Large Diameter Ratio Using Small Crucibles by Creating a Large Low-Temperature Region Inside a Si Melt Contained in an NOC Furnace Developed Using Two Zone Heaters

    NASA Astrophysics Data System (ADS)

    Nakajima, Kazuo; Ono, Satoshi; Murai, Ryota; Kaneko, Yuzuru

    2016-06-01

    Three zone heaters were generally used for a noncontact crucible (NOC) furnace. For practical reasons a simpler NOC furnace was developed with two zone heaters, which had a carbon heat holder to cover the three roles of each heater. Large low-temperature regions were obtained, and silicon ingots were grown in small crucibles with a large diameter and diameter ratio. Here, the diameter ratio is the ratio of the ingot diameter to the crucible diameter and can be as large as 0.90. The diameter ratio was controlled mainly by the temperature reduction of the first heater. Power changes of the second heater did not have a significant impact on the ingot diameter. Using this NOC furnace, maximum ingot diameters of 28.0, 33.5, and 45.0 cm were obtained using crucibles of 33, 40, and 50 cm in diameter, respectively. The oxygen concentration of the ingots did not strongly depend on the diameter ratio and were always low because convection in the Si melt was markedly suppressed by the carbon heat holder. Moreover, the oxygen concentration of the ingots has a tendency to become lower as the crucible diameter becomes larger.

  1. Viscoelasticity of partially molten rocks at mantle P-T

    NASA Astrophysics Data System (ADS)

    Weidner, D.; Li, L.; Wang, L.; Vaughan, M.

    2008-12-01

    The mechanical properties of a partially molten rock are crucial for interpreting the attenuation and velocities of seismic waves. While partial melting is often associated with low seismic shear wave velocity zone (LVZ) (Anderson and Sammis, 1970); studies have also suggested that partial melting may not be required to interpret the large velocity variation in the upper mantle (Faul and Jackson, 2005; Karato and Jung, 1998; Stixrude and Lithgow-Bertelloni, 2005). Extensive studies (Faul et al., 2004; Gribb and Cooper, 2000; Jackson et al., 2004) have been carried out on the attenuation behavior of partially-molten samples using melt-bearing olivine sample but at low-pressure (less than 300 MPa). Our recent developments (Li and Weidner, 2007) have allowed us to study energy dissipation in materials at high P-T (up to 15 GPa-2000K) and seismic frequencies. We have performed some experiments to characterize attenuation and dispersion in a model mantle composition (Kilborne Hole peridotite nodule, KLB- 1) at 1-10 GPa pressures. We use the multi-anvil high pressure device D-DIA (Durham et al., 2002; Wang et al., 2003) coupled with synchrotron X-ray radiation (Weidner et al., 2005). Mechanical testing is done by applying a uniaxial forced oscillation on a sample typically of 1 mm length and 1-1.5 mm diameter. The preliminary results raised many interesting issues. The detected Q and Young's modulus were found to be dependent on the pre-annealing conditions of the sample which may be a result of unrelaxed differential stresses. The geometry of the melted phases highly depends on the magnitude of the stress and melt- fractions. Microscopic analysis of the recovered sample will also be discussed.

  2. Formation of the giant Chalukou porphyry Mo deposit in northern Great Xing'an Range, NE China: Partial melting of the juvenile lower crust in intra-plate extensional environment

    NASA Astrophysics Data System (ADS)

    Li, Zhen-Zhen; Qin, Ke-Zhang; Li, Guang-Ming; Ishihara, Shunso; Jin, Lu-Ying; Song, Guo-Xue; Meng, Zhao-Jun

    2014-08-01

    The Chalukou porphyry Mo deposit (2.46 Mt @ 0.087% Mo), located in the northern Great Xing'an Range, NE China, is the largest Mo deposit discovered in China so far. The host rocks consist of aplite porphyry, granite porphyry and quartz porphyry, and are intruded into Lower Ordovician intermediate-felsic volcanic-sedimentary rocks and pre-ore monzogranite and are cut by post-ore feldspar porphyry, diorite porphyry and quartz monzonite porphyry. Here, we present the zircon U-Pb ages, whole-rock geochemistry, Sr-Nd isotopic and zircon Hf isotopic data for the pre-ore, syn-ore and post-ore intrusive rocks. The Chalukou ore-forming porphyries intruded during 147-148 Ma and have high-silica, alkali-rich, metaluminous to slightly peraluminous compositions and are oxidized. They are enriched in large ion lithophile elements (e.g. K, Rb, U and Th), light REE and depleted in high-field strength elements (e.g. Nb, P and Ti). Depletions in Eu, Ba, Sr, Nb, Ta, P and Ti suggest that they have experienced strong fractional crystallization of plagioclase, biotite, hornblende and accessory minerals. The pre-ore monzogranite (~ 172 Ma) also belongs to the high-K calc-alkaline series. Highly fractionated REE patterns ((La/Yb) N = 19.6-21.7), high values of Sr/Y (54-69) and La/Yb (29-32), are adakite-like geochemical features. The post-ore rocks (~ 141-128 Ma) have similar geochemical characteristics with ore-forming porphyries except that quartz monzonite porphyry shows no Ba-Sr negative anomaly. All intrusive rocks have relative low initial 87Sr/86Sr (0.705413-0.707889) and εNd (t) values (- 1.28 to + 0.92), positive εHf (t) values (+ 2.4 to + 10.1) and young two-stage Nd and Hf model ages (TDM2 (Nd) = 863-977 Ma, TDM2 (Hf) = 552-976 Ma). These geochemical and isotopic data are interpreted to demonstrate that the ore-forming porphyries formed by partial melting of the juvenile lower crust caused by underplating of mafic magmas in an intra-plate extensional setting. The pre

  3. Generation of Palaeoproterozoic tonalites and associated high-K granites in southwestern Tanzania by partial melting of underplated mafic crust in an intracontinental setting: Constraints from geochemical and isotopic data

    NASA Astrophysics Data System (ADS)

    Manya, Shukrani; Maboko, Makenya A. H.

    2016-09-01

    The southwestern part of the 2.0-1.8 Ga Palaeoproterozoic Usagaran Belt in the Njombe area of SW Tanzania is intruded by two types of synchronous granitic rocks with different chemical and petrological characteristics. The first type consists of hornblende-rich tonalites that have major element compositions similar to those of Archaean TTG but differ significantly in their trace element composition. The tonalites are spatially and closely associated with felsic, high-K, I-type granites, some of which are gneissic and/or aplitic. U-Pb zircon geochronology shows that the emplacement of tonalites at 1887 ± 11 Ma was largely contemporaneous with emplacement of high-K granitic gneisses at 1877 ± 15 Ma and aplitic granites at 1857 ± 19 Ma. The data also reveal the presence of Archaean crust of 2648 ± 25 Ma in the zircon cores of some samples in the otherwise Palaeoproterozoic terrane. The tonalites are characterized by MgO contents of 1.60-4.11 wt.% at a SiO2 range of 58.1-67.9 wt.%, the Mg# of 34-55, lower Sr contents (220-462 ppm) and less fractionated REE patterns (La/YbCN = 3.55-12.9) compared to Archaean TTG (Sr > 500 ppm, La/YbCN > 20). These features, coupled with the εNd (1887 Ma) values of + 0.37 to - 0.66 as well as the associated mafic enclaves are suggestive of derivation of the tonalites by low pressure (below the garnet stability) partial melting of a mantle-derived mafic underplate that was subsequently contaminated with small amounts of pre-existing igneous crustal rocks. The evolved nature of the high-K granites (MgO = 0.20-1.30 wt.%, SiO2 = 65.5-73.9 wt.%, Mg# = 25-42, εNd = - 3.20 to - 4.75) coupled with old TDM ages which are 200-1000 Ma older than their emplacement age requires a higher degree of assimilation of older crustal material by the magma derived from partial melting of the underplated mafic crust which was subsequently followed by crystal fractionation involving plagioclase, pyroxene and amphibole. The close spatial and temporal

  4. Rapid hydrothermal cooling above the axial melt lens at fast-spreading mid-ocean ridge.

    PubMed

    Zhang, Chao; Koepke, Juergen; Kirchner, Clemens; Götze, Niko; Behrens, Harald

    2014-01-01

    Axial melt lenses sandwiched between the lower oceanic crust and the sheeted dike sequences at fast-spreading mid-ocean ridges are assumed to be the major magma source of oceanic crust accretion. According to the widely discussed "gabbro glacier" model, the formation of the lower oceanic crust requires efficient cooling of the axial melt lens, leading to partial crystallization and crystal-melt mush subsiding down to lower crust. These processes are believed to be controlled by periodical magma replenishment and hydrothermal circulation above the melt lens. Here we quantify the cooling rate above melt lens using chemical zoning of plagioclase from hornfelsic recrystallized sheeted dikes drilled from the East Pacific at the Integrated Ocean Drilling Program Hole 1256D. We estimate the cooling rate using a forward modelling approach based on CaAl-NaSi interdiffusion in plagioclase. The results show that cooling from the peak thermal overprint at 1000-1050°C to 600°C are yielded within about 10-30 years as a result of hydrothermal circulation above melt lens during magma starvation. The estimated rapid hydrothermal cooling explains how the effective heat extraction from melt lens is achieved at fast-spreading mid-ocean ridges. PMID:25209311

  5. Rapid hydrothermal cooling above the axial melt lens at fast-spreading mid-ocean ridge

    PubMed Central

    Zhang, Chao; Koepke, Juergen; Kirchner, Clemens; Götze, Niko; Behrens, Harald

    2014-01-01

    Axial melt lenses sandwiched between the lower oceanic crust and the sheeted dike sequences at fast-spreading mid-ocean ridges are assumed to be the major magma source of oceanic crust accretion. According to the widely discussed “gabbro glacier” model, the formation of the lower oceanic crust requires efficient cooling of the axial melt lens, leading to partial crystallization and crystal-melt mush subsiding down to lower crust. These processes are believed to be controlled by periodical magma replenishment and hydrothermal circulation above the melt lens. Here we quantify the cooling rate above melt lens using chemical zoning of plagioclase from hornfelsic recrystallized sheeted dikes drilled from the East Pacific at the Integrated Ocean Drilling Program Hole 1256D. We estimate the cooling rate using a forward modelling approach based on CaAl-NaSi interdiffusion in plagioclase. The results show that cooling from the peak thermal overprint at 1000–1050°C to 600°C are yielded within about 10–30 years as a result of hydrothermal circulation above melt lens during magma starvation. The estimated rapid hydrothermal cooling explains how the effective heat extraction from melt lens is achieved at fast-spreading mid-ocean ridges. PMID:25209311

  6. Late Triassic Batang Group arc volcanic rocks in the northeastern margin of Qiangtang terrane, northern Tibet: partial melting of juvenile crust and implications for Paleo-Tethys ocean subduction

    NASA Astrophysics Data System (ADS)

    Zhao, Shao-Qing; Tan, Jun; Wei, Jun-Hao; Tian, Ning; Zhang, Dao-Han; Liang, Sheng-Nan; Chen, Jia-Jie

    2015-03-01

    The Batang Group (BTG) volcanic rocks in the Zhiduo area, with NW-trending outcrops along the northeastern margin of the Qiangtang terrane (northern Tibet), are mainly composed of volcaniclastic rocks, dacite and rhyolite. Major and trace element, Sr and Nd isotope, zircon U-Pb and Hf isotope data are presented for the BTG dacites. Laser ablation inductively coupled plasma mass spectrometry zircon U-Pb dating constrains the timing of volcanic eruption as Late Triassic (221 ± 1 Ma). Major and trace element geochemistry shows that the BTG volcanic rocks are classified as calc-alkaline series. All samples are enriched in large-ion lithophile elements and light rare earth elements with negative-slightly positive Eu anomalies (Eu/Eu* = 0.47-1.15), and depleted in high field strength elements and heavy rare earth elements. In addition, these rocks possess less radiogenic Sr [(87Sr/86Sr) i = 0.7047-0.7078], much radiogenic Nd (ɛNd( t) = -4.2 to -1.3) and Hf (ɛHf( t) = 4.0-6.6) isotopes, suggesting that they probably originated from partial melting of a crustal source containing a mantle-derived juvenile component. The inferred magma was assimilated by crustal materials during ascending and experienced significant fractional crystallization. By combining previously published and the new data, we propose that the BTG volcanic rocks were genetically related to southwestward subduction of the Ganzi-Litang ocean (a branch of Paleo-Tethys) in the northeastern margin of the Qiangtang terrane. Given the coeval arc-affinity magmatic rocks in the region, we envisage that the Ganzi-Litang ocean may extend from the Zhongdian arc through the Yidun terrane to the Zhiduo area, probably even further northwest to the Tuotuohe area.

  7. Reactive transport in a partially molten system with binary solid solution

    NASA Astrophysics Data System (ADS)

    Jordan, Jacob S.; Hesse, Marc A.

    2015-12-01

    Melt extraction from the Earth's mantle through high-porosity channels is required to explain the composition of the oceanic crust. Feedbacks from reactive melt transport are thought to localize melt into a network of high-porosity channels. Recent studies invoke lithological heterogeneities in the Earth's mantle to seed the localization of partial melts. Therefore, it is necessary to understand the reaction fronts that form as melt flows across the lithological interface between the heterogeneity and the ambient mantle. Here we present a chromatographic analysis of reactive melt transport across lithological boundaries, using the theory of hyperbolic conservation laws. This is an extension of linear trace element chromatography to the coupling of major elements and energy transport. Our analysis allows the prediction of the nonlinear feedbacks that arise in reactive melt transport due to changes in porosity. This study considers the special case of a partially molten porous medium with binary solid solution. As melt traverses a lithological contact, binary solid solution leads to the formation of a reacted zone between an advancing reaction front and the initial contact. The analysis also shows that the behavior of a fertile heterogeneity depends on its absolute concentration, in addition to compositional differences between itself and the refractory background. We present a regime diagram that predicts if melt emanating from a fertile heterogeneity localizes into high-porosity channels or develops a zero porosity shell. The theoretical framework presented here provides a useful tool for understanding nonlinear feedbacks in reactive melt transport, because it can be extended to more complex and realistic phase behaviors.

  8. Experimental deformation of partially molten granite and implications for strain localization

    NASA Astrophysics Data System (ADS)

    Goncalves, L.; Hirth, G.; Alkmim, F.; Pedrosa-Soares, A.; Goncalves, C.

    2011-12-01

    To improve our understanding of partially molten systems we conducted a set of hydrostatic, general shear and axial compression experiments on sintered aggregates composed of equal amounts by weight of quartz, albite and microcline (grain size of 37-53μm). All experiments were conducted using a Griggs solid medium apparatus at T=900°C, P=1.5GPa and strain rates from 10-4/s to 10-6/s. Previous hydrostatic and axial compression experiments conducted on partial molten granitic rocks have shown that the initial grain size, amount of melt and strain rate are important parameters for the development of distinct microstructures, LPO, and melt distribution. In addition, some of these studies demonstrated that the strength of granite and aplite decrease significantly for melt contents up to 15%, when compared to similar melt-free rocks. The rock's strength deep within the Earth decreases owing to partial melting which brings up some questions: would strain localization take place when partial melt affects rheology? Would brittle and/or ductile shear zones act as potential regions for concentration of partial melt? Is there a critical fraction of melt responsible for strain localization? How is melt distribution influenced by deformation? How does the kinematics of deformation (i.e., axial compression versus general shear) affect melt distribution? The purpose of our experiments is to investigate the role of melting on the rheological properties of crustal rocks. In addition, we seek to provide new constraints on the grain scale processes that control the properties of partially molten rocks and the importance of these processes in understanding shear localization in the lithosphere. Samples were made from crushed Amelia albite (Ab97Or2An1), Hugo Microcline (Or90) and Black Hills quartzite, which have all been used in previous experimental deformation studies. The albite is essentially pure; the microcline contains ~ 1% of muscovite. The Black Hills quartzite contains < 1

  9. The Velay dome (French Massif Central): melt generation and granite emplacement during orogenic evolution

    NASA Astrophysics Data System (ADS)

    Ledru, P.; Courrioux, G.; Dallain, C.; Lardeaux, J. M.; Montel, J. M.; Vanderhaeghe, O.; Vitel, G.

    2001-12-01

    This paper is a synthesis of available data on the Velay dome that include both small- and large-scale lithologic and structural mapping, strain analysis, isotope geochemistry, geochronology and pressure-temperature estimates. The Velay dome, one of the largest granite-migmatite domes of the Variscan Belt, formed during orogenic collapse at around 300 Ma. Its study allows an assessment of the thermal and geodynamic context leading to voluminous crustal anatexis of the Variscan orogenic crust. A first melting stage developed in connection with south-verging thrust zones during the Early Carboniferous, leading to a crustal thickening estimated at 20 km minimum. The involvement of fertile lithologies and the intrusion of plutons of deep origin contributed to the development of water-saturated melts. The volume of biotite granite extracted from melt during this period was limited. The second phase of melting, corresponded to generalized melting of gneiss achieved by biotite-dehydration melting reactions and accompanied by the generation of cordierite-bearing granites. At this stage, crustal-scale detachment faults were active and partially obliterated the earlier structures. The new structures were progressively tilted to the vertical at the margin of the Velay dome due to the southward and lateral ballooning of the granitic dome. The reconstructed P, T path indicate that the large volume of melt produced was a consequence of a significant increase in temperature at the onset of biotite dehydration melting. At the base of the crust, this melting event is coeval with granulite facies metamorphism associated to underplating of mantle-derived magmas as suggested by the geochemical signature of Late Paleozoic lower crustal xenoliths sampled by Cenozoic volcanoes and with the isotopic signature of the late granitic intrusions. Accordingly, it is proposed that asthenospheric upwelling was responsible for the temperature increase favoring melting of hydrous minerals.

  10. Electrical conductivity measurements on silicate melts using the loop technique

    NASA Technical Reports Server (NTRS)

    Waff, H. S.

    1976-01-01

    A new method is described for measurement of the electrical conductivity of silicate melts under controlled oxygen partial pressure at temperatures to 1550 C. The melt samples are suspended as droplets on platinum-rhodium loops, minimizing iron loss from the melt due to alloying with platinum, and providing maximum surface exposure of the melt to the oxygen-buffering gas atmosphere. The latter provides extremely rapid equilibration of the melt with the imposed oxygen partial pressure. The loop technique involves a minimum of setup time and cost, provides reproducible results to within + or - 5% and is well suited to electrical conductivity studies on silicate melts containing redox cations.

  11. Numerical models of mantle lithosphere weakening, erosion and delamination induced by melt extraction and emplacement

    NASA Astrophysics Data System (ADS)

    Wallner, Herbert; Schmeling, Harro

    2016-06-01

    Continental rifting caused by extension and heating from below affects the lithosphere or cratons in various ways. Volcanism and melt intrusions often occur along with thinning, weakening and even breaking lithosphere. Although mechanical necking models of the lithosphere are often applied, the aspects of melting and the implications due to melt transport and emplacement at shallower depths are not well understood. A two-phase flow approach employing melt extraction and shallow emplacement associated with thermal weakening is developed and compared with observations. The results of this comparison indicate the importance of partial melts and an asthenospheric magma source for increasing the rising rate of the lithosphere-asthenosphere boundary during extension. Thermo-mechanical physics of visco-plastic flow is approximated using the Finite Difference method with Eulerian formulation in 2D. The conservation of mass, momentum and energy equations are solved for a multi-component (crust-mantle) and two-phase (melt-matrix) system. Rheology is temperature- and stress-dependent. In consideration of depletion and enrichment melting and solidification are controlled by a simplified linear binary solid solution model. Melt is extracted and emplaced in predefined depth regions (emplacement zones) in the lithospheric mantle and crust. The Compaction Boussinesq Approximation was applied; its validity was tested against the Full Compaction formulation and found fully satisfactory for the case of sublithospheric melting models. A simple model guided by the geodynamic situation of the Rwenzori region typically results in updoming asthenosphere with melt-assisted erosion of the lithosphere's base. Even with a conservative approach for a temperature anomaly melting alone doubles the lithospheric erosion rate in comparison with a model without melting. With melt extraction and intrusion lithospheric erosion and upwelling of the lithosphere-asthenosphere boundary speeds up by a

  12. Orogenic plateau magmatism of the Arabia-Eurasia collision zone

    NASA Astrophysics Data System (ADS)

    Allen, M. B.; Neill, I.; Kheirkhah, M.; van Hunen, J.; Davidson, J. P.; Meliksetian, Kh.; Emami, M. H.

    2012-04-01

    Magmatism is a common feature of high plateaux created during continental collision, but the causes remain enigmatic. Here we study Pliocene-Quaternary volcanics from the active Arabia-Eurasia collision zone, to determine the chemistry of these rocks and their relations to faulting and deeper lithospheric structure. The great majority of the centres lie within the overriding Eurasian plate in Iran, eastern Turkey and Armenia , implying that mantle fertilised by pre-collision subduction processes plays a significant role in magma generation. The composition of the Pliocene-Quaternary centres is extremely variable, ranging from OIB-like alkali basalts, to intermediate types resembling mature continental arc lavas, to potassic and even ultrapotassic lavas. These centres are erupted across a mosaic of pre-Cenozoic suture zones and heterogeneous lithospheric blocks. The chemical diversity implies a range of partial melting conditions operating on lithospheric and perhaps sub-lithospheric sources. Published data show a thick (>200 km) lithospheric keel beneath the Arabia-Eurasia suture, thinning to near normal thicknesses (~120 km) across much of central and northern Iran. Thin mantle lithosphere under eastern Turkey (max. ~30 km) may relate to the region's juvenile, accretionary lithosphere. These variable thicknesses are constraints on the cause of the melting in each area, and the degree of variation suggests that no one mechanism applies across the plateau. Various melting models have been suggested. Break-off of the subducted Neo-Tethyan oceanic slab is supported by tomographic data, which may have permitted melting related to adiabatic ascent of hot asthenosphere under areas where the lithosphere is thin. This seems a less plausible mechanism where the lithosphere is at normal or greater than normal thickness. The same problem applies to postulated lower lithosphere delamination. Isolated pull-aparts may account for the location of some centres, but are not