Partial dehydration and cryopreservation of Citrus seeds.

PubMed

Graiver, Natalia; Califano, Alicia; Zaritzky, Noemí

2011-11-01

Three categories of seed storage behavior are generally recognized among plant species: orthodox, intermediate and recalcitrant. Intermediate seeds cannot be stored in liquid nitrogen (LN) without a previous partial dehydration process. The water content (WC) of the seeds at the moment of immersion in LN must be regarded as the most critical factor in cryopreservation. The purpose of this study was to investigate the basis of the optimal hydration status for cryopreservation of Citrus seeds: C. sinensis (sweet orange), C. paradisi (grapefruit), C. reticulata (mandarin) in LN. To study the tolerance to dehydration and LN exposure, seeds were desiccated by equilibration at relative humidities between 11 and 95%. Sorption isotherms were determined and modeled; lipid content of the seeds was measured. Seed desiccation sensitivity was quantified by the quantal response model. Differential scanning calorimetry (DSC) thermograms were determined on cotyledon tissue at different moisture contents to measure ice melting enthalpies and unfrozen WC. Samples of total seed lipid extract were also analyzed by DSC to identify lipid transitions in the thermograms. The limit of hydration for LN Citrus seeds treatment corresponded to the unfrozen WC in the tissue, confirming that seed survival strictly depended on avoidance of intracellular ice formation. Copyright © 2011 Society of Chemical Industry.

Experimental evidence supporting a global melt layer at the base of the Earth's upper mantle.

PubMed

Freitas, D; Manthilake, G; Schiavi, F; Chantel, J; Bolfan-Casanova, N; Bouhifd, M A; Andrault, D

2017-12-19

The low-velocity layer (LVL) atop the 410-km discontinuity has been widely attributed to dehydration melting. In this study, we experimentally reproduced the wadsleyite-to-olivine phase transformation in the upwelling mantle across the 410-km discontinuity and investigated in situ the sound wave velocity during partial melting of hydrous peridotite. Our seismic velocity model indicates that the globally observed negative Vs anomaly (-4%) can be explained by a 0.7% melt fraction in peridotite at the base of the upper mantle. The produced melt is richer in FeO (~33 wt.%) and H 2 O (~16.5 wt.%) and its density is determined to be 3.56-3.74 g cm -3 . The water content of this gravitationally stable melt in the LVL corresponds to a total water content in the mantle transition zone of 0.22 ± 0.02 wt.%. Such values agree with estimations based on magneto-telluric observations.

Continental basalts record the crust-mantle interaction in oceanic subduction channel: A geochemical case study from eastern China

NASA Astrophysics Data System (ADS)

Xu, Zheng; Zheng, Yong-Fei

2017-09-01

Continental basalts, erupted in either flood or rift mode, usually show oceanic island basalts (OIB)-like geochemical compositions. Although their depletion in Sr-Nd isotope compositions is normally ascribed to contributions from the asthenospheric mantle, their enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE) is generally associated with variable enrichments in the Sr-Nd isotope compositions. This indicates significant contributions from crustal components such as igneous oceanic crust, lower continental crust and seafloor sediment. Nevertheless, these crustal components were not incorporated into the mantle sources of continental basalts in the form of solidus rocks. Instead they were processed into metasomatic agents through low-degree partial melting in order to have the geochemical fractionation of the largest extent to achieve the enrichment of LILE and LREE in the metasomatic agents. Therefore, the mantle sources of continental basalts were generated by metasomatic reaction of the depleted mid-ocean ridge basalts (MORB) mantle with hydrous felsic melts. Nevertheless, mass balance considerations indicate differential contributions from the mantle and crustal components to the basalts. While the depleted MORB mantle predominates the budget of major elements, the crustal components predominate the budget of melt-mobile incompatible trace elements and their pertinent radiogenic isotopes. These considerations are verified by model calculations that are composed of four steps in an ancient oceanic subduction channel: (1) dehydration of the subducting crustal rocks at subarc depths, (2) anataxis of the dehydrated rocks at postarc depths, (3) metasomatic reaction of the depleted MORB mantle peridotite with the felsic melts to generate ultramafic metasomatites in the lower part of the mantle wedge, and (4) partial melting of the metasomatites for basaltic magmatism. The composition of metasomatites is quantitatively dictated by the crustal metasomatism through melt-peridotite reaction at the slab-mantle interface in oceanic subduction channels. Continental basalts of Mesozoic to Cenozoic ages from eastern China are used as a case example to illustrate the above petrogenetic mechanism. Subduction of the paleo-Pacific oceanic slab beneath the eastern edge of Eurasian continent in the Early Mesozoic would have transferred the crustal signatures into the mantle sources of these basalts. This process would be associated with rollback of the subducting slab at that time, whereas the partial melting of metasomatites takes place mainly in the Late Mesozoic to Cenozoic to produce the continental basalts. Therefore, OIB-like continental basalts are also the product of subduction-zone magmatism though they occur in intraplate settings.

Pathway from subducting slab to surface for melt and fluids beneath Mount Rainier.

PubMed

McGary, R Shane; Evans, Rob L; Wannamaker, Philip E; Elsenbeck, Jimmy; Rondenay, Stéphane

2014-07-17

Convergent margin volcanism originates with partial melting, primarily of the upper mantle, into which the subducting slab descends. Melting of this material can occur in one of two ways. The flow induced in the mantle by the slab can result in upwelling and melting through adiabatic decompression. Alternatively, fluids released from the descending slab through dehydration reactions can migrate into the hot mantle wedge, inducing melting by lowering the solidus temperature. The two mechanisms are not mutually exclusive. In either case, the buoyant melts make their way towards the surface to reside in the crust or to be extruded as lava. Here we use magnetotelluric data collected across the central state of Washington, USA, to image the complete pathway for the fluid-melt phase. By incorporating constraints from a collocated seismic study into the magnetotelluric inversion process, we obtain superior constraints on the fluids and melt in a subduction setting. Specifically, we are able to identify and connect fluid release at or near the top of the slab, migration of fluids into the overlying mantle wedge, melting in the wedge, and transport of the melt/fluid phase to a reservoir in the crust beneath Mt Rainier.

Pathway from subducting slab to surface for melt and fluids beneath Mount Rainier

NASA Astrophysics Data System (ADS)

McGary, R. Shane; Evans, Rob L.; Wannamaker, Philip E.; Elsenbeck, Jimmy; Rondenay, Stéphane

2014-07-01

Convergent margin volcanism originates with partial melting, primarily of the upper mantle, into which the subducting slab descends. Melting of this material can occur in one of two ways. The flow induced in the mantle by the slab can result in upwelling and melting through adiabatic decompression. Alternatively, fluids released from the descending slab through dehydration reactions can migrate into the hot mantle wedge, inducing melting by lowering the solidus temperature. The two mechanisms are not mutually exclusive. In either case, the buoyant melts make their way towards the surface to reside in the crust or to be extruded as lava. Here we use magnetotelluric data collected across the central state of Washington, USA, to image the complete pathway for the fluid-melt phase. By incorporating constraints from a collocated seismic study into the magnetotelluric inversion process, we obtain superior constraints on the fluids and melt in a subduction setting. Specifically, we are able to identify and connect fluid release at or near the top of the slab, migration of fluids into the overlying mantle wedge, melting in the wedge, and transport of the melt/fluid phase to a reservoir in the crust beneath Mt Rainier.

Impact Record of a Asteroid Regolith Recorded in a Carbonaceous Chrondrite

NASA Technical Reports Server (NTRS)

Zolensky, Michael; Mikouchi, Takashi; Hagiya, Kenji; Ohsumi, Kazumasa; Komatsu, Mutsumi; Chan, Queenie H. S.; Le, Loan; Kring, David; Cato, Michael; Fagan, Amy L.;

Structural Studies of NH4-exchanged Natrolites at Ambient Conditions and High Temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Y Lee; D Seoung; Y Jang

2011-12-31

We report here for the first time that fully and partially NH{sub 4}-exchanged natrolites can be prepared in hydrated states using the solution exchange method with potassium-natrolite. The structural models of the as-prepared hydrated phases and their dehydrated forms at elevated temperature were refined in space group Fdd2 using in situ synchrotron X-ray powder diffraction data and Rietveld methods. The unit-cell volumes of the hydrated NH{sub 4}-exchanged natrolites at ambient conditions, (NH{sub 4}){sub 16(2)}Al{sub 16}Si{sub 24}O{sub 80}{center_dot}14.1(9)H{sub 2}O and (NH{sub 4}){sub 5.1(1)}K{sub 10.9(1)}Al{sub 16}Si{sub 24}O{sub 80}{center_dot}15.7(3)H{sub 2}O, are found to be larger than that the original sodium-natrolite by ca. 15.6%more » and 12.8%, respectively. Upon temperature increase, the fully NH{sub 4}-exchanged natrolite undergoes dehydration at ca. 150 C with ca. 16.4% contraction in the unit-cell volume. The dehydrated phase of the fully NH{sub 4}-exchanged natrolite exhibits marginal volume expansion up to 425 C and then becomes amorphized during temperature decrease and exposure to atmospheric condition. In the case of the partially NH{sub 4}-exchanged natrolite, the dehydration starts from ca. 175 C with {approx}15.1% volume contraction and leads to a partial phase separation to show a phase related to the dehydrated K-natrolite. The degree of the phase separation decreases with temperature increase up to 475 C, concomitant to the gradual volume contraction occurring in the partially NH{sub 4}-exchanged natrolite in the dehydrared state. Upon temperature decrease and exposure to atmospheric condition, only the dehydrated K-natrolite is recovered as a crystalline phase from the partially NH{sub 4}-exchanged natrolite. In the hydrated model of the fully NH{sub 4}-exchanged natrolite, the ammonium cations and water molecules are statistically distributed along the elliptical channels, similar to the disordered pattern observed in natrolites exchanged with larger alkali metal cations such as the K-, Rb-, and Cs-forms. The dehydrated model of the fully NH{sub 4}-exchanged natrolite at 400 C is essentially same as the one reported previously from the sample prepared by direct melt exchange method using sodium-natrolite. Both the hydrated and dehydrated structures of the partially NH{sub 4}-exchanged natrolite at RT and at 400 C, respectively, are characterized by having two separate sites for the ammonium and potassium cations. Comparing the structural models of the monovalent cation forms studied so far, we find that the rotation angle of the natrolite chain is inversely proportional to the cation radius both in the hydrated and dehydrated phases. The distribution pattern of the non-framework species along the natrolite channel also seems to be related to the non-framework cation radius and hence to the chain rotation angle.« less

Diffusion-driven D/H fractionation in silicates during hydration, dehydration and degassing

NASA Astrophysics Data System (ADS)

Roskosz, Mathieu; Laporte, Didier; Deloule, Etienne; Ingrin, Jannick; Remusat, Laurent; Depecker, Christophe; Leroux, Hugues

2017-04-01

Understanding how degassing occurs during accretion and differentiation is crucial to explain the water budget of planetary bodies. In this context, the hydrogen isotopic signature of water in mantle minerals and melts is particularly useful to trace reservoirs and their interactions. Nonetheless, little is known on the influence of mantle processes on the D/H signatures of silicates. In this study, we performed controlled hydration/dehydration experiments. We explore the possibility that diffusion-driven fractionation could affect the D/H signature of partially hydrated amorphous or molten silicates and nominally anhydrous minerals (NAMs). High purity synthetic fused silica samples were annealed at between 200 and 1000°C at 20 mbar water partial pressure for 1 to 30 days. Dehydration of initially hydrated silica was also performed at 1000°C for a few hours. A set of rhyolitic samples previously synthesized in order to study bubble nucleation during magma decompression was also analyzed. Finally a natural grossular monocrystal (Zillertaler Alps, Austria), partially dehydrated in air at 800°C for 10 hours was studied. Water content and speciation were measured both by Fourier-Transform Infra-Red and Raman spectroscopies. Isotopic analyses were performed with the IMS 1270 and 1280 ion microprobes. The silica samples, the rhyolitic glasses and the grossular monocrystal exhibit typical water concentration profiles. In all cases, water speciation does not change significantly along concentration profiles. Concerning D/H signatures, no isotopic variation is detectable across amorphous silica and rhyolitic glasses. The situation is however very different in the grossular monocrystal. A strong isotopic gradient appears correlated to the water concentration profile. Our data are interpreted in terms of diffusion mechanisms in both amorphous (and molten) silicates and NAMs. Hydration, dehydration and magma degassing are probably not able to promote large diffusion-driven fractionation of hydrogen in amorphous silicates. Conversely, the diffusion of water through the structure of NAMs affects the overall isotopic composition of dissolved water.

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.

Leucogranites of the Teton Range, Wyoming: A record of Archean collisional orogeny

NASA Astrophysics Data System (ADS)

Frost, Carol D.; Swapp, Susan M.; Frost, B. Ronald; Finley-Blasi, Lee; Fitz-Gerald, D. Braden

2016-07-01

Leucogranitic rocks formed by crustal melting are a prominent feature of collisional orogens of all ages. This study describes leucogranitic gneisses associated with an Archean collisional orogeny preserved in the Teton Range of northwestern Wyoming, USA. These leucogneisses formed at 2.68 Ga, and initial Nd isotopic compositions suggest they are derived from relatively juvenile sources. Two distinct groups of leucogneisses, both trondhjemitic, are identified on the basis of field relations, petrology, and geochemistry. The Webb Canyon gneiss forms large, sheet-like bodies of hornblende biotite trondhjemite and granodiorite. This gneiss is silica-rich (SiO2 = 70-80%), strongly ferroan, comparatively low in alumina, and is characterized by high Zr and Y, low Sr, and high REE contents that define ;seagull;-shaped REE patterns. The Bitch Creek gneiss forms small sills, dikes, and plutons of biotite trondhjemite. Silica, Zr, Y, and REE are lower and alumina and Sr are higher than in the Webb Canyon gneiss. These differences reflect different melting conditions: the Webb Canyon gneiss formed by dehydration melting in which amphibole and quartz breaks down, accounting for the low alumina, high FeO, high silica content and observed trace element characteristics. The Bitch Creek gneiss formed by H2O-excess melting in which plagioclase breaks down leaving an amphibole-rich restite, producing magmas higher in alumina and Sr and lower in FeO and HREE. Both melt mechanisms are expected in collisional environments: dehydration melting accompanies gravitational collapse and tectonic extension of dramatically thickened crust, and water-excess melting may occur when collision places a relatively cool, hydrous lower plate beneath a hotter upper plate. The Archean leucogranitic gneisses of the Teton Range are calcic trondhjemites and granodiorites whereas younger collisional leucogranites typically are true granites. The difference in leucogranite composition reflects the geochemically immature Archean crust that partially melted in the Teton Range compared to the more geochemically evolved rocks typically involved in younger collisional orogens.

Mantle Wedge formation during Subduction Initiation: evidence from the refertilized base of the Oman ophiolitic mantle

NASA Astrophysics Data System (ADS)

Prigent, C.; Guillot, S.; Agard, P.; Godard, M.; Lemarchand, D.; Ulrich, M.

2015-12-01

Although the Oman ophiolite is classically regarded as being the direct analog of oceanic lithosphere created at fast spreading ridges, the geodynamic context of its formation is still highly debated. The other alternative end-member model suggests that this ophiolite entirely formed in a supra-subduction zone setting. The latter one is supported by studies on volcanic sequences whereas studies dealing on the mantle section do not involve a significant influence of subduction processes on its structure and composition. We herein focus on basal peridotites from all along the ophiolite strike in order to decipher and characterize potential fluid/melt transfers relate to subduction processes. Samples were taken across the basal banded unit directly overlying the amphibolitic/granulitic metamorphic sole which represents an accreted part of the lower plate. We carried out a petrological, structural and geochemical study on these rocks and their constitutive minerals. Our results show that basal peridotites range from lherzolites to highly depleted harzburgites in composition. Clinopyroxenes (cpx) display melt impregnation textures and co-crystallized with HT/HP amphiboles (amph), spinels and sulfurs. Major and trace elements of the constitutive minerals indicate that these minerals represent trapped incremental partial melt after hydrous melting. Different cpx-bearing lithologies then result from varying degrees of partial melting and melt extraction. Combined with Boron isotopic data, we demonstrate that fluids responsible for hydrous melting of these ophiolitic basal peridotites are subduction-related, most likely derived from dehydration of the metamorphic sole during its formation in subduction initiation. From these observations and thermal constraints, we interpret the occurrence of these basal lherzolites as representing a freezing front developed by thermal re-equilibration (cooling) during subduction processes: subduction-related hydrous partial melts were extracted at different degrees until getting ultimately trapped, and crystallized cpx, amph and other associated minerals. If our interpretation is correct, the base of the Oman ophiolite could provide the best proxy for the composition of a frozen-in, incipiently forming mantle wedge.

Deformation partitioning and fabric development during shearing of felsic migmatites (Valpelline Series, NW Alps)

NASA Astrophysics Data System (ADS)

Pariani, Federico; Menegon, Luca; Bistacchi, Andrea; Malaspina, Nadia

2014-05-01

The relationships between partial melting and deformation in the continental lower crust are critical for understanding lithosphere rheology and the processes leading to melt segregation. In metapelitic rocks in the lower portions of the crust partial melting typically occurs via dehydration of biotite and is generally characterized by a negative volume change when garnet is produced as a peritectic phase. As a result, segregation of biotite-derived melt by fracturing resulting from dilational strain is not common. Hence segregation of biotite-derived melts in the lower crust is likely to be controlled by active deformation via creation of structural anisotropies (fabric), which define migration pathways from the grain-size to the kilometre scale. This study investigates the relations between deformation mechanisms of minerals, fabric development and grain- and meso-scale deformation partitioning in felsic migmatites. The study area is located in the Valpelline Series of the Dent Blanche Nappe in the north-western Alps, which represents a slice of pre-Alpine lower crust dominated by metapelitic migmatites (i.e. 'kinzigites' in the Alpine literature). The migmatites are stromatic and show a leucosome-melanosome interlayering defining the dominant foliation (S2), which forms along a sinistral shear zone at least 1 km thick and laterally continuous for at least 8 km. Ti-in biotite geothermometry, mineral inclusions in garnet, and literature data indicate that S2 formed at P, T conditions of 800-820°C, 0.4-0.7 GPa, during dehydration melting of biotite. The melanosomes have about 80 vol% of garnet + biotite + sillimanite and are very poor in quartz and feldspars, indicating almost complete removal of melt. Garnet forms slightly elongated grains wrapped by biotite and sillimanite layers. Compositional maps of the elongated garnet do not show any zonation. EBSD analysis indicates that the elongated garnets are actually clusters of individual grains with no internal misorientation. We interpret these microstructures as deriving from amalgamation of individual garnets in elongated sites during shearing. Prismatic sillimanite has a strong crystallographic preferred orientation (CPO) with the c-axes parallel to the stretching lineation. However, evidence for internal misorientaton is scarce, indicating that the CPO was probably achieved by passive rotation during shearing. Elongated K-feldspar grains also do not show any internal misorientation and crystal plasticity features. They are rich of sillimanite and quartz inclusions, suggesting that they represent melt pockets crystallized near the site of production. K-feldspar has a weak CPO with the (010) planes parallel to the foliation and either <100> or <101> axis parallel to the lineation. The high aspect ratio was probably achieved by oriented growth during crystallization of melt. In summary, deformation mechanisms of minerals during melt removal from the melanosome seem to be dominated by passive rotation and oriented growth during magmatic flow, with negligible contribution of dislocation creep. A large (at least several hundred metres thick across foliation) low-strain domain of less pelitic, more quartzofeldspathic composition has escaped the pervasive development of S2. This domain preserves an S1 associated with older stages of partial melting. We speculate that the different bulk and mineralogical composition, reflecting the different nature of the protolith but also the effect of pre-existing melting episodes, determined a reduced melting during D2. This resulted in localization of deformation along melt-richer portions of this lower crustal section.

Adakitic-like volcanism in Southern Mexico and subduction of the Tehuantepec Ridge

NASA Astrophysics Data System (ADS)

Manea, M.; Manea, V. C.

2007-05-01

The origin of El Chichón volcano is poorly understood, and our attempt in this study is to demonstrate that Tehuantepec Ridge, a major tectonic discontinuity on the Cocos plate, plays a key role in the slab dehydration budget and therefore in partial melting of the mantle beneath El Chichón. Using marine magnetic anomalies we show that the upper mantle beneath TR undergo partial serpentinization, a 5-7 km thick serpentinized root extending along TR and below the oceanic crust. Another key aspect of the magnetic anomaly over southern México is a long-wavelength (~150 km) high amplitude (~500 nT) magnetic anomaly located between the trench and the coast. Using a 2D joint magnetic-gravity forward model, constrained by the subduction P-T structure, slab geometry and seismicity, we find a highly magnetic and low-density source located at 40-130 km depth. We interpret this result as a serpentinized mantle wedge by fluids expelled from the subducting Cocos plate beneath southern Mexico. Such a deep hydrated mantle requires a low temperature wedge (T<600° C) because serpentine is stable below this temperature and also the magnetic properties are preserved for temperature less than the Currie point for magnetite (~580° C). This result explains the lack of volcanism in southern México where the slab depth is ~ 100 km. Using phase diagrams for sediments, basalt and peridotite, and the subduction P-T structure beneath El Chichón we find that sediments and basalt dehydrate ~ 50% at depths corresponding with the location of serpentinized mantle wedge, whereas the serpentinized root beneath TR strongly dehydrates (60-80%) at higher depths (170-180 km) comparable with the slab depth beneath El Chichón. We conclude that this strong deserpentinization pulse of mantle lithosphere beneath TR at great depths triggers arc melting, explaining the unusual location and probably the adakitic signature of El Chichón.

Slab melting beneath the Cascade Arc driven by dehydration of altered oceanic peridotite

NASA Astrophysics Data System (ADS)

Walowski, K. J.; Wallace, P. J.; Hauri, E. H.; Wada, I.; Clynne, M. A.

2015-05-01

Water is returned to Earth’s interior at subduction zones. However, the processes and pathways by which water leaves the subducting plate and causes melting beneath volcanic arcs are complex; the source of the water--subducting sediment, altered oceanic crust, or hydrated mantle in the downgoing plate--is debated; and the role of slab temperature is unclear. Here we analyse the hydrogen-isotope and trace-element signature of melt inclusions in ash samples from the Cascade Arc, where young, hot lithosphere subducts. Comparing these data with published analyses, we find that fluids in the Cascade magmas are sourced from deeper parts of the subducting slab--hydrated mantle peridotite in the slab interior--compared with fluids in magmas from the Marianas Arc, where older, colder lithosphere subducts. We use geodynamic modelling to show that, in the hotter subduction zone, the upper crust of the subducting slab rapidly dehydrates at shallow depths. With continued subduction, fluids released from the deeper plate interior migrate into the dehydrated parts, causing those to melt. These melts in turn migrate into the overlying mantle wedge, where they trigger further melting. Our results provide a physical model to explain melting of the subducted plate and mass transfer from the slab to the mantle beneath arcs where relatively young oceanic lithosphere is subducted.

Slab melting beneath the Cascades Arc driven by dehydration of altered oceanic peridotite

USGS Publications Warehouse

Walowski, Kristina J; Wallace, Paul J.; Hauri, E.H.; Wada, I.; Clynne, Michael A.

2015-01-01

Water is returned to Earth’s interior at subduction zones. However, the processes and pathways by which water leaves the subducting plate and causes melting beneath volcanic arcs are complex; the source of the water—subducting sediment, altered oceanic crust, or hydrated mantle in the downgoing plate—is debated; and the role of slab temperature is unclear. Here we analyse the hydrogen-isotope and trace-element signature of melt inclusions in ash samples from the Cascade Arc, where young, hot lithosphere subducts. Comparing these data with published analyses, we find that fluids in the Cascade magmas are sourced from deeper parts of the subducting slab—hydrated mantle peridotite in the slab interior—compared with fluids in magmas from the Marianas Arc, where older, colder lithosphere subducts. We use geodynamic modelling to show that, in the hotter subduction zone, the upper crust of the subducting slab rapidly dehydrates at shallow depths. With continued subduction, fluids released from the deeper plate interior migrate into the dehydrated parts, causing those to melt. These melts in turn migrate into the overlying mantle wedge, where they trigger further melting. Our results provide a physical model to explain melting of the subducted plate and mass transfer from the slab to the mantle beneath arcs where relatively young oceanic lithosphere is subducted.

High Pressure Dehydration of Antigorite in Nature: Embrittlement and melt formation?

NASA Astrophysics Data System (ADS)

Evans, B. W.; Cowan, D. S.

2011-12-01

Trommsdorff and others in 1998 provided field evidence from the Cerro del Almirez ultramafic complex, S. Spain, for the only known example of the high-pressure terminal breakdown reaction of antigorite: Atg = Ol + Opx + Chl + H2O. Pressure-temperature conditions for this reaction have since been refined to around 1.8 GPa and 650-700C. Associated mafic rocks are eclogites. Reaction products were a mixture of more-or-less granoblastic chlorite meta-harzburgite and rock of the same composition with a spinifex-like texture comprising up to 10 cm long needles of olivine and interstitial bundles of enstatite prisms. This texture was interpreted as metamorphic in origin (jackstraw olivine), and this view has apparently generally been accepted. Two earlier studies interpreted the spinifex-like rocks as quenched ultramafic liquid, analogous to komatiites. Given the release of ca. 6-7 wt.% H2O by this reaction, one must surely contemplate the possibility of dehydration embrittlement and frictional slip in shear zones, as many have suggested for antigorite breakdown in subduction zones. The depth and location of earthquake hypocenters have been shown to correlate well with the P-T trace of the experimentally determined antigorite breakdown reaction. A temperature rise of only 300C is needed at 1.8 GPa to initiate partial melting of hydrous peridotite, and another 350C to render it fully molten. These kinds of increase in temperature have been described from pseudotachylytes. We are therefore inclined to interpret the spinifex rocks at Cerro del Almirez as products of quench crystallization of ultramafic pseudotachylyte melt. This view is supported by the curved, branching, and sub-parallel nature of some of the olivine needles. Curved needles (up to 30 degrees) are not a feature of metamorphic jackstraw olivine, although otherwise the textures are very similar. Our view is also supported by the high contents of Cr and Ti (now exsolved into chromite and ilmenite) in the Almirez spinifex olivines, and the presence in them of crystal-rich "fluid" inclusions. Thus, this complex provides not only a unique field example of the high-pressure breakdown reaction of antigorite, but possibly also of dehydration embrittlement and local melt formation.

Tectono-metamorphic evolution of the Jomolhari massif: Variations in timing of syn-collisional metamorphism across western Bhutan

NASA Astrophysics Data System (ADS)

Regis, Daniele; Warren, Clare J.; Young, David; Roberts, Nick M. W.

2014-03-01

Our current understanding of the rates and timescales of mountain-building processes is largely based on information recorded in U-bearing accessory minerals such as monazite, which is found in low abundance but which hosts the majority of the trace element budget. Monazite petrochronology was used to investigate the timing of crustal melting in migmatitic metasedimentary rocks from the Jomolhari massif (NW Bhutan). The samples were metamorphosed at upper amphibolite to granulite facies conditions (~ 0.85 GPa, ~ 800 °C), after an earlier High-Pressure stage (P > 1.4 GPa), and underwent partial melting through dehydration melting reactions involving muscovite and biotite. In order to link the timing of monazite growth/dissolution to the pressure-temperature (P-T) evolution of the samples, we identified 'chemical fingerprints' in major and accessory phases that were used to back-trace specific metamorphic reactions. Variations in Eu anomaly and Ti in garnet were linked to the growth and dissolution of major phases (e.g. growth of K-feldspar and dehydration melting of muscovite/biotite). Differences in M/HREE and Y from garnet core to rim were instead related to apatite breakdown and monazite-forming reactions. Chemically zoned monazite crystals reacted multiple times during the metamorphic evolution suggesting that the Jomolhari massif experienced a prolonged high-temperature metamorphic evolution from 36 Ma to 18 Ma, significantly different from the P-T-time path recorded in other portions of the Greater Himalayan Sequence (GHS) in Bhutan. Our data demonstrate unequivocally that the GHS in Bhutan consists of units that experienced independent high-grade histories and that were juxtaposed across different tectonic structures during exhumation. The GHS may have been exhumed in response to (pulsed) mid-crustal flow but cannot be considered a coherent block.

Estimating the Aqueous Solubility of Pharmaceutical Hydrates

PubMed Central

Franklin, Stephen J.; Younis, Usir S.; Myrdal, Paul B.

2016-01-01

Estimation of crystalline solute solubility is well documented throughout the literature. However, the anhydrous crystal form is typically considered with these models, which is not always the most stable crystal form in water. In this study an equation which predicts the aqueous solubility of a hydrate is presented. This research attempts to extend the utility of the ideal solubility equation by incorporating desolvation energetics of the hydrated crystal. Similar to the ideal solubility equation, which accounts for the energetics of melting, this model approximates the energy of dehydration to the entropy of vaporization for water. Aqueous solubilities, dehydration and melting temperatures, and log P values were collected experimentally and from the literature. The data set includes different hydrate types and a range of log P values. Three models are evaluated, the most accurate model approximates the entropy of dehydration (ΔSd) by the entropy of vaporization (ΔSvap) for water, and utilizes onset dehydration and melting temperatures in combination with log P. With this model, the average absolute error for the prediction of solubility of 14 compounds was 0.32 log units. PMID:27238488

Mantle Flow and Melting Processes Beneath Back-Arc Basins

NASA Astrophysics Data System (ADS)

Hall, P. S.

2007-12-01

The chemical systematics of back-arc basin basalts suggest that multiple mechanisms of melt generation and transport operate simultaneously beneath the back-arc, resulting in a continuum of melts ranging from a relatively dry, MORB-like end-member to a wet, slab-influenced end-member [e.g., Kelley et al., 2006; Langmuir et al., 2006]. Potential melting processes at work include adiabatic decompression melting akin to that at mid-ocean ridges, diapiric upwelling of hydrous and/or partially molten mantle from above the subducting lithospheric slab [e.g., Marsh, 1979; Hall and Kincaid, 2001; Gerya and Yuen, 2003], and melting of back-arc mantle due to a continuous flux of slab-derived hydrous fluid [Kelley et al., 2006]. In this study, we examine the potential for each of these melting mechanisms to contribute to the observed distribution of melts in back-arc basins within the context of upper mantle flow (driven by plate motions) beneath back-arcs, which ultimately controls temperatures within the melting region. Mantle velocities and temperatures are derived from numerical geodynamic models of subduction with back-arc spreading that explicitly include adiabatic decompression melting through a Lagrangian particle scheme and a parameterization of hydrous melting. Dynamical feedback from the melting process occurs through latent heating and viscosity increases related to dehydration. A range of parameters, including subduction rate and trench-back-arc separation distances, is explored. The thermal evolution of individual diapirs is modeled numerically as they traverse the mantle, from nucleation above the subducting slab to melting beneath the back-arc spreading center, and a range of diapir sizes and densities and considered.

Formation of cordierite-bearing lavas during anatexis in the lower crust beneath Lipari Island (Aeolian arc, Italy)

USGS Publications Warehouse

Di, Martino C.; Forni, F.; Frezzotti, M.L.; Palmeri, R.; Webster, J.D.; Ayuso, R.A.; Lucchi, F.; Tranne, C.A.

2011-01-01

Cordierite-bearing lavas (CBL;~105 ka) erupted from the Mt. S. Angelo volcano at Lipari (Aeolian arc, Italy) are high-K andesites, displaying a range in the geochemical and isotopic compositions that reflect heterogeneity in the source and/or processes. CBL consist of megacrysts of Ca-plagioclase and clinopyroxene, euhedral crystals of cordierite and garnet, microphenocrysts of orthopyroxene and plagioclase, set in a heterogeneous rhyodacitic-rhyolitic groundmass containing abundant metamorphic and gabbroic xenoliths. New petrographic, chemical and isotopic data indicate formation of CBL by mixing of basaltic-andesitic magmas and high-K peraluminous rhyolitic magmas of anatectic origin and characterize partial melting processes in the lower continental crust of Lipari. Crustal anatectic melts generated through two main dehydration-melting peritectic reactions of metasedimentary rocks: (1) Biotite + Aluminosilicate + Quartz + Albite = Garnet + Cordierite + K-feldspar + Melt; (2) Biotite + Garnet + Quartz = Orthopyroxene + Cordierite + K-feldspar + Melt. Their position into the petrogenetic grid suggests that heating and consequent melting of metasedimentary rocks occurred at temperatures of 725 < T < 900??C and pressures of 0.4-0.45 GPa. Anatexis in the lower crust of Lipari was induced by protracted emplacement of basic magmas in the lower crust (~130 Ky). Crustal melting of the lower crust at 105 ka affected the volcano evolution, impeding frequent maficmagma eruptions, and promoting magma stagnation and fractional crystallization processes. ?? 2011 Springer-Verlag.

Timing of anatexis and melt crystallization in the Socorro-Guaxupé Nappe, SE Brazil: Insights from trace element composition of zircon, monazite and garnet coupled to Usbnd Pb geochronology

NASA Astrophysics Data System (ADS)

Rocha, B. C.; Moraes, R.; Möller, A.; Cioffi, C. R.; Jercinovic, M. J.

2017-04-01

The timing of partial melting and melt crystallization in granulite facies rocks of the Socorro-Guaxupé Nappe (SGN), Brazil is constrained using a combination of imaging techniques, LA-ICP-MS and EPMA dating, trace element geochemistry and thermobarometry. (Orthopyroxene)-garnet-bearing migmatite that records extensive biotite dehydration melting shows evidence for a clockwise P-T-t path. UHT peak conditions were attained at 1030 ± 110 °C, 11.7 ± 1.4 kbar, with post-peak cooling to 865 ± 38 °C, 8.9 ± 0.8 kbar. Cryogenian igneous inheritance of ca. 720-640 Ma is identified in oscillatory zoned zircon cores (n = 167) with steep HREE patterns. Resorbed, Y-rich monazite cores preserve a prograde growth stage at 631 ± 4 Ma prior to the partial melting event, providing an upper age limit for the granulite facies metamorphism in the SGN. REE-rich, Th-depleted monazite related to apatite records the initial stages of decompression at 628 ± 4 Ma. Multiple monazite growth episodes record melt crystallization events at 624 ± 3 Ma, 612 ± 5 Ma and 608 ± 6 Ma. Stubby, equant "soccer ball" zircon provide evidence for melt crystallization at 613 ± 2 Ma and 607 ± 4 Ma. The excess scatter in zircon and monazite age populations between 629 ± 4 and 601 ± 3 Ma is interpreted as discontinuous and episodic growth within this age range, characterizing a prolonged metamorphic event in the SGN lasting ca. 30 m.y. The development of Y + HREE-rich monazite rims at ca. 600 Ma documents retrograde garnet breakdown, extensive biotite growth and the final stages of melt crystallization. Th-rich, Y + HREE-poor monazite rims at ca. 590 Ma record monazite recrystallization.

Quality of frozen fruit bars manufactured through infrared pre-dehydration

USDA-ARS?s Scientific Manuscript database

In this study, frozen restructured whole apple and strawberry bars were manufactured by partial dehydration, using infrared (IR) heating, followed by restructuring and freezing. The objective of this investigation was to determine the effect of IR partial dehydration on the quality of restructured f...

Tin in granitic melts: The role of melting temperature and protolith composition

NASA Astrophysics Data System (ADS)

Wolf, Mathias; Romer, Rolf L.; Franz, Leander; López-Moro, Francisco Javier

2018-06-01

Granite bound tin mineralization typically is seen as the result of extreme magmatic fractionation and late exsolution of magmatic fluids. Mineralization, however, also could be obtained at considerably less fractionation if initial melts already had enhanced Sn contents. We present chemical data and results from phase diagram modeling that illustrate the dominant roles of protolith composition, melting conditions, and melt extraction/evolution for the distribution of Sn between melt and restite and, thus, the Sn content of melts. We compare the element partitioning between leucosome and restite of low-temperature and high-temperature migmatites. During low-temperature melting, trace elements partition preferentially into the restite with the possible exception of Sr, Cd, Bi, and Pb, that may be enriched in the melt. In high-temperature melts, Ga, Y, Cd, Sn, REE, Pb, Bi, and U partition preferentially into the melt whereas Sc, V, Cr, Co, Ni, Mo, and Ba stay in the restite. This contrasting behavior is attributed to the stability of trace element sequestering minerals during melt generation. In particular muscovite, biotite, titanite, and rutile act as host phases for Sn and, therefore prevent Sn enrichment in the melt as long as they are stable phases in the restite. As protolith composition controls both the mineral assemblage and modal contents of the various minerals, protolith composition eventually also controls the fertility of a rock during anatexis, restite mineralogy, and partitioning behavior of trace metals. If a particular trace element is sequestered in a phase that is stable during partial melting, the resulting melt is depleted in this element whereas the restite becomes enriched. Melt generation at high temperature may release Sn when Sn-hosts become unstable. If melt has not been lost before the breakdown of Sn-hosts, Sn contents in the melt will increase but never will be high. In contrast, if melt has been lost before the decomposition of Sn-hosts, the small volume of the high-temperature melt will not be diluted by low-temperature, low-Sn melts and, therefore, could have high Sn-contents. The combination of multiple melt extractions and Sn-mobilization at high temperature results in strong Sn enrichment in late, high-temperature melts. Metal enrichment during partial melting becomes particularly efficient, if the sedimentary protolith had experienced intense chemical alteration as the loss of Na and Ca together with a relative enrichment of K favors muscovite-rich metamorphic mineral assemblages that produce large amounts of melt during muscovite dehydration melting.

Estimating the Aqueous Solubility of Pharmaceutical Hydrates.

PubMed

Franklin, Stephen J; Younis, Usir S; Myrdal, Paul B

2016-06-01

Estimation of crystalline solute solubility is well documented throughout the literature. However, the anhydrous crystal form is typically considered with these models, which is not always the most stable crystal form in water. In this study, an equation which predicts the aqueous solubility of a hydrate is presented. This research attempts to extend the utility of the ideal solubility equation by incorporating desolvation energetics of the hydrated crystal. Similar to the ideal solubility equation, which accounts for the energetics of melting, this model approximates the energy of dehydration to the entropy of vaporization for water. Aqueous solubilities, dehydration and melting temperatures, and log P values were collected experimentally and from the literature. The data set includes different hydrate types and a range of log P values. Three models are evaluated, the most accurate model approximates the entropy of dehydration (ΔSd) by the entropy of vaporization (ΔSvap) for water, and utilizes onset dehydration and melting temperatures in combination with log P. With this model, the average absolute error for the prediction of solubility of 14 compounds was 0.32 log units. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

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

Barite (BaSO4) is well-known from deep-sea sedimentary environments but has received less attention to its presence in high-grade metamorphic rocks. Recently, barite in ultrahigh pressure (UHP) eclogite has drawn increasing attention from geologists, especially in the Dabie-Sulu orogen, since it is an important indicator for high-salinity fluid events, thus aiding in further understanding HP-UHP fluid / melt evolution. However, its formation time and mechanism in UHP eclogite are still controversial, with three representative viewpoints: (1) Liu et al. (2000) found barite-anhydrite-coesite inclusions in zircon and interpreted them to have formed by UHP metamorphic fluids; (2) Zeng et al. (2007) recognized isolated barite within K-feldspar (Kfs) and Quartz (Qz) surrounded by radial cracks in omphacite, and interpreted Kfs+Qz to be reaction products of potassium-rich fluid/melt and coesite, with the barite formed by prograde metamorphic fluids; (3) Gao et al. (2012) and Chen et al. (2014) found barite-bearing Multiphase Solid (MS) inclusions within garnet and omphacite and assumed that the barite formed by phengite breakdown possibly caused by eclogite partial melting during exhumation, though no direct evidence were proposed. The controversy above is mainly due to the lack of direct formation evidence and absence of a clear link with the metamorphic evolution of UHP eclogite along the subduction-exhumation path. We report detailed petrological and micro-structural analyses revealing four types of barites clearly linked with (1) the prograde, (2) earlier stage of partial melting and (3) later stage of crystallization differentiation, as well as (4) high-grade amphibolite-facies retrogression of a deeply subducted and partially melted intergranular coesite-bearing eclogite from Yangkou Bay, Sulu Orogen. Round barite inclusions (type-I) within UHP-stage garnet and omphacite are formed by internally buffered fluids from mineral dehydration during prograde metamorphism. 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.

Partial melting of amphibolites in the Eastern Segment of the Sveconorwegian orogen, southern Sweden.

NASA Astrophysics Data System (ADS)

Brophy, E.; Hansen, E. C.; Möller, C.; Huffman, M.

2017-12-01

Mafic migmatites with amphibolitic melanosome and tonalitic leucosome are a common feature in continental collision orogenic zones. However, the anatexis of mafic rocks has received much less attention than anatexis in felsic, intermediate or pelitic compositions. We examined mafic migmatites along a traverse within the Eastern Segment of the 1.14-0.9 Ga Sveconorwegian orogen, between Forsheda and Fegen southern Sweden. This traverse occurs in the center of a >150 km metamorphic transition from sub-greenschist facies in the east to high-pressure granulite and eclogite facies in the west (Möller and Andersson, unpublished metamorphic map). The Eastern Segment is a parautochthonous belt made up of rocks of the Fennoscandian shield that were deformed and metamorphosed during the Sveconorwegian orogeny. Within the traverse amphibolite bodies occur within migmatitic felsic to intermediate orthogneisses. The first appearance of tonalitic leucosome in amphibolite was observed towards the eastern edge of the traverse and continued to occur sporadically westward ranging in abundance (by outcrop area) from 0 to 25 %. The mineral assemblage in amphibolite is hbl + plag ( An30) + qtz + bt ± grt ± ilm ± ttn ± py ± SO2-rich scp. No examples of peritectic pyroxene associated with leucosome were found. The lack of peritectic pyroxene suggests that a water-rich phase was present at the onset of anatexis. The highly variable amount of leucosome further suggests that the amount of melt generated was determined by the amount of water available. Together these suggest that partial was driven by the local influx of a water-rich fluid. In the higher grade portions further west migmatitic amphibolite with tonalitic leucosome occurs in two varieties: one with peritectic pyroxene and relatively small amounts of leucosome, interpreted as forming by water-undersaturated dehydration melting, and another without peritectic pyroxene and with larger amounts of leucosome which is interpreted as having formed from water-fluxed melting (Hansen et al., Lithos, 2015). Thus, water-undersaturated melting in mafic rocks appears to have been limited to the higher-grade portions of the orogen. The variable amounts of leucosome produced by partial melting indicate that the presence of water-rich fluids was localized rather than penetrative.

Monazite behaviours during high-temperature metamorphism: a case study from Dinggye region, Tibetan Himalaya

NASA Astrophysics Data System (ADS)

Wang, Jia-Min; Wu, Fu-Yuan; Rubatto, Daniela; Liu, Shi-Ran; Zhang, Jin-Jiang

2017-04-01

Monazite is a key accessory mineral for metamorphic geochronology, but its growth mechanisms during melt-bearing high-temperature metamorphism is not well understood. Therefore, the petrology, pressure-temperature and timing of metamorphism have been investigated in pelitic and psammitic granulites from the Greater Himalayan Crystalline Complex (GHC) in Dinggye, southern Tibet. These rocks underwent an isothermal decompression process from pressure conditions of >10 kbar to <5 kbar with constant temperatures of 750-830°C, and recorded three metamorphic stages of kyanite-grade (M1), sillimanite-grade (M2) and cordierite-spinel grade (M3). Monazite and zircon crystals were analyzed for ages by microbeam techniques either in mounts or thin sections. Ages were linked to specific conditions of mineral growth by comprehensive studies on zoning patterns, trace element signatures, index mineral inclusions (melt inclusions, sillimanite and K-feldspar) in dated domains and textural correlations with coexisting minerals. The results show that inherited domains (500-400 Ma) are common in monazite even at granulite-facies conditions. Few monazites formed at the M1-stage ( 30-29 Ma) and recorded heterogeneous Th, Y, and HREE compositions, which formed by recrystallization related to muscovite dehydration melting reaction. These monazite grains were protected from dissolution or lateral overprinting mainly by the armour effect of matrix crystals (biotite and quartz). Most monazite grains formed at the M3-stage (21-19 Ma) through either dissolution-reprecipitation or recrystallization that was related to biotite dehydration melting reaction. These monazite grains record HREE and Y signatures in local equilibrium with different reactions involving either garnet breakdown or peritectic garnet growth. Another peak of monazite growth occurs during melt crystallization ( 15 Ma), and these monazites are unzoned and have homogeneous compositions. Our results documented the widespread recrystallization to account for monazite growth during high-temperature metamorphism and related melting reactions that trigger monazite recrystallization. In a regional sense, our P-T-t data along with published data indicate that the pre-M1 eclogite-facies metamorphism occurred at 39-30 Ma in the Dinggye Himalaya. Our results are in favour of a steady exhumation of the GHC rocks since Oligocene that was contributed by partial melting. Key words: U-Th-Pb geochronology, Monazite, Recrystallization, Pelitic granulite, Himalaya

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.

Prograde infiltration of Cl-rich fluid into the granulitic continental crust from a collision zone in East Antarctica (Perlebandet, Sør Rondane Mountains)

NASA Astrophysics Data System (ADS)

Kawakami, Tetsuo; Higashino, Fumiko; Skrzypek, Etienne; Satish-Kumar, M.; Grantham, Geoffrey; Tsuchiya, Noriyoshi; Ishikawa, Masahiro; Sakata, Shuhei; Hirata, Takafumi

2017-03-01

Utilizing microstructures of Cl-bearing biotite in pelitic and felsic metamorphic rocks, the timing of Cl-rich fluid infiltration is correlated with the pressure-temperature-time (P-T-t) path of upper amphibolite- to granulite-facies metamorphic rocks from Perlebandet, Sør Rondane Mountains (SRM), East Antarctica. Microstructural observation indicates that the stable Al2SiO5 polymorph changed from sillimanite to kyanite + andalusite + sillimanite, and P-T estimates from geothermobarometry point to a counterclockwise P-T path characteristic of the SW terrane of the SRM. In situ laser ablation inductively coupled plasma mass spectrometry for U-Pb dating of zircon inclusions in garnet yielded ca. 580 Ma, likely representing the age of garnet-forming metamorphism at Perlebandet. Inclusion-host relationships among garnet, sillimanite, and Cl-rich biotite (Cl > 0.4 wt%) reveal that formation of Cl-rich biotite took place during prograde metamorphism in the sillimanite stability field. This process probably predated partial melting consuming biotite (Cl = 0.1-0.3 wt%). This was followed by retrograde, moderately Cl-bearing biotite (Cl = 0.1-0.3 wt%) replacing garnet. Similar timings of Cl-rich biotite formation in different samples, and similar f(H2O)/f(HCl) values of coexisting fluid estimated for each stage can be best explained by prograde Cl-rich fluid infiltration. Fluid-present partial melting at the onset of prograde metamorphism probably contributed to elevate the Cl concentration (and possibly salinity) of the fluid, and consumption of the fluid resulted in the progress of dehydration melting. The retrograde fluid was released from crystallizing Cl-bearing partial melts or derived externally. The prograde Cl-rich fluid infiltration in Perlebandet presumably took place at the uppermost part of the footwall of the collision boundary. Localized distribution of Cl-rich biotite and hornblende along large-scale shear zones and detachments in the SRM supports external input of Cl-rich fluids through tectonic boundaries during continental collision.

Improvement in melting and baking properties of low-fat Mozzarella cheese.

PubMed

Wadhwani, R; McManus, W R; McMahon, D J

2011-04-01

Low-fat cheeses dehydrate too quickly when baked in a forced air convection oven, preventing proper melting on a pizza. To overcome this problem, low-fat Mozzarella cheese was developed in which fat is released onto the cheese surface during baking to prevent excessive dehydration. Low-fat Mozzarella cheese curd was made with target fat contents of 15, 30, 45, and 60 g/kg using direct acidification of the milk to pH 5.9 before renneting. The 4 portions of cheese curd were comminuted and then mixed with sufficient glucono-δ-lactone and melted butter (45, 30, 15, or 0 g/kg, respectively), then pressed into blocks to produce low-fat Mozzarella cheese with about 6% fat and pH 5.2. The cheeses were analyzed after 15, 30, 60, and 120 d of storage at 5°C for melting characteristics, texture, free oil content, dehydration performance, and stretch when baked on a pizza at 250°C for 6 min in a convection oven. Cheeses made with added butter had higher stretchability compared with the control cheese. Melting characteristics also improved in contrast to the control cheese, which remained in the form of shreds during baking and lacked proper melting. The cheeses made with added butter had higher free oil content, which correlated (R2≥0.92) to the amount of butterfat added, and less hardness and gumminess compared with the control low fat cheese. Copyright © 2011 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Hydration, dehydration, and melting of metamorphosed granitic and dioritic rocks at high- and ultrahigh-pressure conditions

NASA Astrophysics Data System (ADS)

Massonne, Hans-Joachim

2009-10-01

Phase relations of three common upper crustal rocks, quartz diorite, granite and evolved granite, with different water contents were studied by calculating P- T pseudosections with the computer program PERPLE_X for the range 0.5 to 4.5 GPa and 500 to 1250 °C. Of particular interest were the generation of fluids and the consumption of H 2O along various P- T paths typical for high-pressure and ultrahigh-pressure (UHP) metamorphism to better understand crustal rocks involved in deep-seated continent-continent collisional environments. The phase relations in all studied rock compositions are similar. Typically, jadeite/omphacite + phengite (Si apfu between 3.3 and 3.5) + garnet + coesite ± kyanite occur at UHP. At T < 700 °C, K-feldspar and lawsonite can also be present at "dry" and "wet" conditions, respectively. The exhumation of a lawsonite-absent UHP assemblage leads either to phengite-dehydration melting accompanied by garnet growth or, at slight cooling, to no dehydration whereas dehydration is typical for exhumation from depths corresponding to 1.5 GPa. These findings are applied to the UHP Sulu terrane in eastern China. The majority of gneisses of this terrane typically do not show garnet. It is assumed that these rocks are of low-pressure nature and would, thus, probably belong to the upper plate during Triassic continent-continent collision. The reported UHP gneisses occur locally, are associated with eclogites, experienced fluid infiltration at UHP, and were exhumed accompanied by slight cooling as no phengite-dehydration melting took place. These characteristics could point to metamorphism in a subduction channel.

Timing and duration of garnet granulite metamorphism in magmatic arc crust, Fiordland, New Zealand

USGS Publications Warehouse

Stowell, H.; Tulloch, A.; Zuluaga, C.; Koenig, A.

2010-01-01

Pembroke Granulite from Fiordland, New Zealand provides a window into the mid- to lower crust of magmatic arcs. Garnet Sm-Nd and zircon U-Pb ages constrain the timing and duration of high-P partial melting that produced trondhjemitic high Sr/Y magma. Trace element zoning in large, euhedral garnet is compatible with little post growth modification and supports the interpretation that garnet Sm-Nd ages of 126.1??2.0 and 122.6??2.0. Ma date crystal growth. Integration of the garnet ages with U-Pb zircon ages elucidates a history of intrusion(?) and a protracted period of high-temperature metamorphism and partial melting. The oldest zircon ages of 163 to 150. Ma reflect inheritance or intrusion and a cluster of zircon ages ca. 134. Ma date orthopyroxene-bearing mineral assemblages that may be magmatic or metamorphic in origin. Zircon and garnet ages from unmelted gneiss and garnet reaction zones record garnet granulite facies metamorphism at 128 to 126. Ma. Peritectic garnet and additional zircon ages from trondhjemite veins and garnet reaction zones indicate that garnet growth and partial melting lasted until ca. 123. Ma. Two single fraction garnet ages and young zircon ages suggest continued high-temperature re-equilibration until ca. 95. Ma. Phase diagram sections constrain orthopyroxene assemblages to <0.6 GPa @ 650??C, peak garnet granulite facies metamorphic conditions to 680-815??C @ 1.1-1.4. GPa, and a P-T path with a P increase of???0.5. GPa. These sections are compatible with water contents???0.28wt.%, local dehydration during garnet granulite metamorphism, and <0.3. GPa P increases during garnet growth. Results demonstrate the utility of integrated U-Pb zircon and Sm-Nd garnet ages, and phase diagram sections for understanding the nature, duration, and conditions of deep crustal metamorphism and melting. Geochronologic and thermobarometric data for garnet granulite indicate that thickening of arc crust, which caused high-pressure metamorphism in northern Fiordland, must have occurred prior to 126. Ma, that loading occurred at a rate of ca. 0.06. GPa/m.y., and that garnet granulite metamorphism lasted 3-7m.y. Locally-derived partial melts formed and crystallized in considerably less than 10 and perhaps as little as 3m.y. ?? 2010 Elsevier B.V.

Dehydration and melting experiments constrain the fate of subducted sediments

NASA Astrophysics Data System (ADS)

Johnson, Marie C.; Plank, Terry

1999-12-01

Geochemical tracers demonstrate that elements are cycled from subducted sediments into the arc melting regime at subduction zones, although the transfer mechanism is poorly understood. Are key elements (Th, Be, Rb) lost during sediment dehydration or is sediment melting required? To investigate this question, we conducted phase equilibria and trace element partitioning experiments on a pelagic red clay for conditions appropriate to the slab beneath arc volcanoes (2-4 GPa, 600°-1000°C). Using both piston cylinders and multianvils, we determined the solidus, phase stabilities, and major element compositions of coexisting phases. The solidus (H2O + Cl fluid-saturated) was located at 775 +/- 25°C at 2 GPa, 810 +/- 15°C at 3 GPa, and 1025 +/- 25°C at 4 GPa with noevidence for complete miscibility between melt and fluid. This sediment composition produces a profusion of phases both above and below the solidus: garnet, jadeitic pyroxene, alkali-rich amphibole, phengite, biotite, magnetite, coesite, kyanite, apatite, zircon, Cl-rich fluids, and peraluminous to peralkaline granitic melts. At 2 GPa the phengite dehydration solidus is at 800°-825°C, while biotite breaks down between 850° and 900°C. To explore trace element partitioning across the solidus at 2 GPa, we used diamonds to trap fluids and melts. Both the bulk sediment residues and diamond traps were analyzed postexperiment by inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES) for 40 elements for which we calculated bulk partition coefficients (D = Csolid/Cfluid). Below the solidus, Rb, Sr, Ba, and Pb showed the greatest mobility (D ~ 0.5-1.0), while at the solidus, Th and Be became notably partitioned into the melt (D values changing from >2.0 to <1.0). K and Rb D values fall below 1.0 when the micas breakdown. Only at the solidus do Th and Rb attain similar partition coefficients, a condition required by arc data. Taken together, the experimental results indicate that critical elements (Th and Be) require sediment melting to be efficiently transferred to the arc. This conclusion is at odds with most thermal models for subduction zones, which predict slab temperatures more than 100°C lower than sediment solidi. Thus the condition of sediment melting (with oceanic crust dehydration) may provide new constraints on the next generation of thermal/geodynamical models of subduction zones.

Dehydration and melting experiments constrain the fate of subducted sediments

NASA Astrophysics Data System (ADS)

Johnson, Marie C.; Plank, Terry

2000-12-01

Geochemical tracers demonstrate that elements are cycled from subducted sediments into the arc melting regime at subduction zones, although the transfer mechanism is poorly understood. Are key elements (Th, Be, Rb) lost during sediment dehydration or is sediment melting required? To investigate this question, we conducted phase equilibria and trace element partitioning experiments on a pelagic red clay for conditions appropriate to the slab beneath arc volcanoes (2-4 GPa, 600°-1000°C). Using both piston cylinders and multianvils, we determined the solidus, phase stabilities, and major element compositions of coexisting phases. The solidus (H2O + Cl fluid-saturated) was located at 775 ± 25°C at 2 GPa, 810 ± 15°C at 3 GPa, and 1025 ± 25°C at 4 GPa with noevidence for complete miscibility between melt and fluid. This sediment composition produces a profusion of phases both above and below the solidus: garnet, jadeitic pyroxene, alkali-rich amphibole, phengite, biotite, magnetite, coesite, kyanite, apatite, zircon, Cl-rich fluids, and peraluminous to peralkaline granitic melts. At 2 GPa the phengite dehydration solidus is at 800°-825°C, while biotite breaks down between 850° and 900°C. To explore trace element partitioning across the solidus at 2 GPa, we used diamonds to trap fluids and melts. Both the bulk sediment residues and diamond traps were analyzed postexperiment by inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES) for 40 elements for which we calculated bulk partition coefficients (D = Csolid/Cfluid). Below the solidus, Rb, Sr, Ba, and Pb showed the greatest mobility (D ˜ 0.5-1.0), while at the solidus, Th and Be became notably partitioned into the melt (D values changing from >2.0 to <1.0). K and Rb D values fall below 1.0 when the micas breakdown. Only at the solidus do Th and Rb attain similar partition coefficients, a condition required by arc data. Taken together, the experimental results indicate that critical elements (Th and Be) require sediment melting to be efficiently transferred to the arc. This conclusion is at odds with most thermal models for subduction zones, which predict slab temperatures more than 100°C lower than sediment solidi. Thus the condition of sediment melting (with oceanic crust dehydration) may provide new constraints on the next generation of thermal/geodynamical models of subduction zones.

Barium isotope geochemistry of subduction-zone magmas

NASA Astrophysics Data System (ADS)

Yu, H.; Nan, X.; Huang, J.; Wörner, G.; Huang, F.

2017-12-01

Subduction zones are crucial tectonic setting to study material exchange between crust and mantle, mantle partial melting with fluid addition, and formation of ore-deposits1-3. The geochemical characteristics of arc lavas from subduction zones are different from magmas erupted at mid-ocean ridges4, because there are addition of fluids/melts from subducted AOC and its overlying sediments into their source regions in the sub-arc mantle4. Ba is highly incompatible during mantle melting5, and it is enriched in crust (456 ppm)6 relative to the mantle (7.0 ppm)7. The subducted sediments are also enriched in Ba (776 ppm of GLOSS)8. Moreover, because Ba is fluid soluble during subduction, it has been used to track contributions of subduction-related fluids to arc magmas9 or recycled sediments to the mantle10-11. To study the Ba isotope fractionation behavior during subduction process, we analyzed well-characterized, chemically-diverse arc lavas from Central American, Kamchatka, Central-Eastern Aleutian, and Southern Lesser Antilles. The δ137/134Ba of Central American arc lavas range from -0.13 to 0.24‰, and have larger variation than the arc samples from other locations. Except one sample from Central-Eastern Aleutian arc with obviously heavy δ137/134Ba values (0.27‰), all other samples from Kamchatka, Central-Eastern Aleutian, Southern Lesser Antilles arcs are within the range of OIB. The δ137/134Ba is not correlated with the distance to trench, partial melting degrees (Mg#), or subducting slab-derived components. The samples enriched with heavy Ba isotopes have low Ba contents, indicating that Ba isotopes can be fractionated at the beginning of dehydration process with small amount of Ba releasing to the mantle wedge. With the dehydration degree increasing, more Ba of the subducted slab can be added to the source of arc lavas, likely homogenizing the Ba isotope signatures. 1. Rudnick, R., 1995 Nature; 2. Tatsumi, Y. & Kogiso, T., 2003; 3. Sun, W., et al., 2015 Ore Geol. Rev.; 4. Pearce, J., & Peate, D., 1995 Annu. Rev. Earth Planet. Sci.; 5. Pilet, S., et al., 2011 J. Petrol.; 6. Sun S. & McDonough, W., 1989; 7. Rudnick, R. & Gao, S., 2003 Treatise on geochem.; 8. Plank, T. & Langmuir, C., 1998, CG; 9. Hawkesworth, C. & Norry, M., 1983 Shiva Pub.; 10. Murphy, D., et al., 2002 J. Petrol.; 11. Kuritani, T., et al., 2011 Nat. Geosci.

U-TH-PA-RA study of the Kamchatka arc: new constraints on the genesis of arc lavas

NASA Astrophysics Data System (ADS)

Dosseto, Anthony; Bourdon, Bernard; Joron, Jean-Louis; Dupré, Bernard

2003-08-01

The 238U- 230Th- 226Ra and 235U- 231Pa disequilibria have been measured by mass spectrometry in historic lavas from the Kamchatka arc. The samples come from three closely located volcanoes in the Central Kamchatka Depression (CKD), the most active region of subducted-related volcanism in the world. The large excesses of 226Ra over 230Th found in the CKD lavas are believed to be linked to slab dehydration. Moreover, the samples show the uncommon feature of ( 230Th/ 238U) activity ratios both lower and higher than 1. The U-series disequilibria are characterized by binary trends between activity ratios, with ( 231Pa/ 235U) ratios all >1. It is shown that these correlations cannot be explained by a simple process involving a combination of slab dehydration and melting. We suggest that they are more likely to reflect mixing between two end-members: a high-magnesia basalt (HMB) end-member with a clear slab fluid signature and a high-alumina andesite (HAA) end-member reflecting the contribution of a slab-derived melt. The U-Th-Ra characteristics of the HMB end-member can be explained either by a two-step fluid addition with a time lag of 150 ka between each event or by continuous dehydration. The inferred composition for the dehydrating slab is a phengite-bearing eclogite. Equilibrium transport or dynamic melting can both account for 231Pa excess over 235U in HMB end-member. Nevertheless, dynamic melting is preferred as equilibrium transport melting requires unrealistically high upwelling velocities to preserve fluid-derived 226Ra/ 230Th. A continuous flux melting model is also tested. In this model, 231Pa- 235U is quickly dominated by fluid addition and, for realistic extents of melting, this process cannot account for ( 231Pa/ 235U) ratios as high as 1.6, as observed in the HMB end-member. The involvement of a melt derived from the subducted oceanic crust is more likely for explaining the HAA end-member compositions than crustal assimilation. Melting of the oceanic crust is believed to occur in presence of residual phengite and rutile, resulting in no 226Ra- 230Th disequilibrium and low 231Pa excess over 235U in the high-alumina andesites. Consequently, it appears that high-alumina andesites and high-magnesia basalts have distinct origins: the former being derived from melting of the subducted oceanic crust and the latter from hydrated mantle. It seems that there is no genetic link between these two magma types, in contrast with what was previously believed.

Melt generation in the West Antarctic Rift System: the volatile legacy of Gondwana subduction?

NASA Astrophysics Data System (ADS)

Aviado, K.; Rilling-Hall, S.; Mukasa, S. B.; Bryce, J. G.; Cabato, J.

2013-12-01

The West Antarctic Rift System (WARS) represents one of the largest extensional alkali volcanic provinces on Earth, yet the mechanisms responsible for driving rift-related magmatism remain controversial. The failure of both passive and active models of decompression melting to explain adequately the observed volume of volcanism has prompted debate about the relative roles of thermal plume-related melting and ancient subduction-related flux melting. The latter is supported by roughly 500 Ma of subduction along the paleo-Pacific margin of Gondwana, although both processes are capable of producing the broad seismic anomaly imaged beneath most of the Southern Ocean. Olivine-hosted melt inclusions from basanitic lavas provide a means to evaluate the volatile budget of the mantle responsible for active rifting beneath the WARS. We present H2O, CO2, F, S and Cl concentrations determined by SIMS and major oxide compositions by EMPA for olivine-hosted melt inclusions from lavas erupted in Northern Victoria Land (NVL) and Marie Byrd Land (MBL). The melt inclusions are largely basanitic in composition (4.05 - 17.09 wt % MgO, 37.86 - 45.89 wt % SiO2, and 1.20 - 5.30 wt % Na2O), and exhibit water contents ranging from 0.5 up to 3 wt % that are positively correlated with Cl and F. Coupling between Cl and H2O indicates metasomatic enrichment by subduction-related fluids produced during dehydration reactions; coupling between H2O and F, which is more highly retained in subducting slabs, may be related to partial melting of slab remnants [1]. Application of source lithology filters [2] to whole rock major oxide data shows that primitive lavas (MgO wt % >7) from the Terror Rift, considered the locus of on-going tectonomagmatic activity, have transitioned from a pyroxenite source to a volatilized peridotite source over the past ~4 Ma. Integrating the volatile data with the modeled characteristics of source lithologies suggests that partial melting of lithosphere modified by subduction processes is the source of pyroxenite and volatiles in the mantle beneath the present-day rift. The earliest magmatic activity preferentially removed the most readily fusible components from the mantle, resulting in transition to a metasomatized peridotite source over time. [1] Straub & Layne, 2003, GCA; [2] Herzberg & Asimow, 2008, G3; [3] Rilling et al., 2009, JGR.

Preservation of Partial Melt Textures in Inclusions in Garnet Megacrysts of Pelitic Paragneiss, UHP Terrane, North-East Greenland Eclogite Province

NASA Astrophysics Data System (ADS)

Lang, H. M.; Gilotti, J. A.

2005-12-01

Although paragneiss is not common in the North-East Greenland Eclogite Province (NEGEP), of the few paragneiss samples collected in the UHP zone, some contain inclusion-rich garnet megacrysts (to 2 cm) in an anatectic matrix. In the matrix, quartz ribbons are segregated from anatectic melt layers and lenses that contain plagioclase, antiperthitic alkali-feldspar, white mica, biotite, small garnets, rutile and minor kyanite. In addition to one-phase and two-phase inclusions of quartz, polycrystalline quartz (no definitive coesite-replacement textures), and phengitic white mica, the garnet megacrysts contain some relatively large polyphase inclusions with all or most of the following phases: kyanite, rutile, phengitic white mica, biotite, quartz, Na-rich plagioclase, K-feldspar and zircon. Textures in these complex, polyphase inclusions suggest that their constituent minerals crystallized from a melt. Crystals are randomly oriented with early crystallizing minerals (kyanite, rutile, micas) forming euhedral grains and later crystallizing minerals (quartz and feldspars) filling the interstitial spaces. The textures and mineral assemblages are consistent with dehydration melting of phengitic white mica + quartz (enclosed in garnet) during decompression of the rocks from UHP metamorphic conditions. Although anatectic minerals in the matrix may have experienced extensive retrograde re-equilibration subsequent to crystallizing from a melt, the minerals trapped in the crystallized melt inclusions in garnet are likely to preserve their original textures and compositions. Microtextures in the melt inclusions and surrounding garnet suggest that partial melting was accompanied by volume expansion and that some melt penetrated garnets. Some radial fractures extend from inclusion margins into surrounding garnet. Individual fractures may have formed by volume expansion on melting or expansion accompanying the coesite-quartz transformation. Small and large polycrystalline quartz inclusions are commonly rimmed by a moat of plagioclase + K-feldspar, which extends into apophyses in garnet. These feldspar rims indicate that the most mobile and volatile-rich portion of the melt was able to penetrate garnets and travel along garnet-inclusion boundaries. Possible melt inclusions have been described in natural garnets from other UHP terranes (Stockert, et al., 2001, Geology; Hwang, et al., 2001, Earth and Planetary Science Letters) and have been produced experimentally (Perchuk, et al., 2005, Terra Nova). In the experiments and at least one of the natural occurrences, patchy microstructures (attributed to high Ca) were observed in BSE images of garnet surrounding the melt inclusions. Although we observe no garnet zoning in BSE images, patchy high-Ca zoning is apparent on X-ray maps of garnet surrounding the melt inclusions in our samples. Small, euhedral, high-Ca garnets are abundant in melt lenses in the matrix, so crystallization or recrystallization of high-Ca garnet surrounding the melt inclusions is not surprising.

Dehydration melting studies in a 'Kyanite terrain', Manali, NW Himalayas

NASA Astrophysics Data System (ADS)

Verma, Pramod; Sengupta, Susmita; Chaddha, D. K.; Pant, N. C.

2005-05-01

The Beas valley section in Himachal Pradesh is characterized by the presence of kyanite as the alumino-silicate phase and a small extent of Neogene quartzo-feldspathic intrusives. The present paper explores the reasons for the lack of extensive granite occurrences through a detailed petrologic study on samples of a drill core (200 m, inclined 60° due ESE) close to Manali, the expected highest point in P-T space in this section. The highest assemblage encountered is quartz+muscovite+biotite+garnet+plagioclase+kyanite±apatite±zircon±tourmaline±ilmenite±rutile. The chemical analyses of mineral grains were carried out on a CAMECA SX51 EPMA. The following two reactions that constrain the P-T regime of the area have been established. St+Qtz→Alm+Ky+HO Bio+Plg+Qtz+Ksp→Gar+Ky+Liq. Our result, P=8.25±1 kbar, T=638±4 °C, falls in a region between curves representing aO=1.0 and aO=0.7 of the fluid in Thompson [Trans. Royal Soc. Edinb. 87 (1996) 1] diagram. The P-T estimate falls in the kyanite field and is very close to the mica dehydration-melting curve. The studies indicate that the core samples are a part of progressive metamorphic sequence. It implies that the absence of sillimanite and large scale melting is perhaps chance brought about by thrusting and erosion. The present section experienced single stage dehydration melting.

Imaging the ascent path of fluids and partial melts at convergent plate boundaries by geophysical characteristics

NASA Astrophysics Data System (ADS)

Luehr, B. G.; Koulakov, I.; Kopp, H.; Rabbel, W.; Zschau, J.

2011-12-01

During the last decades many investigations were carried out at active continental margins to understand the link between the subduction of the fluid saturated oceanic plate and the process of ascent of fluids and partial melts forming a magmatic system that leads to volcanism at the earth surface. For this purpose structural information are needed about the slap itself, the part above it, the ascent paths as well as the storage of fluids and partial melts in the mantle and the crust above the down going slap up to the volcanoes on the surface. If we consider statistically the distance between the trench and the volcanic chain as well as the inclination angle of the down going plate, then the mean value of the depth distance down to the Wadati Benioff zone results of approximately 100 kilometers. Surprisingly, this depth range shows pronounced seismicity at most of all subduction zones. Additionally, mineralogical investigations in the lab have shown that the diving plate is maximal dehydrated around 100 km depth because of temperature and pressure conditions at this depth range. However, assuming a vertical fluid ascent there are exceptions. For instance at the Sunda Arc beneath Central Java the vertical distance results in approximately 150 km. But, in this case seismic investigations have shown that the fluids do not ascend vertically, but inclined even from a source area at around the 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 proved by seismic and seismological methods. With the seismic tomography these areas are imaged by lowered seismic velocities, high Vp/Vs ratios, as well as increased attenuation of seismic shear waves. But, to explore plate boundaries large and complex amphibious experiments are required, in which active and passive seismic investigations should be combined. They have to recover a range from before the trench to far behind the volcanic chain, to provide under favorable conditions information down to a depth of 150 km. In particular the record of the natural seismicity and its distribution allows the three-dimensional imaging of the entire crust and lithosphere structure above the Wadati Benioff zone with the help of tomographic procedures, and therewith the entire ascent path region of the fluids and melts, which are responsible for volcanism. The seismic velocity anomalies detected so far are within a range of a few per cent to more than 30% reduction. In the lecture findings of different subduction zones are compared and discussed.

Kinetic D/H fractionation during hydration and dehydration of silicate glasses, melts and nominally anhydrous minerals

NASA Astrophysics Data System (ADS)

Roskosz, M.; Deloule, E.; Ingrin, J.; Depecker, C.; Laporte, D.; Merkel, S.; Remusat, L.; Leroux, H.

2018-07-01

The distribution of hydrogen isotopes during diffusion-driven aqueous processes in silicate glasses, melts and crystals was investigated. Hydration/dehydration experiments were performed on silica glasses at 1000 °C and 1 bar total pressure. Dehydration triggered by decompression-driven bubble nucleation and growth was performed on rhyolitic melts at 800 °C and a few hundred MPa. Hydrogen extraction from a nominally anhydrous mineral (grossular) single crystal was carried out at 800 °C and ambient pressure. After these three series of experiments, pronounced water (sensu lato) concentration profiles were observed in all recovered samples. In the grossular single-crystal, a large spatial variation in H isotopes (δD variation > 550‰) was measured across the sample. This isotopic distribution correlates with the hydrogen extraction profile. The fit to the data suggests an extreme decoupling between hydrogen and deuterium diffusion coefficients (DH and DD respectively), akin to the decoupling expected in a dilute ideal gas (DH/DD ≈ 1.41). Conversely, no measurable spatially- and time-resolved isotopic variations were measured in silicate glasses and melts. This contrasted behavior of hydrogen isotopes likely stands in the different water speciation and solution mechanisms in the three different materials. Glasses and melts contain essentially hydroxyl and molecular water groups but the mobile species is molecular water in both cases. Protonated defects make up most of the water accommodated in grossular and other nominally anhydrous minerals (NAM). These defects are also the mobile species that diffuse against polarons. These results are crucial to accurately model the degassing behavior of terrestrial and lunar magmas and to derive the initial D/H of water trapped in fluid inclusions commonly analyzed in mantle NAMs, which suffered complex geological histories.

Melting-induced crustal production helps plate tectonics on Earth-like planets

NASA Astrophysics Data System (ADS)

Lourenço, Diogo L.; Rozel, Antoine; Tackley, Paul J.

2016-04-01

Within our Solar System, Earth is the only planet to be in a mobile-lid regime. It is generally accepted that the other terrestrial planets are currently in a stagnant-lid regime, with the possible exception of Venus that may be in an episodic-lid regime (Armann and Tackley, JGR 2012). Using plastic yielding to self-consistently generate plate tectonics on an Earth-like planet with strongly temperature-dependent viscosity is now well-established, but such models typically focus on purely thermal convection, whereas compositional variations in the lithosphere can alter the stress state and greatly influence the likelihood of plate tectonics. For example, Rolf and Tackley (GRL, 2011) showed that the addition of a continent can reduce the critical yield stress for mobile-lid behaviour by a factor of around two. Moreover, it has been shown that the final tectonic state of the system can depend on the initial condition (Tackley, G3 2000 - part 2). Weller and Lenardic (GRL, 2012) found that the parameter range in which two solutions are obtained increases with viscosity contrast. We can also say that partial melting has a major role in the long-term evolution of rocky planets: (1) partial melting causes differentiation in both major elements and trace elements, which are generally incompatible (Hofmann, Nature 1997). Trace elements may contain heat-producing isotopes, which contribute to the heat loss from the interior; (2) melting and volcanism are an important heat loss mechanism at early times that act as a strong thermostat, buffering mantle temperatures and preventing it from getting too hot (Xie and Tackley, JGR 2004b); (3) mantle melting dehydrates and hardens the shallow part of the mantle (Hirth and Kohlstedt, EPSL 1996) and introduces viscosity and compositional stratifications in the shallow mantle due to viscosity variations with the loss of hydrogen upon melting (Faul and Jackson, JGR 2007; Korenaga and Karato, JGR 2008). We present a set of 2D spherical annulus simulations (Hernlund and Tackley, PEPI 2008) using StagYY (Tackley, PEPI 2008), which uses a finite-volume scheme for advection of temperature, a multigrid solver to obtain a velocity-pressure solution at each timestep, tracers to track composition, and a treatment of partial melting and crustal formation. We address the question of whether melting-induced crustal production changes the critical yield stress needed to obtain mobile-lid behaviour (plate tectonics). Our results show that melting-induced crustal production strongly influences plate tectonics on Earth-like planets by strongly enhancing the mobility of the lid, replacing a stagnant lid with an episodic lid, or greatly extending the time in which a smoothly evolving mobile lid is present in a planet. Finally, we show that our results are consistent with analytically predicted critical yield stress obtained with boundary layer theory, whether melting-induced crustal production is considered or not.

Contemporaneous migmitization and granite emplacement during regional metamorphism: Evidence for mid-crustal contribution to the batholiths of the Arabian-Nubian Shield

NASA Astrophysics Data System (ADS)

Elisha, B.; Katzir, Y.; Kylander-Clark, A. R.

2017-12-01

Collision-related granitoid batholiths, like those of the Hercynian and Himalayan orogens, are mostly fed by magma derived from meta-sedimentary sources. However, in the late Neoproterozoic calc-alkaline batholiths of the Arabian Nubian Shield (ANS), which constitutes the northern half of the East African orogen, sedimentary contribution is obscured by the juvenile character of the crust and the scarcity of migmatites. Here we use paired in-situ measurements of U-Th-Pb isotope ratios and REE contents of monazite and xenotime by LASS to demonstrate direct linkage between granites and migmatites in the northernmost ANS. Our results indicate a single prolonged period of monazite growth, 640-600 Ma, in metapelites, migmatites and peraluminous granites of the Abu-Barqa (SW Jordan), Roded (S Israel) and Taba-Nuweiba (Sinai, Egypt) metamorphic suites. Distribution of monazite dates and age zoning in single monazite grains in migmatites suggest that peak thermal conditions and partial melting prevailed for 10 Myr, from 620 to 610 Ma. REE patterns of monazite are well correlated with age, recording garnet growth and garnet breakdown in association with the prograde and retrograde stages of the melting reactions, respectively. Xenotime dates (n=40) cluster at 600-580 Ma recording retrogression to greenschist-facies conditions as garnet continues to destabilize. Phase equilibrium modelling and mineral thermobarometry illustrate that melting occurred either by dehydration of muscovite or by water-fluxed melting at 650-680° and 5-7 kbar. The expected melt production is 8-14%, allowing melt connectivity network to form and eventually melt extraction and segregation. The crystallization time of peritectic melt retained in dia- and metataxites overlaps the emplacement time of a vast calc-alkaline granitic flux throughout the northern ANS, which was previously considered post-collisional. Similar monazite ages ( 620 Ma) of the amphilolite-facies non-anatectic Elat schist indicate that migmatites are the result of widespread regional, rather than local contact metamorphism, representing the climax of East African orogenesis.

Stability of hydrous phases in subducting oceanic crust

USGS Publications Warehouse

Liu, J.; Bohlen, S.R.; Ernst, W.G.

1996-01-01

Experiments in the basalt-H2O system at 600-950??C and 0.8-3.0 GPa, demonstrate that breakdown of amphibole represents the final dehydration of subducting oceanic tholeiite at T ??? 650??C; the dehydration H2O occurs as a free fluid or in silicate melt co-existing with an anhydrous eclogite assemblage. In contrast, about 0.5 wt% of H2O is stored in lawsonite at 600??C, 3.0 GPa. Our results suggest that slab melting occurs at depths shallower than 60 km for subducting young oceanic crust; along a subduction zone with an average thermal gradient higher than 7??C/km, H2O stored in hydrated low-potassium, metabasaltic layers cannot be subducted to depths greater than 100 km, then released to generate arc magma.

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-MORB source and the new D's, shows that a residue with Nb > 2 ppm, 19 < Nb/Ta < 37 (as proposed by Rudnick et al., 2000, Science 287, 278-281), can be produced by ˜30% partial melting. Slightly lower melt fractions (˜15%) reproduce their proposed Nb/La (>1.2).

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.

Adakitic magmas: modern analogues of Archaean granitoids

NASA Astrophysics Data System (ADS)

Martin, Hervé

1999-03-01

Both geochemical and experimental petrological research indicate that Archaean continental crust was generated by partial melting of an Archaean tholeiite transformed into a garnet-bearing amphibolite or eclogite. The geodynamic context of tholeiite melting is the subject of controversy. It is assumed to be either (1) subduction (melting of a hot subducting slab), or (2) hot spot (melting of underplated basalts). These hypotheses are considered in the light of modern adakite genesis. Adakites are intermediate to felsic volcanic rocks, andesitic to rhyolitic in composition (basaltic members are lacking). They have trondhjemitic affinities (high-Na 2O contents and K 2O/Na 2O˜0.5) and their Mg no. (0.5), Ni (20-40 ppm) and Cr (30-50 ppm) contents are higher than in typical calc-alkaline magmas. Sr contents are high (>300 ppm, until 2000 ppm) and REE show strongly fractionated patterns with very low heavy REE (HREE) contents (Yb≤1.8 ppm, Y≤18 ppm). Consequently, high Sr/Y and La/Yb ratios are typical and discriminating features of adakitic magmas, indicative of melting of a mafic source where garnet and/or hornblende are residual phases. Adakitic magmas are only found in subduction zone environments, exclusively where the subduction and/or the subducted slab are young (<20 Ma). This situation is well-exemplified in Southern Chile where the Chile ridge is subducted and where the adakitic character of the lavas correlates well with the young age of the subducting oceanic lithosphere. In typical subduction zones, the subducted lithosphere is older than 20 Ma, it is cool and the geothermal gradient along the Benioff plane is low such that the oceanic crust dehydrates before it reaches the solidus temperature of hydrated tholeiite. Consequently, the basaltic slab cannot melt. The released large ion lithophile element (LILE)-rich fluids rise up into the mantle wedge, inducing both its metasomatism and partial melting. Afterwards, the residue is made up of olivine+clinopyroxene+orthopyroxene, such that the partial melts are HREE-rich (low La/Yb and Sr/Y). Contrarily, when a young (<20 Ma) and hot oceanic lithosphere is subducted, the geothermal gradient along the Benioff plane is high, so the temperature of hydrated tholeiite solidus is reached before dehydration occurs. Under these conditions, garnet and/or hornblende are the main residual phases giving rise to HREE-depleted magmas (high La/Yb). The lack of residual plagioclase accounts for the Sr enrichment (high Sr/Y) of the magma. Experimental petrologic data show that the liquids produced by melting of tholeiite in subduction-like P- T conditions are adakitic in composition. However, natural adakites systematically have higher Mg no., Ni and Cr contents, which are interpreted as reflecting interactions between the ascending adakitic magma generated in the subducted slab and the overlying mantle wedge. This interpretation has been recently corroborated by studies on ultramafic enclaves in Batan lavas where olivine crystals contain glass inclusions with adakitic compositions [Schiano, P., Clochiatti, R., Shimizu, N., Maury, R., Jochum, K.P., Hofmann, A.W., 1995. Hydrous, silica-rich melts in the sub-arc mantle and their relationships with erupted arc lavas. Nature 377 595-600.]. This is interpreted as demonstrating that adakitic magmas passed through the mantle wedge and interacted with it. Sajona [Sajona, F.G., 1995. Fusion de la croûte océanique en contexte de subduction collision: géochimie, géochronologie et pétrologie du magmatisme plioquaternaire de Mindanao (Philippines). Unpublished thesis, Brest University, France, 223 pp.] also considers that the high-Nb basalts, which are associated with adakites, reflect mantle-adakite interactions. Recent structural studies have demonstrated that plate tectonics operated during the first half of Earth history. The very strong similarities that exist between modern adakites and Archaean tonalite, trondhjemite and granodiorite (TTG) attest that both have the same source and petrogenesis. Consequently, when Archaean-like P- T conditions are exceptionally realised in modern subduction zones, Archaean-like magmas are generated. Contrarily, hot spots never produce TTG-like magmas, thus, strongly supporting the hypothesis of the generation of the Archaean continental crust within a subduction environment. However, Archaean TTG are poorer in Mg, Ni and Cr than adakites, indicating that mantle-magma interactions were less efficient, probably due to the shallower depth of slab melting. In this case, the slab-derived magmas rise through a thinner mantle wedge, thus, reducing the efficiency of the interactions. This is corroborated by the absence of a positive Sr anomaly in TTG, which indicates that plagioclase could have been a residual phase during their genesis.

Mantle Flow and Dehydration Beneath the Juan de Fuca Plate Revealed by Shear Velocity and Attenuation

NASA Astrophysics Data System (ADS)

Ruan, Y.; Forsyth, D. W.; Bell, S. W.

2017-12-01

At mid-ocean-ridge spreading centers, it is still unclear to what extent the upwelling is purely passive, driven by viscous drag of the separating plates, or dynamically driven by the buoyancy induced by melt retention and depletion of the mantle matrix. The distinct sensitivities of seismic wavespeed and attenuation to temperature, melt porosity, water content and major element composition yield some of the primary constraints on mid-ocean ridge processes and the associated flow pattern, melt distribution, and the interaction of spreading centers with hotspots. Extensive arrays of ocean-bottom seismometers (OBS) with better quality, longer deployment periods, and the application of noise-removal techniques together provided higher quality data in this study than in any previous regional study of velocity and attenuation of the upper mantle beneath a spreading center. Based on the fundamental-mode Rayleigh waves, we imaged shear wave attenuation and velocity models in the vicinity of the Juan de Fuca plate with the best resolution to date of any spreading center. There is strong attenuation centered at depths of 70-80 km, just below the expected dry solidus and somewhat deeper than predicted for a model of passive mantle upwelling beneath the spreading center. The shear velocity structure shows lowest velocities west of the spreading center, particularly near Axial Seamount and high velocities east of the axis extending to a greater depth than predicted by the passive flow model. Together, these observations support a model in which buoyant upwelling west of the spreading center first depletes and dehydrates the mantle above the dry solidus by melt removal and then the associated downwelling carries depleted, melt-free, residual mantle downward beneath the Juan de Fuca plate. This depleted, dehydrated, melt-free layer can explain why the average attenuation is lower than expected and the velocity is higher than expected in the 30 to 70 km depth range. The compositional buoyancy of the depleted mantle may in most places limit downwelling to the vicinity of the spinel peridotite to garnet peridotite transition at a depth of 80 km.

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.

Slab melting and magma formation beneath the southern Cascade arc

USGS Publications Warehouse

Walowski, Kristina J.; Wallace, Paul J.; Clynne, Michael A.; Rasmussen, D.J.; Weis, D.

2016-01-01

The processes that drive magma formation beneath the Cascade arc and other warm-slab subduction zones have been debated because young oceanic crust is predicted to largely dehydrate beneath the forearc during subduction. In addition, geochemical variability along strike in the Cascades has led to contrasting interpretations about the role of volatiles in magma generation. Here, we focus on the Lassen segment of the Cascade arc, where previous work has demonstrated across-arc geochemical variations related to subduction enrichment, and H-isotope data suggest that H2O in basaltic magmas is derived from the final breakdown of chlorite in the mantle portion of the slab. We use naturally glassy, olivine-hosted melt inclusions (MI) from the tephra deposits of eight primitive (MgO>7 wt%) basaltic cinder cones to quantify the pre-eruptive volatile contents of mantle-derived melts in this region. The melt inclusions have B concentrations and isotope ratios that are similar to mid-ocean ridge basalt (MORB), suggesting extensive dehydration of the downgoing plate prior to reaching sub-arc depths and little input of slab-derived B into the mantle wedge. However, correlations of volatile and trace element ratios (H2O/Ce, Cl/Nb, Sr/Nd) in the melt inclusions demonstrate that geochemical variability is the result of variable addition of a hydrous subduction component to the mantle wedge. Furthermore, correlations between subduction component tracers and radiogenic isotope ratios show that the subduction component has less radiogenic Sr and Pb than the Lassen sub-arc mantle, which can be explained by melting of subducted Gorda MORB beneath the arc. Agreement between pMELTS melting models and melt inclusion volatile, major, and trace element data suggests that hydrous slab melt addition to the mantle wedge can produce the range in primitive compositions erupted in the Lassen region. Our results provide further evidence that chlorite-derived fluids from the mantle portion of the slab (∼7–9 km below the slab top) cause flux melting of the subducted oceanic crust, producing hydrous slab melts that migrate into the overlying mantle, where they react with peridotite to induce further melting.

Oxygen isotope geochemistry of mafic phenocrysts in primitive mafic lavas from the southernmost Cascade Range, California

USGS Publications Warehouse

Underwood, Sandra J.; Clynne, Michael A.

2017-01-01

Previously reported whole-rock δ18O values (5.6–7.8‰) for primitive quaternary mafic lavas from the southernmost Cascades (SMC) are often elevated (up to 1‰) relative to δ18O values expected for mafic magmas in equilibrium with mantle peridotite. Olivine, clinopyroxene, and plagioclase crystals were separated from 29 geochemically well-characterized mafic lavas for δ18O measurements by laser fluorination to assess modification of the mantle sources by ancient and modern subducted components. Oxygen isotope values of olivine phenocrysts in calc-alkaline lavas and contemporaneous high alumina olivine tholeiitic (HAOT) lavas generally exceed depleted mantle olivine values (~4.9–5.3‰). Modern addition of up to 6 wt% slab-derived fluid from Gorda serpentinized peridotite dehydration (~15‰) or chlorite dehydration (~10‰) within the serpentinized peridotite can provide the 18O enrichment detected in olivine phenocrysts (δ18Oolivine = 5.3–6.3‰) in calc-alkaline mafic lavas, and elevate 18O in overlying mantle lithosphere, as well. Specifically, although HAOT δ18Oolivine values (5.5–5.7‰) may reflect partial melting in heterogeneous 18O enriched mantle source domains that developed during multiple subduction events associated with terrane accretion (e.g., <1 wt% of ~15‰ materials), an additional 18O enrichment of up to 2 wt% of 10–15‰ slab-derived hydrous fluids might be accommodated. The calc-alkaline primitive magmas appear to have experienced a continuous range of open system processes, which operate in the mantle and during rapid magma ascent to eruption, and occasionally post quench. Textural relationships and geochemistry of these lava samples are consistent with blends of mafic phenocrysts and degassed melts in varying states of 18O disequilibrium. In lenses of accumulated melt within peridotite near the base of the crust, coexisting olivine and clinopyroxene δ18O values probably are not at isotopic equilibrium because fluids introduced into the system perturbed the δ18Omelt values. A “sudden” melt extraction event interrupts 18O equilibration in phenocrysts and poorly mixed melt(s). Rapid ascent of volatile oversaturated primitive mafic magma through the crust appears to be accompanied by devolatilization and crystallization of anorthite-rich plagioclase with elevated δ18Oplag values. The (Sr/P)N values for the whole rock geochemistry are consistent with a 87Sr/86Sr ~0.7027 slab-derived fluid addition into the infertile peridotite source of magmas, and melt devolatilization is recorded in the mixture of disequilibrium δ18O values for the constituent phases of lavas. Morbidity of the Gorda Plate as it undergoes intense deformation from the spreading ridge to the trench is likely a key factor to developing the carrying capacity of hydrous fluids and mineral phases in the slab subducting into the SMC mantle.

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.

[The influence of low-energy millimeter electromagnetic waves on the stability of DNA molecules in solution].

PubMed

Babaian; Markarian, A Sh; Kalantarian, V P; Kazarian, R S; Parsadanian, M A; Vardevanian, P O

2007-01-01

The influence of low-energy millimeter electromagnetic waves on aqueous saline solution of DNA from the liver of healthy rats and rats with sarcoma 45 has been investigated. The characteristic parameters of irradiated and unirradiated DNA, melting temperature, and the range of melting were obtained from melting curves. The duration of exposure did not practically affect the range of melting, while the thermostability of DNA increased; as irradiation duration increased to 90 min, the melting temperature of tumor increased by approximately 1.5 degrees C. It was assumped that the increase in the thermostability of DNA is due to a more effective stabilization of the DNA double helix caused by the dehydration of Na(+)- ions present in the solution.

Bending-related faulting and mantle serpentinization at the Middle America trench.

PubMed

Ranero, C R; Morgan, J Phipps; McIntosh, K; Reichert, C

2003-09-25

The dehydration of subducting oceanic crust and upper mantle has been inferred both to promote the partial melting leading to arc magmatism and to induce intraslab intermediate-depth earthquakes, at depths of 50-300 km. Yet there is still no consensus about how slab hydration occurs or where and how much chemically bound water is stored within the crust and mantle of the incoming plate. Here we document that bending-related faulting of the incoming plate at the Middle America trench creates a pervasive tectonic fabric that cuts across the crust, penetrating deep into the mantle. Faulting is active across the entire ocean trench slope, promoting hydration of the cold crust and upper mantle surrounding these deep active faults. The along-strike length and depth of penetration of these faults are also similar to the dimensions of the rupture area of intermediate-depth earthquakes.

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.

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 beneath the observed neo-volcanic zone. My models consist of three parts; lithosphere, asthenosphere and a melt extraction region. It is shown that melt migrates vertically within the asthenosphere, and forms a high melt fraction layer beneath the sloping base of the impermeable lithosphere. Within the sloping high melt fraction layer, melt migrates laterally towards the ridge. In order to simulate melt migration via crustal fractures and cracks, melt is extracted from a melt extraction region extending to the base of the crust. Performance of the melt focusing mechanism is not significantly sensitive to the size of melt extraction region, melt extraction threshold and spreading rate. In all of the models, about half of the total melt production freezes beneath the cooling base of the lithosphere, and the rest is effectively focused towards the ridge and forms the crust. To meet the computational demand for a precise tracing of the deforming upwelling plume and including the chemical buoyancy of the partially molten zone in my models, a new numerical method is developed to solve the related pure advection equations. The numerical method is based on Second Moment numerical method of Egan and Mahoney [1972] which is improved to maintain a high numerical accuracy in shear and rotational flow fields. In comparison with previous numerical methods, my numerical method is a cost-effective, non-diffusive and shape preserving method, and it can also be used to trace a deforming body in compressible flow fields.

Hydromechanics in dentine: role of dentinal tubules and hydrostatic pressure on mechanical stress-strain distribution.

PubMed

Kishen, A; Vedantam, S

2007-10-01

This investigation is to understand the role of free water in the dentinal tubules on the mechanical integrity of bulk dentine. Three different experiments were conducted in this study. In experiment 1, three-dimensional models of dentine with gradient elastic modulus, homogenous elastic modulus, and with and without hydrostatic pressure were simulated using the finite element method. Static compressive loads of 15, 50 and 100 N were applied and the distribution of the principal stresses, von Mises stresses, and strains in loading direction were determined. In experiment 2, experimental compression testing of fully hydrated and partially dehydrated dentine (21 degrees C for 72 h) was conducted using a Universal testing machine. In experiment 3, Fourier transform infrared spectroscopic analysis of hydrated and partially dehydrated dentine was carried out. The finite element analysis revealed that the dentine model with simulated hydrostatic pressure displayed residual tensile stresses and strains in the inner region adjacent to the root canal. When external compressive loads were applied to the model, the residual stresses and strains counteracted the applied loads. Similarly the hydrated specimens subjected to experimental compression loads showed greater toughness when compared to the partially dehydrated specimens. The stress at fracture was significantly higher in partially dehydrated specimens (p=0.014), while the strain at fracture was significantly higher in hydrated dentine specimens (p=0.037). These experiments highlighted the distinct role of free water in the dentinal tubules and hydrostatic pressure on the stress-strain distribution within the bulk dentine.

Oceanic slab melting and mantle metasomatism.

PubMed

Scaillet, B; Prouteau, G

2001-01-01

Modern plate tectonic brings down oceanic crust along subduction zones where it either dehydrates or melts. Those hydrous fluids or melts migrate into the overlying mantle wedge trigerring its melting which produces arc magmas and thus additional continental crust. Nowadays, melting seems to be restricted to cases of young (< 50 Ma) subducted plates. Slab melts are silicic and strongly sodic (trondhjemitic). They are produced at low temperatures (< 1000 degrees C) and under water excess conditions. Their interaction with mantle peridotite produces hydrous metasomatic phases such as amphibole and phlogopite that can be more or less sodium rich. Upon interaction the slab melt becomes less silicic (dacitic to andesitic), and Mg, Ni and Cr richer. Virtually all exposed slab melts display geochemical evidence of ingestion of mantle material. Modern slab melts are thus unlike Archean Trondhjemite-Tonalite-Granodiorite rocks (TTG), which suggests that both types of magmas were generated via different petrogenetic pathways which may imply an Archean tectonic model of crust production different from that of the present-day, subduction-related, one.

Porous Flow and Diffusion of Water in the Mantle Wedge: Melting and Hydration Patterns

NASA Astrophysics Data System (ADS)

Conder, J. A.

2005-12-01

It is widely accepted that melting at volcanic arcs is primarily triggered by fluxing the mantle wedge from the dehydrating subducting slab. However, there is less concensus regarding how water moves into and within the mantle wedge. There are at least four possible mechanisms for water migration in the wedge: buoyant porous flow, diffusion through mineral crystals, advection of hydrated minerals, and compositionally buoyant diapers. The latter two mechanisms require at least one of the first two to occur to get water from the slab into the wedge before they can function. Using geodynamic models of mantle flow in a simplified subduction setting, we explore the implications of diffusion and porous flow of water in the wedge, particularly as they would affect the time for recycling water through the subduction factory and the predicted pattern of basalt hydration across the arc. The slab is assumed to dehydrate in a continuous fashion as the solubility of water in subducted oceanic crust decreases with temperature and pressure and the water then enters the wedge via one of the two transport mechanisms. Diffusion is controlled by temperature and by which minerals are present. Although olivine dominates the mantle mineral fraction, pyroxenes may control the diffusion of water in the wedge as the diffusivity of pyroxene is one or more orders of magnitude greater than olivine. Even assuming the faster diffusion rate of orthopyroxene in the models, diffusion can only be an important transport mechanism when subduction rates are slower than ~3 cm/yr. Flux melting occurs in the wedge above where the slab is ~100-160 km deep with the maximum above where the slab is ~120 km deep. Models including porous flow can result in melting at higher subduction rates provided the permeability of the mantle is greater than 10-17 m2. The true magnitude of the permeability likely varies with the corresponding porosity created by the free phase. With porous flow, melting occurs 20-30 km closer to the trench and the degree of melting is larger than when only diffusion is allowed. The rate of dehydration depends on the thermal structure which can affect the permeability. The dependence of permeability and diffusion with temperature may explain the variations in volcanic front location as observed at different arcs.

Modeling the migration of fluids in subduction zones

NASA Astrophysics Data System (ADS)

Spiegelman, M.; Wilson, C. R.; van Keken, P. E.; Hacker, B. R.

2010-12-01

Fluids play a major role in the formation of arc volcanism and the generation of continental crust. Progressive dehydration reactions in the downgoing slab release fluids to the hot overlying mantle wedge, causing flux melting and the migration of melts to the volcanic front. While the qualitative concept is well established the quantitative details of fluid release and especially that of fluid migration and generation of hydrous melting in the wedge is still poorly understood. Here we present new models of the fluid migration through the mantle wedge for subduction zones that span the spectrum of arcs worldwide. We focus on the flow of water and use an existing set of high resolution thermal and metamorphic models (van Keken et al., JGR, in review) to predict the regions of water release from the sediments, upper and lower crust, and upper most mantle. We use this water flux as input for the fluid migration calculation based on new finite element models built on advanced computational libraries (FEniCS/PETSc) for efficient and flexible solution of coupled multi-physics problems. The first generation of these models solves for the evolution of porosity and fluid-pressure/flux throughout the slab and wedge given solid flow, viscosity and thermal fields from the existing thermal models. Fluid flow in the new models depends on both permeability and the rheology of the slab-wedge system as interaction with rheological variability can induce additional pressure gradients that affect the fluid flow pathways. We will explore the sensitivity of fluid flow paths for a range of subduction zones and fluid flow parameters with emphasis on variability of the location of the volcanic arc with respect to flow paths and expected degrees of hydrous melting which can be estimated given a variety of wet-melting parameterizations (e.g. Katz et al, 2003, Kelley et al, 2010). The current models just include dehydration reactions but work continues on the next generation of models which will include both dehydration and hydration reactions as well as parameterized flux melting in a consistent reactive-flow framework. We have also begun work on re-implementing the solid-flow thermal calculations in FEniCS/PETSc which are open-source libraries in preparation for developing a fully coupled fluid-solid dynamics models for exploring subduction zone processes

Melt segregation during Poiseuille flow of partially molten rocks

NASA Astrophysics Data System (ADS)

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

2015-12-01

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

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

NASA Astrophysics Data System (ADS)

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

2017-07-01

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

Mantle plume capture, anchoring, and outflow during Galápagos plume-ridge interaction

NASA Astrophysics Data System (ADS)

Gibson, S. A.; Geist, D. J.; Richards, M. A.

2015-05-01

Compositions of basalts erupted between the main zone of Galápagos plume upwelling and adjacent Galápagos Spreading Center (GSC) provide important constraints on dynamic processes involved in transfer of deep-mantle-sourced material to mid-ocean ridges. We examine recent basalts from central and northeast Galápagos including some that have less radiogenic Sr, Nd, and Pb isotopic compositions than plume-influenced basalts (E-MORB) from the nearby ridge. We show that the location of E-MORB, greatest crustal thickness, and elevated topography on the GSC correlates with a confined zone of low-velocity, high-temperature mantle connecting the plume stem and ridge at depths of ˜100 km. At this site on the ridge, plume-driven upwelling involving deep melting of partially dehydrated, recycled ancient oceanic crust, plus plate-limited shallow melting of anhydrous peridotite, generate E-MORB and larger amounts of melt than elsewhere on the GSC. The first-order control on plume stem to ridge flow is rheological rather than gravitational, and strongly influenced by flow regimes initiated when the plume was on axis (>5 Ma). During subsequent northeast ridge migration material upwelling in the plume stem appears to have remained "anchored" to a contact point on the GSC. This deep, confined NE plume stem-to-ridge flow occurs via a network of melt channels, embedded within the normal spreading and advection of plume material beneath the Nazca plate, and coincides with locations of historic volcanism. Our observations require a more dynamically complex model than proposed by most studies, which rely on radial solid-state outflow of heterogeneous plume material to the ridge.

Light Stable Isotopic Compositions of Enriched Mantle Sources: Resolving the Dehydration Paradox

NASA Astrophysics Data System (ADS)

Dixon, J. E.; Bindeman, I. N.; Kingsley, R. H.

2017-12-01

An outstanding puzzle in mantle geochemistry has been the origin and evolution of Earth's volatile components. The "dehydration paradox" refers to the following conundrum. Mantle compositions for some enriched mid-ocean ridge (MORB) and ocean island (OIB) basalts basalts require involvement of a mostly dehydrated slab component to explain the trace element ratios and radiogenic isotopic compositions, but a fully hydrated slab component to explain the stable isotopic compositions. Volatile and stable isotopic data on enriched MORB show a diversity of enriched components. Pacific PREMA-type basalts (H2O/Ce = 215 ± 30, δDSMOW = -45 ± 5 ‰) are similar to those in the north Atlantic (H2O/Ce = 220 ± 30; δDSMOW = -30 to -40 ‰). Basalts with EM-type signatures have regionally variable volatile compositions. North Atlantic EM-type basalts are wetter (H2O/Ce = 330 ± 30) and have isotopically heavier hydrogen (δDSMOW = -57 ± 5 ‰) than north Atlantic MORB. South Atlantic EM-type basalts are damp (H2O/Ce = 120 ± 10) with intermediate δDSMOW (-68 ± 2 ‰), similar to dDSMOW for Pacific MORB. North EPR EM-type basalts are dry (H2O/Ce = 110 ± 20) and isotopically light (δDSMOW = -94 ± 3 ‰). Boron and lithium isotopic ratios parallel the trends observed for dDSMOW. A multi-stage metasomatic and melting model accounts for the origin of the enriched components by extending the subduction factory concept down through the mantle transition zone, with slab temperature a key variable. The dehydration paradox is resolved by decoupling of volatiles from lithophile elements, reflecting primary dehydration of the slab followed by secondary rehydration and re-equilibration by fluids derived from subcrustal hydrous phases (e.g., antigorite) in cooler, deeper parts of the slab. The "expanded subduction factory" model includes melting at several key depths, including 1) 180 to 280 km, where EM-type mantle compositions are generated above slabs with average to hot thermal profiles by addition of <1% carbonated sediment-derived supercritical fluids/melts to depleted asthenospheric or subcontinental lithospheric mantle, and 2) 410 to 660 km, where PREMA-type mantle sources are generated, above slabs with average to cool thermal profiles, by addition of <1% carbonated eclogite ± sediment-derived supercritical fluids to depleted mantle.

Constraints on upper mantle Vp/Vs ratio variations beneath eastern North China from receiver function tomography

NASA Astrophysics Data System (ADS)

Si, Shaokun; Tian, Xiaobo; Gao, Rui

2017-05-01

To detect the thinning, modification, and replacement of the basement of the lithosphere is a key step in understanding the destruction mechanism of the North China lithosphere. The difference of the basement of the lithosphere is mainly displayed by the variation of the peridotite composition and its physical state. Vp/Vs ratio (hereafter referred to as velocity ratio) is more sensitive to this change than Vp or Vs alone. By means of the strong dependence of the travel-time of the wave converted at the 410-km discontinuity (P410s) observed in the receiver function (RF) on the velocity ratio in the upper mantle, we developed a new mapping method to constrain the velocity ratio between the Moho and 410-km discontinuity. Using the RFs extracted from 246 broadband stations beneath the North China Craton (NCC), we obtained a high-resolution velocity ratio image of the upper mantle. The abnormal velocity ratio indicates a strong lateral variation of the mineral composition in the upper mantle beneath North China. Two low-velocity-ratio patches are imaged at the top of the upper mantle and the 410 km depth, respectively. The former may be related to the orthopyroxene enrichment in the lithospheric mantle, and the latter may reflect the stagnant Pacific slab in the mantle transition zone (MTZ). A prominent high-velocity-ratio anomaly is also imaged in the upper mantle beneath the Shaanxi-Shanxi rift system in the central NCC, with the highest anomaly reaching 10%. We speculate that the high velocity ratio of upper mantle is related to convective flow due to slab dehydration in the MTZ. The dehydration of the retained slab in the MTZ results in partial melting and upwelling of upper mantle materials. Such convective flow and their melting are closely related to the Cenozoic basalt eruption in the northern section of the Shaanxi-Shanxi rift system.

Effect of leaf dehydration duration and dehydration degree on PSII photochemical activity of papaya leaves.

PubMed

Liu, Meijun; Zhang, Zishan; Gao, Huiyuan; Yang, Cheng; Fan, Xingli; Cheng, Dandan

2014-09-01

Although the effect of dehydration on photosynthetic apparatus has been widely studied, the respective effect of dehydration duration and dehydration degree was neglected. This study showed that, when leaves dehydrated in air, the PSII activities of leaves decreased with the decline of leaf relative water content (RWC). Unexpectedly, when leaves dehydrated to same RWC, the decreases in Fv/Fm, Ψo and RC/CSm were lower in leaves dehydrating at 43 °C than those at 25 °C. However, to reach the same RWC, leaves dehydrating at 43 °C experienced 1/6 of the dehydration duration for leaves dehydrating at 25 °C. To distinguish the respective effect of dehydration degree and dehydration duration on photosynthetic apparatus, we studied the PSII activities of leaves treated with different concentration of PEG solutions. Increasing dehydration degree aggravated the decline of Fv/Fm, Ψo and RC/CSm in leaves with the same dehydration duration, while prolonging the dehydration duration also exacerbated the decline of Fv/Fm, Ψo and RC/CSm in leaves with identical dehydration degree. With the same dehydration degree and duration, high temperature enhanced the decrease of Fv/Fm, Ψo and RC/CSm in the leaves. When leaves dehydrated in air, the effect of high temperature was underestimated due to reduction of dehydration duration. The results demonstrated that, dehydration degree and duration both play important roles in damage to photosynthetic apparatus. We suggest that, under combined stresses, the effects of dehydration degree and duration on plants should be considered comprehensively, otherwise, partial or incorrect results may be obtained. Copyright © 2014 Elsevier Masson SAS. All rights reserved.

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

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 agreement with our observations of partial melting. The presence of partial melts in crustal carbonates has important physical and chemical implications, including a drastic drop in rock viscosity and significant change in the dynamics and distribution of fluids within both the contact aureole and the intrusive body.

Modeling the Migration of Fluids in Subduction Zones

NASA Astrophysics Data System (ADS)

Wilson, C. R.; Spiegelman, M.; Van Keken, P. E.; Vrijmoed, J. C.; Hacker, B. R.

2011-12-01

Fluids play a major role in the formation of arc volcanism and the generation of continental crust. Progressive dehydration reactions in the downgoing slab release fluids to the hot overlying mantle wedge, causing flux melting and the migration of melts to the volcanic front. While the qualitative concept is well established, the quantitative details of fluid release and especially that of fluid migration and generation of hydrous melting in the wedge is still poorly understood. Here we present new models of the fluid migration through the mantle wedge for subduction zones. We use an existing set of high resolution metamorphic models (van Keken et al, 2010) to predict the regions of water release from the sediments, upper and lower crust, and upper most mantle. We use this water flux as input for the fluid migration calculation based on new finite element models built on advanced computational libraries (FEniCS/PETSc) for efficient and flexible solution of coupled multi-physics problems. The first generation of one-way coupled models solves for the evolution of porosity and fluid-pressure/flux throughout the slab and wedge given solid flow, viscosity and thermal fields from separate solutions to the incompressible Stokes and energy equations in the mantle wedge. These solutions are verified by comparing to previous benchmark studies (van Keken et al, 2008) and global suites of thermal subduction models (Syracuse et al, 2010). Fluid flow depends on both permeability and the rheology of the slab-wedge system as interaction with rheological variability can induce additional pressure gradients that affect the fluid flow pathways. These non-linearities have been shown to explain laboratory-scale observations of melt band orientation in labratory experiments and numerical simulations of melt localization in shear bands (Katz et al 2006). Our second generation of models dispense with the pre-calculation of incompressible mantle flow and fully couple the now compressible system of mantle and fluid flow equations, introducing complex feedbacks between the rheology, temperature, permeability, strain rate and porosity. Using idealized subduction zone geometries we investigate the effects of this non-linearity and explore the sensitivity of fluid flow paths for a range of fluid flow parameters with emphasis on variability of the location of the volcanic arc with respect to flow paths. We also estimate the expected degrees of hydrous melting using a variety of wet-melting parameterizations (e.g., Katz et al, 2003, Kelley et al, 2010). The current models only include dehydration reactions but work continues on the next generation of models which will include both dehydration and hydration reactions as well as parameterized flux melting in a consistent reactive-flow framework.

Quantitative characterization of 3-dimensional melt distribution in partially molten olivine-basalt aggregates using X-ray synchrotron microtomography

NASA Astrophysics Data System (ADS)

Zhu, W.; Gaetani, G. A.; Fusseis, F.

2009-12-01

Quantitative knowledge of the distribution of small amounts of silicate melt in peridotite and of its influence on permeability are critical to our understanding of melt migration and segregation processes in the upper mantle. Estimates for the permeability of partially molten rock require 3D melt distribution at the grain-scale. Existing studies of melt distribution, carried out on 2D slices through experimental charges, have produced divergent models for melt distribution at small melt fractions. While some studies conclude that small amounts of melt are distributed primarily along triple junctions [e.g., Wark et al., 2003], others predict an important role for melt distribution along grain boundaries at low melt fractions [e.g., Faul 1997]. Using X-ray synchrotron microtomography, we have obtained the first high quality non-destructive imaging of 3D melt distribution in olivine-basalt aggregates. Textually equilibrated partially molten samples consisting of magnesian olivine plus 2, 5, 10, or 20% primitive basalt were synthesized at 1.5 GPa and 1350°C in experiments lasting 264-336 hours. Microtomographic images of melt distribution were obtained on cylindrical cores, 1 mm in diameter, at a spatial resolution of 1 micron. Textual information such as melt channel size, dihedral angle and channel connectivity was then quantified using AVIZO and MATLAB. Our results indicate that as melt fraction decreases, melt becomes increasingly distributed along 3 grain junctions, in agreement with theoretical predictions. We do not find significant amounts of melt along grain boundaries at low melt fractions. We found that the true dihedral angle ranges from 50 to 70°, in agreements with results using 2D microcopy. Comparison between the samples provides a quantitative characterization of how melt fraction affects melt distribution including connectivity. The geometrical data have been incorporated into our network model to obtain macroscale transport properties for partially molten dunite. Results from this tomographic study thus provide constraints on rates of melt migration and melt extraction within the partially molten regions beneath ocean ridges. Fig 1. Melt channels in an olivine-basalt sample with 10 vol% melt.

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.

Metamorphic and geochronogical study of the Triassic El Oro metamorphic complex, Ecuador: Implications for high-temperature metamorphism in a forearc zone

NASA Astrophysics Data System (ADS)

Riel, N.; Guillot, S.; Jaillard, E.; Martelat, J.-E.; Paquette, J.-L.; Schwartz, S.; Goncalves, P.; Duclaux, G.; Thebaud, N.; Lanari, P.; Janots, E.; Yuquilema, J.

2013-01-01

In the forearc of the Andean active margin in southwest Ecuador, the El Oro metamorphic complex exhibits a well exposed tilted forearc section partially migmatized. We used Raman spectroscopy on carbonaceous matter (RSCM) thermometry and pseudosections coupled with mineralogical and textural studies to constrain the pressure-temperature (P-T) evolution of the El Oro metamorphic complex during Triassic times. Our results show that anatexis of the continental crust occurred by white-mica and biotite dehydration melting along a 10 km thick crustal domain (from 4.5 to 8 kbar) with increasing temperature from 650 to 700 °C. In the biotite dehydration melting zone, temperature was buffered at 750-820 °C in a 5 km thick layer. The estimated average thermal gradient during peak metamorphism is of 30 °C/km within the migmatitic domain can be partitioned into two apparent gradients parts. The upper part from surface to 7 km depth records a 40-45 °C/km gradient. The lower part records a quasi-adiabatic geotherm with a 10 °C/km gradient consistent with an isothermal melting zone. Migmatites U-Th-Pb geochronology yielded zircon and monazite ages of 229.3 ± 2.1 Ma and 224.5 ± 2.3 Ma, respectively. This thermal event generated S-type magmatism (the Marcabeli granitoid) and was immediately followed by underplating of the high-pressure low-temperature (HP-LT) Arenillas-Panupalí unit at 225.8 ± 1.8 Ma. The association of high-temperature low-pressure (HT-LP) migmatites with HP-LT unit constitutes a new example of a paired metamorphic belt along the South American margin. We propose that in addition to crustal thinning, underplating of the Piedras gabbroic unit before 230 Ma provided the heat source necessary to foster crustal anatexis. Furthermore, its MORB signature shows that the asthenosphere was involved as the source of the heat anomaly. S-type felsic magmatism is widespread during this time and suggests that a large-scale thermal anomaly affected a large part of the South American margin during the late Triassic. We propose that crustal anatexis is related to an anomaly that arose during subduction of the Panthalassa ocean under the South American margin. Slab verticalization or slab break-off can be invoked as the origin of the upwelling of the asthenosphere.

Preliminary results of sulfide melt/silicate wetting experiments in a partially melted ordinary chondrite

NASA Technical Reports Server (NTRS)

Jurewicz, Stephen R.; Jones, John H.

1994-01-01

Recently, mechanisms for core formation in planetary bodies have received considerable attention. Most current theories emphasize the need for large degrees of silicate partial melting to facilitate the coalescence and sinking of sulfide-metal liquid blebs through a low strength semi-crystalline silicate mush. This scenario is based upon observations that sulfide-metal liquid tends to form circular blebs in partially molten meteorites during laboratory experiments. However, recent experimental work by Herpfer and Larimer indicates that some sulfide-Fe liquids have wetting angles at and slightly below 60 deg in an olivine aggregate, implying an interconnected melt structure at any melt fraction. Such melt interconnectivity provides a means for gravitational compaction and extraction of the majority of a sulfide liquid phase in small planetary bodies without invoking large degrees of silicate partial melting. Because of the important ramifications of these results, we conducted a series of experiments using H-chondrite starting material in order to evaluate sulfide-liquid/silicate wetting behavior in a more complex natural system.

Gel electrophoresis of partially denatured DNA. Retardation effect: its analysis and application.

PubMed Central

Lyamichev, V I; Panyutin, I G; Lyubchenko YuL

1982-01-01

The hypothesis about the role of partial denaturation in DNA retardation during its electrophoresis in denaturing gel /1,2/ was tested. We used partially melted DNA molecules in which the size of the melted regions and their location were known. They were obtained through glyoxal treatment of the melted regions by a procedure allowing the denatured state to be fixed at any point within the melting range. The approach and the availability of the melting maps of DNAs made it possible to investigate DNA molecules differing in length and in the size of the melted regions. The presence of a denatured region at the end of the molecule or inside of it was shown to decrease its electrophoretic mobility, the effect depending on the size of the melted region and on the DNA length. On the basis of the experimental results an explanation is proposed for the cause of retardation in the case of partially denatured DNA. Images PMID:7133999

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

NASA Astrophysics Data System (ADS)

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

2017-08-01

To investigate the behavior of Cu isotopes during partial melting and melt percolation in the mantle, we have analyzed Cu isotopic compositions of a suite of well-characterized Paleozoic peridotites from the Balmuccia and Baldissero massifs in the Ivrea-Verbano Zone (IVZ, Northern Italy). Our results show that fresh lherzolites and harzburgites have a large variation of δ65Cu ranging from -0.133 to 0.379‰, which are negatively correlated with Al2O3 contents as well as incompatible platinum-group (e.g., Pd) and chalcophile element (e.g., Cu, S, Se, and Te) contents. The high δ65Cu can be explained by Cu isotope fractionation during partial melting of a sulfide-bearing peridotite source, with the light isotope (63Cu) preferentially entering the melts. The low δ65Cu can be attributed to precipitation of sulfides enriched in 63Cu during sulfur-saturated melt percolation. Replacive dunites from the Balmuccia massif display high δ65Cu from 0.544 to 0.610‰ with lower Re, Pd, S, Se, and Te contents and lower Pd/Ir ratios relative to lherzolites, which may result from dissolution of sulfides during interactions between S-undersaturated melts and lherzolites at high melt/rock ratios. Thus, our results suggest that partial melting and melt percolation largely account for the Cu isotopic heterogeneity of the upper mantle. The correlation between δ65Cu and Cu contents of the lherzolites and harzburgites was used to model Cu isotope fractionation during partial melting of a sulfide-bearing peridotite, because Cu is predominantly hosted in sulfide. The modelling results indicate an isotope fractionation factor of αmelt-peridotite = 0.99980-0.99965 (i.e., 103lnαmelt-peridotite = -0.20 to -0.35‰). In order to explain the Cu isotopic systematics of komatiites and mid-ocean ridge basalts reported previously, the estimated αmelt-peridotite was used to simulate Cu isotopic variations in melts generated by variable degrees of mantle melting. The results suggest that high degrees (>25%) of partial melting extracts nearly all source Cu and it cannot produce Cu isotope fractionation in komatiites relative to their mantle source, and that sulfide segregation during magma evolution have modified Cu isotopic compositions of mid-ocean ridge basalts.

Comment on 'Water-fluxed melting of the continental crust: A review' by R.F. Weinberg and P. Hasalová

NASA Astrophysics Data System (ADS)

Clemens, J. D.; Stevens, G.

2015-10-01

In this invited 'review' article, the authors come to the conclusion that fluid-present partial melting reactions are of widespread occurrence and critical importance in the processes of high-grade metamorphism and crustal differentiation. In their abstract, the authors correctly restate the conclusions of Clemens and Droop (1998) that it is not necessarily the case that melts formed by fluid-present reactions (even by H2O-saturated melting) cannot leave their sources. This realisation is not actually relevant to the question of formation and ascent of granitic magmas by crustal partial melting. Although they refer to Clemens and Watkins (2001), the authors seem ignore the main point of the argument presented therein, namely that the distribution of temperature and H2O contents in felsic igneous systems is only compatible with derivation of the magmas by fluid-absent partial melting reactions at high-temperature, granulite-facies conditions. Neither fluid-saturated nor fluid-deficient partial melting could have resulted in the observed covariation in temperature and melt H2O content.

On the formation of continental silicic melts in thermochemical mantle convection models: implications for early Earth

NASA Astrophysics Data System (ADS)

van Thienen, P.; van den Berg, A. P.; Vlaar, N. J.

2004-12-01

Important constituents of Archean cratons, formed in the early and hot history of the Earth, are Tonalite-Trondhjemite-Granodiorite (TTG) plutons and greenstone belts. The formation of these granite-greenstone terrains is often ascribed to plate-tectonic processes. Buoyancy considerations, however, do not allow plate tectonics to take place in a significantly hotter Earth. We therefore propose an alternative mechanism for the coeval and proximate production of TTG plutons and greenstone-like crustal successions. That is, when a locally anomalously thick basaltic crust has been produced by continued addition of extrusive or intrusive basalts due to partial melting of the underlying convecting mantle, the transition of a sufficient amount of basalt in the lower crust to eclogite may trigger a resurfacing event, in which a complete crustal section of over 1000 km long sinks into the mantle in less than 2 million years. Pressure release partial melting in the complementary upwelling mantle produces large volumes of basaltic material replacing the original crust. Partial melting at the base of this newly produced crust may generate felsic melts which are added as intrusives and/or extrusives to the generally mafic crustal succession, adding to what resembles a greenstone belt. Partial melting of metabasalt in the sinking crustal section produces a significant volume of TTG melt which is added to the crust directly above the location of 'subduction', presumably in the form of a pluton. This scenario is self-consistently produced by numerical thermochemical mantle convection models, presented in this paper, including partial melting of mantle peridotite and crustal (meta)basalt. The metamorphic p, T conditions under which partial melting of metabasalt takes place in this scenario are consistent with geochemical trace element data for TTGs, which indicate melting under amphibolite rather than eclogite facies. Other geodynamical settings which we have also investigated, including partial melting in small scale delaminations of the lower crust, at the base of a anomalously thick crust and due to the influx of a lower mantle diapir fail to reproduce this behavior unequivocally and mostly show melting of metabasalt in the eclogite stability field instead.

A crystallographic and thermal study of pridinol mesylate and its monohydrated solvate.

PubMed

Gaztañaga, Pablo; Baggio, Ricardo; Vega, Daniel Roberto

2018-06-01

Herein are reported the crystal and molecular structures of the pridinol mesylate salt (C 20 H 25 NO + ·CH 3 O 3 S - ) (I) and its monohydrated solvate form (C 20 H 25 NO + ·CH 3 O 3 S - ·H 2 O) (II). A comparison of both with the already reported structure of pure pridinol [1,1-diphenyl-3-piperidino-1-propanol, C 20 H 25 NO; Tacke et al. (1980). Chem. Ber. 113, 1962-1980] is made. Molecular structures (I) and (II) are alike in bond distances and bond angles, but differ in their spatial conformation, and, more relevant still, in their hydrogen-bonding motifs. This gives rise to quite different packing schemes, in the form of simple dimers in (I) but water-mediated hydrogen-bonded chains in (II). The dehydration behaviour of form (II) is highly dependent on the heating rate, with slow rates leading to a clear endothermic dehydration step, towards anhydrous (I), with subsequent melting of this latter phase. Increased heating rates result in a more unclear behaviour ending in a structural collapse (melting of the hydrated phase), at temperatures significantly lower than the melting point of the anhydrous phase. The eventual relevance of the water link in the structure of (II) is discussed in regard to this behaviour.

Geochemical constraints on possible subduction components in lavas of Mayon and Taal Volcanoes, Southern Luzon, Philippines

USGS Publications Warehouse

Castillo, P.R.; Newhall, C.G.

2004-01-01

Mayon is the most active volcano along the east margin of southern Luzon, Philippines. Petrographic and major element data indicate that Mayon has produced a basaltic to andesitic lava series by fractional crystallization and magma mixing. Trace element data indicate that the parental basalts came from a heterogeneous mantle source. The unmodified composition of the mantle wedge is similar to that beneath the Indian Ocean. To this mantle was added a subduction component consisting of melt from subducted pelagic sediment and aqueous fluid dehydrated from the subducted basaltic crust. Lavas from the highly active Taal Volcano on the west margin of southern Luzon are compositionally more variable than Mayon lavas. Taal lavas also originated from a mantle wedge metasomatized by aqueous fluid dehydrated from the subducted basaltic crust and melt plus fluid derived from the subducted terrigenous sediment. More sediment is involved in the generation of Taal lavas. Lead isotopes argue against crustal contamination. Some heterogeneity of the unmodified mantle wedge and differences in whether the sediment signature is transferred into the lava source through an aqueous fluid or melt phase are needed to explain the regional compositional variation of Philippine arc lavas. ?? Oxford University Press 2004; all rights reserved.

How to build stable geochemical reservoirs on Mars?

NASA Astrophysics Data System (ADS)

Plesa, Ana-Catalina; Tosi, Nicola; Breuer, Doris

2014-05-01

To explain the complex thermo-chemical processes needed for the formation of distinct and stable geochemical reservoirs early in the thermo-chemical evolution of Mars, most geochemical studies argue that fractional crystallization of a global magma ocean may reproduce the isotopic characteristic of the SNCs [1, 2]. However, geodynamical models show that such scenario is difficult to reconcile with other observations like late volcanic activity and crustal density values as obtained from gravity and topography modelling [3, 4]. The stable density gradient, which establishes after the mantle overturn has completed, inhibits thermal convection. Albeit capable to provide stable reservoirs, this scenario suggests a conductive mantle after the overturn which on the one hand fails to sample deep regions of the mantle and on the other hand is clearly at odds with the volcanic history of Mars. This is best explained by assuming a convective mantle and partial melting as the principal agents responsible for the generation and evolution of Martian volcanism. Therefore, in this work an alternative scenario for the formation of early stable geochemical reservoirs is presented similar to the model of [5]. We investigate the influence of partial melting on mantle dynamics, crustal formation, and volcanic outgassing of a one-plate planet using a 2D mantle convection code. When melt is extracted to form crust, the mantle material left behind is more buoyant than its parent material and depleted in radioactive heat sources. The extracted heat-producing elements are then enriched in the crust, which also has an insulating effect due to its lower thermal conductivity compared to the mantle. In addition, partial melting can influence the mantle rheology through the dehydration (water depletion) of the mantle material by volcanic outgassing. As a consequence, the viscosity of water-depleted regions increases more than two orders of magnitude compared to water-saturated rocks resulting in slower cooling rates. The most important parameter influencing the thermo-chemical evolution is the assumed density difference between the primitive and the depleted mantle material (i.e., between peridotite and harzburgite). With small or negligible values of compositional buoyancy, crustal formation including crustal delamination is very efficient, also resulting in efficient processing and degassing of the mantle. The entire convecting mantle below the stagnant lid depletes continuously with time. In contrast, with increasing compositional buoyancy, crustal formation and mantle degassing are strongly suppressed although partial melting is substantially prolonged in the thermal evolution. The crust shows strong lateral variations in thickness, and crustal delamination is reduced and occurs only locally. Furthermore, two to four different mantle reservoirs can form depending on the initial temperature distribution [6]. Some of these reservoirs can be sustained during the entire evolution whereas others change with time - a scenario possibly valid for Mars as it may explain the isotope characteristic of the Martian meteorites. References: [1] Elkins-Tanton et al., 2005, EPSL; [2] Debaille et al., 2009, Nature; [3] Tosi et al., 2013, JGR; [4] Plesa et al., submitted to EPSL; [5] Ogawa and Yanagisawa 2011, JGR; [6] Plesa and Breuer, 2013, PSS.

How to make a craton

NASA Astrophysics Data System (ADS)

Lee, C.; Chin, E. J.; Erdman, M.; Gaschnig, R. M.; Lederer, G. W.; Savage, P. S.; Zhong, S.; Zincone, S.

2013-12-01

Most Archean cratons are underlain by long-lived 200-300 km thick thermal boundary layers, significantly thicker than oceanic boundary layers, which eventually subduct. The longevity of cratons is perplexing because cold thermal boundary layers should be gravitationally unstable or should thermally erode with time. However, it is agreed that thermal contraction of the cratonic root is compensated by intrinsic compositional buoyancy due to extreme melt depletion. This melt depletion is also thought to have dehydrated the peridotitic residue, strengthening the cratonic mantle, making it resistant to thermo-mechanical erosion. Exactly how cratonic mantle arrives at this chemically buoyant and dehydrated state is unknown. Possible scenarios include formation by melting within a large plume head, accretion of oceanic lithosphere, and accretion of sub-arc mantle. The high degrees of melting would seem to imply formation in hot plume heads, but low Al and heavy rare earth element contents suggest formation in the spinel stability field, implying formation at shallower depths than their current equilibration pressures. We present a new thermobarometer designed to estimate the average melting pressures and temperatures of residual peridotites using whole rock major element compositions. We find that the average melting pressures and temperatures of cratonic peridotites range between 3-4 GPa and 1600 °C. If cratonic peridotites melted via adiabatic decompression, these average pressures represent maximum bounds on the final pressures of melt extraction. Currently, cratonic peridotites derive from 4-7 GPa, implying that the building blocks of peridotites experienced an increase of 1-3 GPa, equivalent to 30-90 km of overburden. Our results thus imply that cratonic mantle most likely formed by tectonic thickening of oceanic or arc lithospheres. But because both arc and oceanic lithospheres might be expected to be wet due to hydrous flux melting and serpentinization, respectively, cratons should be weak. This dilemma can be reconciled by considering the thermal and magmatic evolution of juvenile crust formed in the Archean. Thickening of juvenile crust increases total heat production within the upper part of the nascent lithosphere. With higher heat production in the past, such thickening causes the crust to heat up on timescales of 100 Myr, resulting in a post-orogenic thermal pulse that generates a wave of crustal anatexis and downward heating of the lithospheric mantle, driving off residual water and increasing the kinetics of grain growth, both of which strengthen the lithosphere. Crustal melting will also advectively concentrate radiogenics towards the surface with no observable change in surface heat flow. This upward migration of radiogenics will be followed by cooling of the lower crust and lithospheric mantle, causing further strengthening. With secular cooling of the ambient convecting mantle over much longer timescales, cratons emerge in elevation, leading to erosion of the radiogenically enriched upper crust and leaving behind a continental block with the low surface heat flow characteristic of cratons today. In summary, cratons form by tectonic thickening of cold building blocks, followed by a thermal pulse that further dehydrates and anneals the cratonic mantle. The last step requires sufficient radiogenics to operate, which may explain why cratons formed early in Earth's history.

Magmatic water contents determined through clinopyroxene: Examples from the Western Canary Islands, Spain

NASA Astrophysics Data System (ADS)

Weis, Franz A.; Skogby, Henrik; Troll, Valentin R.; Deegan, Frances M.; Dahren, Börje

2015-07-01

Water is a key parameter in magma genesis, magma evolution, and resulting eruption styles, because it controls the density, the viscosity, as well as the melting and crystallization behavior of a melt. The parental water content of a magma is usually measured through melt inclusions in minerals such as olivine, a method which may be hampered, however, by the lack of melt inclusions suitable for analysis, or postentrapment changes in their water content. An alternative way to reconstruct the water content of a magma is to use nominally anhydrous minerals (NAMs), such as pyroxene, which take up low concentrations of hydrogen as a function of the magma's water content. During magma degassing and eruption, however, NAMs may dehydrate. We therefore tested a method to reconstruct the water contents of dehydrated clinopyroxene phenocrysts from the Western Canary islands (n = 28) through rehydration experiments followed by infrared and Mössbauer spectroscopy. Employing currently available crystal/melt partitioning data, the results of the experiments were used to calculate parental water contents of 0.71 ± 0.07 to 1.49 ± 0.15 wt % H2O for Western Canary magmas during clinopyroxene crystallization at upper mantle conditions. This H2O range is in agreement with calculated water contents using plagioclase-liquid-hygrometry, and with previously published data for mafic lavas from the Canary Islands and comparable ocean island systems elsewhere. Utilizing NAMs in combination with hydrogen treatment can therefore serve as a proxy for pre-eruptive H2O contents, which we anticipate becoming a useful method applicable to mafic rocks where pyroxene is the main phenocryst phase.

Shock effects on hydrous minerals and implications for carbonaceous meteorites

NASA Technical Reports Server (NTRS)

Lange, M. A.; Ahrens, T. J.; Lambert, P.

1985-01-01

The effect of shock loading over the pressure range of 29-59 GPa on the shock-recovered specimens of antigorite serpentine, Mg3Si2O5(OH)4, were investigated employing infrared (IR) spectroscopy, thermogravimetric analysis, and optical and scanning electron microscopy. With increasing shock pressure, there was an increase in H2O IR absorption peaks at the expense of OH peaks, while the changes in SiO bond vibration modes were identical to those seen for other, nonhydrous minerals. Thermogravimetric results on vented assembly samples showed linear relationships between the shock pressure and both the length of dehydration interval and the effective activation energy for releasing post-shock structural water. Optical and scanning electron microscopy revealed gas bubbles, which appeared to be injected into zones of partial melting, and vesicular dark veins distributed throughout the shocked samples. It is suggested that shock loading of hydrous minerals would release and redistribute free water in the regoliths of carbonaceous chondrite parent bodies, giving rise to observed hydrous alterations.

Effect of osmotic dehydration of olives as pre-fermentation treatment and partial substitution of sodium chloride by monosodium glutamate in the fermentation profile of Kalamata natural black olives.

PubMed

Bonatsou, Stamatoula; Iliopoulos, Vasilis; Mallouchos, Athanasios; Gogou, Eleni; Oikonomopoulou, Vasiliki; Krokida, Magdalini; Taoukis, Petros; Panagou, Efstathios Z

2017-05-01

This study examined the effect of osmotic dehydration of Kalamata natural black olives as pre-fermentation treatment in combination with partial substitution of NaCl by monosodium glutamate (MSG) on the fermentation profile of olives. Osmotic dehydration was undertaken by immersing the olives in 70% (w/w) glucose syrup overnight at room temperature. Further on, three different mixtures of NaCl and MSG with/without prior osmotic dehydration of olives were investigated, namely (i) 6.65% NaCl - 0.35% MSG (5% substitution), (ii) 6.30% NaCl - 0.70% MSG (10% substitution), (iii) 5.95% NaCl - 1.05% MSG (15% substitution), and (iv) 7% NaCl without osmotic dehydration (control treatment). Changes in the microbial association (lactic acid bacteria [LAB], yeasts, Enterobacteriaceae), pH, titratable acidity, organic acids, sugars, and volatile compounds in the brine were analyzed for a period of 4 months. The final product was subjected to sensory analysis and the content of MSG in olives was determined. Results demonstrated that osmotic dehydration of olives prior to brining led to vigorous lactic acid processes as indicated by the obtained values of pH (3.7-4.1) and acidity (0.7-0.8%) regardless of the amount of MSG used. However, in non-osmotically dehydrated olives, the highest substitution level of MSG resulted in a final pH (4.5) that was beyond specification for this type of olives. MSG was degraded in the brines being almost completely converted to γ-aminobutyric acid (GABA) at the end of fermentation. Finally, the sensory assessment of fermented olives with/without osmotic dehydration and at all levels of MSG did not show any deviation compared to the control treatment. Copyright © 2016 Elsevier Ltd. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2017-04-01

Voluminous low-T granite: fluid present partial melting of the crust? Martin Hand(1), Karin Barovich(1), Laura Morrissey(1), Vicki Lau(1), Kiara Bockmann(1), David Kelsey(1), Megan Williams(1) (1) Department of Earth Sciences, University of Adelaide, Adelaide, Australia Two general schools of thought exist for the formation of granites from predominantly crustal sources. One is that large-scale anatexis occurs via fluid-absent partial melting. This essentially thermal argument is based on the reasonable premise that the lower crust is typically fluid depleted, and experimental evidence which indicates that fluid-absent partial melting can produce significant volumes of melt, creating compositionally depleted residua that many believe are recorded by granulite facies terranes. The other school of thought is that large-scale anatexis can occur via fluid-fluxed melting. This essentially compositional-based contention is also supported by experimental evidence which shows that fluid-fluxed melting is efficient, including at temperatures not much above the solidus. However, generating significant volumes of melt at low temperatures requires a large reservoir of fluid. If fluid-fluxed melting is a realistic model, the resultant granites should be comparatively low temperature compared to those derived from predominantly fluid-absent partial melting. Using a voluminous suite of aluminous granites in the Aileron Province in the North Australian Craton together with metasedimentary granulites as models for source behaviour, we evaluate fluid-absent verse fluid-present regimes for generating large volumes of crustally-derived melt. The central Aileron Province granites occupy 32,500km2, and in places are in excess of 8 km thick. They are characterised by abundant zircon inheritance that can be matched with metasedimentary successions in the region, suggesting they were derived in large part from melting of crust similar to that presently exposed. A notable feature of many of the granites is their enriched Th concentrations compared to typical Aileron Province sub solidus metapelitic successions. However, based on continuous transects within metasedimentary rocks from a number of different regions that record transitions from sub-solidus assemblages to supra-solidus rocks petrologically characterised by typical fluid-absent peritectic assemblages (central Aileron Province, Broken Hill Zone, Ivrea-Verbano Zone), fluid-absent partial melting does not deplete Th concentrations in the residuum with respect to their sub-solidus protoliths. If these compositional transects are used as a guide to the general behaviour of Th during fluid-absent partial melting, the voluminous Th-enriched granites in the Aileron Province are unlikely to be the products of fluid-absent partial melting. This contention is supported by phase equilibria modelling of sub-solidus metasedimentary units whose detrital zircons match in age the granite-hosted xenocrysts, which indicate that temperatures in excess of 840°C are required to generate significant volumes (ie ≥ 30%) of melt under fluid-absent conditions. However, zircon saturation temperatures for the granites have a weighted mean of 776 ± 4 °C (n = 220). Because the granites contain abundant inheritance, this is an upper-T limit that also suggests fluid-absent partial melting was not the primary mechanism for granite formation. We suggest that voluminous granite formation in the Aileron Province occurred in a fluid-rich regime that was particularly effective at destabilising monazite and liberating Th into melt. Because of the propensity of monazite to destabilise in the presence of fluid, we suggest that high-grade metasedimentary terrains that are notably depleted in Th may be residuum associated with fluid-fluxed melt loss.

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.

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 planar and no channels develop. However, if the melt migration velocity exceeds ˜5 μm/s the reaction layer locally protrudes into the partially molten rock forming finger-like melt-rich channels. The morphology and spacing of the channels depends on the initial melt fraction. With 20 vol% melt, multiple and voluminous channels with an elliptical core formed of pure melt develop. At lower melt contents, fewer and thinner channels develop. Our experiments demonstrate that melt-rock reactions can lead to melt channelization in mantle lithologies. The morphology of the channels seems to depend on the initial permeability perturbations present in the starting material. The observed lithological transformations are in broad agreement with natural observations. However, the resulting channels lack the tabular anastomozing shapes which are likely caused by shear deformation in nature. Therefore, both reaction-driven as well as stress-driven melt segregation have to interact in nature to form the observed dunite channels. Szymczak, P., and A. J. C. Ladd (2014), Reactive-infiltration instabilities in rocks. Part 2. Dissolution of a porous matrix, J. Fluid Mech., 738, 591-630. Pec, M., B. K. Holtzman, M. Zimmerman, and D. L. Kohlstedt (2015), Reaction infiltration instabilities in experiments on partially molten mantle rocks, Geology, 43(7), 575-578, doi:10.1130/G36611.1.

The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England

NASA Astrophysics Data System (ADS)

Simons, B.; Shail, Robin K.; Andersen, Jens C. Ø.

2016-09-01

The Early Permian Cornubian Batholith was generated during an extensional regime following Variscan convergence within the Rhenohercynian Zone of SW England. Its component granites can be classified, using mineralogical, textural and geochemical criteria, into five main types, all of which are peraluminous (A/CNK > 1.1): G1 (two-mica), G2 (muscovite), G3 (biotite), G4 (tourmaline) and G5 (topaz). G1 granites formed through up to 20% muscovite and minor biotite dehydration melting of a metagreywacke source at moderate temperatures and pressures (731-806 °C, > 5 kbar). Younger G3 granites formed through higher temperature, lower pressure (768-847 °C, < 4 kbar) biotite-dominated melting of a similar source. Partial melting was strongly influenced by the progressive lower-mid crustal emplacement of mafic igneous rocks during post-Variscan extension and a minor (< 5%-10%) mantle-derived component in the granites is possible. Two distinct fractionation series, G1-G2 and G3-G4, are defined using whole-rock geochemical and mineral chemical data. Variations in the major elements, Ba, Sr and Rb indicate that G1 and G3 granites underwent 15%-30% fractionation of an assemblage dominated by plagioclase, alkali feldspar and biotite to form more evolved G2 and G4 granites, respectively. Decreasing whole-rock abundances of Zr, Th and REE support the fractionation of zircon, monazite, apatite and allanite. Subsolidus alteration in G2 and G4 granites is indicated by non-primary muscovite and tourmaline and modification of major and trace element trends for G3-G4 granites, particularly for P2O5 and Rb. Topaz (G5) granites show low Zr, REE and extreme enrichment in Rb (up to 1530 ppm) and Nb (79 ppm) that cannot be related in a straightforward manner to continued differentiation of the G1-G2 or G3-G4 series. Instead, they are considered to represent partial melting, mediated by granulite facies fluids, of a biotite-rich restite following extraction of G1 and/or G3 magmas; they do not exhibit the typical geochemical characteristics of intraplate A-type granites.

Geochemical constraints on adakites of different origins and copper mineralization

USGS Publications Warehouse

Sun, W.-D.; Ling, M.-X.; Chung, S.-L.; Ding, X.; Yang, X.-Y.; Liang, H.-Y.; Fan, W.-M.; Goldfarb, R.; Yin, Q.-Z.

2012-01-01

The petrogenesis of adakites holds important clues to the formation of the continental crust and copper ?? gold porphyry mineralization. However, it remains highly debated as to whether adakites form by slab melting, by partial melting of the lower continental crust, or by fractional crystallization of normal arc magmas. Here, we show that to form adakitic signature, partial melting of a subducting oceanic slab would require high pressure at depths of >50 km, whereas partial melting of the lower continental crust would require the presence of plagioclase and thus shallower depths and additional water. These two types of adakites can be discriminated using geochemical indexes. Compiled data show that adakites from circum-Pacific regions, which have close affinity to subduction of young hot oceanic plate, can be clearly discriminated from adakites from the Dabie Mountains and the Tibetan Plateau, which have been attributed to partial melting of continental crust, in Sr/Y-versus-La/Yb diagram. Given that oceanic crust has copper concentrations about two times higher than those in the continental crust, whereas the high oxygen fugacity in the subduction environment promotes the release of copper during partial melting, slab melting provides the most efficient mechanism to concentrate copper and gold; slab melts would be more than two times greater in copper (and also gold) concentrations than lower continental crust melts and normal arc magmas. Thus, identification of slab melt adakites is important for predicting exploration targets for copper- and gold-porphyry ore deposits. This explains the close association of ridge subduction with large porphyry copper deposits because ridge subduction is the most favorable place for slab melting. ?? 2012 by The University of Chicago.

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.

Experimental test of the viscous anisotropy hypothesis for partially molten rocks

PubMed Central

Qi, Chao; Kohlstedt, David L.; Katz, Richard F.; Takei, Yasuko

2015-01-01

Chemical differentiation of rocky planets occurs by melt segregation away from the region of melting. The mechanics of this process, however, are complex and incompletely understood. In partially molten rocks undergoing shear deformation, melt pockets between grains align coherently in the stress field; it has been hypothesized that this anisotropy in microstructure creates an anisotropy in the viscosity of the aggregate. With the inclusion of anisotropic viscosity, continuum, two-phase-flow models reproduce the emergence and angle of melt-enriched bands that form in laboratory experiments. In the same theoretical context, these models also predict sample-scale melt migration due to a gradient in shear stress. Under torsional deformation, melt is expected to segregate radially inward. Here we present torsional deformation experiments on partially molten rocks that test this prediction. Microstructural analyses of the distribution of melt and solid reveal a radial gradient in melt fraction, with more melt toward the center of the cylinder. The extent of this radial melt segregation grows with progressive strain, consistent with theory. The agreement between theoretical prediction and experimental observation provides a validation of this theory. PMID:26417107

Experimental test of the viscous anisotropy hypothesis for partially molten rocks.

PubMed

Qi, Chao; Kohlstedt, David L; Katz, Richard F; Takei, Yasuko

2015-10-13

Chemical differentiation of rocky planets occurs by melt segregation away from the region of melting. The mechanics of this process, however, are complex and incompletely understood. In partially molten rocks undergoing shear deformation, melt pockets between grains align coherently in the stress field; it has been hypothesized that this anisotropy in microstructure creates an anisotropy in the viscosity of the aggregate. With the inclusion of anisotropic viscosity, continuum, two-phase-flow models reproduce the emergence and angle of melt-enriched bands that form in laboratory experiments. In the same theoretical context, these models also predict sample-scale melt migration due to a gradient in shear stress. Under torsional deformation, melt is expected to segregate radially inward. Here we present torsional deformation experiments on partially molten rocks that test this prediction. Microstructural analyses of the distribution of melt and solid reveal a radial gradient in melt fraction, with more melt toward the center of the cylinder. The extent of this radial melt segregation grows with progressive strain, consistent with theory. The agreement between theoretical prediction and experimental observation provides a validation of this theory.

Hydrous partial melting in the sheeted dike complex at fast spreading ridges: experimental and natural observations

NASA Astrophysics Data System (ADS)

France, Lydéric; Koepke, Juergen; Ildefonse, Benoit; Cichy, Sarah B.; Deschamps, Fabien

2010-11-01

In ophiolites and in present-day oceanic crust formed at fast spreading ridges, oceanic plagiogranites are commonly observed at, or close to the base of the sheeted dike complex. They can be produced either by differentiation of mafic melts, or by hydrous partial melting of the hydrothermally altered sheeted dikes. In addition, the hydrothermally altered base of the sheeted dike complex, which is often infiltrated by plagiogranitic veins, is usually recrystallized into granoblastic dikes that are commonly interpreted as a result of prograde granulitic metamorphism. To test the anatectic origin of oceanic plagiogranites, we performed melting experiments on a natural hydrothermally altered dike, under conditions that match those prevailing at the base of the sheeted dike complex. All generated melts are water saturated, transitional between tholeiitic and calc-alkaline, and match the compositions of oceanic plagiogranites observed close to the base of the sheeted dike complex. Newly crystallized clinopyroxene and plagioclase have compositions that are characteristic of the same minerals in granoblastic dikes. Published silicic melt compositions obtained in classical MORB fractionation experiments also broadly match the compositions of oceanic plagiogranites; however, the compositions of the coexisting experimental minerals significantly deviate from those of the granoblastic dikes. Our results demonstrate that hydrous partial melting is a likely common process in the root zone of the sheeted dike complex, starting at temperatures exceeding 850°C. The newly formed melt can either crystallize to form oceanic plagiogranites or may be recycled within the melt lens resulting in hybridized and contaminated MORB melts. It represents the main MORB crustal contamination process. The residue after the partial melting event is represented by the granoblastic dikes. Our results support a model with a dynamic melt lens that has the potential to trigger hydrous partial melting reactions in the previously hydrothermally altered sheeted dikes. A new thermometer using the Al content of clinopyroxene is also elaborated.

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.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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 largelymore » 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.« less

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

NASA Astrophysics Data System (ADS)

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

2005-12-01

The mass of carbon stored in the mantle exceeds that in all other Earth's reservoirs combined1 and large fluxes of carbon are cycled into and out of the mantle via subduction and volcanic emission. Outgassing of CO2 from the mantle has a critical influence on Earth's climate for time scales of 108-109 yr1. The residence time for carbon in the mantle is thought to exceed the age of the Earth1,2, but it could be significantly less owing to pervasive deep melting beneath oceanic ridges. The chief flux of subducted carbon is via carbonate in altered ocean-floor basalts, which survives dehydration during subduction. Because solidi of carbonated eclogite remain hotter than average subduction geotherms at least up to transition zone3, significant subducted C is delivered to the deep Earth. In upwelling mantle, however, partial melting of carbonated eclogite releases calcio-dolomitic carbonatite melt at depths near ~400 km and metasomatically implants carbonate to surrounding peridotite. Thus, volcanic release of CO2 to basalt source regions is controlled by the solidus of carbonated peridotite. We conducted experiments with nominally anhydrous, carbonated garnet lherzolite (PERC: MixKLB-1+2.5 wt.% CO2) using Pt/C capsules in piston cylinder (3 GPa) and Walker-style multi-anvil presses (4 to 10 GPa) and between 1075-1500 °C. The stable near-solidus crystalline carbonate is dolomitess at 3 GPa and magnesitess from 4 to 10 GPa. Carbonate melt is stabilized at the solidus and crystalline carbonate disappears within 20-60°. The solidus increases from ≥1075 °C at 3 GPa to 1110-1140 °C at 4.1 GPa as the stable carbonate transforms from dolomitess to magnesitess. From 4.1 GPa, the solidus of PERC magnesite lherzolite increases to ~1500 °C at 10 GPa. In upwelling mantle the solidus of carbonated lherzolite is ~100-200 km shallower than that of eclogite+CO2, but beneath oceanic ridges, initial melting occurs as deep as 300-330 km. For peridotite with ~120-1200 ppm CO2, this initial melting yields 0.03-0.3% carbonatite melt. Extraction of such melts from the mantle above 300 km implies residence times of 1 to 4 Gyr for carbon and other highly incompatible elements in the convecting mantle. Such short residence times suggest that large fractions of mantle carbon must be recycled rather than primordial. Implied CO2 fluxes are 0.12-3.4 × 1015 g/yr, which matches or exceeds direct estimates for CO2 fluxes at ridges (0.04-0.66 × 1015 g/yr)1,4. However, not all of this deep extracted CO2 may reach ridges; some may instead be implanted into oceanic lithosphere, providing a widespread source for metasomatic fluids highly enriched in incompatible elements. 1Sleep, N. H. and Zahnle, K. 2001, JGR 106, 1373-1399. 2Zhang, Y. and Zindler, A. 1993, EPSL 117, 331-345. 3Dasgupta et al. 2004, EPSL 227, 73-85. 4Javoy, M. and Pineau, F. 1991, EPSL 107, 598-611.

Evidence for Impact Shock Melting in CM and CI Chondrite Regolith Samples

NASA Technical Reports Server (NTRS)

Zolensky, Michael; Mikouchi, Takashi; Hagiya, Kenji; Ohsumi, Kazumasa; Komatsu, Mutsumi; Le, Loan

2014-01-01

C class asteroids frequently exhibit reflectance spectra consistent with thermally metamorphosed carbonaceous chondrites, or a mixture of phyllosilicate-rich material along with regions where they are absent. One particularly important example appears to be near-Earth asteroid 1999 JU3, the target of the Hayabusa II sample return mission [1], although not all spectra indicate this. In fact most spectra of 1999 JU3 are featureless, suggesting a heterogeneous regolith. Here we explore an alternative cause of dehydration of regolith of C class asteroids - impact shock melting. Impact shock melting has been proposed to explain some mineralogical characteristics of CB chondrites, but has not been considered a major process for hydrous carbonaceous chondrites. What evidence is there for significant shock melting in the very abundant CMs, or less abundant but still important CI chondrites?

Seismic evidence for water transport out of the mantle transition zone beneath the European Alps

NASA Astrophysics Data System (ADS)

Liu, Zhen; Park, Jeffrey; Karato, Shun-ichiro

2018-01-01

The mantle transition zone has been considered a major water reservoir in the deep Earth. Mass transfer across the transition-zone boundaries may transport water-rich minerals from the transition zone into the water-poor upper or lower mantle. Water release in the mantle surrounding the transition zone could cause dehydration melting and produce seismic low-velocity anomalies if some conditions are met. Therefore, seismic observations of low-velocity layers surrounding the transition zone could provide clues of water circulation at mid-mantle depths. Below the Alpine orogen, a depressed 660-km discontinuity has been imaged clearly using seismic tomography and receiver functions, suggesting downwellings of materials from the transition zone. Multitaper-correlation receiver functions show prominent ∼0.5-1.5% velocity reductions at ∼750-800-km depths, possibly caused by partial melting in the upper part of lower mantle. The gap between the depressed 660-km discontinuity and the low-velocity layers is consistent with metallic iron as a minor phase in the topmost lower mantle reported by laboratory studies. Velocity drops atop the 410-km discontinuity are observed surrounding the Alpine orogeny, suggesting upwelling of water-rich rock from the transition zone in response to the downwelled materials below the orogeny. Our results provide evidence that convective penetration of the mantle transition zone pushes hydrated minerals both upward and downward to add hydrogen to the surrounding mantle.

Intermediate-depth earthquakes within young Cocos plate beneath Central Mexico: A hypothesis test for dehydration embrittlement and shear instability

NASA Astrophysics Data System (ADS)

Song, T.

2010-12-01

Subducting slab undergoes a series of dehydration reactions on their ways into the mantle and these processes are responsible for transporting water, recycling volatiles and chemical elements in arc magmas. It is generally accepted that the SOC is hydrated. However, it is not clear if subducting oceanic mantle (SOM) is hydrated and how deep the hydration is. Seismic refraction studies found that normal-fault type faulting can extend 12-20 km deep into the interior of the slab off Nicaragua, suggesting deep hydration of the SOM. Seismic refraction studies also found that the uppermost SOM is seismically slow and is partially serpentinized. The fluids released from dehydration inside the SOM can reduce the normal stress locally and facilitate the occurrences of intra-slab events through dehydration embrittlement and hydraulic fracture. It has been suggested that the dehydration of antigorite at about 600C is particularly important in facilitating the lower plane of the double seismic zone. To link the dehydration process to the occurrences of intra-slab events, it is critical to clarify where these events are located, either located at the dehydration boundary or in the neighborhood rocks. However, if the SOM is anhydrous, other mechanism, such as shear instabilities, has to be invoked to explain the occurrences of intermediate-depth intraslab earthquakes. Here I discuss locations of intermediate-depth intraslab earthquakes in Central Mexico subduction zone, where young Cocos plate subducts beneath North America plate. Recent studies involving local converted wave modeling and receiver function analysis indicate the presence of an ultra-slow velocity layer (USL) of about 3 km thick, likely an over-pressured upper oceanic crust. Most events display anomalously large converted SP waves that are 2-2.5 secs after direct P waves and finite difference modeling converge the location of these events about 9 km below the lower boundary USL. With a lower oceanic crust of about 3-5 km estimated from receiver function, these intermediate-depth earthquakes are about 6 km inside the SOM. There is no clear evidence yet indicating the presence of a partially serpentinized layer in such a young plate (10-15 Ma). Further waveform modeling is undertaken to explore the presence of such a partially serpentinized layer.

The Role of Brines in the Fluid Induced Dehydration of the Mafic Lower Crust from Amphibolite to Granulite Grade: Nature and Experiment

NASA Astrophysics Data System (ADS)

Harlov, D. E.

2016-12-01

Natural evidence for the role of low H2O activity fluids (CO2 or concentrated brines) in the dehydration of H2O-rich, mafic amphibolite-facies rocks to H2O-poor, Opx-bearing granulite-facies rocks (700-900 °C and 500-1000 MPa) for both highly localised dehydration zones (CO2; cm's) (Harlov et al. 2006, J Petrol, 47, 3) as well as regional terranes (NaCl-KCl brines; km's) (Harlov and Förster 2002, J Petrol, 43, 769; Hansen and Harlov 2007, 48, 1641) include the presence of Kfs micro-veins along Qtz-Plg grain boundaries; Plg grains metasomatised in a K-rich fluid; Mnz and/or Xn inclusions in the FAp grains; Bt enriched in Ti, F, and Cl; and FAp enriched in Cl and F. These features are not seen in the "source" amphibolite facies terrane along the same traverse. When log(fHF/fH2O) for either Bt or FAp is plotted as a function of the distance from the fluid/heat source, a uniform decrease in log(fHF/fH2O) is observed across the granulite to amphibolite facies traverse suggesting the presence of a uniform low H2O activity uniform fluid front. Dehydration experiments (900 °C; 1000 MPa; 3 weeks; Au capsule; quenched) involving a cylinder of natural tonalitic Bt gneiss (Plg, Qtz, Bt) (220 mg) and a concentrated KCl brine (20-30 % H2O; 70-80 % KCl) (8 mg) placed at the base of the cylinder have been conducted in the piston cylinder apparatus (CaF2 setup). Micro-veins primarily of Kfs, with some evidence of partial melting, formed along Qtz/Plg grain boundaries though only where Bt and Qtz were in contact. Here the Bt reacted with Qtz to form numerous small Opx and Cpx grains as well as minor Ilm from the 2-3 wt % of TiO2 present in the Bt. The two principle reactions responsible for both the formation of the Kfs micro-veins as well as the pyroxenes include: (1) An (in Plg) + Qtz + KCl (in fluid) = Kfs + CaCl2 (in fluid) and (2) Bt + Qtz = Opx + Kfs + H2O. The same experiment performed under the same P-T conditions involving either a concentrated NaCl brine (20-30 % H2O; 70-80 % NaCl) or a CO2-rich fluid (80 % CO2, 20 % H2O) or a fluid absent dry melt resulted in micro-veins approximating a granitic composition along Qtz/Plg grain boundaries with numerous small Opx grains minor Ilm forming along biotite grain boundaries, again only when the Bt and Qtz were in contact. Due to an absence of KCl in these three cases, only reaction (2) was relevant.

Identification of mothball powder composition by float tests and melting point tests.

PubMed

Tang, Ka Yuen

2018-07-01

The aim of the study was to identify the composition, as either camphor, naphthalene, or paradichlorobenzene, of mothballs in the form of powder or tiny fragments by float tests and melting point tests. Naphthalene, paradichlorobenzene and camphor mothballs were blended into powder and tiny fragments (with sizes <1/10 of the size of an intact mothball). In the float tests, the mothball powder and tiny fragments were placed in water, saturated salt solution and 50% dextrose solution (D50), and the extent to which they floated or sank in the liquids was observed. In the melting point tests, the mothball powder and tiny fragments were placed in hot water with a temperature between 53 and 80 °C, and the extent to which they melted was observed. Both the float and melting point tests were then repeated using intact mothballs. Three emergency physicians blinded to the identities of samples and solutions visually evaluated each sample. In the float tests, paradichlorobenzene powder partially floated and partially sank in all three liquids, while naphthalene powder partially floated and partially sank in water. Naphthalene powder did not sink in D50 or saturated salt solution. Camphor powder floated in all three liquids. Float tests identified the compositions of intact mothball accurately. In the melting point tests, paradichlorobenzene powder melted completely in hot water within 1 min while naphthalene powder and camphor powder did not melt. The melted portions of paradichlorobenzene mothballs were sometimes too small to be observed in 1 min but the mothballs either partially or completely melted in 5 min. Both camphor and naphthalene intact mothballs did not melt in hot water. For mothball powder, the melting point tests were more accurate than the float tests in differentiating between paradichlorobenzene and non-paradichlorobenzene (naphthalene or camphor). For intact mothballs, float tests performed better than melting point tests. Float tests can identify camphor mothballs but melting point tests cannot. We suggest melting point tests for identifying mothball powder and tiny fragments while float tests are recommended for intact mothball and large fragments.

On the Preservation of Intergranular Coesite in UHP Eclogite at Yangkou Bay, Sulu belt of eastern China

NASA Astrophysics Data System (ADS)

Wang, L.; Wang, S.; Brown, M.

2016-12-01

In contrast to coesite that occurs as inclusions in zircon and rock-forming minerals, intergranular coesite is preserved in UHP eclogite at Yangkou in the Sulu belt. The survival of intergranular coesite is intriguing because the eclogite experienced phengite growth and partial melting during exhumation. The coesite eclogite occurs as rootless isoclinal fold noses within quartz-rich schist which contains 10-20 vol% phengite, whereas phengite is absent from coesite eclogite in the fold noses. To evaluate the factors that control preservation of intergranular coesite, four samples representative of different stages along the retrograde P-T path were selected for study. For each sample we determined the number of intergranular coesite grains per cm2 and the OH content of garnet and omphacite. As the number of coesite grains decreases, the bulk rock OH content increases from <200 ppm in phengite-free coesite eclogite to 200-260 ppm in phengite-bearing (<5 vol%) coesite eclogite and up to a maximum of 430-438 ppm in quartz eclogite ( 10 vol% phengite). However, the OH content drops to a minimum of 59 ppm in residual eclogite resulting from melt drainage. This trend implies that the volume of fluid increased sufficiently during exhumation to facilitate the growth of phengite and the transformation to quartz of intergranular coesite outside of the fold noses. The fluid is inferred to have been a supercritical fluid probably residual from prograde dehydration but also derived by dissolution of nominally anhydrous minerals. Post-metamorphic-peak deformation combined with fluid percolation along sheared fold limbs induced phengite growth during initial exhumation and then facilitated partial melting. In contrast, fold hinges in competent layers are unfavourable sites for fluid penetration. At Yangkou, the intergranular coesite is preserved in the fold noses where it was protected from both penetrative deformation and fluid ingress. Therefore, the fold noses maintained a relatively dry environment that allowed preservation of the intergranular coesite. Thus, deformation partitioning and strain localization impose local controls on fluid distribution and migration in UHP eclogite. This study informs our understanding of variations in fluid regime during exhumation of deeply subducted continental crust.

Tectonic Mechanism for the Mid-Cretaceous - Early Paleogene Intraplate Magmatism from the Gulf of Mexico to Northwestern Canada

NASA Astrophysics Data System (ADS)

Liu, Y.; Murphy, M. A.; Snow, J. E.; van Wijk, J.; Cannon, J. M.; Parsons, C.

2017-12-01

Tectonic mechanisms have remained controversial for a number of intraplate igneous suites of mid-Cretaceous - early Paleogene age across North America. They span the northern Gulf of Mexico (GoM), through Arkansas and Kansas in the US, to Saskatchewan and Northwestern Territories in Canada, resembling a belt that is located 1000+ km inboard from, and aligned sub-parallel to, the western margin of North America. The northern GoM magmatism is characterized by lamproites, carbonatites, nephelinites, with other alkaline rocks, whereas the rest igneous provinces are dominated by kimberlites. Their geochemical signatures, in general, point to a sub-lithospheric mantle origin. Hypotheses that explain the tectonic origin of these magmatic rocks include: (1) hotspots and mantle plumes, (2) edge-driven convection, (3) lithospheric reactivation, and (4) low-angle subduction. Evaluation based on our integration of published geological and geophysical data shows that contradictions exist in each model between observations and predictions. To explain this plate-scale phenomenon, we propose that the Farallon slab may have stagnated within or around the mantle transition zone during the Early Cretaceous, with its leading edge reaching ca. 1600 km inland beneath the North American plate. Dehydration and decarbonation of the slab produces sporadic, dense, low-degree partial melts at the mantle transition zone depths. As the slab descends into the lower mantle, Rayleigh-Taylor instabilities are induced at slab edges, causing passive upwelling that brings alkali-rich carbonate silicate melts to the base of the overriding plate. Subsequently, the North American lithosphere with varying thicknesses, discontinuities, and compositions interacts with the rising partial melts, generating a spectrum of igneous rocks. Fragments of the once-stagnated slab may still be detectable in the lower mantle beneath eastern US in seismic tomography models. This study highlights a profound plate-scale relationship between the intraplate magmatism and the subduction factory down to the transition zone depth, and anticipates future discoveries of kimberlites, potentially diamondiferous, in the mid-west of the North American continent.

Petrogenesis and tectonic implications of the Yadong leucogranites, southern Himalaya

NASA Astrophysics Data System (ADS)

Gou, Zhengbin; Zhang, Zeming; Dong, Xin; Xiang, Hua; Ding, Huixia; Tian, Zuolin; Lei, Hengcong

2016-07-01

The leucogranites in the Higher Himalayan Sequence (HHS) provide a probe to elucidate the crustal melting of continental collisional orogen. An integrated geochemical and geochronological study of the Yadong leucogranites, southern Himalaya, shows that these rocks have relatively high SiO2 contents of 69.77 to 75.32 wt.% and alumina saturation index (A/CNK) of 1.09-1.40, typical of peraluminous granites. They show moderately fractionated REE patterns with negative Eu anomalies, and are characterized by enriched LILE (Rb and Cs) and depleted HFSE (Zr, Hf, Nb and Ta). LA-ICP-MS U-Pb zircon dating of ten samples yields crystallization ages ranging from 21.0 to 11.7 Ma. The zircons have variable εHf(t) values of - 26.3 to - 3.5 and corresponding Hf two-stage model ages of 2.77-1.33 Ga. The present study reveals that the muscovite-biotite leucogranites (2ML) have higher TiO2, MgO, CaO, Sr, Ba and Zr contents, lower Rb/Sr ratios than the tourmaline-muscovite leucogranites (TML). Zircon and monazite saturation thermometry results show that the melt temperatures (681-784 °C) of the 2ML are 20-80 °C higher than those (663-705 °C) of the TML. Combining with previous results, we propose that the TML were derived from the muscovite-dehydration melting, whereas the 2ML dominantly resulted from the biotite-dehydration melting during the prograde metamorphism of the pelitic and felsic granulites of the HHS. Therefore, the Himalayan leucogranites were probably formed during the subduction of the Indian crust following the India and Asia collision.

The density, compressibility and seismic velocity of hydrous melts at crustal and upper mantle conditions

NASA Astrophysics Data System (ADS)

Ueki, K.; Iwamori, H.

2015-12-01

Various processes of subduction zone magmatism, such as upward migration of partial melts and fractional crystallization depend on the density of the hydrous silicate melt. The density and the compressibility of the hydrous melt are key factors for the thermodynamic calculation of phase relation of the hydrous melt, and the geophysical inversion to predict physicochemical conditions of the melting region based on the seismic velocity. This study presents a new model for the calculations of the density of the hydrous silicate melts as a function of T, P, H2O content and melt composition. The Birch-Murnaghan equation is used for the equation of state. We compile the experimentally determined densities of various hydrous melts, and optimize the partial molar volume, compressibility, thermal expansibility and its pressure derivative, and K' of the H2O component in the silicate melt. P-T ranges of the calibration database are 0.48-4.29 GPa and 1033-2073 K. As such, this model covers the P-T ranges of the entire melting region of the subduction zone. Parameter set provided by Lange and Carmichael [1990] is used for the partial molar volume and KT value of the anhydrous silicate melt. K' of anhydrous melt is newly parameterized as a function of SiO2 content. The new model accurately reproduces the experimentally determined density variations of various hydrous melts from basalt to rhyolite. Our result shows that the hydrous melt is more compressive and less dense than the anhydrous melt; with the 5 wt% of H2O in melt, density and KT decrease by ~10% and ~30% from those of the anhydrous melt, respectively. For the application of the model, we calculated the P-wave velocity of the hydrous melt. With the 5 wt% of H2O, P-wave velocity of the silicate melt decreases by >10%. Based on the melt P-wave velocity, we demonstrate the effect of the melt H2O content on the seismic velocity of the partially molten zone of the subduction zone.

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 lithologic melt partitioning in our samples, we digitally segment each grain and then fit a sample window, slightly larger than the grain, to calculate the local melt volume fraction. Our results show strong evidence for lithologic partitioning in partially molten harzburgite systems, in a ~2 to 1 ratio of local melt fraction, between olivine and opx across the range of melt fractions tested. We also present permeability, grain size, and connectivity analyses of our samples in order to evaluate the effects of melt partitioning on melt migration rates at mid-ocean ridges, as well as at other locations in the Earth where partial melting occurs. References Watson, E. B. (1999), Lithologic partitioning of fluids and melts, American Minerologist, 84, 1693-1710. Zhu, W., and G. Hirth (2003), A network model for permeability in partially molten rocks, Earth Planet. Sci. Lett., 212(3-4), 407-416, doi:10.1016/S0012-821X(03)00264-4. Zhu, W., G. A. Gaetani, F. Fusseis, L. G. J. Montési, and F. De Carlo (2011), Microtomography of partially molten rocks: three-dimensional melt distribution in mantle peridotite, Science, 332(6025), 88-91, doi:10.1126/science.1202221.

Observations on saliva osmolality during progressive dehydration and partial rehydration.

PubMed

Taylor, Nigel A S; van den Heuvel, Anne M J; Kerry, Pete; McGhee, Sheena; Peoples, Gregory E; Brown, Marc A; Patterson, Mark J

2012-09-01

A need exists to identify dehydrated individuals under stressful settings beyond the laboratory. A predictive index based on changes in saliva osmolality has been proposed, and its efficacy and sensitivity was appraised across mass (water) losses from 1 to 7%. Twelve euhydrated males [serum osmolality: 286.1 mOsm kg(-1) H(2)O (SD 4.3)] completed three exercise- and heat-induced dehydration trials (35.6°C, 56% relative humidity): 7% dehydration (6.15 h), 3% dehydration (with 60% fluid replacement: 2.37 h), repeat 7% dehydration (5.27 h). Expectorated saliva osmolality, measured at baseline and at each 1% mass change, was used to predict instantaneous hydration state relative to mass losses of 3 and 6%. Saliva osmolality increased linearly with dehydration, although its basal osmolality and its rate of change varied among and within subjects across trials. Receiver operating characteristic curves indicated a good predictive power for saliva osmolality when used with two, single-threshold cutoffs to differentiate between hydrated and dehydrated individuals (area under curve: 3% cutoff = 0.868, 6% cutoff = 0.831). However, when analysed using a double-threshold detection technique (3 and 6%), as might be used in a field-based monitor, <50% of the osmolality data could correctly identify individuals who exceeded 3% dehydration. Indeed, within the 3-6% dehydration range, its sensitivity was 64%, while beyond 6% dehydration, this fell to 42%. Therefore, while expectorated saliva osmolality tracked mass losses within individuals, its large intra- and inter-individual variability limited its predictive power and sensitivity, rendering its utility questionable within a universal dehydration monitor.

Partial melting kinetics of plagioclase-diopside pairs

NASA Astrophysics Data System (ADS)

Tsuchiyama, Akira

1985-09-01

Partial melting experiments on plagioclase (An60) and diopside have been carried out using pairs of large crystals to investigate textures and kinetics of melting. The experiments were done at one atmosphere pressure as a function of temperature (1,190 1,307° C) and time (1.5 192 h). Melting took place mainly at the plagioclase-diopside contact planes. Reaction zones composed of fine mixtures of calcic plagioclase and melt were developed from the surface of the plagioclase crystal inward. There exists a critical temperature, below which only a few % melting can occur over the duration of the experiments. This sluggish melting is caused by slow NaSi-CaAl diffusion in plagioclase, because the plagioclase crystal must change its composition to produce albite-rich cotectic melts. Diffusion in the solid also affects the chemical composition of the melts. During initial melting, potassium is preferentially extracted from plagioclase because K-Na diffusion in plagioclase is faster than that of NaSi-CaAl. This also causes a shift in the cotectic compositions. Above the “critical temperature”, on the other hand, melting is promoted by a metastable reaction in which the plagioclase composition does not change, and which produces melts with compositional gradients along the original An60-diopside tie line. The critical temperature is determined by the intersection of the cotectic and the An60-diopside tie line. Interdiffusion coefficients of plagioclase-diopside components in the melt are estimated from melting rates above the critical temperature by using a simplified steady-state diffusion model (e.g., 10-8 cm2/sec at 1,300° C). Many examples of reaction zones due to partial melting have been described as spongy or fingerprint-like textures in xenoliths. Metastable melting above the critical temperature is considered to take place in natural melting where there is a high degree of melting. However, we cannot exclude the possibility of disequilibrium created by sluggish melting controlled by diffusion in the minerals. If melting occurs close to the solidus, this process can be important even for partial melting in the upper mantle.

The Influence of Lithology on the Formation of Reaction Infiltration Instabilities in Mantle Rocks

NASA Astrophysics Data System (ADS)

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

2017-12-01

The formation of oceanic plates requires extraction of large volumes of melt from the mantle. Several lines of evidence suggest that melt extraction is rapid and, therefore, necessitates high-permeability pathways. Such pathways may form as a result of melt-rock reactions. We report the results of a series of Darcy-type experiments designed to study the development of channels due to melt-solid reactions in mantle lithologies. We sandwiched a partially molten rock between a melt source and a porous sink and annealed it at high pressure (P = 300 MPa) and high temperatures (T = 1200° or 1250°C) with a controlled pressure gradient (∂P/∂z = 0-100 MPa/mm). To study the influence of lithology on the channel formation, we synthesized partially molten rocks of harzburgitic (40:40:20 Ol - Opx - basalt), wehrlitic (40:40:20 Ol - Cpx - basalt) and lherzolitic (65:25:10 Ol - Opx - Cpx) composition. The melt source was a disk of alkali basalt. In all experiments, irrespective of the exact mineralogy, melt - undersaturated in silica - from the source dissolved pyroxene in the partially molten rock and precipitated olivine ( Fo82), thereby forming a dunite reaction layer at the interface between the source and the partially molten rock. In samples annealed under a small pressure gradient, the reaction layer was roughly planar. However, if the velocity of melt due to porous flow exceeded 0.1 µm/s, the reaction layer locally protruded into the partially molten rock forming finger-like, melt-rich channels in rocks of wehrlitic and harzburgitic composition. The lherzolitic rocks were generally impermeable to the melt except at highest-pressure gradients where a narrow fracture developed, forming a dyke which drained the melt reservoir. Three-dimensional reconstructions using micro-CT images revealed clear differences between the dyke (a narrow, through-going planar feature) and the channels formed by reactive infiltration (multiple sinuous finger-like features). Apparently, the fraction of soluble minerals together with the melt fraction in the partially molten rock control whether dykes or reactive channels develop. Our experiments demonstrate that melt-rock reactions can lead to channelization in mantle lithologies, and the observed lithological transformations broadly agree with those observed in nature

The Effect of CO2 on Partial Reactive Crystallization of MORB-Eclogite-derived Basaltic Andesite in Peridotite and Generation of Silica-Undersaturated Basalts

NASA Astrophysics Data System (ADS)

Mallik, A.; Dasgupta, R.

2012-12-01

Recycled oceanic crust (MORB-eclogite) is considered to be the dominant heterogeneity in Earth's mantle. Because MORB-eclogite is more fusible than peridotite, siliceous partial melt derived from it must react with peridotite while the latter is still in the subsolidus state. Thus, studying such reactive process is important in understanding melting dynamics of the Earth's mantle. Reaction of MORB-eclogite-derived andesitic partial melt with peridotite can produce alkalic melts by partial reactive crystallization but these melts are not as silica-undersaturated as many natural basanites, nephelinites or melititites [1]. In this study, we constrain how dissolved CO2 in a siliceous MORB-eclogite-derived partial melt affects the reaction phase equilibria involving peridotite and can produce nephelinitic melts. Here we compare experiments on CO2-free [1] and 2.6 wt.% CO2 bearing andesitic melt+lherzolite mixtures conducted at 1375 °C and 3 GPa with added melt fraction of 8-50 wt.%. In both CO2-free and CO2-bearing experiments, melt and olivine are consumed and opx and garnet are produced, with the extent of modal change for a given melt-rock ratio being greater for the CO2-bearing experiments. While the residue evolves to a garnet websterite by adding 40% of CO2-bearing melt, the residue becomes olivine-free by adding 50% of the CO2-free melt. Opx mode increases from 12 to ~55 wt.% for 0 to 40% melt addition in CO2-bearing system and 12 to ~43 wt.% for 0 to 50% melt addition in CO2-free system. Garnet mode, for a similar range of melt-rock ratio, increases from ~10 to ~15 wt.% for CO2 bearing system and to ~11 wt.% for CO2-free system. Reacted melts from 25-33% of CO2-bearing melt-added runs contain ~39 wt.% SiO2 , ~11-13 wt.% TiO2, ~9 wt.% Al2O3, ~11 wt.% FeO*, 16 wt.% MgO, 10-11 wt.% CaO, and 3 wt.% Na2O whereas experiments with a similar melt-rock ratio in a CO2-free system yield melts with 44-45 wt.% SiO2, 6-7 wt.% TiO2, 13-14 wt.% Al2O3, 10-11 wt.% FeO*, 12-13 wt.% MgO, ~8 wt.% CaO, and ~4 wt.% Na2O. Our study shows that with only 2.6 wt.% CO2, andesites, owing to partial reactive crystallization in a peridotite matrix, can evolve to nephelinites (as opposed to basanites for CO2-free runs) that match with silica-undersaturated oceanic basalts better than reacted melts from CO2-free conditions. The effects of CO2 on the partial reactive crystallization of andesite in a fertile peridotite matrix thus are: a) lowered melt- SiO2 owing to increased stability of opx at the liquidus of basalt, b) lowered Al2O3 content of basalts owing to increased crystallization of garnet. Experiments with 1 and 5 wt.% CO2-bearing andesite-peridotite mixture are underway and will be presented. [1] Mallik and Dasgupta (2012), EPSL, 329-330, 97-108.

On the time-scales of magmatism at island-arc volcanoes.

PubMed

Turner, S P

2002-12-15

Precise information on time-scales and rates of change is fundamental to an understanding of natural processes and the development of quantitative physical models in the Earth sciences. U-series isotope studies are revolutionizing this field by providing time information in the range 10(2)-10(4) years, which is similar to that of many modern Earth processes. I review how the application of U-series isotopes has been used to constrain the time-scales of magma formation, ascent and storage beneath island-arc volcanoes. Different elements are distilled-off the subducting plate at different times and in different places. Contributions from subducted sediments to island-arc lava sources appear to occur some 350 kyr to 4 Myr prior to eruption. Fluid release from the subducting oceanic crust into the mantle wedge may be a multi-stage process and occurs over a period ranging from a few hundred kyr to less than one kyr prior to eruption. This implies that dehydration commences prior to the initiation of partial melting within the mantle wedge, which is consistent with recent evidence that the onset of melting is controlled by an isotherm and thus the thermal structure within the wedge. U-Pa disequilibria appear to require a component of decompression melting, possibly due to the development of gravitational instabilities. The preservation of large (226)Ra disequilibria permits only a short period of time between fluid addition and eruption. This requires rapid melt segregation, magma ascent by channelled flow and minimal residence time within the lithosphere. The evolution from basalt to basaltic andesite probably occurs rapidly during ascent or in magma reservoirs inferred from some geophysical data to lie within the lithospheric mantle. The flux across the Moho is broadly andesitic, and some magmas subsequently stall in more shallow crustal-level magma chambers, where they evolve to more differentiated compositions on time-scales of a few thousand years or less.

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

NASA Technical Reports Server (NTRS)

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

1992-01-01

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

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 formation. Such models imply that the inner core may be somewhat older than models in which it crystallizes from a homogeneous outer core, although without any significant benefits for driving the geodynamo.

From Purgatory to Paradise: The Volatile Life of Hawaiian Magma

NASA Astrophysics Data System (ADS)

Marske, J. P.; Hauri, E. H.; Trusdell, F.; Garcia, M. O.; Pietruszka, A. J.

2014-12-01

Variations in radiogenic isotope ratios and magmatic volatile abundances (e.g., CO2 or H2O) in Hawaiian lavas reveal key processes within a deep-seated mantle plume (e.g., mantle heterogeneity, source lithology, partial melting, and magma degassing). Shield-stage Hawaiian lavas likely originate from a mixed plume source containing peridotite and recycled oceanic crust (pyroxenite) based on variations of radiogenic isotopes (e.g., 206Pb/204Pb). The mantle source region may also be heterogeneous with respect to volatile contents, yet the link between pre-eruptive volatile budgets and mantle source lithology in the Hawaiian plume is poorly constrained due to shallow magmatic degassing and mixing. Here, we use a novel approach to investigate this link using Os isotopic ratios, and major, trace, and volatile elements in olivines and mineral-hosted melt inclusions (MIs) from 34 samples from Koolau, Mauna Loa, Hualalai, Kilauea, and Loihi. These samples reveal a strong correlation between volatile contents in olivine-hosted MIs and Os isotopes of the same olivines, in which lavas that originated from greater proportions of recycled oceanic crust/pyroxenite (i.e. 'Loa' chain volcanoes: Koolau, Mauna Loa, Loihi) have MIs with the lower H2O, F, and Cl contents than 'Kea' chain volcanoes (i.e. Kilauea) that contain greater amounts of peridotite in the source region. No correlation is observed with CO2 or S. The depletion of fluid-mobile elements (H2O, F, and Cl) in 'Loa' chain volcanoes indicates ancient dehydrated oceanic crust is a plume component that controls much of the compositional variation of Hawaiian Volcanoes. The presence of dehydrated recycled mafic material in the plume source suggests that subduction effectively devolatilizes the mafic part of the oceanic crust. These results are similar to the observed shifts in H2O/Ce ratios near the Easter and Samoan hotspots [1,2]. Thus, it appears that multiple hotspots may record relative H2O depletions and possibly other volatiles. [1] Dixon et al. 2002, Nature 420:385-89 [2] Workman et al. 2006, EPSL 241:932-51

THE PRODUCTS OF THE CYCLIZING DEHYDRATION OF 1-BETA-PHENYLETHYLCYCLOHEXANOL-1 AND THE SYNTHESIS OF SPIROCYCLOHEXANE-1,1-INDANONE-3.

PubMed

Levitz, M; Perlman, D; Bogert, M T

1939-08-04

(1) Spirocyclohexane-1,1-indanone (VI) has been found among the oxidation products of the hydrocarbon mixture which results when 1-beta-phenylethylcyclohexanol-1 is dehydrated, or when 1-beta-phenylethylcyclohexene is cyclized by aluminum trichloride, and its constitution has been proved by synthesis (2) Its oxime melts at 137-137.8 degrees (corr.). The oxime of m.p. 187.5 degrees , reported by Cook et al. therefore must be derived from some other ketone, perhaps the trans-ketoöctahydrophenanthrene, since we were unable to isolate any oxime of m.p. 177 degrees , the figure which they reported for this compound.

A Model for Siderophile Element Distribution in Planetary Differentiation

NASA Technical Reports Server (NTRS)

Humayun, M.; Rushmer, T.; Rankenburg, K.; Brandon, A. D.

2005-01-01

Planetary differentiation begins with partial melting of small planetesimals. At low degrees of partial melting, a sulfur-rich liquid segregates by physical mechanisms including deformation-assisted porous flow. Experimental studies of the physical mechanisms by which Fe-S melts segregate from the silicate matrix of a molten H chondrite are part of a companion paper. Geochemical studies of these experimental products revealed that metallic liquids were in equilibrium with residual metal in the H chondrite matrix. This contribution explores the geochemical signatures produced by early stages of core formation. Particularly, low-degree partial melt segregation of Fe-S liquids leaves residual metal in the silicate matrix. Some achondrites appear to be residues of partial melting, e.g., ureilites, which are known to contain metal. The metal in these achondrites may show a distinct elemental signature. To quantify the effect of sulfur on siderophile element contents of residual metal we have developed a model based on recent parametrizations of equilibrium solid metal-liquid metal partitioning experiments.

Permeability and 3-Dimensional Melt Distribution in Partially Molten Rocks

NASA Astrophysics Data System (ADS)

Zhu, Wen-Lu; Gaetani, Glenn; Fusseis, Florian

2010-05-01

Quantitative knowledge of the distribution of small amounts of silicate melt in peridotite and of its influence on permeability are critical to our understanding of melt migration and segregation processes in the upper mantle, as well as interpretations of the geochemical and geophysical observations at ocean ridges. For a system containing a single solid phase of isotropic interfacial energy, chemical and mechanical equilibrium requires a constant mean curvature of solid-melt interfaces and a single dihedral angle. Under these conditions, a simple power-law relationship between permeability, grain size and melt fraction, has been derived [e.g., von Bargen and Waff, 1986]. However, microstructural observations on texturally equilibrated, partially molten rocks reveal that the melt distribution is more complex than predicted by the isotropic model. Several factors, such as non-hydrostatic stress, anisotropic interfacial energy, or the presence of a second solid phase, will alter the power-law relationship. Better estimates for the permeability of partially molten rock require an accurate assessment of 3-dimensional melt distribution at the grain-scale. Existing studies of melt distribution, carried out on 2-D slices through experimental charges, have produced divergent models for melt distribution at small melt fractions. While some studies conclude that small amounts of melt are distributed primarily along 3-grain junctions [e.g., Wark et al., 2003], others predict an important role for melt distribution along grain boundaries at low melt fractions [e.g., Faul 1997]. Using X-ray synchrotron microtomography, we have carried out the first high quality non-destructive imaging of 3-dimensional melt distribution in experimentally equilibrated olivine-basalt aggregates [Zhu et al., 2009]. Microtomographic images of melt distribution were obtained on 1 mm cylindrical cores with melt fractions of 0.2, 0.1, and 0.02, at a spatial resolution of 0.7 microns. Textual information such as melt channel size and channel connectivity was determined using AVIZO and MATLAB. Our data indicate that as melt fraction decreases from 0.2 to 0.02, grain size increases slightly whereas melt interconnectivity decreases. Network modeling and the Lattice Boltzmann method provide a quantitative link between the macroscale transport properties and microscale melt distribtution. Incorporating our quantitative 3-D melt distribution data into these models allow us to simulate melt transport and, thereby, calculate the permeability and electrical conductivity of partially molten peridotite, especially at low melt fractions.

Petrogenesis of Neogene basaltic volcanism associated with the Lut block, eastern Iran: Implication for tectonic and metallogenic evolution

NASA Astrophysics Data System (ADS)

Saadat, Saeed

This dissertation presents petrochemical data concerning Neogene olivine basalts erupted both along the margins and within the micro-continental Lut block, eastern Iran, which is a part of the active Alpine-Himalayan orogenic belt. These data demonstrate the following: (1) Basalts that erupted from small monogenetic parasitic cones around the Bazman stratovolcano, Makran arc area, in the southern Lut block, are low-Ti sub-alkaline olivine basalts. Enrichments of LILE relative to LREE, and depletions in Nb and Ta relatively to LILE, are similar to those observed for other convergent plate boundary arc magmas around the world and suggest that these basalts formed by melting of subcontinental mantle modified by dehydration of the subducted Oman Sea oceanic lithosphere. (2) Northeast of Iran, an isolated outcrop of Neogene/Quaternary alkali olivine basalt, containing mantle and crustal xenoliths, formed by mixing of small melt fractions from both garnet and spinel-facies mantle. These melts rose to the surface along localized pathways associated with extension at the junction between the N-S right-lateral strike-slip faults and E-W left-lateral strike slip faults. The spinel-peridotite mantle xenoliths contained in the basalts, which equilibrated in the subcontinental lithosphere at depths of 30 to 60 km and temperatures of 965°C to 1065°C, do not preserve evidence of extensive metasomatic enrichment as has been inferred for the mantle below the Damavand volcano further to the west in north-central Iran. (3) Neogene mafic rocks within the central Lut block represent the last manifestation of a much more extensive mid-Tertiary magmatic event. These basalts formed from both OIB-like asthenosphere and subcontinental lithosphere which preserved chemical characteristics inherited from mid-Tertiary subduction associated with the collision of the Arabian with the Eurasian plate and closing of the Neotethys Ocean. Neogene/Quternary alkali olivine basalts erupted mainly along the major faults that bound the Lut block on the east and west. These low-volumes, low-degree melts have been formed by low variable degrees of partial melting of mantle source produced by upwelling asthenosphere replaced the thinned lithospheric mantle.

The thermochemical, two-phase dynamics of subduction zones: results from new, fully coupled models

NASA Astrophysics Data System (ADS)

Rees Jones, D. W.; Katz, R. F.; May, D.; Tian, M.; Rudge, J. F.

2017-12-01

Subduction zones are responsible for most of Earth's subaerial volcanism. However, previous geodynamic modelling of subduction zones has largely neglected magmatism. We previously showed that magmatism has a significant thermal impact, by advecting sensible heat into the lithosphere beneath arc volcanos [1]. Inclusion of this effect helps reconcile subduction zone models with petrological and heat flow observations. Many important questions remain, including how magma-mantle dynamics of subduction zones affects the position of arc volcanos and the character of their lavas. In this presentation, we employ a fully coupled, thermochemical, two-phase flow theory to investigate the dynamics of subduction zones. We present the first results from our new software (SubFUSc), which solves the coupled equations governing conservation of mass, momentum, energy and chemical species. The presence and migration of partial melts affect permeability and mantle viscosity (both directly and through their thermal impact); these, in turn, feed back on the magma-mantle flow. Thus our fully coupled modelling improves upon previous two-phase models that decoupled the governing equations and fixed the thermal structure [2]. To capture phase change, we use a novel, simplified model of the mantle melting in the presence of volatile species. As in the natural system, volatiles are associated with low-degree melting at temperatures beneath the anhydrous solidus; dehydration reactions in the slab supply volatiles into the wedge, triggering silicic melting. We simulate the migration of melts under buoyancy forces and dynamic pressure gradients. We thereby demonstrate the dynamical controls on the pattern of subduction-zone volcanism (particularly its location, magnitude, and chemical composition). We build on our previous study of the thermal consequences of magma genesis and segregation. We address the question of what controls the location of arc volcanoes themselves [3]. [1] Rees Jones, D. W., Katz, R. F., Tian, M and Rudge, J. F. (2017). Thermal impact of magmatism in subduction zones. arxiv.org/abs/1701.02550 [2] Wilson, C. R., Spiegelman, M., van Keken, P. E., & Hacker, B. R. (2014). EPSL, doi:10.1016/j.epsl.2014.05.052 [3] England, P. C., Katz, Richard F. (2010). Nature, doi:10.1038/nature09417

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 front that followes a stationary melting front which creates low porosity intermediate states. Therefore, localization of the melt flow is not observed because the precipitation front is stable and the melting front is always stationary under these conditions. This analysis illustrates the counterintuitive behavior that can arise when the phase behavior is taken into account and is a first step to understanding reactive melt transport and the reactive constraints on channelization in partial melts. ¬¬

The Effect of Large Melt Fraction on the Deformation Behavior of Peridotite: Implications for the Rheology of Io' Mantle

NASA Technical Reports Server (NTRS)

Scott, T.; Kohlstedt, D. L.

2004-01-01

One key constraint needed for refinement of the interior geochemical and geodynamic models of Io is the viscosity of the convecting partially- molten silicate mantle. To date, laboratory studies of partially molten mantle rocks have reached melt fractions up to approx.0.12, a value much smaller than thought to be appropriate for the asthenosphere of Io where the degree of partial melting may be 0.15 0.40 or higher. Therefore, we have performed a series of high temperature, triaxial compressive creep experiments on dry synthetic peridotites in a gas medium apparatus at a confining pressure of 300 MPa and temperatures from 1473 to 1573 K in order to understand the influence of large amounts of melt (0.15 < phi < 0.40) on the rheological behavior of partially molten rocks.

Preparation and characterization of the magnetic superconductor EuSr2RuCu2O8-δ (RuEu-1212) by partial melting

NASA Astrophysics Data System (ADS)

Yamaki, K.; Kitagawa, N.; Funahashi, S.; Bamba, Y.; Irie, A.

2018-07-01

In this study, fine single crystals of the magnetic superconductor EuSr2RuCu2O8-δ (RuEu-1212) were successfully prepared using the partial melting technique. The obtained single crystals had a cubic shape, which coincides with the results of previous studies of RuGd-1212 single crystals. The single crystals had a typical length of 20-30 μm and the diffraction pattern observed from a sample prepared by partial melting was consistent with patterns of previously reported polycrystalline RuEu-1212 samples. A sample subjected to prolonged sintering, which consisted of a large number of combined micro single crystals prepared by partial melting, exhibited a superconducting transition with Tc-onset of 30.9 K and Tc-zero of 10.5 K.

Continental Subduction: Mass Fluxes and Interactions with the Wider Earth System

NASA Astrophysics Data System (ADS)

Cuthbert, S. J.

2011-12-01

Substantial parts of ultra-high pressure (UHP) terrains probably represent subducted passive continental margins (PCM). This contribution reviews and synthesises research on processes operating in such systems and their implication for the wider Earth system. PCM sediments are large repositories of volatiles including hydrates, nitrogen species, carbonates and hydrocarbons. Sediments and upper/ mid-crustal basement are rich in incompatible elements and are fertile for melting. Lower crust may be more mafic and refractory. Juvenile rift-related mafic rocks also have the potential to generate substantial volumes of granitoid melts, especially if they have been hydrated. Exposed UHP terrains demonstrate the return of continental crust from mantle depths, show evidence for substantial fluxes of aqueous fluid, anatexis and, in entrained orogenic peridotites, metasomatism of mantle rocks by crust- derived C-O-H fluids. However, substantial bodies of continental material may never return to the surface as coherent masses of rock, but remain sequestered in the mantle where they melt or become entrained in the deeper mantle circulation. Hence during subduction, PCM's become partitioned by a range of mechanisms. Mechanical partitioning strips away weaker sediment and middle/upper crust, which circulate back up the subduction channel, while denser, stronger transitional pro-crust and lower crust may "stall" near the base of the lithosphere or be irreversibly subducted to join the global mantle circulation. Under certain conditions sediment and upper crustal basement may reach depths for UHPM. Further partitioning takes place by anatexis, which either aids stripping and exhumation of the more melt-prone rock-masses through mechanical softening, or separates melt from residuum so that melt escapes and is accreted to the upper plate leading to "undercrusting", late-orogenic magmatism and further refinement of the crust. Melt that traverses sections of mantle will interact with it causing metasomatism and refertilisation. Partitioning also takes place by solid-fluid and melt-fluid partitioning. Dehydration may take place both during subduction and exhumation, and fluxes between dehydrating and hydrating rock masses influence the internal fluid budget of the orogen (essential for eclogitisation and densification of mafic lithologies). Ascending granitic melts advect dissolved water to shallow levels, or even the atmosphere. Irreversible subduction of PCM sediment carries water plus nitrogen species to the deeper mantle. Decarbonation of voluminous PCM carbonates depends on thermal regime and may release a pulse of CO2 to the atmosphere, but is limited in colder subduction zones hence transferring large volumes of carbon to the deep mantle. This may ultimately be mobilised by melting or dissolution to form fluid media for diamond formation.

Electrical conductivity of basaltic and carbonatite melt-bearing peridotites at high pressures: Implications for melt distribution and melt fraction in the upper mantle

NASA Astrophysics Data System (ADS)

Yoshino, Takashi; Laumonier, Mickael; McIsaac, Elizabeth; Katsura, Tomoo

2010-07-01

Electrical impedance measurements were performed on two types of partial molten samples with basaltic and carbonatitic melts in a Kawai-type multi-anvil apparatus in order to investigate melt fraction-conductivity relationships and melt distribution of the partial molten mantle peridotite under high pressure. The silicate samples were composed of San Carlos olivine with various amounts of mid-ocean ridge basalt (MORB), and the carbonate samples were a mixture of San Carlos olivine with various amounts of carbonatite. High-pressure experiments on the silicate and carbonate systems were performed up to 1600 K at 1.5 GPa and up to at least 1650 K at 3 GPa, respectively. The sample conductivity increased with increasing melt fraction. Carbonatite-bearing samples show approximately one order of magnitude higher conductivity than basalt-bearing ones at the similar melt fraction. A linear relationship between log conductivity ( σbulk) and log melt fraction ( ϕ) can be expressed well by the Archie's law (Archie, 1942) ( σbulk/ σmelt = Cϕn) with parameters C = 0.68 and 0.97, n = 0.87 and 1.13 for silicate and carbonate systems, respectively. Comparison of the electrical conductivity data with theoretical predictions for melt distribution indicates that the model assuming that the grain boundary is completely wetted by melt is the most preferable melt geometry. The gradual change of conductivity with melt fraction suggests no permeability jump due to melt percolation at a certain melt fraction. The melt fraction of the partial molten region in the upper mantle can be estimated to be 1-3% and ˜ 0.3% for basaltic melt and carbonatite melt, respectively.

Recent development in osmotic dehydration of fruit and vegetables: a review.

PubMed

Chandra, Suresh; Kumari, Durvesh

2015-01-01

Osmotic dehydration of fruits and vegetables is achieved by placing the solid/semi solid, whole or in pieces, in a hypertonic solution (sugar and/or salt) with a simultaneous counter diffusion of solutes from the osmotic solution into the tissues. Osmotic dehydration is recommended as a processing method to obtain better quality of food products. Partial dehydration allows structural, nutritional, sensory, and other functional properties of the raw material to be modified. However, the food industry uptake of osmotic dehydration of foods has not been extensive as expected due to the poor understanding of the counter current flow phenomena associated with it. However, these flows are in a dynamic equilibrium with each other and significantly influence the final product in terms of preservation, nutrition, and organoleptic properties. The demand of healthy, natural, nutritious, and tasty processed food products continuously increases, not only for finished products, but also for ingredient to be included in complex foods such as ice cream, cereals, dairy, confectionaries, and bakery products.

Polymer Inverse Temperature-Dependent Solubility: A Visual Demonstration of the Importance of "T[Delta]S" in the Gibbs Equation

ERIC Educational Resources Information Center

Bergbreiter, David E.; Mijalis, Alexander J.; Fu, Hui

2012-01-01

Reversible polymer dehydration and precipitation from water due to the unfavorable entropy of hydration is examined using a melting-point apparatus. The thermoresponsive lower critical solution temperature (LCST) behavior of poly(N-isopropylacrylamide) (PNIPAM) is responsible for these effects. An experiment is described that allows students to…

Water circulation and global mantle dynamics: Insight from numerical modeling

NASA Astrophysics Data System (ADS)

Nakagawa, Takashi; Nakakuki, Tomoeki; Iwamori, Hikaru

2015-05-01

We investigate water circulation and its dynamical effects on global-scale mantle dynamics in numerical thermochemical mantle convection simulations. Both dehydration-hydration processes and dehydration melting are included. We also assume the rheological properties of hydrous minerals and density reduction caused by hydrous minerals. Heat transfer due to mantle convection seems to be enhanced more effectively than water cycling in the mantle convection system when reasonable water dependence of viscosity is assumed, due to effective slab dehydration at shallow depths. Water still affects significantly the global dynamics by weakening the near-surface oceanic crust and lithosphere, enhancing the activity of surface plate motion compared to dry mantle case. As a result, including hydrous minerals, the more viscous mantle is expected with several orders of magnitude compared to the dry mantle. The average water content in the whole mantle is regulated by the dehydration-hydration process. The large-scale thermochemical anomalies, as is observed in the deep mantle, is found when a large density contrast between basaltic material and ambient mantle is assumed (4-5%), comparable to mineral physics measurements. Through this study, the effects of hydrous minerals in mantle dynamics are very important for interpreting the observational constraints on mantle convection.

Origins of two types of serpentinites from the Qinling orogenic belt, central China and associated fluid/melt-rock interactions

NASA Astrophysics Data System (ADS)

Wu, Kai; Ding, Xing; Ling, Ming-Xing; Sun, Wei-dong; Zhang, Li-Peng; Hu, Yong-Bin; Huang, Rui-Fang

2018-03-01

Serpentinites are important volatile and fluid mobile element repositories in oceanic lithosphere and subduction zones, and thus provide significant constraints on global geochemical cycles and tectonic evolution at convergent margins. In this contribution, two types of serpentinites from the Mianlue suture zone in the Qinling orogenic belt, central China, are identified on the basis of detailed mineralogical and geochemical study. Serpentinites from the Jianchaling region (Group 1) are composed of lizardite/chrysotile + magnesite + magnetite. Most of these serpentinites (Group 1a), consist of pseudomorphic orthopyroxene and olivine, and are characterized by low Al2O3/SiO2, high MgO/SiO2 and Ir-type PGEs to Pt ratios, suggesting a residual mantle origin. Meanwhile, the U-shape REE pattern and positive Eu, Sr and Ba anomalies of these serpentinites indicate that serpentinization fluids have interacted with gabbroic cumulates at moderately high temperatures or associate with the chlorinity and redox conditions of the fluid. Considering the limited mobility of U in the hydrating fluids for the Group 1a serpentinites, hydrating fluids for these serpentinites are most likely derived from the dehydrated slab, and have been in equilibrium with subducting sediments. There are also some serpentinites with low-grade metamorphic recrystallization from the Jianchaling region (Group 1b), represented by recrystallized serpentine minerals (antigorite). The trace element compositions of these Group 1b serpentinites suggest that partial dehydration of serpentinites associated with the transformation from lizardite to antigorite in subduction zone is also likely to affect the geochemistry of serpentinites. Serpentinites from the Liangyazi region (Group 2) are composed of antigorite + dolomite + spinel + magnetite. The high Cr number (0.65-0.80) and low Ti concentrations of spinels in Group 2 serpentinites indicate a refractory mantle wedge origin. Fertile major element compositions (e.g., high Al2O3 content and Al2O3/SiO2) and conjoint enrichment in light rare earth elements and high field strength elements, however, suggest melt-rock interactions before serpentinization. Combined with their geochemical affinity to "subducted serpentinites", we conclude that their protoliths (refractory mantle wedge peridotite) experienced melt-rock interactions and then were incorporated into the subduction channel before serpentinization. Studies on these two types of serpentinites indicate that serpentinites from the orogenic belt are most likely characterized by multi-source, multi-stage and multi-genesis, further providing important constraints on subduction channel processes.

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 the felsite, accompanied locally by partial assimilation. The interstitial melt in the felsite has similar normalized SiO2 content as the rhyolite melt but is distinguished by higher K2O and lower CaO and plots near the minimum melt composition in the granite system. Augite in the partially melted felsite has re-equilibrated to more calcic metamorphic compositions. Rare quenched glass fragments containing glomeroporphyritic crystals derived from the felsite show textural evidence for resorption of alkali feldspar and quartz. The glass in these fragments is enriched in SiO2 relative to the rhyolite melt or the interstitial felsite melt, consistent with the textural evidence for quartz dissolution. The quenching of these melts by drilling fluids at in situ conditions preserves details of the melt–wall rock interaction that would not be readily observed in rocks that had completely crystallized. However, these processes may be recognizable by a combination of textural analysis and in situ analytical techniques that document compositional heterogeneity due to partial melting and local assimilation.

Estimates of olivine-basaltic melt electrical conductivity using a digital rock physics approach

NASA Astrophysics Data System (ADS)

Miller, Kevin J.; Montési, Laurent G. J.; Zhu, Wen-lu

2015-12-01

Estimates of melt content beneath fast-spreading mid-ocean ridges inferred from magnetotelluric tomography (MT) vary between 0.01 and 0.10. Much of this variation may stem from a lack of understanding of how the grain-scale melt geometry influences the bulk electrical conductivity of a partially molten rock, especially at low melt fraction. We compute bulk electrical conductivity of olivine-basalt aggregates over 0.02 to 0.20 melt fraction by simulating electric current in experimentally obtained partially molten geometries. Olivine-basalt aggregates were synthesized by hot-pressing San Carlos olivine and high-alumina basalt in a solid-medium piston-cylinder apparatus. Run conditions for experimental charges were 1.5 GPa and 1350 °C. Upon completion, charges were quenched and cored. Samples were imaged using synchrotron X-ray micro-computed tomography (μ-CT). The resulting high-resolution, 3-dimensional (3-D) image of the melt distribution constitutes a digital rock sample, on which numerical simulations were conducted to estimate material properties. To compute bulk electrical conductivity, we simulated a direct current measurement by solving the current continuity equation, assuming electrical conductivities for olivine and melt. An application of Ohm's Law yields the bulk electrical conductivity of the partially molten region. The bulk electrical conductivity values for nominally dry materials follow a power-law relationship σbulk = Cσmeltϕm with fit parameters m = 1.3 ± 0.3 and C = 0.66 ± 0.06. Laminar fluid flow simulations were conducted on the same partially molten geometries to obtain permeability, and the respective pathways for electrical current and fluid flow over the same melt geometry were compared. Our results indicate that the pathways for flow fluid are different from those for electric current. Electrical tortuosity is lower than fluid flow tortuosity. The simulation results are compared to existing experimental data, and the potential influence of volatiles and melt films on electrical conductivity of partially molten rocks is discussed.

Petrochemistry of late miocene peraluminous silicic volcanic rocks from the Morococala field, Bolivia

USGS Publications Warehouse

Morgan, VI G.B.; London, D.; Luedke, R.G.

1998-01-01

Late Miocene peraluminous volcanic rocks of the Morococala field, Bolivia, define a layered stratigraphy of basal andalusite-, biotite-(?? Muscovite)-bearing rhyolite tuffs (AR), overlain by cordierite-, biotite-bearing rhyolite tuffs (CR), and capped by biotite-beanng quartz latite tuffs, lavas, and late domal flows (QL). Mineral and whole-rock compositions become more evolved from top to bottom, with differentiation reflected by decreasing Ca, Ba, Mg, Fe, and rare earth elements (REE) versus increasing F, Na/K, and aluminosity from QL to AR. Mineral, whole-rock, and glass inclusion compositions are consistent with derivation of all three rock types from a single stratified magma reservoir, but age and spatial relations between the three units make this unlikely. Genesis of the QL involved biotite-dehydration melting of an aluminous source at T > 750??C and P ??? 4-6 kbar. If not co-magmatic with QL, the other units were generated primarily by muscovite-dehydration melting at T = 730-750??C and P ??? 3??5-4??5 kbar for CR, and T ??? 750??C for AR with pre-emptive residence at low pressure (1??5-3??0 kbar). Low hematite contents (XHem ??? 0??06) of ilmenite grains in AR, CR, and early grains (as inclusions in plagioclase and sanidine cores) in QL indicate reduced conditions imposed by a graphite-bearing source. Compositional variability among texturally later oxides (ilmenite with XHem = 0??06-0??50, primary magnetite), however, apparently records progressive increases in pre-eruptive f(O2) in QL. Plagioclase-melt equilibria and electron microprobe analysis difference for quartz-hosted glass inclusions suggest pre-emptive melt H2O contents ??? 5-7 wt % for the AR, ???4-6 wt % for the CR, and ???3-5 wt % for the QL.

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

NASA Technical Reports Server (NTRS)

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

1985-01-01

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

Stability of Carbonated Eclogite in the Upper Mantle: Experimental Solidus from 2 to 9 GPa

NASA Astrophysics Data System (ADS)

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

2003-12-01

Carbonates are pervasive alteration products of the oceanic crust and likely survive subduction-related dehydration and/or melting. Thus, significant quantities of carbonated refractory eclogite are probably delivered to the deeper mantle. The melting behavior of such recycled carbonate influences the fate of recycled carbon, determines the possible sources and depths of carbonated metasomatic melts in the mantle, and delimits the conditions under which carbonated eclogite may act as a source of carbonatite and other types of magmatic CO2. We present partial melting experiments of carbonated eclogite that constrain the solidus and near solidus phase relations from 2 to 9 GPa. To simulate the near-isochemical nature of ocean floor carbonation, the starting material was prepared by adding 5 wt.% CO2 in the form of a mixture of Fe-Mg-Ca-Na-K carbonates to a bimineralic eclogite from Salt Lake crater, Oahu, Hawaii. The starting composition is a reasonable approximation of carbonated oceanic crust from which siliceous hydrous fluid has been extracted by subduction. We find that melt-present versus melt-absent conditions can be distinguished based on textural criteria. Garnet and cpx appear in all the experiments. Between 2 and 3 GPa, the subsolidus assemblage also includes calcite-dolomitess + ilmenite, whereas above the solidus (950-975 ° C at 2 GPa and 1050-1075 ° C at 3 GPa) calcio-dolomitic liquid appears. From 3 to 4.5 GPa, dolomitess becomes stable at the solidus and the near solidus melt becomes increasingly dolomitic. Appearance of dolomite above 3 GPa is accompanied by a negative Clapeyron slope of the solidus, with the cusp located between 995 and 1025 ° C at ca. 4 GPa. Above 4-4.5 GPa, the solidus again rises with increasing pressure to ca. 1245 ° C at 9 GPa and magnesite becomes the subsolidus carbonate. Dolomitic melt coexists with magnesite + garnet + cpx + rutile between 5 and 9 GPa. If extrapolated to higher pressures, the carbonated eclogite solidus intersects the oceanic geotherm deeper than 400 km. Thus, eclogite cannot host carbonates in the asthenosphere. Carbonated eclogite bodies entering the convecting upper mantle would release carbonate melt in the mantle transition zone. Upon release, this small volume, highly reactive melt could be an effective agent of deep mantle metasomatism. Comparison of our eclogite-CO2 solidus with that of peridotite-CO2 shows a shallower solidus-geotherm intersection for the latter. This implies that carbonated peridotite is a more likely proximal source of magmatic carbon in oceanic provinces. However, carbonated eclogite is a potential source of continental carbonatites, as its solidus crosses the continental shield geotherm at ca. 4 GPa.

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).

Reactive transport in a partially molten system with binary solid solution

NASA Astrophysics Data System (ADS)

Jordan, J.; Hesse, M. A.

2017-12-01

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 of a heterogeneity and the background mantle. Simplified melting models of such systems aide in the interpretation and formulation of larger scale mantle models. Motivated by the aforementioned facts, we present a chromatographic analysis of reactive melt transport across lithological boundaries, using theory for hyperbolic conservation laws. This is an extension of well-known linear trace element chromatography to the coupling of major elements and energy transport. Our analysis allows the prediction of the feedbacks that arise in reactive melt transport due to melting, freezing, dissolution and precipitation for frontal reactions. This study considers the simplified case of a rigid, partially molten porous medium with binary solid solution. As melt traverses a lithological contact-modeled as a Riemann problem-a rich set of features arise, including a reacted zone between an advancing reaction front and partial chemical preservation of the initial contact. Reactive instabilities observed in this study originate at the lithological interface rather than along a chemical gradient as in most studies of mantle dynamics. We present a regime diagram that predicts where reaction fronts become unstable, thereby allowing melt localization into high-porosity channels through reactive instabilities. After constructing the regime diagram, we test the one-dimensional hyperbolic theory against two-dimensional numerical experiments. The one-dimensional hyperbolic theory is sufficient for predicting the qualitative behavior of reactive melt transport simulations conducted in two-dimensions. The theoretical framework presented can be extended to more complex and realistic phase behavior, and is therefore a useful tool for understanding nonlinear feedbacks in reactive melt transport problems relevant to mantle dynamics.

The System Forsterite-Diopside-Enstatite up to 70 kbar and its Significance to the Genesis of Komatiites

NASA Astrophysics Data System (ADS)

Dasgupta, S.; Gupta, A. K.

2011-12-01

Liquidus phase relations in the system forsterite-diopside-enstatite has been made at 70 kbar under anhydrous conditions using a Walker-type multi-anvil high pressure apparatus. Positions of the pseudoeutectic/ invariant, minimum points and amount of solid solutions of appearing phases are summarized in table 1. Comparison of these phase relations with those conducted by previous investigators at lower pressures and temperatures shows that the fosterite-pyroxene liquidus boundary shifts toward forsterite and away from the diopside apex with increasing pressure. Microprobe analyses indicate that the maximum amount of MgSiO3 that can be incorporated in diopside increases with pressure, and at the solidus (70 kbar, 2010°C), it is about 82%. On the basis of EPMA analyses of coexisting liquid and crystalline phases, three-phase triangles have been constructed. It is observed that at 70 kbar, the early partial melt generated from a model peridotite does not precipitate orthopyroxene. If such a melt instead of crystallizing in-situ, ascend to the surface, then the polybaric-polythermal crystallization path should never intersect the liquidus phase field of orthopyroxene, enstatitess may then appear in the solidus as an exsolution product. Our calculation shows that at 31% partial melting of a model mantle, orthopyroxene should appear as a liquidus phase. With further increase in the degree of partial melting (42-60%), proportion of orthopyroxene crystallizing from the melt progressively increases. With reference to the above discussion we propose that the Gorgona komatiites which are primarily orthopyroxene-deficient komatiites, are an outcome of low degree of partial melting, whereas the orthopyroxene-bearing Commondale komatiites of the southern Kaapvaal Craton, South Africa, are the outcome of a larger degree of partial melting, both generated from melting of an anhydrous mantle.

Thorium-uranium fractionation by garnet - Evidence for a deep source and rapid rise of oceanic basalts

NASA Technical Reports Server (NTRS)

Latourrette, T. Z.; Kennedy, A. K.; Wasserburg, G. J.

1993-01-01

Mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs) are derived by partial melting of the upper mantle and are marked by systematic excesses of thorium-230 activity relative to the activity of its parent, uranium-238. Experimental measurements of the distribution of thorium and uranium between the melt and solid residue show that, of the major phases in the upper mantle, only garnet will retain uranium over thorium. This sense of fractionation, which is opposite to that caused by clinopyroxene-melt partitioning, is consistent with the thorium-230 excesses observed in young oceanic basalts. Thus, both MORBs and OIBs must begin partial melting in the garnet stability field or below about 70 kilometers. A calculation shows that the thorium-230-uranium-238 disequilibrium in MORBs can be attributed to dynamic partial melting beginning at 80 kilometers with a melt porosity of 0.2 percent or more. This result requires that melting beneath ridges occurs in a wide region and that the magma rises to the surface at a velocity of at least 0.9 meter per year.

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.

Selective photooxidation of hydrocarbons in zeolites by oxygen

DOEpatents

Frei, Heinz; Blatter, Fritz; Sun, Hai

1998-01-01

A selective photooxidation process for the conversion of hydrocarbon molecules to partially oxygenated derivatives, which comprises the steps of adsorbing a hydrocarbon and oxygen onto a dehydrated zeolite support matrix to form a hydrocarbon-oxygen contact pair, and subsequently exposing the hydrocarbon-oxygen contact pair to visible light, thereby forming a partially oxygenated derivative.

Experimental petrology and origin of rocks from the Descartes Highlands

NASA Technical Reports Server (NTRS)

Walker, D.; Longhi, J.; Grove, T. L.; Stolper, E.; Hays, J. F.

1973-01-01

Petrographic studies of Apollo 16 samples indicate that rocks 62295 and 68415 are crystallization products of highly aluminous melts. 60025 is a shocked, crushed and partially annealed plagioclase cumulate. 60315 is a recrystallized noritic breccia of disputed origin. 60335 is a feldspathic basalt filled with xenoliths and xenocrysts of anorthosite, breccia, and anorthite. The Fe/(Fe+Mg) of plagioclase appears to be a relative crystallization index. Low pressure melting experiments with controlled Po2 indicate that the igneous samples crystallized at oxygen fugacities well below the Fe/FeO buffer. Crystallization experiments at various pressures suggest that the 62295 and 68415 compositions were produced by partial or complete melting of lunar crustal materials, and not by partial melting of the deep lunar interior.

Network topology of olivine-basalt partial melts

NASA Astrophysics Data System (ADS)

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

2017-07-01

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

Partial melting of lower oceanic crust gabbro: Constraints from poikilitic clinopyroxene primocrysts

NASA Astrophysics Data System (ADS)

Leuthold, Julien; Lissenberg, C. Johan; O'Driscoll, Brian; Karakas, Ozge; Falloon, Trevor; Klimentyeva, Dina N.; Ulmer, Peter

2018-03-01

Successive magma batches underplate, ascend, stall and erupt along spreading ridges, building the oceanic crust. It is therefore important to understand the processes and conditions under which magma differentiates at mid ocean ridges. Although fractional crystallization is considered to be the dominant mechanism for magma differentiation, open-system igneous complexes also experience Melting-Assimilation-Storage-Hybridization (MASH, Hildreth and Moorbath, 1988) processes. Here, we examine crystal-scale records of partial melting in lower crustal gabbroic cumulates from the slow-spreading Atlantic oceanic ridge (Kane Megamullion; collected with Jason ROV) and the fast-spreading East Pacific Rise (Hess Deep; IODP expedition 345). Clinopyroxene oikocrysts in these gabbros preserve marked intra-crystal geochemical variations that point to crystallization-dissolution episodes of the gabbro eutectic assemblage. Kane Megamullion and Hess Deep clinopyroxene core1 primocrysts and their plagioclase inclusions indicate crystallization from high temperature basalt (>1160 and >1200°C, respectively), close to clinopyroxene saturation temperature (<50% and <25% crystallization). Step-like compatible Cr (and co-varying Al) and incompatible Ti, Zr, Y and rare earth elements (REE) decrease from anhedral core1 to overgrown core2, while Mg# and Sr/Sr* ratios increase. We show that partial resorption textures and geochemical zoning result from partial melting of REE-poor lower oceanic crust gabbroic cumulate (protolith) following intrusion by hot primitive mantle-derived melt, and subsequent overgrowth crystallization (refertilization) from a hybrid melt. In addition, towards the outer rims of crystals, Ti, Zr, Y and the REE strongly increase and Al, Cr, Mg#, Eu/Eu* and Sr/Sr* decrease, suggesting crystallization either from late-stage percolating relatively differentiated melt or from in situ trapped melt. Intrusion of primitive hot reactive melt and percolation of interstitial differentiated melt are two distinct MASH processes in the lower oceanic crust. They are potentially fundamental mechanisms for generating the wide compositional variation observed in mid-ocean ridge basalts. We furthermore propose that such processes operate at both slow- and fast-spreading ocean ridges. Thermal numerical modelling shows that the degree of lower crustal partial melting at slow-spreading ridges can locally increase up to 50%, but the overall crustal melt volume is low (less than ca. 5% of total mantle-derived and crustal melts; ca. 20% in fast-spreading ridges).

The Divnoe meteorite: Petrology, chemistry, oxygen isotopes and origin

NASA Technical Reports Server (NTRS)

Petaev, M. I.; Barsukova, L. D.; Lipschultz, M. E.; Wang, M.-S.; Ariskin, A. A.; Clayton, R. N.; Mayeda, T. K.

1994-01-01

The Divnoe meteorite is an olivine-rich primitive achondrite with subchondritic chemistry and mineralogy. It has a granoblastic, coarse-grained, olivine groundmass (CGL: coarse-grained lithology) with relatively large pyroxene-plagioclase poiklitic patches (PP) and small fine-grained domains of an opaque-rich lithology (ORL). Both PP and ORL are inhomogeneously distributed and display reaction boundaries with the groundmass. Major silicates, olivine Fa(20-28) and orthopyroxyene Fs(20-28 Wo(0.5-2.5), display systematic differences in composition between CGL and ORL as well as a complicated pattern of variations within CGL. Accessory plagioclase has low K content and displays regular igneous zoning with core compositions An(40-45) and rims An(32-37). The bulk chemical composition of Divnoe is similar to that of olivine-rich primitive achondrites, except for a depletion of incompatible elements and minor enrichment of refractory siderophiles. Oxygen isotope compositions for whole-rock and separated minerals from Divnoe fall in a narrow range, with mean delta O-18 = +4.91, delta O-17 = +2.24, and Delta O-17 = -0.26 +/- 0.11. The isotopic composition is not within the range of any previously recognized group but is very close to that of the brachinites. To understand the origin of Divnoe lithologies, partial melting and crystallization were modelled using starting compositions equal to that of Divnoe and some chondritic meteorites. It was found that the Divnoe composition could be derived from a chondritic source region by approximately 20 wt% partial melting at Ta approximately 1300 C and log(fO2) = IW-1.8, followed by approximtely 60 wt% crystallization of the partial melt formed, and removal of the still-liquid portion of the partial melt. Removal of the last partial melt resulted in depletion of the Divnoe plagioclase in Na and K. In this scenario, CGL represents the residue of partial melting, and PP is a portion of the partial melt that crystallized in situ. The ORL was formed during the final stages of partial melting by reaction between gaseous sulfur and residual olivine in the source region. A prominent feature of Divnoe is fine micron-scale chemical variations within olivine grains, related to lamellar structures the olivines display. The origin of these structures is not known.

An Assessment of Hydrazine, Hydrazine Hydrate and Liquid Ammonia as Fuels for Rocket Propulsion

DTIC Science & Technology

1949-08-01

oxide, hyponitrites, or potassium nitrososulphite; decomposition of aminogunnidine; hydrolysis of bis-dinzo acetic acid; and nlso n cyclic process due to... Dehydration of hydrnzinc hydrnte. This may be carried out with caustic alknli, quick- lime or baryto. The method is probably suitable for laboratory scale...certaini that it can be opernted under safe conditions. These disadvontages should not be so formidable if only a partial dehydration were desired. In this

Quantitative analysis of dehydration in porcine skin for assessing mechanism of optical clearing

NASA Astrophysics Data System (ADS)

Yu, Tingting; Wen, Xiang; Tuchin, Valery V.; Luo, Qingming; Zhu, Dan

2011-09-01

Dehydration induced by optical clearing agents (OCAs) can improve tissue optical transmittance; however, current studies merely gave some qualitative descriptions. We develop a model to quantitatively evaluate water content with partial least-squares method based on the measurements of near-infrared reflectance spectroscopy and weight of porcine skin. Furthermore, a commercial spectrometer with an integrating sphere is used to measure the transmittance and reflectance of skin after treatment with different OCAs, and then the water content and optical properties of sample are calculated, respectively. The results show that both the reduced scattering coefficient and dehydration of skin decrease with prolongation of action of OCAs, but the relative change in former is larger than that in latter after a 60-min treatment. The absorption coefficient at 1450 nm decreases completely coincident with dehydration of skin. Further analysis illustrates that the correlation coefficient between the relative changes in the reduced scattering coefficient and dehydration is ~1 during the 60-min treatment of agents, but there is an extremely significant difference between the two parameters for some OCAs with more hydroxyl groups, especially, glycerol or D-sorbitol, which means that the dehydration is a main mechanism of skin optical clearing, but not the only mechanism.

A New Freezing Method Using Pre-Dehydration by Microwave-Vacuum Drying

NASA Astrophysics Data System (ADS)

Tsuruta, Takaharu; Hamidi, Nurkholis

Partial dehydration by microwave-vacuum drying has been applied to tuna and strawberry in order to reduce cell-damages caused by the formation of large ice-crystals during freezing. The samples were subjected to microwave vacuum drying at pressure of 5 kPa and temperature less than 27°C to remove small amount of water prior to freezing. The tuna were cooled by using the freezing chamber at temperature -50°C or -150°C, while the strawberries were frozen at temperature -30°C or -80°C, respectively. The temperature transients in tuna showed that removing some water before freezing made the freezing time shorter. The observations of ice crystal clearly indicated that rapid cooling and pre-dehydration prior to freezing were effective in minimizing the size of ice crystal. It is also understood that the formation of large ice crystals has a close relation to the cell damages. After thawing, the observation of microstructure was done on the tuna and strawberry halves. The pre-dehydrated samples showed a better structure than the un-dehydrated one. It is concluded that the pre-dehydration by microwave-vacuum drying is one promising method for the cryo-preservation of foods.

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

USGS Publications Warehouse

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

2008-01-01

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

The Nature of C Asteroid Regolith Revealed from the Jbilet Winselwan CM Chondrite

NASA Technical Reports Server (NTRS)

Zolensky, Michael; Mikouchi, Takashi; Hagiya, Kenji; Ohsumi, Kazumasa; Komatsu, Mutsumi; Chan, Queenie H. S.; Le, Loan; Kring, David; Cato, Michael; Fagan, Amy L.

2016-01-01

C-class asteroids frequently exhibit reflectance spectra consistent with thermally metamorphosed carbonaceous chondrites, or a mixture of phyllosilicate-rich material along with regions where they are absent. One particularly important example appears to be asteroid 162173 Ryugu, the target of the Hayabusa 2 mission, although most spectra of Ryugu are featureless, suggesting a heterogeneous regolith. Here we explore an alternative cause of dehydration of regolith of C-class asteroids - impact shock melting. Impact shock melting has been proposed to ex-plain some mineralogical characteristics of CB chondrites, but has rarely been considered a major process for hydrous carbonaceous chondrites.

Constraints on melt content of off-axis magma lenses at the East Pacific Rise from analysis of 3-D seismic amplitude variation with angle of incidence

NASA Astrophysics Data System (ADS)

Aghaei, Omid; Nedimović, Mladen R.; Marjanović, Milena; Carbotte, Suzanne M.; Pablo Canales, J.; Carton, Hélène; Nikić, Nikola

2017-06-01

We use 3-D multichannel seismic data to form partial angle P wave stacks and apply amplitude variation with angle (AVA) crossplotting to assess melt content and melt distribution within two large midcrustal off-axis magma lenses (OAMLs) found along the East Pacific Rise from 9°37.5'N to 9°57'N. The signal envelope of the partial angle stacks suggests that both OAMLs are partially molten with higher average melt content and more uniform melt distribution in the southern OAML than in the northern OAML. For AVA crossplotting, the OAMLs are subdivided into seven 1 km2 analysis windows. The AVA crossplotting results indicate that the OAMLs contain a smaller amount of melt than the axial magma lens (AML). For both OAMLs, a higher melt fraction is detected within analysis windows located close to the ridge axis than within the most distant windows. The highest average melt concentration is interpreted for the central sections of the OAMLs. The overall low OAML melt content could be indicative of melt lost due to recent off-axis eruptions, drainage to the AML, or limited mantle melt supply. Based on the results of this and earlier bathymetric, morphological, geochemical, and geophysical investigations, we propose that the melt-poor OAML state is largely the result of limited melt supply from the underlying mantle source reservoir with smaller contribution attributed to melt leakage to the AML. We hypothesize that the investigated OAMLs have a longer period of melt replenishment, lower eruption recurrence rates, and lower eruption volumes than the AML, though some could be single intrusion events.

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.

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

NASA Technical Reports Server (NTRS)

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

2014-01-01

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

Use of osmotic dehydration to improve fruits and vegetables quality during processing.

PubMed

Maftoonazad, Neda

2010-11-01

Osmotic treatment describes a preparation step to further processing of foods involving simultaneous transient moisture loss and solids gain when immersing in osmotic solutions, resulting in partial drying and improving the overall quality of food products. The different aspects of the osmotic dehydration (OD) technology namely the solutes employed, solutions characteristics used, process variables influence, as well as, the quality characteristics of the osmodehydrated products will be discussed in this review. As the process is carried out at mild temperatures and the moisture is removed by a liquid diffusion process, phase change that would be present in the other drying processes will be avoided, resulting in high quality products and may also lead to substantial energy savings. To optimize this process, modeling of the mass transfer phenomenon can improve high product quality. Several techniques such as microwave heating, vacuum, high pressure, pulsed electric field, etc. may be employed during or after osmotic treatment to enhance performance of the osmotic dehydration. Moreover new technologies used in osmotic dehydration will be discussed. Patents on osmotic dehydration of fruits and vegetables are also discussed in this article.

Kinetics and selectivity of 2-propanol conversion on oxidized anatase TiO{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rekoske, J.E.; Barteau, M.A.

1997-01-01

The steady-state kinetics of 2-propanol decomposition on oxidized anatase TiO{sub 2} have been determined at temperatures ranging from 448 to 598 K and 2-propanol partial pressures from 8.9 to 102.7 Torr. The effects of the addition of O{sub 2} and water to the carrier gas were also investigated. The steady-state reaction results primarily in the formation of a dehydration product, propylene, and a dehydrogenation product, acetone, with small amounts of carbon oxides also being observed. Depending on the reaction conditions, the selectivity to either propylene or acetone can range between 5 and 95%. The rate of dehydrogenation increases dramatically withmore » the addition of both O{sub 2} and water, while the dehydration rate is unaffected by their presence. Accordingly, the kinetics of 2-propanol decomposition were investigated using both air and an inert carrier. Using air as the carrier gas, the dehydration and dehydrogenation reactions were determined to be approximately one-half order with respect to 2-propanol partial pressure. The activation energies determined for the two processes are substantially different, 68 kJ mol{sup -1} for dehydrogenation and 130 kJ mol{sup -1} for dehydration, as evidenced by the strong temperature dependence of the decomposition selectivity. Using an inert carrier, the reaction kinetics depend in a complex fashion on the conversion of 2-propanol. The dependence on conversion was found to arise from the influence of water on the dehydrogenation kinetics. The presence of water, whether produced by 2-propanol dehydration or added independently, was found to increase the rate of 2-propanol dehydrogenation. 48 refs., 9 figs., 6 tabs.« less

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

Partial melts of subducting sediments are thought to be critical agents in carrying trace elements and water to arc basalt source regions. Sediment partial melts may also act as a carrier of CO2. However, the CO2 carrying capacity of natural rhyolitic melts that derive from partial fusion of downgoing sediment at sub-arc depths remains unconstrained. We conducted CO2-solubility experiments on a rhyolitic composition similar to average, low-degree experimental partial melt of pelitic sediments between 1.5 and 3.0 GPa at 1300 °C and containing variable water content. Concentrations of water and carbon dioxide were measured using FTIR. Molecular CO2(CO2mol.) and carbonate anions (CO32-) both appear as equilibrium species in our experimental melts. Estimated total CO2 concentrations (CO2mol.+CO32-) increased with increasing pressure and water content. At 3.0 GPa, the bulk CO2 solubility are in the range of ∼1-2.5 wt.%, for melts with H2O contents between 0.5 and 3.5 wt.%. For melts with low H2O content (∼0.5 wt.%), CO2mol. is the dominant carbon species, while in more H2O-rich melts CO32- becomes dominant. The experimentally determined, speciation-specific CO2 solubilities yielded thermodynamic parameters that control dissolution of CO2 vapor both as CO2mol. and as CO32- in silicate melt for each of our compositions with different water content; CO2vapor ↔CO2melt :lnK0=-15 to -18, ΔV0 = 29 to 14 cm3 mol-1 and CO2vapor +Omelt →CO32-melt :lnK0=-20 to -14, ΔV0 = 9 to 27 cm3 mol-1, with ΔV0 of reaction being larger for formation of CO2mol. in water-poor melts and for formation of CO32- in water-rich melts. Our bulk CO2 solubility data, [CO2] (in wt.%) can be fitted as a function of pressure, P (in GPa) and melt water content, [H2O] (in wt.%) with the following function: [CO2](wt.%)=(-0.01108[H2O]+0.03969)P2+(0.10328[H2O]+0.41165)P. This parameterization suggests that over the range of sub-arc depths of 72-173 km, water-rich sediment partial melt may carry as 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 sediment melt will have the opportunity to dissolve and carry CO2. For hot subduction zones, even if sedimentary layer itself does not carry carbonate, CO2 released from basalt-hosted carbonates may be dissolved in sediment partial melt. Experiments conducted on subducted sediment compositions show that the partial melt compositions are generally rhyolitic (Johnson and Plank, 1999; Hermann and Green, 2001; Schmidt et al., 2004; Auzanneau et al., 2006; Hermann and Spandler, 2008; Spandler et al., 2010; Tsuno and Dasgupta, 2011). Therefore, solubility of CO2 in rhyolitic sediment partial melts needs to be known. Previous studies on rhyolitic melts experimentally determined CO2 solubility from 0.05 to 0.66 GPa (Fig. 1; Fogel and Rutherford, 1990; Blank et al., 1993; Tamic et al., 2001). This pressure range is not appropriate for global sub-arc depth range of 72-173 km (Syracuse and Abers, 2006) settings (P = 2-5 GPa). Carbon dioxide solubility experiments at pressures from 1.5 to 3.5 GPa are available but only on simple compositions - i.e., albite, which does not have the chemical complexity of natural sediment partial melts (Fig. 1; Brey, 1976; Mysen, 1976; Mysen et al., 1976; Mysen and Virgo, 1980; Stolper et al., 1987; Brooker et al., 1999). For example, natural rhyolitic melt derived from partial fusion of pelitic sediments contain non-negligible concentrations of Ca2+, Mg2+, Fe2+. Many of these studies were also conducted under mixed-volatile conditions (CO2 + H2O) with H2O contents from 0.06 to 3.3 wt.%. These studies were used in calculating various solubility models: Volatile-Calc (Newman and Lowenstern, 2002), that of Liu et al. (2005), and that of Papale et al. (2006). Volatile-Calc can be used to calculate CO2 solubility only on a generic rhyolite composition up to 0.5 GPa. The model of Liu et al. (2005) is also on a generic rhyolite up to 0.5 GPa, but can calculate mixed volatile concentrations provided the vapor composition is known. The model of Papale et al. (2006) can be used to calculate mixed volatile concentrations for a melt composition of interest, but only up to 1.0 GPa.The literature data show that CO2 solubility increases with increasing pressure and decreases with increasing melt silica content (decreasing NBO/T; e.g., Brooker et al., 2001). The effect of temperature remains somewhat ambiguous, but is thought to be relatively smaller than the pressure or compositional effects, with Mysen (1976) measuring increasing CO2 solubility with temperature for albite melt, Brooker et al. (2001) and Fogel and Rutherford (1990) noticing decreasing CO2 solubility with increasing temperature, and Stolper et al. (1987) concluding that temperature has essentially no effect on total melt CO2 concentration at saturation. The presence of water in the melt also is known to affect CO2 solution (e.g., Mysen, 1976; Eggler and Rosenhauer, 1978), yet quantitative effect of water on CO2 solution in natural rhyolitic melt has only been investigated up to 0.5 GPa (Tamic et al., 2001). In order to determine the CO2 carrying capacity of sediment partial melts, experiments must be conducted at conditions (pressure, temperature, major element compositions, and XH2O) relevant to sub-arc settings.In this study we measured the solubility and speciation of CO2 in rhyolitic sediment partial melts. Experiments were conducted from 1.5 to 3.0 GPa at 1300 °C with variable water contents and synthesized glasses were analyzed for water and carbon speciation using Fourier-transformed infrared spectroscopy. Our measured solubility data allowed us to constrain volume change and equilibrium constant of the CO2 dissolution reactions. Moreover, we parameterize CO2 solubility in sediment partial melt as a function of pressure and melt water content. Our data and empirical model suggest that the CO2 carrying capacity of sediment partial melts is sufficiently high at sub-arc depths and hydrous sediment melt can potentially carry the necessary dose of CO2 to arc mantle source regions.

Molybdenum isotope systematics in subduction zones

NASA Astrophysics Data System (ADS)

König, Stephan; Wille, Martin; Voegelin, Andrea; Schoenberg, Ronny

2016-08-01

This study presents Mo isotope data for arc lavas from different subduction zones that range between δ 98 / 95 Mo = - 0.72 and + 0.07 ‰. Heaviest isotope values are observed for the most slab fluid dominated samples. Isotopically lighter signatures are related to increasing relevance of terrigenous sediment subduction and sediment melt components. Our observation complements previous conclusions that an isotopically heavy Mo fluid flux likely mirrors selective incorporation of isotopically light Mo in secondary minerals within the subducting slab. Analogue to this interpretation, low δ 98 / 95 Mo flux that coincides with terrigenous sediment subduction and sediment melting cannot be simply related to a recycled input signature. Instead, breakdown of the controlling secondary minerals during sediment melting may release the light component and lead to decreasing δ 98 / 95 Mo influx into subarc mantle sources. The natural range between slab dehydration and hydrous sediment melting may thus cause a large spread of δ 98 / 95 Mo in global subduction zone magmas.

Geophysical signature of hydration-dehydration processes in active subduction zones

NASA Astrophysics Data System (ADS)

Reynard, Bruno

2013-04-01

Seismological and magneto-telluric tomographies are potential tools for imaging fluid circulation when combined with petrophysical models. Recent measurements of the physical properties of serpentine allow refining hydration of the mantle and fluid circulation in the mantle wedge from geophysical data. In the slab lithospheric mantle, serpentinization caused by bending at the trench is limited to a few kilometers below the oceanic crust (<5 km). Double Wadati-Benioff zones, 20-30 km below the crust, are explained by deformation of dry peridotites, not by serpentine dehydration. It reduces the required amount of water stored in solid phases in the slab (Reynard et al., 2010). In the cold (<700°C) fore-arc mantle wedge above the subducting slab, serpentinization is caused by the release of large amounts of hydrous fluids in the cold mantle above the dehydrating subducted plate. Low seismic velocities in the wedge give a time-integrated estimate of hydration and serpentinization. Serpentinization reaches 50-100% in hot subduction, while it is below 10% in cold subduction (Bezacier et al., 2010; Reynard, 2012). Electromagnetic profiles of the mantle wedge reveal high electrical-conductivity bodies. In hot areas of the mantle wedge (> 700°C), water released by dehydration of the slab induces melting of the mantle under volcanic arcs, explaining the observed high conductivities. In the cold melt-free wedge (< 700°C), high conductivities in electromagnetic profiles provide "instantaneous" images of fluid circulation because the measured electrical conductivity of serpentine is below 0.1 mS/m (Reynard et al., 2011). A small fraction (ca. 1% in volume) of connective high-salinity fluids accounts for the highest observed conductivities. Low-salinity fluids (≤ 0.1 m) released by slab dehydration evolve towards high-salinity (≥ 1 m) fluids during progressive serpentinization in the wedge. These fluids can mix with arc magmas at depths and account for high-chlorine melt inclusions in arc lavas. High electrical conductivities up to 1 S/m in the hydrated wedge of the hot subductions (Ryukyu, Kyushu, Cascadia) reflect high fluid concentration, while low to moderate (<0.01 S/m) conductivities in the cold subductions (N-E Japan, Bolivia) reflect low fluid flow. This is consistent with the seismic observations of extensive shallow serpentinization in hot subduction zones, while serpentinization is sluggish in cold subduction zones. Bezacier, L., et al. 2010. Elasticity of antigorite, seismic detection of serpentinites, and anisotropy in subduction zones. Earth and Planetary Science Letters, 289, 198-208. Reynard, B., 2012. Serpentine in active subduction zones. Lithos, http://dx.doi.org/10.1016/j.lithos.2012.10.012. Reynard, B., Mibe, K. & Van de Moortele, B., 2011. Electrical conductivity of the serpentinised mantle and fluid flow in subduction zones. Earth and Planetary Science Letters, 307, 387-394. Reynard, B., Nakajima, J. & Kawakatsu, H., 2010. Earthquakes and plastic deformation of anhydrous slab mantle in double Wadati-Benioff zones. Geophysical Research Letters, 37, L24309.

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

NASA Astrophysics Data System (ADS)

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

2016-11-01

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

Compositional dependent partial molar volume and compressibility of CO2 in rhyolite, phonolite and basalt glasses

NASA Astrophysics Data System (ADS)

Lerch, P.; Seifert, R.; Malfait, W. J.; Sanchez-Valle, C.

2012-12-01

Carbon dioxide is the second most abundant volatile in magmatic systems and plays an important role in many magmatic processes, e.g. partial melting, volatile saturation, outgassing. Despite this relevance, the volumetric properties of carbon-bearing silicates at relevant pressure and temperature conditions remain largely unknown because of considerable experimental difficulties associated with in situ measurements. Density and elasticity measurements on quenched glasses can provide an alternative source of information. For dissolved water, such measurements indicate that the partial molar volume is independent of compositions at ambient pressure [1], but the partial molar compressibility is not [2, 3]. Thus the partial molar volume of water may depend on melt composition at elevated pressure. For dissolved CO2, no such data is available. In order to constrain the effect of magma composition on the partial molar volume and compressibility of dissolved carbon, we determined the density and elasticity for three series of carbon-bearing basalt, phonolite and rhyolite glasses, quenched from 3.5 GPa and relaxed at ambient pressure. The CO2 content varies between 0 to 3.90 wt% depending on the glass composition. Glass densities were determined using the sink/float method in a diiodomethane (CH2I2) - acetone mixture. Brillouin measurements were conducted on relaxed and unrelaxed silicate glasses in platelet geometry to determine the compressional (VP) and shear (VS) wave velocities and elastic moduli. The partial molar volume of CO2 in rhyolite, phonolite and basalt glasses is 25.4 ± 0.9, 22.1 ± 0.6 and 26.6 ±1.8 cm3/mol, respectively. Thus, unlike for dissolved water, the partial molar volume of CO2 displays a resolvable compositional effect. Although the composition and CO2/carbonate speciation of the phonolite glasses is intermediate between that of the rhyolite and basalt glasses, the molar volume is not. Similar to dissolved water, the partial molar bulk modulus of CO2 displays a strong compositional effect. If these compositional dependencies persist in the analogue melts, the partial molar volume of dissolved CO2 will depend on melt composition, both at low and elevated pressure. Thus, for CO2-bearing melts, a full quantitative understanding of density dependent magmatic processes, such as crystal fractionation, magma mixing and melt extraction will require in situ measurements for a range of melt compositions. [1] Richet, P. et al., 2000, Contrib Mineral Petrol, 138, 337-347. [2] Malfait et al. 2011, Am. Mineral. 96, 1402-1409. [3] Whittington et al., 2012, Am. Mineral. 97, 455-467.

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

Partial melting of continental crust is a strong weakening process controlling its rheological behavior and ductile flow of orogens. This strength weakening due to partial melting is commonly constrained experimentally on synthetic starting material with derived rheological law. Such analog starting materials are preferentially used because of their well-constrained composition to test the impact of melt fraction, melt viscosity and melt distribution upon rheology. In nature, incipient melting appears in particular locations where mineral and water contents are favorable, leading to stromatic migmatites with foliation-parallel leucosomes. In addition, leucosomes are commonly located in dilatants structural sites like boudin-necks, in pressure shadows, or in fractures within more competent layers of migmatites. The compositional layering is an important parameter controlling melt flow and rheological behavior of migmatite but has not been tackled experimentally for natural starting material. In this contribution we performed in-situ deformation experiments on natural rock samples in order to test the effect of initial gneissic layering on melt distribution, melt flow and rheological response. In-situ deformation experiments using a Paterson apparatus were performed on two partially melted natural gneissic rocks, named NOP1 & PX28. NOP1, sampled in the Western Gneiss Region (Norway), is biotite-muscovite bearing gneiss with a week foliation and no gneissic layering. PX28, sampled from the Sioule Valley series (French Massif Central), is a paragneiss with a very well pronounced layering with quartz-feldspar-rich and biotite-muscovite-rich layers. Experiments were conducted under pure shear condition at axial strain rate varying from 5*10-6 to 10-3 s-1. The main stress component was maintained perpendicular to the main plane of anisotropy. Confining pressure was 3 kbar and temperature ranges were 750°C and 850-900°C for NOP1 and PX28, respectively. For the 750°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.

Evidence for CO2-rich fluids in rocks from the type charnockite area near Pallavaram, Tamil Nadu

NASA Technical Reports Server (NTRS)

Hansen, E.; Hunt, W.; Jacob, S. C.; Morden, K.; Reddi, R.; Tacy, P.

1988-01-01

Fluid inclusion and mineral chemistry data was presented for samples from the type charnockite area near Pallavaram (Tamil Nadu, India). The results indicate the presence of a dense CO2 fluid phase, but the data cannot distinguish between influx of this fluid from elsewhere or localized migration of CO2-rich fluids associated with dehydration melting.

A Compilation of Hazard and Test Data for Pyrotechnic Compositions

DTIC Science & Technology

1980-10-01

heated. These changes may be related to dehydration , decomposition , crystal- line transition, melting, boiling, vaporization, polymerization, oxidation...123 180 + 66 162 + 16 506 +169 447 +199 448+ 159 Decomposition temperature °C 277 + 102 561 j; 135 205 + 75 182 + 24 550 + 168 505 +224 517 + 153...of compatibility or classification. The following tests are included in the parametric tests: 1. Autoignition Temperature 2. Decomposition

Ultrasonic Acoustic Velocities During Partial Melting of a Mantle Peridotite KLB-1

NASA Astrophysics Data System (ADS)

Weidner, Donald J.; Li, Li; Whitaker, Matthew L.; Triplett, Richard

2018-02-01

Knowledge of the elastic properties of partially molten rocks is crucial for understanding low-velocity regions in the interior of the Earth. Models of fluid and solid mixtures have demonstrated that significant decreases in seismic velocity are possible with small amounts of melt, but there is very little available data for testing these models, particularly with both P and S waves for mantle compositions. We report ultrasonic measurements of P and S velocities on a partially molten KLB-1 sample at mantle conditions using a multi-anvil device at a synchrotron facility. The P, S, and bulk sound velocities decrease as melting occurs. We find that the quantity, ∂lnVS/∂lnVB (where VB is the bulk sound velocity) is lower than mechanical models estimate. Instead, our data, as well as previous data in the literature, are consistent with a dynamic melting model in which melting and solidification interact with the stress field of the acoustic wave.

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.

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

NASA Astrophysics Data System (ADS)

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

2016-04-01

Presence of melt significantly influences rheological properties of partially molten rocks by providing fast diffusional pathways. Under stress, melt aligns at the grain scale and this alignment induces viscous anisotropy in the deforming aggregate. One of the consequences of viscous anisotropy is melt segregation into melt-rich sheets oriented at low angle to the shear plane on much larger scales than the grain scale. The magnitude and orientation of viscous anisotropy with respect to the applied stress are important parameters for constitutive models (Takei and Holtzman 2009) that must be constrained by experimental studies. In this contribution, we analyze the shape preferred orientation (SPO) of individual grain-scale melt pockets in deformed partially molten mantle rocks. The starting materials were obtained by isostatically hot-pressing olivine + basalt and olivine + chromite + basalt powders. These partially molten rocks were deformed in general shear or torsion at a confining pressure, Pc = 300 MPa, temperature, T = 1200° - 1250° C, and strain rates of 10-3 - 10-5 s-1to finite shear strains, γ, of 0.5 - 5. After the experiment, high resolution backscattered electron images were obtained using a SEM equipped with a field emission gun. Individual melt pockets were segmented and their SPO analyzed using the paror and surfor methods and Fourier transforms (Heilbronner and Barret 2014). Melt segregation into melt-rich sheets inclined at 15° -20° antithetic with respect to the shear plane occurs in three-phase system (olivine + chromite + basalt) and in two-phase systems (olivine + basalt) twisted to high strain. The SPO of individual melt pockets within the melt-rich bands is moderately strong (b/a ≈ 0.8) and is always steeper (20° -40°) than the average melt-rich band orientation. In the two-phase system (olivine + basalt) sheared to lower strains, no distinct melt-rich sheets are observed. Individual grain-scale melt pockets are oriented at 45° -55° antithetic with respect to the shear plane (i.e., sub-perpendicular to σ3) with a strong SPO (b/a ≈ 0.7) that decreases with increasing finite strain. Our observations of melt alignment at low strains are in agreement with observations performed on analogue materials (borneol, Takei 2010) and provide further constraints for the orientation of viscous anisotropy in the Earth's mantle. The systematic difference in grain-scale melt alignment between samples in which melt segregation did and did not occur - irrespective of the deformation geometry and mineralogy - suggests that melt segregation into bands leads to local stress rotation within the samples.

Single-Molecule Denaturation Mapping of DNA in Nanofluidic Channels

NASA Astrophysics Data System (ADS)

Reisner, Walter; Larsen, Niels; Silahtaroglu, Asli; Kristensen, Anders; Tommerup, Niels; Tegenfeldt, Jonas O.; Flyvbjerg, Henrik

2010-03-01

Nanochannel based DNA stretching can serve as a platform for a new optical mapping technique based on measuring the pattern of partial melting along the extended molecules. We partially melt DNA extended in nanofluidic channels via a combination of local heating and added chemical denaturants. The melted molecules, imaged via a standard fluorescence videomicroscopy setup, exhibit a nonuniform fluorescence profile corresponding to a series of local dips and peaks in the intensity trace along the stretched molecule. We show that this barcode is consistent with the presence of locally melted regions along the molecule and can be explained by calculations of sequence-dependent melting probability. Specifically, we obtain experimental melting profiles for T4, T7, lambda-phage and bacterial artificial chromosome DNA (from human chromosome 12) and compare these profiles to theory. In addition, we demonstrate that the BAC melting profile can be used to align the BAC to its correct position on chromosome 12.

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.

Derivation of intermediate to silicic magma from the basalt analyzed at the Vega 2 landing site, Venus.

PubMed

Shellnutt, J Gregory

2018-01-01

Geochemical modeling using the basalt composition analyzed at the Vega 2 landing site indicates that intermediate to silicic liquids can be generated by fractional crystallization and equilibrium partial melting. Fractional crystallization modeling using variable pressures (0.01 GPa to 0.5 GPa) and relative oxidation states (FMQ 0 and FMQ -1) of either a wet (H2O = 0.5 wt%) or dry (H2O = 0 wt%) parental magma can yield silicic (SiO2 > 60 wt%) compositions that are similar to terrestrial ferroan rhyolite. Hydrous (H2O = 0.5 wt%) partial melting can yield intermediate (trachyandesite to andesite) to silicic (trachydacite) compositions at all pressures but requires relatively high temperatures (≥ 950°C) to generate the initial melt at intermediate to low pressure whereas at high pressure (0.5 GPa) the first melts will be generated at much lower temperatures (< 800°C). Anhydrous partial melt modeling yielded mafic (basaltic andesite) and alkaline compositions (trachybasalt) but the temperature required to produce the first liquid is very high (≥ 1130°C). Consequently, anhydrous partial melting is an unlikely process to generate derivative liquids. The modeling results indicate that, under certain conditions, the Vega 2 composition can generate silicic liquids that produce granitic and rhyolitic rocks. The implication is that silicic igneous rocks may form a small but important component of the northeast Aphrodite Terra.

Derivation of intermediate to silicic magma from the basalt analyzed at the Vega 2 landing site, Venus

PubMed Central

2018-01-01

Geochemical modeling using the basalt composition analyzed at the Vega 2 landing site indicates that intermediate to silicic liquids can be generated by fractional crystallization and equilibrium partial melting. Fractional crystallization modeling using variable pressures (0.01 GPa to 0.5 GPa) and relative oxidation states (FMQ 0 and FMQ -1) of either a wet (H2O = 0.5 wt%) or dry (H2O = 0 wt%) parental magma can yield silicic (SiO2 > 60 wt%) compositions that are similar to terrestrial ferroan rhyolite. Hydrous (H2O = 0.5 wt%) partial melting can yield intermediate (trachyandesite to andesite) to silicic (trachydacite) compositions at all pressures but requires relatively high temperatures (≥ 950°C) to generate the initial melt at intermediate to low pressure whereas at high pressure (0.5 GPa) the first melts will be generated at much lower temperatures (< 800°C). Anhydrous partial melt modeling yielded mafic (basaltic andesite) and alkaline compositions (trachybasalt) but the temperature required to produce the first liquid is very high (≥ 1130°C). Consequently, anhydrous partial melting is an unlikely process to generate derivative liquids. The modeling results indicate that, under certain conditions, the Vega 2 composition can generate silicic liquids that produce granitic and rhyolitic rocks. The implication is that silicic igneous rocks may form a small but important component of the northeast Aphrodite Terra. PMID:29584745

Craton destruction and related resources

NASA Astrophysics Data System (ADS)

Zhu, Rixiang; Zhang, Hongfu; Zhu, Guang; Meng, Qingren; Fan, Hongrui; Yang, Jinhui; Wu, Fuyuan; Zhang, Zhiyong; Zheng, Tianyu

2017-10-01

Craton destruction is a dynamic event that plays an important role in Earth's evolution. Based on comprehensive observations of many studies on the North China Craton (NCC) and correlations with the evolution histories of other cratons around the world, craton destruction has be defined as a geological process that results in the total loss of craton stability due to changes in the physical and chemical properties of the involved craton. The mechanisms responsible for craton destruction would be as the follows: (1) oceanic plate subduction; (2) rollback and retreat of a subducting oceanic plate; (3) stagnation and dehydration of a subducting plate in the mantle transition zone; (4) melting of the mantle above the mantle transition zone caused by dehydration of a stagnant slab; (5) non-steady flow in the upper mantle induced by melting, and/or (6) changes in the nature of the lithospheric mantle and consequent craton destruction caused by non-steady flow. Oceanic plate subduction itself does not result in craton destruction. For the NCC, it is documented that westward subduction of the paleo-Pacific plate should have initiated at the transition from the Middle-to-Late Jurassic, and resulted in the change of tectonic regime of eastern China. We propose that subduction, rollback and retreat of oceanic plates and dehydration of stagnant slabs are the main dynamic factors responsible for both craton destruction and concentration of mineral deposits, such as gold, in the overriding continental plate. Based on global distribution of gold deposits, we suggest that convergent plate margins are the most important setting for large gold concentrations. Therefore, decratonic gold deposits appear to occur preferentially in regions with oceanic subduction and overlying continental lithospheric destruction/modification/growth.

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.

Generation, ascent and eruption of magma on the Moon: New insights into source depths, magma supply, intrusions and effusive/explosive eruptions (Part 1: Theory)

NASA Astrophysics Data System (ADS)

Wilson, Lionel; Head, James W.

2017-02-01

We model the ascent and eruption of lunar mare basalt magmas with new data on crustal thickness and density (GRAIL), magma properties, and surface topography, morphology and structure (Lunar Reconnaissance Orbiter). GRAIL recently measured the broad spatial variation of the bulk density structure of the crust of the Moon. Comparing this with the densities of lunar basaltic and picritic magmas shows that essentially all lunar magmas were negatively buoyant everywhere within the lunar crust. Thus positive excess pressures must have been present in melts at or below the crust-mantle interface to enable them to erupt. The source of such excess pressures is clear: melt in any region experiencing partial melting or containing accumulated melt, behaves as though an excess pressure is present at the top of the melt column if the melt is positively buoyant relative to the host rocks and forms a continuously interconnected network. The latter means that, in partial melt regions, probably at least a few percent melting must have taken place. Petrologic evidence suggests that both mare basalts and picritic glasses may have been derived from polybaric melting of source rocks in regions extending vertically for at least a few tens of km. This is not surprising: the vertical extent of a region containing inter-connected partial melt produced by pressure-release melting is approximately inversely proportional to the acceleration due to gravity. Translating the ∼25 km vertical extent of melting in a rising mantle diapir on Earth to the Moon then implies that melting could have taken place over a vertical extent of up to 150 km. If convection were absent, melting could have occurred throughout any region in which heat from radioisotope decay was accumulating; in the extreme this could have been most of the mantle. The maximum excess pressure that can be reached in a magma body depends on its environment. If melt percolates upward from a partial melt zone and accumulates as a magma reservoir, either at the density trap at the base of the crust or at the rheological trap at the base of the elastic lithosphere, the excess pressure at the top of the magma body will exert an elastic stress on the overlying rocks. This will eventually cause them to fail in tension when the excess pressure has risen to close to twice the tensile strength of the host rocks, perhaps up to ∼10 MPa, allowing a dike to propagate upward from this point. If partial melting occurs in a large region deep in the mantle, however, connections between melt pockets and veins may not occur until a finite amount, probably a few percent, of melting has occurred. When interconnection does occur, the excess pressure at the top of the partial melt zone will rise abruptly to a high value, again initiating a brittle fracture, i.e. a dike. That sudden excess pressure is proportional to the vertical extent of the melt zone, the difference in density between the host rocks and the melt, and the acceleration due to gravity, and could readily be ∼100 MPa, vastly greater than the value needed to initiate a dike. We therefore explored excess pressures in the range ∼10 to ∼100 MPa. If eruptions take place through dikes extending upward from the base of the crust, the mantle magma pressure at the point where the dike is initiated must exceed the pressure due to the weight of the magmatic liquid column. This means that on the nearside the excess pressure must be at least ∼19 ± 9 MPa and on the farside must be ∼29 ± 15 MPa. If the top of the magma body feeding an erupting dike is a little way below the base of the crust, slightly smaller excess pressures are needed because the magma is positively buoyant in the part of the dike within the upper mantle. Even the smallest of these excess pressures is greater than the ∼10 MPa likely maximum value in a magma reservoir at the base of the crust or elastic lithosphere, but the values are easily met by the excess pressures in extensive partial melt zones deeper within the mantle. Thus magma accumulations at the base of the crust would have been able to intrude dikes part-way through the crust, but not able to feed eruptions to the surface; in order to be erupted, magma must have been extracted from deeper mantle sources, consistent with petrologic evidence. Buoyant dikes growing upward from deep mantle sources of partial melt can disconnect from their source regions and travel through the mantle as isolated bodies of melt that encounter and penetrate the crust-mantle density boundary. They adjust their lengths and internal pressure excesses so that the stress intensity at the lower tip is zero. The potential total vertical extent of the resulting melt body depends on the vertical extent of the source region from which it grew. For small source extents, the upper tip of the resulting dike crossing the crust-mantle boundary cannot reach the surface anywhere on the Moon and therefore can only form a dike intrusion; for larger source extents, the dike can reach the surface and erupt on the nearside but still cannot reach the surface on the farside; for even larger source extents, eruptions could occur on both the nearside and the farside. The paucity of farside eruptions therefore implies a restricted range of vertical extents of partial melt source region sizes, between ∼16 and ∼36 km. When eruptions can occur, the available pressure in excess of what is needed to support a static magma column to the surface gives the pressure gradient driving magma flow. The resulting typical turbulent magma rise speeds are ∼10 to a few tens of m s-1, dike widths are of order 100 m, and eruption rates from 1 to 10 km long fissure vents are of order 105 to 106 m3 s-1. Volume fluxes in lunar eruptions derived from lava flow thicknesses and surface slopes or rille lengths and depths are found to be of order 105 to 106 m3 s-1 for volume-limited lava flows and >104 to 105 m3 s-1 for sinuous rilles, with dikes widths of ∼50 m. The lower end of the volume flux range for sinuous rilles corresponds to magma rise speeds approaching the limit set by the fact that excessive cooling would occur during flow up a 30 km long dike kept open by a very low excess pressure. These eruptions were thus probably fed by partial melt zones deep in the mantle. Longer eruption durations, rather than any subtle topographic slope effects, appear to be the key to the ability of these flows to erode sinuous rille channels. We conclude that: (1) essentially all lunar magmas were negatively buoyant everywhere within the crust; (2) positive excess pressures of at least 20-30 MPa must have been present in mantle melts at or below the crust-mantle interface to drive magmas to the surface; (3) such pressures are easily produced in zones of partial melting by pressure-release during mantle convection or simple heat accumulation from radioisotopes; (4) magma volume fluxes available from dikes forming at the tops of partial melt zones are consistent with the 105 to 106 m3 s-1 volume fluxes implied by earlier analyses of surface flows; (5) eruptions producing thermally-eroded sinuous rille channels involved somewhat smaller volume fluxes of magma where the supply rate may be limited by the rate of extraction of melt percolating through partial melt zones.

Investigation of the H7 ordinary chondrite, Watson 012: Implications for recognition and classification of Type 7 meteorites

NASA Astrophysics Data System (ADS)

Tait, Alastair W.; Tomkins, Andrew G.; Godel, Bélinda M.; Wilson, Siobhan A.; Hasalova, Pavlina

2014-06-01

Despite the fact that the number of officially classified meteorites is now over 45,000, we lack a clearly defined sequence of samples from a single parent body that records the entire range in metamorphic temperatures from pristine primitive meteorites up to the temperatures required for extensive silicate partial melting. Here, we conduct a detailed analysis of Watson 012, an H7 ordinary chondrite, to generate some clarity on the textural and chemical changes associated with equilibrium-based silicate partial melting in chondritic meteorites. To do this we compare the textures in the meteorite with those preserved in metamorphic contact aureoles on Earth. The most distinctive texture generated by the partial melting that affected Watson 012 is an extensively interconnected plagioclase network, which is clearly observable with a petrographic microscope. Enlarged metal-troilite grains are encapsulated at widenings in this plagioclase network, and this is clearly visible in reflected light. Together with these features, we define a series of other characteristics that can be used to more clearly classify chondritic meteorites as being of petrologic Type 7. To provide comprehensive evidence of silicate partial melting and strengthen the case for using simple petrographic observations to classify similar meteorites, we use high-resolution X-ray computed tomography to demonstrate that the plagioclase network has a high degree of interconnectedness and crystallised as large (cm-scale) skeletal crystals within an olivine-orthopyroxene-clinopyroxene framework, essentially pseudomorphing a melt network. Back-scattered electron imaging and element mapping are used to show that some of the clino- and orthopyroxene in Watson 012 also crystallised from silicate melt, and the order of crystallisation was orthopyroxene → clinopyroxene → plagioclase. X-ray diffraction data, supported by bulk geochemistry, are used to show that plagioclase and ortho- and clinopyroxene were added to the Watson 012 sample by through-flowing basaltic melt. Along with the absence of glass and granophyre, this interconnected network of coarse-grained skeletal plagioclase indicates that the sample cooled slowly at depth within the parent body. The evidence of melt flux indicates that Watson 012 formed in the presence of a gravitational gradient, and thus at significant distance from the centre of the H chondrite parent body (the gravitational gradient at the centre would be zero). Our interpretation is that incipient silicate partial melting in Watson 012 occurred when a region of radiogenically heated H6 material located at considerable depth (possibly at ∼15-20 km from surface) was heated by an additional ca. 200-300 °C in association with a large shock event. Due to insulation at depth within an already hot parent body, the post-shock temperature equilibrated and remained above the solidus long enough for widespread equilibrium-based silicate partial melting, and for melt to migrate. Although the observed melting may have been facilitated by additional heating from an impact event, this is not an example of instantaneous shock melting, which produces thermal disequilibrium at short length scales and distinctly different textures. A small number of H, L and LL chondrites have been previously classified as being of petrologic Type 7; with our new criteria to support that classification, these represent our best opportunity to explore the transition from high temperature sub-solidus metamorphism through the onset of silicate partial melting in three different parent bodies.

Powder formation of {gamma} uranium-molybdenum alloys via hydration-dehydration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vaz de Oliveira, Fabio Branco; Durazzo, Michelangelo; Fontenele Urano de Carvalho, Elita

2008-07-15

Gamma uranium-molybdenum alloys has been considered as fuel phase in plate type fuel elements for MTR reactors, mainly due to their acceptable performance under irradiation and metallurgical processing. To its use as a dispersion phase in aluminum matrix, a necessary step is the conversion of the as cast structure into powder, and one of the techniques considered at IPEN / CNEN - Brazil is HDH (hydration-dehydration). The alloys were produced by the induction melting technique, and samples were obtained from the alloys for the thermal treatments, under constant flow of hydrogen, for temperatures varying from 400 deg C to 600more » deg C and times from 1 to 4 hours, followed by dehydration. A preliminary characterization of the powders was made and the curves of mass variation versus time were obtained and related to the powder characteristics. This paper describes the first results on the development of the technology to the powder formation of the (5 to 10) % weight molybdenum {gamma}-UMo alloys, and discusses some of its aspects, mainly those related to the {gamma} {yields} {alpha} equilibrium data. (author)« less

Methods for Converter Sludge Dehydration Intensification

NASA Astrophysics Data System (ADS)

Vakhromeev, M. I.; Moreva, Y. A.; Starkova, L. G.

2017-11-01

The article considers the intensification methods for converter sludge dehydration exemplified by the sludges of the Oxygen Converter Workshop (OCW) of the Open Joint-Stock Company “Magnitogorsk Iron and Steel Works” (MMK, OJSC), one of the largest metallurgical companies in the Southern Urals. Converter sludges can contain up to 45-70% of ferrum [21] which is interesting in terms of their use as an addition to a sinter-feed mixture. Sludge intensifies the sintering process. It positively influences pelletizing and fusion mixture melting dynamics at sintering. Over the period of the converter sludge dehydration complex operation at the OCW, MMK, OJSC, it was revealed that processing results in obtaining of high humidity sludge. It causes sludge freezing during the winter period, thus, its transportation involves extra costs for sludge warming up. To resolve the above-mentioned problem, the following works were performed in 2016: - experimental studies of how the application of the low-molecular anionic flocculate “SEURVEY” FL-3 influences sludge humidity reduction. - experimental studies of how the filtering press process operation parameters influence sludge humidity reduction. The new flocculate application didn't lower the dehydrated sludge humidity (the objective was the humidity of not more than 15%). Basing upon the conducted research results, we can make a conclusion that putting into operation the sewage water reactant treatment technology with the use of “SEURVEY”, FL-3 (H-10) is not recommended. The research of the influence the filtering press process parameters have on the dehydration process intensification demonstrated that reaching of the obtained residue humidity value lower than 15% is possible under the reduction of the filtering press chamber depths to 30 mm and with the application of additional operation “Residue drying” with compressed air. This way of the sludge dehydration problem resolving at filtering presses of the converter sludge dehydration complex of the OCW, MMK, OJSC, can be recommended for application.

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.

Anatexis at the roof of an oceanic magma chamber at IODP Site 1256 (equatorial Pacific): an experimental study

NASA Astrophysics Data System (ADS)

Erdmann, Martin; Fischer, Lennart A.; France, Lydéric; Zhang, Chao; Godard, Marguerite; Koepke, Jürgen

2015-04-01

Replenished axial melt lenses at fast-spreading mid-oceanic ridges may move upward and intrude into the overlying hydrothermally altered sheeted dikes, resulting in high-grade contact metamorphism with the potential to trigger anatexis in the roof rocks. Assumed products of this process are anatectic melts of felsic composition and granoblastic, two-pyroxene hornfels, representing the residue after partial melting. Integrated Ocean Drilling Program Expeditions 309, 312, and 335 at Site 1256 (eastern equatorial Pacific) sampled such a fossilized oceanic magma chamber. In this study, we simulated magma chamber roof rock anatectic processes by performing partial melting experiments using six different protoliths from the Site 1256 sheeted dike complex, spanning a lithological range from poorly to strongly altered basalts to partially or fully recrystallized granoblastic hornfels. Results show that extensively altered starting material lacking primary magmatic minerals cannot reproduce the chemistry of natural felsic rocks recovered in ridge environments, especially elements sensitive to hydrothermal alteration (e.g., K, Cl). Natural geochemical trends are reproduced through partial melting of moderately altered basalts from the lower sheeted dikes. Two-pyroxene hornfels, the assumed residue, were reproduced only at low melting degrees (<20 vol%). The overall amphibole absence in the experiments confirms the natural observation that amphibole is not produced during peak metamorphism. Comparing experimental products with the natural equivalents reveals that water activity ( aH2O) was significantly reduced during anatectic processes, mainly based on lower melt aluminum oxide and lower plagioclase anorthite content at lower aH2O. High silica melt at the expected temperature (1000-1050 °C; peak thermal overprint of two-pyroxene hornfels) could only be reproduced in the experimental series performed at aH2O = 0.1.

The occurrence of fluor-wagnerite in UHT granulites and its implications towards understanding fluid regimes in the evolution of deep crust: a case study from the Eastern Ghats Belt, India

NASA Astrophysics Data System (ADS)

Das, Kaushik; Tomioka, Naotaka; Bose, Sankar; Ando, Jun-ichi; Ohnishi, Ichiro

2017-06-01

We report the occurrence of a rare phosphate mineral, fluor-wagnerite (Mg1.91-1.94Fe0.06-0.07Ca<0.01) (P0.99-1.00O4)(OH0.02-0.17F0.98-0.83) from the Eastern Ghats Belt of India, an orogenic belt evolved during Meso- to Neoproterozoic time. The host rock, i.e. high- to ultrahigh temperature (UHT) granulites ( 1000 °C, 8-9 kbar) of the studied area was retrogressed after emplacement to mid-crustal level (800-850 °C, 6-6.5 kbar) as deduced from their pressure -temperature histories. Based on mineral chemical data and micro-Raman analyses, we document an unusual high Mg-F-rich chemistry of the F-wagnerite, which occur both in peak metamorphic porphyroblastic assemblages as well as in the retrograde matrix assemblage. Therefore, in absence of other common phosphates like apatite, fluor-wagnerite can act as an indicator for the presence of F-bearing fluids for rocks with high X Mg and/or fO2. The occurrence of F-rich minerals as monitors for fluid compositions has important implications for the onset of biotite dehydration melting and hence melt production in the deep crust. We propose that fluor-wagnerite can occur as an accessory mineral associated with F-rich fluids in lower-mid crustal rocks, and F in coexisting minerals should be taken into consideration when reconciling the petrogenetic grid of biotite-dehydration melting.

Metamorphic and tectonic evolution of the Greater Himalayan Crystalline Complex in Nyalam region, south Tibet

NASA Astrophysics Data System (ADS)

Wang, Jia-Min; Zhang, Jin-Jiang; Rubatto, Daniela

2016-04-01

Recent studies evoke dispute whether the Himalayan metamorphic core - Greater Himalayan Crystalline Complex (GHC) - was exhumed as a lateral crustal flow or a critical taper wedge during the India-Asia collision. This contribution investigated the evolution of the GHC in the Nyalam region, south Tibet, with comprehensive studies on structural kinematics, metamorphic petrology and geochronology. The GHC in the Nyalam region can be divided into the lower and upper GHC. Phase equilibria modelling and conventional thermobarometric results show that peak temperature conditions are lower in the lower GHC (~660-700°C) and higher in the upper GHC (~740-780°C), whereas corresponding pressure conditions at peak-T decrease from ~9-13 kbar to ~4 kbar northward. Monazite, zircon and rutile U-Pb dating results reveal two distinct blocks within the GHC of the Nyalam region. The upper GHC underwent higher degree of partial melting (15-25%, via muscovite dehydration melting) that initiated at ~32 Ma, peaked at ~29 Ma to 25 Ma, possibly ended at ~20 Ma. The lower GHC underwent lower degree of melting (0-10%) that lasted from 19 to 16 Ma, which was produced mainly via H2O-saturated melting. At different times, both the upper and lower blocks underwent initial slow cooling (35 ± 8 and 10 ± 5°C/Myr, respectively) and subsequent rapid cooling (120 ± 40°C/Myr). The established timescale of metamorphism suggests that high-temperature metamorphism within the GHC lasted a long duration (~15 Myr), whereas duration of partial melting lasted for ~3 Myr in the lower GHC and lasted for 7-12 Myr in the upper GHC. The documented diachronous metamorphism and discontinuity of peak P-T conditions implies the presence of the Nyalam Thrust in the study area. This thrust is probably connected to the other thrusts in Nepal and Sikkim Himalaya, which extends over ~800 km and is named the "High Himalayan Thrust". Timing of activity along this thrust is at ~25-16 Ma, which is coeval with active timing along the South Tibetan detachment (27-16 Ma) but precedes that along the MCT (16-10 Ma). Comparison between the obtained P-T-t data and model predictions implies that a lateral crustal flow process dominated the exhumation of the high-grade upper GHC migmitites during 25-16 Ma, whereas a critical taper thrusting process dominated the exhumation of the MCT zone nonmigmatites and cooled migmatites in the lower GHC at 16-10 Ma. In other words, at different temporal and spatial scale, both propagating thrusting along large tectonic boundaries and a low-viscosity melting crust could contribute to the exhumation of high-grade metamorphic rocks in Himalaya-like large hot collisional orogens. KEY WORDS: Greater Himalayan Crystalline Complex; P-T path; U-Pb geochronology; channel flow; tectonic discontinuity References: Wang, J.M., Rubatto, D., Zhang, J.J., 2015a. Timing of partial melting and cooling across the Greater Himalayan Crystalline Complex (Nyalam, central Himalaya): in-sequence thrusting and its implications. Journal of Petrology, 56, 1677-1702. Wang, J.M., Zhang, J.J., Wei, C.J., Rai, S.M., Wang, M., Qian, J.H., 2015b. Characterizing the metamorphic discontinuity across the Main Central Thrust Zone of eastern-central Nepal. Journal of Asian Earth Sciences 101, 83-100. Wang, J.M., Zhang, J.J., Wang, X.X., 2013. Structural kinematics, metamorphic P-T profiles and zircon geochronology across the Greater Himalayan Crystalline Complex in south-central Tibet: implication for a revised channel flow. Journal of Metamorphic Geology 31, 607-628.

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

NASA Astrophysics Data System (ADS)

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

2016-12-01

This study investigates the partial melting of variable bulk H2O-bearing parcels of mantle-wedge hybridized by partial melt derived from subducted metapelites, at pressure-temperature (P-T) conditions applicable to the hotter core of the mantle beneath volcanic arcs. Experiments are performed on mixtures of 25% sediment-melt and 75% fertile peridotite, from 1200 to 1300 °C, at 2 and 3 GPa, with bulk H2O concentrations of 4 and 6 wt.%. Combining the results from these experiments with previous experiments containing 2 wt.% bulk H2O (Mallik et al., 2015), it is observed that all melt compositions, except those produced in the lowest bulk H2O experiments at 3 GPa, are saturated with olivine and orthopyroxene. Also, higher bulk H2O concentration increases melt fraction at the same P-T condition, and causes exhaustion of garnet, phlogopite and clinopyroxene at lower temperatures, for a given pressure. The activity coefficient of silica (ϒSiO2) for olivine-orthopyroxene saturated melt compositions (where the activity of silica, aSiO2 , is buffered by the reaction olivine + SiO2 = orthopyroxene) from this study and from mantle melting studies in the literature are calculated. In melt compositions generated at 2 GPa or shallower, with increasing H2O concentration, ϒSiO2 increases from <1 to ∼1, indicating a transition from non-ideal mixing as OH- in the melt (ϒSiO2 <1) to ideal mixing as molecular H2O (ϒSiO2 ∼1). At pressures >2 GPa, ϒSiO2 >1 at higher H2O concentrations in the melt, indicate requirement of excess energy to incorporate molecular H2O in the silicate melt structure, along with a preference for bridging species and polyhedral edge decorations. With vapor saturation in the presence of melt, ϒSiO2 decreases indicating approach towards ideal mixing of H2O in silicate melt. For similar H2O concentrations in the melt, ϒSiO2 for olivine-orthopyroxene saturated melts at 3 GPa is higher than melts at 2 GPa or shallower. This results in melts generated at 3 GPa being more silica-poor than melts at 2 GPa. Thus, variable bulk H2O and pressure of melt generation results in the partial melts from this study varying in composition from phonotephrite to basaltic andesite at 2 GPa and foidite/phonotephrite to basalt at 3 GPa, forming a spectrum of arc magmas. Modeling suggests that the trace element patterns of sediment-melt are unaffected by the process of hybridization within the hotter core of the mantle-wedge. K2O/H2O and H2O/Ce ratios of the sediment-melts are unaffected, within error, by the process of hybridization of the mantle-wedge. This implies that thermometers based on K2O/H2O and H2O/Ce ratios of arc lavas may be used to estimate slab-top temperatures when (a) sediment-melt from the slab reaches the hotter core of the mantle-wedge by focused flow (b) sediment-melt freezes in the overlying mantle at the slab-mantle interface and the hybridized package rises as a mélange diapir and partially melts at the hotter core of the mantle-wedge. Based on the results from this study and previous studies, both channelized and porous flow of sediment-melt/fluid through the sub-arc mantle can explain geochemical signatures of arc lavas under specific geodynamic scenarios of fluid/melt fluxing, hybridization, and subsequent mantle melting.

Against the grain: The physical properties of anisotropic partially molten rocks

NASA Astrophysics Data System (ADS)

Ghanbarzadeh, S.; Hesse, M. A.; Prodanovic, M.

2014-12-01

Partially molten rocks commonly develop textures that appear close to textural equilibrium, where the melt network evolves to minimize the energy of the melt-solid interfaces, while maintaining the dihedral angle θ at solid-solid-melt contact lines. Textural equilibrium provides a powerful model for the melt distribution that controls the petro-physical properties of partially molten rocks, e.g., permeability, elastic moduli, and electrical resistivity. We present the first level-set computations of three-dimensional texturally equilibrated melt networks in rocks with an anisotropic fabric. Our results show that anisotropy induces wetting of smaller grain boundary faces for θ > 0 at realistic porosities ϕ < 3%. This was previously not thought to be possible at textural equilibrium and reconciles the theory with experimental observations. Wetting of the grain boundary faces leads to a dramatic redistribution of the melt from the edges to the faces that introduces strong anisotropy in the petro-physical properties such as permeability, effective electrical conductivity and mechanical properties. Figure, on left, shows that smaller grain boundaries become wetted at relatively low melt fractions of 3% in stretched polyhedral grains with elongation factor 1.5. Right plot represents the ratio of melt electrical conductivity to effective conductivity of medium (known as formation factor) as an example of anisotropy in physical properties. The plot shows that even slight anisotropy in grains induces considerable anisotropy in electrical properties.

Single-Molecule Denaturation Mapping of Genomic DNA in Nanofluidic Channels

NASA Astrophysics Data System (ADS)

Reisner, Walter; Larsen, Niels; Kristensen, Anders; Tegenfeldt, Jonas O.; Flyvbjerg, Henrik

2009-03-01

We have developed a new DNA barcoding technique based on the partial denaturation of extended fluorescently labeled DNA molecules. We partially melt DNA extended in nanofluidic channels via a combination of local heating and added chemical denaturants. The melted molecules, imaged via a standard fluorescence videomicroscopy setup, exhibit a nonuniform fluorescence profile corresponding to a series of local dips and peaks in the intensity trace along the stretched molecule. We show that this barcode is consistent with the presence of locally melted regions and can be explained by calculations of sequence-dependent melting probability. We believe this melting mapping technology is the first optically based single molecule technique sensitive to genome wide sequence variation that does not require an additional enzymatic labeling or restriction scheme.

Distribution of lithium in the Cordilleran Mantle wedge

NASA Astrophysics Data System (ADS)

Shervais, J. W.; Jean, M. M.; Seitz, H. M.

2015-12-01

Enriched fluid-mobile element (i.e., B, Li, Be) concentrations in peridotites from the Coast Range ophiolite are compelling evidence that this ophiolite originated in a subduction environment. A new method presented in Shervais and Jean (2012) for modeling the fluid enrichment process, represents the total addition of material to the mantle wedge source region and can be applied to any refractory mantle peridotite that has been modified by melt extraction and/or metasomatism. Although the end-result is attributed to an added flux of aqueous fluid or fluid-rich melt phase derived from the subducting slab, in the range of tens of parts per million - the nature and composition of this fluid could not be constrained. To address fluid(s) origins, we have analyzed Li isotopes in bulk rock peridotite and eclogite, and garnet separates, to identify possible sources, and fluid flow mechanisms and pathways. Bulk rock Li abundances of CRO peridotites (δ7Li = -14.3 to 5.5‰; 1.9-7.5 ppm) are indicative of Li addition and δ7Li-values are lighter than normal upper mantle values. However, Li abundances of clino- and orthopyroxene appear to record different processes operating during the CRO-mantle evolution. Low Li abundances in orthopyroxene (<1 ppm) suggest depletion via partial melting, whereas high concentrations in clinopyroxenes (>2 ppm) record subsequent interaction with Li-enriched fluids (or melts). The preferential partitioning of lithium in clinopyroxene could be indicative of a particular metasomatic agent, e.g., fluids from a dehydrating slab. Future in-situ peridotite isotope studies via laser ablation will further elucidate the fractionation of lithium between orthopyroxene, clinopyroxene, and serpentine. To obtain a more complete picture of the slab to arc transfer processes, we also measured eclogites and garnet separates to δ7Li= -18 to 3.5‰ (11.5-32.5 ppm) and δ7Li= 1.9 to 11.7‰ (0.7-3.9 ppm), respectively. In connection with previous studies focused on high-grade metamorphic assemblages within the Franciscan complex, an overall framework exists to reconstruct the Li architecture of the Middle Jurassic-Cordilleran subduction zone.

Dehydration of 1-octadecanol over H-BEA: A combined experimental and computational study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Wenji; Liu, Yuanshuai; Barath, Eszter

Liquid phase dehydration of 1-octdecanol, which is intermediately formed during the hydrodeoxygenation of microalgae oil, has been explored in a combined experimental and computational study. The alkyl chain of C18 alcohol interacts with acid sites during diffusion inside the zeolite pores, resulting in an inefficient utilization of the Brønsted acid sites for samples with high acid site concentrations. The parallel intra- and inter- molecular dehydration pathways having different activation energies pass through alternative reaction intermediates. Formation of surface-bound alkoxide species is the rate-limiting step during intramolecular dehydration, whereas intermolecular dehydration proceeds via a bulky dimer intermediate. Octadecene is the primarymore » dehydration product over H-BEA at 533 K. Despite of the main contribution of Brønsted acid sites towards both dehydration pathways, Lewis acid sites are also active in the formation of dioctadecyl ether. The intramolecular dehydration to octadecene and cleavage of the intermediately formed ether, however, require strong BAS. L. Wang, D. Mei and J. A. Lercher, acknowledge the partial support from the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. Computing time was granted by the grand challenge of computational catalysis of the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL) and by the National Energy Research Scientific Computing Center (NERSC). EMSL is a national scientific user facility located at Pacific Northwest National Laboratory (PNNL) and sponsored by DOE’s Office of Biological and Environmental Research.« less

Dehydration and Dehydrogenation of Ethylene Glycol on Rutile TiO2(110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zhenjun; Kay, Bruce D.; Dohnalek, Zdenek

2013-08-07

The interactions of ethylene glycol (EG) with partially reduced rutile TiO2(110) surface have been studied using temperature programmed desorption (TPD). The saturation coverage on the surface Ti rows is determined to be 0.43 monolayer (ML), slightly less than one EG per two Ti sites. Most of the adsorbed ethanol (~80%) undergoes further reactions to other products. Two major channels are observed, dehydration yielding ethylene and water and dehydrogenation yielding acetaldehyde and hydrogen. Hydrogen formation is rather surprising as it has not been observed previously on TiO2(110) from simple organic molecules. The coverage dependent yields of ethylene and acetaldehyde correlate wellmore » with that of water and hydrogen, respectively. Dehydration dominates at lower EG coverages (< 0.2 ML) and plateaus as the coverage is increased to saturation. Dehydrogenation is observed primarily at higher EG coverages (>0.2 ML). Our results suggest that the observed dehydration and dehydrogenation reactions proceed via different surface intermediates.« less

Partial melting and melt percolation in the mantle: The message from Fe isotopes

NASA Astrophysics Data System (ADS)

Weyer, Stefan; Ionov, Dmitri A.

2007-07-01

High precision Fe isotope measurements have been performed on various mantle peridotites (fertile lherzolites, harzburgites, metasomatised Fe-enriched peridotites) and volcanic rocks (mainly oceanic basalts) from different localities and tectonic settings. The peridotites yield an average δ 56Fe = 0.01‰ and are significantly lighter than the basalts (average δ 56Fe = 0.11‰). Furthermore, the peridotites display a negative correlation of δ 56Fe with Mg# indicating a link between δ 56Fe and degrees of melt extraction. Taken together, these findings imply that Fe isotopes fractionate during partial melting, with heavy isotopes preferentially entering the melt. The slope of depletion trends (δ 56Fe versus Mg#) of the peridotites was used to model Fe isotope fractionation during partial melting, resulting in αmantle-melt ≈ 1.0001-1.0003 or ln αmantle-melt ≈ 0.1-0.3‰. In contrast to most other peridotites investigated in this study, spinel lherzolites and harzburgites from three localities (Horoman, Kamchatka and Lherz) are virtually unaffected by metasomatism. These three sites display a particularly good correlation and define an isotope fractionation factor of ln αmantle-melt ≈ 0.3‰. This modelled value implies Fe isotope fractionation between residual mantle and mantle-derived melts corresponding to Δ56Fe mantle-basalt ≈ 0.2-0.3‰, i.e. significantly higher than the observed difference between averages for all the peridotites and the basalts in this study (corresponding to Δ56Fe mantle-basalt ≈ 0.1‰). Either disequilibrium melting increased the modelled αmantle-melt for these particular sites or the difference between average peridotite and basalt may be reduced by partial re-equilibration between the isotopically heavy basalts and the isotopically light depleted lithospheric mantle during melt ascent. The slope of the weaker δ 56Fe-Mg# trend defined by the combined set of all mantle peridotites from this study is more consistent with the generally observed difference between peridotites and basalts; this slope was used here to estimate the Fe isotope composition of the fertile upper mantle (at Mg# = 0.894, δ 56Fe ≈ 0.02 ± 0.03‰). Besides partial melting, the Fe isotope composition of mantle peridotites can also be significantly modified by metasomatic events, e.g. melt percolation. At two localities (Tok, Siberia and Tariat, Mongolia) δ 56Fe correlates with iron contents of the peridotites, which was increased from about 8% to up to 14.5% FeO by post-melting melt percolation. This process produced a range of Fe isotope compositions in the percolation columns, from extremely light (δ 56Fe = - 0.42‰) to heavy (δ 56Fe = + 0.17‰). We propose reaction with isotopically heavy melts and diffusion (enrichment of light Fe isotopes) as the most likely processes that produced the large isotope variations at these sites. Thus, Fe isotopes might be used as a sensitive tracer to identify such metasomatic processes in the mantle.

Petrogenesis of mesozoic, peraluminous granites in the Lamoille canyon area, Ruby mountains, Nevada, USA

USGS Publications Warehouse

Lee, S.-Y.; Barnes, C.G.; Snoke, A.W.; Howard, K.A.; Frost, C.D.

2003-01-01

Two groups of closely associated, peraluminous, two-mica granitic gneiss were identified in the area. The older, sparsely distributed unit is equigranular (EG) with initial ??Nd ??? -8??8 and initial 87Sr/86Sr ???0??7098. Its age is uncertain. The younger unit is Late Cretaceous (???80 Ma), pegmatitic, and sillimanite-bearing (KPG), with ??Nd from -15??8 to -17??3 and initial 87Sr/86Sr from 0??7157 to 0??7198. The concentrations of Fe, Mg, Na, Ca, Sr, V, Zr, Zn and Hf are higher, and K, Rb and Th are lower in the EG. Major- and trace-element models indicate that the KPG was derived by muscovite dehydration melting (<35 km depth) of Neoproterozoic metapelitic rocks that are widespread in the eastern Great Basin. The models are broadly consistent with anatexis of crust tectonically thickened during the Sevier orogeny; no mantle mass or heat contribution was necessary. As such, this unit represents one crustal end-member of regional Late Cretaceous peraluminous granites. The EG was produced by biotite dehydration melting at greater depths, with garnet stable in the residue. The source of the EG was probably Paleoproterozoic metagraywacke. Because EG magmatism probably pre-dated Late Cretaceous crustal thickening, it required heat input from the mantle or from mantle-derived magma.

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.

On mass transport in magmatic porosity waves

NASA Astrophysics Data System (ADS)

Jordan, J.; Hesse, M. A.; Rudge, J. F.

2017-12-01

Geochemical analyses of oceanic basalts indicate the mantle is lithologically heterogenous and subject to partial melting. Here we show that porosity waves-which arise naturally in models of buoyancy driven melt migration-transport mass and preserve geochemical signatures, at least partially. Prior studies of tracer transport in one dimensional porosity waves conclude that porosity waves do not transfer mass. However, it is well known that one-dimensional porosity waves are unstable in two and three dimensions and break up into sets of cylindrical or spherical porosity waves. We show that tracer transport in higher dimensional porosity waves is dramatically different than in one dimension. Lateral melt focusing into these high porosity regions leads to melt recirculating in the center of the wave. Melt focusing and recirculation are not resolvable in one dimension where no sustained transport is observed in numerical experiments of solitary porosity waves. In two and three dimensions, the recirculating melt is separated from the background melt-flow field by a circular or spherical dividing streamline and transported with the phase velocity of the porosity wave. The amount of melt focusing that occurs within any given porosity wave, and thus, the extent of the dividing streamline, and resultant volume of transported melt is extremely sensitive to the selection of porosity-permeability and porosity-rheology relationships. Therefore, we present a regime diagram spanning common parameterizations that illustrates the minimum amplitude and phase velocity required for a solitary porosity wave to transport mass as a function of material properties and common parameters used in magma dynamics and mid-ocean ridge models. The realization that solitary waves are capable of sustaining melt transport may require the reinterpretation of previous studies. For example, transport in porosity waves may allow melts that originated from the partial melting of fertile heterogeneities to retain their incompatible trace element signatures as they rise through the mantle. Porosity waves may also provide a mechanism for mixing melts derived from heterogeneities with ambient melts derived from different depths in the mantle.

Partial melting of UHP calc-gneiss from the Dabie Mountains

NASA Astrophysics Data System (ADS)

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

2014-04-01

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

Detection of melting by X-ray imaging at high pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Li; Weidner, Donald J.

2014-06-15

The occurrence of partial melting at elevated pressure and temperature is documented in real time through measurement of volume strain induced by a fixed temperature change. Here we present the methodology for measuring volume strains to one part in 10{sup −4} for mm{sup 3} sized samples in situ as a function of time during a step in temperature. By calibrating the system for sample thermal expansion at temperatures lower than the solidus, the onset of melting can be detected when the melting volume increase is of comparable size to the thermal expansion induced volume change. We illustrate this technique withmore » a peridotite sample at 1.5 GPa during partial melting. The Re capsule is imaged with a CCD camera at 20 frames/s. Temperature steps of 100 K induce volume strains that triple with melting. The analysis relies on image comparison for strain determination and the thermal inertia of the sample is clearly seen in the time history of the volume strain. Coupled with a thermodynamic model of the melting, we infer that we identify melting with 2 vol.% melting.« less

Tracing mantle processes with Fe isotopes

NASA Astrophysics Data System (ADS)

Weyer, S.; Ionov, D.

2006-12-01

High precision Fe isotope measurements have been performed on various mantle peridotites (fertile lherzolites, harzburgites, metasomatised Fe-enriched rocks) and volcanic rocks (mainly oceanic basalts) from different localities and tectonic settings. Pimitive peridotites (Mg# = 0.894) yield delta56Fe = 0.02 and are significantly lighter than the basalts (average delta56Fe = 0.11). Furthermore, the peridotites display a negative correlation of iron isotopes with Mg#. Taken together, these findings imply that Fe isotopes fractionate during partial melting, with heavy isotopes preferentially entering the melt [1, 2]. A particularly good correlation of the Fe isotope composition and Mg# shown by poorly metasomatised spinel lherzolites of three localities (Horoman, Kamchatka and Lherz) was used to model Fe isotope fractionation during partial melting, resulting in alphamantle-melt = 1.0003. This value implies higher Fe isotope fractionation between residual mantle and mantle-derived melts (i.e. Delta56Femantle-melt = 0.2-0.3) than the observed difference between the peridotites and the basalts in this study. Our data on plagioclase lherzolites from Horoman and spinel lherzolites from other localities indicate that the difference in Fe isotope composition between mantle and basalts may be reduced by partial re-equilibration between the isotopically heavy basalts and the isotopically light depleted lithospheric mantle during melt ascent. Besides partial melting, the Fe isotope composition of mantle peridotites can also be significantly modified by metasomatic events. At two localities (Tok, Siberia and Tariat, Mongolia) Fe isotopes correlates with the Fe concentration of the peridotites, which was increased up to 14.5% FeO by melt percolation. Such processes can be accompanied by chromatographic effects and produce a range of Fe isotope compositions in the percolation columns, from extremely light to heavy (delta56Fe = -0.42 to +0.17). We propose that Fe isotopes can be used as a sensitive tracer to identify such metasomatic processes in the mantle. [1] Weyer et al. (2005) EPSL 240: 251-264 [2] Williams et al. (2005) EPSL 235 : 435-452

Dehydration of chlorite explains anomalously high electrical conductivity in the mantle wedges.

PubMed

Manthilake, Geeth; Bolfan-Casanova, Nathalie; Novella, Davide; Mookherjee, Mainak; Andrault, Denis

2016-05-01

Mantle wedge regions in subduction zone settings show anomalously high electrical conductivity (~1 S/m) that has often been attributed to the presence of aqueous fluids released by slab dehydration. Laboratory-based measurements of the electrical conductivity of hydrous phases and aqueous fluids are significantly lower and cannot readily explain the geophysically observed anomalously high electrical conductivity. The released aqueous fluid also rehydrates the mantle wedge and stabilizes a suite of hydrous phases, including serpentine and chlorite. In this present study, we have measured the electrical conductivity of a natural chlorite at pressures and temperatures relevant for the subduction zone setting. In our experiment, we observe two distinct conductivity enhancements when chlorite is heated to temperatures beyond its thermodynamic stability field. The initial increase in electrical conductivity to ~3 × 10(-3) S/m can be attributed to chlorite dehydration and the release of aqueous fluids. This is followed by a unique, subsequent enhancement of electrical conductivity of up to 7 × 10(-1) S/m. This is related to the growth of an interconnected network of a highly conductive and chemically impure magnetite mineral phase. Thus, the dehydration of chlorite and associated processes are likely to be crucial in explaining the anomalously high electrical conductivity observed in mantle wedges. Chlorite dehydration in the mantle wedge provides an additional source of aqueous fluid above the slab and could also be responsible for the fixed depth (120 ± 40 km) of melting at the top of the subducting slab beneath the subduction-related volcanic arc front.

Dehydration of chlorite explains anomalously high electrical conductivity in the mantle wedges

PubMed Central

Manthilake, Geeth; Bolfan-Casanova, Nathalie; Novella, Davide; Mookherjee, Mainak; Andrault, Denis

2016-01-01

Mantle wedge regions in subduction zone settings show anomalously high electrical conductivity (~1 S/m) that has often been attributed to the presence of aqueous fluids released by slab dehydration. Laboratory-based measurements of the electrical conductivity of hydrous phases and aqueous fluids are significantly lower and cannot readily explain the geophysically observed anomalously high electrical conductivity. The released aqueous fluid also rehydrates the mantle wedge and stabilizes a suite of hydrous phases, including serpentine and chlorite. In this present study, we have measured the electrical conductivity of a natural chlorite at pressures and temperatures relevant for the subduction zone setting. In our experiment, we observe two distinct conductivity enhancements when chlorite is heated to temperatures beyond its thermodynamic stability field. The initial increase in electrical conductivity to ~3 × 10−3 S/m can be attributed to chlorite dehydration and the release of aqueous fluids. This is followed by a unique, subsequent enhancement of electrical conductivity of up to 7 × 10−1 S/m. This is related to the growth of an interconnected network of a highly conductive and chemically impure magnetite mineral phase. Thus, the dehydration of chlorite and associated processes are likely to be crucial in explaining the anomalously high electrical conductivity observed in mantle wedges. Chlorite dehydration in the mantle wedge provides an additional source of aqueous fluid above the slab and could also be responsible for the fixed depth (120 ± 40 km) of melting at the top of the subducting slab beneath the subduction-related volcanic arc front. PMID:27386526

Impact of protective agents and drying methods on desiccation tolerance of Salix nigra L. seeds.

PubMed

Santagapita, Patricio R; Ott Schneider, Helena; Agudelo-Laverde, Lina M; Buera, M Pilar

2014-09-01

Willow seeds are classified as orthodox, but they show some recalcitrant characteristics, as they lose viability in a few weeks at room temperature. The aim of this work was to improve the desiccation tolerance of willow seeds (Salix nigra L.), as a model of sensitive materials to dehydration, through imbibition in solutions and later vacuum (VD) or freeze-drying (FD). Imbibition was conducted with 45% w/v trehalose or polyethylene glycol 400 -PEG- or water prior to dehydration treatments. Water- and especially trehalose-imbibed seeds subjected to VD showed better germination capability with respect to the freeze-dried ones. Water crystallization was mainly responsible for the great loss of capability germination observed in water- or trehalose-imbibed seeds subjected to FD. PEG behavior was better when seeds were FD instead of VD. DSC thermograms of seeds allowed to identify two thermal transitions corresponding to lipids melting and to proteins denaturation. This last transition reveals information about proteins state/functionality. Dehydration of control and PEG- or water-imbibed seeds affected proteins functionality leading to lower germinability. In the case of trehalose-imbibed seeds subjected to VD, proteins maintained their native state along dehydration, and the seeds showed a great germination capacity for all the water content range. Germinated seeds showed higher luminosity (L*), greenness (a*) and yellowness (b*) values than not-germinated seeds independently of the employed agent. Present work reveals that the presence of adequate protective agents as well the dehydration method were the main critical factors involved in willow seed desiccation tolerance. Copyright © 2014 Elsevier Masson SAS. All rights reserved.

Major, Trace, and Volatile (CO2, H2O, S, F, and Cl) Elements from 1000+ Hawaiian Olivine-hosted Melt Inclusions Reveal the Dynamics of Crustal Recycling

NASA Astrophysics Data System (ADS)

Marske, J. P.; Hauri, E. H.; Trusdell, F.; Garcia, M. O.; Pietruszka, A. J.

2015-12-01

Global cycling of volatile elements (H2O, CO2, F, S, Cl) via subduction to deep mantle followed by entrainment and melting within ascending mantle plumes is an enigmatic process that controls key aspects of hot spot volcanism (i.e. melting rate, magma supply, degassing, eruptive style). Variations in radiogenic isotope ratios (e.g.187Os/188Os) at hot spots such as Hawaii reveal magmatic processes within deep-seated mantle plumes (e.g. mantle heterogeneity, lithology, and melt transport). Shield-stage lavas from Hawaii likely originate from a mixed plume source containing peridotite and recycled oceanic crust (pyroxenite) based on variations of radiogenic isotopes. Hawaiian lavas display correlations among isotopes, major and trace elements [1] that might be expected to have an expression in the volatile elements. To investigate this link, we present Os isotopic ratios (n=51), and major, trace, and volatile elements from 1003 olivine-hosted melt inclusions (MI) and their host minerals from tephra from Koolau, Mauna Loa, Hualalai, Kilauea, and Loihi volcanoes. The data show a strong correlation between MI volatile contents and incompatible trace element ratios (La/Yb) with Os isotopes of the same host olivines and reveal large-scale volatile heterogeneity and zonation exists within the Hawaiian plume. 'Loa' chain lavas, which are thought to originate from greater proportions of recycled oceanic crust/pyroxenite, have MIs with lower H2O, S, F, and Cl contents compared to 'Kea' chain lavas that were derived from more peridotite-rich sources. The depletion of volatile elements in the 'Loa' volcano MIs can be explained if they tapped an ancient dehydrated oceanic crust component within the Hawaiian plume. Higher extents of melting beneath 'Loa' volcanoes can also explain these depletions. The presence of dehydrated recycled mafic material in the plume source suggests that subduction effectively devolatilizes part of the oceanic crust. These results are similar to the observed shifts in H2O/Ce ratios near the Easter and Samoan hotspots [2,3]. Thus, it appears that multiple hotspots may record relative H2O depletions and possibly other volatiles. [1] Hauri et al. 1996, Nature 382, 415-419. [2] Dixon et al. 2002, Nature 420:385-89 [3] Workman et al. 2006, EPSL 241:932-51.

Titanium stable isotope investigation of magmatic processes on the Earth and Moon

NASA Astrophysics Data System (ADS)

Millet, Marc-Alban; Dauphas, Nicolas; Greber, Nicolas D.; Burton, Kevin W.; Dale, Chris W.; Debret, Baptiste; Macpherson, Colin G.; Nowell, Geoffrey M.; Williams, Helen M.

2016-09-01

We present titanium stable isotope measurements of terrestrial magmatic samples and lunar mare basalts with the aims of constraining the composition of the lunar and terrestrial mantles and evaluating the potential of Ti stable isotopes for understanding magmatic processes. Relative to the OL-Ti isotope standard, the δ49Ti values of terrestrial samples vary from -0.05 to +0.55‰, whereas those of lunar mare basalts vary from -0.01 to +0.03‰ (the precisions of the double spike Ti isotope measurements are ca. ±0.02‰ at 95% confidence). The Ti stable isotope compositions of differentiated terrestrial magmas define a well-defined positive correlation with SiO2 content, which appears to result from the fractional crystallisation of Ti-bearing oxides with an inferred isotope fractionation factor of ΔTi49oxide-melt = - 0.23 ‰ ×106 /T2. Primitive terrestrial basalts show no resolvable Ti isotope variations and display similar values to mantle-derived samples (peridotite and serpentinites), indicating that partial melting does not fractionate Ti stable isotopes and that the Earth's mantle has a homogeneous δ49Ti composition of +0.005 ± 0.005 (95% c.i., n = 29). Eclogites also display similar Ti stable isotope compositions, suggesting that Ti is immobile during dehydration of subducted oceanic lithosphere. Lunar basalts have variable δ49Ti values; low-Ti mare basalts have δ49Ti values similar to that of the bulk silicate Earth (BSE) while high-Ti lunar basalts display small enrichment in the heavy Ti isotopes. This is best interpreted in terms of source heterogeneity resulting from Ti stable isotope fractionation associated with ilmenite-melt equilibrium during the generation of the mantle source of high-Ti lunar mare basalts. The similarity in δ49Ti between terrestrial samples and low-Ti lunar basalts provides strong evidence that the Earth and Moon have identical stable Ti isotope compositions.

Thermal and mass implications of magmatic evolution in the Lassen volcanic region, California, and minimum constraints on basalt influx to the lower crust

USGS Publications Warehouse

Guffanti, M.; Clynne, M.A.; Muffler, L.J.P.

1996-01-01

We have analyzed the heat and mass demands of a petrologic model of basaltdriven magmatic evolution in which variously fractionated mafic magmas mix with silicic partial melts of the lower crust. We have formulated steady state heat budgets for two volcanically distinct areas in the Lassen region: the large, late Quaternary, intermediate to silicic Lassen volcanic center and the nearby, coeval, less evolved Caribou volcanic field. At Caribou volcanic field, heat provided by cooling and fractional crystallization of 52 km3 of basalt is more than sufficient to produce 10 km3 of rhyolitic melt by partial melting of lower crust. Net heat added by basalt intrusion at Caribou volcanic field is equivalent to an increase in lower crustal heat flow of ???7 mW m-2, indicating that the field is not a major crustal thermal anomaly. Addition of cumulates from fractionation is offset by removal of erupted partial melts. A minimum basalt influx of 0.3 km3 (km2 Ma)-1 is needed to supply Caribou volcanic field. Our methodology does not fully account for an influx of basalt that remains in the crust as derivative intrusives. On the basis of comparison to deep heat flow, the input of basalt could be ???3 to 7 times the amount we calculate. At Lassen volcanic center, at least 203 km3 of mantle-derived basalt is needed to produce 141 km3 of partial melt and drive the volcanic system. Partial melting mobilizes lower crustal material, augmenting the magmatic volume available for eruption at Lassen volcanic center; thus the erupted volume of 215 km3 exceeds the calculated basalt input of 203 km3. The minimum basalt input of 1.6 km3 (km2 Ma)-1 is >5 times the minimum influx to the Caribou volcanic field. Basalt influx high enough to sustain considerable partial melting, coupled with locally high extension rate, is a crucial factor in development of Lassen volcanic center; in contrast. Caribou volcanic field has failed to develop into a large silicic center primarily because basalt supply there has been insufficient.

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.

Do Hf isotopes in magmatic zircons represent those of their host rocks?

NASA Astrophysics Data System (ADS)

Wang, Di; Wang, Xiao-Lei; Cai, Yue; Goldstein, Steven L.; Yang, Tao

2018-04-01

Lu-Hf isotopic system in zircon is a powerful and widely used geochemical tracer in studying petrogenesis of magmatic rocks and crustal evolution, assuming that zircon Hf isotopes can represent initial Hf isotopes of their parental whole rock. However, this assumption may not always be valid. Disequilibrium partial melting of continental crust would preferentially melt out non-zircon minerals with high time-integrated Lu/Hf ratios and generate partial melts with Hf isotope compositions that are more radiogenic than those of its magma source. Dissolution experiments (with hotplate, bomb and sintering procedures) of zircon-bearing samples demonstrate this disequilibrium effect where partial dissolution yielded variable and more radiogenic Hf isotope compositions than fully dissolved samples. A case study from the Neoproterozoic Jiuling batholith in southern China shows that about half of the investigated samples show decoupled Hf isotopes between zircons and the bulk rocks. This decoupling could reflect complex and prolonged magmatic processes, such as crustal assimilation, magma mixing, and disequilibrium melting, which are consistent with the wide temperature spectrum from ∼630 °C to ∼900 °C by Ti-in-zircon thermometer. We suggest that magmatic zircons may only record the Hf isotopic composition of their surrounding melt during crystallization and it is uncertain whether their Hf isotopic compositions can represent the primary Hf isotopic compositions of the bulk magmas. In this regard, using zircon Hf isotopic compositions to trace crustal evolution may be biased since most of these could be originally from disequilibrium partial melts.

Constraints on the rheology of the partially molten mantle from numerical models of laboratory experiments

NASA Astrophysics Data System (ADS)

Rudge, J. F.; Alisic Jewell, L.; Rhebergen, S.; Katz, R. F.; Wells, G. N.

2015-12-01

One of the fundamental components in any dynamical model of melt transport is the rheology of partially molten rock. This rheology is poorly understood, and one way in which a better understanding can be obtained is by comparing the results of laboratory deformation experiments to numerical models. Here we present a comparison between numerical models and the laboratory setup of Qi et al. 2013 (EPSL), where a cylinder of partially molten rock containing rigid spherical inclusions was placed under torsion. We have replicated this setup in a finite element model which solves the partial differential equations describing the mechanical process of compaction. These computationally-demanding 3D simulations are only possible due to the recent development of a new preconditioning method for the equations of magma dynamics. The experiments show a distinct pattern of melt-rich and melt-depleted regions around the inclusions. In our numerical models, the pattern of melt varies with key rheological parameters, such as the ratio of bulk to shear viscosity, and the porosity- and strain-rate-dependence of the shear viscosity. These observed melt patterns therefore have the potential to constrain rheological properties. While there are many similarities between the experiments and the numerical models, there are also important differences, which highlight the need for better models of the physics of two-phase mantle/magma dynamics. In particular, the laboratory experiments display more pervasive melt-rich bands than is seen in our numerics.

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 compare the major and trace element characteristics of bulk rock and minerals found in orthopyroxenites from supra-subduction zones with the residua formed in our experiments, to differentiate between melt versus fluid, and sediment- versus basalt-derived flux in the mantle wedge. [1] Mallik et al. (2015) CMP169(5) [2] Sekine & Wyllie (1982) CMP 81(3)

Partitioning of V, Mn, Co, Ni, Cu, Zn, As, Mo, Ag, Sn, Sb, W, Au, Pb, and Bi between sulfide phases and hydrous basanite melt at upper mantle conditions

NASA Astrophysics Data System (ADS)

Li, Yuan; Audétat, Andreas

2012-11-01

The partitioning of 15 major to trace metals between monosulfide solid solution (MSS), sulfide liquid (SL) and mafic silicate melt (SM) was determined in piston-cylinder experiments performed at 1175-1300 °C, 1.5-3.0 GPa and oxygen fugacities ranging from 3.1 log units below to 1.0 log units above the quartz-fayalite-magnetite fO2 buffer, which conditions are representative of partial melting in the upper mantle in different tectonic settings. The silicate melt was produced by partial melting of a natural, amphibole-rich mantle source rock, resulting in hydrous (˜5 wt% H2O) basanitic melts similar to low-degree partial melts of metasomatized mantle, whereas the major element composition of the starting sulfide (˜52 wt% Fe; 39 wt% S; 7 wt% Ni; 2 wt% Cu) was similar to the average composition of sulfides in this environment. SL/SM partition coefficients are high (≥100) for Au, Ni, Cu, Ag, Bi, intermediate (1-100) for Co, Pb, Sn, Sb (±As, Mo), and low (≤1) for the remaining elements. MSS/SM partition coefficients are generally lower than SL/SM partition coefficients and are high (≥100) for Ni, Cu, Au, intermediate (1-100) for Co, Ag (±Bi, Mo), and low (≤1) for the remaining elements. Most sulfide-silicate melt partition coefficients vary as a function of fO2, with Mo, Bi, As (±W) varying by a factor >10 over the investigated fO2 range, Sb, Ag, Sn (±V) varying by a factor of 3-10, and Pb, Cu, Ni, Co, Au, Zn, Mn varying by a factor of 3-10. The partitioning data were used to model the behavior of Cu, Au, Ag, and Bi during partial melting of upper mantle and during fractional crystallization of primitive MORB and arc magmas. Sulfide phase relationships and comparison of the modeling results with reported Cu, Au, Ag, and Bi concentrations from MORB and arc magmas suggest that: (i) MSS is the dominant sulfide in the source region of arc magmas, and thus that Au/Cu ratios in the silicate melt and residual sulfides may decrease with increasing degree of partial melting, (ii) both MSS and sulfide liquid are precipitated during fractional crystallization of MORB, and (iii) fractional crystallization of arc magmas is strongly dominated by MSS.

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 phases that are within the mineralogy and mineral compositions of the brachinites. These experiments provide further evidence for the formation of brachinites as a result of partial melting of a chondritic precursor similar in mineralogy and mineral compositions to the R chondrites.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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 moremore » 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.« less

Effects of pH2O, pH2 and fO2 on the Diffusion of H-Bearing Species in Lunar Basalt and an Iron-Free Basaltic Analog at 1 atm

NASA Astrophysics Data System (ADS)

Newcombe, M. E.; Beckett, J. R.; Baker, M. B.; Newman, S.; Guan, Y.; Eiler, J. M.; Stolper, E. M.

2016-12-01

We have conducted water diffusion experiments in synthetic Apollo 15 "yellow glass" (LG) and an iron-free basaltic analog melt (AD) at 1 atm and 1350 °C over a range of fO2 conditions from IW-2.2 to IW+6.7 and over a range of pH2/pH2O from nominally zero to 10. The water concentrations measured in our quenched experimental glasses by SIMS and FTIR vary from a few ppm to 430 ppm. Many studies of water diffusion at higher water concentrations indicate that the apparent diffusivity of total water (D*water; see [1]) in silicate melts is highly concentration dependent at water contents >0.1 wt% (e.g., [1]). However, water concentration gradients in each of our AD and LG experiments are well described by models in which D*water is assumed to be constant. Best-fit values of D*water obtained for our AD and LG experiments are consistent with a modified speciation model [2] in which both molecular water and hydroxyl are allowed to diffuse, and in which hydroxyl is the dominant diffusing species at the low total water concentrations of our experiments. Water concentration gradients generated during hydration and dehydration experiments conducted simultaneously propagate approximately equal distances into the melt and have the same concentration of water dissolved in the melt at the melt-vapor interface, suggesting that hydration and dehydration are symmetric under the conditions of our experiments. Best-fit values of D*water for our LG experiments vary within a factor of 2 over a range of pH2/pH2O from 0.007 to 9.7 (a range of ƒO2 from IW-2.2 to IW+4.9) and a water concentration range from 80 ppm to 280 ppm. The relative insensitivity of D*water to variations in pH2 suggests that loss of H during the degassing of the lunar melts described by [3] was not primarily by loss of dissolved H2. The value of D*water chosen by [3] for modeling diffusive degassing of lunar volcanic glasses is within a factor of three of our measured value in LG melt at 1350 °C. [1] Zhang et al. (1991) GCA 55, 441-456; [2] Ni et al. (2013) GCA 103, 36-48; [3] Saal et al. (2008) Nature 454, 192-195.

Dehydration of Glucose to 5‐Hydroxymethylfurfural Using Nb‐doped Tungstite

PubMed Central

Yue, Chaochao; Li, Guanna; Pidko, Evgeny A.; Wiesfeld, Jan J.; Rigutto, Marcello

2016-01-01

Abstract Dehydration of glucose to 5‐hydroxymethylfurfural (HMF) remains a significant problem in the context of the valorization of lignocellulosic biomass. Hydrolysis of WCl6 and NbCl5 leads to precipitation of Nb‐containing tungstite (WO3⋅H2O) at low Nb content and mixtures of tungstite and niobic acid at higher Nb content. Tungstite is a promising catalyst for the dehydration of glucose to HMF. Compared with Nb2O5, fewer by‐products are formed because of the low Brønsted acidity of the (mixed) oxides. In water, an optimum yield of HMF was obtained for Nb–W oxides with low Nb content owing to balanced Lewis and Brønsted acidity. In THF/water, the strong Lewis acidity and weak Brønsted acidity caused the reaction to proceed through isomerization to fructose and dehydration of fructose to a partially dehydrated intermediate, which was identified by LC‐ESI‐MS. The addition of HCl to the reaction mixture resulted in rapid dehydration of this intermediate to HMF. The HMF yield obtained in this way was approximately 56 % for all tungstite catalysts. Density functional theory calculations show that the Lewis acid centers on the tungstite surface can isomerize glucose into fructose. Substitution of W by Nb lowers the overall activation barrier for glucose isomerization by stabilizing the deprotonated glucose adsorbate. PMID:27493127

Determination of Activities of Niobium in Cu-Nb Melts Containing Dilute Nb

NASA Astrophysics Data System (ADS)

Wang, Daya; Yan, Baijun; Sichen, Du

2015-04-01

The activity coefficients of niobium in Cu-Nb melts were measured by equilibrating solid NbO2 with liquid copper under controlled oxygen potentials in the temperature range of 1773 K to 1898 K (1500 °C to 1625 °C). Either CO-CO2 gas mixture or H2-CO2 gas mixture was employed to obtain the desired oxygen partial pressures. Cu-Nb system was found to follow Henry's law in the composition range studied. The temperature dependence of Henry's constant in the Cu-Nb melts could be expressed as follows: The partial molar excess Gibbs energy change of niobium in Cu-Nb melts can be expressed as follows:

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 ppm CO2 (CO2/Nb = 505 ± 168, CO2/Ba = 133 ± 44), whereas enriched sources of intraplate basalts similar in concentrations to primitive mantle have 600 ± 200 ppm CO2. If all mantle reservoirs are expressed in the current inventory of oceanic basalts for which nearly undegassed CO2 concentrations are available, then we estimate the likely range of mantle C concentrations to be 1.4-4.8 × 1023 grams of C, or 1.5-5.2 times the mass of the current C surface reservoir. Depending on the assumed Ba and Nb contents of average oceanic crust, resulting ridge fluxes of C range from 7.2 × 1013 to 2.9 × 1014 g/yr.

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

Recent studies prove that the partial melting in some eclogite xenoliths in kimberlites is closely related to formation of diamonds in these rocks at 4-6 GPa and 1150-12500C [e.g. 1, 2]. Along with specific mineral assemblages, the products of the eclogite partial melting commonly include relics of potassium-rich silicic melts (45-65 wt. % of SiO2, 4-14 wt. % of K2O and K2O/Na2O > 1.0) [1, 2]. Available experimental data, however, demonstrate that such melts can not be produced by 'dry' or hydrous melting of a common eclogite. It implies that partial melting and conjugate diamond formation in mantle eclogites was triggered by infiltration of potassic fluids/melts. Assemblages of Cl-bearing phases and carbonates in eclogite xenoliths [1], and eclogitic diamonds [3-6] suggest that these agents were chloride-carbonate-H2O melts or/and chloride-H2O-CO2 fluids. In order to characterize interaction of both types of liquids with eclogites and their minerals, experiments in the eclogite-related systems with participation of CaCO3-Na2CO3-KCl-H2O or H2O-CO2-KCl are reviewed. Melting relations in the system eclogite-CaCO3-Na2CO3-KCl-H2O follow the general scheme proposed earlier for chloride-carbonate-silicate systems [7]. Below 12000C, Grt, Cpx and phlogopite (Phl) coexist with LCC only. Formation of Phl and Ca-rich Grt after Cpx indicate active reactions of Cpx with LCC accompanied by CO2 degassing and depletion of the clinopyroxene in jadeite. Subsequent dissolution of silicates in LCC at >1200OC results in formation of potassic silica-undersaturated carbonate and Cl-bearing melt (LCS) (37-40 wt. % of SiO2, 10-12 wt. % of K2O, ~3.5 wt. % of Cl) immiscible with the LCC. Compositional feature of this melt is very comparable to those of low-Mg carbonate-silicate melt inclusions in diamonds [6]. However, it is not relevant to the melt relics preserved in the partially molten eclogite xenoliths. Melting of eclogites with participation of the H2O-CO2-KCl fluid at 5 GPa at 1200-13000C [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 et al. (2007) Doklady Earth Sci., 415, 961-964; [5] Tomlinson et al. (2006), Earth Planet. Sci. Lett., 250, 581-585; [6] Weiss et al. (2009), Lithos, 112S, 660-674; [7] Safonov et al. (2009), Lithos, 112S, 260-273; [8] Butvina et al. (2009), Doklady Earth Sci., 427A, 956-960.

Constraints on the dynamics of melt migration, flow and emplacement across the continental crust

NASA Astrophysics Data System (ADS)

Cavalcante, Carolina; Viegas, Gustavo

2015-04-01

The presence of partial melting during deformation produces a drastic change in the rheological behavior of the continental crust. The rock strength decreases with melt fractions as low as ~0.7 %. At pressure/temperature conditions typical of the middle crust, melt-bearing systems may play a critical role in the processes of strain localization and in the overall strength of the continental lithosphere. In eastern Brazil, Neoproterozoic tectonics are often associated with wide partial melting and shear zone development, that promote the exhumation of mid- to lower crustal layers where compositionally heterogeneous anatexites with variable melt fractions and leucosome structures are exposed. The leucosomes usually form interconnected networks of magma that reflect the high melt content present during deformation. In this contribution we address two case studies encompassing the dynamics of melt flow at magma chambers, represented by the Carlos Chagas anatexite, and the mechanisms of melt migration and channeling through shear zones, in which the Patos shear zone serves as an analogue. Through detailed petrostructural studies of anatexites exposed at these settings, we aim to demonstrate the way melt deforms and localizes strain, the different patterns of melt flow pathways across the crust, and the implications for the mechanical behaviour of the Earth's lithosphere during orogenic deformation.

Dynamic Crystallization Experiments on LEW97008: Experimental Reproduction of Chondroid Textures

NASA Technical Reports Server (NTRS)

Nettles, J. W.; Le, L.; Lofgren, G. E.; McSween, H. Y, Jr.

2003-01-01

Dynamic crystallization experiments were conducted using LEW97008 (L3.4) as starting material. Experiments were melted at temperatures well below its liquidus (1250-1450 C) in order to document the textural and compositional changes that occur in UOC material with modest amounts of partial melting and subsequent crystallization. The textures of the experimental products compare very well to natural chondroids (partially melted nebular particles that would become chondrules if more completely melted). Thus it is possible to use the textures in these experiments as a guide to unraveling the melting and cooling histories of natural chondroids. The Antarctic meteorite LEW97008 was chosen as the starting material for our experiments. As an L3.4 it is slightly more metamorphosed than would ordinarily be preferred, but this meteorite is unusually fresh for an Antarctic meteorite, which made it attractive.

A model for foam formation, stability, and breakdown in glass-melting furnaces.

PubMed

van der Schaaf, John; Beerkens, Ruud G C

2006-03-01

A dynamic model for describing the build-up and breakdown of a glass-melt foam is presented. The foam height is determined by the gas flux to the glass-melt surface and the drainage rate of the liquid lamellae between the gas bubbles. The drainage rate is determined by the average gas bubble radius and the physical properties of the glass melt: density, viscosity, surface tension, and interfacial mobility. Neither the assumption of a fully mobile nor the assumption of a fully immobile glass-melt interface describe the observed foam formation on glass melts adequately. The glass-melt interface appears partially mobile due to the presence of surface active species, e.g., sodium sulfate and silanol groups. The partial mobility can be represented by a single, glass-melt composition specific parameter psi. The value of psi can be estimated from gas bubble lifetime experiments under furnace conditions. With this parameter, laboratory experiments of foam build-up and breakdown in a glass melt are adequately described, qualitatively and quantitatively by a set of ordinary differential equations. An approximate explicit relationship for the prediction of the steady-state foam height is derived from the fundamental model.

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 coming from subducted crust and investigate the possible role this process may play in the deep carbon cycle. [1] Dasgupta (2013) RiMG. [2] Shirey, et al. (2013) RiMG. [3] Frost & McCammon (2008) Ann Rev Earth Plan Sci. [4] Stagno, et al. (2015) CMP. [5] Kiseeva, et al. (2012) JPet. [6] Mallik & Dasgupta (2014) G3. [7] Spandler, et al. (2008) JPet.

Relative chronology in high-grade crystalline terrain of the Eastern Ghats, India: new insights

NASA Astrophysics Data System (ADS)

Bhattacharya, S.; Kar, R.; Saw, A. K.; Das, P.

2011-01-01

The two major lithology or gneiss components in the polycyclic granulite terrain of the Eastern Ghats, India, are the supracrustal rocks, commonly described as khondalites, and the charnockite-gneiss. Many of the workers considered the khondalites as the oldest component with unknown basement and the charnockite-protoliths as intrusive into the khondalites. However, geochronological data do not corroborate the aforesaid relations. The field relations of the hornblende- mafic granulite with the two gneiss components together with geocronological data indicate that khondalite sediments were deposited on older mafic crustal rocks. We propose a different scenario: Mafic basement and supracrustal rocks were subsequently deformed and metamorphosed together at high to ultra-high temperatures - partial melting of mafic rocks producing the charnockitic melt; and partial melting of pelitic sediments producing the peraluminous granitoids. This is compatible with all the geochronological data as well as the petrogenetic model of partial melting for the charnockitic rocks in the Eastern Ghats Belt.

Use of a computer model in the understanding of erythropoietic control mechanisms

NASA Technical Reports Server (NTRS)

Dunn, C. D. R.

1978-01-01

During an eight-week visit approximately 200 simulations using the computer model for the regulation of erythopoiesis were carries out in four general areas: with the human model simulating hypoxia and dehydration, evaluation of the simulation of dehydration using the mouse model. The experiments led to two considerations for the models. Firstly, a direct relationship between erythropoietin concentration and bone marrow sensitivity to the hormone and, secondly, a partial correction of tissue hypoxia prior to compensation by an increased hematocrit. This latter change in particular produced a better simuation of the effects of hypoxia on plasma erythropoietin concentrations.

Effect of structural modification on second harmonic generation in collagen

NASA Astrophysics Data System (ADS)

Stoller, Patrick C.; Reiser, Karen M.; Celliers, Peter M.; Rubenchik, Alexander M.

2003-07-01

The effects of structural perturbation on second harmonic generation in collagen were investigated. Type I collagen fascicles obtained from rat tails were structurally modified by increasing nonenzymatic cross-linking, by thermal denaturation, by collagenase digestion, or by dehydration. Changes in polarization dependence were observed in the dehydrated samples. Surprisingly, no changes in polarization dependence were observed in highly crosslinked samples, despite significant alterations in packing structure. Complete thermal denaturation and collagenase digestion produced samples with no detectable second harmonic signal. Prior to loss of signal, no change in polarization dependence was observed in partially heated or digested collagen.

Partial melting of metagreywackes, Part II. Compositions of minerals and melts

NASA Astrophysics Data System (ADS)

Montel, Jean-Marc; Vielzeuf, Daniel

A series of experiments on the fluid-absent melting of a quartz-rich aluminous metagreywacke has been carried out. In this paper, we report the chemical composition of the phases present in the experimental charges as determined by electron microprobe. This analytical work includes biotite, plagioclase, orthopyroxene, garnet, cordierite, hercynite, staurolite, gedrite, oxide, and glass, over the range 100-1000MPa, 780-1025°C. Biotites are Na- and Mg-rich, with Ti contents increasing with temperature. The compositions of plagioclase range from An17 to An35, with a significant orthoclase component, and are always different from the starting minerals. At high temperature, plagioclase crystals correspond to ternary feldspars with Or contents in the range 11-20 mol%. Garnets are almandine pyrope grossular spessartine solid solutions, with a regular and significant increase of the grossular content with pressure. All glasses are silicic (SiO2=67.6-74.4 wt%), peraluminous, and leucocratic (FeO+MgO=0.9-2.9 wt%), with a bulk composition close to that of peraluminous leucogranites, even for degrees of melting as high as 60 vol.%. With increasing pressure, SiO2 contents decrease while K2O increases. At any pressure, the melt compositions are more potassic than the water-saturated granitic minima. The H2O contents estimated by mass balance are in the range 2.5-5.6 wt%. These values are higher than those predicted by thermodynamic models. Modal compositions were estimated by mass balance calculations and by image processing of the SEM photographs. The positions of the 20 to 70% isotects (curves of equal proportion of melt) have been located in the pressure-temperature space between 100MPa and 1000MPa. With increasing pressure, the isotects shift toward lower temperature between 100 and 200MPa, then bend back toward higher temperature. The melting interval increases with pressure; the difference in temperature between the 20% and the 70% isotects is 40°C at 100MPa, and 150°C at 800MPa. The position of the isotects is interpreted in terms of both the solubility of water in the melt and the nature of the reactions involved in the melting process. A comparison with other partial melting experiments suggests that pelites are the most fertile source rocks above 800MPa. The difference in fertility between pelites and greywackes decreases with decreasing pressure. A review of the glass compositions obtained in experimental studies demonstrates that partial melting of fertile rock types in the crust (greywackes, pelites, or orthogneisses) produces only peraluminous leucogranites. More mafic granitic compositions such as the various types of calk-alkaline rocks, or mafic S-type rocks, have never been obtained during partial melting experiments. Thus, only peraluminous leucogranites may correspond to liquids directly formed by partial melting of metasediments. Other types of granites involve other components or processes, such as restite unmixing from the source region, and/or interaction with mafic mantle-derived materials.

Coincidence in Time of the Imbrium Basin Impact and Apollo 15 KREEP Volcanic Flows: The Case for Impact-Induced Melting

NASA Technical Reports Server (NTRS)

Ryder, Graham

1994-01-01

On the Earth there is no firm evidence that impacts can induce volcanic activity. However, the Moon does provide a very likely example of volcanism induced by an immense impact: the Imbrium basin-forming event was immediately succeeded by a crustal partial melting event that released basalt flows characterized by K, rare-earth elements (REE), P, and other trace elements (KREEP) over a wide area creating the Apennine Bench Formation. Impact total melting is inconsistent with the chemistry and petrography of these Apollo 15 KREEP basalts, which are quite unlike the impact melts recognized at Taurus-Littrow as the products of the Serenitatis impact. The Imbrium impact and the KREEP volcanic events are indistinguishable in radiometric age, and thus the volcanism occurred less than about 20 Ma later than the impact (less than about 0.5% of lunar history). The sample record indicates that such KREEP volcanism had not occurred in the region prior to that time, and demonstrates that it never occurred again. Such coincidence in time implies a genetic relationship between the two events, and impact-induced partial melting or release appears to be the only feasible process. Nonetheless, the characteristics of the Apollo 15 KREEP basalts suggest large-degree crustal melting that is not easy to reconcile with the inability of lunar pressure release alone to induce partial melting unless the source was already almost at its melting point. The earliest history of the surface of the Earth, at a time of greater internal heat production and basin-forming impacts, could have been greatly influenced by impact-induced melting.

Linking Serpentinite Geochemistry with Possible Alteration and Evolution of Supra-Subduction Wedge Mantle

NASA Astrophysics Data System (ADS)

Scambelluri, M.; Cannaò, E.; Agostini, S.; Gilio, M.

2016-12-01

Serpentinites are able to transport and release volatiles and fluid-mobile elements (FME) found in arc magmas. Constraining the trace element compositions of these rocks and of fluids released by de-serpentinization improves our knowledge of mass transfer from subduction zones to volcanic arcs, and of the role of slab and wedge mantle in this global process. Studies of high-pressure ultramafic rocks exhumed from plate interface settings reveal the fluid/rock interactions atop the slab and the processes that can affect the mantle wedge. Alpine eclogite-facies antigorite serpentinite (Voltri Massif) and fully de-serpentinized meta-peridotite (Cima di Gagnone) are enriched in sediment-derived As, Sb, U, Pb before peak dehydration. Their Sr, Pb and B isotopic compositions are reset during prograde (forearc) interaction with slab fluids. The eclogitic garnet and olivine from the Cima di Gagnone metaperidotite trap primary inclusions of the fluid released during breakdown of antigorite and chlorite. The inclusions display FME enrichments (high Cl, S; variable Cs, Rb, Ba, B, Pb, As, Sb) indicating element release from rocks to fluids during dehydration under subarc conditions. Our studies show that serpentinized mantle rocks from subduction zones sequester FME from slab fluids and convey these components and radiogenic isotopes into the mantle wedge upon dehydration. The geochemical processes revealed by such plate-interface rocks can apply to the supra-subduction mantle. Shallow element release from slabs to mantle wedge, downdrag of this altered mantle and its subsequent (subarc) dehydration transfers crust-derived FMEs to the arc magma sources without the need of concomitant subarc dehydration/melting of metasedimentary slab components. The slab signature detected in arc lavas can thus result from geochemical mixing of sediment, oceanic crust and ultramafic reservoirs into altered wedge-mantle rocks, rather than being attributed to multiple fluids.

An Evaluation of Quantitative Methods of Determining the Degree of Melting Experienced by a Chondrule

NASA Technical Reports Server (NTRS)

Nettles, J. W.; Lofgren, G. E.; Carlson, W. D.; McSween, H. Y., Jr.

2004-01-01

Many workers have considered the degree to which partial melting occurred in chondrules they have studied, and this has led to attempts to find reliable methods of determining the degree of melting. At least two quantitative methods have been used in the literature: a convolution index (CVI), which is a ratio of the perimeter of the chondrule as seen in thin section divided by the perimeter of a circle with the same area as the chondrule, and nominal grain size (NGS), which is the inverse square root of the number density of olivines and pyroxenes in a chondrule (again, as seen in thin section). We have evaluated both nominal grain size and convolution index as melting indicators. Nominal grain size was measured on the results of a set of dynamic crystallization experiments previously described, where aliquots of LEW97008(L3.4) were heated to peak temperatures of 1250, 1350, 1370, and 1450 C, representing varying degrees of partial melting of the starting material. Nominal grain size numbers should correlate with peak temperature (and therefore degree of partial melting) if it is a good melting indicator. The convolution index is not directly testable with these experiments because the experiments do not actually create chondrules (and therefore they have no outline on which to measure a CVI). Thus we had no means to directly test how well the CVI predicted different degrees of melting. Therefore, we discuss the use of the CVI measurement and support the discussion with X-ray Computed Tomography (CT) data.

Evidence for small-scale convection in the Pacific and Atlantic upper mantle from joint analysis of surface wave phase velocity and seafloor bathymetry

NASA Astrophysics Data System (ADS)

Ma, Z.; Dalton, C. A.

2017-12-01

It has been long observed that the rate of seafloor subsidence in the Pacific Ocean is lower than predicted by half-space cooling at ages older than 70 Myr. The magnitude, geographical distribution, onset time, and physical origin of the flattening are fundamental to our understanding of the evolution of oceanic lithosphere, and give important constraints on the Earth's heat budget and ocean volume throughout its history. However, none of these quantities is well established even after a long history of debates. Here, we present evidence from bathymetry and seismic tomography for the wide-scale operation of small-scale convection in the Pacific and Atlantic upper mantle. We track the temporal evolution of surface wave phase velocity and seafloor topography along age trajectories, which connect each piece of seafloor with the ridge segment that created it. The half-space cooling model (HSCM) and plate cooling model are used to predict the age dependence of phase velocity and bathymetry and to identify, for each age trajectory, the age at which the HSCM fails to explain the observations. The phase velocity and bathymetry are analyzed independently and yet yield identical results for more than 80% of points. We observe a wide range of ages at which the HSCM fails in the Atlantic and a much narrower range in the Pacific. We find that the age at which the HSCM fails is anti-correlated with the present-day depth of the ridge axis, with younger failure ages corresponding to deeper ridge axes and therefore colder mantle beneath the ridge.Such dependence is best explained by the small-scale convection model in which the effective viscosity of the lithosphere is regulated by the dehydration process that happens at the mid-ocean ridges. Decompression melting at a ridge removes water from the mantle and generates a depleted, dehydrated, and viscous layer. Since high mantle potential temperatures cause decompression melting to begin at greater depths, the thickness of the dehydrated layer is expected to scale with potential temperature. Moreover, numerical models have shown that such rheological layering controls the onset time of small-scale convection, with delayed onset for thicker layers. Our results therefore suggest that the stability of oceanic lithosphere is governed by the extent of melting at the ridge that created it.

Microscale models of partially molten rocks and their macroscale physical properties

NASA Astrophysics Data System (ADS)

Rudge, J. F.

2017-12-01

Any geodynamical model of melt transport in the Earth's mantle requires constitutive laws for the rheology of partially molten rock. These constitutive laws are poorly known, and one way to make progress in our understanding is through the upscaling of microscale models which describe physics at the scale of individual mineral grains. Crucially, many upscaled physical properties (such as permeability) depend not only on how much melt is present, but on how that melt is arranged at the microscale; i.e. on the geometry of the melt network. Here I will present some new calculations of equilibrium melt network geometries around idealised tetrakaidecahedral grains. In contrast to several previous calculations of textural equilibrium, these calculations allow for a both a liquid-phase and a solid-phase topology that can tile 3D space. The calculations are based on a simple minimisation of surface energy using the finite element method. In these simple models just two parameters control the topology of the melt network: the porosity (volume fraction of melt), and the dihedral angle. The consquences of these melt geometries for upscaled properties such as permeability; electrical conductivity; and importantly, effective viscosity will be explored. Recent theoretical work [1,2] has suggested that in diffusion creep a small amount of melt may dramatically reduce the effective shear viscosity of a partially molten rock, with profound consequences for the nature of the asthenosphere. This contribution will show that this reduction in viscosity may have been significantly overestimated, so that the drop in the effective viscosity at onset of melting is more modest. [1] Takei, Y., and B. K. Holtzman (2009), Viscous constitutive relations of solid-liquid composites in terms of grain boundary contiguity: 1. Grain boundary diffusion control model, J. Geophys. Res., 114, B06205.[2] Holtzmann B. K. (2016) Questions on the existence, persistence, and mechanical effects of a very small melt fraction in the asthenosphere, Geophys. Geochem. Geosyst. 17, 470-484.

The Effect of Fe-Ti-rich Cumulate Overturn on Evolution of the Lunar Interior

NASA Astrophysics Data System (ADS)

Mallik, A.; Ejaz, T.; Shcheka, S.; Garapic, G.; Petitgirard, S.; Blanchard, I.

2017-12-01

The last 5% of magma ocean crystallized Fe-Ti rich cumulates (FTC) emplaced below the anorthitic crust [1]. Due to gravitational instability, FTC underwent diapiric downwelling [2], associated with overturn of the lunar mantle. Petrological studies on Apollo basalts with variable TiO2 place their sources between 1.5-3 GPa. This indicates the presence of heterogeneous Ti-rich domains in the lunar interior which could either be produced by inefficient overturn and mixing [3], or due to post-overturn upwelling of FTC from the core-mantle boundary (CMB) [4]. Also, a seismically attenuating layer at the CMB ( 4.5 GPa) maybe associated with partial melt of overturned FTC [5]. Thus, it is important to investigate the phase equilibria of FTC with and without assimilation with the surrounding mantle, to understand better the effect of the overturn process on lunar evolution. We performed phase equilibria experiments at 2 and 4.5 GPa, 1230 to 1700 °C using a multi-anvil apparatus on FTC and a 1:1 mixture of FTC and mantle composition. FTC produced Fe-Ti rich (FeO 13-26 wt.%, TiO2 11-18 wt.%), Mg-poor (MgO 6-10 wt.%) basalts with residues of clinopyroxene+quartz+Fe-metal±spinel, while the mixture of FTC and mantle produced Fe-Ti-Mg rich (FeO 10-13 wt.%, TiO2 5-11 wt.% and MgO 20-30 wt.%) basalts with residues of orthopyroxene+olivine+Fe-metal±spinel±garnet. We find that partial melting of overturned cumulates within the lunar mantle can reproduce certain chemical attributes of Apollo high Ti basalts. Also, to test whether the partial melt of overturned cumulates can be stable at the CMB to produce the attenuating layer, we estimated the densities of these melt compositions using the published range of KT and K' of high Fe-Ti picrites. We find that the densities obtained from the published spread in K' and KT values yield inconclusive results about the stability of these partial melts at the CMB. This is being resolved by in-situ experimental determination of the densities of the high Fe-Ti melt compositions, currently underway. If these partial melts are indeed stable at the CMB, they bracket the present-day CMB temperature between 1300-1490 °C (5 to 30% partial melting [5]).[1] Snyder et al. (1992), GCA [2] Hess & Permentier (1995), EPSL [3] Brown & Grove (2015), GCA [4] Zhong et al. (2000), EPSL [5] Weber et al. (2011), Science

Intermediate-depth earthquake generation: what hydrous minerals can tell us

NASA Astrophysics Data System (ADS)

Deseta, N.; Ashwal, L.; Andersen, T. B.

2012-04-01

Subduction zone seismicity has commonly been causally related to the dehydration of minerals within the subducting slab(Hacker et al. 2004, Jung et al. (2004), Dobson et al. 2002, Rondenay et al. 2008). Other models for release of intermediate- and deep earthquakes include spontaneous reaction(s) affecting large rock-bodies along overstepped phase boundaries ( e.g. Green and Houston, 1995) and various shear heating-localization models (e.g. Kelemen and Hirth 2007, John et al. 2009). These concepts are principally reliant on seismic and thermo-petrological modeling; both of which are indirect methods of analysis. Recent discoveries of pseudotachylytes (PST) formed under high pressure conditions (Ivrea-Verbano Zone, Italy, Western Gneiss Region, Norway and Corsica) provide the first tangible opportunity to evaluate these models (Austrheim and Andersen, 2004, Lund and Austrheim, 2003, Obata and Karato, 1995, Jin et al., 1998). This case study focuses on observations based on ultramafic and mafic PST within the Ligurian Ophiolite of the high pressure-low temperature metamorphic (HP-LT) 'Shistes Lustres' complex in Cima di Gratera, Corsica (Andersen et al. 2008). These PST have been preserved in pristine lenses of peridotite and gabbro surrounded by schistose serpentinites. The PST range in thickness from 1mm to 25 cm (Andersen and Austrheim, 2006). Petrography and geochemistry on PST from the peridotite and gabbro samples indicates that total/near-total fusion of the local host rock mineral assemblage occurred; bringing up the temperature of shear zone from 350° C to 1400 - 1700° C; depending on the host rock (Andersen and Austrheim, 2006). The composition of the PST is highly variable, even at the thin section scale and this has been attributed to the coarse-grained nature of the host rock, its small scale inhomogeneity and poor mixing of the fusion melt. Almost all the bulk analyses of the PST are hydrous; the peridotitic PST is always hydrous (H2O content from 3.8 to 14 wt %) but the gabbro is not (H2O content from 0 to 2.6 wt%). The hydrous nature of the PST is due to the preferential melting of hydrous minerals (chlorite and serpentine - peridotite, glaucophane, epidote, Mg-hornblende - gabbro) in the host rock, rather than later hydration associated with exhumation (greenschist facies metamorphism and later alteration). However, in the case of the gabbro, the melt can be hydrous, but is not always. Anhydrous, glassy PST is formed in association with hydrous PST in the gabbro host rock. The gabbroic PST nucleate at the boundary between a coarse-grained pegmatoidal gabbro and a fine-grained gabbro, whereas the exclusively hydrous peridotite-hosted PST only nucleate along pre-existing hydrated fractures. These facts are significant when considering the mechanism of formation of the pseudotachylyte; which is commonly thought to be associated with the preferential melting of hydrous minerals. An anhydrous melt in proximity to other hydrous melts formed contemporaneously must have formed by the same mechanism; one which can exploit more than just one rheological characteristic in the rock vis. hydrous mineralogy AND grain size changes. Furthermore the presence of anhydrous PST suggests that little or no fluid ingress occurred prior to or during PST generation. Hydrous crystallisation products in the gabbro such as glaucophane and edenite indicate that whole-sale melting of the wallrock amphiboles (glaucophane, edenite, actinolite) took place to produce a melt with dissolved H2O, out of which such blue amphiboles were able to crystallise. It is important to note that in order for amphiboles to crystallise out of a melt, H2O is required but necessarily to an under-saturated degree. i.e. it cannot be 'free' water occurring as a separate phase in the melt (Carmen and Gilbert, 1983 and Koons, 1982). It is unlikely therefore that the water in the gabbro-derived fusion melt was the result of solid-state dehydration of the wallrock amphiboles. Microtextural observations of sheared out, kinked, twinned, prolate wallrock grains millimetres from vein boundaries and thermally rounded clasts, similarly deformed, entrained into the melt suggest that the process initiating fusion melting and seismic failure is spatially and temporally related to a high temperature ductile process rather than a brittle one. Together, the microtextural and geochemical observations provide ample support for a ductile thermal run-away process to initiate high pressure PST development and seismic failure and preclude dehydration embrittlement.

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.

Partial structure factors reveal atomic dynamics in metallic alloy melts

NASA Astrophysics Data System (ADS)

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

2017-07-01

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

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

Major Element Geochemistry of Peridotites from Santa Elena Ophiolite Complex, NW Costa Rica and Their Tectonic Implications

NASA Astrophysics Data System (ADS)

Wright, S.; Snow, J. E.; Gazel, E.; Sisson, V.

2010-12-01

The Santa Elena Ophiolite Complex (SEOC) is located on the west coast of Northern Costa Rica, near the Nicaraguan border. It consists primarily of preserved oceanic crustal rocks and underlying upper mantle thrust onto an accretionary complex. The petrogenesis and tectonic origin of this complex have widely been interpreted to be either a preserved mantle portion of the Caribbean Large Igneous Province (CLIP) as it drifted between North and South America from the Galapagos hotpot into the present day Caribbean Ocean around 80 Ma or as the mantle section to the nearby Nicoya complex. Previous structural work suggests that SEOC is a supra-subduction complex, not related to the CLIP or Nicoya. Our preliminary results agree. Mantle peridotites collected from the Santa Elena Ophiolite Complex consist primarily of spinel lherzolite (61 %) with minor amounts of harzburgite and dunite (22 % and 16 % respectively). Spinel Cr# [molar Cr / (Cr+Al)*100] is widely accepted to constrain mantle partial melting and lithospheric melt stagnation. Cr# of spinels within Santa Elena lherzolites fall between 12 and 35, suggesting an extent of 3 % to 13 % partial melting. Cr# of harzburgites range from 35 to 39, suggesting 13 % to 14 % partial melting. This range of partial melting suggests only modest depletion of this exposed portion of the ancient uppermost mantle. TiO2 concentrations of the lherzolite and harzburgite range from 0.004% to 0.128%, with the exception of one sample, SE10 - 17 (0.258%), and fall within the normal melting trend for mantle peridotites. The presence of dunite indicates that melt flow and associated melt - rock reaction with the surrounding peridotite took place within this portion of the mantle. A Cr# of 84.5 from one of these dunite samples indicate that significant melt rock reaction with refractory melts took place. Such results are rarely found in mid-ocean ridge abyssal peridotite settings, and are currently found primarily in forearc tectonic settings. However, due to the overall "normal" TiO2 concentrations in all but one spinel peridotite requires that if melt flow did occur, that the melt be nearly depleted in titanium. The relatively low Cr#'s and TiO2 concentrations of spinel in these peridotites that suggest low degrees of partial melting along with the paleo presence of melt flow and melt-rock reaction by low titanium melts, such as boninites, point toward a young fore-arc model for the tectonic origin of this ophiolite body rather than a preserved mantle portion of the CLIP. Additionally, two lines of evidence suggest SEOC was emplaced prior to the collision of the CLIP with North and South America. The SEOC is 1) capped by a Campanian (83.5 - 70.6 Ma) rudist limestone and 2) lies uncomformably atop Cenomanian (93.6 - 99.6 Ma) radiolarite beds. This suggests that the mantle portion of the SEOC was emplaced and exposed at the Caribbean ocean floor prior to the Late Cretaceous (Campanian), but no earlier than the Cenomanian. This combined tectonic and geochemical evidence suggests SEOC may be a portion of the proto-arc that existed between the Americas in the Cretaceous prior to assault by the CLIP.

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

PubMed Central

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

2016-01-01

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

Numerical Mantle Convection Models of Crustal Formation in an Oceanic Environment in the Early Earth

NASA Astrophysics Data System (ADS)

van Thienen, P.; van den Berg, A. P.; Vlaar, N. J.

2001-12-01

The generation of basaltic crust in the early Earth by partial melting of mantle rocks, subject to investigation in this study, is thought to be a first step in the creation of proto-continents (consisting largely of felsic material), since partial melting of basaltic material was probably an important source for these more evolved rocks. In the early Archean the earth's upper mantle may have been hotter than today by as much as several hundred degrees centigrade. As a consequence, partial melting in shallow convective upwellings would have produced a layering of basaltic crust and underlying depleted (lherzolitic-harzburgitic) mantle peridotite which is much thicker than found under modern day oceanic ridges. When a basaltic crustal layer becomes sufficiently thick, a phase transition to eclogite may occur in the lower parts, which would cause delamination of this dense crustal layer and recycling of dense eclogite into the upper mantle. This recycling mechanism may have contributed significantly to the early cooling of the earth during the Archean (Vlaar et al., 1994). The delamination mechanism which limits the build-up of a thick basaltic crustal layer is switched off after sufficient cooling of the upper mantle has taken place. We present results of numerical modelling experiments of mantle convection including pressure release partial melting. The model includes a simple approximate melt segregation mechanism and basalt to eclogite phase transition, to account for the dynamic accumulation and recycling of the crust in an upper mantle subject to secular cooling. Finite element methods are used to solve for the viscous flow field and the temperature field, and lagrangian particle tracers are used to represent the evolving composition due to partial melting and accumulation of the basaltic crust. We find that this mechanism creates a basaltic crust of several tens of kilometers thickness in several hundreds of million years. This is accompanied by a cooling of some hundred degrees centigrade. Vlaar, N.J., P.E. van Keken and A.P. van den Berg (1994), Cooling of the Earth in the Archaean: consequences of pressure-release melting in a hotter mantle, Earth and Planetary Science Letters, vol 121, pp. 1-18

A molecular dynamics study of chloride binding by the cryptand SC24

NASA Technical Reports Server (NTRS)

Owenson, B.; MacElroy, R. D.; Pohorille, A.

1988-01-01

The capture of chloride from water by the tetraprotonated form of the spherical macrotricyclic molecule SC24 was studied using molecular dynamics simulation methods. This model ionophore represents a broad class of molecules which remove ions from water. Two binding sites for the chloride were found, one inside and one outside the ligand. These sites are separated by a potential energy barrier of approximately 20 kcal mol-1. The major contribution to this barrier comes from dehydration of the chloride. The large, unfavorable dehydration effect is compensated for by an increase in electrostatic attraction between the oppositely charged chloride and cryptand, and by energetically favorable rearrangements of water structure. Additional assistance in crossing the barrier and completing the dehydration of the ion is provided by the shift of three positively charged hydrogen atoms of the cryptand towards the chloride. This structural rigidity is partially responsible for its selectivity.

Eclogite-associated potassic silicate melts and chloride-rich fluids in the mantle: a possible connection

NASA Astrophysics Data System (ADS)

Safonov, O.; Butvina, V.

2009-04-01

Relics of potassium-rich (4-14 wt. % of K2O and K2O/Na2O > 1.0) melts are a specific features of some partially molten diamondiferous eclogite xenoliths in kimberlites worldwide [1, 2]. In addition, potassic silicic melt inclusions with up to 16 wt. % of K2O are associated with eclogite phases in kimberlitic diamonds (O. Navon, pers. comm.). According to available experimental data, no such potassium contents can be reached by "dry" and hydrous melting of eclogite. These data point to close connection between infiltration of essentially potassic fluids, partial melting and diamond formation in mantle eclogites [2]. Among specific components of these fluids, alkali chlorides, apparently, play an important role. This conclusion follows from assemblages of the melt relics with chlorine-bearing phases in eclogite xenoliths [1], findings of KCl-rich inclusions in diamonds from the xenoliths [3], and concentration of Cl up to 0.5-1.5 wt. % in the melt inclusions in diamonds. In this presentation, we review our experimental data on reactions of KCl melts and KCl-bearing fluids with model and natural eclogite-related minerals and assemblages. Experiments in the model system jadeite(±diopside)-KCl(±H2O) at 4-7 GPa showed that, being immiscible, chloride liquids provoke a strong K-Na exchange with silicates (jadeite). As a result, low-temperature ultrapotassic chlorine-bearing (up to 3 wt. % of Cl) aluminosilicate melts form. These melts is able to produce sanidine, which is characteristic phase in some partially molten eclogites. In addition, in presence of water Si-rich Cl-bearing mica (Al-celadonite-phlogopite) crystallizes in equilibrium with sanidine and/or potassic melt and immiscible chloride liquid. This mica is similar to that observed in some eclogitic diamonds bearing chloride-rich fluid inclusions [4], as well as in diamonds in partially molten eclogites [2]. Interaction of KCl melt with pyrope garnet also produce potassic aluminosilicate melt because of high affinity of Al and Si to potassium. Additional products of this interaction are spinel and, possibly, olivine. These minerals are common products of garnet breakdown within the zones of partial melting of eclogite xenoliths [1, 2]. It is evident that simultaneous action of fluid species (H2O, CO2) and chlorides would produce much stronger effect. Following to this assumption, we further performed experiments on melting of model and natural eclogites with participation of the H2O-CO2-KCl fluids at 5 GPa. Comparison with the KCl-free melting (i.e. H2O-CO2 fluid only) shows that addition of KCl to the fluid intensifies melting. This effect is related both to high Cl content (up to 3-5.5 wt. %) in the newly formed silicate melt and its enrichment in K2O via K-Na exchange reactions with the immiscible chloride melt. Owing to these reactions, 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. However, the KCl/(H2O+CO2) ratio in the fluid does not influence on the K2O/Cl ratio in the melts suggesting that solubility of KCl in the melts practically does not depends on a presence of the H2O-CO2 fluid. Thus, the experiments imply that the KCl-bearing fluids or aqueous(±carbonic) KCl liquids could serve as a possible factor assisting to formation of the K-rich Cl-bearing aluminosilicate melts during the eclogite melting in the mantle. In turn, it means that the KCl content in such rock-melt-fluid systems could exceed 5 wt. %. The study is supported by the RFBR (07-05-00499), the Leading Scientific Schools Program (1949.2008.5), 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] Zedgenizov et al. (2007) Doklady Earth Sci. 415. 961-964; [4] Izraeli et al. (2001) Earth Planet. Sci. Lett. 5807. 1-10.

Magmatism during the accretion of the late Archaean Dharwar Craton (South India): sanukitoids and related rocks in their geological context.

NASA Astrophysics Data System (ADS)

Moyen, J.-F.; Martin, H.; Jayananda, M.; Peucat, J.-J.

2003-04-01

The South Indian Dharwar Craton assembled during the late-Archaean (ca. 2.5 Ga). This event was associated with intense granite genesis and emplacement. Based on petrography and geochemistry, 4 main types of late Archaean granitoids were distinguished: (1) Anatectic granites (and diatexites), formed by partial melting of TTG gneisses; (2) Classical TTGs; (3) Sanukitoids, generated by interaction between slab melts (TTG) and mantle peridotite; (4) The high HFSE Closepet granite, interpreted as derived from partial melting of a mantle metasomatized by slab melts (TTG). While the 3 later groups all are interpreted as resulting from slab melt/mantle wedge interactions, their differences are related to decreasing felsic melt/peridotite ratios during the ascent “slab melts” in the mantle wedge above an active subduction zone. Field data together with geochronology and isotope geochemistry allow to subdivide the Dharwar craton into three main domains: (1) The Western Dharwar Craton (WDC) is an old (3.3 2.9 Ga ), stable continental block with limited amounts of 2.5 Ga old anatectic granites. (2) The Eastern Dharwar Craton (EDC) is subdivided into two parts: (2a) West of Kolar Schist Belt, a region of 3.0-2.7 Ga old basement intruded by 2.5 Ga old anatectic granites; (2b) East of Kolar, an area featuring mainly 2.5 Ga old diatexites and granites, derived of partial melting of a newly accreted TTG crust. Anatectic granites are ubiquitous, and late in the cratonic evolution; they witnessed generalized melting of a juvenile crust. In contrast, deep-originated granites emplaced before this melting and are restricted to the boundaries between the blocks. This structure of distinct terranes separated by narrow bands operating as channels for deep-originated magmas provides independent evidences for a two-stage evolution: an arc accretion context for the TTG, sanukitoids and related rocks, immediately followed by high temperature reworking of the newly accreted craton, yielding diatexites and anatectic granites. From West to East, granitoids emplaced during the subduction stage evidence increasing slab-melt/peridotite interactions, from Closepet granite to TTG gneisses East of Kolar. These features are consistent with a model of westward subduction/accretion against a stable cratonic nucleus: partial melting along the subducting slab takes place at deeper and deeper levels from East to West, thus resulting in increasing melt/mantle interactions. Sanukitoids and Closepet type granites thus appear to be related to slab melt/mantle wedge interactions similar to those responsible for the secular evolution of TTG (Martin and Moyen, this session), but with still lower melt/peridotite ratios.

Metasomatic processes in the mantle beneath the Arkhangelsk province, Russia: evidence from garnet in mantle peridotite xenoliths, Grib pipe

NASA Astrophysics Data System (ADS)

Kargin, Alexei; Sazonova, Lyudmila; Nosova, Anna; Kovalchuk, Elena; Minevrina, Elena

2015-04-01

The Arkhangelsk province is located in the northern East European Craton and includes more than 80 bodies of kimberlite, alkaline picrite and other ultramafic and mafic rocks. They erupted through the Archean-Early Proterozoic basement into the Riphean-Paleozoic sedimentary cover. The Grib kimberlite pipe is located in the central part of the Arkhangelsk province in the Verkhotina (Chernoozerskoe) kimberlite field. The age of the Grib kimberlite is 376+-3 Ma (Rb-Sr by phlogopite). The Grib kimberlite pipe is the moderate-Ti kimberlites (TiO2 1-2 wt %) with strongly fractionated REE pattern , (La/Yb)n = 38-87. The Nd isotopic composition of the Grib pipe ranges epsilon Nd from -0.4 to + 1.0 and 87Sr/86Sr(t) from 0.7042 to 0.7069 (Kononova et al., 2006). Geochemical (Jeol JXA-8200 electron microprobe; SIMS; LA-ICP-MS) composition of clinopyroxene and garnet from mantle-derived xenoliths of the Grib kimberlite pipe was studied to provide new insights into metasomatic processes in the mantle beneath the Arkhangelsk province. Based on both major and trace element data, five geochemical groups of peridotitic garnet were distinguished. The partial melting of metasomatic peridotite with crystallization of a garnet-clinopyroxene association, and orthopyroxene assimilation by protokimberlitic melts was simulated and a model of garnet and clinopyroxene metasomatic origin was proposed. The model includes three stages: 1. Mantle peridotite was fertilized by subduction-derived sediment partial melts/fluids at the lithosphere-asthenosphere boundary to yield a CO2-bearing mantle peridotite (source I). 2. The partial melting of the carbonate-bearing mantle source 1 produced carbonatite-like melts (a degree of partial melting was 1,5 %), which could form the carbonatite-kimberlite rocks of the Mela River (Arkhangelsk province, 50 km North-West of Grib kimberlite) and also produce the metasomatic reworking of (carbonate-bearing) mantle peridotite (mantle source II) and form type-1 garnets. 3. The melting of the reworked carbonate-bearing mantle peridotite (mantle source II, degree of partial melting was 1 %) resulted in the generation of proto-kimberlite melts and type-2 garnet. These proto-kimberlite melts interacted with lithospheric mantle orthopyroxene to produce megacryst garnets and melts that formed the Grib kimberlite. This stage was responsible for the formation of the metasomatic equilibrium clinopyroxene -- garnet assemblage (type-3) in lithospheric peridotite and metasomatic transformation of deformed peridotite (type 4 and 5 garnet). This model suggests that peridotitic garnet originated at the first stage in the presence of subduction-generated melts or fluids. Kononova V.A., Nosova A.A., Pervov V.A., Kondrashov I.A. (2006). Compositional variations in kimberlites of the east European platform as a manifestation of sublithospheric geodynamic processes // Doklady Earth Sciences. V. 409. Is. 2. Pp. 952-957.

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.

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

NASA Astrophysics Data System (ADS)

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

2015-12-01

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

Numerical modeling of fluid migration in subduction zones

NASA Astrophysics Data System (ADS)

Walter, M. J.; Quinteros, J.; Sobolev, S. V.

2015-12-01

It is well known that fluids play a crucial role in subduction evolution. For example, mechanical weakening along tectonic interfaces, due to high fluid pressure, may enable oceanic subduction. Hence, the fluid content seems to be a critical parameter for subduction initiation. Studies have also shown a correlation between the location of slab dehydration and intermediate seismic activity. Furthermore, expelled fluids from the subduction slab affect the melting temperature, consequently, contributing to partial melting in the wedge above the down-going plate and extensive volcanism. In summary, fluids have a great impact on tectonic processes and therefore should be incorporated into geodynamic numerical models. Here we use existing approaches to couple and solve fluid flow equations in the SLIM-3D thermo-mechanical code. SLIM-3D is a three-dimensional thermo-mechanical code capable of simulating lithospheric deformation with elasto-visco-plastic rheology. It has been successfully applied to model geodynamic processes at different tectonic settings, including subduction zones. However, although SLIM-3D already includes many features, fluid migration has not been incorporated into the model yet. To this end, we coupled solid and fluid flow assuming that fluids flow through a porous and deformable solid. Thereby, we introduce a two-phase flow into the model, in which the Stokes flow is coupled with the Darcy law for fluid flow. Ultimately, the evolution of porosity is governed by a compaction pressure and the advection of the porous solid. We show the details of our implementation of the fluid flow into the existing thermo-mechanical finite element code and present first results of benchmarks and experiments. We are especially interested in the coupling of subduction processes and the evolution of the magmatic arc. Thereby, we focus on the key factors controlling magma emplacement and its influence on subduction processes.

Partial-melting of fertile metasedimentary rocks controlling the ore formation in the Jiangnan porphyry-skarn tungsten belt, south China: A case study at the giant Zhuxi W-Cu skarn deposit

NASA Astrophysics Data System (ADS)

Song, Shiwei; Mao, Jingwen; Zhu, Yongfeng; Yao, Zaiyu; Chen, Guohua; Rao, Jianfeng; Ouyang, Yongpeng

2018-04-01

The Zhuxi W-Cu deposit, located in the Jiangnan porphyry-skarn W belt, is a world-class W deposit. We studied three coeval mineralization-related intrusions composed of biotite monzogranite, fine-grained granite, and granite porphyry in the Zhuxi mine. These rocks contain peritectic garnet and K-feldspar. The LA-ICP-MS U-Pb dating of zircon from the biotite monzogranite, fine-grained granite, and granite porphyry yields average ages of 149.38 ± 0.86 Ma, 149.0 ± 1.0 Ma, and 148.30 ± 1.4 Ma, respectively. The Zhuxi granites are enriched in Cs, Rb, and U and depleted in Ba, Sr, and Ti, with ASI [molar Al2O3 / (CaO + Na2O + K2O)] values of 1.03-2.15. The fine-grained granite exhibits initial 87Sr/86Sr values of 0.716-0.717 and εNd(t) values ranging from -9.61 to -9.21. The εHf(t) values of the biotite monzogranite and fine-grained granite range from -8.83 to -6.30 and from -9.86 to -7.62, respectively. The Sr-Nd-Hf isotopic compositions of these rocks are similar to those of the fertile Neoproterozoic metasedimentary rocks in the Jiangnan W belt. The Zhuxi granites are S-type granites based on their mineral assemblages and geochemical characteristics. The Hf isotopic compositions, Sr-Nd isotopic characteristics, and trace element modelling suggest that the studied granites formed from the dehydration melting of fertile Neoproterozoic metasedimentary rocks caused by the Late Jurassic underplating of OIB-like basaltic magma.

A benchmark initiative on mantle convection with melting and melt segregation

NASA Astrophysics Data System (ADS)

Schmeling, Harro; Dannberg, Juliane; Dohmen, Janik; Kalousova, Klara; Maurice, Maxim; Noack, Lena; Plesa, Ana; Soucek, Ondrej; Spiegelman, Marc; Thieulot, Cedric; Tosi, Nicola; Wallner, Herbert

2016-04-01

In recent years a number of mantle convection models have been developed which include partial melting within the asthenosphere, estimation of melt volumes, as well as melt extraction with and without redistribution at the surface or within the lithosphere. All these approaches use various simplifying modelling assumptions whose effects on the dynamics of convection including the feedback on melting have not been explored in sufficient detail. To better assess the significance of such assumptions and to provide test cases for the modelling community we carry out a benchmark comparison. The reference model is taken from the mantle convection benchmark, cases 1a to 1c (Blankenbach et al., 1989), assuming a square box with free slip boundary conditions, the Boussinesq approximation, constant viscosity and Rayleigh numbers of 104 to 10^6. Melting is modelled using a simplified binary solid solution with linearly depth dependent solidus and liquidus temperatures, as well as a solidus temperature depending linearly on depletion. Starting from a plume free initial temperature condition (to avoid melting at the onset time) five cases are investigated: Case 1 includes melting, but without thermal or dynamic feedback on the convection flow. This case provides a total melt generation rate (qm) in a steady state. Case 2 is identical to case 1 except that latent heat is switched on. Case 3 includes batch melting, melt buoyancy (melt Rayleigh number Rm) and depletion buoyancy, but no melt percolation. Output quantities are the Nusselt number (Nu), root mean square velocity (vrms), the maximum and the total melt volume and qm approaching a statistical steady state. Case 4 includes two-phase flow, i.e. melt percolation, assuming a constant shear and bulk viscosity of the matrix and various melt retention numbers (Rt). These cases are carried out using the Compaction Boussinseq Approximation (Schmeling, 2000) or the full compaction formulation. For cases 1 - 3 very good agreement is achieved among the various participating codes. For case 4 melting/freezing formulations require some attention to avoid sub-solidus melt fractions. A case 5 is planned where all melt will be extracted and, reinserted in a shallow region above the melted plume. The motivation of this presentation is to summarize first experiences and to finalize the case definitions. References: Blankenbach, B., Busse, F., Christensen, U., Cserepes, L. Gunkel, D., Hansen, U., Harder, H. Jarvis, G., Koch, M., Marquart, G., Moore D., Olson, P., and Schmeling, H., 1989: A benchmark comparison for mantle convection codes, J. Geophys., 98, 23-38. Schmeling, H., 2000: Partial melting and melt segregation in a convecting mantle. In: Physics and Chemistry of Partially Molten Rocks, eds. N. Bagdassarov, D. Laporte, and A.B. Thompson, Kluwer Academic Publ., Dordrecht, pp. 141 - 178.

The effects of buoyancy on shear-induced melt bands in a compacting porous medium

NASA Astrophysics Data System (ADS)

Butler, S. L.

2009-03-01

It has recently been shown [Holtzman, B., Groebner, N., Zimmerman, M., Ginsberg, S., Kohlstedt, D., 2003. Stress-driven melt segregation in partially molten rocks. Geochem. Geophys. Geosyst. 4, Art. No. 8607; Holtzman, B.K., Kohlstedt, D.L., 2007. Stress-driven melt segregation and strain partitioning in partially molten rocks: effects of stress and strain. J. Petrol. 48, 2379-2406] that when partially molten rock is subjected to simple shear, bands of high and low porosity are formed at a particular angle to the direction of instantaneous maximum extension. These have been modeled numerically and it has been speculated that high porosity bands may form an interconnected network with a bulk, effective permeability that is enhanced in a direction parallel to the bands. As a result, the bands may act to focus mantle melt towards the axis of mid-ocean ridges [Katz, R.F., Spiegelman, M., Holtzman, B., 2006. The dynamics of melt and shear localization in partially molten aggregates. Nature 442, 676-679]. In this contribution, we examine the combined effects of buoyancy and matrix shear on a deforming porous layer. The linear theory of Spiegelman [Spiegelman, M., 1993. Flow in deformable porous media. Part 1. Simple analysis. J. Fluid Mech. 247, 17-38; Spiegelman, M., 2003. Linear analysis of melt band formation by simple shear. Geochem. Geophys. Geosyst. 4, doi:10.1029/2002GC000499, Article 8615] and Katz et al. [Katz, R.F., Spiegelman, M., Holtzman, B., 2006. The dynamics of melt and shear localization in partially molten aggregates. Nature 442, 676-679] is generalized to include both the effects of buoyancy and matrix shear on a deformable porous layer with strain-rate dependent rheology. The predictions of linear theory are compared with the early time evolution of our 2D numerical model and they are found to be in excellent agreement. For conditions similar to the upper mantle, buoyancy forces can be similar to or much greater than matrix shear-induced forces. The results of the numerical model indicate that bands form when buoyancy forces are large and that these can significantly alter the direction of the flow of liquid away from vertical. The bands form at angles similar to the angle of maximum instantaneous growth rate. Consequently, for strongly strain-rate dependent rheology, there may be two sets of bands formed that are symmetric about the direction of maximum compressive stress in the background mantle flow. This second set of bands would reduce the efficiency with which melt bands would focus melts towards the ridge axis.

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.

Deep-level magma dehydration and ascent rates at Mt. Etna (Sicily, Italy)

NASA Astrophysics Data System (ADS)

Armienti, P.; Perinelli, C.; Putirka, K.

2012-04-01

Magma ascent velocity, v (dH/dt; H = depth, t = time),can be determined from ascent rate (dP/dt), and rate of cooling (dT/dt): v= 1/(rgpg) (dP/dT)(dT/dt) where r is magma density, P is pressure, T is temperature and g is the acceleration of gravity. This equation for v provides a key to investigating the relationships between initial ascent rate of magma and the depths of magma dehydration, and v can be calculated using pressure and temperature (P - PH2O - T) estimates from mineral-liquid thermobarometry, and cooling rates inferred from Crystal Size Distribution (CSD) theory. For recent Mt. Etna lava flows, both dP/dT and dT/dt have been well characterized based, respectively, on clinopyroxene thermobarometry, and clinopyroxene CSDs (the latter yields dT/dt = 2x10-6 °C/s). Deep-level (>20 km) magma ascent rates range from practically 0 (where clinopyroxene P - T estimates form a cluster, and so dP/dT ≈ 0), to about 10 m/hr for flows that yield very steep P - T trajectories. Many lava flows at Mt. Etna yield P - T paths that follow a hydrous (about 3% water) clinopyroxene saturation surface, which closely approximates water contents obtained from melt inclusions. Independent assessments of deep level water content yield ascent rates of ~1 m/hr, in agreement with the slowest rates derived for magma effusion or vapor-driven ascent (~0.001 to >0.2 m/s, or 3.6 to 720 m/hr). Changes in P - T slopes, as obtained by pyroxene thermobarometry, indicate an upward acceleration of magma, which may be due to the onset of deep-level magma dehydration linked to the non-ideal behavior of water and CO2 mixtures that induce a deep-level maximum of water loss at P ≈ 0.4 MPa at T ≈ 1200 ° C for a CO2 content >1000ppm. Melt inclusion data on CO2 and H2O contents are successfully reproduced and interpreted in a context of magma dehydration induced by a CO2 flux possibly deriving by decarbonation reaction of the carbonate fraction of the Capo D'Orlando flysch.

Dehydration of diasporite to corundite in nature and experiment

NASA Astrophysics Data System (ADS)

Feenstra, A.; Wunder, B.

2002-02-01

The diasporite-corundite rock transformation, which releases 6 8 wt% H2O in an average metabauxite, was studied experimentally. The results are compared with petrological observations on the island of Naxos (Greece), where the transformation occurred in metakarst bauxites during prograde regional metamorphism. Dehydration experiments were started with fine-grained natural diasporite embedded in marble. The samples were first annealed in the diaspore stability field, then slowly brought to the final pressure-temperature (P-T) conditions in the corundum field and kept there five to seven days. Overstepping the diaspore-corundum equilibrium by ˜30 °C at 8 kbar resulted in partial dehydration of diaspore. As with the corundum-in isograd on Naxos, the corundum grew preferentially along the bauxite-marble contact. Experiments at 17 40 kbar with T oversteps of 40 150 °C resulted in complete diaspore breakdown. A high-porosity zone containing corundum and silicates developed along the bauxite-marble boundary, resulting from the solid volume decreases associated with the diaspore-corundum and decarbonation reactions. In nature, the marble similarly behaved as a barrier for liberated fluid, as indicated by coarse corundum- chloritoid segregations along metabauxite rims. In the 30 40 kbar experiments, the porous contact zone acted as fluid pathway, allowing partial dissolution of metabauxite. This demonstrates pronounced Al, Fe, and Ti mobility at high P and T of 600 800 °C.

Redox state of recycled crustal lithologies in the convective upper mantle constrained using oceanic basalt CO2-trace element systematics

NASA Astrophysics Data System (ADS)

Eguchi, J.; Dasgupta, R.

2017-12-01

Investigating the redox state of the convective upper mantle remains challenging as there is no way of retrieving samples from this part of the planet. Current views of mantle redox are based on Fe3+/∑Fe of minerals in mantle xenoliths and thermodynamic calculations of fO2 [1]. However, deep xenoliths are only recoverable from continental lithospheric mantle, which may have different fO2s than the convective oceanic upper mantle [1]. To gain insight on the fO2 of the deep parts of the oceanic upper mantle, we probe CO2-trace element systematics of basalts that have been argued to receive contributions from subducted crustal lithologies that typically melt deeper than peridotite. Because CO2 contents of silicate melts at graphite saturation vary with fO2 [2], we suggest CO2-trace element systematics of oceanic basalts which sample deep heterogeneities may provide clues about the fO2 of the convecting mantle containing embedded heterogeneities. We developed a new model to predict CO2 contents in nominally anhydrous silicate melts from graphite- to fluid-saturation over a range of P (0.05- 5 GPa), T (950-1600 °C), and composition (foidite-rhyolite). We use the model to calculate CO2 content as a function of fO2 for partial melts of lithologies that vary in composition from rhyolitic sediment melt to silica-poor basaltic melt of pyroxenites. We then use modeled CO2 contents in mixing calculations with partial melts of depleted mantle to constrain the fO2 required for partial melts of heterogeneities to deliver sufficient CO2 to explain CO2-trace element systematics of natural basalts. As an example, Pitcairn basalts, which show evidence of a subducted crustal component [3] require mixing of 40% of partial melts of a garnet pyroxenite at ΔFMQ -1.75 at 3 GPa. Mixing with a more silicic composition such as partial melts of a MORB-eclogite cannot deliver enough CO2 at graphite saturation, so in this scenario fO2 must be above the EMOG/D buffer at 4 GPa. Results suggest convecting upper mantle may be more oxidized than continental lithospheric mantle, and fO2 profiles of continental lithospheric mantle may not be applicable to convective upper mantle.[1] Frost, D, McCammon, C. 2008. An Rev E & P Sci. (36) p.389-420; [2] Holloway, J, et al. 1992. Eu J. Min. (4) p. 105-114; [3] Woodhead, J, Devey C. 1993. EPSL. (116) p. 81-99.

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 Mineralogist, 81, 202-212, 1996. Duret, F., N.M. Shapiro, Z. Cao, V. Levin, P. Molnar, and S. Roecker, Surface wave dispersion across Tibet: Direct evidence for radial anisotropy in the crust, Geophysical Research Letters, 37, doi:10.1029/2010GL043811, 2010. Hacker, B.R., E. Gnos, L. Ratschbacher, M. Grove, M. McWilliams, S.V. Sobolev, W. Jiang, and Z. Wu, Hot and dry xenoliths from the lower crust of Tibet, Science, 287, 2463-2466, 2000. Mechie, J., S.V. Sobolev, L. Ratschbacher, A.Y. Babeyko, G. Bock, A.G. Jones, K.D. Nelson, K.D. Solon, L.D. Brown, and W. Zhao, Precise temperature estimation in the Tibetan crust from seismic detection of the a-b quartz transition, Geology, 32, 601-604, 2004. Xie, J., M.H. Ritzwoller, W. Shen, Y. Yang, Y. Zheng, and L. Zhou, Crustal radial anisotropy across Eastern Tibet and the Western Yangtze Craton, Journal of Geophysical Research, in press, 2013. Xu, Z.J., X. Song, and L. Zhu, Crustal and uppermost mantle S velocity structure under Hi-CLIMB seismic array in central Tibetan Plateau from joint inversion of surface wave dispersion and receiver function data, Tectonophysics, 584, 209-220, 2013. Yang, Y., M.H. Ritzwoller, Y. Zheng, W. Shen, A.L. Levshin, and Z. Xie, A synoptic view of the distribution and connectivity of the mid-crustal low velocity zone beneath Tibet, Journal of Geophysical Research, 117, 10.1029/2011JB008810, 2012.

AFM and SFG studies of pHEMA-based hydrogel contact lens surfaces in saline solution: adhesion, friction, and the presence of non-crosslinked polymer chains at the surface.

PubMed

Kim, Seong Han; Opdahl, Aric; Marmo, Chris; Somorjai, Gabor A

2002-04-01

The surfaces of two types of soft contact lenses neutral and ionic hydrogels--were characterized by atomic force microscopy (AFM) and sum-frequency-generation (SFG) vibrational spectroscopy. AFM measurements in saline solution showed that the presence of ionic functional groups at the surface lowered the friction and adhesion to a hydrophobic polystyrene tip. This was attributed to the specific interactions of water and the molecular orientation of hydrogel chains at the surface. Friction and adhesion behavior also revealed the presence of domains of non-crosslinked polymer chains at the lens surface. SFG showed that the lens surface became partially dehydrated upon exposure to air. On this partially dehydrated lens surface, the non-crosslinked domains exhibited low friction and adhesion in AFM. Fully hydrated in saline solution, the non-crosslinked domains extended more than tens of nanometers into solution and were mobile.

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.

Deep solid-state equilibration and deep melting of plagioclase-free spinel peridotite from the slow-spreading Mid-Atlantic Ridge, ODP Leg 153

NASA Astrophysics Data System (ADS)

Will, Thomas M.; Schmädicke, Esther; Frimmel, Hartwig E.

2010-11-01

A petrological investigation of abyssal, plagioclase-free spinel peridotite drilled during ODP cruise 153 in the North Atlantic revealed that the peridotite represent refractory, partial residual mantle material that experienced depletion of incompatible trace elements during upper mantle melting. The degree of partial melting as estimated from spinel compositions was c. 12%. Fractionated middle and heavy rare earth elements imply polybaric melting, with c. 1-4% initial melting in the garnet peridotite stability field and subsequent partial melting of ~7-10% in the spinel peridotite stability field. Geothermobarometric investigations revealed that the solid-state equilibration of the spinel peridotite occurred at some 1,100-1,150°C and c. 20-23 kbar, corresponding to an equilibration depth of c. 70 ± 5 km and an unusually low thermal gradient of some 11-17°C/km. A thermal re-equilibration of the peridotite occurred at ~850-1,000°C at similar depths. Naturally, the initial mantle melting in the garnet-peridotite stability field must have commenced at depths greater than 70 ± 5 km. It is likely that the residual peridotite rose rapidly through the lithospheric cap towards the ridge axis. The exhumation of the abyssal peridotite occurred, at least in parts, via extensional detachment faulting. Given the shallow to moderate dip angles of the fault surfaces, the exhumation of the peridotite from its equilibration depth would imply an overall ridge-normal horizontal displacement of c. 50-160 km if tectonic stretching and detachment faulting were the sole exhumation mechanism.

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

NASA Astrophysics Data System (ADS)

Mallik, A.; Dasgupta, R.

2013-12-01

The presence of heterogeneity in the form of recycled altered oceanic crust (MORB-eclogite) has been proposed in the source of HIMU ocean island basalts (OIBs) [1]. Partial melts of recycled oceanic crust, however, are siliceous and Mg-poor and thus do not resemble the major element compositions of alkalic OIBs that are silica-poor and Mg-rich. In an upwelling heterogenous mantle, MORB-eclogite undergoes melting deeper than volatile-free peridotite, hence, andesitic partial melt derived from eclogite will react with subsolidus peridotite. We have examined the effect of such a melt-rock reaction under volatile-free conditions at 1375 °C, 3 GPa by varying the melt-rock ratio from 8 to 50 wt.% [2]. We concluded that the reacted melts reproduce certain major element characteristics of oceanic basanites, but not nephelinites. Also, the melt-rock reaction produces olivine and garnet-bearing websteritic residue. Because presence of CO2 has been invoked in the source of many HIMU ocean islands, the effect of CO2 on such a melt-rock reaction needs to be evaluated. Accordingly, we performed reaction experiments on mixtures of 25% and 33% CO2-bearing andesitic partial melt and peridotite at 1375 °C, 3 GPa by varying the dissolved CO2 content of the reacting melts from 1 to 5 wt.% (bulk CO2 from 0.25 to 1.6 wt.%) [3, this study]. Owing to melt-rock reaction, with increasing CO2 in the bulk mixture, (a) modes of olivine and cpx decrease while melt, opx and garnet increase, (b) reacted melts evolve to greater degree of Si-undersaturation (from andesite through basanite to nephelinite), (c) enhanced crystallization of garnet take place with higher CO2 in the melt, reducing alumina content of the reacted melts, and (d) CaO and MgO content of the reacted melts increase, without affecting FeO* and Na2O contents (indicating greater propensity of Ca2+ and Mg2+ over Fe2+ and Na+ to enter silicate melt as carbonate). For a given melt-MgO, the CO2-bearing reacted melts are a better match for alkalic basalts in terms of SiO2, Al2O3, CaO and CaO/Al2O3 than the CO2-free ones [3]. Using the experimental data, we have further developed an empirical model to predict mineral modes in residue and reacted melt compositions for olivine-opx saturated lithologies as a function of melt:rock ratio and bulk CO2 content. For example, in case of 5 wt.% eclogite melt infiltrating in fertile peridotite, with bulk CO2 from 0 to 2 wt.%, the derivative melts show an increase in CaO and MgO from 11 to 16 wt.%, 15 to 24 wt.%, respectively and decrease in SiO2 and Al2O3 from 45 to 39 wt.% and 14 to 5 wt.%, respectively. From this model, we have created a major element composition space of MORB-eclogite-derived reactive melt mass vs. bulk CO2 and we predict that primary HIMU-type magmas require <5 to 10 wt.% of MORB-eclogite melt input and up to 0.8 wt.% bulk CO2 in their source. Our model also allows determining the residual lithology at the source of alkalic basalts, produced owing to eclogite melt-peridotite reaction with or without CO2. [1] Jackson & Dasgupta (2008) EPSL 276, 175-186. [2] Mallik & Dasgupta (2012) EPSL 329-330, 97-108. [3] Mallik & Dasgupta (in press) JPetrol.

Mild dehydration modifies the cerebrovascular response to the cold pressor test.

PubMed

Perry, Blake G; Bear, Tracey L K; Lucas, Samuel J E; Mündel, Toby

2016-01-01

The cold pressor test (CPT) is widely used in clinical practice and physiological research. It is characterized by a robust autonomic response, with associated increases in heart rate (HR), mean arterial pressure (MAP) and mean middle cerebral artery blood flow velocity (MCAv(mean)). Hydration status is not commonly reported when conducting this test, yet blood viscosity alone can modulate MCAv(mean), potentially modifying the MCAv(mean) response to the CPT. We investigated the effect of mild dehydration on the physiological response to the CPT in 10 healthy men (mean ± SD: age 28 ± 5 years; body mass 83 ± 5 kg). All participants completed two CPTs, cold water (0°C) immersion of both feet for 90 s, with the order of the euhydration and dehydration trials counterbalanced. Beat-to-beat MCAv, MAP, HR and breath-by-breath partial pressure of end-tidal CO2 (P(ET,CO2)) were measured continuously. Participants' pain perception was measured 1 min into the CPT using a visual analog scale (no pain = 0; maximal pain = 10). Dehydration significantly elevated plasma osmolality and urine specific gravity and reduced body mass (all P < 0.01). The MAP and HR responses were not different between treatments (both P > 0.05). After 90 s of immersion, the change in MCAv(mean) from baseline was less in the dehydration compared with the euhydration trial (change 0 ± 5 versus 7 ± 7 cm s(-1), P = 0.01), as was P(ET,CO2) (change -3 ± 2 versus 0 ± 3 mmHg, P = 0.02). Dehydration was associated with greater relative pain sensation during the CPT (7.0 ± 1.3 vs 5.8 ± 1.8, P = 0.02). Our results demonstrate that mild dehydration can modify the cerebrovascular response to the CPT, with dehydration increasing perceived pain, lowering P ET ,CO2 and, ultimately, blunting the MCAv(mean) response. © 2015 The Authors. Experimental Physiology © 2015 The Physiological Society.

Permian magmatic sequences of the Bilihe gold deposit in central Inner Mongolia, China: Petrogenesis and tectonic significance

NASA Astrophysics Data System (ADS)

Liu, Chunhua; Nie, Fengjun

2015-08-01

The Bilihe gold deposit is located in the eastern section of the Ondor Sum-Yanji Suture at the southern margin of the Xing'an-Mongolian Orogenic Belt (XMOB) and the northern margin of the North China Craton (NCC), central Inner Mongolia. The magmatic rocks in the ore district are generally high-K calc-alkaline, enriched in LREE, Zr, and Hf, and depleted in HREE, Nb, Ta, and P. The magmatic evolution sequences are norite gabbro → granodiorite porphyry → granite or norite gabbro → andesite → dacite porphyry → granodiorite, which show a trend of decreasing TiO2, FeO, MgO, CaO, and P2O5 with increasing SiO2. In the Bilihe ore district, hydrothermal processes were coeval with granitic magmatism for a period of ~ 17 Myr (272-255 Ma). The ages of the granite, granodiorite porphyry, granodiorite, and dacite porphyry are 271.5-264.1 Ma, 269.8-255.8 Ma, 268.3 Ma, and 268.6-259.4 Ma, respectively. The magmatic rocks contain magmatic, hydrothermal, and magmatic-hydrothermal zircons. The magmatic zircons have δCe > 4, La < 3 ppm, and SmN/LaN > 2.5; the hydrothermal zircons have δCe < 4, La > 3 ppm, and SmN/LaN < 2.5. The Nb/Ta and Zr/Hf ratios of granodiorite are 12.7-14.99 and 40.2-46.56, respectively. The Zr/Hf ratios successively increase in the sequence of granite (27.4-29.02) → granodiorite porphyry (29.19-32.18) → dacite porphyry (33.54-38.5) → norite gabbro (36.75-38.37), and their Nb/Ta ratios are 9.09-12.38. Zircons in granodiorite yield ε Hf (t) values of - 0.29 to - 56 (n = 13) and 2.07-7.62 (n = 5), and they give a Hf two-stage model age (tDM2) of 807-4765 Ma. The ε Hf (t) values of the zircons in granite, granodiorite porphyry, and dacite porphyry are - 0.46 to 8.03, 3.17 to 10.32, and - 0.78 to 6.58, respectively, and their Hf tDM2 ages are 787-1324 Ma, 638-1091 Ma, and 868-1343 Ma, respectively. Dehydration partial melting of subducted oceanic crust resulted in the formation of dacite porphyry; partial melting of depleted mantle resulted in the formation of norite gabbro; mixing of depleted mantle and lower crust resulted in the formation of granodiorite porphyry; partial melting of lower crust resulted in the formation of granite; and mixing of lower crust and old upper crust resulted in the formation of granodiorite. Magmatic rocks in the ore district with ages of 272-255 Ma were formed during the late stages of closure of the Paleoasian Ocean; i.e., during the transformation from a collisional to extensional setting.

Combined analysis of mRNA and miRNA identifies dehydration and salinity responsive key molecular players in citrus roots.

PubMed

Xie, Rangjin; Zhang, Jin; Ma, Yanyan; Pan, Xiaoting; Dong, Cuicui; Pang, Shaoping; He, Shaolan; Deng, Lie; Yi, Shilai; Zheng, Yongqiang; Lv, Qiang

2017-02-06

Citrus is one of the most economically important fruit crops around world. Drought and salinity stresses adversely affected its productivity and fruit quality. However, the genetic regulatory networks and signaling pathways involved in drought and salinity remain to be elucidated. With RNA-seq and sRNA-seq, an integrative analysis of miRNA and mRNA expression profiling and their regulatory networks were conducted using citrus roots subjected to dehydration and salt treatment. Differentially expressed (DE) mRNA and miRNA profiles were obtained according to fold change analysis and the relationships between miRNAs and target mRNAs were found to be coherent and incoherent in the regulatory networks. GO enrichment analysis revealed that some crucial biological processes related to signal transduction (e.g. 'MAPK cascade'), hormone-mediated signaling pathways (e.g. abscisic acid- activated signaling pathway'), reactive oxygen species (ROS) metabolic process (e.g. 'hydrogen peroxide catabolic process') and transcription factors (e.g., 'MYB, ZFP and bZIP') were involved in dehydration and/or salt treatment. The molecular players in response to dehydration and salt treatment were partially overlapping. Quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) analysis further confirmed the results from RNA-seq and sRNA-seq analysis. This study provides new insights into the molecular mechanisms how citrus roots respond to dehydration and salt treatment.

Combined analysis of mRNA and miRNA identifies dehydration and salinity responsive key molecular players in citrus roots

PubMed Central

Xie, Rangjin; Zhang, Jin; Ma, Yanyan; Pan, Xiaoting; Dong, Cuicui; Pang, Shaoping; He, Shaolan; Deng, Lie; Yi, Shilai; Zheng, Yongqiang; Lv, Qiang

2017-01-01

Citrus is one of the most economically important fruit crops around world. Drought and salinity stresses adversely affected its productivity and fruit quality. However, the genetic regulatory networks and signaling pathways involved in drought and salinity remain to be elucidated. With RNA-seq and sRNA-seq, an integrative analysis of miRNA and mRNA expression profiling and their regulatory networks were conducted using citrus roots subjected to dehydration and salt treatment. Differentially expressed (DE) mRNA and miRNA profiles were obtained according to fold change analysis and the relationships between miRNAs and target mRNAs were found to be coherent and incoherent in the regulatory networks. GO enrichment analysis revealed that some crucial biological processes related to signal transduction (e.g. ‘MAPK cascade’), hormone-mediated signaling pathways (e.g. abscisic acid- activated signaling pathway’), reactive oxygen species (ROS) metabolic process (e.g. ‘hydrogen peroxide catabolic process’) and transcription factors (e.g., ‘MYB, ZFP and bZIP’) were involved in dehydration and/or salt treatment. The molecular players in response to dehydration and salt treatment were partially overlapping. Quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) analysis further confirmed the results from RNA-seq and sRNA-seq analysis. This study provides new insights into the molecular mechanisms how citrus roots respond to dehydration and salt treatment. PMID:28165059

Depth and degree of melting of komatiites

NASA Astrophysics Data System (ADS)

Herzberg, Claude

1992-04-01

High pressure melting experiments have permitted new constraints to be placed on the depth and degree of partial melting of komatiites. Komatiites from Gorgona Island were formed by relatively low degrees of pseudoinvariant melting involving L + Ol + Opx + Cpx + Gt on the solidus at 40 kbar, about 130 km depth. Munro-type komatiites were separated from a harzburgite residue (L + Ol + Opx) at pressures that were poorly constrained, but were probably around 50 kbar, about 165 km depth; the degree of partial melting was less than 40 percent. Secular variations in the geochemistry of komatiites could have formed in response to a reduction in the temperature and pressure of melting with time. The 3.5 Ga Barberton komatiites and the 2.7 Ga Munro-type komatiities could have formed in plumes that were hotter than the present-day mantle by 500 deg and 300 deg, respectively. When excess temperatures are this size, melting is deeper and volcanism changes from basaltic to momatiitic. The komatiities from Gorgona Island, which are Mesozoic in age, may be representative of komatiities that are predicted to occur in oceanic plateaus of Cretaceous age throughout the Pacific (Storey et al., 1991).

Chemical interactions in the subduction factory: New insights from an in situ trace element and hydrogen study of the Ichinomegata and Oki-Dogo mantle xenoliths (Japan)

NASA Astrophysics Data System (ADS)

Satsukawa, Takako; Godard, Marguerite; Demouchy, Sylvie; Michibayashi, Katsuyoshi; Ildefonse, Benoit

2017-07-01

The uppermost mantle in back arc regions is the site of complex interactions between partial melting, melt percolation, and fluid migration. To constrain these interactions and evaluate their consequences on geochemical cycles, we carried out an in situ trace element and water study of a suite of spinel peridotite xenoliths from two regions of the Japan back arc system, Ichinomegata (NE Japan) and Oki-Dogo (SW Japan), using LA-ICPMS and FTIR spectrometry, respectively. This study provides the first full dataset of trace element and hydrogen compositions in peridotites including analyses of all their main constitutive silicate minerals: olivine, orthopyroxene and clinopyroxene. The Ichinomegata peridotites sample a LREE-depleted refractory mantle (Mg# olivine = 0.90; Cr# spinel = 0.07-0.23; Yb clinopyroxene = 7.8-13.3 × C1-chondrite, and La/Yb clinopyroxene = 0.003-0.086 × C1-chondrite), characterized by Th-U positive anomalies and constant values of Nb/Ta. The composition of the studied Ichinomegata samples is consistent with that of an oceanic mantle lithosphere affected by cryptic metasomatic interactions with hydrous/aqueous fluids (crypto-hydrous metasomatism). In contrast, the Oki-Dogo peridotites have low Mg# olivine (0.86-0.93) and a broad range of compositions with clinopyroxene showing "spoon-shaped" to flat, and LREE-enriched patterns. They are also characterized by their homogeneous compositions in the most incompatible LILE (e.g., Rb clinopyroxene = 0.01-0.05 × primitive mantle) and HFSE (e.g., Nb clinopyroxene = 0.01-2.16 × primitive mantle). This characteristic is interpreted as resulting from various degrees of melting and extensive melt-rock interactions. FTIR spectroscopy shows that olivine in both Ichinomegata and Oki-Dogo samples has low water contents ranging from 2 to 7 ppm wt. H2O. In contrast, the water contents of pyroxenes from Ichinomegata peridotites (113-271 ppm wt. H2O for orthopyroxene, and 292-347 ppm wt. H2O for clinopyroxene) are significantly higher than in Oki-Dogo peridotites (9-35 ppm wt. H2O for orthopyroxene, and 15-98 ppm wt. H2O for clinopyroxene). This indicates a relationship between melt-rock interaction and water concentrations in pyroxenes. Our study suggests that the water content of the Japan mantle wedge is controlled by the late melt/fluid/rock interactions evidenced by trace element geochemistry: a mechanism triggered by magma-rock interactions may have acted as an efficient dehydrating process in the Oki-Dogo region while the Ichinomegata mantle water content is controlled by slab-derived crypto-hydrous metasomatism.

Experimental determination of U and Th partitioning between clinopyroxene and natural and synthetic basaltic liquid

NASA Technical Reports Server (NTRS)

Latourrette, T. Z.; Burnett, D. S.

1992-01-01

Experimental measurements of U and the partition coefficients between clinopyroxene and synthetic and natural basaltic liquid are presented. The results demonstrate that crystal-liquid U-Th fractionation is fO2-dependent and that U in terrestrial magmas is not entirely tetravalent. During partial melting, the liquid will have a Th/U ratio less than the clinopyroxene in the source. The observed U-238 - Th-230 disequilibrium in MORB requires that the partial melt should have a U/Th ratio greater than the bulk source and therefore cannot result from clinopyroxene-liquid partitioning. Further, the magnitudes of the measured partition coefficients are too small to generate significant U-Th fractionation in either direction. Assuming that clinopyroxene contains the bulk of the U and Th in the MORB source, the results indicate that U-238 - Th-230 disequilibrium in MORB may not be caused by partial melting at all.

Mantle ingredients for making the fingerprint of Etna alkaline magmas: implications for shallow partial melting within the complex geodynamic framework of Eastern Sicily

NASA Astrophysics Data System (ADS)

Viccaro, Marco; Zuccarello, Francesco

2017-09-01

Mantle ingredients responsible for the signature of Etnean Na- and K-alkaline magmas and their relationships with short-term geochemical changes of the erupted volcanic rocks have been constrained through a partial melting model that considers major, trace elements and water contents in the produced liquids. Characteristics of the Etnean source for alkaline magmas have been supposed similar to those of the mantle accessible at a regional scale, namely below the Hyblean Plateau. The assumption that the Etnean mantle resembles the one beneath the Hyblean Plateau is justified by the large geochemical affinities of the Etnean hawaiites/K-trachybasalts and the Hyblean hawaiites/alkali basalts for what concerns both trace elements and isotope systematics. We have modeled partial melting of a composite source constituted by two rock types, inferred by lithological and geochemical features of the Hyblean xenoliths: 1) a spinel lherzolite bearing metasomatic, hydrous phases and 2) a garnet pyroxenite in form of veins intruded into the spinel lherzolite. The partial melting modeling has been applied to each rock type and the resulting primary liquids have been then mixed in various proportions. These compositions have been compared with some Etnean alkaline magmas of the post ∼60 ka activity, which were firstly re-equilibrated to mantle conditions through mass balance calculations. Our results put into evidence that concentrations of major and trace elements along with the water obtained from the modeling are remarkably comparable with those of Etnean melts re-equilibrated at primary conditions. Different proportions of the spinel lherzolite with variable modal contents of metasomatic phases and of the garnet pyroxenite can therefore account for the signature of a large spectrum of Etnean alkaline magmas and for their geochemical variability through time, emphasizing the crucial role played by compositional small-scale heterogeneity of the source. These heterogeneities are able to produce magmas with variable compositions and volatile contents, which can then undergo distinct histories of ascent and evolution, leading to the wide range of eruptive styles observed at Mt. Etna volcano. Being partial melting confined in the spinel facies of the mantle, our model implies that the source of Mt. Etna magmas might be rather shallow (<2 GPa; i.e., lesser than ca. 60 km), excluding the presence of deep, plume-like mantle structures responsible for magma generation. Partial melting should occur consequently as a response of mantle decompression within the framework of regional tectonics affecting the Eastern Sicily, which could be triggered by extensional tectonics and/or subduction-induced mantle upwelling.

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.

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 composition as well as pressure in natural silicate melts. The changes of the fraction of highly coordinated Al in multi-component silicate glasses and melts with composition can provide insight into the changes of macroscopic properties (e.g., entropy, viscosity, and diffusivity) with varying composition of melt.

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

NASA Astrophysics Data System (ADS)

Machida, Shiki; Kogiso, Tetsu; Hirano, Naoto

2017-02-01

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

Geochemical evidence for the melting of subducting oceanic lithosphere at plate edges

NASA Astrophysics Data System (ADS)

Yogodzinski, G. M.; Lees, J. M.; Churikova, T. G.; Dorendorf, F.; Wöerner, G.; Volynets, O. N.

2001-01-01

Most island-arc magmatism appears to result from the lowering of the melting point of peridotite within the wedge of mantle above subducting slabs owing to the introduction of fluids from the dehydration of subducting oceanic crust. Volcanic rocks interpreted to contain a component of melt (not just a fluid) from the subducting slab itself are uncommon, but possible examples have been recognized in the Aleutian islands, Baja California, Patagonia and elsewhere. The geochemically distinctive rocks from these areas, termed `adakites', are often associated with subducting plates that are young and warm, and therefore thought to be more prone to melting. But the subducting lithosphere in some adakite locations (such as the Aleutian islands) appears to be too old and hence too cold to melt. This implies either that our interpretation of adakite geochemistry is incorrect, or that our understanding of the tectonic context of adakites is incomplete. Here we present geochemical data from the Kamchatka peninsula and the Aleutian islands that reaffirms the slab-melt interpretation of adakites, but in the tectonic context of the exposure to mantle flow around the edge of a torn subducting plate. We conclude that adakites are likely to form whenever the edge of a subducting plate is warmed or ablated by mantle flow. The use of adakites as tracers for such plate geometry may improve our understanding of magma genesis and thermal structure in a variety of subduction-zone environments.

Geochemical evidence for the melting of subducting oceanic lithosphere at plate edges.

PubMed

Yogodzinski, G M; Lees, J M; Churikova, T G; Dorendorf, F; Wöerner, G; Volynets, O N

2001-01-25

Most island-arc magmatism appears to result from the lowering of the melting point of peridotite within the wedge of mantle above subducting slabs owing to the introduction of fluids from the dehydration of subducting oceanic crust. Volcanic rocks interpreted to contain a component of melt (not just a fluid) from the subducting slab itself are uncommon, but possible examples have been recognized in the Aleutian islands, Baja California, Patagonia and elsewhere. The geochemically distinctive rocks from these areas, termed 'adakites, are often associated with subducting plates that are young and warm, and therefore thought to be more prone to melting. But the subducting lithosphere in some adakite locations (such as the Aleutian islands) appears to be too old and hence too cold to melt. This implies either that our interpretation of adakite geochemistry is incorrect, or that our understanding of the tectonic context of adakites is incomplete. Here we present geochemical data from the Kamchatka peninsula and the Aleutian islands that reaffirms the slab-melt interpretation of adakites, but in the tectonic context of the exposure to mantle flow around the edge of a torn subducting plate. We conclude that adakites are likely to form whenever the edge of a subducting plate is warmed or ablated by mantle flow. The use of adakites as tracers for such plate geometry may improve our understanding of magma genesis and thermal structure in a variety of subduction-zone environments.

A benchmark initiative on mantle convection with melting and melt segregation

NASA Astrophysics Data System (ADS)

Schmeling, Harro; Dohmen, Janik; Wallner, Herbert; Noack, Lena; Tosi, Nicola; Plesa, Ana-Catalina; Maurice, Maxime

2015-04-01

In recent years a number of mantle convection models have been developed which include partial melting within the asthenosphere, estimation of melt volumes, as well as melt extraction with and without redistribution at the surface or within the lithosphere. All these approaches use various simplifying modelling assumptions whose effects on the dynamics of convection including the feedback on melting have not been explored in sufficient detail. To better assess the significance of such assumptions and to provide test cases for the modelling community we initiate a benchmark comparison. In the initial phase of this endeavor we focus on the usefulness of the definitions of the test cases keeping the physics as sound as possible. The reference model is taken from the mantle convection benchmark, case 1b (Blanckenbach et al., 1989), assuming a square box with free slip boundary conditions, the Boussinesq approximation, constant viscosity and a Rayleigh number of 1e5. Melting is modelled assuming a simplified binary solid solution with linearly depth dependent solidus and liquidus temperatures, as well as a solidus temperature depending linearly on depletion. Starting from a plume free initial temperature condition (to avoid melting at the onset time) three cases are investigated: Case 1 includes melting, but without thermal or dynamic feedback on the convection flow. This case provides a total melt generation rate (qm) in a steady state. Case 2 includes batch melting, melt buoyancy (melt Rayleigh number Rm), depletion buoyancy and latent heat, but no melt percolation. Output quantities are the Nusselt number (Nu), root mean square velocity (vrms) and qm approaching a statistical steady state. Case 3 includes two-phase flow, i.e. melt percolation, assuming a constant shear and bulk viscosity of the matrix and various melt retention numbers (Rt). These cases should be carried out using the Compaction Boussinseq Approximation (Schmeling, 2000) or the full compaction formulation. Variations of cases 1 - 3 may be tested, particularly studying the effect of melt extraction. The motivation of this presentation is to summarize first experiences, suggest possible modifications of the case definitions and call interested modelers to join this benchmark exercise. References: Blanckenbach, B., Busse, F., Christensen, U., Cserepes, L. Gun¬kel, D., Hansen, U., Har¬der, H. Jarvis, G., Koch, M., Mar¬quart, G., Moore D., Olson, P., and Schmeling, H., 1989: A benchmark comparison for mantle convection codes, J. Geo¬phys., 98, 23 38. Schmeling, H., 2000: Partial melting and melt segregation in a convecting mantle. In: Physics and Chemistry of Partially Molten Rocks, eds. N. Bagdassarov, D. Laporte, and A.B. Thompson, Kluwer Academic Publ., Dordrecht, pp. 141 - 178.

Planetesimal core formation with partial silicate melting using in-situ high P, high T, deformation x-ray microtomography

NASA Astrophysics Data System (ADS)

Anzures, B. A.; Watson, H. C.; Yu, T.; Wang, Y.

2017-12-01

Differentiation is a defining moment in formation of terrestrial planets and asteroids. Smaller planetesimals likely didn't reach high enough temperatures for widescale melting. However, we infer that core formation must have occurred within a few million years from Hf-W dating. In lieu of a global magma ocean, planetesimals likely formed through inefficient percolation. Here, we used in-situ high temperature, high pressure, x-ray microtomography to track the 3-D evolution of the sample at mantle conditions as it underwent shear deformation. Lattice-Boltzmann simulations for permeability were used to characterize the efficiency of melt percolation. Mixtures of KLB1 peridotite plus 6.0 to 12.0 vol% FeS were pre-sintered to achieve an initial equilibrium microstructure, and then imaged through several consecutive cycles of heating and deformation. The maximum calculated melt segregation velocity was found to be 0.37 cm/yr for 6 vol.% FeS and 0.61 cm/year for 12 vol.% FeS, both below the minimum velocity of 3.3 cm/year required for a 100km planetesimal to fully differentiate within 3 million years. However, permeability is also a function of grain size and thus the samples having smaller grains than predicted for small planetesimals could have contributed to low permeability and also low migration velocity. The two-phase (sulfide melt and silicate melt) flow at higher melt fractions (6 vol.% and 12 vol.% FeS) was an extension of a similar study1 containing only sulfide melt at lower melt fraction (4.5 vol.% FeS). Contrary to the previous study, deformation did result in increased permeability until the sample was sheared by twisting the opposing Drickamer anvils by 360 degrees. Also, the presence of silicate melt caused the FeS melt to coalesce into less connected pathways as the experiment with 6 vol.% FeS was found to be less permeable than the one with 4.5 vol.% FeS but without any partial melt. The preliminary data from this study suggests that impacts as well as higher temperature leading to partial melting of the silicate portion of the mantle could have contributed to fast enough core formation. 1. Todd, K.A., Watson, H.C., Yu, T., Wang, Y., American Mineralogist, 101.9, 1996-2004, 2016

Amphibole incongruent melting under Lithospheric Mantle conditions in spinel peridotites from Balaton area, Hungary

NASA Astrophysics Data System (ADS)

Ntaflos, Theodoros; Abart, Rainer; Bizimis, Michel

2017-04-01

Pliocene alkali basalts from the western Pannonian Basin carry mantle xenoliths comprising hydrous and anhydrous spinel peridotites. We studied coarse and fine grained fertile to depleted spinel lherzolites, spinel harzubrgites and dunites from Szentbékálla, Balaton, in detail, using XRF, EPMA and LA-ICP-MS and MC-ICP-MS techniques. Pliocene alkali basalts containing mantle xenoliths with three major types of textures are widespread in the studied area: fine-grained primary and secondary equigranular, coarse-grained protogranular and transitional between equigranular and protogranular textures. Melt pockets, are common in the studied xenoliths. The shape of several melt pockets resembles euhedral amphibole. Other samples have thin films of intergranular glass attributed to the host basalt infiltration. Calculations have shown that such xenoliths experienced an up to 2.4% host basalt infiltration. The bulk rock Al2O3 and CaO concentrations vary from 0.75 to 4.1 and from 0.9 to 3.6 wt% respectively, and represent residues after variable degrees of partial melting. Using bulk rock major element abundances, the estimated degree of partial melting ranges from 4 to 20%.. The Primitive Mantle normalized clinopyroxene trace element abundances reveal a complicated evolution of the Lithospheric mantle underneath Balaton, which range from partial melting to modal and cryptic metasomatism. Subduction-related melt/fluids and/or infiltration of percolating undersaturated melts could be account for the metasomatic processes. The radiogenic isotopes of Sr, Nd and Hf in clinopyroxene suggest that this metasomatism was a relatively recent event. Textural evidence suggests that the calcite filling up the vesicles in the melt pockets and in veinlets cross-cutting the constituent minerals is of epigenetic nature and not due to carbonatite metasomatism. Mass balance calculations have shown that the bulk composition of the melt pockets is identical to small amphibole relics found as inclusions in second generation clinopyroxene within the melt pockets. Evidently the melt pockets represent amphibole, which have been incongruently molten. The necessary heat for the amphibole breakdown was derived from the host basalt. The estimated time for diffusive Ca exchange between matrix olivine and olivine overgrowth in contact with the melt pockets is very short, ranging between 21 and 200 days, indicating that amphibole breakdown took place immediately before or during the xenolith entrainment in the alkali basalt.

Investigating the principles of recrystallization from glyceride melts.

PubMed

Windbergs, Maike; Strachan, Clare J; Kleinebudde, Peter

2009-01-01

Different lipids were melted and resolidified as model systems to gain deeper insight into the principles of recrystallization processes in lipid-based dosage forms. Solid-state characterization was performed on the samples with differential scanning calorimetry and X-ray powder diffraction. Several recrystallization processes could be identified during storage of the lipid layers. Pure triglycerides that generally crystallize to the metastable alpha-form from the melt followed by a recrystallization process to the stable beta-form with time showed a chain-length-dependent behavior during storage. With increasing chain length, the recrystallization to the stable beta-form was decelerated. Partial glycerides exhibited a more complex recrystallization behavior due to the fact that these substances are less homogenous. Mixtures of a long-chain triglyceride and a partial glyceride showed evidence of some interaction between the two components as the partial glyceride hindered the recrystallization of the triglyceride to the stable beta-form. In addition, the extent of this phenomenon depended on the amount of partial glyceride in the mixture. Based on these results, changes in solid dosage forms based on glycerides during processing and storage can be better understood.

Conversion of Nuclear Waste to Molten Glass: Cold-Cap Reactions in Crucible Tests

DOE PAGES

Xu, Kai; Hrma, Pavel; Rice, Jarrett A.; ...

2016-05-23

The feed-to-glass conversion, which comprises complex chemical reactions and phase transitions, occurs in the cold cap during nuclear waste vitrification. Here, to investigate the conversion process, we analyzed heat-treated samples of a simulated high-level waste feed using X-ray diffraction, electron probe microanalysis, leaching tests, and residual anion analysis. Feed dehydration, gas evolution, and borate phase formation occurred at temperatures below 700°C before the emerging glass-forming melt was completely connected. Above 700°C, intermediate aluminosilicate phases and quartz particles gradually dissolved in the continuous borosilicate melt, which expanded with transient foam. Finally, knowledge of the chemistry and physics of feed-to-glass conversion willmore » help us control the conversion path by changing the melter feed makeup to maximize the glass production rate.« less

Enriched continental flood basalts from depleted mantle melts: modeling the lithospheric contamination of Karoo lavas from Antarctica

NASA Astrophysics Data System (ADS)

Heinonen, Jussi S.; Luttinen, Arto V.; Bohrson, Wendy A.

2016-01-01

Continental flood basalts (CFBs) represent large-scale melting events in the Earth's upper mantle and show considerable geochemical heterogeneity that is typically linked to substantial contribution from underlying continental lithosphere. Large-scale partial melting of the cold subcontinental lithospheric mantle and the large amounts of crustal contamination suggested by traditional binary mixing or assimilation-fractional crystallization models are difficult to reconcile with the thermal and compositional characteristics of continental lithosphere, however. The well-exposed CFBs of Vestfjella, western Dronning Maud Land, Antarctica, belong to the Jurassic Karoo large igneous province and provide a prime locality to quantify mass contributions of lithospheric and sublithospheric sources for two reasons: (1) recently discovered CFB dikes show isotopic characteristics akin to mid-ocean ridge basalts, and thus help to constrain asthenospheric parental melt compositions and (2) the well-exposed basaltic lavas have been divided into four different geochemical magma types that exhibit considerable trace element and radiogenic isotope heterogeneity (e.g., initial ɛ Nd from -16 to +2 at 180 Ma). We simulate the geochemical evolution of Vestfjella CFBs using (1) energy-constrained assimilation-fractional crystallization equations that account for heating and partial melting of crustal wall rock and (2) assimilation-fractional crystallization equations for lithospheric mantle contamination by using highly alkaline continental volcanic rocks (i.e., partial melts of mantle lithosphere) as contaminants. Calculations indicate that the different magma types can be produced by just minor (1-15 wt%) contamination of asthenospheric parental magmas by melts from variable lithospheric reservoirs. Our models imply that the role of continental lithosphere as a CFB source component or contaminant may have been overestimated in many cases. Thus, CFBs may represent major juvenile crustal growth events rather than just recycling of old lithospheric materials.

Leaf water dynamics of Arabidopsis thaliana monitored in-vivo using terahertz time-domain spectroscopy

NASA Astrophysics Data System (ADS)

Castro-Camus, E.; Palomar, M.; Covarrubias, A. A.

2013-10-01

The declining water availability for agriculture is becoming problematic for many countries. Therefore the study of plants under water restriction is acquiring extraordinary importance. Botanists currently follow the dehydration of plants comparing the fresh and dry weight of excised organs, or measuring their osmotic or water potentials; these are destructive methods inappropriate for in-vivo determination of plants' hydration dynamics. Water is opaque in the terahertz band, while dehydrated biological tissues are partially transparent. We used terahertz spectroscopy to study the water dynamics of Arabidopsis thaliana by comparing the dehydration kinetics of leaves from plants under well-irrigated and water deficit conditions. We also present measurements of the effect of dark-light cycles and abscisic acid on its water dynamics. The measurements we present provide a new perspective on the water dynamics of plants under different external stimuli and confirm that terahertz can be an excellent non-contact probe of in-vivo tissue hydration.

Dehydration of trehalose dihydrate at low relative humidity and ambient temperature.

PubMed

Jones, Matthew D; Hooton, Jennifer C; Dawson, Michelle L; Ferrie, Alan R; Price, Robert

2006-04-26

The physico-chemical behaviour of trehalose dihydrate during storage at low relative humidity and ambient temperature was investigated, using a combination of techniques commonly employed in pharmaceutical research. Weight loss, water content determinations, differential scanning calorimetry and X-ray powder diffraction showed that at low relative humidity (0.1% RH) and ambient temperature (25 degrees C) trehalose dihydrate dehydrates forming the alpha-polymorph. Physical examination of trehalose particles by scanning electron microscopy and of the dominant growth faces of trehalose crystals by environmentally controlled atomic force microscopy revealed significant changes in surface morphology upon partial dehydration, in particular the formation of cracks. These changes were not fully reversible upon complete rehydration at 50% RH. These findings should be considered when trehalose dihydrate is used as a pharmaceutical excipient in situations where surface properties are key to behaviour, for example as a carrier in a dry powder inhalation formulations, as morphological changes under common processing or storage conditions may lead to variations in formulation performance.

Melt inclusion constraints on petrogenesis of the 2014-2015 Holuhraun eruption, Iceland

NASA Astrophysics Data System (ADS)

Hartley, Margaret E.; Bali, Enikö; Maclennan, John; Neave, David A.; Halldórsson, Sæmundur A.

2018-02-01

The 2014-2015 Holuhraun eruption, on the Bárðarbunga volcanic system in central Iceland, was one of the best-monitored basaltic fissure eruptions that has ever occurred, and presents a unique opportunity to link petrological and geochemical data with geophysical observations during a major rifting episode. We present major and trace element analyses of melt inclusions and matrix glasses from a suite of ten samples collected over the course of the Holuhraun eruption. The diversity of trace element ratios such as La/Yb in Holuhraun melt inclusions reveals that the magma evolved via concurrent mixing and crystallization of diverse primary melts in the mid-crust. Using olivine-plagioclase-augite-melt (OPAM) barometry, we calculate that the Holuhraun carrier melt equilibrated at 2.1 ± 0.7 kbar (7.5 ± 2.5 km), which is in agreement with the depths of earthquakes (6 ± 1 km) between Bárðarbunga central volcano and the eruption site in the days preceding eruption onset. Using the same approach, melt inclusions equilibrated at pressures between 0.5 and 8.0 kbar, with the most probable pressure being 3.2 kbar. Diffusion chronometry reveals minimum residence timescales of 1-12 days for melt inclusion-bearing macrocrysts in the Holuhraun carrier melt. By combining timescales of diffusive dehydration of melt inclusions with the calculated pressure of H2O saturation for the Holuhraun magma, we calculate indicative magma ascent rates of 0.12-0.29 m s-1. Our petrological and geochemical data are consistent with lateral magma transport from Bárðarbunga volcano to the eruption site in a shallow- to mid-crustal dyke, as has been suggested on the basis of seismic and geodetic datasets. This result is a significant step forward in reconciling petrological and geophysical interpretations of magma transport during volcano-tectonic episodes, and provides a critical framework for the interpretation of premonitory seismic and geodetic data in volcanically active regions.

Phase equilibria constraints on models of subduction zone magmatism

NASA Astrophysics Data System (ADS)

Myers, James D.; Johnston, Dana A.

Petrologic models of subduction zone magmatism can be grouped into three broad classes: (1) predominantly slab-derived, (2) mainly mantle-derived, and (3) multi-source. Slab-derived models assume high-alumina basalt (HAB) approximates primary magma and is derived by partial fusion of the subducting slab. Such melts must, therefore, be saturated with some combination of eclogite phases, e.g. cpx, garnet, qtz, at the pressures, temperatures and water contents of magma generation. In contrast, mantle-dominated models suggest partial melting of the mantle wedge produces primary high-magnesia basalts (HMB) which fractionate to yield derivative HAB magmas. In this context, HMB melts should be saturated with a combination of peridotite phases, i.e. ol, cpx and opx, and have liquid-lines-of-descent that produce high-alumina basalts. HAB generated in this manner must be saturated with a mafic phase assemblage at the intensive conditions of fractionation. Multi-source models combine slab and mantle components in varying proportions to generate the four main lava types (HMB, HAB, high-magnesia andesites (HMA) and evolved lavas) characteristic of subduction zones. The mechanism of mass transfer from slab to wedge as well as the nature and fate of primary magmas vary considerably among these models. Because of their complexity, these models imply a wide range of phase equilibria. Although the experiments conducted on calc-alkaline lavas are limited, they place the following limitations on arc petrologic models: (1) HAB cannot be derived from HMB by crystal fractionation at the intensive conditions thus far investigated, (2) HAB could be produced by anhydrous partial fusion of eclogite at high pressure, (3) HMB liquids can be produced by peridotite partial fusion 50-60 km above the slab-mantle interface, (4) HMA cannot be primary magmas derived by partial melting of the subducted slab, but could have formed by slab melt-peridotite interaction, and (5) many evolved calc-alkaline lavas could have been formed by crystal fractionation at a range of crustal pressures.

A hybrid composite dike suite from the northern Arabian Nubian Shield, southwest Jordan: Implications for magma mixing and partial melting of granite by mafic magma

NASA Astrophysics Data System (ADS)

Jarrar, Ghaleb H.; Yaseen, Najel; Theye, Thomas

2013-03-01

The Arabian Nubian Shield is an exemplary juvenile continental crust of Neoproterozoic age (1000-542 Ma). The post-collisional rift-related stage (~ 610 to 542 Ma) of its formation is characterized among others by the intrusion of several generations of simple and composite dikes. This study documents a suite of hybrid composite dikes and a natural example of partial melting of granite by a mafic magma from the northernmost extremity of Arabian Nubian Shield in southwest Jordan. The petrogenesis of this suite is discussed on the basis of field, petrographic, geochemical, and Rb/Sr isotopic data. These dikes give spectacular examples of the interaction between basaltic magma and the granitic basement. This interaction ranges from brecciation, partial melting of the host alkali feldspar granite to complete assimilation of the granitic material. Field structures range from intrusive breccia (angular partially melted granitic fragments in a mafic groundmass) to the formation of hybrid composite dikes that are up to 14 m in thickness. The rims of these dikes are trachyandesite (latite) with alkali feldspar ovoids (up to 1 cm in diameter); while the central cores are trachydacite to dacite and again with alkali feldspar ovoids and xenoliths from the dike rims. The granitic xenoliths in the intrusive breccia have been subjected to at least 33% partial melting. A seven-point Rb/Sr isochron from one of these composite dikes yields an age of 561 ± 33 Ma and an initial 87Sr/86Sr ratio of 0.70326 ± 0.0003 (2σ) and MSWD of 0.62. Geochemical modeling using major, trace, rare earth elements and isotopes suggests the generation of the hybrid composite dike suite through the assimilation of 30% to 60% granitic crustal material by a basaltic magma, while the latter was undergoing fractional crystallization at different levels in the continental crust.

Geochemistry and petrogenesis of the Laramie anorthosite complex, Wyoming

USGS Publications Warehouse

Fountain, J.C.; Hodge, D.S.; Allan, Hills F.

1981-01-01

A geochemical investigation of the Laramie anorthosite complex determined that monsonite associated with the complex are characterized by positive Eu anomalies and display a regular variation in composition with distance from the monzonite/county rock contact. Anorthositic rocks have major and trace element abundance typical of similar complexes. The internal variations in the monzonite were produced by in situ fractionation and contamination. The data indicate that anorthosite and monzonite cannot be comagmatic. It is proposed that the anorthosite and monzonite of the complex evolved from two distinct magmas, and that two stages of anatectic melting contributed to the evolution of the monzonite. An initial stage of partial melting was induced by intrusion of a gabbroic anorthosite magma into the lower crust; a second partial melting event occurred after emplacement where heat from the intrusions melted country rocks resulting in extensive contamination ofthe monzonite. ?? 1981.

Geochemistry of peraluminous tonalite and trondhjemite, the Cornucopia stock, Blue Mountains, NE Oregon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, K.; Barnes, C.G.; Kistler, R.W.

1993-04-01

The Cretaceous Cornucopia stock was emplaced into a greenschist-facies Permo-Triassic arc terrane. The stock comprises five distinct units: hornblende biotite tonalite, biotite trondhjemite, and three cordierite biotite trondhjemites, all with late dacitic and granitic dikes. Tonalite and trondhjemites span a narrow range of SiO[sub 2] contents and exhibit characteristics of a high-Al tonalite-trondhjemite-dacite (TTD) suite: LREE enrichment, low Y (< 15 ppm), Nb (< 10 ppm), Rb/Sr ([le]0.04), and high Sr (550--800 ppm). Euhedral cordierite phenocrysts imply the trondhjemites were H[sub 2]O-rich and were emplaced at pressures of < 2 kbars. Trace element and REE models are consistent with anmore » origin for the tonalite and trondhjemites by variable degrees (< 40%) of partial melting of a low-K tholeiitic source, with a garnet amphibolite residuum. Individual units are not related by fractional crystallization, but instead represent distinct partial melts. High Sr contents in the TTD rocks, the presence of residual garnet, and abundant residual amphibole implied by partial melting models suggest that melting occurred under H[sub 2]O-rich conditions at P [ge] 8--10 kbars.« less

The role of silver in the processing and properties of Bi-2212

NASA Technical Reports Server (NTRS)

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

1995-01-01

The influence of the silver content and the oxygen partial pressure on the solidus temperature and the weight loss during melting of Bi2Sr2Ca1Cu2O(x) has been examined by means of DTA and TGA. By decreasing the oxygen partial pressure the solidus is lowered (e.g. del T = 59 C by decreasing pO2 from 1 atm to 0.001 atm) and the weight loss is increased. The addition of silver causes two effects: (1) the solidus is further decreased (e.g. 2 wt% Ag lower T (solidus) by up to 25 C, depending on the oxygen partial pressure); and (2) the weight loss during melting is reduced. Thick films (10-20 micron in thickness) with 0 and 5 wt% silver and bulk samples with) and 2.7 wt% silver were melt processed in flowing oxygen on a silver substrate in the DTA, allowing the observation of the melting process and a good temperature control. The critical current densities are vigorously dependent on the maximum processing temperature. The highest j(sub c) in thick films (8000 A/sq cm at 77 K, O T) was reached by melting 7 C above the solidus temperature. The silver addition shows no significant effect on the processing parameters or the superconducting properties. The highest j(sub c) for bulk samples (1 mm in thickness) was obtained by partial melting at 900 C or 880 C, depending on the silver content of the powder (0 or 2.7 wt%). The j(sub c) of the samples is slightly enhanced from 1800 A/sq cm (at 77 K, O T) to 2000 A/sq cm by the silver addition. To be able to reach at least 80% of the maximum critical current density, the temperature has to be controlled in a window of 5 C for thick films and 17 C for bulk samples.

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.

Calcium Isotopic Compositions of Normal Mid-Ocean Ridge Basalts From the Southern Juan de Fuca Ridge

NASA Astrophysics Data System (ADS)

Zhu, Hongli; Liu, Fang; Li, Xin; Wang, Guiqin; Zhang, Zhaofeng; Sun, Weidong

2018-02-01

Mantle peridotites show that Ca is isotopically heterogeneous in Earth's mantle, but the mechanism for such heterogeneity remains obscure. To investigate the effect of partial melting on Ca isotopic fractionation and the mechanism for Ca isotopic heterogeneity in the mantle, we report high-precision Ca isotopic compositions of the normal Mid-Ocean Ridge Basalts (N-MORB) from the southern Juan de Fuca Ridge. δ44/40Ca of these N-MORB samples display a small variation ranging from 0.75 ± 0.05 to 0.86 ± 0.03‰ (relative to NIST SRM 915a, a standard reference material produced by the National Institute of Standards and Technology), which are slightly lower than the estimated Upper Mantle value of 1.05 ± 0.04‰ and the Bulk Silicate Earth (BSE) value of 0.94 ± 0.05‰. This phenomenon cannot be explained by fractional crystallization, because olivine and orthopyroxene fractional crystallization has limited influence on δ44/40Ca of N-MORB due to their low CaO contents, while plagioclase fractional crystallization cannot lead to light Ca isotopic compositions of the residue magma. Instead, the lower δ44/40Ca of N-MORB samples compared to their mantle source is most likely caused by partial melting. The offset in δ44/40Ca between N-MORB and BSE indicates that at least 0.1-0.2‰ fractionation would occur during partial melting and light Ca isotopes are preferred to be enriched in magma melt, which is in accordance with the fact that δ44/40Ca of melt-depleted peridotites are higher than fertile peridotites in literature. Therefore, partial melting is an important process that can decrease δ44/40Ca in basalts and induce Ca isotopic heterogeneity in Earth's mantle.

An amyloid-forming peptide from the yeast prion Sup35 reveals a dehydrated β-sheet structure for amyloid

PubMed Central

Balbirnie, Melinda; Grothe, Robert; Eisenberg, David S.

2001-01-01

X-ray diffraction and other biophysical tools reveal features of the atomic structure of an amyloid-like crystal. Sup35, a prion-like protein in yeast, forms fibrillar amyloid assemblies intrinsic to its prion function. We have identified a polar peptide from the N-terminal prion-determining domain of Sup35 that exhibits the amyloid properties of full-length Sup35, including cooperative kinetics of aggregation, fibril formation, binding of the dye Congo red, and the characteristic cross-β x-ray diffraction pattern. Microcrystals of this peptide also share the principal properties of the fibrillar amyloid, including a highly stable, β-sheet-rich structure and the binding of Congo red. The x-ray powder pattern of the microcrystals, extending to 0.9-Å resolution, yields the unit cell dimensions of the well-ordered structure. These dimensions restrict possible atomic models of this amyloid-like structure and demonstrate that it forms packed, parallel-stranded β-sheets. The unusually high density of the crystals shows that the packed β-sheets are dehydrated, despite the polar character of the side chains. These results suggest that amyloid is a highly intermolecularly bonded, dehydrated array of densely packed β-sheets. This dry β-sheet could form as Sup35 partially unfolds to expose the peptide, permitting it to hydrogen-bond to the same peptide of other Sup35 molecules. The implication is that amyloid-forming units may be short segments of proteins, exposed for interactions by partial unfolding. PMID:11226247

Muscovite-Dehydration Melting: A Textural Study of a Key Reaction in Transforming Continental Margin Strata Into a Migmatitic Orogenic Core

NASA Astrophysics Data System (ADS)

Dyck, B. J.; St Onge, M. R.; Waters, D. J.; Searle, M. P.

2015-12-01

Metamorphosed continental margin sedimentary sequences, which comprise the dominant tectonostratigraphic assemblage exposed in orogenic hinterlands, are crucial to understanding the architecture and evolution of collisional mountain belts. This study explores the textural effect of anatexis in amphibolite-grade conditions and documents the mineral growth mechanisms that control nucleation and growth of K-feldspar, sillimanite and silicate melt. The constrained textural evolution follows four stages: 1) Nucleation - K-feldspar is documented to nucleate epitaxially on isomorphic plagioclase in quartzofeldspathic (psammitic) domains, whereas sillimanite nucleates in the Al-rich (pelitic) domain, initially on [001] mica planes. The first melt forms at the site of muscovite breakdown. 2) Chemically driven growth - In the quartzofeldspathic domain, K-feldspar progressively replaces plagioclase by a K+ - Na+ cation transfer reaction, driven by the freeing of muscovite-bound K+ during breakdown of the mica. Sillimanite forms intergrowths with the remaining hydrous melt components, contained initially in ovoid clots. 3) Merge and coarsening - With an increase in pressure, melt and sillimanite migrate away from clots along grain boundaries. A melt threshold is reached once the grain-boundary network is wetted by melt, increasing the length-scale of diffusion, resulting in grain boundary migration and grain-size coarsening. The melt threshold denotes the transition to an open-system on the lithology scale, where melt is a transient phase. 4) Residual melt crystallization - Residual melt crystallizes preferentially on existing peritectic grains as anatectic quartz, plagioclase, and K-feldspar. As the system cools and closes, grain growth forces melt into the intersections of grain-boundaries, recognized as irregular shaped melt films, or as intergrowths of the volatile-rich phases (i.e. Tur-Ms-Ap). In the Himalayan metamorphic core these processes result in the formation of: pelitic K-feldspar augen gneiss, stockwork leucogranites, and an effective strengthening of the hinterland, as evidenced by a switch in tectonic deformation style, from thin-skinned cover sequence thrust imbrication and folding to out-of-sequence basement-involved thick-skinned thrusting and folding.

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

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.

Thermodynamic Simulation of Equilibrium Composition of Reaction Products at Dehydration of a Technological Channel in a Uranium-Graphite Reactor

NASA Astrophysics Data System (ADS)

Pavliuk, A. O.; Zagumennov, V. S.; Kotlyarevskiy, S. G.; Bespala, E. V.

2018-01-01

The problems of accumulation of nuclear fuel spills in the graphite stack in the course of operation of uranium-graphite nuclear reactors are considered. The results of thermodynamic analysis of the processes in the graphite stack at dehydration of a technological channel, fuel element shell unsealing and migration of fission products, and activation of stable nuclides in structural elements of the reactor and actinides inside the graphite moderator are given. The main chemical reactions and compounds that are produced in these modes in the reactor channel during its operation and that may be hazardous after its shutdown and decommissioning are presented. Thermodynamic simulation of the equilibrium composition is performed using the specialized code TERRA. The results of thermodynamic simulation of the equilibrium composition in different cases of technological channel dehydration in the course of the reactor operation show that, if the temperature inside the active core of the nuclear reactor increases to the melting temperature of the fuel element, oxides and carbides of nuclear fuel are produced. The mathematical model of the nonstationary heat transfer in a graphite stack of a uranium-graphite reactor in the case of the technological channel dehydration is presented. The results of calculated temperature evolution at the center of the fuel element, the replaceable graphite element, the air gap, and in the surface layer of the block graphite are given. The numerical results show that, in the case of dehydration of the technological channel in the uranium-graphite reactor with metallic uranium, the main reaction product is uranium dioxide UO2 in the condensed phase. Low probability of production of pyrophoric uranium compounds (UH3) in the graphite stack is proven, which allows one to disassemble the graphite stack without the risk of spontaneous graphite ignition in the course of decommissioning of the uranium-graphite nuclear reactor.

Partial Melt Processing of Solid-Solution Bi2Sr2CaCu2O8+delta Thick-Film Conductors with Nanophase Al2O3 Additions

DTIC Science & Technology

2006-04-01

characterize the superconducting properties of powders, field-cooled (FC) Meissner and ZFC measure- ments were performed from 5 to 125 K.46 The SQUID magnet ...measured magnetic susceptibility, and D 0.3333 is the demagnetization factor assuming a spherical particle distribution.6,46 The applied magnetic ...and superconducting properties was studied for a range of partial-melt temperatures. Results were compared to Al203-free films with compositions lying

Altering surface fluctuations by blending tethered and untethered chains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, J. K.; Akgun, B.; Jiang, Z.

"Partially tethering" a thin film of a polymer melt by covalently attaching to the substrate a fraction of the chains in an unentangled melt dramatically increases the relaxation time of the surface height fluctuations. This phenomenon is observed even when the film thickness, h, is 20 times the unperturbed chain radius, R g,tethered, of the tethered chains, indicating that partial tethering is more influential than any physical attraction with the substrate. Furthermore, a partially tethered layer of a low average molecular weight of 5k showed much slower surface fluctuations than did a reference layer of pure untethered chains of muchmore » greater molecular weight (48k), so the partial tethering effect is stronger than the effects of entanglement and increase in glass transition temperature, Tg, with molecular weight. Partial tethering offers a means of tailoring these fluctuations which influence wetting, adhesion, and tribology of the surface.« less

Altering surface fluctuations by blending tethered and untethered chains

DOE PAGES

Lee, J. K.; Akgun, B.; Jiang, Z.; ...

2017-10-16

"Partially tethering" a thin film of a polymer melt by covalently attaching to the substrate a fraction of the chains in an unentangled melt dramatically increases the relaxation time of the surface height fluctuations. This phenomenon is observed even when the film thickness, h, is 20 times the unperturbed chain radius, R g,tethered, of the tethered chains, indicating that partial tethering is more influential than any physical attraction with the substrate. Furthermore, a partially tethered layer of a low average molecular weight of 5k showed much slower surface fluctuations than did a reference layer of pure untethered chains of muchmore » greater molecular weight (48k), so the partial tethering effect is stronger than the effects of entanglement and increase in glass transition temperature, Tg, with molecular weight. Partial tethering offers a means of tailoring these fluctuations which influence wetting, adhesion, and tribology of the surface.« less

The dynamics of serpentinite dehydration reactions in subduction zones: Constrains from the Cerro del Almirez ultramafic massif (Betic Cordillera, SE Spain)

NASA Astrophysics Data System (ADS)

Dilissen, Nicole; Garrido, Carlos J.; López Sánchez-Vizcaíno, Vicente; Padrón-Navarta, José Alberto

2015-04-01

Arc volcanism, earthquakes and subduction dynamics are controlled by fluids from downgoing slabs and their effect on the melting and rheology of the overlying mantle wedge. High pressure dehydration of serpentinite in the slab and the subduction channel is considered as one of the main sources of fluids in subduction zones. Even though this metamorphic reaction is essential in subduction activities, the behavior of the fluids, the kinetics and thermodynamics during the breakdown reaction are still poorly understood. The Cerro del Almirez (Nevado-Filábride Complex, Betic Cordillera, SE Spain) uniquely preserves the dehydration front from antigorite serpentinite to chlorite-harzburgite and constitutes a unique natural laboratory to investigate high-pressure dehydration of serpentinite. This reaction occurred in a subduction setting releasing up to 13 wt% of water, contributing significantly to the supply of fluids to the overlying mantle wedge. A key to the understanding of the metamorphic conditions prevailing during serpentinite dehydration is to study the two prominent textures -granofels and spinifex-like chlorite harzburgite- occurring in this reaction product. The detailed texture differences in the Chl-harzburgite can provide insights into diverse kinetic and thermodynamic conditions of this dehydration reaction due to variations in effective pressure and drainage conditions. It has been proposed that difference in overpressure (P') and deviation from growth equilibrium, i.e. overstepping, is responsible for these two types of textures [Padrón-Navarta et al., 2011]. The magnitude and duration of P' is highly dependent on dehydration kinetics [Connolly, 1997]. The fast pressure drop, with spinifex-texture as a product, can be linked to draining events expected after hydrofracturing, which are recorded in grain size reduction zones in this massif. According to this hypothesis, mapping of textural variation in Chl-harzburgite might be used as a proxy to investigate the hydrodynamics of serpentinite dehydration reaction. During an intensive detailed field mapping of a well-exposed area of ca. 0.87 km2 in the W-SW part of the massif, we mapped textural variations of Chl-harzburgite every three to ten meters. Granofels and spinifex lenses occur within scales of decimetres to decametres. These spatial scale constrains can be linked to temporal scales of the reactions and to the spatial and temporal variation of fluid release during dehydration of serpentinite. REFERENCES Connolly, J. A. D. (1997), Devolatilization-generated fluid pressure and deformation-propagated fluid flow during prograde regional metamorphism, J. Geophys. Res.-Solid Earth, 102(B8), 18149-18173, doi:10.1029/97jb00731. Padrón-Navarta, J. A., V. López Sánchez-Vizcaíno, C. J. Garrido, and M. T. Gómez-Pugnaire (2011), Metamorphic record of high-pressure dehydration of antigorite serpentinite to chlorite harzburgite in a subduction setting (Cerro del Almirez, Nevado-Filábride Complex, southern Spain), Journal of Petrology, 52(10), 2047-2078.

Comparison of fortified, sfursat, and passito wines produced from fresh and dehydrated grapes of aromatic black cv. Moscato nero (Vitis vinifera L.).

PubMed

Ossola, Carolina; Giacosa, Simone; Torchio, Fabrizio; Río Segade, Susana; Caudana, Alberto; Cagnasso, Enzo; Gerbi, Vincenzo; Rolle, Luca

2017-08-01

Moscato nero d'Acqui is an Italian aromatic black winegrape variety characterized by a low content of anthocyanins (mostly tri-substituted), a satisfactory content of high molecular mass tannins, and a fair amount of terpenes. The grapes were subjected to a postharvest dehydration process under controlled thermohygrometric conditions (16-18°C, 55-70 RH%, 0.6m/s air speed) with the aim to produce three different special wine types (fortified, sfursat, and passito) from fresh, partially dehydrated (27°Brix), and withered (36°Brix) grapes, respectively. Chemical traits of produced grapes and wines were then evaluated through spectrophotometric, HPLC, and GC-MS methods. Increased contents of skin phenolic compounds and reduced extractable contents of seed phenolic compounds were observed as dehydration progressed. Few significant differences were found in the anthocyanin profile of grapes, although the relative abundance of coumaroylated anthocyanins was higher in dehydrated grapes. The predominant free volatile compound found in grapes was geraniol, which decreased with increasing water loss, whereas the contents of major glycosylated volatile compounds increased even above the concentration effect. The changes in the phenolic composition among wines agreed with those among grape skins. Fortified wines were chromatically unsatisfactory probably due to the low content of total anthocyanins, whereas sfursat and passito wines meet good chromatic characteristics as a result of the concentration effect during grape dehydration. Fortified and sfursat wines had free aroma profiles richer in 2-phenylethanol and citronellol, whereas passito wines were mainly composed of 2-phenylethanol and 2-phenylethyl acetate, citronellol being the predominant terpenol in all the wine types studied. Copyright © 2016 Elsevier Ltd. All rights reserved.

The effects of dehydration, moderate alcohol consumption, and rehydration on cognitive functions.

PubMed

Irwin, Christopher; Leveritt, Michael; Shum, David; Desbrow, Ben

2013-05-01

This study investigated the impact of mild-moderate dehydration on alcohol-induced deteriorations in cognitive functions. Sixteen healthy males participated in a single-blind, placebo-controlled cross-over design study involving 4 experimental trials (separated by ≥7 d). In each trial, participants were dehydrated by 2.5% body mass through exercise. After 1 h recovery in a thermo-neutral environment (22 ± 2 °C, 60-70% relative humidity) 4 tasks from the Cambridge Neuropsychological Test Automated Battery (CANTAB) were administered to the participants (test 1). In two of the trials, participants were provided with water equivalent to either 50% or 150% body mass loss and given salt (NaCl) capsules (50 mmol/L). A set volume of alcohol or placebo was then consumed in each trial, incorporating the conditions: dehydration-placebo (DP), dehydration-alcohol (DA), partial rehydration-alcohol (PA), and full rehydration-alcohol (FA). The same 4 CANTAB tasks were then re-administered (test 2). Subjective ratings of mood and estimates of alcohol intoxication and driving impairment were also recorded in each trial. Alcohol consumption caused deterioration on 3 of the 4 CANTAB measures (viz., choice reaction time, executive function and response inhibition). This reduction in performance was exacerbated when participants were dehydrated compared to trials where full rehydration occurred. Subjective ratings of impairment and intoxication were not significantly different between any of the trials where alcohol was consumed; however ratings for alcohol trials were significantly higher than in the placebo trial. These findings suggest that rehydration after exercise that causes fluid loss can attenuate alcohol-related deterioration of cognitive functions. This may pose implications for post match fluid replacement if a moderate amount of alcohol is also consumed. Copyright © 2013 Elsevier Inc. All rights reserved.

The use of plant stress biomarkers in assessing the effects of desiccation in zygotic embryos from recalcitrant seeds: challenges and considerations.

PubMed

Sershen; Varghese, B; Naidoo, C; Pammenter, N W

2016-05-01

Zygotic embryos from recalcitrant seeds are sensitive to desiccation. In spite of their sensitivity, rapid partial dehydration is necessary for their successful cryopreservation. However, dehydration to water contents (WCs) that preclude lethal ice crystal formation during cooling and rewarming generally leads to desiccation damage. This study investigated the effects of rapid dehydration on selected stress biomarkers (electrolyte leakage, respiratory competence, rate of protein synthesis, superoxide production, lipid peroxidation, antioxidant activity and degree of cellular vacuolation) in zygotic embryos of four recalcitrant-seeded species. Most biomarkers indicated differences in the levels of stress/damage incurred by embryos dried to WCs < and >0.4 g·g(-1) , within species; however, these changes were often unrelated to viability and percentage water loss when data for the four species were pooled for regression analyses. Dehydration-induced electrolyte leakage was, however, positively related with percentage water loss, while biomarkers of cellular vacuolation were positively related with both percentage water loss and viability. This suggests that electrolyte leakage and degree of cellular vacuolation can be used to quantify dehydration-induced stress/damage. Biomarkers such as superoxide production, whilst useful in establishing the nature of the dehydration stress incurred may not be able to distinguish the effects of different WCs/drying times. Irrespective of which biomarker is used, the data suggest that understanding differences in desiccation sensitivity across recalcitrant-seeded species will remain a challenge unless these biomarkers are related to a generic desiccation stress index that integrates the effects of percentage water loss and drying time. © 2016 German Botanical Society and The Royal Botanical Society of the Netherlands.

CUMULATE ROCKS ASSOCIATED WITH CARBONATE ASSIMILATION, HORTAVÆR COMPLEX, NORTH-CENTRAL NORWAY

NASA Astrophysics Data System (ADS)

Barnes, C. G.; Prestvik, T.; Li, Y.

2009-12-01

The Hortavær igneous complex intruded high-grade metamorphic rocks of the Caledonian Helgeland Nappe Complex at ca. 466 Ma. The complex is an unusual mafic-silicic layered intrusion (MASLI) because the principal felsic rock type is syenite and because the syenite formed in situ rather than by deep-seated partial melting of crustal rocks. Magma differentiation in the complex was by assimilation, primarily of calc-silicate rocks and melts with contributions from marble and semi-pelites, plus fractional crystallization. The effect of assimilation of calcite-rich rocks was to enhance stability of fassaitic clinopyroxene at the expense of olivine, which resulted in alkali-rich residual melts and lowering of silica activity. This combination of MASLI-style emplacement and carbonate assimilation produced three types of cumulate rocks: (1) Syenitic cumulates formed by liquid-crystal separation. As sheets of mafic magma were loaded on crystal-rich syenitic magma, residual liquid was expelled, penetrating the overlying mafic sheets in flame structures, and leaving a cumulate syenite. (2) Reaction cumulates. Carbonate assimilation, illustrated by a simple assimilation reaction: olivine + calcite + melt = clinopyroxene + CO2 resulted in cpx-rich cumulates such as clinopyroxenite, gabbro, and mela-monzodiorite, many of which contain igneous calcite. (3) Magmatic skarns. Calc-silicate host rocks underwent partial melting during assimilation, yielding a Ca-rich melt as the principal assimilated material and permitting extensive reaction with surrounding magma to form Kspar + cpx + garnet-rich ‘cumulate’ rocks. Cumulate types (2) and (3) do not reflect traditional views of cumulate rocks but instead result from a series of melt-present discontinuous (peritectic) reactions and partial melting of calc-silicate xenoliths. In the Hortavær complex, such cumulates are evident because of the distinctive peritectic cumulate assemblages. It is unclear whether assimilation of ‘normal’ silicate rocks results in peritectic assemblages, or whether they could be identified as such if they exist.

Geochemical Evidence Against Pyroxenites in the Sources of Hawaiian Volcanoes

NASA Astrophysics Data System (ADS)

Humayun, M.; Yang, S.; Clague, D. A.

2017-12-01

Hawaiian lavas exhibit high Fe/Mn ratios, and other elemental and isotopic characteristics, that have been argued to be evidence for chemical interactions at the core-mantle boundary. Alternatively, the enrichment in silica relative to 3 GPa melts of garnet peridotite, and the high Fe/Mn, has been argued to represent the contributions of garnet pyroxenite melts generated beneath a thick lithosphere. Here, we present a set of new elemental ratios designed to effectively discriminate partial melts of peridotite from pyroxenite in mantle sources. A set of 200 Hawaiian volcanic glasses from 7 volcanoes were analyzed by LA-ICP-MS for the abundances of 63 elements, with an emphasis on obtaining precise Ge/Si ratios. From experimental partitioning, silica-rich partial melts of MORB-like garnet pyroxenite are expected to have low Ge/Si ratios relative to their sources due to the retention of Ge in the residue by both garnet and pyroxene. In contrast, partial melts of peridotite are expected to have high Ge/Si ratios relative to mantle peridotites due to the incompatibility of Ge in olivine. We observed that Ge abundances in subaerial Hawaiian volcanoes are correlated with indicators of volcanic degassing, including S, Re and As. Subaerial and submarine lavas exhibit a correlation between Ge/Si ratio and S content that indicates that all Hawaiian lavas share the same pre-eruptive Ge/Si ratio. Submarine glasses with the least evidence of degassing exhibit a constant Ge/Si ratio over the range of SiO2 (44-52 %) observed in Hawaiian volcanics. Surprisingly, MORB glasses exhibit more variation in Ge/Si ratio than the pre-eruptive Ge/Si of Hawaiian glasses, implying the presence of 0-12% recycled crust in the MORB source. The constant Ge/Si ratio of Hawaiian glasses implies that pyroxenite melting did not enrich Hawaiian lavas in silica. Processes that could yield Si-rich melts without changing the Ge/Si ratio may involve melt-lithosphere interaction or bridgmanite/ferropericlase fractionation in the deep mantle.

NisT, the transporter of the lantibiotic nisin, can transport fully modified, dehydrated, and unmodified prenisin and fusions of the leader peptide with non-lantibiotic peptides.

PubMed

Kuipers, Anneke; de Boef, Esther; Rink, Rick; Fekken, Susan; Kluskens, Leon D; Driessen, Arnold J M; Leenhouts, Kees; Kuipers, Oscar P; Moll, Gert N

2004-05-21

Lantibiotics are lanthionine-containing peptide antibiotics. Nisin, encoded by nisA, is a pentacyclic lantibiotic produced by some Lactococcus lactis strains. Its thioether rings are posttranslationally introduced by a membrane-bound enzyme complex. This complex is composed of three enzymes: NisB, which dehydrates serines and threonines; NisC, which couples these dehydrated residues to cysteines, thus forming thioether rings; and the transporter NisT. We followed the activity of various combinations of the nisin enzymes by measuring export of secreted peptides using antibodies against the leader peptide and mass spectroscopy for detection. L. lactis expressing the nisABTC genes efficiently produced fully posttranslationally modified prenisin. Strikingly, L. lactis expressing the nisBT genes could produce dehydrated prenisin without thioether rings and a dehydrated form of a non-lantibiotic peptide. In the absence of the biosynthetic NisBC enzymes, the NisT transporter was capable of excreting unmodified prenisin and fusions of the leader peptide with non-lantibiotic peptides. Our data show that NisT specifies a broad spectrum (poly)peptide transporter that can function either in conjunction with or independently from the biosynthetic genes. NisT secretes both unmodified and partially or fully posttranslationally modified forms of prenisin and non-lantibiotic peptides. These results open the way for efficient production of a wide range of peptides with increased stability or novel bioactivities.

Magma ocean formation due to giant impacts

NASA Technical Reports Server (NTRS)

Tonks, W. B.; Melosh, H. J.

1993-01-01

The thermal effects of giant impacts are studied by estimating the melt volume generated by the initial shock wave and corresponding magma ocean depths. Additionally, the effects of the planet's initial temperature on the generated melt volume are examined. The shock pressure required to completely melt the material is determined using the Hugoniot curve plotted in pressure-entropy space. Once the melting pressure is known, an impact melting model is used to estimate the radial distance melting occurred from the impact site. The melt region's geometry then determines the associated melt volume. The model is also used to estimate the partial melt volume. Magma ocean depths resulting from both excavated and retained melt are calculated, and the melt fraction not excavated during the formation of the crater is estimated. The fraction of a planet melted by the initial shock wave is also estimated using the model.

From crustal protoliths to mantle garnet pyroxenites: a highly siderophile elements and Os isotope perspective from the Ligurian mantle section (N. Apennine, Italy)

NASA Astrophysics Data System (ADS)

Montanini, A.; Luguet, A.; van Acken, D.; Tribuzio, R.

2017-12-01

Pyroxenites are a major form of mantle heterogeneity and may originate through migration of melts or recycling of mafic crustal lithologies. Here, we present HSE (Os, Ir, Pt, Pd, Re) and 187Os/188Os isotopic systematics of "aged" pyroxenites (Mg-rich, Al-poor garnet websterites and Al-rich garnet clinopyroxenites) enclosed in fertile mantle sequences of the Jurassic Alpine-Apennine ophiolites. The garnet clinopyroxenites have heterogeneous mafic crustal precursors that experienced a long-lived evolution of recycling into the mantle (1.5-1.0 Ga) as inferred from Lu-Hf isotope systematics. They originated as melt-dominated systems by crystallization of eclogite-derived melts. The websterites were interpreted as hybrid lithologies with a crustal geochemical fingerprint and a larger peridotite wall rock contribution. The host lherzolites show flat CI-chondrite-normalized HSE patterns. All the pyroxenites are variably depleted in Os and Ir and enriched in the incompatible HSE (Pt, Pd and Re) with respect to host peridotites and have flat to negatively sloping Pd-Re segments. Centimetre- to metre-scale 187Os isotopic heterogeneity is observed in the investigated mantle sequence. The initial 187Os/188Os ratios recalculated for the age of the Mesozoic partial melting event inferred from Nd-Hf isotope systematics are unradiogenic to slightly radiogenic in the peridotites (0.124-0.134) and vary from moderately to highly radiogenic in the pyroxenites (0.149-2.190). Bulk rock HSE compositions of the pyroxenites do not match gabbroic eclogites nor residua after eclogite partial melting, in agreement with lithophile element geochemistry. The HSE patterns of the garnet clinopyroxenites are related to sulphur saturation and sulfide crystallization from partial melts of gabbro-derived eclogites. Decoupling between Re/Os (TMa = 2.0-2.8 Ga) and Lu-Hf isotope systematics of the pyroxenites may be due to fractionation of Re/Os ratios with no Os isotopic homogenization of the sulfide melt fraction during the eclogite partial melting. We show that observed relics of ancient subducted crust are heterogeneous as a consequence of initial geochemical variation in the protoliths, modification during mantle recycling and different degrees of interaction with the host peridotites.

Geochemistry of southern Pagan Island lavas, Mariana arc: The role of subduction zone processes

USGS Publications Warehouse

Marske, J.P.; Pietruszka, A.J.; Trusdell, F.A.; Garcia, M.O.

2011-01-01

New major and trace element abundances, and Pb, Sr, and Nd isotopic ratios of Quaternary lavas from two adjacent volcanoes (South Pagan and the Central Volcanic Region, or CVR) located on Pagan Island allow us to investigate the mantle source (i.e., slab components) and melting dynamics within the Mariana intra-oceanic arc. Geologic mapping reveals a pre-caldera (780-9.4ka) and post-caldera (<9.4ka) eruptive stage for South Pagan, whereas the eruptive history of the older CVR is poorly constrained. Crystal fractionation and magma mixing were important crustal processes for lavas from both volcanoes. Geochemical and isotopic variations indicate that South Pagan and CVR lavas, and lavas from the northern volcano on the island, Mt. Pagan, originated from compositionally distinct parental magmas due to variations in slab contributions (sediment and aqueous fluid) to the mantle wedge and the extent of mantle partial melting. A mixing model based on Pb and Nd isotopic ratios suggests that the average amount of sediment in the source of CVR (~2.1%) and South Pagan (~1.8%) lavas is slightly higher than Mt. Pagan (~1.4%) lavas. These estimates span the range of sediment-poor Guguan (~1.3%) and sediment-rich Agrigan (~2.0%) lavas for the Mariana arc. Melt modeling demonstrates that the saucer-shaped normalized rare earth element (REE) patterns observed in Pagan lavas can arise from partial melting of a mixed source of depleted mantle and enriched sediment, and do not require amphibole interaction or fractionation to depress the middle REE abundances of the lavas. The modeled degree of mantle partial melting for Agrigan (2-5%), Pagan (3-7%), and Guguan (9-15%) lavas correlates with indicators of fluid addition (e.g., Ba/Th). This relationship suggests that the fluid flux to the mantle wedge is the dominant control on the extent of partial melting beneath Mariana arc volcanoes. A decrease in the amount of fluid addition (lower Ba/Th) and extent of melting (higher Sm/Yb), and an increase in the sediment contribution (higher Th/Nb, La/Sm, and Pb isotopic ratios) from Mt. Pagan to South Pagan could reflect systematic cross-arc or irregular along-arc melting variations. These observations indicate that the length scale of compositional heterogeneity in the mantle wedge beneath Mariana arc volcanoes is small (~10km).

Near-isothermal conditions in the middle and lower crust induced by melt migration.

PubMed

Depine, Gabriela V; Andronicos, Christopher L; Phipps-Morgan, Jason

2008-03-06

The thermal structure of the crust strongly influences deformation, metamorphism and plutonism. Models for the geothermal gradient in stable crust predict a steady increase of temperature with depth. This thermal structure, however, is incompatible with observations from high-temperature metamorphic terranes exhumed in orogens. Global compilations of peak conditions in high-temperature metamorphic terranes define relatively narrow ranges of peak temperatures over a wide range in pressure, for both isothermal decompression and isobaric cooling paths. Here we develop simple one-dimensional thermal models that include the effects of melt migration. These models show that long-lived plutonism results in a quasi-steady-state geotherm with a rapid temperature increase in the upper crust and nearly isothermal conditions in the middle and lower crust. The models also predict that the upward advection of heat by melt generates granulite facies metamorphism, and widespread andalusite-sillimanite metamorphism in the upper crust. Once the quasi-steady-state thermal profile is reached, the middle and lower crust are greatly weakened due to high temperatures and anatectic conditions, thus setting the stage for gravitational collapse, exhumation and isothermal decompression after the onset of plutonism. Near-isothermal conditions in the middle and lower crust result from the thermal buffering effect of dehydration melting reactions that, in part, control the shape of the geotherm.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

1981-12-01

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

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.

Aspects of forming metal-clad melt-processed Y-Ba-Cu-O tapes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozlowski, G.; Oberly, C.E.; Ho, J.

1991-03-01

This paper reports on melt-processing of Y-Ba-Cu-O superconductor in a usable form for magnet winding which requires the development of a cladding with demanding properties. Numerous recent efforts in cold forming Bi-based superconductor tapes have been successful because a silver tube can be used to constrain the ceramic material, which is sintered at much lower temperature than the Y-Ba-Cu-O. Typical high temperature metals which can be used to encase Y-Ba-Cu-O during sintering do not permit ready diffusion of oxygen as silver does. Recently, the full or partial recovery of superconductivity has been achieved in transition-metal- doped Y-Ba-Cu-O due to themore » partial-melt processing.« less

Three-dimensional electrical resistivity model of the hydrothermal system in Long Valley Caldera, California, from magnetotellurics

USGS Publications Warehouse

Peacock, Jared R.; Mangan, Margaret T.; McPhee, Darcy K.; Wannamaker, Phil E.

2016-01-01

Though shallow flow of hydrothermal fluids in Long Valley Caldera, California, has been well studied, neither the hydrothermal source reservoir nor heat source has been well characterized. Here a grid of magnetotelluric data were collected around the Long Valley volcanic system and modeled in 3-D. The preferred electrical resistivity model suggests that the source reservoir is a narrow east-west elongated body 4 km below the west moat. The heat source could be a zone of 2–5% partial melt 8 km below Deer Mountain. Additionally, a collection of hypersaline fluids, not connected to the shallow hydrothermal system, is found 3 km below the medial graben, which could originate from a zone of 5–10% partial melt 8 km below the south moat. Below Mammoth Mountain is a 3 km thick isolated body containing fluids and gases originating from an 8 km deep zone of 5–10% basaltic partial melt.

Preparation of fine single crystals of magnetic superconductor RuSr2GdCu2O8-δ by partial melting

NASA Astrophysics Data System (ADS)

Yamaki, Kazuhiro; Bamba, Yoshihiro; Irie, Akinobu

2018-03-01

In this study, fine uniform RuSr2GdCu2O8-δ (RuGd-1212) single crystals have been successfully prepared by partial melting. Synthesis temperature could be lowered to a value not exceeding the decomposition temperature of RuGd-1212 using the Sr-Gd-Cu-O flux. The crystals grown by alumina boats are cubic, which coincides with the result of a previous study of RuGd-1212 single crystals using platinum crucibles. The single crystals were up to 15 × 15 × 15 µm3 in size and their lattice constants were consistent with those of polycrystalline samples reported previously. Although the present size of single crystals is not sufficient for measurements, the partial melting technique will be beneficial for future progress of research using RuGd-1212 single crystals. Appropriate nominal composition, sintering atmosphere, and temperature are essential factors for growing RuGd-1212 single crystals.

Markers of the pyroxenite contribution in the major-element compositions of oceanic basalts: Review of the experimental constraints

NASA Astrophysics Data System (ADS)

Lambart, Sarah; Laporte, Didier; Schiano, Pierre

2013-02-01

Based on previous and new results on partial melting experiments of pyroxenites at high pressure, we attempt to identify the major element signature of pyroxenite partial melts and to evaluate to what extent this signature can be transmitted to the basalts erupted at oceanic islands and mid-ocean ridges. Although peridotite is the dominant source lithology in the Earth's upper mantle, the ubiquity of pyroxenites in mantle xenoliths and in ultramafic massifs, and the isotopic and trace elements variability of oceanic basalts suggest that these lithologies could significantly contribute to the generation of basaltic magmas. The question is how and to what degree the melting of pyroxenites can impact the major-element composition of oceanic basalts. The review of experimental phase equilibria of pyroxenites shows that the thermal divide, defined by the aluminous pyroxene plane, separates silica-excess pyroxenites (SE pyroxenites) on the right side and silica-deficient pyroxenites (SD pyroxenites) on the left side. It therefore controls the melting phase relations of pyroxenites at high pressure but, the pressure at which the thermal divide becomes effective, depends on the bulk composition; partial melt compositions of pyroxenites are strongly influenced by non-CMAS elements (especially FeO, TiO2, Na2O and K2O) and show a progressive transition from the liquids derived from the most silica-deficient compositions to those derived from the most silica-excess compositions. Another important aspect for the identification of source lithology is that, at identical pressure and temperature conditions, many pyroxenites produce melts that are quite similar to peridotite-derived melts, making the determination of the presence of pyroxenite in the source regions of oceanic basalts difficult; only pyroxenites able to produce melts with low SiO2 and high FeO contents can be identified on the basis of the major-element compositions of basalts. In the case of oceanic island basalts, high CaO/Al2O3 ratios can also reveal the presence of pyroxenite in the source-regions. Experimental and thermodynamical observations also suggest that the interactions between pyroxenite-derived melts and host peridotites play a crucial role in the genesis of oceanic basalts by generating a wide range of pyroxenites in the upper mantle: partial melting of such secondary pyroxenites is able to reproduce the features of primitive basalts, especially their high MgO contents, and to impart, at least in some cases, the major-element signature of the original pyroxenite melt to the oceanic basalts. Finally, we highlight that the fact the very silica depleted compositions (SiO2 < 42 wt.%) and high TiO2 contents of some ocean island basalts seem to require the contribution of fluids (CO2 or H2O) through melting of either carbonated lithologies (peridotite or pyroxenite) or amphibole-rich veins.

Toward a coherent model for the melting behavior of the deep Earth's mantle

NASA Astrophysics Data System (ADS)

Andrault, D.; Bolfan-Casanova, N.; Bouhifd, M. A.; Boujibar, A.; Garbarino, G.; Manthilake, G.; Mezouar, M.; Monteux, J.; Parisiades, P.; Pesce, G.

2017-04-01

Knowledge of melting properties is critical to predict the nature and the fate of melts produced in the deep mantle. Early in the Earth's history, melting properties controlled the magma ocean crystallization, which potentially induced chemical segregation in distinct reservoirs. Today, partial melting most probably occurs in the lowermost mantle as well as at mid upper-mantle depths, which control important aspects of mantle dynamics, including some types of volcanism. Unfortunately, despite major experimental and theoretical efforts, major controversies remain about several aspects of mantle melting. For example, the liquidus of the mantle was reported (for peridotitic or chondritic-type composition) with a temperature difference of ∼1000 K at high mantle depths. Also, the Fe partitioning coefficient (DFeBg/melt) between bridgmanite (Bg, the major lower mantle mineral) and a melt was reported between ∼0.1 and ∼0.5, for a mantle depth of ∼2000 km. Until now, these uncertainties had prevented the construction of a coherent picture of the melting behavior of the deep mantle. In this article, we perform a critical review of previous works and develop a coherent, semi-quantitative, model. We first address the melting curve of Bg with the help of original experimental measurements, which yields a constraint on the volume change upon melting (ΔVm). Secondly, we apply a basic thermodynamical approach to discuss the melting behavior of mineralogical assemblages made of fractions of Bg, CaSiO3-perovskite and (Mg,Fe)O-ferropericlase. Our analysis yields quantitative constraints on the SiO2-content in the pseudo-eutectic melt and the degree of partial melting (F) as a function of pressure, temperature and mantle composition; For examples, we find that F could be more than 40% at the solidus temperature, except if the presence of volatile elements induces incipient melting. We then discuss the melt buoyancy in a partial molten lower mantle as a function of pressure, F and DFeBg/melt. In the lower mantle, density inversions (i.e. sinking melts) appear to be restricted to low F values and highest mantle pressures. The coherent melting model has direct geophysical implications: (i) in the early Earth, the magma ocean crystallization could not occur for a core temperature higher than ∼5400 K at the core-mantle boundary (CMB). This temperature corresponds to the melting of pure Bg at 135 GPa. For a mantle composition more realistic than pure Bg, the right CMB temperature for magma ocean crystallization could have been as low as ∼4400 K. (ii) There are converging arguments for the formation of a relatively homogeneous mantle after magma ocean crystallization. In particular, we predict the bulk crystallization of a relatively large mantle fraction, when the temperature becomes lower than the pseudo-eutectic temperature. Some chemical segregation could still be possible as a result of some Bg segregation in the lowermost mantle during the first stage of the magma ocean crystallization, and due to a much later descent of very low F, Fe-enriched, melts toward the CMB. (iii) The descent of such melts could still take place today. There formation should to be related to incipient mantle melting due to the presence of volatile elements. Even though, these melts can only be denser than the mantle (at high mantle depths) if the controversial value of DFeBg/melt is indeed as low as suggested by some experimental studies. This type of melts could contribute to produce ultra-low seismic velocity anomalies in the lowermost mantle.

Origin of conductivity anomalies in the asthenosphere

NASA Astrophysics Data System (ADS)

Yoshino, T.; Zhang, B.

2013-12-01

Electrical conductivity anomalies with anisotropy parallel to the plate motion have been observed beneath the oceanic lithosphere by electromagnetic studies (e.g., Evans et al., 2005; Baba et al., 2010; Naif et al., 2013). Electrical conductivity of the oceanic asthenosphere at ~100 km depth is very high, about 10-2 to 10-1 S/m. This zone is also known in seismology as the low velocity zone. Since Karato (1990) first suggested that electrical conductivity is sensitive to water content in NAMs, softening of asthenosphere has been regarded as a good indicator for constraining the distribution of water. There are two difficulties to explain the observed conductivity features in the asthenosphere. Recent publications on electrical conductivity of hydrous olivine suggested that olivine with the maximum soluble H2O content at the top of the asthenosphere has much lower conductivity less than 0.1 S/m (e.g., Yoshino et al., 2006; 2009a; Poe et al., 2010; Du Frane and Tyburczy, 2012; Yang, 2012), which is a typical value of conductivity anomaly observed in the oceanic mantle. Partial melting has been considered as an attractive agent for substantially raising the conductivity in this region (Shankland and Waff, 1977), because basaltic melt has greater electrical conductivity (> 100.5 S/m) and high wetting properties. However, dry mantle peridotite cannot reach the solidus temperature at depth 100 km. Volatile components can dramatically reduce melting temperature, even if its amount is very small. Recent studies on conductivity measurement of volatile-bearing melt suggest that conductivity of melt dramatically increases with increasing volatile components (H2O: Ni et al., 2010a, b; CO2: Gaillard et al., 2008; Yoshino et al., 2010; 2012a). Because incipient melt includes higher amount of volatile components, conductivity enhancement by the partial melt is very effective at temperatures just above that of the volatile-bearing peridotite solidus. In this study, the electrical conductivity of peridotite with trace amount of volatile phases was measured in single crystal olivine capsule to protect escape of water from the sample at 3 GPa. The conductivity values were significantly higher than those of dry peridotite, suggesting that the observed conductivity anomalies at the asthenosphere are caused by a presence of trace amount of volatile component in fluid or melt. On the other hand, conductivity of partial molten peridotite measured under shear showed that the conductivity parallel to the shear direction becomes one order of magnitude higher than that normal direction. These observations suggest that partial melting can explain softening and the observed geophysical anomalies of asthenosphere.

Influence of thermal treatment on the stability of phenolic compounds and the microbiological quality of sucrose solution following osmotic dehydration of highbush blueberry fruits.

PubMed

Kucner, Anna; Papiewska, Agnieszka; Klewicki, Robert; Sójka, Michał; Klewicka, Elżbieta

2014-01-01

Osmotic dehydration is a process of the partial removal of water which is based on immersion of material having cellular structure in a hypertonic solution. Osmotic dehydration is used as a pretreatment for the dehydration of foods before they are subjected to further processing such as freezing, freeze drying, vacuum drying. Management of spent syrup is one of the most important problems related to osmotic dewatering. Osmotic solutions are heavily polluted with of carbohydrates, remains of the dehydrated material and microorganisms. The aim of this study was to determine the effect of thermal treatment on the content of phenolic compounds and the microbiological quality of sucrose solution used in 15 cycles of osmotic dehydration of highbush blueberry (Vaccinium corymbosum L.) fruits. The tested material was 65.0 ±0.5°Brix sucrose solution used for 15 cycles of osmotic dehydration of highbush blueberry (Vaccinium corymbosum L.). Osmotic dehydration was conducted at 40°C for 120 min using fruits previously subjected to enzymatic pretreatment. The thermal treatment of sucrose solution was conducted at 70, 80, 90, 100 and 115°C for 20, 40 and 60 s. The sucrose solution was analysed in terms of total polyphenols, particular polyphenols using high performance liquid chromatography and microbiological analysis was subjected. Thermal treatment at 70-115°C for 20 s caused degradation of 8.5% to 12.7% of polyphenols, while as much as 23.1% of polyphenols were degraded at 115°C after 60 s. The present paper proposes heating parameters that are optimal from the point of view of phenolic compound retention and microbiological quality: thermal treatment of syrup at 100°C for 40 s. Under these conditions, total polyphenols retention was 94.5%, while the retention of individual phenolic compounds varied from 89.2% to 37.2%, and that of flavan-3-ols amounted to 89.5%. The studied manner of syrup treatment eliminated the problem of syrup contamination with yeasts and molds (reducing their levels to less than 1 CFU/mL).

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

PubMed Central

Machida, Shiki; Kogiso, Tetsu; Hirano, Naoto

2017-01-01

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

Dehydration protection provided by a maternal cuticle improves offspring fitness in the moss Funaria hygrometrica.

PubMed

Budke, Jessica M; Goffinet, Bernard; Jones, Cynthia S

2013-05-01

In bryophytes the sporophyte offspring are in contact with, nourished from, and partially surrounded by the maternal gametophyte throughout their lifespan. During early development, the moss sporophyte is covered by the calyptra, a cap of maternal gametophyte tissue that has a multilayered cuticle. In this study the effects on sporophyte offspring fitness of removing the maternal calyptra cuticle, in combination with dehydration stress, is experimentally determined. Using the moss Funaria hygrometrica, calyptra cuticle waxes were removed by chemical extraction and individuals were exposed to a short-term dehydration event. Sporophytes were returned to high humidity to complete development and then aspects of sporophyte survival, development, functional morphology, and reproductive output were measured. It was found that removal of calyptra cuticle under low humidity results in significant negative impacts to moss sporophyte fitness, resulting in decreased survival, increased tissue damage, incomplete sporophyte development, more peristome malformations, and decreased reproductive output. This study represents the strongest evidence to date that the structure of the calyptra cuticle functions in dehydration protection of the immature moss sporophyte. The investment in a maternal calyptra with a multilayered cuticle increases offspring fitness and provides a functional explanation for calyptra retention across mosses. The moss calyptra may represent the earliest occurance of maternal protection via structural provisioning of a cuticle in green plants.

Rehydration properties of hybrid method dried fruit enriched by natural components

NASA Astrophysics Data System (ADS)

Kowalska, Hanna; Marzec, Agata; Kowalska, Jolanta; Ciurzyńska, Agnieszka; Samborska, Kinga; Bialik, Michał; Lenart, Andrzej

2018-04-01

The aim of the study was to determine the impact of osmotic pre-dehydration and drying of fruit on the rehydration properties of dried fruit. Herein, the effect of fruit juice, applied as a natural enriching substance was very important. In addition, the properties of dried fruits obtained through combined air-drying and subsequent microwave-vacuum drying with `puffing' effect were similar to the freeze-dried fruits, but showed other rehydration properties. As raw material, frozen strawberry (Honeoye variety) and fresh apples (Idared variety) were used in the study. The apples and partially defrosted strawberries were prior dehydrated in solutions of sucrose and a mixture of sucrose with chokeberry juice concentrate at 50°C for 2 h. Next, the fruit samples were dried by one of two ways: air-drying (50°C, 5 h) and microwavevacuum drying for about 360 s; and freeze-drying (30°C, 63 Pa, 24 h). The rehydration was carried out in distilled water (20°C, 5 h). The osmotic pre-dehydration hindered fruit drying process. The impact of drying method became particularly evident while examining the kinetics of rehydration. During the rehydration of the pre-dehydrated dried fruit a slower hydration could be observed. Freeze-dried strawberries absorbed 2-3 times more water than those dried by the `puffing' effect.

Rapakivi texture formation via disequilibrium melting in a contact partial melt zone, Antarctica

NASA Astrophysics Data System (ADS)

Currier, R. M.

2017-12-01

In the McMurdo Dry Valleys of Antarctica, a Jurassic aged dolerite sill induced partial melting of granite in the shallow crust. The melt zone can be traced in full, from high degrees of melting (>60%) along the dolerite contact, to no apparent signs of melting, 10s of meters above the contact. Within this melt zone, the well-known rapakivi texture is found, arrested in various stages of development. High above the contact, and at low degrees of melting, K-feldspar crystals are slightly rounded and unmantled. In the lower half of the melt zone, mantles of cellular textured plagioclase appear on K-feldspar, and thicken towards the contact heat source. At the highest degrees of melting, cellular-textured plagioclase completely replaces restitic K-feldspar. Because of the complete exposure and intact context, the leading models of rapakivi texture formation can be tested against this system. The previously proposed mechanisms of subisothermal decompression, magma-mixing, and hydrothermal exsolution all fail to adequately describe rapakivi generation in this melt zone. Preferred here is a closed system model that invokes the production of a heterogeneous, disequilibrium melt through rapid heating, followed by calcium and sodium rich melt reacting in a peritectic fashion with restitic K-feldspar crystals. This peritectic reaction results in the production of plagioclase of andesine-oligoclase composition—which is consistent with not just mantles in the melt zone, but globally as well. The thickness of the mantle is diffusion limited, and thus a measure of the diffusive length scale of sodium and calcium over the time scale of melting. Thermal modeling provides a time scale of melting that is consistent with the thickness of observed mantles. Lastly, the distribution of mantled feldspars is highly ordered in this melt zone, but if it were mobilized and homogenized—mixing together cellular plagioclase, mantled feldspars, and unmantled feldspars—the result would be akin to rapakivi granites observed globally in Proterozoic systems. In essence, the melt zone is an embryonic rapakivi granite; not yet fully developed and displaying clear ties to its parental rock.

Study of Chromium Oxide Activities in EAF Slags

NASA Astrophysics Data System (ADS)

Yan, Baijun; Li, Fan; Wang, Hui; Sichen, Du

2016-02-01

The activity coefficients of chromium in Cu-Cr melts were determined by equilibrating liquid copper with solid Cr2O3 in CO-CO2 atmosphere. The temperature dependence of the activity coefficients of chromium in Cu-Cr melts could be expressed as lg γ_{Cr}(s)^{0} = { 3 2 5 9( ± 1 8 6} )/T - 0. 5 9( { ± 0. 1} ). Based on the above results, the activities of bivalent and trivalent chromium oxide in some slags at 1873 K (1600 °C) were measured. The slags were equilibrated with Cu-Cr melts under two oxygen partial pressures ( {p_{O}_{ 2} }} } = 6.9 × 10-4 and 1.8 × 10-6 Pa, respectively). The morphology of the quenched slags and the solubility of chromium oxide in the melts were investigated by EPMA, SEM, and XRD. Under both oxygen partial pressures, the slags were saturated by the solid solution MgAl2- x Cr x O4- δ . At the low oxygen partial pressure (1.8 × 10-6 Pa), the content of Cr in the liquid phase varied from 0.4 to 1.6 mass pct with the total Cr content in the slags increasing from 1.3 to 10.8 mass pct. At the high oxygen partial pressure (6.9 × 10-4 Pa), the content of Cr in the liquid phase decreased to the level of 0.2 to 0.6 mass pct. Both the activities of CrO and Cr2O3 in slag were found to increase approximately linearly with the increase of the total Cr content in slag. While the oxygen partial pressure had minor effect on the activity of Cr2O3 in the slag, it had significant effect on the activity of CrO.

Void-Free Lid for Food Packaging

NASA Technical Reports Server (NTRS)

Watson, C. D.; Farris, W. P.

1986-01-01

Flexible cover eliminates air pockets in sealed container. Universal food-package lid formed from flexible plastic. Partially folded, lid unfolded by depressing center portion. Height of flat portion of lid above flange thereby reduced. Pressure of food against central oval depression pops it out, forming dome that provides finger grip for mixing contents with water or opening lid. Therefore food stays fresh, allows compact stacking of partially filled containers, and resists crushing. Originally developed for packaging dehydrated food for use in human consumption on Space Shuttle missions. Other uses include home canning and commercial food packaging.

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 bulk CO2 solubility. To meet the minimum requirement of 3000 ppm CO2 in primary arc magma [5,6], the required sediment melt contribution is 0.18-0.28 wt.% CO2, which is distinctly lower than the solubility limit of graphite-saturated melt. However, 1.7 wt.% CO2 in primary arc basalts [5] exceeds the solubility limit of reduced, hydrous melts, which is in contrast to more oxidized, hydrous melts which can contribute up to 2 wt.% CO2. We determine that ~1.7-15% of sediment melt would be required to meet 3000 ppm CO2 in the primary arc basalt depending on the depth of melting (1.5-3.0 GPa) and the degree of mantle wedge melting (15-30%). This contribution is higher than that previously calculated for the more oxidized melts, but still may not be an unreasonable slab flux. [1] Dasgupta (2013) RiMG, 75, 183-229; [2] Plank and Langmuir (1993) Nature, 362, 739-743. [3] Duncan and Dasgupta. (in review) GCA; [4] Tsuno and Dasgupta (2011) CMP, 161, 743-763; [5] Blundy et al. (2010) EPSL, 290, 289-301; [6] Wallace (2005) JVGR, 140, 217-240.

Geochemistry of Intra-Transform Lavas from the Galápagos Transform Fault

NASA Astrophysics Data System (ADS)

Morrow, T. A.; Mittelstaedt, E. L.; Harpp, K. S.

2013-12-01

The Galápagos plume has profoundly affected the development and evolution of the nearby (<250 km) Galápagos Transform Fault (GTF), a ~100km right-stepping offset in the Galápagos Spreading Center (GSC). The GTF can be divided into two sections that represent different stages of transform evolution: the northern section exhibits fully developed transform fault morphology, whereas the southern section is young, and deformation is more diffuse. Both segments are faulted extensively and include numerous small (<0.5km3) monogenetic volcanic cones, though volcanic activity is more common in the south. To examine the composition of the mantle source and melting conditions responsible for the intra-transform lavas, as well as the influence of the plume on GTF evolution, we present major element, trace element, and radiogenic isotope analysis of samples collected during SON0158, EWI0004, and MV1007 cruises. Radiogenic isotope ratio variations in the Galápagos Archipelago require four distinct mantle reservoirs across the region: PLUME, DM, FLO, and WD. We find that Galápagos Transform lavas are chemically distinct from nearby GSC lavas and neighboring seamounts. They have radiogenic isotopic compositions that lie on a mixing line between DM and PLUME, with little to no contribution from any other mantle reservoirs despite their geographic proximity to WD-influenced lavas erupted along the GSC and at nearby (<50km away) seamounts. Within the transform, lavas from the northern section are more enriched in radiogenic isotopes than lavas sampled in the southern section. Transform lavas are anomalously depleted in incompatible trace elements (ITEs) relative to GSC lavas, suggesting unique melting conditions within the transform. Isotopic variability along the transform axis indicates that mantle sources and/or melting mechanisms vary between the northern and southern sections, which may relate to their distances from the plume or the two-stage development and evolution of the Galápagos Transform Fault. We present a melting model that reproduces GTF lava chemistry from a mixture of two partial melts of PLUME and DM. We assume that the DM source has an ITE composition similar to the depleted upper mantle, melting is purely fractional, and lavas do not fractionate during ascent. Solutions were achieved using a Metropolis algorithm and constrained by observed GTF lava chemistry. Model results predict that GTF lavas are produced by a mixture of a ~3%×1% partial melt of the PLUME source and a ~5%×4% partial melt of the DM source. Our model predicts that a larger proportion of PLUME melts contribute to GTF lavas than DM melts. Absence of the WD component and relatively low concentrations of ITEs may indicate that lavas in the GTF are produced from a source that has already undergone partial melting and is being re-melted beneath the TF. Re-melting may be caused by extension across the GTF, or development of the southern section of the GTF via the ~1Ma ridge jump.

Stability and growth of continental shields in mantle convection models including recurrent melt production

NASA Astrophysics Data System (ADS)

de Smet, J. H.; van den Berg, A. P.; Vlaar, N. J.

1998-10-01

The long-term growth and stability of compositionally layered continental upper mantle has been investigated by numerical modelling. We present the first numerical model of a convecting mantle including differentiation through partial melting resulting in a stable compositionally layered continental upper mantle structure. This structure includes a continental root extending to a depth of about 200 km. The model covers the upper mantle including the crust and incorporates physical features important for the study of the continental upper mantle during secular cooling of the Earth since the Archaean. Among these features are: a partial melt generation mechanism allowing consistent recurrent melting, time-dependent non-uniform radiogenic heat production, and a temperature- and pressure-dependent rheology. The numerical results reveal a long-term growth mechanism of the continental compositional root. This mechanism operates through episodical injection of small diapiric upwellings from the deep layer of undepleted mantle into the continental root which consists of compositionally distinct depleted mantle material. Our modelling results show the layered continental structure to remain stable during at least 1.5 Ga. After this period mantle differentiation through partial melting ceases due to the prolonged secular cooling and small-scale instabilities set in through continental delamination. This stable period of 1.5 Ga is related to a number of limitations in our model. By improving on these limitations in the future this stable period will be extended to more realistic values.

Genetic interpretation of lead-isotopic data from the Columbia River basalt group, Oregon, Washington, and Idaho.

USGS Publications Warehouse

Church, S.E.

1985-01-01

Lead-isotopic data for the high-alumina olivine plateau basalts and most of the Colombia River basalt group plot within the Cascade Range mixing array. The data for several of the formations form small, tight clusters and the Nd and Sr isotopic data show discrete variation between these basalt groups. The observed isotopic and trace-element data from most of the Columbia River basalt group can be accounted for by a model which calls for partial melting of the convecting oceanic-type mantle and contamination by fluids derived from continental sediments which were subducted along the trench. These sediments were transported in the low-velocity zone at least 400 km behind the active arc into a back-arc environment represented by the Columbia Plateau province. With time, the zone of melting moved up, resulting in the formation of the Saddle Mt basalt by partial melting of a 2600 m.y.-old sub-continental lithosphere characterized by high Th/U, Th/Pb, Rb/Sr and Nd/Sm ratios and LREE enrichment. Partial melting of old sub-continental lithosphere beneath the continental crust may be an important process in the formation of continental tholeiite flood basalt sequences world-wide. -L.di H.

Juvenile crustal recycling in an accretionary orogen: Insights from contrasting Early Permian granites from central Inner Mongolia, North China

NASA Astrophysics Data System (ADS)

Yuan, Lingling; Zhang, Xiaohui; Xue, Fuhong; Liu, Fulin

2016-11-01

Coeval high-K calc-alkaline to alkaline granites constitute important components of post-collisional to post-orogenic igneous suites in most orogenic belts of various ages on Earth and their genesis harbors a key to ascertaining critical geodynamic controls on continental crustal formation and differentiation. This zircon U-Pb dating and geochemical study documents three contrasting Early Permian granites from Erenhot of central Inner Mongolia, eastern Central Asian Orogenic Belt (CAOB) and reveals concurrent high-K calc-alkaline to alkaline granite association derived from successive partial melting of distinct protoliths. The ca. 280 Ma Gancihuduge (GCG) pluton shows a calc-alkaline I-type character, with initial 87Sr/86Sr ratios of 0.7035 to 0.7039, εNd(t) of + 1.87 to + 4.70, zircon εHf(t) of + 8.0 to + 13.2 and δ18O from 7.4 to 8.7‰. The ca. 276 Ma Cailiwusu (CLS) pluton is magnesian and peraluminous, with initial 87Sr/86Sr ratios of 0.7036 to 0.7040, εNd(t) of + 1.9 to + 2.4, zircon εHf(t) of + 6.5 to + 12.1 and δ18O from 9.7 to 10.9‰. These features are consistent with partial melts of mixed sources composed of newly underplated meta-basaltic to -andesitic protoliths and variable supracrustal components, with distinctively higher proportion of the latter in the CLS pluton. By contrast, the ca. 279 Ma Kunduleng (KDL) suite exhibits an A-type magmatic affinity, with typical enrichment in alkalis, Ga, Zr, Nb and Y, εNd(t) of + 2.39 to + 3.55, zircon εHf(t) from + 8.3 to + 12.3 and δ18O values from 6.8 to 7.5‰. These features suggest that they stem from high-temperature fusion of dehydrated K-rich mafic to intermediate protoliths. Besides presenting a snapshot into a stratified crustal architecture in δ18O, these contrasting granites could not only serve as a temporal marker for monitoring post-collisional extension in the aftermath of a retreating subduction zone, but also present spatial magmatic proxy for tracing crustal formation and differentiation within back-arc basin environments in the CAOB.

Modelling the seismic properties of fast-spreading ridge crustal Low-Velocity Zones: insights from Oman gabbro textures

NASA Astrophysics Data System (ADS)

Lamoureux, Gwenaëlle; Ildefonse, Benoı̂t; Mainprice, David

1999-11-01

Although considerable progress has been made in the study of fast-spreading, mid-ocean ridge magma chambers over the past fifteen years, the fraction of melt present in the chamber remains poorly constrained and controversial. We present new constraints obtained by modelling the seismic properties of partially molten gabbros at the ridge axis. P-wave velocities at low frequencies are calculated in the foliation/lineation reference frame using a differential effective medium technique. The model takes into account the lattice preferred orientation of the crystalline phase and the average shape of the melt phase. The structural parameters are obtained from the Oman ophiolite. The structural reference frame is given by the general trend of the gabbro foliation and the melt fraction and shape are estimated using the textures of nine upper gabbro samples. The estimated melt fraction and shape depend on the assumptions regarding which part of the observed textures represent the melt in the gabbroic mush of the magma chamber. However, we can put limits on the reasonable values for the melt fraction and shape. Our results are consistent with a melt fraction of the order of 10 to 20% in the Low-Velocity Zone (i.e. the magma chamber), which is anisotropically distributed with the melt pockets preferentially aligned parallel to the foliation and approximated by oblate ellipsoids with approximate dimensions of 4 : 4 : 1. These results are also consistent with the seismic structure of the East Pacific rise at 9°30'. The anisotropic melt distribution can, at least partially, explain the vertical velocity gradient described in the LVZ.

Melting in super-earths.

PubMed

Stixrude, Lars

2014-04-28

We examine the possible extent of melting in rock-iron super-earths, focusing on those in the habitable zone. We consider the energetics of accretion and core formation, the timescale of cooling and its dependence on viscosity and partial melting, thermal regulation via the temperature dependence of viscosity, and the melting curves of rock and iron components at the ultra-high pressures characteristic of super-earths. We find that the efficiency of kinetic energy deposition during accretion increases with planetary mass; considering the likely role of giant impacts and core formation, we find that super-earths probably complete their accretionary phase in an entirely molten state. Considerations of thermal regulation lead us to propose model temperature profiles of super-earths that are controlled by silicate melting. We estimate melting curves of iron and rock components up to the extreme pressures characteristic of super-earth interiors based on existing experimental and ab initio results and scaling laws. We construct super-earth thermal models by solving the equations of mass conservation and hydrostatic equilibrium, together with equations of state of rock and iron components. We set the potential temperature at the core-mantle boundary and at the surface to the local silicate melting temperature. We find that ancient (∼4 Gyr) super-earths may be partially molten at the top and bottom of their mantles, and that mantle convection is sufficiently vigorous to sustain dynamo action over the whole range of super-earth masses.

Viscous constitutive relations of solid-liquid composites in terms of grain boundary contiguity: 1. Grain boundary diffusion control model

NASA Astrophysics Data System (ADS)

Takei, Yasuko; Holtzman, Benjamin K.

2009-06-01

Viscous constitutive relations of partially molten rocks deforming in the regime of grain boundary (GB) diffusion creep are derived theoretically on the basis of microstructural processes at the grain scale. The viscous constitutive relation developed in this study is based on contiguity as an internal state variable, which enables us to take into account the detailed effects of grain-scale melt distribution observed in experiments. Compared to the elasticities derived previously for the same microstructural model, the viscosities are much more sensitive to the presence of melt and variations in contiguity. As explored in this series of three companion papers, this "contiguity" model predicts that a very small amount of melt (ϕ < 0.01) significantly reduces the bulk and shear viscosities. Furthermore, a large anisotropy in viscosity is produced by anisotropy in contiguity, which occurs in deforming partially molten rocks. These results have important implications for deformation and melt extraction at small melt fractions, as well as for shear-induced melt segregation. The viscous and elastic constitutive relations derived in terms of contiguity bridge microscopic grain-scale and macroscopic continuum properties. These constitutive relations are essential for investigating melt migration dynamics in a forward sense on the basis of the basic equations of two-phase dynamics and in an inverse sense on the basis of seismological observations.

Lateral variations in lower mantle seismic velocity

NASA Technical Reports Server (NTRS)

Duffy, Thomas S.; Ahrens, Thomas J.

1992-01-01

To obtain a theoretical model which provides a rationale for the observed high values of velocity variations, the effect of a 0.1 to 0.2 percent partially molten volatile-rich material in various geometries which are heterogeneously dispersed in the lower mantle is examined. Data obtained indicate that, depending on aspect ratio and geometry, 0.1-0.2 percent partial melting in conjunction with about 100 K thermal anomalies can explain the seismic variations provided the compressibility of the melt differs by less than about 20 percent from the surrounding solid.

First results from analysis of coordinated AVIRIS, TIMS, and ISM (French) data for the Ronda (Spain) and Beni Bousera (Morocco) peridotites

NASA Technical Reports Server (NTRS)

Mustard, J. F.; Hurtrez, S.; Pinet, P.; Sotin, C.

1992-01-01

Ultramafic rocks are relatively rare at the Earth's surface but constitute the vast majority of the Earth by volume. Exposures of ultramafic bodies are therefore crucial for deducing many important processes that occur in the Earth's mantle. An important science question regarding the spatial distribution, abundance, and composition of mafic minerals in ultramafic bodies that can be examined with advanced sensor data is the melting process. When a lherzolite melts, clinopyroxene (cpx) melts first and therefore variations in the modal amount of cpx remaining in the mantle are a reflection of the amount of fractional melting that has occurred. Fe goes preferentially into the melt during melting but a 20 percent batch melting (i.e. closed system) acquires less Fe relative to 20 percent fractional melting (i.e. open system). Since the strength and wavelength of diagnostic absorptions is a strong function of Fe content, it is possible to make maps of the variation in Fe:Mg ratios which can be related to the general melting process. Accurate ground-truth information about local mineralogy provides internal calibration and consistency checks. Investigations using imaging spectrometer are very complementary to field studies because advanced sensor data can provide a synoptic view of modal mineralogy and chemical composition whereas field studies focus on detailed characterization of local areas. Two excellent exposures of ultramafic lithologies are being investigated with visible to mid-infrared imaging spectrometer data: the Ronda peridotite near Ronda, Spain and the Beni Bousera ophiolitic fragment in northern Morocco. Although separated by the Alboran Sea, these bodies are thought to be related and represent fertile sub-continental mantle. The Ronda peridotite is predominantly spinel lherzolite but grades into harzburgite and shows considerable variation in major and trace element compositions. Mafic layering and dykes (i.e. olivine gabbro) are also observed. This indicates some sections of the peridotite have experienced greater degrees of partial melting. The Beni Bousera peridotite also contains mafic layers and dykes and grades into harzburgite representing similar fundamental shifts in the bulk chemistry of this ultramafic body probably related to an episode of partial melting. The specific mode of emplacement of these bodies is controversial and important for understanding the tectonic evolution of this region. Our investigations are not necessarily designed to help resolve this controversy. Rather, these exposures provide excellent and unusual examples of fertile mantle which have undergone variable degrees of partial melting.

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 mixed with the basaltic melt of the AML, resulting in intermediate compositions that can be observed in the isotropic gabbro horizon. Our study suggests that assimilation of previously hydrothermalized lithologies in the melt lens is a common process at fast spreading ridges. This process should consequently be carefully considered in geochemical studies that deal with the origin of MORB. France L., Ildefonse B., Koepke J., (2008) The fossilisation of a dynamic melt lens at fast spreading centers: insights from the Oman ophiolite. Eos Trans. AGU, 89(53), Fall Meet. Suppl. Abstract V51F-2111

Halogen content in Lesser Antilles arc volcanic rocks : exploring subduction recycling

NASA Astrophysics Data System (ADS)

Thierry, Pauline; Villemant, Benoit; Caron, Benoit

2016-04-01

Halogens (F, Cl, Br and I) are strongly reactive volatile elements which can be used as tracers of igneous processes, through mantle melting, magma differentiation and degassing or crustal material recycling into mantle at subduction zones. Cl, Br and I are higly incompatible during partial melting or fractional cristallization and strongly depleted in melts by H2O degassing, which means that no Cl-Br-I fractionation is expected through magmatic differenciation [current thesis]. Thus, Cl/Br/I ratios in lavas reflect the halogen content of their mantle sources. Whereas these ratios seemed quite constant (e.g. Cl/Br =300 as seawater), recent works suggest significant variations in arc volcanism [1,2]. In this work we provide high-precision halogen measurements in volcanic rocks from the recent activity of the Lesser Antilles arc (Montserrat, Martinique, Guadeloupe, Dominique). Halogen contents of powdered samples were determined through extraction in solution by pyrohydrolysis and analysed by Ion Chromatography for F and Cl and high performance ICP-MS (Agilent 8800 Tripe Quad) for Cl, Br and I [3,4]. We show that lavas - and mantle sources - display significant vraiations in Cl/Br/I ratios along the Lesser Antilles arc. These variations are compared with Pb, Nd and Sr isotopes and fluid-mobile elements (Ba, U, Sr, Pb etc.) compositions which vary along the arc from a nothern ordinary arc compositions to a southern 'crustal-like' composition [5,6]. These characteristics are attributed to subducted sediments recycling into the mantle wedge, whose contribution vary along the arc from north to south [7,8]. The proportion of added sediments is also related to the distance to the trench as sediment melting and slab dehydration may occur depending on the slab depth [9]. Further Cl-Br-I in situ measurements by LA-ICP-MS in Lesser Antilles arc lavas melt inclusions will be performed, in order to provide better constraints on the deep halogen recycling cycle from crust to mantle. 1. Villemant, B., Mouatt, J. & Michel, A., 2008. Earth Planet. Sci. Lett. 269(1), 212-229. 2. Kutterolf, S. et al., 2015. Earth Planet. Sci. Lett. 429, 234-246. 3. Michel, A. & Villemant, B., 2003. Geostand. Geoanalytical Res. 27(2), 163-171. 4. Balcone-Boissard, H., Michel, A. & Villemant, B., 2009. Geostand. Geoanalytical Res. 33(4), 477-485. 5. White, W. M. & Dupré, B., 1986. J. Geophys. Res. 91(B6), 5927. 6. Labanieh, S. et al., 2010. Earth Planet. Sci. Lett. 298(1-2), 35-46. 7. Turner, S. et al., 1996. Earth Planet. Sci. Lett. 142(1-2), 191-207. 8. Carpentier, M., Chauvel, C. & Mattielli, N., 2008. Earth Planet. Sci. Lett. 272(1-2), 199-211. 9. Labanieh, S. et al., 2012. J. Petrol. 53(12), 2441-2464.

Implications of a reducing and warm (not hot) Archaean ambient mantle for ancient element cycles

NASA Astrophysics Data System (ADS)

Aulbach, Sonja

2016-04-01

There is considerable uncertainty regarding the oxygen partial pressure (fO2) and potential temperature (TP) of the ambient convecting mantle throughout Earth's history. Rare Archaean eclogite suites have elemental and isotopic compositions indicative of formation of crustal protoliths in oceanic spreading ridges, hence unaffected by continental sources. These include some eclogite xenoliths derived from cratonic mantle lithosphere and orogenic eclogites marking the exhumation of oceanic crust at Pacific-type margins. Their compositions may retain a memory of the thermal and redox state of the Archaean convecting mantle sources that gave rise to their low-pressure protoliths. Archaean eclogites have TiO2-REE relationships consistent with fractional crystallisation of olivine±plagioclase and cpx during formation of picritic protoliths from a melt that separated from a garnet-free peridotite source, implying intersection of the solidus at ≤2.5 to 3.0 GPa [1]. Low melt fractions (<0.25) inferred from samples with the least fractionated (lowest TiO2) protoliths further argue against deep intersection of the mantle solidus. This suggests a moderately elevated TP ~ 1420-1470 degrees C (lower than some estimates for the ambient convecting mantle at that time [2]), which would support an early onset of plate tectonics [3] and emergence of continents [4], heralding a transition to modern chemical cycles. Moderate TP further indicates that deep recycling of carbon and water, though reduced compared to today, may have been possible in the Archaean [5,6]. Carefully screened eclogites have V/Sc (reflecting the redox state of the ambient mantle during protolith formation [7]) corresponding to ΔFMQ corrected to 1 GPa as low as -1.7 at 3 Ga [1]. Such low oxygen fugacities have consequences for the location of the peridotite solidus and for the types of melts generated during redox melting [5,8]. They also modulate the redox state of volatiles liberated at oceanic spreading ridges [7] in the Archaean, with implications for the composition and oxygenation of the palaeo-atmosphere. Subsequent subduction of such reducing oceanic crust must have also affected the cycling of volatile elements (soluble instead of molecular species [9]) and of redox-sensitive ore-forming metals [10] during metamorphic dehydration and melting reactions. [1] Aulbach&Viljoen (2015) Earth Planet Sci Lett 431; [2] Herzberg et al. (2010) Earth Planet Sci Lett 292; [3] Sizova et al. (2010) Lithos 116; [4] Rey&Coltice (2008) Geology 36; [5] Dasgupta (2013) RIMG 75; [6] Magni et al. (2014) G3 15; [7] Li&Lee (2004) EPSL 228; [8] Stagno et al. (2013) Nature 493; [9] Sverjensky et al. (2014) Nat Geosci 7; [10] Evans & Tomkins (2011) Earth Planet Sci Lett 308.

Partial Pressures of Te2 and Thermodynamic Properties of Ga-Te System

NASA Technical Reports Server (NTRS)

Su, Ching-Hua; Curreri, Peter A. (Technical Monitor)

2001-01-01

The partial pressures of Te2 in equilibrium with Ga(1-x)Te(x) samples were measured by optical absorption technique from 450 to 1100 C for compositions, x, between 0.333 and 0.612. To establish the relationship between the partial pressure of Te, and the measured optical absorbance, the calibration runs of a pure Te sample were also conducted to determine the Beer's Law constants. The partial pressures of Te2 in equilibrium with the GaTe(s) and Ga2Te3(s)compounds, or the so-called three-phase curves, were established. These partial pressure data imply the existence of the Ga3Te4(s) compound. From the partial pressures of Te2 over the Ga-Te melts, partial molar enthalpy and entropy of mixing for Te were derived and they agree reasonable well with the published data. The activities of Te in the Ga-Te melts were also derived from the measured partial pressures of Te2. These data agree well with most of the previous results. The possible reason for the high activity of Te measured for x less than 0.60 is discussed.

Ar-Ar and I-Xe Ages of Caddo County and Thermal History of IAB Iron Meteorites

NASA Technical Reports Server (NTRS)

Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

2005-01-01

Inclusions in IAB iron meteorites include non-chondritic silicate and those with more primitive chondritic silicate composition. Coarse-grained gabbroic material rich in plagioclase and diopside occurs in the Caddo County IAB iron meteorite and represents a new type of chemically differentiated, extra-terrestrial, andesitic silicate. Other parts of Caddo contain mostly andesitic material. Caddo thus exhibits petrologic characteristics of parent body metamorphism of a chondrite-like parent and inhomogeneous segregation of melts. Proposed IAB formation models include parent body partial melting and fractional crystallization or incomplete differentiation due to internal heat sources, and impact/induced melting and mixing. Benedix et al. prefer a hybrid model whereby the IAB parent body largely melted, then underwent collisional breakup, partial mixing of phases, and reassembly. Most reported 129I- Xe-129 ages of IABs are greater than 4.56 Gyr and a few are greater than or = 4.567 Gyr. These oldest ages exceed the 4.567 Gyr Pb-Pb age of Ca, Al-rich inclusions in primitive meteorites,

Petrogenesis of high-Ti and low-Ti basalts: high-pressure and high-temperature experimental study

NASA Astrophysics Data System (ADS)

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

2017-12-01

Geochemical and petrological studies have revealed the existence of high-Ti and low-Ti basalts in large igneous provinces. However, the petrogenesis of them 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 or delaminated lower crust (Spandler et al., 2008) while low-Ti basalts are formed by the melting of subcontinental lithospheric mantle (Xiao et al., 2004); (2) both of them are from mantle plume or asthenospheric source, but the production of high-Ti basalts are associated with the thick lithosphere and relevant low degrees of melting while the low-Ti basalts are controlled by the thin lithosphere with high degrees of melting (Arndt et al., 1993; Xu et al., 2001). Almost all authors emphasize the role of partial melting but less discuss the crystallization differentiation process. The low Mg# (< 0.7) of these basalts provides that they are far away from direct melting of mantle peridotite. In addition, seismic data indicate unusually high seismic velocities bodies beneath 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 these basalts, a series of high pressure and high temperature partial crystallization experiments were performed by using piston-cylinder and multi-anvil press at pressures of 1.5, 3.0 and 5.0 GPa and a temperature range of 1200-1700°. Two synthetic picrite glass with different chemical compositions were used as starting materials. Our experimental results show that Ti is preferred to be concentrated in the residual melt during crystallization differentiation. For the same melt fraction, the residual melt of higher pressure experiments has relatively higher TiO2 concentration and higher Mg#. Thus, we propose that most of the high-Ti and low-Ti basalts are inherited from picritic parental magmas which could be formed by high degree partial melting of garnet peridotite. The high-Ti basalts are generated through relatively high pressure crystallization process while the low-Ti basalts are generated at relatively low pressure.

Synthesis of single-site copper catalysts for methane partial oxidation

DOE PAGES

Grundner, S.; Luo, W.; Sanchez-Sanchez, M.; ...

2015-12-24

Cu-Exchanged zeolites are known as active materials for methane oxidation to methanol. However, understanding of the formation of Cu active species during synthesis, dehydration and activation is fragmented and rudimentary. We show here how a synthesis protocol guided by insight in the ion exchange elementary steps leads to highly uniform Cu species in mordenite (MOR).

Char yield on pyrolysis of cellulose

Treesearch

A. Broido; Maxine A. Nelson

1975-01-01

Whether the pyrolysis of cellulose is conducted in an inert medium or in air, partial pyrolysis at a lower temperature increases the char yield subsequently obtained after 1 hour at 370°C. The results are consistent with a pyrolysis scheme in which two competing sequences of cellulose pyrolysis reactions are initiated by (1) an intermolecular dehydration leading to...

Origin of silicic magmas along the Central American volcanic front: Genetic relationship to mafic melts

NASA Astrophysics Data System (ADS)

Vogel, Thomas A.; Patino, Lina C.; Eaton, Jonathon K.; Valley, John W.; Rose, William I.; Alvarado, Guillermo E.; Viray, Ela L.

2006-09-01

Silicic pyroclastic flows and related deposits are abundant along the Central American volcanic front. These silicic magmas erupted through both the non-continental Chorotega block to the southeast and the Paleozoic continental Chortis block to the northwest. The along-arc variations of the silicic deposits with respect to diagnostic trace element ratios (Ba/La, U/Th, Ce/Pb), oxygen isotopes, Nd and Sr isotope ratios mimic the along-arc variation in the basaltic and andesitic lavas. This variation in the lavas has been interpreted to indicate relative contributions from the slab and asthenosphere to the basaltic magmas [Carr, M.J., Feigenson, M.D., Bennett, E.A., 1990. Incompatible element and isotopic evidence for tectonic control of source mixing and melt extraction along the Central American arc. Contributions to Mineralogy and Petrology, 105, 369-380.; Patino, L.C., Carr, M.J. and Feigenson, M.D., 2000. Local and regional variations in Central American arc lavas controlled by variations in subducted sediment input. Contributions to Mineralogy and Petrology, 138 (3), 265-283.]. With respect to along-arc trends in basaltic lavas the largest contribution of slab fluids is in Nicaragua and the smallest input from the slab is in central Costa Rica — similar trends are observed in the silicic pyroclastic deposits. Data from melting experiments of primitive basalts and basaltic andesites demonstrate that it is difficult to produce high K 2O/Na 2O silicic magmas by fractional crystallization or partial melting of low-K 2O/Na 2O sources. However fractional crystallization or partial melting of medium- to high-K basalts can produce these silicic magmas. We interpret that the high-silica magmas associated Central America volcanic front are partial melts of penecontemporaneous, mantle-derived, evolved magmas that have ponded and crystallized in the mid-crust — or are melts extracted from these nearly completely crystallized magmas.

Site-specific hydration and dehydration of San Carlos olivine

NASA Astrophysics Data System (ADS)

Ferriss, E.; Plank, T. A.; Walker, D.

2016-12-01

Hydrogen incorporation and diffusion in olivine is critical to understanding fundamental Earth processes such as mantle rheology, plate tectonics, melt generation and magma ascent. Interpreting measured H profiles in olivine requires a more comprehensive understanding of H point defect reactions than currently exists because H diffusivity (D) ranges over 6 orders of magnitude, from slow diffusing H incorporated as (4H+)Si­ [1] to rapid `proton-polaron' bulk H diffusion [2]. Here we present the first experiments on H diffusing into and then out of Fe-bearing olivine using the whole-block method [3], which allows a finely-resolved time series of H profiles in 3 crystallographic directions using the same sample for all dehydration steps. A piece of nearly-dry, oriented San Carlos olivine was hydrated in a piston cylinder apparatus using H2O and solid buffers of Ni/NiO and San Carlos olivine and enstatite at 800 °C and 10 kbar for 17.5 hours, just long enough to saturate the `proton-polaron' mechanism. The sample was then dehydrated in a CO/CO2 gas-mixing furnace at 800°C and 10-14 bar fO2 for total heating times of 1, 3, 7, 13, 19, 43, and 68 hrs, at which point most, but not all, of the H had left the crystal. FTIR profiles at 1, 3, and 7 hours show bulk H profiles consistent with `proton-polaron' diffusion. Later the pace of dehydration slowed, and in several cases the bulk H profile shape differed from what would be expected during simple diffusive loss. The small peak at 3600 cm-1, (4H+)Si, remained essentially unchanged throughout all experiments. The peak at 3573 cm-1, (Ti4+)Mg(2H+)Mg, was initially present but tiny, grew to become the largest peak after hydration, and then during dehydration returned to its initial height. The apparent diffusivity of this peak during hydration and the initial stages of dehydration is 4 orders of magnitude faster than the same peak in synthetic forsterite [2]. Peaks at 3542, 3525, 3489, and 3480 cm-1 were not present initially, grew during hydration, and were removed completely during dehydration. No lower-wavenumber H peaks were observed. These results represent a major step toward reconciling the peak-specific understanding of H diffusion [1] with the 2-mechanism H bulk diffusion model [2]. [1] Padrón-Navarta et al. 2014 [2] Kohlstedt & Mackwell 1998 [3] Ferriss et al. 2015

Seismological Signature of Chemical Differentiation of Earth's Upper Mantle

NASA Astrophysics Data System (ADS)

Matsukage, K. N.; Nishihara, Y.; Karato, S.

2004-12-01

Chemical differentiation from a primitive rock (such as pyrolite) to harzburgite due to partial melting and melt extraction is one of the most important mechanisms that causes the chemical heterogeneity in Earth's upper mantle. In this study, we investigate the seismic signature of chemical differentiation that helps mapping chemical heterogeneity in the upper mantle. The relation between chemical differentiation and its seismological signature is not straightforward because a large number of unknown parameters are involved although the seismological observations provide only a few parameters (e.g., VP, VS, QP). Therefore it is critical to identify a small number of parameters by which the gross trend of chemical evolution can be described. The variation in major element composition in natural samples reflect complicated processes that include not only partial melting but also other complex processes (e.g., metasomatism, influx melting). We investigate the seismic velocities of hypothetical but well-defined simple chemical differentiation processes (e.g., partial melting of various pressure conditions, addition of Si-rich melt or fluid), which cover the chemical variation of the natural mantle peridotites with various tectonic settings (mid ocean ridge, island arc and continent). The seismic velocities of the peridotites were calculated to 13 GPa and 1730 K. We obtained two major conclusions. First is that the variations of seismic velocities of upper mantle peridotites can be interpreted in terms of a few distinct parameters. For one class of peridotites which is formed by simple partial melting (e.g. mid-ocean ridges peridotites), seismic velocities can be described in terms of one parameter, namely Mg# (=Mg/(Mg+Fe) atomic ratio). In contrast, some of the peridotites in the continental (cratonic) environment with high silica content and high Mg# need at least two parameters (such as Mg# and Opx# (the volume fraction of orthopyroxene)) are needed to characterize their seismic velocities. Second is the jump of seismic velocity at 300 km in harzburgite that is caused by orthorhombic (opx) to high-pressure monoclinic phase transition in MgSiO3 pyroxene. If opx-rich harzburgite (the maximum content of opx in continental harzburgite is ˜45 vol%) exists at around 300km, the maximum contrast of jump would be 2.5 % for VS and 0.9 % for VP. This phase transition will correspond to the seismological discontinuity around 300km (X-discontinuity).

Consequences of Melt-Preferred Orientation for Magmatic Segregation in Deforming Mantle Rock

NASA Astrophysics Data System (ADS)

Katz, R. F.; Taylor-West, J.; Allwright, J.; Takei, Y.; Qi, C.; Kohlstedt, D. L.

2014-12-01

In partially molten regions of the mantle, deviatoric stresses cause large-scale deformation and mantle flow. The same stresses also lead to preferential wetting of coherently oriented grain boundaries [DK97, T10]. This alignment is called melt-preferred orientation (MPO). Because of the contrast between the physical properties of melt and solid grains, MPO has the potential to introduce anisotropy into the mechanical and transport properties of the liquid/solid aggregate. Here we consider the possible consequences for (and of) anisotropic viscosity and permeability of the partially molten aggregate. The consequences are evaluated in the context of laboratory experiments on partially molten rocks. The controlled experiments involve deformation of an initially uniform mixture of solid olivine and liquid basalt [KZK10]. The resultant patterns of melt segregation include two robust features: (i) melt segregation into bands with high melt fraction oriented at a low angle to the shear plane; and (ii) melt segregation associated with an imposed gradient in shear stress, in experiments where this is present. Although there are other reproducible features of experiments, these are the most robust and provide a challenge to models. A theoretical model for the effect of MPO on mantle viscosity under diffusion creep is available [TH09] and makes predictions that are consistent with laboratory experiments [TK13,KT13,QKKT14,AK14]. We review the mechanics of this model and the predictions for flow in torsional and pipe Poiseuille flow, showing a quantitative comparison with experimental results. Furthermore, it is logical to expect MPO to lead to anisotropy of permeability, and we present a general model of tensorial permeability. We demonstrate the consequences of this anisotropy for simple shear deformation of a partially molten rock. REFERENCES: DK97 = Daines & Kohlstedt (1997), JGR, 10.1029/97JB00393. T10 = Takei (2010), JGR, 10.1029/2009JB006568. KZK10 = King, Zimmerman, & Kohlstedt (2010), J Pet, 10.1093/petrology/egp062. TH09 = Takei & Holtzman (2009a), JGR, 10.1029/2008JB005850. TK13 = Takei & Katz (2013), JFM, 10.1017/jfm.2013.482. KT13 = Katz & Takei (2013), JFM, 10.1017/jfm.2013.483. QKKT14 = Qi, Kohlstedt, Katz, Takei (in prep). AK14 = Allwright & Katz (2014), in revision for GJI.

Osmium mass balance in peridotite and the effects of mantle-derived sulphides on basalt petrogenesis

NASA Astrophysics Data System (ADS)

Harvey, J.; Dale, C. W.; Gannoun, A.; Burton, K. W.

2011-10-01

Analyses of enriched mantle (EM)-basalts, using lithophile element-based isotope systems, have long provided evidence for discrete mantle reservoirs with variable composition. Upon partial melting, the mantle reservoir imparts its isotopic fingerprint upon the partial melt produced. However, it has increasingly been recognised that it may not be simple to delimit these previously well-defined mantle reservoirs; the "mantle zoo" may contain more reservoirs than previously envisaged. Here we demonstrate that a simple model with varying contributions from two populations of compositionally distinct mantle sulphides can readily account for the observed heterogeneities in Os isotope systematics of such basalts without additional mantle reservoirs. Osmium elemental and isotopic analyses of individual sulphide grains separated from spinel lherzolites from Kilbourne Hole, New Mexico, USA demonstrate that two discrete populations of mantle sulphide exist in terms of both Re-Os systematics and textural relationship with co-existing silicates. One population, with a rounded morphology, is preserved in silicate grains and typically possesses high [Os] and low [Re] with unradiogenic, typically sub-chondritic 187Os/ 188Os attributable to long term isolation in a low-Re environment. By contrast, irregular-shaped sulphides, preserved along silicate grain boundaries, possess low [Os], higher [Re] and a wider range of, but generally supra-chondritic 187Os/ 188Os ([Os] typically ⩽ 1-2 ppm, 187Os/ 188Os ⩽ 0.3729; this study). This population is thought to represent metasomatic sulphide. Uncontaminated silicate phases contain negligible Os (<100 ppt) therefore the Os elemental and isotope composition of basalts is dominated by volumetrically insignificant sulphide ([Os] ⩽ 37 ppm; this study). During the early stages of partial melting, supra-chondritic interstitial sulphides are mobilised and incorporated into the melt, adding their radiogenic 187Os/ 188Os signature. Only when sulphides armoured within silicates are exposed to the melt through continued partial melting will enclosed sulphides add their high [Os] and unradiogenic 187Os/ 188Os to the aggregate melt. Platinum-group element data for whole rocks are also consistent with this scenario. The sequence of (i) addition of all of the metasomatic sulphide, followed by (ii) the incorporation of small amounts of armoured sulphide can thus account for the range of both [Os] and 187Os/ 188Os of EM-basalts worldwide without the need for contributions from additional silicate mantle reservoirs.

Investigation of solid phase composition on tablet surfaces by grazing incidence X-ray diffraction.

PubMed

Koradia, Vishal; Tenho, Mikko; Lopez de Diego, Heidi; Ringkjøbing-Elema, Michiel; Møller-Sonnergaard, Jørn; Salonen, Jarno; Lehto, Vesa-Pekka; Rantanen, Jukka

2012-01-01

To investigate solid state transformations of drug substances during compaction using grazing incidence X-ray diffraction (GIXD). The solid forms of three model drugs-theophylline (TP), nitrofurantoin (NF) and amlodipine besylate (AMB)-were compacted at different pressures (from 100 to 1000 MPa); prepared tablets were measured using GIXD. After the initial measurements of freshly compacted tablets, tablets were subjected to suitable recrystallization treatment, and analogous measurements were performed. Solid forms of TP, NF and AMB showed partial amorphization as well as crystal disordering during compaction; the extent of these effects generally increased as a function of pressure. The changes were most pronounced at the outer surface region. The different solid forms showed difference in the formation of amorphicity/crystal disordering. Dehydration due to compaction was observed for the TP monohydrate, whereas hydrates of NF and AMB were stable towards dehydration. With GIXD measurements, it was possible to probe the solid form composition at the different depths of the tablet surfaces and to obtain depth-dependent information on the compaction-induced amorphization, crystal disordering and dehydration.

Crystal growth of GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.; Pawlowicz, L. M.; Dabkowski, F.; Li, C. J.

1984-01-01

It is shown that stoichiometry variations in the GaAs melt during growth constitute the most critical parameter regarding defect formations and their interactions; this defect structure determines all relevant characteristics of GaAs. Convection in the melt leads to stoichiometric variations. Growth in axial magnetic fields reduces convection and permits the study of defect structure. In order to control stoichiometry in space and to accommodate expansion during solidification, a partially confined configuration was developed. A triangular prism is employed to contain the growth melt. This configuration permits the presence of the desired vapor phase in contact with the melt for controlling the melt stoichiometry.

Small amounts of CO2-H2O-rich melt in the lithosphere-asthenosphere.

NASA Astrophysics Data System (ADS)

Gaillard, Fabrice; Sifre, David; 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 so far ignored, including partial melting; (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 long been discussed (30 years ago) when petrologists have defined the petrological LAB as the 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 this 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 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. Incipient melts most likely trigger both the seismic low velocities and the high electrical conductivities in the upper part of the asthenosphere.

Deep Crustal Melting and the Survival of Continental Crust

NASA Astrophysics Data System (ADS)

Whitney, D.; Teyssier, C. P.; Rey, P. F.; Korchinski, M.

2017-12-01

Plate convergence involving continental lithosphere leads to crustal melting, which ultimately stabilizes the crust because it drives rapid upward flow of hot deep crust, followed by rapid cooling at shallow levels. Collision drives partial melting during crustal thickening (at 40-75 km) and/or continental subduction (at 75-100 km). These depths are not typically exceeded by crustal rocks that are exhumed in each setting because partial melting significantly decreases viscosity, facilitating upward flow of deep crust. Results from numerical models and nature indicate that deep crust moves laterally and then vertically, crystallizing at depths as shallow as 2 km. Deep crust flows en masse, without significant segregation of melt into magmatic bodies, over 10s of kms of vertical transport. This is a major mechanism by which deep crust is exhumed and is therefore a significant process of heat and mass transfer in continental evolution. The result of vertical flow of deep, partially molten crust is a migmatite dome. When lithosphere is under extension or transtension, the deep crust is solicited by faulting of the brittle upper crust, and the flow of deep crust in migmatite domes traverses nearly the entire thickness of orogenic crust in <10 million years. This cycle of burial, partial melting, rapid ascent, and crystallization/cooling preserves the continents from being recycled into the mantle by convergent tectonic processes over geologic time. Migmatite domes commonly preserve a record of high-T - low-P metamorphism. Domes may also contain rocks or minerals that record high-T - high-P conditions, including high-P metamorphism broadly coeval with host migmatite, evidence for the deep crustal origin of migmatite. There exists a spectrum of domes, from entirely deep-sourced to mixtures of deep and shallow sources. Controlling factors in deep vs. shallow sources are relative densities of crustal layers and rate of extension: fast extension (cm/yr) promotes efficient ascent of deep crust, whereas slow extension (mm/yr) produces significantly less exhumation. Recognition of the importance of migmatite (gneiss) domes as archives of orogenic deep crust is applicable to determining the chemical and physical properties of continental crust, as well as mechanisms and timescales of crustal differentiation.

Foveated Wide Field-of-View Imaging for Missile Warning/Tracking using Adaptive Optics

DTIC Science & Technology

2007-11-30

their melting temperatures are relatively high because of their long molecular conjugation. To lower the melting points, we have formulated eutectic ...compounds during recrystallization processes. 3. Polar, partially dissociated like organic acids, phenols or bases. Their dissociation level depends on the

Experimental segregation of iron-nickel metal, iron-sulfide, and olivine in a thermal gradient: Preliminary results

NASA Technical Reports Server (NTRS)

Jurewicz, Stephen R.; Jones, J. H.

1993-01-01

Speculation about the possible mechanisms for core formation in small asteroids raises more questions than answers. Petrologic evidence from iron meteorites, pallasites, and astronomical observations of M asteroids suggests that many small bodies were capable of core formation. Recent work by Taylor reviews the geochemical evidence and examines the possible physical/mechanical constraints on segregation processes. Taylor's evaluation suggests that extensive silicate partial melting (preferably 50 vol. percent or greater) is required before metal can segregate from the surrounding silicate and form a metal core. The arguments for large degrees of silicate partial melting are two-fold: (1) elemental trends in iron meteorites require that the metal was at is liquidus; and (2) experimental observations of metal/sulfide inclusions in partially molten silicate meteorites show that the metal/sulfide tends to form spherules in the liquid silicate due to surface tension effects. Taylor points out that for these metal spherules to sink through a silicate mush, high degrees of silicate partial melting are required to lower the silicate yield strength. Although some qualitative experimental data exists, little is actually known about the behavior of metals and liquid sulfides dispersed in silicate systems. In addition, we have been impressed with the ability of cumulative olivine to expel trapped liquid when placed in a thermal gradient. Consequently, we undertook to accomplish the following: (1) experimentally evaluate the potential for metal/sulfide/silicate segregation in a thermal gradient; and (2) obtain quantitative data of the wetting parameters of metal-sulfide melts among silicate grains.

CO2 content of andesitic melts at graphite-saturated upper mantle conditions with implications for redox state of oceanic basalt source regions and remobilization of reduced carbon from subducted eclogite

NASA Astrophysics Data System (ADS)

Eguchi, James; Dasgupta, Rajdeep

2017-03-01

We have performed experiments to determine the effects of pressure, temperature and oxygen fugacity on the CO2 contents in nominally anhydrous andesitic melts at graphite saturation. The andesite composition was specifically chosen to match a low-degree partial melt composition that is generated from MORB-like eclogite in the convective, oceanic upper mantle. Experiments were performed at 1-3 GPa, 1375-1550 °C, and fO2 of FMQ -3.2 to FMQ -2.3 and the resulting experimental glasses were analyzed for CO2 and H2O contents using FTIR and SIMS. Experimental results were used to develop a thermodynamic model to predict CO2 content of nominally anhydrous andesitic melts at graphite saturation. Fitting of experimental data returned thermodynamic parameters for dissolution of CO2 as molecular CO2: ln( K 0) = -21.79 ± 0.04, Δ V 0 = 32.91 ± 0.65 cm3mol-1, Δ H 0 = 107 ± 21 kJ mol-1, and dissolution of CO2 as CO3 2-: ln (K 0 ) = -21.38 ± 0.08, Δ V 0 = 30.66 ± 1.33 cm3 mol-1, Δ H 0 = 42 ± 37 kJ mol-1, where K 0 is the equilibrium constant at some reference pressure and temperature, Δ V 0 is the volume change of reaction, and Δ H 0 is the enthalpy change of reaction. The thermodynamic model was used along with trace element partition coefficients to calculate the CO2 contents and CO2/Nb ratios resulting from the mixing of a depleted MORB and the partial melt of a graphite-saturated eclogite. Comparison with natural MORB and OIB data suggests that the CO2 contents and CO2/Nb ratios of CO2-enriched oceanic basalts cannot be produced by mixing with partial melts of graphite-saturated eclogite. Instead, they must be produced by melting of a source containing carbonate. This result places a lower bound on the oxygen fugacity for the source region of these CO2-enriched basalts, and suggests that fO2 measurements made on cratonic xenoliths may not be applicable to the convecting upper mantle. CO2-depleted basalts, on the other hand, are consistent with mixing between depleted MORB and partial melts of a graphite-saturated eclogite. Furthermore, calculations suggest that eclogite can remain saturated in graphite in the convecting upper mantle, acting as a reservoir for C.

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

NASA Astrophysics Data System (ADS)

Hill, Graham J.; Caldwell, T. Grant; Heise, Wiebke; Chertkoff, Darren G.; Bibby, Hugh M.; Burgess, Matt K.; Cull, James P.; Cas, Ray A. F.

2009-11-01

Three prominent volcanoes that form part of the Cascade mountain range in Washington State (USA)-Mounts St Helens, Adams and Rainier-are located on the margins of a mid-crustal zone of high electrical conductivity. Interconnected melt can increase the bulk conductivity of the region containing the melt, 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 this volcano 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 Helens, and explains the distribution of seismicity observed at the time of the catastrophic eruption in 1980 (refs 9, 10).

The evolution of continental roots in numerical thermo-chemical mantle convection models including differentiation by partial melting

NASA Astrophysics Data System (ADS)

de Smet, J. H.; van den Berg, A. P.; Vlaar, N. J.

1999-09-01

Incorporating upper mantle differentiation through decompression melting in a numerical mantle convection model, we demonstrate that a compositionally distinct root consisting of depleted peridotite can grow and remain stable during a long period of secular cooling. Our modeling results show that in a hot convecting mantle partial melting will produce a compositional layering in a relatively short time of about 50 Ma. Due to secular cooling mantle differentiation finally stops before 1 Ga. The resulting continental root remains stable on a billion year time scale due to the combined effects of its intrinsically lower density and temperature-dependent rheology. Two different parameterizations of the melting phase-diagram are used in the models. The results indicate that during the Archaean melting occurred on a significant scale in the deep regions of the upper mantle, at pressures in excess of 15 GPa. The compositional depths of continental roots extend to 400 km depending on the potential temperature and the type of phase-diagram parameterization used in the model. The results reveal a strong correlation between lateral variations of temperature and the thickness of the continental root. This shows that cold regions in cratons are stabilized by a thick depleted root.

Highly Siderophile Elements and Osmium Isotope Systematics in Ureilites: Are the Carbonaceous Veins Primary Components?

NASA Technical Reports Server (NTRS)

Rankenburg, K.; Brandon, A. D.; Humayun, M.

2005-01-01

Ureilites are an enigmatic group of primitive carbon-bearing achondrites of ultramafic composition. The majority of the 143 ureilite meteorites consist primarily of olivine and pyroxene (and occasionally chromite) [1]. They are coarse-grained, slowly cooled, and depleted in incompatible lithophile elements. Minor amounts of dark interstitial material consisting of carbon, metal, sulfides, and fine-grained silicates occur primarily along silicate grain boundaries, but also intrude the silicates along fractures and cleavage planes. Variable degrees of impact shock features have also been imparted on ureilites. The prevailing two origins proposed for these rocks are either as melting residues of carbonaceous chondritic material [2], [3], or alternatively, derivation as mineral cumulates from such melts [4], [5], [6]. It has recently been proposed that ureilites are the residues of a smelting event, i.e. residues of a partial melting event under highly reducing conditions, where a solid Fe-bearing phase reacts with a melt and carbon to form Fe metal and carbon monoxide [7]. Rapid, localized extraction and loss of the basaltic component into space resulting from high eruption velocities could preserve unequilibrated oxygen isotopes and produce the observed olivine-pyroxene residues via 25-30% partial melting of chondritic-like precursor material.

The birth, growth and ageing of the Kaapvaal subcratonic mantle

NASA Astrophysics Data System (ADS)

Brey, Gerhard P.; Shu, Qiao

2018-06-01

The Kaapvaal craton and its underlying mantle is probably one of the best studied Archean entity in the world. Despite that, discussion is still vivid on important aspects. A major debate over the last few decades is the depth of melting that generated the mantle nuclei of cratons. Our new evaluation of melting parameters in peridotite residues shows that the Cr2O3/Al2O3 ratio is the most useful pressure sensitive melting barometer. It irrevocably constrains the pressure of melting (melt separation) to less than 2 GPa with olivine (ol), orthopyroxene (opx) and spinel (sp) as residual phases. Garnet (grt) grows at increasing pressure during lithosphere thickening and subduction via the reaction opx + sp → grt + ol. The time of partial melting is constrained by Re-depletion model ages (TRD) mainly to the Archean (Pearson and Wittig 2008). However, only 3% of the ages are older than 3.1 Ga while crustal ages lie mainly between 3.1 to 2.8 Ga for the W- and 3.7 to 2.8 Ga for the E-block. Many TRD-ages are probably falsified by metasomatism and the main partial melting period was older than 3.1 Ga. Also, Nd- and Hf- model ages of peridotitic lithologies from the W-block are 3.2 to 3.6 Ga old. The corresponding very negative ɛNd (-40) and ɛHf values (-65) signal the presence of subducted crustal components in these old mantle portions. Subducted components diversify the mantle in its chemistry and thermal structure. Adjustment towards a stable configuration occurs by fluid transfer, metasomatism, partial melting and heat transfer. Ages of metasomatism from the Lu-Hf isotope system are 3.2 Ga (Lace), 2.9 Ga (Roberts Victor) and 2.62 Ga (Finsch) coinciding with the collision of cratonic blocks, the growth of diamonds, metamorphism of eclogites and of Ventersdoorp magmatism. The cratonic lithosphere was stabilized thermally by the end of the Archean and cooled since then with a rate of 0.07 °C/Ma.

Processes in continental collision zones: Preface

NASA Astrophysics Data System (ADS)

Zheng, Yong-Fei; Zhang, Lifei; McClelland, William C.; Cuthbert, Simon

2012-04-01

Formation and exhumation of high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks in continental subduction zones are the two fundamental geodynamic aspects of collisional orogensis. This volume is based on the Session 08c titled "Geochemical processes in continental collision zones" at Goldschmidt 2010 in Knoxville, USA. It focuses on micro- to macro-scale processes that are temporally and spatially linked to different depths of crustal subduction/exhumation and associated mineralogical changes. They are a key to understanding a wide spectrum of phenomena, involving HP/UHP metamorphism and syn-/post-collisional magmatism. Papers in this volume report progresses in petrological, geochronological and geochemical studies of UHP metamorphic rocks and their derivatives in China, with tectonic settings varying from arc-continent collision to continent-continent collision. Microbeam in-situ analyses of metamorphic and magmatic minerals are successfully utilized to solve various problems in the study of continental deep subduction and UHP metamorphism. In addition to their geochronological applications to dating of HP to UHP metamorphic events during continental collision, microbeam techniques have also served as an efficient means to recognize different generations of mineral growth during continental subduction-zone metamorphism. Furthermore, metamorphic dehydration and partial melting of UHP metamorphic rocks during subduction and exhumation are highlighted with respect to their effects on fluid action and element mobilization. These have provided new insights into chemical geodynamics in continental subduction zones.

Characterisation of nimesulide-betacyclodextrins systems prepared by supercritical fluid impregnation.

PubMed

Moneghini, M; Kikic, I; Perissutti, B; Franceschinis, E; Cortesi, A

2004-11-01

The purpose of this study was to apply the supercritical CO(2) impregnation process for preparing solvent-free nimesulide (NMS)-betacyclodextrins (BCD) association systems with enhanced drug dissolution rate. Several drug-to-carrier molar ratios were tested (1:1; 1:2.5; 1:3.5) at different conditions of temperatures (40, 100, and 130 degrees C) and pressures (140, 190 or 220 bar). The physical and morphological characterisation of the systems using powder X-ray diffraction, thermal analysis, diffuse reflectance Fourier transform-infrared spectroscopy and scanning electron microscopy was carried out to understand the influence of this technological process on the physical status of single components and binary systems and to detect possible interactions between drug and carrier. These analyses provided no evidence of a complete inclusion of NMS in the carrier but the existence of interactions between drug and carrier together with a partial dehydration of the BCD and the formation of drug crystallites with lower melting point and heat of fusion than the native NMS. These phenomena were more intense when severe conditions of pressure and temperature (220 bar and 130 degrees C) were used during impregnation trials and when the amount of BCD augmented in the systems. These activated solid state of the impregnated systems promoted an enhancement of drug dissolution rate that, in keeping with the results of the physical characterisation, was function of the process conditions and BCD content.

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 quantify the amounts of H_2O. This is necessary, as Pt capsules are to some extent open to H_2 diffusion. All melts were found to contain CO_2 (<0.7 wt%), which appears to come mainly from the hydroxide starting materials but also by C diffusion through the Pt capsule. Since CO_2 is experimentally correlated with H_2O, its presence significantly effects the interpretation of the results. Ignoring this complication, we find that 1 wt% H_2O decreases the solidus by ˜40 K; melt compositions do not change greatly, the main effect being a small decrease in MgO.

Is EETA79001 Lithology B A True Melt Composition?

NASA Technical Reports Server (NTRS)

Arauza, S. J.; Jones, John H.; Mittlefehldt, D. W.; Le, L.

2010-01-01

EETA79001 is a member of the SNC (shergottite, nakhlite, chassignite) group of Martian meteorites. Most SNC meteorites are cumulates or partial cumulates [1] inhibiting calculation of parent magma compositions; only two (QUE94201 and Y- 980459) have been previously identified as true melt compositions. The goal of this study is to test whether EETA79001-B may also represent an equilibrium melt composition, which could potentially expand the current understanding of martian petrology.

Interpretation of trace element and isotope features of basalts: relevance of field relations, petrology, major element data, phase equilibria, and magma chamber modeling in basalt petrogenesis

NASA Astrophysics Data System (ADS)

O'Hara, M. J.; Herzberg, C.

2002-06-01

The concentrations and ratios of the major elements determine the physical properties and the phase equilibria behavior of peridotites and basalts in response to the changing energy contents of the systems. The behavior of the trace elements and isotopic features are influenced in their turn by the phase equilibria, by the physical character of the partial melting and partial crystallization processes, and by the way in which a magma interacts with its wall rocks. Concentrating on the trace element and isotope contents of basalts to the exclusion of the field relations, petrology, major element data, and phase equilibria is as improvident as slaughtering the buffalo for the sake of its tongue. The crust is a cool boundary layer and a density filter, which impedes the upward transfer of hot, dense "primary" picritic and komatiitic liquids. Planetary crusts are sites of large-scale contamination and extensive partial crystallization of primitive melts striving to escape to the surface. Escape of truly unmodified primitive melts to the surface is a rare event, requiring the resolution of daunting problems in chemical and mechanical engineering. Primary status for volumetrically abundant basalts such as mid-ocean ridge basalt, ocean island basalt, and continental flood basalts is denied by their low-pressure cotectic character, first remarked upon on petrological grounds in 1928 and on experimental grounds in 1962. These basalt liquids are products of crystal-liquid separation at low pressure. Primary status for these common basalts is further denied by the phase equilibria of such compositions at elevated pressures, when the required residual mantle mineralogy (magnesian olivine and orthopyroxene) is not stable at the liquidus. It is also denied by the picritic or komatiitic nature of partial melts of candidate upper-mantle compositions at high pressures - a conclusion supported by calculation of the melt composition, which would need to be extracted in order to explain the chemical variation between fertile and residual peridotite in natural ultramafic rock suites. The subtleties of magma chamber partial crystallization processes can produce an astounding array of "pseudospidergrams," a small selection of which have been explored here. Major modification of the trace element geochemistry and trace element ratios, even those of the highly incompatible elements, must always be entertained whenever the evidence suggests the possibility of partial crystallization. At one extreme, periodically recharged, periodically tapped magma chambers might undergo partial crystallization by ˜95% consolidation of a succession of small packets of the magma. Refluxing of the 5% residual melts from such a process into the main body of melt would lead to eventual discrimination between highly incompatible elements in that residual liquid comparable with that otherwise achieved by 0.1 to 0.3% liquid extraction in equilibrium partial melting. Great caution needs to be exercised in attempting the reconstruction of more primitive compositions by addition of troctolite, gabbro, and olivine to apparently primitive lava compositions. Special attention is focussed on the phase equilibria involving olivine, plagioclase (i.e., troctolite), and liquid because a high proportion of erupted basalts carry these two phases as phenocrysts, yet the equilibria are restricted to crustal pressures and are only encountered by wide ranges of basaltic compositions at pressures less than 0.5 GPa. The mere presence of plagioclase phenocrysts may be sufficient to disqualify candidate primitive magmas. Determination of the actual contributions of crustal processes to petrogenesis requires a return to detailed field, experimental, and forensic petrologic studies of individual erupted basalt flows; of a multitude of cumulate gabbros and their contacts; and of upper-mantle outcrops.

The Meaning of "Magma"

NASA Astrophysics Data System (ADS)

Bartley, J. M.; Glazner, A. F.; Coleman, D. S.

2016-12-01

Magma is a fundamental constituent of the Earth, and its properties, origin, evolution, and significance bear on issues ranging from volcanic hazards to planetary evolution. Unfortunately, published usages indicate that the term "magma" means distinctly different things to different people and this can lead to miscommunication among Earth scientists and between scientists and the public. Erupting lava clearly is magma; the question is whether partially molten rock imaged at depth and too crystal-rich to flow should also be called magma. At crystal fractions > 50%, flow can only occur via crystal deformation and solution-reprecipitation. As the solid fraction increases to 90% or more, the material becomes a welded crystal framework with melt in dispersed pores and/or along grain boundaries. Seismic images commonly describe such volumes of a few % melt as magma, yet the rheological differences between melt-rich and melt-poor materials make it vital not to confuse a large rock volume that contains a small melt fraction with melt-rich material. To ensure this, we suggest that "magma" be reserved for melt-rich materials that undergo bulk fluid flow on timescales consonant with volcanic eruptions. Other terms should be used for more crystal-rich and largely immobile partially molten rock (e.g., "crystal mush," "rigid sponge"). The distinction is imprecise but useful. For the press, the public, and even earth scientists who do not study magmatic systems, "magma" conjures up flowing lava; reports of a large "magma" body that contains a few percent melt can engender the mistaken perception of a vast amount of eruptible magma. For researchers, physical processes like crystal settling are commonly invoked to account for features in plutonic rocks, but many such processes are only possible in melt-rich materials.

Petro-tectonic Analysis of the Plagiogranite Intrusions in the Khor Fakkan Block of the Semail Ophiolites

NASA Astrophysics Data System (ADS)

Kokkalas, S.; Joun, H.; Tombros, S.

2017-12-01

Plagiogranite intrusions are common in the Khor Fakkan block of the Semail ophiolite, where the mantle sequence is predominant. Several models have been proposed for the source of these leucocratic intrusions, but their genesis is still under debate. The examined plagiogranites are characterized by 68 wt. % SiO2 and display volcanic-arc granite affinity. They have crystallize at temperatures that range from 550° to 720o C and pressures ranging from 5.0 to 6.5 Kbars. The parental plagiogranite melts, based on the relations of the δ18Omelt or δ18OH2O versus eSr suggest mixing of subducted crust with overlying upper mantle. The relatively wide range of the 87Rb/86Sr ratios, at almost constant 87Sr/86Sr, implies that partial melting and mixing was followed by fractional crystallization. The isotopic ages from the examined plagiogranites range between 94.9-98.5 Ma, predating the sole metamorphism. Based on our source contribution calculations, 96% of the igneous and 4% of sedimentary end-member components are involved in formation of plagiogranitic melts. The igneous end-member derived from partial melting of 3 % upper mantle and 97% recycled oceanic crust. We propose that the mafic melts were initially produced by the off-axis melting of recycled oceanic slab under a compressional regime a supra-subduction zone (SSZ) setting. The mafic melts were modified due to mixing with small amount of melts from the upper mantle by influx of slab-derived fluids. Then these melts underwent extended fractional crystallization with crystallization of An-enriched plagioclase and emplaced on the Moho level to form Dadnah plagiogranites in the Khor Fakkan block.

Modeling of axial vibrational control technique for CdTe VGF crystal growth under controlled cadmium partial pressure

NASA Astrophysics Data System (ADS)

Avetissov, I.; Kostikov, V.; Meshkov, V.; Sukhanova, E.; Grishechkin, M.; Belov, S.; Sadovskiy, A.

2014-01-01

A VGF growth setup assisted by axial vibrations of baffle submerged into CdTe melt with controlled Cd partial pressure was designed. An influence of baffle shape on flow velocity map, temperature distribution in CdTe melt and interface shape of growing crystal was analyzed by numerical simulation and physical modeling. To produce the desirable shape of crystal melt interface we slant under different angles vertical generatrix in a cylindrical disk and made chasing on faceplates of a disk. It was ascertained that a disk with conical generatrix formed more intensive convective flows from a faceplate with larger diameter. It was shown that at CdTe VGF crystal growth rate about 10 mm/h application of AVC technique made it possible to produce convex interface for 2 in. crystal diameter.

Petrogenesis of granodiorite in the Balong region, eastern Kunlun Orogen, China: Constraints from zircon U-Pb geochronology, geochemistry and Sr-Nd-Hf isotopes

NASA Astrophysics Data System (ADS)

Huang, X.; Li, H.; Wang, Y.; Liu, Y.

2017-12-01

Numerous granitoid intrusions that close to the Balong region have great scientific significance to reveal tectonic evolution and geodynamic background of eastern Kunlun Orogen (EKO). Balong granodiorite (BLG) is located at the northern of the EKO. It generally emplaced into the Proterozoic to Lower Palaeozoic rocks and contains abundant mafic microgranular enclaves. LA-ICP-MS zircon U-Pb dating of the BLG gives a 206Pb/238U age of 230.7±1.9 Ma, indicating that it was emplaced in the Late Triassic. The BLG is high-K calc-alkaline series and metaluminous, with SiO2 of 59.86 61.83%, K2O+Na2O of 5.98 6.40%, CaO of 4.95 5.77% and P2O5 of 0.14% 0.18%. The granodioritic rocks are enriched in LILE (Ba, Rb, Sr), but depleted in HFSE (Nb, Ta, P, Ti), with weak negative Eu anomalies (δEu=0.70 0.82). Mineralogy and geochemistry of the rocks show an affinity to I-type granite. The BLG, having (87Sr/86Sr)i ratios of 0.70819 to 0.70832, ɛNd(t) values of -5.27 to -5.75, and zircon ɛHf(t) values ranging from -3.86 to -1.34. The whole-rock Nd isotopic model ages (1432 1471 Ma) and zircon Hf isotopic model ages (1205 1357 Ma) indicate that the BLG is generated by partial melting of lower crust (Precambrian metabasaltic basement rocks) with different degree of involvement of mantle material. Combined with regional geological data, the granodiorite was derived from dehydration melting of mafic lower crustal rocks during the subduction of the Anyemaqen ocean lithosphere at Late Permian-Triassic in a subduction setting. Basaltic magma underplating and crust-mantle mixing are main mechanisms for the origin of large-scale I-type granitoid in Balong.

Transfer of subduction fluids into the deforming mantle wedge during nascent subduction: Evidence from trace elements and boron isotopes (Semail ophiolite, Oman)

NASA Astrophysics Data System (ADS)

Prigent, C.; Guillot, S.; Agard, P.; Lemarchand, D.; Soret, M.; Ulrich, M.

2018-02-01

The basal part of the Semail ophiolitic mantle was (de)formed at relatively low temperature (LT) directly above the plate interface during "nascent subduction" (the prelude to ophiolite obduction). This subduction-related LT deformation was associated with progressive strain localization and cooling, resulting in the formation of porphyroclastic to ultramylonitic shear zones prior to serpentinization. Using petrological and geochemical analyses (trace elements and B isotopes), we show that these basal peridotites interacted with hydrous fluids percolating by porous flow during mylonitic deformation (from ∼850 down to 650 °C). This process resulted in 1) high-T amphibole crystallization, 2) striking enrichments of minerals in fluid mobile elements (FME; particularly B, Li and Cs with concentrations up to 400 times those of the depleted mantle) and 3) peridotites with an elevated δ11B of up to +25‰. These features indicate that the metasomatic hydrous fluids are most likely derived from the dehydration of subducting crustal amphibolitic materials (i.e., the present-day high-T sole). The rapid decrease in metasomatized peridotite δ11B with increasing distance to the contact with the HT sole (to depleted mantle isotopic values in <1 km) suggests an intense interaction between peridotites and rapid migrating fluids (∼1-25 m.y-1), erasing the initial high-δ11B subduction fluid signature within a short distance. The increase of peridotite δ11B with increasing deformation furthermore indicates that the flow of subduction fluids was progressively channelized in actively deforming shear zones parallel to the contact. Taken together, these results also suggest that the migration of subduction fluids/melts by porous flow through the subsolidus mantle wedge (i.e., above the plate interface at sub-arc depths) is unlikely to be an effective mechanism to transport slab-derived elements to the locus of partial melting in subduction zones.

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).

Melt-Vapor Phase Diagram of the Te-S System

NASA Astrophysics Data System (ADS)

Volodin, V. N.; Trebukhov, S. A.; Kenzhaliyev, B. K.; Nitsenko, A. V.; Burabaeva, N. M.

2018-03-01

The values of partial pressure of saturated vapor of the constituents of the Te-S system are determined from boiling points. The boundaries of the melt-vapor phase transition at atmospheric pressure and in vacuum of 2000 and 100 Pa are calculated on the basis of partial pressures. A phase diagram that includes vapor-liquid equilibrium fields whose boundaries allow us to assess the behavior of elements upon distillation fractioning is plotted. It is established that the separation of elements is possible at the first evaporation-condensation cycle. Complications can be caused by crystallization of a sulfur solid solution in tellurium.

Melt inclusions in alluvial sapphires from Montana, USA: Formation of sapphires as a restitic component of lower crustal melting?

NASA Astrophysics Data System (ADS)

Palke, Aaron C.; Renfro, Nathan D.; Berg, Richard B.

2017-05-01

We report here compositions of glassy melt inclusions hosted in sapphires (gem quality corundum) from three alluvial deposits in Montana, USA including the Rock Creek, Dry Cottonwood Creek, and Missouri River deposits. While it is likely that sapphires in these deposits were transported to the surface by Eocene age volcanic events, their ultimate origin is still controversial with many models suggesting the sapphires are xenocrysts with a metamorphic or metasomatic genesis. Melt inclusions are trachytic, dacitic, and rhyolitic in composition. Microscopic observations allow separation between primary and secondary melt inclusions. The primary melt inclusions represent the silicate liquid that was present at the time of sapphire formation and are enriched in volatile components (8-14 wt.%). Secondary melt inclusions analyzed here for Dry Cottonwood Creek and Rock Creek sapphires are relatively volatile depleted and represent the magma that carried the sapphires to the surface. We propose that alluvial Montana sapphires from these deposits formed through a peritectic melting reaction during partial melting of a hydrated plagioclase-rich protolith (e.g. an anorthosite). The heat needed to drive this reaction was likely derived from the intrusion of mantle-derived mafic magmas near the base of the continental lithosphere during rollback of the Farallon slab around 50 Ma. These mafic magmas may have ended up as the ultimate carrier of the sapphires to the surface as evidenced by the French Bar trachybasalt near the Missouri River deposit. Alternatively, the trachytic, rhyolitic, and dacitic secondary melt inclusions at Rock Creek and Dry Cottonwood Creek suggests that the same magmas produced during the partial melting event that generated the sapphires may have also transported them to the surface. Determining the genesis of these deposits will further our understanding of sapphire deposits around the world and may help guide future sapphire prospecting techniques. This work is also important to help reveal the history of mantle-derived mafic magmas as they pass through the continental crust.

Interpreting Continental Break-Up From Surface Observations: Analysis of 1D Partial Melting Using Synthetic Waveform Propagation

NASA Astrophysics Data System (ADS)

Franken, T.; Armitage, J. J.; Fuji, N.; Fournier, A.

2017-12-01

Low shear-wave velocity zones underneath margins of continental break-up are believed to be related to the presence of melt. Many models attempt to model the process of melt production and transportation during mantle upwelling, yet there is a disconnect between geodynamic models, seismic observations, and petrological studies of melt flow velocities. Geodynamic models that emulate melt retention of 2 %, suggested by shear-wave velocity anomalies (Forsyth & MELT Seismic Team, 1998), fail to adequately reproduce the seismic signal as seen in receiver functions (Rychert, 2012; Armitage et al., 2015). Furthermore, numerical models of melt migration conclude mean melt flow velocities up to 1,3 m yr-1(Weatherley & Katz, 2015), whereas Uranium isotope migration rates advocate velocities up to two orders of magnitude higher. This study aims to reconcile the diverting assertions on the partial melting process by analysing the effect of melt presence on the coda of the seismic signal. A 1D forward model has been created to emulate melt production and transportation in an upwelling mantle environment. Scenarios have been modelled for variable upwelling velocities v (1 - 100 mm yr-1), initial temperatures T0 (1200 - 1800 °C) and permeabilities k0 (10-9 - 10-5 m2). The 1D model parameters are converted to anharmonic seismic parameters using look-up tables from phase diagrams (Goes et al., 2012) to generate synthetic seismograms with the Direct Solution Method. The maximum frequency content of the synthetics is 1,25 Hz, sampled at 20 Hz with a low-pass filter of 0,1 Hz. A comparison between the synthetics and seismic observations of the La Reunion mantle plume from the RER Geoscope receiver is performed using a Monte-Carlo approach. The synthetic seismograms show highest sensitivity to the presence of melt in S-waves within epicentral distances of 0-20 degrees. In the 0-10 degree range only a time-shift is observed proportional to the melt fraction at the onset of melting. Within the 10-20 degree range the presence of melt causes an additional change in the coda of the signal compared to a no-melt model. By analysing these altered synthetic waveforms we search for a seismic signature corresponding to melt presence to form a benchmark for the comparison between the Monte-Carlo results and the seismic observations.

A Tale of Two Melt Rocks: Equilibration and Metal/Sulfide-Silicate Segregation in the L7 Chondrites PAT 91501 and LEW 88663

NASA Astrophysics Data System (ADS)

Harvey, R. P.

1993-07-01

Type 7 ordinary chondrites have experienced temperatures near or beyond those necessary for partial melting. Two recently collected Antarctic specimens, PAT91501 (PAT) and LEW88663 (LEW), have been tentatively identified as L7 chondrites based on mineral and oxygen isotope compositions [1,2]. The petrology and mineralogy of these meteorites suggests that they have undergone significant metal/sulfide-silicate segregation, with implications for meteorite parent bodies. PAT consists of an equigranular contact-framework of nearly euhedral olivine grains, with interstitial spaces filled by plagioclase, pyroxenes, and several minor phases. Ortho- and clinopyroxene occur in an exsolution relationship. Olivine and pyroxene are highly equilibrated, varying <<1% in Fe-endmember content. Pyroxene equilibration temperatures calculated for PAT using the methods of [3] are self-consistent at about 1180 degrees C. In thin section, PAT contains only traces of metal, as tiny isolated blebs in sulfide grains; large (>1 cm) globular sulfide inclusions are seen in hand-sample [1], but are not present in the section examined. LEW was originally classified as an achondrite with olivine and pyroxene compositions similar to those in L chondrites [2]. Metal is absent in LEW, although the specimen is small and heavily rusted, making it impossible to gauge the original metal content. Olivine grains are commonly rounded in shape and seldom in contact with more than a few other grains. LEW olivine and pyroxene are also highly equilibrated. Veins of Ni-bearing metal oxides and sulfides are common. Both low- and high-Ca pyroxene occur as discrete grains, orthopyroxene often poikilitically enclosing olivine. Pyroxene equilibration temperatures for LEW are more variable than those for PAT and consistently lower, with an average around 900 degrees C. The various textural and compositional characteristics of PAT and LEW suggest they have experienced partial melting to varying degrees. Both visually resemble charges from experimental melting of ordinary chondrites [4-6]. The cumulate-like framework of olivine crystals in PAT suggests a high degree of partial melting, at peak temperatures sufficient to melt all other phases (above 1400 degrees C) [6]. The spheroidal sulfide nodules in PAT and the occurrence of metal (when present) only in association with sulfide strongly suggest gravitational segregation of a metal/sulfide liquid from a partial melt of the original chondritic assemblage. LEW features suggest less partial melting. Veins and grain coatings of sulfides and Fe-Ni oxides (that were probably metal before weathering) infer exposure to temperatures of 900-1000 degrees C [5]. The non-uniform olivine grain size and presence of remnant clinopyroxene grains in LEW imply that peak temperatures reached by this meteorite were not higher than 1200 degrees C [6]. The partial melting observed in PAT and LEW is probably a result of shock heating during impacts, as proposed in studies of Shaw (L7) and other similar lithologies [7]. If significant metal/sulfide-silicate segregation can occur in the relatively small volumes and short heating times associated with impact melting, even small planetesimals might be differentiated. This implies that the timescale necessary for planetary differentiation might have been significantly shortened by the assembly of already differentiated planetesimals to form meteorite parent bodies [8]. References: [1] Mason B. et al. (1992) Ant. Met. News., 15(2), 30. [2] Mason B. and Marlow R. (1992) Ant. Met. News., 15(1), 16. [3] Fonarev V. I. and Graphchikov A. A. (1991) In Progress in Metamorphic and Magmatic Petrology (L. L. Perchuk, ed.), 65-92, Cambridge University. [4] Smith B. A. and Goldstein J. I. (1977) GCA, 41, 1061-1072. [5] McSween H. Y. Jr. et al. (1978) LPS IX, 1437-1447. [6] Takahashi E. (1983) NIPR Spec. Is., 30, 168-180. [7] Taylor G. J. et al. (1979) GCA, 43, 323-337. [8] Taylor G. J. JGR, 97, 14717-14726.

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

NASA Astrophysics Data System (ADS)

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

2016-12-01

Alkaline lavas occur globally in subduction-related volcanic arcs. Existing explanations for the occurrence of alkaline lavas in volcanic arcs invoke at least one - and in some cases multiple - `metasomatic' events in addition to the traditional three-component mixing of altered oceanic crust (AOC), sediment melt, and depleted mantle, in order to explain the range of rock types found in a given region. These multi-stage models posit the existence of metasomatized mantle wedge peridotite containing phlogopite or amphibole-enriched veins, which partially melt when fluxed by the addition of materials from the subducted slab. The mélange diapir model is informed by observations and modeling of the subduction side of the arc system, and predicts the generation of alkaline arc magmas by advection of buoyant material from the slab-wedge interface into the mantle wedge below arcs. Here we report results from experiments in which natural mélange materials partially melted at upper mantle conditions were found to produce alkaline magmas compositionally similar to those found in arcs worldwide. The starting material for our experiments is a chlorite-omphacite fels (SY400) from the island of Syros, Greece, that is representative of a hybrid rock containing AOC, sediment, and mantle components. Melting experiments were performed using a piston cylinder apparatus at conditions relevant to the heating-decompression path of mélange diapirs (1000-1300 °C, 1.5-2.5 GPa). The compositions of experimentally produced melts range from 51-61 wt% SiO2, and fall within the trachyte and tephrite-phonolite series (7.5-12.9 wt% Na2O+K2O). Restitic phases in equilibrium with melt include clinopyroxene, garnet (at high P), phlogopite (at high P), amphibole, olivine, rutile, and ilmenite. Partial melts produced in our experiments have trace-element abundance patterns that are typical of alkaline arc lavas, such as enrichment in large ion lithophile elements (Cs, Rb, Ba, Pb, Sr) and alkalis (K and Na), and depletion in Nb and Ta. The presence of a light rare earth element (LREE)-bearing accessory phase results in trace element fractionation by a factor of 4.2 for Nd/Hf and 2.6 for Sr/Nd. Melting of mélange diapirs provides a simple, single-stage model for the origin of alkaline magmatism in the arc and backarc regions of subduction zones.

Poly(ethylene glycol) layered silicate nanocomposites for retarded drug release prepared by hot-melt extrusion.

PubMed

Campbell, Kayleen; Craig, Duncan Q M; McNally, Tony

2008-11-03

Composites of paracetamol loaded poly(ethylene glycol) (PEG) with a naturally derived and partially synthetic layered silicate (nanoclay) were prepared using hot-melt extrusion. The extent of dispersion and distribution of the paracetamol and nanoclay in the PEG matrix was examined using a combination of field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and wide-angle X-ray diffraction (WAXD). The paracetamol polymorph was shown to be well dispersed in the PEG matrix and the nanocomposite to have a predominately intercalated and partially exfoliated morphology. The form 1 monoclinic polymorph of the paracetamol was unaltered after the melt mixing process. The crystalline behaviour of the PEG on addition of both paracetamol and nanoclay was investigated using differential scanning calorimetry (DSC) and polarised hot-stage optical microscopy. The crystalline content of PEG decreased by up to 20% when both drug and nanoclay were melt blended with PEG, but the average PEG spherulite size increased by a factor of 4. The time taken for 100% release of paracetamol from the PEG matrix and corresponding diffusion coefficients were significantly retarded on addition of low loadings of both naturally occurring and partially synthetic nanoclays. The dispersed layered silicate platelets encase the paracetamol molecules, retarding diffusion and altering the dissolution behaviour of the drug molecule in the PEG matrix.

Faulting induced by precipitation of water at grain boundaries in hot subducting oceanic crust.

PubMed

Zhang, Junfeng; Green, Harry W; Bozhilov, Krassimir; Jin, Zhenmin

2004-04-08

Dehydration embrittlement has been proposed to explain both intermediate- and deep-focus earthquakes in subduction zones. Because such earthquakes primarily occur at shallow depths or within the core of the subducting plate, dehydration at relatively low temperatures has been emphasized. However, recent careful relocation of subduction-zone earthquakes shows that at depths of 100-250 km, earthquakes continue in the uppermost part of the slab (probably the former oceanic crust that has been converted to eclogite) where temperatures are higher. Here we show that at such pressures and temperatures, eclogite lacking hydrous phases but with significant hydroxyl incorporated as defects in pyroxene and garnet develops a faulting instability associated with precipitation of water at grain boundaries and the production of very small amounts of melt. This new faulting mechanism satisfactorily explains high-temperature earthquakes in subducting oceanic crust and could potentially be involved in much deeper earthquakes in connection with similar precipitation of water in the mantle transition zone (400-700 km depth). Of potential importance for all proposed high-pressure earthquake mechanisms is the very small amount of fluid required to trigger this instability.

The structure and mechanical properties of articular cartilage are highly resilient towards transient dehydration.

PubMed

Boettcher, K; Kienle, S; Nachtsheim, J; Burgkart, R; Hugel, T; Lieleg, O

2016-01-01

Articular cartilage is a mechanically highly challenged material with very limited regenerative ability. In contrast to elastic cartilage, articular cartilage is exposed to recurring partial dehydration owing to ongoing compression but maintains its functionality over decades. To extend our current understanding of the material properties of articular cartilage, specifically the interaction between the fluid and solid phase, we here analyze the reversibility of tissue dehydration. We perform an artificial dehydration that extends beyond naturally occurring levels and quantify material recovery as a function of the ionic strength of the rehydration buffer. Mechanical (indentation, compression, shear, and friction) measurements are used to evaluate the influence of de- and rehydration on the viscoelastic properties of cartilage. The structure and composition of native and de/rehydrated cartilage are analyzed using histology, scanning electron microscopy, and atomic force microscopy along with a 1,9-dimethylmethylene blue (DMMB) assay. A broad range of mechanical and structural properties of cartilage can be restored after de- and rehydration provided that a physiological salt solution is used for rehydration. We detect only minor alterations in the microarchitecture of rehydrated cartilage in the superficial zone and find that these alterations do not interfere with the viscoelastic and tribological properties of the tissue. We here demonstrate the sturdiness of articular cartilage towards changes in fluid content and show that articular cartilage recovers a broad range of its material properties after dehydration. We analyze the reversibility of tissue dehydration to extend our current understanding of how the material properties of cartilage are established, focusing on the interaction between the fluid and solid phase. Our findings suggest that the high resilience of the tissue minimizes the risk of irreversible material failure and thus compensates, at least in part, its poor regenerative abilities. Tissue engineering approaches should thus not only reproduce the correct tissue mechanics but also its pronounced sturdiness to guarantee a similar longevity. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The Phillips pluton, Maine, USA: evidence of heterogeneous crustal sources and implications for granite ascent and emplacement mechanisms in convergent orogens

NASA Astrophysics Data System (ADS)

Pressley, Rachel A.; Brown, Michael

1999-03-01

The Phillips pluton (age of 403.8±1.3 Ma) was assembled at a crustal level below the contemporary brittle-plastic transition during regional dextral-reverse transpressive deformation. The pluton is composed dominantly of medium- to coarse-grained leucogranite sensu lato (s.l.), but within its bounds includes decametric massive outcrop of fine- to medium-grained granodiorite (s.l.). In places, the leucogranite contains centimetric enclaves apparently of the granodiorite. Granodiorite is host to more biotite than muscovite, and more calcic, oscillatory-zoned plagioclase, compared to the leucogranite. Pegmatitic granite and composite pegmatite-aplite occur as metric sheets within the pluton and as larger bodies outside the pluton to the SW. Magmatic fabrics, defined by biotite schlieren, occur locally in the leucogranite; the attitude of these fabrics and layering within the leucogranite are concordant with the NE-striking, steeply-dipping country rock foliation. K 2O contents, Rb/Sr ratios, Rb, Sr and Ba covariations, and chondrite-normalized rare earth element (REE) patterns of leucogranite are consistent with high-to-moderate a(H 2O) muscovite dehydration equilibrium eutectic melting of a predominantly pelite source similar to metasedimentary rocks of the surrounding central Maine belt (CMB). The REE patterns and Rb/Sr ratios of granodiorite also suggest derivation from a metasedimentary source, but more likely by moderate-to-low a(H 2O) (muscovite-) biotite dehydration equilibrium eutectic to non-eutectic (minimum) melting of a protolith dominated by greywacke in which garnet and plagioclase were residual phases. Both granite (s.l.) types have heterogeneous initial Nd isotope compositions. Samples of granodiorite define a range in ɛNd (404 Ma) of -1.8 to +0.1 (±0.3 2 σ uncertainty), and samples of leucogranite define a range in ɛNd (404 Ma) of -8.0 to -5.3 (±0.3 2 σ uncertainty). This bimodal distribution suggests that melts were derived from a minimum of two sources. The data are consistent with these sources being CMB metasedimentary rocks ( ɛNd (404 Ma)<-4) for the leucogranite, and Avalon-like (peri-Gondwanan) metasedimentary crust ( ɛNd (404 Ma)>-4) for the granodiorite. The range of Nd isotope compositions within each granite type most likely reflects isotopic heterogeneity inherited from the source. These data imply that the integrity of individual melt batches was maintained during ascent, and that extensive mixing of melt batches during emplacement at this level in the pluton did not occur, although centimetric enclaves have intermediate Nd isotope compositions consistent with small-scale interactions between magmas. We infer that the Phillips pluton represents the root of a larger pluton, and that what remains of this larger pluton is the feeder constructed from multiple melt batches arrested during waning flow of granite magma through a crustal-scale shear zone system.

Melting Inside the Tibetan Crust? Constraint From Electrical Conductivity of Peraluminous Granitic Melt

NASA Astrophysics Data System (ADS)

Guo, Xuan; Zhang, Li; Su, Xue; Mao, Zhu; Gao, Xiao-Ying; Yang, Xiaozhi; Ni, Huaiwei

2018-05-01

Magnetotelluric and seismological studies suggested the presence of partial melts in the middle to lower Himalaya-Tibetan crust. However, the melt fractions inferred by previous work were based on presumed electrical conductivity of melts. We performed measurements on the electrical conductivity of peraluminous granitic melts with 0.16-8.4 wt % H2O (the expected compositions in the Tibetan crust) at 600-1,300°C and 0.5-1.0 GPa. Peraluminous melt exhibits lower electrical conductivity than peralkaline melt at dry condition, but this difference diminishes at H2O > 2 wt %. With our data, the observed electrical anomalies in the Tibetan crust could be explained by 2-33 vol % of peraluminous granitic melts with H2O > 6 wt %. Possible reasons for our inferred melt fractions being higher than seismological constraints include the following: (1) The real melts are more Na and H2O rich, (2) the effect of melt reducing seismic velocities was overestimated, and (3) the anomalies at some locations are due to fluids.

The Origin of the Compositional Diversity of Mercury's Surface Constrained From Experimental Melting of Enstatite Chondrites

NASA Technical Reports Server (NTRS)

Boujibar, A.; Righter, K.; Pando, K.; Danielson, L.

2015-01-01

Mercury is known as an endmember planet as it is the most reduced terrestrial planet with the highest core/mantle ratio. MESSENGER spacecraft has shown that its surface is FeO-poor (2-4 wt%) and Srich (up to 6-7 wt%), which confirms the reducing nature of its silicate mantle. Moreover, high resolution images revealed large volcanic plains and abundant pyroclastic deposits, suggesting important melting stages of the Mercurian mantle. This interpretation was confirmed by the high crustal thickness (up to 100 km) derived from Mercury's gravity field. This is also corroborated by a recent experimental result that showed that Mercurian partial melts are expected to be highly buoyant within the Mercurian mantle and could have risen from depths as high as the core-mantle boundary. In addition MESSENGER spacecraft provided relatively precise data on major elemental compositions of Mercury's surface. These results revealed important chemical and mineralogical heterogeneities that suggested several stages of differentiation and re-melting processes. However, the extent and nature of compositional variations produced by partial melting remains poorly constrained for the particular compositions of Mercury (very reducing conditions, low FeO-contents and high sulfur-contents). Therefore, in this study, we investigated the processes that lead to the various compositions of Mercury's surface. Melting experiments with bulk Mercury-analogue compositions were performed and compared to the compositions measured by MESSENGER.

Komatiite genesis in the Archaean mantle, with implications for the tectonics of Archaean greenstone belts

NASA Technical Reports Server (NTRS)

Elthon, D.

1986-01-01

The presence of ultramafic lavas (komatiites) associated with Archean greenstone belts has been suggested to indicate very high increments (50-80%) of partial melting of the Archean mantle. Such extensive melting of the Earth's mantle during the Archean might have profound effects on the early tectonic and chemical evolution of the planet, although problems associated with keeping the komatiite liquid in equilibrium with the residual mantle at such high increments of melting has cast doubt upon aspects of extensive melting. Two important aspects of the origin of komatiites are discussed below.

Petrochemical evolution of the White Mfolozi Granite pluton: Evidence for a late Palaeoarchaean A-type granite from the SE Kaapvaal Craton, South Africa

NASA Astrophysics Data System (ADS)

Misra, Saumitra; Reinhardt, Jürgen; Wilson, Allan H.

2017-08-01

One of the major limitations in understanding the geochemical evolution of the Kaapvaal Craton, South Africa, is the scarcity of whole rock trace element data of the granitoid and other rocks compared to the vastness of this cratonic block. Here we present new XRF major oxide and ICP-MS trace element analyses of the White Mfolozi Granitoid (WMG) pluton, SE Kaapvaal Craton, which suggest that the 3.25 Ga (U-Pb zircon age) old WMG pluton is a peraluminous A-type granite and could be equivalent to the intrusive potassic granite phase of the Anhalt Granitoid suite, occurring to the North of the WMG pluton. The pluton was generated by batch partial melting of a pre-existing TTG source in two major phases under relatively anhydrous conditions, and the heat of partial melting could have been provided by a voluminous mantle-derived mafic magma, which intruded into mid-crustal levels (c. 17 km), perhaps during a period of crustal extension. The estimated pressure and temperature of generation of the WMG parent magma with average molar [or/(or + ab)] 0.48 could be 500 MPa and close to 1000 °C, respectively, when compared with the results of experimental petrology. Interstitial occurrence of relatively iron-rich biotite [Mg/(Mg + Fe) 0.41-0.45] suggests that the final temperature of crystallization of the pluton was close to 800 °C. An important magmatic event following the main phase of partial melting was limited mixing between the intrusive mafic magma and co-existing newly generated granitic melt. This magma mixing resulted in distinct variations in SiO2 and a low initial Sr isotopic ratio (0.7013) of the WMG pluton. Although both the models of partial melting of quartzo-feldspathic sources and fractional crystallization of basaltic magmas with or without crustal assimilation have been proposed for the origin of A-type granites, the model of magmatic evolution of the WMG pluton presented here can also be an alternative model for the generation of A-type granites. In this model, post-partial melting magma mixing is perhaps critical in explaining the Daly gap in composition and extreme variations in chemical (e.g., SiO2) and isotopic compositions observed in many bimodal A-type granite suites. The emplacement of the oldest known A-type granitoid suite in the Kaapvaal Craton, the WMG pluton, marks a period of stabilization of the craton before erosion and deposition of the overlying volcano-sedimentary succession of the Pongola Supergroup.

Along-strike variability of primitive magmas (major and volatile elements) inferred from olivine-hosted melt inclusions, southernmost Andean Southern Volcanic Zone, Chile

NASA Astrophysics Data System (ADS)

Weller, D. J.; Stern, C. R.

2018-01-01

Glass compositions of melt inclusions in olivine phenocrysts found in tephras derived from explosive eruptions of the four volcanoes along the volcanic front of the southernmost Andean Southern Volcanic Zone (SSVZ) are used to constrain primitive magma compositions and melt generation parameters. Primitive magmas from Hudson, Macá, and Melimoyu have similar compositions and are formed by low degrees (8-18%) of partial melting. Compared to these other three centers, primitive magmas from Mentolat have higher Al2O3 and lower MgO, TiO2 and other incompatible minor elements, and are generated by somewhat higher degrees (12-20%) of partial melting. The differences in the estimated primitive parental magma compositions between Mentolat and the other three volcanic centers are consistent with difference in the more evolved magmas erupted from these centers, Mentolat magmas having higher Al2O3 and lower MgO, TiO2 and other incompatible minor element contents, suggesting that these differences are controlled by melting processes in the mantle source region above the subducted oceanic plate. Parental magma S = 1430-594 and Cl = 777-125 (μg/g) contents of Hudson, Macá, and Melimoyu are similar to other volcanoes further north in the SVZ. However, Mentolat primitive magmas have notably higher concentrations of S = 2656-1227 and Cl = 1078-704 (μg/g). The observed along-arc changes in parental magma chemistry may be due to the close proximity below Mentolat of the subducted Guamblin Fracture Zone that could efficiently transport hydrous mineral phases, seawater, and sediment into the mantle, driving enhanced volatile fluxed melting beneath this center compared to the others. Table S2. Olivine-hosted melt inclusion compositions, host-olivine compositions, and the post-entrapment crystallization corrected melt inclusion compositions. Table S3. Olivine-hosted melt inclusion modeling information. Table S4. Major element compositions of the fractionation corrected melt inclusion in equilibrium with mantle olivine. Table S5. Melting parameters Fm and CoH2O. Table S6. Major element compositions of phenocrysts and glasses occurring with the olivine-hosted melt inclusions.

Microstructures and Petrology of Melt Inclusions in the Anatectic Sequence of Jubrique (Betic Cordillera, S Spain): Implications for Crustal Anatexis

NASA Astrophysics Data System (ADS)

Acosta-vigil, A.; Barich, A.; Garrido, C. J.; Cesare, B.; Tajčmanová, L.; Bartoli, O.

2014-12-01

We report a new occurrence of melt inclusions in polymetamorphic granulitic gneisses of the Jubrique unit, a complete though thinned crustal section located above the Ronda peridotite slab (Betic Cordillera, S Spain). The gneissic sequence is composed of mylonitic gneisses at the bottom and porphyroblastic gneisses on top. Mylonitic gneisses are strongly deformed rocks with abundant garnet and rare biotite. Except for the presence of melt inclusions, microstructures indicating the former presence of melt are rare or absent. Upwards in the sequence garnet decreases whereas biotite increases in proportion. Melt inclusions are present from cores to rims of garnets throughout the entire sequence. Most of the former melt inclusions are now totally crystallized and correspond to nanogranites, whereas some of them are partially made of glass or, more rarely, are totally glassy. They show negative crystal shapes and range in size from ≈5 to 200 micrometers, with a mean size of ≈30-40 micrometers. Daughter phases in nanogranites and partially crystallized melt inclusions include quartz, feldspars, biotite and muscovite; accidental minerals include kyanite, graphite, zircon, monazite, rutile and ilmenite; glass has a granitic composition. Melt inclusions are mostly similar throughout all the gneissic sequence. Some fluid inclusions, of possible primary origin, are spatially associated with melt inclusions, indicating that at some point during the suprasolidus history of these rocks granitic melt and fluid coexisted. Thermodynamic modeling and conventional thermobarometry of mylonitic gneisses provide peak conditions of ≈850 ºC and 12-14 kbar, corresponding to cores of large garnets with inclusions of kyanite and rutile. Post-peak conditions of ≈800-850 ºC and 5-6 kbar are represented by rim regions of large garnets with inclusions of sillimanite and ilmenite, cordierite-quartz-biotite coronas replacing garnet rims, and the matrix with oriented sillimanite. Previous conventional petrologic studies on these strongly deformed rocks have proposed that anatexis started during decompression from peak to post-peak conditions and in the field of sillimanite. The study of melt inclusions shows, however, that melt was already present in the system at peak conditions, and that most garnet grew in the presence of melt.

Assessment of radicular dentin permeability after irradiation with CO2 laser and endodontic irrigation treatments with thermal imaging

NASA Astrophysics Data System (ADS)

Cho, Heajin; Lee, Robert C.; Chan, Kenneth H.; Fried, Daniel

2017-02-01

Previous studies have demonstrated that the permeability changes due to the surface modification of dentin can be quantified via thermal imaging during dehydration. The CO2 laser has been shown to remove the smear layer and disinfect root canals. Moreover, thermal modification via CO2 laser irradiation can be used to convert dentin into a highly mineralized enamel-like mineral. The purpose of this study is to evaluate the radicular dentin surface modification after CO2 laser irradiation by measuring the permeability with thermal imaging. Human molar specimens (n=12) were sectioned into 4 axial walls of the pulp chamber and treated with either 10% NaClO for 1 minute, 5% EDTA for 1 minute, CO2 laser or none. The CO2 laser was operated at 9.4 μm with a pulse duration of 26 μs, pulse repetition rate of 300 Hz and a fluence of 13 J/cm2. The samples were dehydrated using an air spray for 60 seconds and imaged using a thermal camera. The resulting surface morphological changes were assessed using 3D digital microscopy. The images from digital microscopy confirmed melting of the mineral phase of dentin. The area enclosed by the time-temperature curve during dehydration, ▵Q, measured with thermal imaging increased significantly with treatments with EDTA and the CO2 laser (P<0.05). These results indicate that the surface modification due to CO2 laser treatment increases permeability of radicular dentin.

On the nature of the reversibility of hydration-dehydration on the crystal structure and magnetism of the ferrimagnet [MnII(enH)(H2O)][CrIII(CN)6].H2O.

PubMed

Yoshida, Yusuke; Inoue, Katsuya; Kurmoo, Mohamedally

2009-01-05

We report the synthesis, crystal structure, and thermal and magnetic properties of the two-dimensional achiral soft ferrimagnet [Mn(II)(enH)(H(2)O)][Cr(III)(CN)(6)].H(2)O (1), en = 1,2-diaminoethane, as well as the recyclability of the dehydration and rehydration and their influence on the crystal structure and its magnetic properties. Unlike [Mn(S-pnH)(H(2)O)][Cr(CN)(6)].H(2)O (2S, pn = 1,2-diaminopropane), which is a chiral (P2(1)2(1)2(1)) enantiopure ferrimagnet (T(C) = 38 K), 1 crystallizes in the achiral orthorhombic Pcmn space group, having a similar two-dimensional square network of Mn-Cr with bridging cyanide, and 1 behaves also as a soft ferrimagnet (T(C) = 42 K). X-ray diffraction experiments on a single crystal of 1 indicate a transformation from a single crystal to an amorphous phase upon dehydrataion and partial recovery of its crystallinity upon rehydration. The dehydrated phase 1-DP exhibits long-range ordering at 75 K to a ferrimagnetic state and coercive field at 2 K of 100 Oe, which are a higher critical temperature and coercive field than for the virgin sample (H(C) = 60 Oe). Thermogravimetric analyses indicate that the crystallinity deteriorates upon hydration-dehydration cycling, with persistence toward the amorphous phase, as also seen by magnetization measurements. This effect is associated with an increase of statistical disorder inherent in the dehydration-rehydration process. X-ray powder diffraction suggests that 1-DP may retain order within the layers but loses coherence in the stacking of the layers.

Fully determined scaling laws for volumetrically heated convective systems, a tool for assessing habitability of exoplanets

NASA Astrophysics Data System (ADS)

Vilella, Kenny; Kaminski, Edouard

2017-05-01

The long-term habitability of a planet rises from its ability to generate and maintain an atmosphere through partial melting and volcanism. This question has been mainly addressed in the framework of plate tectonics, which may be too specific to apply to the wide range of internal dynamics expected for exoplanets, and even to the thermal evolution of the early Earth. Here we propose a more general theoretical approach of convection to build a regime diagram giving the conditions for partial melting to occur, in planetary bodies, as a function of key parameters that can be estimated for exoplanets, their size and internal heating rate. To that aim, we introduce a refined view of the Thermal Boundary Layer (TBL) in a convective system heated from within, that focuses on the temperature and thickness of the TBL at the top of the hottest temperature profiles, along which partial melting shall first occur. This ;Hottest Thermal Boundary Layer; (HotTBL) is first characterized using fully theoretical scaling laws based on the dynamics of thermal boundary layers. These laws are the first ones proposed in the literature that do not rely on empirical determinations of dimensionless constants and that apply to both low Rayleigh and high Rayleigh convective regimes. We show that the scaling laws can be successfully applied to planetary bodies by comparing their predictions to full numerical simulations of the Moon. We then use the scaling laws to build a regime diagram for exoplanets. Combined with estimates of internal heating in exoplanets, the regime diagram predicts that in the habitable zone partial melting occurs in planets younger than the Earth.

Fully Determined Scaling Laws for Volumetrically Heated Convective Systems, a Tool for Assessing Habitability of Exoplanets.

NASA Astrophysics Data System (ADS)

Vilella, K.; Kaminski, E. C.

2016-12-01

The long-term habitability of a planet rises from its ability to generate and maintain an atmosphere through partial melting and volcanism. This question has been mainly addressed in the framework of plate tectonics, which may be too specific to apply to the wide range of internal dynamics expected for exoplanets, and even to the thermal evolution of the early Earth. Here we propose a more general theoretical approach of convection to build a regime diagram giving the conditions for partial melting to occur in planetary bodies, as a function of key parameters that can be estimated for exoplanets, their size and internal heating rate. To that aim, we introduce a refined view of the Thermal Boundary layer (TBL) in a convective system heated from within, that focuses on the temperature and thickness of the TBL at the top of the hottest temperature profiles, along which partial melting shall first occur. This "Hottest Thermal Boundary Layer" (HotTBL) is first characterized using fully theoretical scaling laws based on the dynamics of thermal boundary layers. These laws are the first ones proposed in the literature that do not rely on empirical determinations of dimensionless constants and that apply to both low Rayleigh and high Rayleigh convective regimes. We show that the scaling laws can be successfully applied to planetary bodies by comparing their predictions to full numerical simulations of the Moon. We then use the scaling laws to build a regime diagram for exoplanets. Combined with estimates of internal heating in exoplanets, the regime diagram predicts that in the habitable zone partial melting occurs in planets younger than the Earth.

Extent of partial melting beneath the Cascade Range, Oregon: Constraints from gravity anomalies and ideal-body theory

NASA Astrophysics Data System (ADS)

Blakely, Richard J.

1994-02-01

The spatial correlation between a horizontal gradient in heat flow and a horizontal gradient in residual gravity in the Western Cascades of central Oregon has been interpreted by others as evidence of the western edge of a pervasive zone of high temperatures and partial melting at midcrustal depths (5-15 km). Both gradients are steep and relatively linear over north-south distances in excess of 150 km. The Western Cascades gravity gradient is the western margin of a broad gravity depression over most of the Oregon Cascade Range, implying that the midcrustal zone of anomalous temperatures lies throughout this region. Ideal-body theory applied to the gravity gradient, however, shows that the source of the Western Cascades gravity gradient cannot be deeper than about 2.5 km and is considerably shallower in some locations. These calculations are unique determinations, assuming that density contrasts associated with partial melting and elevated temperatures in the crust do not exceed 500 kg/cu m. Consequently, the gravity gradient and the heat flow gradient in the Western Cascades cannot be caused directly by the same source if the heat flow gradient originates at midcrustal depths. This conclusion in itself does not disprove the existence of a widespread midcrustal zone of anomalously high temperatures and partial melting in this area, but it does eliminate a major argument in support of its existence. The gravity gradient is most likely caused by lithologic varitions in the shallow crust, perhaps reflecting a relict boundary between the Cascade extensional trough to the west and Tertiary oceanic crust to the west. The boundary must have formed prior to Oligocene time, the age of the oldest rocks that now conceal it.

Effects of fabrication procedures and weld melt-through on fatigue resistance of orthotropic steel deck welds.

DOT National Transportation Integrated Search

2008-12-01

A common practice for the fabrication of orthotropic bridge deck in the US involves using 80% partial-joint-penetration groove welds (PJP) to join : closed ribs to a deck plate. Avoiding weld melt-through with the thin rib plate may be difficult to a...

The diffusion of water in haploanesite

NASA Astrophysics Data System (ADS)

Ni, H.; Zhang, Y.

2008-12-01

Diffusive transport of water in silicate melts is a key process in magma dynamics and volcanic eruptions, including bubble growth. Previous studies demonstrate that in additional to temperature, water content and pressure, melt composition also plays an important role in determining water diffusivity. We carried out high temperature (1311-1512°C) diffusion-couple experiments and intermediate temperature (470- 600°C) dehydration experiments to investigate H2O diffusion in a melt of haploandesitic composition. The diffusion couple is composed of an anhydrous (with <0.1 wt.% H2O) and a hydrous (with 2 wt.% H2O) haploandesitic glass. A platinum capsule is used to contain the couple and then it is welded shut. Diffusion runs are carried out in a 12.7-mm piston-cylinder apparatus at 1 GPa and superliquidus temperatures of 1584-1785 K. Infrared microscopy is applied on quenched glass to measure the profile of total H2O concentration (H2Ot). The profile shape is best fit by an error function, indicating an H2O diffusivity virtually independent of H2O concentration, consistent with the results of Behrens et al. (2004) on an Fe-bearing andesite. Dehydration experiments are performed at 743-873 K in a rapid-quench cold-seal vessel, with a heated hydrous glass losing water to 0.1 GPa Ar atmosphere. Measured diffusion profiles, however, show that water diffusivity is dependent on water content. Experimental data can be explained by H2Om being the dominating diffusant or a total H2O diffusivity proportional to total H2O content. The distinction between the high-temperature experiments where H2Ot diffusivity is apparently independent of H2Ot content, and the intermediate-temperature experiments where H2Ot diffusivity depends on H2Ot can be rationalized if OH diffusion has a higher activation energy than molecular H2O diffusion, and their comparable diffusivities at high T gradually diverge as temperature is lowered. At below 1 wt.% H2O, water diffusivity increases from rhyolite to dacite to andesite at >1300°C, and this sequence is reversed at <600°C.

Interactions between magma and the lithospheric mantle during Cenozoic rifting in Central Europe

NASA Astrophysics Data System (ADS)

Meyer, Romain; Elkins-Tanton, Linda T.

2010-05-01

During the Cenozoic, extensive intraplate volcanic activity occurred throughout Central Europe. Volcanic eruptions extend over France (the Massif Central), central Germany (Eifel, Vogelsberg, Rhön; Heldburg), the Czech Republic (the Eger graben) and SW Poland (Lower Silesia), a region ~1,200 km wide. The origin of this predominantly alkaline intraplate magmatism is often genetically linked to one or several mantle plumes, but there is no convincing evidence for this. We have measured Pb isotope ratios, together with major and trace elements, in a representative set of mafic to felsic igneous rocks from the intra-plate Cenozoic Rhön Mts. and the Heldburg dike swarm in order to gain insight into the melting source and petrogenetic history of these melts. Three different mafic rock types (tholeiitic basalt, alkali basalt, basanite) were distinguished based on petrography and geochemistry within the investigated areas. Except for the lherzolite-bearing phonolite from the Veste Heldburg all other evolved magmas are trachytes. REE geochemistry and calculated partial melting modeling experiments for the three mafic magma types point to different degrees of partial melting in a garnet-bearing mantle source. In addition a new version of the ternary Th-Hf-Ta diagram is presented in this study as a useful petrological tool. This diagram is not only able to define potentially involved melting source end-members (e.g. asthenosphere, sub-continental lithospheric mantle and continental crust) but also interactions between these members are illustrated. An advantage of this diagram compared to partial melting degree sensitive multi-element diagrams is that a ternary diagram is a closed system. An earlier version of this diagram has been recently used to establish the nature and extent of crust mantle melt interaction of volcanic rifted margins magmas (Meyer et al. 2009). The Th-Hf-Ta geochemistry of the investigated magmas is similar to spinel and garnet xenoliths from different continental intra-plate volcanic fields The in the Rhön Mts. and the Heldburg dike swarm tapped mantle source is characterized by an enriched Pb-isotope geology. The highest HIMU component has been measured in the lherzolite-bearing Veste Heldburg phonolite. This higher enriched Pb isotope signature compared to the mafic magmas cannot be explained by crustal contamination. Assimilation fractionation crystallization (AFC) modeling of the Heldburg phonolite allows us to petrogenetically link this melt with HIMU rich shallow mantle amphibole-bearing xenoliths. These new observations suggest that melting started in more depleted mantle segments. And that these melts interacted with more enriched metasomatic overprinted lithospheric mantle domains.

Interactions between magma and the lithospheric mantle during Cenozoic rifting in Central Europe

NASA Astrophysics Data System (ADS)

Meyer, R.; Song, X.; Elkins-Tanton, L. T.

2009-12-01

During the Cenozoic, extensive intraplate volcanic activity occurred throughout Central Europe. Volcanic eruptions extend over France (the Massif Central), central Germany (Eifel, Vogelsberg, Rhön; Heldburg), the Czech Republic (the Eger graben) and SW Poland (Lower Silesia), a region ~1,200 km wide. The origin of this predominantly alkaline intraplate magmatism is often genetically linked to one or several mantle plumes, but there is no convincing evidence for this. We have measured Pb isotope ratios, together with major and trace elements, in a representative set of mafic to felsic igneous rocks from the intra-plate Cenozoic Rhön Mts. and the Heldburg dike swarm in order to gain insight into the melting source and petrogenetic history of these melts. Three different mafic rock types (tholeiitic basalt, alkali basalt, basanite) were distinguished based on petrography and geochemistry within the investigated areas. Except for the lherzolite-bearing phonolite from the Veste Heldburg all other evolved magmas are trachytes. REE geochemistry and calculated partial melting modeling experiments for the three mafic magma types point to different degrees of partial melting in a garnet-bearing mantle source. In addition a new version of the ternary Th-Hf-Ta diagram is presented in this study as a useful petrological tool. This diagram is not only able to define potentially involved melting source end-members (e.g. asthenosphere, sub-continental lithospheric mantle and continental crust) but also interactions between these members are illustrated. An advantage of this diagram compared to partial melting degree sensitive multi-element diagrams is that a ternary diagram is a closed system. An earlier version of this diagram has been recently used to establish the nature and extent of crust mantle melt interaction of volcanic rifted margins magmas (Meyer et al. 2009). The Th-Hf-Ta geochemistry of the investigated magmas is similar to spinel and garnet xenoliths from different continental intra-plate volcanic fields The in the Rhön Mts. and the Heldburg dike swarm tapped mantle source is characterized by an enriched Pb-isotope geology. The highest HIMU component has been measured in the lherzolite-bearing Veste Heldburg phonolite. This higher enriched Pb isotope signature compared to the mafic magmas cannot be explained by crustal contamination. Assimilation fractionation crystallization (AFC) modeling of the Heldburg phonolite allows us to petrogenetically link this melt with HIMU rich shallow mantle amphibole-bearing xenoliths. These new observations suggest that melting started in more depleted mantle segments. And that these melts interacted with more enriched metasomatic overprinted lithospheric mantle domains.

Immiscible Transition from Carbonate-rich to Silicate-rich Melts in Eclogite+CO2 and Genesis of Ocean Island Melilitite

NASA Astrophysics Data System (ADS)

Dasgupta, R.; Stalker, K.; Hirschmann, M. M.

2004-12-01

Derivation of highly silica-undersaturated lavas such as olivine melilitites and melilite nephelinites from the mantle has been attributed to the effects of CO2. However, experimental studies have so far failed to demonstrate equilibrium of melilititic melts with a four-phase peridotite assemblage. Instead, the liquidus mineralogy of these silica-undersaturated magmas at high-pressures appears to be dominated by cpx1. Although, experimental partial melts from natural peridotite+CO2 span a continuum from carbonatite to alkali-basalts2, ocean-island melilitites have distinctly higher TiO2, FeO*, and CaO/(CaO+MgO)3,4 than compositions derived thus far from a carbonated lherzolite source. Partial melting experiments of a nominally anhydrous, natural eclogite with a small amount of added carbonate (SLEC1; 5 wt.% bulk CO2) were performed to investigate the transition between carbonate and silicate melts with increasing temperature. Experiments were conducted in a piston cylinder at 3 GPa from 1050 to 1400 ° C. Garnet and cpx appear in all the experiments and ilmenite is observed from 1075 to ˜1200 ° C. An Fe-bearing calcio-dolomitic melt is present from the solidus (1050-1075 ° C) up to 1375 ° C. Beginning at 1275 ° C, it coexists with a silica-poor silicate melt. Textural criteria indicate only a single CO2-rich silicate melt phase at 1400 ° C, coexisting with garnet and minor cpx. The liquidus temperature is estimated to be ˜1415 ° C from the melt fraction-temperature trend. With increasing temperature, the carbonate melt becomes richer in SiO2 ( ˜2 to 5 wt.%) and Al2O3 ( ˜0.75 to 2.25 wt.%) and poorer in CaO ( ˜30 to 25 wt.% from ˜1200 to 1375 ° C). Compositions of silicate partial melts change systematically with increasing temperature, increasing in SiO2 ( ˜36 to 41 wt.%), Al2O3 ( ˜4.5 to 9.5 wt.%), MgO ( ˜9.5 to 13 wt.%), CaO ( ˜8 to 14 wt.%) and decreasing in TiO2 ( ˜14 to 2.5 wt.%), FeO ( ˜20 to 13 wt.%), Na2O ( ˜3.3 to 1.7 wt.%). A wide temperature interval of coexisting carbonate and silicate partial melts of carbonated eclogite is distinct from the continuous transition from carbonate to silicate melts observed in carbonated peridotite systems2,5. At high-temperature, the silicate melts generated from SLEC1 are comparable to strongly silica-undersaturated, alkalic OIB lavas and closely resembles ocean island melilitite and nepheline melilitite3,4 in its SiO2, FeO*, MgO, CaO, TiO2, and Na2O content. They are also similar to melilite bearing lavas of continental affinity, though the match is not as close. Although the SLEC1 derived immiscible silicate melts are lower in Al2O3 than primitive alkalic OIB lavas, liquids richer in Al2O3 may be produced at slightly lower pressures. Geochemical and geodynamical investigations of carbonated eclogite sources for melilitic volcanic series thus merit consideration. 1. Brey, G and Green, D. H. 1977, CMP 61, 141-162. 2. Hirose, K. 1997, GRL 24, 2837-2840. 3. Clague, D. A. and Frey, F. A. 1982, JP 23, 447-504. 4. Hoernle, K. and Schmincke, H.-U. 1993, JP 34, 573-597. 5. Moore, K. R. and Wood, B. J. 1998, JP 39, 1943-1951.

Thorium isotope evidence for melting of the mafic oceanic crust beneath the Izu arc

NASA Astrophysics Data System (ADS)

Freymuth, Heye; Ivko, Ben; Gill, James B.; Tamura, Yoshihiko; Elliott, Tim

2016-08-01

We address the question of whether melting of the mafic oceanic crust occurs beneath ordinary volcanic arcs using constraints from U-Series (238U/232Th, 230Th/232Th and 226Ra/230Th) measurements. Alteration of the top few hundred meters of the mafic crust leads to strong U enrichment. Via decay of 238U to 230Th, this results in elevated (230Th/232Th) (where brackets indicate activity ratios) over time-scales of ∼350 ka. This process leads to the high (230Th/232Th), between 2.6 and 11.0 in the mafic altered oceanic crust (AOC) sampled at ODP Sites 801 and 1149 near the Izu-Bonin-Mariana arc. Th activity ratios in the Izu arc lavas range from (230Th/232Th) = 1.2-2.0. These values are substantially higher than those in bulk sediment subducting at the Izu trench and also extend to higher values than in mid-ocean ridge basalts and the Mariana arc. We show that the range in Th isotope ratios in the Izu arc lavas is consistent with the presence of a slab melt from a mixed source consisting of AOC and subducted sediments with an AOC mass fraction of up to approximately 80 wt.% in the component added to the arc lava source. The oceanic plate subducting at the Izu arc is comparatively cold which therefore indicates that temperatures high enough for fluid-saturated melting of the AOC are commonly achieved beneath volcanic arcs. The high ratio of AOC/sediments of the slab melt component suggested for the Izu arc lavas requires preferential melting of the AOC. This can be achieved when fluid-saturated melting of the slab is triggered by fluids derived from underlying subducted serpentinites. Dehydration of serpentinites and migration of the fluid into the overlying crust causes melting to start within the AOC. The absence of a significant sediment melt component suggests there was insufficient water to flux both AOC and overlying sediments.

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.

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

NASA Astrophysics Data System (ADS)

Soltis, Jared T.

High altitude ice crystal clouds created by highly convective storm cells are dangerous to jet transport aircraft because the crystals are ingested into the compressor section, partially melt, accrete, and cause roll back or flame out. Current facilities to test engine particle icing are not ideal for fundamental mixed-phase ice accretion experiments or do not generate frozen droplet clouds under representative conditions. The goal of this research was to develop a novel facility capable of testing fundamental partially melted ice particle icing physics and to collect ice accretion data related to mixed-phase ice accretion. The Penn State Icing Tunnel (PSIT) has been designed and fabricated to conduct partially melted ice particle cloud accretion. The PSIT generated a cloud with air assisted atomizing nozzles. The water droplets cool from the 60psi pressure drop as the water exited the nozzle and fully glaciate while flowing in the -11.0°C tunnel air flow. The glaciated cloud flowed through a duct in the center of the tunnel where hot air was introduced. The temperature of the duct was regulated from 3.3°C to 24°C which melted particle the frozen particle from 0% to 90%. The partially melted particle cloud impinged on a temperature controlled flat plate. Ice accretion data was taken for a range of duct temperature from 3.3°C to 24°C and plate temperature from -4.5°C to 7.0°C. The particle median volumetric diameter was 23mum, the total water content was 4.5 g/m 3, the specific humidity was 1.12g/kg, and the wet bulb temperature ranged from 1.0°C to 7.0°C depending on the duct temperature. The boundaries between ice particle bounce off, ice accretion, and water run off were determined. When the particle were totally frozen and the plate surface was below freezing, the ice particle bounced off as expected. Ice accretion was seen for all percent melts tested, but the plate temperature boundary between water runoff and ice accretion increased from 0°C at 8% melt to 3°C at 90%. There were two types of ice accretion with a transition zone in between. The first type of ice was opaque in color and had a rough surface. This ice occurred roughly from 6.0°C to 12.0°C duct temperatures (8% to 50% melt). The qualitative characteristics of the ice were produced from the low water content in the cloud. The water that was available froze instantly and trapped ice particle. Duct temperatures greater than 17.5°C (80% melt) produced ice that was clear and smooth. The water in the surface did not freeze instantly due to the high water content creating a water film that froze. A mixed-phase cloud dynamics model from NASA Glenn was used to estimate the percent melt of the cloud exiting the duct. There was no way to validate the model by directly measuring the percent melt of the cloud, so single particle melt experiments were conducted and compared to the model. A 0.05g/L solution of rhodamine b was sprayed into a levitator and droplets formed at the nodes of the wave. A 532nm green laser was used to illuminate the dye, and the water emitted orange 593nm light given the luminescent properties of the ink. The emitted light intensity was recorded, and a linear relationship between the light intensity of ice to the light intensity of water was used to determine the percent melt of a droplet. The droplets were frozen with a cold flow of nitrogen gas via a liquid nitrogen heat exchanger. The droplets melted under natural convection when the cold nitrogen was shut off. Fifteen cases were compared with droplet diameters ranging from 324mum to 1112mum, air temperatures from 16°C to 31°C, and relative humidities from 41% to 100%. The average discrepancy between predictions and results for the cases that melted slower than ten seconds was 13% while the cases that melted faster than 10 second had 64% discrepancy between the model and experiment. To explain the discrepancy between the experiment and model, sensitivity studies of the model were conducted. It was seen that the melt time from the model was most sensitive to ambient temperature (1s/°C). It was also seen that the thermistors used in the experiment were accurate to 0.7°C. Transient effects of the rhodamine b caused an overshoot in light intensity, making it difficult to accurately determine the melting stop time. These factors led to the difference in melt time between the model and experiments. A 2.7s difference between model and experiments was deemed to be a successful correlation between predictions and experimental results given the model sensitivity to temperature, the difficulty in measuring temperatures at the position of the droplet, and the transient characteristics of rhodamine b.

The chemical signatures of progressive dehydration stages in subducted serpentinites

NASA Astrophysics Data System (ADS)

Pettke, T.; Spandler, C.; Kodolanyi, J.; Scambelluri, M.

2009-04-01

Fluids mediate chemical cycling in subduction zones. Nonetheless, the chemistry of serpentinite-dehydration fluids from down-going slabs and their chemical effects on ascent are only very poorly constrained. We report new data on discontinuous dehydration reactions, including the measurement of individual fluid inclusions in prograde minerals from natural occurrences, and one case study tracing the infiltration of serpentinite-derived fluid in mafic eclogite. Together, these studies demonstrate that serpentinite-derived fluids are commonly dilute, but that there may be selected trace element abundances (and ratios ?) that characterize such fluid provenance. Brucite dehydration represents the first relevant liberation of crystal-bound water from serpentinites formed on the ocean floor (ocean floor mantle hydration chemistry is addressed in Kodolanyi et al., this session). Discordant olivine-Ti-clinohumite-antigorite-clinopyroxene-magnetite veins in ca. 2.3 GPa antigorite serpentinites of the Erro Tobbio in the Ligurian Alps, Italy, formed from aqueous, dilute fluids containing Li, Sr, Ba, Rb, Pb as determined on texturally-early fluid inclusions in olivine. This prograde olivine preserves high Ni (1500 - 3000 µg/g) and is identified most readily by elevated Li (1-20 µg/g), B (1-20 µg/g) and Mn contents. Aqueous fluid inclusions in some clinopyroxene (Cpx) of the same veins host variably (sometimes highly) saline fluid inclusions, interpreted to represent the "spent" fluid after formation of hydrous vein minerals (chlorite, antigorite). Vein bulk-rock trace-element concentrations show enrichment in Ti, Ba, Nb, Li, HREE and Cu relative to the wall rocks, accompanied by depletion in Cr. This mostly reflects the mineral transformations (sources / sinks) occurring at this stage of serpentinite dehydration. Antigorite-breakdown is arguably the most prominent water release from down-going slabs. Olivine-orthopyroxene-chlorite rocks at Cerro del Almirez (Spain), recording this dehydration event, contain olivine-hosted polyphase inclusions interpreted to represent fluid inclusions trapped during antigorite breakdown. Preliminary compositional data show enrichments in B, Cs, Pb, Li, Sr, Rb, K, Ba (decreasing order) and depletions in Ca, Ti, La relative to primitive mantle, closely corresponding to the incompatible element pattern of typical island arc lavas. Transfer of such fluids to the melting source of island arc magmas may be critical to developing their distinctive trace element signatures. Omphacite-rich (± garnet, rutile, talc and zircon) veins cutting eclogite (Fe-Ti gabbro protolith, Monviso, W Italian Alps) record serpentinite-derived fluid pathways though the subducted slab at ca. 70 km depth. Although these veins largely formed by local eclogite-derived fluids, they also preserve discrete generations of vein minerals enriched in Mg, Cr, Ni, B, As and Sb, and zircon with elevated Epsilon(Hf) compared to host-rock eclogite zircon. These chemical and isotopic characteristics suggest external fluid input, from serpentinite dehydration. Moreover, distinctive oscillatory or irregular Cr zonations observed in omphacite, garnet and rutile from the veins are interpreted to record episodic fracturing and fluid infiltration over >10 m along transient brittle fractures at high pressures. Our current data suggest that dehydration fluid pervades the rock at the site of liberation, and that episodic fluid escape from the dehydration site may be effectively channelized. This supports growing evidence for highly focused reactive fluid flow through slabs. Robust constraints on the chemical composition and nature of dehydration fluids from serpentinites and how they evolve during ascent may greatly aid in recognizing such features from outcrop to thin-section scales, in turn providing us with more comprehensive sample material to advance our understanding on fluid-mediated cycling in subduction zones. Reference Kodolanyi et al., this session

Electro-physical properties of superconducting ceramic thick film prepared by partial melting method.

PubMed

Lee, Sang Heon

2013-05-01

BiSrCaCuO superconductor thick films were prepared at several curing temperatures, and their electro-physical properties were determined to find an optimum fabrication conditions. Critical temperatures of the superconductors were decreased with increasing melting temperature, which was related to the amount of equilibrium phases of the superconducting materials with temperature. The critical temperature of BiSrCaCuO bulk and thick film superconductors were 107 K and 96 K, respectively. The variation of susceptibility of the superconductor thick film formed at 950 degrees C had multi-step-type curve for 70 G externally applied field, whereas, a superconductor thick film formed at 885 degrees C had a single step-type curve like a bulk BiSrCaCuO ceramic superconductor in the temperature-susceptibility curves. A partial melting at 865 degrees C is one of optimum conditions for making a superconductor thick film with a relatively homogeneous phase.

Relaxation of the bulk modulus in partially molten dunite?

NASA Astrophysics Data System (ADS)

Cline, C. J.; Jackson, I.

2016-11-01

To address the possibility of melt-related bulk modulus relaxation, a forced oscillation experiment was conducted at seismic frequencies on a partially molten synthetic dunite specimen (melt fraction = 0.026) utilizing the enhanced capacity of the Australian National University attenuation apparatus to operate in both torsional and flexural oscillation modes. Shear modulus and dissipation data are consistent with those for melt-bearing olivine specimens previously tested in torsion, with a pronounced dissipation peak superimposed on high-temperature background. Flexural data exhibit a monotonic decrease in complex Young's modulus with increasing temperature under transsolidus temperatures. The observed variation of Young's modulus is well described by the relationship 1/E 1/3G, without requiring relaxation of the bulk modulus. At high homologous temperatures, when shear modulus is low, extensional and flexural oscillation measurements have little resolution of bulk modulus, and thus, only pressure oscillation measurements can definitively constrain bulk properties at these conditions.

Numerical models of the magmatic processes induced by slab breakoff

NASA Astrophysics Data System (ADS)

Freeburn, Rebecca; Bouilhol, Pierre; Maunder, Ben; Magni, Valentina; van Hunen, Jeroen

2017-11-01

After the onset of continental collision, magmatism often persists for tens of millions of years, albeit with a different composition, in reduced volumes, and with a more episodic nature and more widespread spatial distribution, compared to normal arc magmatism. Kinematic modelling studies have suggested that slab breakoff can account for this post-collisional magmatism through the formation of a slab window and subsequent heating of the overriding plate and decompression melting of upwelling asthenosphere, particularly if breakoff occurs at depths shallower than the overriding plate. To constrain the nature of any melting and the geodynamic conditions required, we numerically model the collision of two continental plates following a period of oceanic subduction. A thermodynamic database is used to determine the (de)hydration reactions and occurrence of melt throughout this process. We investigate melting conditions within a parameter space designed to generate a wide range of breakoff depths, timings and collisional styles. Under most circumstances, slab breakoff occurs deeper than the depth extent of the overriding plate; too deep to generate any decompressional melting of dry upwelling asthenosphere or thermal perturbation within the overriding plate. Even if slab breakoff is very shallow, the hot mantle inflow into the slab window is not sustained long enough to sufficiently heat the hydrated overriding plate to cause significant magmatism. Instead, for relatively fast, shallow breakoff we observe melting of asthenosphere above the detached slab through the release of water from the tip of the heating detached slab. Melting of the subducted continental crust during necking and breakoff is a more common feature and may be a more reliable indicator of the occurrence of breakoff. We suggest that magmatism from slab breakoff alone is unable to explain several of the characteristics of post-collisional magmatism, and that additional geodynamical processes need to be considered when interpreting magmatic observations.

Hydrous metasomatism of oceanic sub-arc mantle, Lihir, Papua New Guinea. Part 2. Trace element characteristics of slab-derived fluids

NASA Astrophysics Data System (ADS)

Grégoire, Michel; McInnes, Brent I. A.; O'Reilly, Suzanne Y.

2001-11-01

Spinel peridotite xenoliths recovered from the Tubaf and Edison volcanoes, south of Lihir Island in the Tabar-Lihir-Tanga-Feni island arc in Papua New Guinea, are predominantly fresh, refractory harzburgites. Many of the harzburgite xenoliths have cross-cutting vein networks and show evidence of modal metasomatism. These metasomatic veins contain a secondary mineral assemblage consisting of fibrous, radiating orthopyroxene and fine-grained Fe-Ni sulfide with minor olivine, clinopyroxene, phlogopite, amphibole and magnetite. Adjacent to the veins, primary clinopyroxene is cloudy while orthopyroxene exhibits replacement by secondary fibrous orthopyroxene, similar in habit to orthopyroxene occurring in the veins. The mineralogical and geochemical characteristics of the Tubaf mantle xenoliths are the product of two major processes: an early partial melting depletion event that was overprinted by oxidation and alkali enrichment related to percolation of slab-derived, hydrous melts. HREE and MREE concentrations in clinopyroxene from the least metasomatised harzburgites indicate that they are the residues from a 15% to 25% partial melting event, consistent with formation in a MOR setting. The secondary vein assemblages show strong enrichment in the LILE (primarily Sr, Ba, Rb, Th, U and Pb) and the REE (primarily La, Ce, Nd, Sm, Eu and Gd), while the HFSE (Nb, Ta, Zr, Hf, and Ti) are neither enriched nor depleted. The mineral precipitates in the vein assemblages have high LREE/HFSE and LILE/HFSE, and reflect the relative solubility of these elements in hydrous melts. These trace element characteristics are similar to those of the Tabar-Lihir-Tanga-Feni arc lavas, and display the commonly observed HFSE depletion of arc magmatism. These findings support the hypothesis that this so-called "arc signature" is primarily dependent on the relative solubility of elements in slab-derived, hydrous melts, and the enrichment of these soluble elements in metasomatised mantle regions that are prone to preferential partial melting.

Imaging rifting at the lithospheric scale in the northern East African Rift using S-to-P receiver functions

NASA Astrophysics Data System (ADS)

Lavayssiere, A.; Rychert, C.; Harmon, N.; Keir, D.; Hammond, J. O. S.; Kendall, J. M.; Leroy, S. D.; Doubre, C.

2017-12-01

The lithosphere is modified during rifting by a combination of mechanical stretching, heating and potentially partial melt. We image the crust and upper mantle discontinuity structure beneath the northern East African Rift System (EARS), a unique tectonically active continental rift exposing along strike the transition from continental rifting in the Main Ethiopian rift (MER) to incipient seafloor spreading in Afar and the Red Sea. S-to-P receiver functions from 182 stations across the northern EARS were generated from 3688 high quality waveforms using a multitaper technique and then migrated to depth using a regional velocity model. Waveform modelling of data stacked in large conversion point bins confirms the depth and strength of imaged discontinuities. We image the Moho at 29.6±4.7 km depth beneath the Ethiopian plateaux with a variability in depth that is possibly due to lower crustal intrusions. The crust is 27.3±3.9 km thick in the MER and thinner in northern Afar, 17.5±0.7 km. The model requires a 3±1.2% reduction in shear velocity with increasing depth at 68.5±1.5 km beneath the Ethiopian plateaux, consistent with the lithosphere-asthenosphere boundary (LAB). We do not resolve a LAB beneath Afar and the MER. This is likely associated with partial melt near the base of the lithosphere, reducing the velocity contrast between the melt-intruded lithosphere and the partially molten asthenosphere. We identify a 4.5±0.7% increase in velocity with depth at 91±3 km beneath the MER. This change in velocity is consistent with the onset of melting found by previous receiver functions and petrology studies. Our results provide independent constraints on the depth of melt production in the asthenosphere and suggest melt percolation through the base of the lithosphere beneath the northernmost East African rift.

Solidus and liquidus profiles of chondritic mantle: Implication for melting of the Earth across its history

NASA Astrophysics Data System (ADS)

Andrault, Denis; Bolfan-Casanova, Nathalie; Nigro, Giacomo Lo; Bouhifd, Mohamed A.; Garbarino, Gaston; Mezouar, Mohamed

2011-04-01

We investigated the melting properties of a synthetic chondritic primitive mantle up to core-mantle boundary (CMB) pressures, using laser-heated diamond anvil cell. Melting criteria are essentially based on the use of X-rays provided by synchrotron radiation. We report a solidus melting curve lower than previously determined using optical methods. The liquidus curve is found between 300 and 600 K higher than the solidus over the entire lower mantle. At CMB pressures (135 GPa), the chondritic mantle solidus and liquidus reach 4150 (± 150) K and 4725 (± 150) K, respectively. We discuss that the lower mantle is unlikely to melt in the D″-layer, except if the highest estimate of the temperature profile at the base of the mantle, which is associated with a very hot core, is confirmed. Therefore, recent suggestions of partial melting in the lowermost mantle based on seismic observations of ultra-low velocity zones indicate either (1) a outer core exceeding 4150 K at the CMB or (2) the presence of chemical heterogeneities with high concentration of fusible elements. Our observations of a high liquidus temperature as well as a large gap between solidus and liquidus temperatures have important implications for the properties of the magma ocean during accretion. Not only complete melting of the lower mantle would require excessively high temperatures, but also, below liquidus temperatures partial melting should take place over a much larger depth interval than previously thought. In addition, magma adiabats suggest very high surface temperatures in case of a magma ocean that would extend to more than 40 GPa, as suggested by siderophile metal-silicate partitioning data. Such high surface temperature regime, where thermal blanketing is inefficient, points out to a transient character of the magma ocean, with a very fast cooling rate.

Petrology of spinel lherzolite xenoliths from Youkou volcano, Adamawa Massif, Cameroon Volcanic Line: mineralogical and geochemical fingerprints of sub-rift mantle processes

NASA Astrophysics Data System (ADS)

Njombie, Merlin Patrick Wagsong; Temdjim, Robert; Foley, Stephen F.

2018-02-01

The basaltic maar of Youkou, situated in the Adamawa Volcanic Massif in the eastern branch of the continental segment of the Cameroon Volcanic Line, contains mantle-derived xenoliths of various types in pyroclastites. Spinel-bearing lherzolite xenoliths from the Youkou volcano generally exhibit protogranular textures with olivine (Fo89.4-90.5), enstatite (En89 - 91Fs8.7-9.8Wo0.82-1.13), clinopyroxene, spinel (Cr#Sp = 9.4-13.8), and in some cases amphibole (Mg# = 88.5-89.1). Mineral equilibration temperatures in the lherzolite xenoliths have been estimated from three-two pyroxene thermometers and range between 835 and 937 °C at pressures of 10-18 kbar, consistent with shallow mantle depths of around 32-58 km. Trends displayed by bulk-rock MgO correlate with Al2O3, indicating that the xenoliths are refractory mantle residues after partial melting. The degree of partial melting estimated from spinel compositions is less than 10%: evidences for much higher degrees of depletion are preserved in one sample, but overprinted by refertilization in others. Trace element compositions of the xenoliths are enriched in highly incompatible elements (LREE, Sr, Ba, and U), indicating that the spinel lherzolites underwent later cryptic metasomatic enrichment induced by plume-related hydrous silicate melts. The extreme fertility (Al2O3 = 6.07-6.56 wt% in clinopyroxene) and the low CaO/Al2O3 ratios in the spinel lherzolites suggest that they could not be a simple residue of partial melting of primitive mantle and must have experienced refertilization processes driven by the infiltration of carbonatite or carbonated silicate melts.

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.

Production and recycling of oceanic crust in the early Earth

NASA Astrophysics Data System (ADS)

van Thienen, P.; van den Berg, A. P.; Vlaar, N. J.

2004-08-01

Because of the strongly different conditions in the mantle of the early Earth regarding temperature and viscosity, present-day geodynamics cannot simply be extrapolated back to the early history of the Earth. We use numerical thermochemical convection models including partial melting and a simple mechanism for melt segregation and oceanic crust production to investigate an alternative suite of dynamics which may have been in operation in the early Earth. Our modelling results show three processes that may have played an important role in the production and recycling of oceanic crust: (1) Small-scale ( x×100 km) convection involving the lower crust and shallow upper mantle. Partial melting and thus crustal production takes place in the upwelling limb and delamination of the eclogitic lower crust in the downwelling limb. (2) Large-scale resurfacing events in which (nearly) the complete crust sinks into the (eventually lower) mantle, thereby forming a stable reservoir enriched in incompatible elements in the deep mantle. New crust is simultaneously formed at the surface from segregating melt. (3) Intrusion of lower mantle diapirs with a high excess temperature (about 250 K) into the upper mantle, causing massive melting and crustal growth. This allows for plumes in the Archean upper mantle with a much higher excess temperature than previously expected from theoretical considerations.

Chromium isotope heterogeneity in the mantle

NASA Astrophysics Data System (ADS)

Xia, Jiuxing; Qin, Liping; Shen, Ji; Carlson, Richard W.; Ionov, Dmitri A.; Mock, Timothy D.

2017-04-01

To better constrain the Cr isotopic composition of the silicate Earth and to investigate potential Cr isotopic fractionation during high temperature geological processes, we analyzed the Cr isotopic composition of different types of mantle xenoliths from diverse geologic settings: fertile to refractory off-craton spinel and garnet peridotites, pyroxenite veins, metasomatised spinel lherzolites and associated basalts from central Mongolia, spinel lherzolites and harzburgites from North China, as well as cratonic spinel and garnet peridotites from Siberia and southern Africa. The δ53CrNIST 979 values of the peridotites range from - 0.51 ± 0.04 ‰ (2SD) to + 0.75 ± 0.05 ‰ (2SD). The results show a slight negative correlation between δ53Cr and Al2O3 and CaO contents for most mantle peridotites, which may imply Cr isotopic fractionation during partial melting of mantle peridotites. However, highly variable Cr isotopic compositions measured in Mongolian peridotites cannot be caused by partial melting alone. Instead, the wide range in Cr isotopic composition of these samples most likely reflects kinetic fractionation during melt percolation. Chemical diffusion during melt percolation resulted in light Cr isotopes preferably entering into the melt. Two spinel websterite veins from Mongolia have extremely light δ53Cr values of - 1.36 ± 0.04 ‰ and - 0.77 ± 0.06 ‰, respectively, which are the most negative Cr isotopic compositions yet reported for mantle-derived rocks. These two websterite veins may represent crystallization products from the isotopically light melt that may also metasomatize some peridotites in the area. The δ53Cr values of highly altered garnet peridotites from southern Africa vary from - 0.35 ± 0.04 ‰ (2SD) to + 0.12 ± 0.04 ‰ (2SD) and increase with increasing LOI (Loss on Ignition), reflecting a shift of δ53Cr to more positive values by secondary alteration. The Cr isotopic composition of the pristine, fertile upper mantle is estimated as δ53Cr = - 0.14 ± 0.12 ‰, after corrections for the effects of partial melting and metasomatism. This value is in line with that estimated for the BSE (- 0.12 ± 0.10 ‰) previously.

Earth's Various Recipes for Making Lherzolites

NASA Astrophysics Data System (ADS)

Becker, H.; van Acken, D.

2007-12-01

Petrological and cosmochemical arguments suggest that the convecting upper mantle overall should have a lherzolitic composition, otherwise, continous production of MORB would not be feasible. The predominance of harzburgites among ocean floor peridotites fits this picture because harzburgites are commonly believed to be the residue of high degrees of partial melting at shallow depths, with fertile components lost during polybaric partial melting. Implicitly, it is commonly assumed that the deeper parts of the asthenosphere and new-formed lithosphere should be residues of low-degree partial melting. This view has been supported by the abundance of lherzolites among mantle xenoliths and orogenic peridotite massifs. But is this model really correct? Data and observations on oceanic and continental peridotites accumulated over recent years hint that reality is more complicated. On the basis of mineral and whole rock compositions, and isotopic data, it has long been suspected that many continental peridotites have undergone some form of pyroxene addition via percolating melts, yet the efficacy of these processes has been uncertain. Novel combination of structural and chemical work by Le Roux et al. (2007) indicates that melt influx may have converted deformed harzburgitic rocks of the Lherz peridotite massif into little-deformed spinel lherzolites. Refertilization by MORB-like sub-lithospheric melts, and marble cake style stretching of pyroxenites have been implicated as major processes that affected the composition of peridotites from the Totalp spinel lherzolite body, a fragment of Jurassic ultra-slow spreading Thetys ocean floor in the Swiss Alps (van Acken et al., 2007). Refertilization by melts has been associated with lherzolites from oceanic fracture zones (e. g., Seyler and Bonatti, 1997) and may be responsible for lherzolites alternating with harzburgitic domains at the Arctic Gakkel ridge (Liu et al. 2007). Evidence for compositional transformation of depleted peridotites into fertile rocks, both in young oceanic and in continental settings brings up questions that need to be addressed in the future: How common are truly residual lherzolites? Are lherzolites suitable to constrain the composition of the primitive mantle? How are fertile components in the asthenosphere distributed? Mantle rocks may have more surprises in stock.

Adakites from collision-modified lithosphere

NASA Astrophysics Data System (ADS)

Haschke, M.; Ben-Avraham, Z.

2005-08-01

Adakitic melts from Papua New Guinea (PNG) show adakitic geochemical characteristics, yet their geodynamic context is unclear. Modern adakites are associated with hot-slab melting and/or remelting of orogenic mafic underplate at convergent margins. Rift-propagation over collision-modified lithosphere may explain the PNG adakite enigma, as PNG was influenced by rapid creation and subduction of oceanic microplates since Mesozoic times. In a new (rift) tectonic regime, decompressional rift melts encountered and melted remnant mafic eclogite and/or garnet-amphibolite slab fragments in arc collisional-modified mantle, and partially equilibrated with metasomatized mantle. Alternatively, hot-slab melting in a proposed newborn subduction zone along the Trobriand Trough could generate adakitic melts, but recent seismic P-wave tomographic models lack evidence for subducting oceanic lithosphere in the adakite melt region; however they do show deep subduction zone remnants as a number of high P-wave anomalies at lithospheric depths, which supports our proposed scenario.

Experimental constraints on the fate of subducted upper continental crust beyond the "depth of no return"

NASA Astrophysics Data System (ADS)

Zhang, Y.; Wu, Y.; WANG, C.; Jin, Z.

2015-12-01

Large-scale oceanic/continental subduction introduces a range of crustal materials into the Earth's mantle. These subducted material will be gravitationally trapped in the deep mantle when they have been transported to a depth of greater than ~250-300 km ("depth of no return"). However, little is known about the fate of these trapped continental material. Here, we conduct experimental study on a natural continental rock which compositionally similar to the average upper continental crust (UCC) over a pressure and temperature range of 9-16 GPa and 1300-1800 oC to constraint the fate of these trapped continental materials. The experimental results demonstrate that subducted UCC produces ~20-30 wt% K-rich melt (>55 wt% SiO2) in the upper mantle (9-13 GPa). The melting residue is mainly composed of coesite/stishovite + clinopyroxene + kyanite. In contrast, partial melting of subducted UCC in the MTZ produces ~10 wt% K-rich melt (<50 wt% SiO2), together with stishovite, clinopyroxene, K-Hollandite, garnet and CAS-phase as the residue phases. The melting residue phases achieve densities greater than the surrounding mantle, which provides a driving force for descending across the 410 km seismic discontinuity into the MTZ. However, this density relationship is reversed at the base of MTZ, leaving the descended residues being accumulated above the 660 km seismic discontinuity and may contribute to the stagnated "second continent". On the other hand, the melt is ~0.3-0.7 g/cm3 less dense than the surrounding mantle and provides a buoyancy force for the ascending of melt to shallow depth. The ascending melt preserves a significant portion of the bulk-rock REEs and LILEs. Thus, chemical reaction between the melt and the surrounding mantle would leads to a variably metasomatised mantle. Re-melting of the metasomatised mantle may contribute to the origin of the "enriched mantle sources" (EM-sources). Therefore, through subduction, stagnation, partial melting and melt segregation of continental crust may create EM-sources and"second continent" at shallow depth and the base of the MTZ respectively, which may contribute to the observed geochemical/geophysical heterogeneity in Earth's interior.

Ladder polymers for use as high temperature stable resins or coatings

NASA Technical Reports Server (NTRS)

Meador, Mary Ann (Inventor)

1990-01-01

An object of the invention is to synthesize a new class of ladder and partial ladder polymers. In accordance with the invention, the new class of ladder and partial ladder polymers are synthesized by polymerizing a bis-dienophile with a bis-diene. Another object of the invention is to provide a fabricated, electrically conducting, void free composite comprising the new class of the ladder and partial ladder polymers described above. The novelty of the invention relates to a new class of ladder and partial ladder polymers and a process for synthesizing these polymers. These polymers are soluble in common organic solvents and are characterized with a unique dehydration property at temperatures of 300 to 400 C to provide thermo-oxidatively stable pentiptycene units along the polymeric backbone. These polymers are further characterized with high softening points and good thermo-oxidative stability properties. Thus these polymers have potential as processable, matrix resins for high temperature composite applications.

Methods and systems for monitoring a solid-liquid interface

DOEpatents

Stoddard, Nathan G.; Clark, Roger F.; Kary, Tim

2010-07-20

Methods and systems are provided for monitoring a solid-liquid interface, including providing a vessel configured to contain an at least partially melted material; detecting radiation reflected from a surface of a liquid portion of the at least partially melted material that is parallel with the liquid surface; measuring a disturbance on the surface; calculating at least one frequency associated with the disturbance; and determining a thickness of the liquid portion based on the at least one frequency, wherein the thickness is calculated based on.times. ##EQU00001## where g is the gravitational constant, w is the horizontal width of the liquid, and f is the at least one frequency.

Crustal Structure of the Iceland Region from Spectrally Correlated Free-air and Terrain Gravity Data

NASA Technical Reports Server (NTRS)

Leftwich, T. E.; vonFrese, R. R. R. B.; Potts, L. V.; Roman, D. R.; Taylor, Patrick T.

2003-01-01

Seismic refraction studies have provided critical, but spatially restricted constraints on the structure of the Icelandic crust. To obtain a more comprehensive regional view of this tectonically complicated area, we spectrally correlated free-air gravity anomalies against computed gravity effects of the terrain for a crustal thickness model that also conforms to regional seismic and thermal constraints. Our regional crustal thickness estimates suggest thickened crust extends up to 500 km on either side of the Greenland-Scotland Ridge with the Iceland-Faeroe Ridge crust being less extended and on average 3-5 km thinner than the crust of the Greenland-Iceland Ridge. Crustal thickness estimates for Iceland range from 25-35 km in conformity with seismic predictions of a cooler, thicker crust. However, the deepening of our gravity-inferred Moho relative to seismic estimates at the thermal plume and rift zones of Iceland suggests partial melting. The amount of partial melting may range from about 8% beneath the rift zones to perhaps 20% above the plume core where mantle temperatures may be 200-400 C above normal. Beneath Iceland, areally limited regions of partial melting may also be compositionally and mechanically layered

Effect of oxygen partial pressure on superconducting properties of Bi-2212/Ag tapes prepared by doctor-blade method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Inoue, N.; Okada, M.; Higashiyama, K.

1997-06-01

The authors have investigated the relationship between oxygen partial pressure (P{sub O{sub 2}}) during the partial-melting process and superconducting properties for doctor-blade processed Bi-2212/Ag tapes. Tapes were heat-treated at various P{sub O{sub 2}} value of 0.01-1.00 atm. The DTA results for the doctor-blade tapes showed the melting point of the oxide rose with increasing P{sub O{sub 2}}. Correspondingly, the optimum heat-treatment temperature also increased with increasing P{sub O{sub 2}}. The tapes at P{sub O{sub 2}}=1.00 atm had the highest J{sub c} values of over 10{sup 5} A/cm{sup 2} at conditions of 4.2K, 10T, and their a.c. susceptibility showed a sharpmore » transition indicating improved intergrain coupling. Examination of cross sections for tapes melted above 0.20atm PO{sub 2} showed the good crystal alignment. From these results, it was concluded that processing at high PO{sub 2} was an effective method to obtain good superconducting properties for doctor-blade tapes.« less

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 between carbonates and silicates. Carbonates in natural mantle eclogite, which have low bulk CO2 concentration, will have Ca/Mg buffered by reactions with silicates. Consequently, experiments with high bulk CO2 may not mimic natural carbonated eclogite phase equilibria unless care is taken to ensure that CO2 enrichment does not result in inappropriate equilibrium carbonate compositions. Compositions of eclogite-derived carbonate melt span the range of natural carbonatites from oceanic and continental settings. Ca#s of carbonatitic partial melts of eclogite vary significantly and overlap those of partial melts of carbonated lherzolite, however, for a constant Ca-content, Mg# of carbonatites derived from eclogitic sources are likely to be lower than the Mg# of those generated from peridotite.

Impact induced dehydration of serpentine and the evolution of planetary atmospheres

NASA Technical Reports Server (NTRS)

Lange, M. A.; Ahrens, T. J.

1982-01-01

Results of shock recovery experiments carried out on antigorite serpentine Mg3Si2O5(OH)4 are reported. The main objective of the present study is the determination of critical shock pressures for partial and complete dehydration of serpentine under shock loading. It is pointed out that serpentine and serpentine-like layer silicates are the major water-bearing phases in carbonaceous chondrites. It appears that these minerals, and a poorly defined cometary contribution, were the most likely water-bearing phases in accreting planetesimals which led to the formation of the terrestrial planets. The obtained results imply that the process of impact induced devolatilization of volatile bearing minerals during accretion is likely to have occurred on earth. The findings lend support to the model of a terrestrial atmosphere/hydrosphere forming during the later stages of accretion of the earth.

Rocks of the early lunar crust

NASA Technical Reports Server (NTRS)

James, O. B.

1980-01-01

Data are summarized which suggest a model for the early evolution of the lunar crust. According to the model, during the final stages of accretion, the outer part of the moon melted to form a magma ocean approximately 300 km deep. This ocean fractionated to form mafic and ultramafic cumulates at depth and an overlying anorthositic crust made up of ferroan anorthosites. Subsequent partial melting in the primitive mantle underlying the crystallized magma ocean produced melts which segregated, moved upward, intruded the primordial crust, and crystallized to form layered plutons consisting of Mg-rich plutonic rocks. Intense impact bombardment at the lunar surface mixed and melted the rocks of the two suites to form a thick layer of granulated debris, granulitic breccias, and impact-melt rocks.

Controlled dehydration of a ruthenium complex-DNA crystal induces reversible DNA kinking.

PubMed

Hall, James P; Sanchez-Weatherby, Juan; Alberti, Cora; Quimper, Caroline Hurtado; O'Sullivan, Kyra; Brazier, John A; Winter, Graeme; Sorensen, Thomas; Kelly, John M; Cardin, David J; Cardin, Christine J

2014-12-17

Hydration-dependent DNA deformation has been known since Rosalind Franklin recognized that the relative humidity of the sample had to be maintained to observe a single conformation in DNA fiber diffraction. We now report for the first time the crystal structure, at the atomic level, of a dehydrated form of a DNA duplex and demonstrate the reversible interconversion to the hydrated form at room temperature. This system, containing d(TCGGCGCCGA) in the presence of Λ-[Ru(TAP)2(dppz)](2+) (TAP = 1,4,5,8-tetraazaphenanthrene, dppz = dipyrido[3,2-a:2',3'-c]phenazine), undergoes a partial transition from an A/B hybrid to the A-DNA conformation, at 84-79% relative humidity. This is accompanied by an increase in kink at the central step from 22° to 51°, with a large movement of the terminal bases forming the intercalation site. This transition is reversible on rehydration. Seven data sets, collected from one crystal at room temperature, show the consequences of dehydration at near-atomic resolution. This result highlights that crystals, traditionally thought of as static systems, are still dynamic and therefore can be the subject of further experimentation.

Catalytic dehydration of biomass derived 1-propanol to propene over M-ZSM-5 (M = H, V, Cu, or Zn)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lepore, Andrew W.; Li, Zhenglong; Davison, Brian H.

Here, the impetus to explore biomass derived chemicals arises from a desire to enable renewable and sustainable commodity chemicals. To this end, we report catalytic production of propene, a building-block molecule, from 1-propanol. We found that zeolite catalysts are quite versatile and can produce propene at or below 230 C with high selectivity. Increasing the reaction temperature above 230 C shifted product selectivity towards C4+ hydrocarbons. Cu-ZSM-5 was found to exhibit a broader temperature window for high propene selectivity and could function at higher 1-propanol space velocities than H-ZSM-5. A series of experiments with 1-propan(ol-D) showed deuterium incorporation in themore » hydrocarbon product stream including propene suggesting that hydrocarbon pool type pathway might be operational concurrent with dehydration to produce C4+ hydrocarbons. Diffuse reflectance infra-red spectroscopy of 1-propanol and 1-propan(ol-D) over Cu-ZSM-5 in combination with deuterium labeling experiments suggest that deuterium incorporation occurs in two steps. Incorporation of deuterium occurs post dehydration via exchange with the partially deuterated catalyst surface.« less

Catalytic dehydration of biomass derived 1-propanol to propene over M-ZSM-5 (M = H, V, Cu, or Zn)

DOE PAGES

Lepore, Andrew W.; Li, Zhenglong; Davison, Brian H.; ...

2017-04-03

Here, the impetus to explore biomass derived chemicals arises from a desire to enable renewable and sustainable commodity chemicals. To this end, we report catalytic production of propene, a building-block molecule, from 1-propanol. We found that zeolite catalysts are quite versatile and can produce propene at or below 230 C with high selectivity. Increasing the reaction temperature above 230 C shifted product selectivity towards C4+ hydrocarbons. Cu-ZSM-5 was found to exhibit a broader temperature window for high propene selectivity and could function at higher 1-propanol space velocities than H-ZSM-5. A series of experiments with 1-propan(ol-D) showed deuterium incorporation in themore » hydrocarbon product stream including propene suggesting that hydrocarbon pool type pathway might be operational concurrent with dehydration to produce C4+ hydrocarbons. Diffuse reflectance infra-red spectroscopy of 1-propanol and 1-propan(ol-D) over Cu-ZSM-5 in combination with deuterium labeling experiments suggest that deuterium incorporation occurs in two steps. Incorporation of deuterium occurs post dehydration via exchange with the partially deuterated catalyst surface.« less

Solid-state NMR study of various mono- and divalent cation forms of the natural zeolite natrolite.

PubMed

Park, Min Bum; Vicente, Aurélie; Fernandez, Christian; Hong, Suk Bong

2013-05-28

Here we present the one-dimensional (29)Si and (27)Al MAS NMR and two-dimensional (27)Al MQMAS and DQF-STMAS NMR spectra of the monovalent (Na(+), K(+), Rb(+), Cs(+) and NH4(+)) and divalent (Ca(2+), Sr(2+) and Ba(2+)) cation forms of the natural zeolite natrolite (framework type NAT) with complete Si-Al ordering over the crystallographically distinct tetrahedral sites and with the same hydration state (hydrated, partially dehydrated or fully dehydrated). In the case of monovalent cation-exchanged natrolites, the differences in their crystal symmetry evidenced by (29)Si MAS NMR were found to be in good agreement with those determined by crystallographic analyses. However, (27)Al DQF-STMAS NMR spectroscopy shows the presence of two distinct Al sites in dehydrated K-NAT, Rb-NAT and NH4-NAT, suggesting that their actual crystal symmetry is lower than the reported one (i.e., orthorhombic Fdd2). The MAS NMR results also show that the space group of hydrated Ca-NAT is lower than that (monoclinic F1d1) of hydrated scolecite, the natural calcium counterpart of natrolite, which is also the case with hydrated Sr-NAT and Ba-NAT. We believe that the unexpected diversity in the crystal symmetry of natrolite caused by exchange of various mono- and divalent ions, as well as by dehydration, may be inherently due to the high framework flexibility of this natural zeolite.

Phase equilibrium constraints on the origin of basalts, picrites, and komatiites

NASA Astrophysics Data System (ADS)

Herzberg, C.; O'Hara, M. J.

1998-07-01

Experimental phase equilibrium studies at pressures ranging from 1 atm to 10 GPa are sufficient to constrain the origin of igneous rocks formed along oceanic ridges and in hotspots. The major element geochemistry of MORB is dominated by partial crystallization at low pressures in the oceanic crust and uppermost mantle, forcing compliance with liquid compositions in low-pressure cotectic equilibrium with olivine, plagioclase and often augite too; parental magmas to MORB formed by partial melting, mixing, and pooling have not survived these effects. Similarly, picrites and komatiites can transform to basalts by partial crystallization in the crust and lithosphere. However, parental picrites and komatiites that were successful in erupting to the surface typically have compositions that can be matched to experimentally-observed anhydrous primary magmas in equilibrium with harzburgite [L+Ol+Opx] at 3.0 to 4.5 GPa. This pressure is likely to represent an average for pooled magmas that collected at the top of a plume head as it flattened below the lithosphere. There is substantial uniformity in the normative olivine content of primary magmas at all depths in a plume melt column, and this results in pooled komatiitic magmas that are equally uniform in normative olivine. However, the imposition of pressure above 3 GPa produces picrites and komatiites with variations in normative enstatite and Al 2O 3 that reveal plume potential temperature and depths of initial melting. Hotter plumes begin to melt deeper than cooler plumes, yielding picrites and komatiites that are enriched in normative enstatite and depleted in Al 2O 3 because of a deeper column within which orthopyroxene can dissolve during decompression. Pressures of initial melting span the 4 to 10 GPa range, increasing in the following order: Iceland, Hawaii, Gorgona, Belingwe, Barberton. Parental komatiites and picrites from a single plume also exhibit internal variability in normative enstatite and Al 2O 3, indicating either a poorly mixed partial melt aggregation process in the plume or the imposition of partial crystallization of olivine-orthopyroxenite on a well-mixed parental magma. Plume shape and thermal structure can also influence the petrology and geochemistry of picrites and komatiites. Liquids extracted from harzburgite residues [L+Ol+Opx] will dominate magmatism in a plume head, and can erupt to form komatiites in oceanic plateaus. Liquids extracted from garnet peridotite residues in a plume axis will gain in importance when the plume head partially solidifies and is removed from the hotspot by a moving lithosphere, as is the case for Hawaii. The paradoxical involvement of garnet indicated by the heavy rare earth elements in picrites that otherwise have a harzburgite signature in Hawaii can be explained by the mixing and collection of magmas from the plume axis. Volcanic rocks from Hawaii and Gorgona and xenoliths from cratonic mantle provide evidence for the importance of partial crystallization of plume magmas when they encounter a cold lithosphere. Harzburgite residua and olivine-orthopyroxene cumulates formed in plumes can yield compositionally distinct lithospheric mantle which is buoyant, and this could have provided an important foundation for the stabilization of the first continents.

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

NASA Astrophysics Data System (ADS)

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

2017-02-01

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

Research On Bi-Based High-Temperature Superconductors

NASA Technical Reports Server (NTRS)

Banks, Curtis; Doane, George B., III; Golben, John

1993-01-01

Brief report describes effects of melt sintering on Bi-based high-temperature superconductor system, as well as use of vibrating-sample magnetometer to determine hysteresis curves at 77 K for partially melt-sintered samples. Also discussed is production of high-temperature superconducting thin films by laser ablation: such films potentially useful in detection of signals of very low power.

Magmatic record of Late Devonian arc-continent collision in the northern Qiangtang, Tibet: Implications for the early evolution of East Paleo-Tethys Ocean

NASA Astrophysics Data System (ADS)

Dan, Wei; Wang, Qiang; Zhang, Xiu-Zheng; Zhang, Chunfu; Tang, Gong-Jian; Wang, Jun; Ou, Quan; Hao, Lu-Lu; Qi, Yue

2018-05-01

Recognizing the early-developed intra-oceanic arc is important in revealing the early evolution of East Paleo-Tethys Ocean. In this study, new SIMS zircon U-Pb dating, O-Hf isotopes, and whole-rock geochemical data are reported for the newly-discovered Late Devonian-Early Carboniferous arc in Qiangtang, central Tibet. New dating results reveal that the eastern Riwanchaka volcanic rocks were formed at 370-365 Ma and were intruded by the 360 Ma Gangma Co alkali feldspar granites. The volcanic rocks consist of basalts, andesites, dacites, and rhyodacites, whose geochemistry is similar to that typical of subduction-related volcanism. The basalts and andesites were generated by partial melting of the fluid and sediment-melt metasomatized mantle, respectively. The rhyodacites and dacites were probably derived from the fractional crystallization of andesites and from partial melting of the juvenile underplated mafic rocks, respectively. The Gangma Co alkali feldspar granites are A-type granites, and were possibly derived by partial melting of juvenile underplated mafic rocks in a post-collisional setting. The 370-365 Ma volcanic arc was characterized by basalts with oceanic arc-like Ce/Yb ratios and by rhyodacites with mantle-like or slightly higher zircon δ18O values, and it was associated with the contemporary ophiolites. Thus, we propose that it is the earliest intra-oceanic arc in the East Paleo-Tethys Ocean, and was accreted to the Northern Qiangtang Terrane during 365-360 Ma.

Low electrical resistivity associated with plunging of the Nazca flat slab beneath Argentina.

PubMed

Booker, John R; Favetto, Alicia; Pomposiello, M Cristina

2004-05-27

Beneath much of the Andes, oceanic lithosphere descends eastward into the mantle at an angle of about 30 degrees (ref. 1). A partially molten region is thought to form in a wedge between this descending slab and the overlying continental lithosphere as volatiles given off by the slab lower the melting temperature of mantle material. This wedge is the ultimate source for magma erupted at the active volcanoes that characterize the Andean margin. But between 28 degrees and 33 degrees S the subducted Nazca plate appears to be anomalously buoyant, as it levels out at about 100 km depth and extends nearly horizontally under the continent. Above this 'flat slab', volcanic activity in the main Andean Cordillera terminated about 9 million years ago as the flattening slab presumably squeezed out the mantle wedge. But it is unknown where slab volatiles go once this happens, and why the flat slab finally rolls over to descend steeply into the mantle 600 km further eastward. Here we present results from a magnetotelluric profile in central Argentina, from which we infer enhanced electrical conductivity along the eastern side of the plunging slab, indicative of the presence of partial melt. This conductivity structure may imply that partial melting occurs to at least 250 km and perhaps to more than 400 km depth, or that melt is supplied from the 410 km discontinuity, consistent with the transition-zone 'water-filter' model of Bercovici and Karato.

Chlorite Stability in the Mantle Wedge and its Role in Subduction Zone Melting Processes

NASA Astrophysics Data System (ADS)

Grove, T. L.; Chatterjee, N.; Medard, E.; Parman, S. W.

2006-12-01

New experimental constraints on the H2O-saturated melting behavior of mantle peridotite (Grove et al., 2006, EPSL 249: 74 - 89) show that chlorite is a stable phase on the vapor-saturated solidus of peridotite at a pressure of 2 GPa and higher. Hydrous melting in the presence of chlorite begins at 860 °C at 2 GPa and the solidus temperature decreases continuously to 800 °C at 3.2 GPa. The solidus phases include olivine, orthopyroxene, high-Ca clinopyroxene and spinel + chlorite over the pressure range of 2 to 2.4 GPa. Garnet + chlorite + ilmenite are present above 2.4 GPa. At 2.8 to 3.2 GPa, chlorite is stable on the vapor- saturated solidus, but it reacts out 20 to 40 °C above the solidus. The temperature-pressure range for chlorite stability and vapor-saturated melting behavior involving chlorite are similar to those inferred for the mantle wedge above the subducted slab by geodynamic thermal models. Thus, chlorite may be a stable phase within the mantle wedge and may play a role in the onset of hydrous mantle melting. The factors that lead to the initiation of melting in subduction zones have remained enigmatic. The occurrence of volcanic fronts above the mantle wedge-subducted slab interface near a depth of 100 km in most arcs has not been conclusively explained. Melting must somehow be linked to processes that involve the release of water from the slab into the overlying mantle wedge, but why does melting always begin at or below 100 km? A potential melt triggering mechanism is that H2O released from dehydration reactions in the subducted oceanic lithosphere at pressures > 2 GPa rises into the overlying mantle and reacts with peridotite to form chlorite. This chloritized peridotite is pulled down by mantle flow to pressures of 3 to 3.5 GPa. Increases in temperature in the mantle wedge above the subducted slab lead to chlorite breakdown and/or vapor-saturated melting initiation. When mantle peridotite is hydrated ~ 13 wt. % chlorite is produced for a bulk H2O content of 2 wt. %. This is a large amount of H2O sufficient to produce melts with elevated H2O contents observed in primitive arc magmas (6 wt. % H2O) by flux melting. Thus, the uniform depth of 100 km from slab/wedge interface to overlying volcanic arc may be related to melting of chloritized mantle.

Adakitic volcanism in the eastern Aleutian arc: Petrology and geochemistry of Hayes volcano, Cook Inlet, Alaska

NASA Astrophysics Data System (ADS)

McHugh, K.; Hart, W. K.; Coombs, M. L.

2012-12-01

Located in south-central Alaska, 135 km northwest of Anchorage, Hayes volcano is responsible for the most widespread tephra fall deposit in the regional Holocene record (~3,500 BP). Hayes is bounded to the west by the Cook Inlet volcanoes (CIV; Mt. Spurr, Redoubt, Iliamna, and Augustine) and separated from the nearest volcanism to the east, Mount Drum of the Wrangell Volcanic Field (WVF), by a 400 km-wide volcanic gap. We report initial results of the first systematic geochemical and petrologic study of Hayes volcano. Hayes eruptive products are calc-alkaline dacites and rhyolites that have anomalous characteristics within the region. Major and trace element analyses reveal that the Hayes rhyolites are more silicic (~74 wt. % SiO2) than compositions observed in other CIV, and its dacitic products possess the distinctive geochemical signatures of adakitic magmas. Key aspects of the Hayes dacite geochemistry include: 16.03 - 17.54 wt. % Al2O3, 0.97 - 2.25 wt. % MgO, Sr/Y = 60 - 78, Yb = 0.9 - 1.2 ppm, Ba/La = 31 - 79. Such signatures are consistent with melting of a metamorphosed basaltic source that leaves behind a residue of garnet ± amphibole ± pyroxene via processes such as melting of a subducting oceanic slab or underplated mafic lower crust, rather than flux melting of the mantle wedge by dehydration of the down-going slab. Additionally, Hayes tephras display a distinctive mineralogy of biotite with amphibole in greater abundance than pyroxene, a characteristic not observed at other CIV. Furthermore, Hayes rhyolites and dacites exhibit little isotopic heterogeneity (87Sr/86Sr = 0.70384 - 0.70395, 206Pb/204Pb = 18.866 - 18.889) suggesting these lavas originate from the same source. Hayes volcano is approximately situated above the western margin of the subducting Yakutat terrane and where the dip of the Pacific slab beneath Cook Inlet shallows northward. Due to its position along the margin of the subducting Yakutat terrane, it is plausible that Hayes magmas are the result of partial melting of this slab where thermal erosion and weakening of the crust occurs along the Pacific plate-Yakutat terrane transition. Additionally, flat slab subduction may be responsible for producing adakitic magmas by equilibration of the hydrous slab with ambient mantle temperatures. In contrast, it is possible that the adakitic signature at Hayes is from underplated mafic lower crust that melted as the result of pooling mantle melt at depth. Two volcanoes within the WVF, Mt. Drum and Mt. Churchill, are adakitic with an abundance of biotite and amphibole similar to Hayes volcano and have been suggested to have slab melt origins. Mt. Drum lavas have less radiogenic 87Sr/86Sr but overlapping 206Pb/204Pb signatures while Mt. Churchill, which approximately overlies the eastern edge of the Yakutat terrane, has similar 87Sr/86Sr compositions, but more radiogenic 206Pb/204Pb than Hayes. Mt. Spurr, the nearest CIV to Hayes volcano (90 km south), does not share its adakitic signature but exhibits overlapping, more heterogeneous isotopic compositions. Thus, understanding the petrogenetic history of Hayes volcano is essential not only to explain the development of an adakitic volcanic system but how this relates to regional, arc-wide volcanism.

Wüstite in the fusion crust of Almahata Sitta sulfide-metal assemblage MS-166: Evidence for oxygen in metallic melts

NASA Astrophysics Data System (ADS)

Horstmann, Marian; Humayun, Munir; Harries, Dennis; Langenhorst, Falko; Chabot, Nancy L.; Bischoff, Addi; Zolensky, Michael E.

2013-05-01

Meteorite fusion crusts form during the passage of a meteoroid through the Earth's atmosphere and are highly oxidized intergrowths as documented by the presence of e.g., oxides. The porous and irregular fusion crust surrounding the Almahata Sitta sulfide-metal assemblage MS-166 was found highly enriched in wüstite (Fe1-xO). Frictional heating of the outer portions of the assemblage caused partial melting of predominantly the Fe-sulfide and minor amounts of the outer Ni-rich portions of the originally zoned metal in MS-166. Along with melting significant amounts of oxygen were incorporated into the molten fusion crust and mainly FeS was oxidized and desulfurized to form wüstite. Considerable amounts of FeS were lost due to ablation, whereas the cores of the large metal grains appear largely unmelted leaving behind metal grains and surrounding wüstite-rich material (matte). Metal grains along with the surrounding matte typically form an often highly porous framework of globules interconnected with the matte. Although textures and chemical composition suggest that melting of Fe,Ni metal occurred only partially (Ni-rich rims), there is a trace elemental imprint of siderophile element partitioning influenced by oxygen in the metallic melt as indicated by the behavior of W and Ga, the two elements significantly affected by oxygen in a metallic melt. It is remarkable that MS-166 survived the atmospheric passage as troilite inclusions in iron meteorites are preferentially destroyed.

Evidence for shallow dehydration of the subducting plate beneath the Mariana forearc: New insights into the water cycle at subduction zones

NASA Astrophysics Data System (ADS)

Ribeiro, J.; Stern, R. J.; Kelley, K. A.; Shaw, A. M.; Martinez, F.; Ohara, Y.

2014-12-01

Water is efficiently recycled at subduction zones. It is fluxed from the surface into the mantle by the subducted plate and back to the surface or crust through explosive arc volcanism and degassing. Fluids released from dehydrating the subducting plate are transfer agents of water. Geophysical modeling [1] and the geochemistry of arc glasses [2] suggest that at cold-slab subduction zones, such as the Mariana convergent margin, the downgoing plate mostly dehydrates beneath the volcanic arc front (≥ ~ 80 -100 km depth to slab) to trigger volcanism. However, there is a gap in our understanding of the water fluxes released beneath forearcs, as examples of forearc magmatism are extremely rare. Here, we investigate the Southernmost Mariana Forearc Rift (SEMFR), where MORB-like spreading occurred unusually close to the trench, sampling slab-derived aqueous fluids released at ~ 30 to 100 km depth from the subducted plate. Examining the trace element and water contents of olivine-hosted melt inclusions and glassy rinds from the young (2 - 4 Ma) and fresh SEMFR pillowed basalts provide new insights into the global water cycle. SEMFR lavas contain ~2 wt % H2O, and the olivine-hosted melt inclusions have the highest subduction-related H2O/Ce ratios (H2O/Ce = 6000 - 19000) ever recorded in arc magmas (H2O/Ce < 10600 and global averaged H2O/Ce < 3000). Our findings show that (i) slab-derived fluids released beneath forearcs are water-rich compared to the deeper fluids released beneath the arc system; and (ii) cold downgoing plates lose most of their water at shallow depths (~ 70 - 80 km slab depth), suggesting that water is efficiently recycled beneath the forearc (≥ 90%). 1. Van Keken, P.E., et al., Subduction factory: 4. Depth-dependent flux of H2O from subducting slabs worldwide. Journal of Geophysical Research: Solid Earth, 2011. 116(B1): p. B01401, DOI: 10.1029/2010jb007922. 2. Ruscitto, D.M., et al., Global variations in H2O/Ce: 2. Relationships to arc magma geochemistry and volatile fluxes. Geochemistry Geophysics Geosystems, 2012. 13(3): p. Q03025, DOI: 10.1029/2011gc003887.

Full Food Service Contract for Army Dining Facilities

DTIC Science & Technology

1982-01-01

I LB - — —- COP’JE *">ältfO tlA INSTANT VA 0/ 1.** ." CN I» ’v — —. 1 »M 1 it IB 5r ».!•. 4<j l.?n I.Ti .6) • e...1 i f*»n*j MfDI»"* T#BTAC SA’lCF tO-| 1| AFAISEC MM AND NOODLES II-1TI AA«FD •’’TATTf S (Q-441 SCuA f»FA« H-T *MCf O...degree F preheated oven for about 15 minutes or until cheese is melted. 8 Beef Noodle Soup (Dehydrated) Prepare in accordance with directions

Sound velocity measurement in liquid water up to 25 GPa and 900 K: Implications for densities of water at lower mantle conditions

NASA Astrophysics Data System (ADS)

Asahara, Yuki; Murakami, Motohiko; Ohishi, Yasuo; Hirao, Naohisa; Hirose, Kei

2010-01-01

We extended the pressure range of sound velocity measurements for liquid water to 25 GPa and 900 K along the melting curve using a laser heated diamond anvil cell with a combined system of Brillouin scattering and synchrotron X-ray diffraction. Experimental pressure and temperature were obtained by solving simultaneous equations: the melting curve of ice and the equation of state for gold. The sound velocities obtained in liquid water at high pressures and melting temperatures were converted to density using Murnaghan's equation of state by fitting a parameter of the pressure derivative of bulk modulus at 1 GPa. The results are in good agreement with the values predicted by a previously reported equation of state for water based on sound velocity measurements. The equation of state for water obtained in this study could be applicable to water released by dehydration reactions of dense hydrous magnesium silicate phases in cold subducting slabs at lower mantle conditions, although the validity of Murnaghan's equation of state for water should be evaluated in a wider pressure and temperature ranges. The present velocity data provides the basis for future improvement of the accurate thermodynamic model for water at high pressures.

The Ge/Si ratio quantifies the role of recycled crust in the generation of MORBs

NASA Astrophysics Data System (ADS)

Yang, S.; Humayun, M.; Salters, V. J. M.

2017-12-01

Global MORBs cover a broad spectrum of incompatible element compositions from depleted [(La/Sm)N < 0.5] to enriched [(La/Sm)N 0.5-2]. Two explanations for the origin of the enriched mantle sources of E-MORBs from ridge segments not associated with plumes have been proposed: (1) re-fertilization of Depleted Mantle (DM) by infiltration of low-degree melts (<1%) from subducted crust, or (2) by entrainment of solid recycled crust in the Depleted Mantle (DM). Whether pyroxenite contributes melt to E-MORB can be resolved by chemically distinguishing between partial melts of a peridotite source vs. those of a lithologically heterogeneous source of peridotite and pyroxenite. In this study, we exploit the mineralogical preferences of elements like Ge and Si to distinguish melts formed from peridotite or pyroxenite. In-situ analyses of 60 elements in 319 MORB glasses from north (10-36 °N) Mid-Atlantic Ridge (MAR) and Mid-Cayman Rise were performed by LA-ICP-MS. Use of a large laser spot size (150 μm) and high repetition rate (50 Hz) yielded a low blank correction (< 5%) for Ge, and high external precision for the Ge/Si ratio (± 3%, 1σ) in MORB glasses. E-MORBs (6.4±0.2) are systematically lower in Ge/Si than D-MORBs (7.2±0.2), while N-MORBs fall in between and are not fully resolved from either D- or E-MORB. Based on experimental Ds, partial melts from pyroxenites are always lower in Ge/Si than partial melts from peridotites because Ge is more compatible in garnet and clinopyroxene than in olivine [1]. E-MORBs also have lower Sc abundances (37 vs. 43 ppm) but slightly higher Fe/Mn ratios (55 vs. 53) than D-MORBs, and lower La/Nb (0.6 vs. 1-2) and Sr/Nb (<20 vs. >40), consistent with addition of 27% pyroxenite-derived melts to a D-MORB-like composition. This requires that the amount of solid recycled garnet pyroxenite in a peridotite source is 12%. The Ge/Si ratio is a new tool that effectively discriminates between melts derived from peridotite sources and melts derived from pyroxenite sources. Extrapolating from the correlation between K2O/TiO2 and Ge/Si established in this study, we estimated the distribution of pyroxenite, solid recycled crust, in the mantle sources of global MORB segments, which reveals a mode of 3-4% pyroxenite in the MORB source. [1] Davis et al., 2013

Sources and mobility of carbonate melts beneath cratons, with implications for deep carbon cycling, metasomatism and rift initiation

NASA Astrophysics Data System (ADS)

Tappe, Sebastian; Romer, Rolf L.; Stracke, Andreas; Steenfelt, Agnete; Smart, Katie A.; Muehlenbachs, Karlis; Torsvik, Trond H.

2017-05-01

Kimberlite and carbonatite magmas that intrude cratonic lithosphere are among the deepest probes of the terrestrial carbon cycle. Their co-existence on thick continental shields is commonly attributed to continuous partial melting sequences of carbonated peridotite at >150 km depths, possibly as deep as the mantle transition zone. At Tikiusaaq on the North Atlantic craton in West Greenland, approximately 160 Ma old ultrafresh kimberlite dykes and carbonatite sheets provide a rare opportunity to study the origin and evolution of carbonate-rich melts beneath cratons. Although their Sr-Nd-Hf-Pb-Li isotopic compositions suggest a common convecting upper mantle source that includes depleted and recycled oceanic crust components (e.g., negative ΔεHf coupled with > + 5 ‰ δ7Li), incompatible trace element modelling identifies only the kimberlites as near-primary low-degree partial melts (0.05-3%) of carbonated peridotite. In contrast, the trace element systematics of the carbonatites are difficult to reproduce by partial melting of carbonated peridotite, and the heavy carbon isotopic signatures (-3.6 to - 2.4 ‰ δ13C for carbonatites versus -5.7 to - 3.6 ‰ δ13C for kimberlites) require open-system fractionation at magmatic temperatures. Given that the oxidation state of Earth's mantle at >150 km depth is too reduced to enable larger volumes of 'pure' carbonate melt to migrate, it is reasonable to speculate that percolating near-solidus melts of carbonated peridotite must be silicate-dominated with only dilute carbonate contents, similar to the Tikiusaaq kimberlite compositions (e.g., 16-33 wt.% SiO2). This concept is supported by our findings from the North Atlantic craton where kimberlite and other deeply derived carbonated silicate melts, such as aillikites, exsolve their carbonate components within the shallow lithosphere en route to the Earth's surface, thereby producing carbonatite magmas. The relative abundances of trace elements of such highly differentiated 'cratonic carbonatites' have only little in common with those of metasomatic agents that act on the deeper lithosphere. Consequently, carbonatite trace element systematics should only be used with caution when constraining carbon mobility and metasomatism at mantle depths. Regardless of the exact nature of carbonate-bearing melts within the mantle lithosphere, they play an important role in enrichment processes, thereby decreasing the stability of buoyant cratons and promoting rift initiation - as exemplified by the Mesozoic-Cenozoic breakup of the North Atlantic craton.

Consequences of viscous anisotropy for melt localization in a deforming, two-phase aggregate

NASA Astrophysics Data System (ADS)

Takei, Y.; Katz, R. F.

2012-12-01

Melt localization in the deforming, partially molten mantle has been of interest because it affects the melt extraction rate, mantle deformability, and chemical interaction between the melt and host rock. Experimental studies have reported the spontaneous segregation of melt into melt-rich bands in samples deformed under simple shear and torsion (Holtzman et al, 2003, King et al, 2010). Efforts to clarify the instability mechanism have so far revealed that rheological properties of partially molten rocks control the occurrence of instability. Porosity-weakening viscosity, empirically written as exp(- λ × f) with porosity f and constant λ(= 25-45), plays an essential role in the destabilization of porosity perturbation in the shear flow of a two-phase aggregate (eg., pure shear flow, simple shear flow): the perturbation growth rate is proportional to the product of shear strain rate and the factor λ (Stevenson, 1989). The stress exponent n of the viscosity affects the angle of the perturbation plane with maximum growthrate, where n=3-6 (power-law creep) explains the experimentally observed low angle to the shear plane (Katz et al, 2006). However, in-situ experimental measurements of n indicate that it takes values as low as unity without affecting the observed orientation of melt bands. Viscous anisotropy provides an alternative explanation for the observed band angles. It is produced by the stress-induced microstructural anisotropy (Daines and Kohlstedt, 1997; Zimmermann et al., 1999; Takei, 2010), and it enhances the coupling between melt migration and matrix shear deformation (Takei and Holtzman, 2009). Even without any porosity perturbation, viscous anisotropy destabilizes simple patterns of two-phase flow with a stress/strain gradient (eg., Poiseuille flow, torsional flow) and gives rise to shear-induced melt localization: the growth rate of this mechanism depends on the shear strain rate and the compaction length relative to the spatial scale of the gradient. When a porosity perturbation is added to the anisotropic system, both localization mechanisms work simultaneously, where the dominant angle of perturbation is decreased by the viscous anisotropy, similarly to the effect of n. Although viscous anisotropy plays an important role in melt localization, previous studies were limited to some simple or linearized cases (Takei and Holtzman, 2009, Butler 2012). Using linearised stability analysis and numerical simulation, we perform a systematic study of viscous anisotropy for behavior of partially molten rocks under forced deformation. Fully nonlinear solutions are obtained for melt localization under simple shear flow, 2D Poiseuille flow, and torsional flow. We show that Poiseuille flow causes melt-lubrication instability, but torsional flow does not. Results for simple shear and torsional flow are compared to the experimental results. Through the comparison between model predictions and experiments, we can test the validity of current theory, ascertain its deficiencies, and refine it to better describe the natural system.

The role of silver in the processing and properties of Bi-2212

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

1994-12-31

The influence of the silver content and the oxygen partial pressure on the solidus temperature and the weight loss during melting of Bi{sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub x} has been examined by means of DTA and TGA. By decreasing the oxygen partial pressure the solidus is lowered (e.g. {triangle}T=59{degrees}C by decreasing pO{sub 2} from 1 atm to 0.001 atm) and the weight loss is increased. The addition of silver causes two effects: (a) the solidus is further decreased (e.g. 2wt% Ag lower T{sub solidus} by up to 25{degrees}C, depending on the oxygen partial pressure), (b) the weight loss during meltingmore » is reduced. Thick films (10-20 {mu}m in thickness) with 0 and 5 wt% silver and bulk samples with 0 and 2.7 wt% silver were melt processed in flowing oxygen on a silver substrate in the DTA, allowing the observation of the melting process and a good temperature control. The critical current densities are vigorously dependent on the maximum processing temperature. The highest j{sub c} in thick films (8000 A/cm{sup 2} at 77 K, O T) was reached by melting 7{degrees}C above the solidus temperature. The silver addition shows no significant effect on the processing parameters or the superconducting properties. The highest j{sub c} for bulk samples (1 mm in thickness) was obtained by partial melting at 900{degrees}C or 880{degrees}C, depending on the silver content of the powder (0 or 2.7 wt%). The j{sub c} of the samples is slightly enhanced from 1800 A/cm{sup 2} (at 77 K, O T) to 2000 A/cm{sup 2} by the silver addition. To be able to reach at least 80% of the maximum critical current density, the temperature has to be controlled in a window of 5{degrees}C for thick films and 17{degrees}C for bulk samples.« less

Pristine Igneous Rocks and the Early Differentiation of Planetary Materials

NASA Technical Reports Server (NTRS)

Warren, Paul H.

1998-01-01

Our studies are highly interdisciplinary, but are focused on the processes and products of early planetary and asteroidal differentiation, especially the genesis of the ancient lunar crust. Most of the accessible lunar crust consists of materials hybridized by impact-mixing. Rare pristine (unmixed) samples reflect the original genetic diversity of the early crust. We studied the relative importance of internally generated melt (including the putative magma ocean) versus large impact melts in early lunar magmatism, through both sample analysis and physical modeling. Other topics under investigation included: lunar and SNC (martian?) meteorites; igneous meteorites in general; impact breccias, especially metal-rich Apollo samples and polymict eucrites; effects of regolith/megaregolith insulation on thermal evolution and geochronology; and planetary bulk compositions and origins. We investigated the theoretical petrology of impact melts, especially those formed in large masses, such as the unejected parts of the melts of the largest lunar and terrestrial impact basins. We developed constraints on several key effects that variations in melting/displacement ratio (a strong function of both crater size and planetary g) have on impact melt petrology. Modeling results indicate that the impact melt-derived rock in the sampled, megaregolith part of the Moon is probably material that was ejected from deeper average levels than the non-impact-melted material (fragmental breccias and unbrecciated pristine rocks). In the largest lunar impacts, most of the impact melt is of mantle origin and avoids ejection from the crater, while most of the crust, and virtually all of the impact-melted crust, in the area of the crater is ejected. We investigated numerous extraordinary meteorites and Apollo rocks, emphasizing pristine rocks, siderophile and volatile trace elements, and the identification of primary partial melts, as opposed to partial cumulates. Apollo 15 sample 15434,28 is an extraodinarily large glass spherule, nearly if not entirely free of meteoritic contamination, and provides insight into the diversity of mare basalts in the Hadley-Apennine region. Apollo 14 sample 14434 is in many respects a new rock type, intermediate between nonmare gabbronorites and mare basalts. We helped to both plan and implement a consortium to study the Yamato-793605 SNC/martian meteorite.

Melt production in large-scale impact events: Implications and observations at terrestrial craters

NASA Technical Reports Server (NTRS)

Grieve, Richard A. F.; Cintala, Mark J.

1992-01-01

The volume of impact melt relative to the volume of the transient cavity increases with the size of the impact event. Here, we use the impact of chondrite into granite at 15, 25, and 50 km s(sup -1) to model impact-melt volumes at terrestrial craters in crystalline targets and explore the implications for terrestrial craters. Figures are presented that illustrate the relationships between melt volume and final crater diameter D(sub R) for observed terrestrial craters in crystalline targets; also included are model curves for the three different impact velocities. One implication of the increase in melt volumes with increasing crater size is that the depth of melting will also increase. This requires that shock effects occurring at the base of the cavity in simple craters and in the uplifted peaks of central structures at complex craters record progressively higher pressures with increasing crater size, up to a maximum of partial melting (approx. 45 GPa). Higher pressures cannot be recorded in the parautochthonous rocks of the cavity floor as they will be represented by impact melt, which will not remain in place. We have estimated maximum recorded pressures from a review of the literature, using such observations as planar features in quartz and feldspar, diaplectic glasses of feldspar and quartz, and partial fusion and vesiculation, as calibrated with estimates of the pressures required for their formation. Erosion complicates the picture by removing the surficial (most highly shocked) rocks in uplifted structures, thereby reducing the maximum shock pressures observed. In addition, the range of pressures that can be recorded is limited. Nevertheless, the data define a trend to higher recorded pressures with crater diameter, which is consistent with the implications of the model. A second implication is that, as the limit of melting intersects the base of the cavity, central topographic peaks will be modified in appearance and ultimately will not occur. That is, the peak will first develop a central depression, due to the flow of low-strength melted materials, when the melt volume begins to intersect the transient-cavity base.

A Re-Os Study of Depleted Trench Peridotites from Northern Mariana

NASA Astrophysics Data System (ADS)

Ghosh, T.; Snow, J. E.; Heri, A. R.; Brandon, A. D.; Ishizuka, O.

2017-12-01

Trench peridotites provide information about the influence of subduction initiation on the extent of mantle wedge melting. They preserve melting records throughout subduction history, and as a result, likely experience multiple melt extraction events leading to successive depletion of melt/fluid mobile major and trace elements. To track melting histories of trench peridotites, Re-Os and PGEs can be used as reliable tracers to constrain early melt extraction or re-fertilization events. The Izu-Bonin-Mariana arc, being the largest intra-oceanic subduction system, provides an excellent area to study the formation of supra-subduction zone mantle and crust. Residual peridotite (harzburgite and dunite) samples were collected by dredging from the landward slope of the northern Mariana Trench. The samples are serpentinized to various extents (typical of abyssal peridotites), leaving behind relict grains of spinel, enstatite and olivine embedded within a serpentine matrix along with occasional interstitial diopside. Major element analyses of primary minerals reveal a wide range of variations in Cr# of spinels from 0.31-0.85 indicating 16-20% of melt fraction with dunites apparently experiencing the highest amount of partial melting. For Re-Os and PGE geochemistry, samples with high amounts of spinel (>4 vol %) and variable Cr# were chosen. Initial results show that bulk rock 187Os/188Os ratios range from 0.1113 to 0.1272. All of the samples are sub-chondritic, but in some cases, they are more radiogenic than average abyssal peridotites. Os abundances vary from 1-9 ppb. Sub-chondritic values can be attributed to the samples having evolved from a Re-depleted mantle source indicating a previous melt-extraction event. The cpx-harzburgites, having lower Cr# ( 0.4) are more radiogenic than ultra depleted dunites (Cr# 0.8), which might indicate preferential removal of Os during an apparent higher degree of partial melting experienced by dunites. The higher 187Os/188Os ratios of cpx-harzburgites possibly imply a late stage melt-rock interaction event, which had refertilized the depleted samples in radiogenic Os. Since there are only trace amounts of sediments in the accretionary prism of N. Mariana, Os ratios of these trench peridotites are not influenced by Os from sediments.

Mild to moderate dehydration combined with moderate alcohol consumption has no influence on simulated driving performance.

PubMed

Irwin, Christopher; Leveritt, Michael; Shum, David H K; Desbrow, Ben

2014-01-01

Many people consume alcoholic beverages following a period of physical activity that results in fluid loss through sweating (e.g., after sports, work). Adequate rehydration following physical activity may not occur, consequently resulting in the consumption of alcohol in a dehydrated state. This may have serious implications for the safety of individuals operating motor vehicles. Therefore, this study investigated the impact of mild-moderate dehydration in combination with moderate alcohol consumption on simulated driving performance. Fourteen healthy males participated in a placebo-controlled crossover design study involving 4 experimental trials (separated by 4 days or more). In each trial, participants were dehydrated by ∼2 percent body mass through exercise. After a 30-min recovery, participants completed a 15-min computerized simulated driving task (drive 1). In 2 of the trials, participants were provided with water equivalent to either 50 or 150 percent body mass loss and also received salt capsules (NaCl, 50 mmol/L). A set volume of alcohol or placebo was then consumed in each trial, incorporating the conditions: dehydration-placebo (DP), dehydration-alcohol (DA), partial rehydration-alcohol (PA), and full rehydration-alcohol (FA). The volume of the alcoholic beverage was individually calculated and intended to raise the blood alcohol content (BAC) to ∼0.05 percent. The same driving task was then readministered (drive 2). Primary outcome measures of driving consisted of standard deviation of lateral position (SDLP), number of side and center line crossings (LC), number of failures to stop at red traffic signals (FTS), number of impacts/collisions with other vehicles or objects (IMP), and time to collision with a specified lead vehicle (TTC). In addition, reaction time (RT) and incorrect inhibition response (IIR) behavior to critical events were collected throughout each experimental drive. Subjective ratings of mood and estimates of alcohol intoxication and driving impairment were also recorded in each trial. No effects of trial condition were observed on any of the driving performance measures or on subjective ratings of mood, alcohol intoxication, and driving impairment. SDLP was higher following the consumption of alcohol compared to the placebo trial. However, no differences in SDLP were recorded between the alcohol trials, indicating that hydration level had no observable interaction with alcohol to influence SDLP performance. Overall, it appears that dehydration does not exacerbate impairment in driving performance caused by mild-moderate alcohol intoxication. Further research is required to clarify the effects of alcohol and dehydration at various alcohol doses.

Reactive Transport of Slab-Derived Carbonatitic Melts in the Deep Upper Mantle and Generation of Kimberlites

NASA Astrophysics Data System (ADS)

Sun, C.; Dasgupta, R.

2017-12-01

Kimberlite is a diamond-bearing CO2-rich ultramafic magma from the mantle at depths of >200 km, featured by enrichment of incompatible elements [1]. It has been considered significant for understanding mantle geochemistry and particularly for providing information of deep carbon cycle. Recent experimental studies suggested that partial melts of carbonated peridotites at high pressures and temperatures could resemble the MgO (>20 wt%) and enriched incompatible elements in kimberlites only when the source experienced refertilization with perhaps prior depletion (e.g., [2]). Although addition of CO2 and incompatible elements in the deep mantle is often linked to subducted components, partial melts directly from carbonated oceanic crusts do not have high enough MgO (e.g., ≤8.2 wt%; [3]). A crucial question is how slab-derived CO2-rich melt evolves in reaction with ambient mantle, which may provide a feasible mechanism for kimberlite generation. To investigate the fate of slab-derived carbonatitic melt in the deep ambient mantle, we have performed multi-anvil experiments at 7-10 GPa and 1400-1450 °C. The starting compositions were synthesized by mixing a fertile peridotite composition, KLB-1, with variable proportions (0-45 wt.%) of Ca-rich carbonatitic melt similar to those derived from a carbonated ocean crust at 13-21 GPa [3]. Experiments were performed in Pt, Pt/Gr, Au-Pd and Au-Pd/Gr capsules, and the experimental phases include olivine ± opx + cpx + majoritic garnet ± carbonated silicate melt. With the increase of melt-rock ratios, experimental melts become progressively enriched in CaO (13.0-23.1 wt%) and CO2 (14.2-38.7 wt%) but depleted in MgO (28.9-19.9 wt%), SiO2 (33.1-7.9 wt%), and Al2O3 (2.7-0.2 wt%). The net flux of melt increases with the increase of infiltrating carbonatitic melt proportion and with the decrease of pressure. Kimberlite melts were produced from experiments with 5-25 wt% infiltrating carbonatitic melts by dissolution of olivine and orthopyroxene and precipitation of clinopyroxene. Thus, a localized influx of slab-derived CO2-rich melts can enlarge the mantle porosity, enhance melt focusing, and initiate a channelized flow of kimberlite melts. [1] Becker & Le Roex (2006) J. Pet. 47: 673-703; [2] Brey et al. (2008) J. Pet. 49: 797-821; [3] Thomson et al. (2016) Nature 529: 76-79.

Large-ion lithophile elements delivered by saline fluids to the sub-arc mantle

NASA Astrophysics Data System (ADS)

Kawamoto, Tatsuhiko; Mibe, Kenji; Bureau, Hélène; Reguer, Solenn; Mocuta, Cristian; Kubsky, Stefan; Thiaudière, Dominique; Ono, Shigeaki; Kogiso, Tetsu

2014-12-01

Geochemical signatures of arc basalts can be explained by addition of aqueous fluids, melts, and/or supercritical fluids from the subducting slab to the sub-arc mantle. Partitioning of large-ion lithophile elements between aqueous fluids and melts is crucial as these two liquid phases are present in the sub-arc pressure-temperature conditions. Using a micro-focused synchrotron X-ray beam, in situ X-ray fluorescence (XRF) spectra were obtained from aqueous fluids and haplogranite or jadeite melts at 0.3 to 1.3 GPa and 730°C to 830°C under varied concentrations of (Na, K)Cl (0 to 25 wt.%). Partition coefficients between the aqueous fluids and melts were calculated for Pb, Rb, and Sr ([InlineEquation not available: see fulltext.]). There was a positive correlation between [InlineEquation not available: see fulltext.] values and pressure, as well as [InlineEquation not available: see fulltext.] values and salinity. As compared to the saline fluids with 25 wt.% (Na, K)Cl, the Cl-free aqueous fluids can only dissolve one tenth (Pb, Rb) to one fifth (Sr) of the amount of large-ion lithophile elements when they coexist with the melts. In the systems with 13 to 25 wt.% (Na, K)Cl, [InlineEquation not available: see fulltext.] values were greater than unity, which is indicative of the capacity of such highly saline fluids to effectively transfer Pb and Rb. Enrichment of large-ion lithophile elements such as Pb and Rb in arc basalts relative to mid-oceanic ridge basalts (MORB) has been attributed to mantle source fertilization by aqueous fluids from dehydrating oceanic plates. Such aqueous fluids are likely to contain Cl, although the amount remains to be quantified.

Hydrodynamic instabilities of flows involving melting in under-saturated porous media

NASA Astrophysics Data System (ADS)

Sajjadi, M.; Azaiez, J.

2016-03-01

The process of melting in partially saturated porous media is modeled for flow displacements prone to hydrodynamic instabilities due to adverse mobility ratios. The effects of the development of instabilities on the melting process are investigated through numerical simulations as well as analytical solution to unravel the physics of the flow. The effects of melting parameters, namely, the melting potential of the fluid, the rate of heat transfer to the frozen phase, and the saturation of the frozen material along with the parameters defining the viscous forces, i.e., the thermal and solutal log mobility ratios are examined. Results are presented for different scenarios and the enhancement or attenuation of instabilities are discussed based on the dominant physical mechanisms. Beside an extensive qualitative analysis, the performance of different displacement scenarios is compared with respect to the melt production and the extent of contribution of instability to the enhancement of melting. It is shown that the hydrodynamic instabilities tend in general to enhance melting but the rate of enhancement depends on the interplay between the instabilities and melting at the thermal front. A larger melting potential and a smaller saturation of the frozen material tend to increase the contribution of instability to melting.

Silicate melts density, buoyancy relations and the dynamics of magmatic processes in the upper mantle

NASA Astrophysics Data System (ADS)

Sanchez-Valle, Carmen; Malfait, Wim J.

2016-04-01

Although silicate melts comprise only a minor volume fraction of the present day Earth, they play a critical role on the Earth's geochemical and geodynamical evolution. Their physical properties, namely the density, are a key control on many magmatic processes, including magma chamber dynamics and volcanic eruptions, melt extraction from residual rocks during partial melting, as well as crystal settling and melt migration. However, the quantitative modeling of these processes has been long limited by the scarcity of data on the density and compressibility of volatile-bearing silicate melts at relevant pressure and temperature conditions. In the last decade, new experimental designs namely combining large volume presses and synchrotron-based techniques have opened the possibility for determining in situ the density of a wide range of dry and volatile-bearing (H2O and CO2) silicate melt compositions at high pressure-high temperature conditions. In this contribution we will illustrate some of these progresses with focus on recent results on the density of dry and hydrous felsic and intermediate melt compositions (rhyolite, phonolite and andesite melts) at crustal and upper mantle conditions (up to 4 GPa and 2000 K). The new data on felsic-intermediate melts has been combined with in situ data on (ultra)mafic systems and ambient pressure dilatometry and sound velocity data to calibrate a continuous, predictive density model for hydrous and CO2-bearing silicate melts with applications to magmatic processes down to the conditions of the mantle transition zone (up to 2773 K and 22 GPa). The calibration dataset consist of more than 370 density measurements on high-pressure and/or water-and CO2-bearing melts and it is formulated in terms of the partial molar properties of the oxide components. The model predicts the density of volatile-bearing liquids to within 42 kg/m3 in the calibration interval and the model extrapolations up to 3000 K and 100 GPa are in good agreement with results from ab initio calculations. The density model has been applied to examine the mineral-melt buoyancy relations at depth and the implications of these results for the dynamics of magma chambers, crystal settling and the stability and mobility of magmas in the upper mantle will be discussed.

Melting and Its Influence on the Long-term Evolution of the Lower Mantle Heterogeneities (LLSVP and ULVZ)

NASA Astrophysics Data System (ADS)

Fomin, I.; Tackley, P. J.

2017-12-01

Recent investigations have shown mantle solidus close to the range of proposed core-mantle boundary (CMB) temperatures (e.g. [Andrault et al., 2011, 2014], [de Koker et al., 2013]). Certain fraction of distinct rocks may reduce the effective melting temperature to values below the CMB temperature. It is especially true for iron enriched materials such as MORB [Nomura et al., 2011], BIF [Kato et al., 2016], iron-rich periclase [Boukare et al., 2015] and other rock species used to explain observed seismic anomalies. Computer simulations allow to study evolution and stability for chemically distinct piles proposed from geophysical data. Previous researches (e.g. [Mulyukova et al., 2015]) found those piles stirring in several hundreds of Ma. Our investigation adds influence of melting and following chemical differentiation on preservation of such structures.We present StagYY code [Tackley et al., 2008] with extended set of routines to model melting, melt redistribution and melt-dependent rheology in addition to solid-state mantle convection to reveal fate of chemically distinct piles in long-term (millions of years) perspective. A new point of our approach is usage of chemically independent oxides to describe rock composition and physical properties. Thin layers homogenize in few tens of millions of years despite whether melting happens or not. Thick structures (like periclase piles proposed for ULVZ [Wicks et al., 2010] or MORB-bearing domes for LLSVP [Ohta et al., 2008]) undergo partial melting if CMB temperature is above 3700K. Melt migration results in extraction of fusible components and therefore segregation of iron-enriched material. However, we weren't able to obtain any stabilized layer of iron-rich partially molten material at the CMB, because ongoing interaction and reequilibration of melt and solid results in buoyant liquids spreading to the adjacent mantle. Rheological influence of melt on bulk rock properties reduces time pile can exist.Our modeling puts severe constraints on the presence and fate of chemical heterogeneities in the lowermost mantle. Melting enhances stirring of such heterogeneities and generally no silicate melt can be stabilized at CMB for long time. Only low CMB temperatures (generally lower than 3700 K) allow anomalies to exist for geological periods of time (hundreds of Ma).

Microstructures and petrology of melt inclusions in the anatectic sequence of Jubrique (Betic Cordillera, S Spain): Implications for crustal anatexis

NASA Astrophysics Data System (ADS)

Barich, Amel; Acosta-Vigil, Antonio; Garrido, Carlos J.; Cesare, Bernardo; Tajčmanová, Lucie; Bartoli, Omar

2014-10-01

We report a new occurrence of melt inclusions in polymetamorphic granulitic gneisses of the Jubrique unit, a complete though strongly thinned crustal section located above the Ronda peridotite slab (Betic Cordillera, S Spain). The gneissic sequence is composed of mylonitic gneisses at the bottom and in contact with the peridotites, and porphyroblastic gneisses on top. Mylonitic gneisses are strongly deformed rocks with abundant garnet and rare biotite. Except for the presence of melt inclusions, microstructures indicating the former presence of melt are rare or absent. Upwards in the sequence, garnet decreases whereas biotite increases in modal proportion. Melt inclusions are present from cores to rims of garnets throughout the entire sequence. Most of the former melt inclusions are now totally crystallized and correspond to nanogranites, whereas some of them are partially made of glass or, more rarely, are totally glassy. They show negative crystal shapes and range in size from ≈ 5 to 200 μm, with a mean size of ≈ 30-40 μm. Daughter phases in nanogranites and partially crystallized melt inclusions include quartz, feldspars, biotite and muscovite; accidental minerals include kyanite, graphite, zircon, monazite, rutile and ilmenite; glass has a granitic composition. Melt inclusions are mostly similar throughout all the gneissic sequence. Some fluid inclusions, of possible primary origin, are spatially associated with melt inclusions, indicating that at some point during the suprasolidus history of these rocks granitic melt and fluid coexisted. Thermodynamic modeling and conventional thermobarometry of mylonitic gneisses provide peak conditions of ≈ 850 °C and 12-14 kbar, corresponding to cores of large garnets with inclusions of kyanite and rutile. Post-peak conditions of ≈ 800-850 °C and 5-6 kbar are represented by rim regions of large garnets with inclusions of sillimanite and ilmenite, cordierite-quartz-biotite coronas replacing garnet rims, and the matrix with oriented sillimanite. Previous conventional petrologic studies on these strongly deformed rocks have proposed that anatexis started during decompression from peak to post-peak conditions and in the field of sillimanite. The study of melt inclusions shows, however, that melt was already present in the system at peak conditions, and that most garnet grew in the presence of melt.

Melting Efficiency During Plasma Arc Welding

NASA Technical Reports Server (NTRS)

McClure, J.C.; Evans, D. M.; Tang, W.; Nunes, A. C.

1999-01-01

A series of partial penetration Variable Polarity Plasma Arc welds were made at equal power but various combinations of current and voltage on 2219 aluminum. Arc Efficiency was measured calorimetrically and ranged between 48% and 66%. Melting efficiency depends on the weld pool shape. Increased current increases the melting efficiency as it increases the depth to width ratio of the weld pool. Higher currents are thought to raise arc pressure and depress the liquid at the bottom of the weld pool causing a more nearly two dimensional heat flow condition.

Destabilization of yttria-stabilized zirconia induced by molten sodium vanadate-sodium sulfate melts

NASA Technical Reports Server (NTRS)

Nagelberg, A. S.; Hamilton, J. C.

1985-01-01

The extent of surface destabilization of ZrO2 - 8 wt percent Y2O3 ceramic disks was determined after exposure to molten salt mixtures of sodium sulfate containing up to 15 mole percent sodium metavanadate (NaVO3) at 1173 K. The ceramic surface was observed to transform from the cubic/tetragonal to monoclinic phase, concurrent with chemical changes in the molten salt layer in contact with the ceramic. Significant attack rates were observed in both pure sulfate and metavanadate sulfate melts. The rate of attack was found to be quite sensitive to the mole fraction of vanadate in the molten salt solution and the partial pressure of sulfur trioxide in equilibrium with the salt melt. The observed parabolic rate of attack is interpreted to be caused by a reaction controlled by diffusion in the salt that penetrates into the porous layer formed by the destabilization. The parabolic rate constant in mixed sodium metavanadate - sodium sulfate melts was found to be proportional to the SO3 partial pressure and the square of the metavanadate concentration. In-situ Raman spectroscopic measurements allowed simultaneous observations of the ceramic phases and salt chemistry during the attack process.

Holographic measurement of distortion during laser melting: Additive distortion from overlapping pulses

NASA Astrophysics Data System (ADS)

Haglund, Peter; Frostevarg, Jan; Powell, John; Eriksson, Ingemar; Kaplan, Alexander F. H.

2018-03-01

Laser - material interactions such as welding, heat treatment and thermal bending generate thermal gradients which give rise to thermal stresses and strains which often result in a permanent distortion of the heated object. This paper investigates the thermal distortion response which results from pulsed laser surface melting of a stainless steel sheet. Pulsed holography has been used to accurately monitor, in real time, the out-of-plane distortion of stainless steel samples melted on one face by with both single and multiple laser pulses. It has been shown that surface melting by additional laser pulses increases the out of plane distortion of the sample without significantly increasing the melt depth. The distortion differences between the primary pulse and subsequent pulses has also been analysed for fully and partially overlapping laser pulses.

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 the aim to achieve full re-homogenization and reproduce the system garnet+melt present during anatexis. References Bakun-Czubarow, N., 1992. Quartz pseudomorphs after coesite and quartz exsolutions in eclogitic omphacites of the Zlote Mountains in the Sudetes, SW Poland. Archeological Mineralogy, 48, 3-25. Bartoli, O., Cesare, B., Poli, S., Bodnar, R.J., Acosta-Vigil, A., Frezzotti, M.L. & Meli, S., 2013. Recovering the composition of melt and the fluid regime at the onset of crustal anatexis and S-type granite formation. Geology, 41, 115-118. Cesare, B., Ferrero, S., Salvioli-Mariani, E., Pedron, D. & Cavallo, A., 2009. Nanogranite and glassy inclusions: the anatectic melt in migmatites and granulites. Geology, 37, 627-630. Ferrero, S., Bartoli, O., Cesare, B., Salvioli Mariani, E., Acosta-Vigil, A., Cavallo, A., Groppo, C. & Battiston, S., 2012. Microstructures of melt inclusions in anatectic metasedimentary rocks. Journal of Metamorphic Geology, 30, 303-322. Holness, M.B. & Sawyer, E.W., 2008. On the pseudomorphing of melt-filled pores during the crystallization of migmatites. Journal of Petrology, 49, 1343-1363. Walczak, K., 2011. "Interpretation of Sm-Nd and Lu-Hf dating of garnets from high pressure and high temperature rocks in the light of the trace elements distribution." Doctoral dissertation, Institute of Geological Sciences, Polish Academy of Sciences, Poland.

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.

Early Paleozoic high-Mg granodiorite from the Erlangping unit, North Qinling orogen, central China: Partial melting of metasomatic mantle during the initial back-arc opening

NASA Astrophysics Data System (ADS)

Abdallsamed, Mohammed I. M.; Wu, Yuan-Bao; Zhang, Wenxiang; Zhou, Guangyan; Wang, Hao; Yang, Saihong

2017-09-01

This study discussed the petrological classification, petrogenesis, and tectonic significance of early Paleozoic high-Mg granodiorite from the Erlangping unit, in the North Qinling orogen. To achieve this target, we conducted integrated investigation of in situ zircon U-Pb dating, whole-rock geochemical, as well as Sr-Nd-Hf-O isotopic compositions for the Kanfenggou pluton from the Erlangping unit. LA-ICP-MS zircon dating for the Kanfenggou samples yields U-Pb ages of 442.9 ± 6.2 and 438.0 ± 6.7 Ma, suggesting that the pluton was emplaced at ca. 440 Ma. Whole-rock geochemical compositions of the samples display intermediate SiO2 (60.48-64.67 wt%) and K2O (1.21 to 2.10 wt%), but high Al2O3 (15.44 to 16.51 wt%) and Na2O (4.01 to 4.81 wt%) contents. The granodiorite samples are characterized by elevated MgO ranging from 2.30 to 3.44 wt% and Mg# values of 53.35to 56.66, implying they are high-Mg granodiorites. They are characterized by very high Ba (524-1132 ppm) and Sr (684-980 ppm) contents, but depleted in HREE, and high (La/Yb)N ratios of 6.34 to 16.5 and slightly negative to weak positive Eu anomalies (Eu/Eu* = 0.68-1.09). These evidence that the Kanfenggou pluton belongs to the sanukitoid series. The high-Mg granodiorite samples exhibit a mantle signature with high Mg# values (53.35-56.66), Cr (45.8 to 93.3 ppm) and Ni (28.2 to 48.2 ppm) contents, but enriched in LILE, pointing to an enriched mantle source. The samples show relatively depleted radiogenic isotopic compositions with initial 87Sr/86Sr ratios varying from 0.7044 to 0.7047, εNd(t) values from 0.31 to 4.21, and zircon εHf (t) values from 7.3 to 8.3. The zircons have a mean δ18O value of 5.20 ± 0.17 ‰. Based on the trace element geochemical features, the metasomatic agent was suggested to be the fluids generated from dehydration of subducted slab. Therefore, we suggest two-stage processes for the formation of the Erlangping high-Mg granodiorites: (1) interaction between slab fluids and mantle peridotite; (2) partial melting of metasomatized mantle peridotite caused by the asthenosphere mantle upwelling and the initial back-arc opening resulted from the oceanic slab rollback.

Metamorphic density controls on early-stage subduction dynamics

NASA Astrophysics Data System (ADS)

Duesterhoeft, Erik; Oberhänsli, Roland; Bousquet, Romain

2013-04-01

Subduction is primarily driven by the densification of the downgoing oceanic slab, due to dynamic P-T-fields in subduction zones. It is crucial to unravel slab densification induced by metamorphic reactions to understand the influence on plate dynamics. By analyzing the density and metamorphic structure of subduction zones, we may gain knowledge about the driving, metamorphic processes in a subduction zone like the eclogitization (i.e., the transformation of a MORB to an eclogite), the breakdown of hydrous minerals and the release of fluid or the generation of partial melts. We have therefore developed a 2D subduction zone model down to 250 km that is based on thermodynamic equilibrium assemblage computations. Our model computes the "metamorphic density" of rocks as a function of pressure, temperature and chemical composition using the Theriak-Domino software package at different time stages. We have used this model to investigate how the hydration, dehydration, partial melting and fractionation processes of rocks all influence the metamorphic density and greatly depend on the temperature field within subduction systems. These processes are commonly neglected by other approaches (e.g., gravitational or thermomechanical in nature) reproducing the density distribution within this tectonic setting. The process of eclogitization is assumed as being important to subduction dynamics, based on the very high density (3.6 g/cm3) of eclogitic rocks. The eclogitization in a MORB-type crust is possible only if the rock reaches the garnet phase stability field. This process is primarily temperature driven. Our model demonstrates that the initiation of eclogitization of the slab is not the only significant process that makes the descending slab denser and is responsible for the slab pull force. Indeed, our results show that the densification of the downgoing lithospheric mantle (due to an increase of pressure) starts in the early subduction stage and makes a significant contribution to the slab pull, where eclogitization does not occur. Thus, the lithospheric mantle acts as additional ballast below the sinking slab shortly after the initiation of subduction. Our calculation shows that the dogma of eclogitized basaltic, oceanic crust as the driving force of slab pull is overestimated during the early stage of subduction. These results improve our understanding of the force budget for slab pull during the intial and early stage of subduction. Therefore, the complex metamorphic structure of a slab and mantle wedge has an important impact on the development and dynamics of subduction zones. Further Reading: Duesterhoeft, Oberhänsli & Bousquet (2013), submitted to Earth and Planetary Science Letters

Mantle Metasomatism under Island Arcs, Magnetic Implications

NASA Astrophysics Data System (ADS)

Friedman, S. A.; Ferre, E. C.; Arai, S.

2013-12-01

The wedge of upper mantle beneath oceanic and island arcs receives an abundant flux of fluids derived from dehydration of subducted slabs. These fluids may cause metasomatism, serpentinization or partial melting at increasing distance from the trench. Each one of these processes profoundly modifies the oxygen fugacity, mineral assemblage, rheology and seismic properties of mantle rocks. Mantle xenoliths in arcs are relatively rare compared to other tectonic settings yet, due to their rapid ascent, they provide the best record of mantle rocks at depth. Previous studies on the metasomatism of the arc mantle wedge focused on the geochemistry and mineralogy of these xenoliths. Here we present new rock magnetic and paleomagnetic results to track changes in the magnetic assemblage of mantle peridotites. Peridotites undergo a wide range of fluid-reactions that involve formation of magnetically remanent phases such as magnetite, maghemite, hematite or monosulfide solutions. Samples for this study originate from three localities displaying different degrees of metasomatism: a) Five samples from Ichinomegata crater, Megata volcano, in NE Japan are characteristically lherzolitic with metasomatic pargasite present; b) Six samples from Kurose, Hakata Bay, in SW Japan are mainly harzburgites that contain rare, late stage metasomatic sulfides; and c) Ten samples from the Iraya volcano, Batan Island, in the Philippines are lherzolites, harzburgites, and dunites that contain metasomatic olivine, orthopyroxene, clinopyroxene and pargasite. Both remanent and induced magnetizations of these mantle peridotites exhibit systematic variations as a function of the degrees of metasomatism. The contribution of these mantle peridotites to long wavelength magnetic anomalies might be significant.

Fluid transfer into the wedge controlled by high-pressure hydrofracturing in the cold top-slab mantle

NASA Astrophysics Data System (ADS)

Padrón-Navarta, José Alberto; Tommasi, Andréa; Garrido, Carlos J.; Sánchez-Vizcaíno, Vicente López; Gómez-Pugnaire, María Teresa; Jabaloy, Antonio; Vauchez, Alain

2010-08-01

Before attaining the mantle wedge, where they trigger partial melting, volatiles released from dehydration reactions in the slab have to migrate across a relatively cold (< 750 °C), peridotite-layer above the incoming slab. In order to unravel the mechanisms allowing for this initial stage of fluid transport, we performed a detailed field and microstructural study of metamorphic prograde peridotites in the Cerro del Almirez ultramafic massif (Betic Cordillera, Spain), where evidences of one of the most important dehydration reactions in subduction zones, the high-pressure antigorite breakdown ( P = 1.6-1.9 GPa and T ≈ 680 °C), can be mapped in the field. This reaction led to arborescent growth of centimeter-size olivine and orthopyroxene, producing a chlorite-harzburgite with a spinifex-like texture. Microstructural observations and crystal preferred orientations (CPO) mapping show no evidences of solid-state deformation during the prograde growth of olivine and orthopyroxene at the expenses of antigorite. However, a few tens to a hundred meters away from the reaction front, the metamorphic texture is partially obliterated by grain-size reduction in roughly planar conjugate zones, a few mm to meters wide. Grain size reduction zones (GSRZ) are characterized by (1) sharp contacts with undeformed spinifex-like texture domains, (2) important reduction of the olivine grain size (60-250 μm), (3) olivine color change from brownish to colorless, (4) decrease in the modal amount of orthopyroxene, and (5) at the mm- to cm-scale, irregular shapes and abrupt terminations. Field and microstructural observations exclude that relative displacement took place across these GSRZ. Changes in modal composition imply reactions with fluids undersaturated in silica. Analysis of olivine crystal-preferred orientations (CPO) in GSRZ shows patterns similar, but more dispersed, than those in neighboring spinifex-like domains. It also reveals mm- to cm-scale discrete domains with rather homogeneous crystallographic orientations suggesting inheritance from the preexisting spinifex-like olivines in the host peridotite. Misorientation angles between neighboring grains in the GSRZ show peaks at ˜ 5-10° and ˜ 20°, but rotations are not crystallographically controlled. Based on these observations, we rule out the formation of the GSRZ by dynamic recrystallization during dislocation creep and propose that they record brittle deformation (microcraking) of the spinifex-like chlorite-harzburgite, probably induced by hydrofracturing at high pressure and relative low temperature conditions (680-710 °C). High-pressure hydrofracturing can, thus, be invoked as an efficient mechanism for fluid flow across the cold top-slab mantle layer, hence allowing the slab-derived fluids to ingress in the wedge.

Chemical modification of projectile residues and target material in a MEMIN cratering experiment

NASA Astrophysics Data System (ADS)

Ebert, Matthias; Hecht, Lutz; Deutsch, Alexander; Kenkmann, Thomas

2013-01-01

In the context of the MEMIN project, a hypervelocity cratering experiment has been performed using a sphere of the iron meteorite Campo del Cielo as projectile accelerated to 4.56 km s-1, and a block of Seeberger sandstone as target material. The ejecta, collected in a newly designed catcher, are represented by (1) weakly deformed, (2) highly deformed, and (3) highly shocked material. The latter shows shock-metamorphic features such as planar deformation features (PDF) in quartz, formation of diaplectic quartz glass, partial melting of the sandstone, and partially molten projectile, mixed mechanically and chemically with target melt. During mixing of projectile and target melts, the Fe of the projectile is preferentially partitioned into target melt to a greater degree than Ni and Co yielding a Fe/Ni that is generally higher than Fe/Ni in the projectile. This fractionation results from the differing siderophile properties, specifically from differences in reactivity of Fe, Ni, and Co with oxygen during projectile-target interaction. Projectile matter was also detected in shocked quartz grains. The average Fe/Ni of quartz with PDF (about 20) and of silica glasses (about 24) are in contrast to the average sandstone ratio (about 422), but resembles the Fe/Ni-ratio of the projectile (about 14). We briefly discuss possible reasons of projectile melting and vaporization in the experiment, in which the calculated maximum shock pressure does not exceed 55 GPa.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryabova, N. Yu., E-mail: rny03@nf.jinr.ru; Kiselev, M. A.; Balagurov, A. M.

The structural changes in the multilamellar lipid membranes of dipalmitoylphosphatidylcholine (DPPC)/cholesterol and DPPC/ceramide VI binary systems during hydration and dehydration have been studied by neutron diffraction. The effect of cholesterol and ceramide on the kinetics of water exchange in DPPC membranes is characterized. Compared to pure DPPC, membranes of binary systems swell faster during hydration (with a characteristic time of {approx}30 min). Both compounds, ceramide VI and cholesterol, similarly affect the hydration of DPPC membranes, increasing the repeat distance due to the bilayer growth. However, in contrast to cholesterol, ceramide significantly reduces the thickness of the membrane water layer. Themore » introduction of cholesterol into a DPPC membrane slows down the change in the parameters of the bilayer internal structure during dehydration. In the DPPC/ceramide VI/cholesterol ternary system (with a molar cholesterol concentration of 40%), cholesterol is partially released from the lamellar membrane structure into the crystalline phase.« less

[Hyponatremia in ultraendurance exercises. Effects on health and performance].

PubMed

Ortega Porcel, Francisco B; Ruiz Ruiz, Jonatan; Castillo Garzón, Manuel J; Gutiérrez Sainz, Angel

2004-06-01

Dehydration is one of the main problems associated to endurance sports. In order to avoid the negative effects of dehydration athletes tend to drink well above their current needs. The negative effect of drinking too much fluid is hyponatremia. Hyponatremia is defined as a plasma sodium concentration lower than 135 mmol/L. Hyponatremia is the first cause of severe illness in ultraendurance sports and has been associated with sudden death. In this article, we analyze the causes, consequences, associated factors, therapeutic treatment and prevention of ultraendurance sports-associated hyponatremia. It is concluded that an adequate fluid ingestion is the best method to avoid hyponatremia. There is not conclusive data about the amount and necessity of sodium supplementation to avoid hyponatremia. However, it might be that it is not necessary to ingest additional sodium to prevent the development of hyponatremia in athletes who only partially replace their fluid losses during prolonged exercise.

Oxygen and U-Th isotopes and the timescales of hydrothermal exchange and melting in granitoid wall rocks at Mount Mazama, Crater Lake, Oregon

USGS Publications Warehouse

Ankney, Meagan E.; Bacon, Charles R.; Valley, John W.; Beard, Brian L.; Johnson, Clark M.

2017-01-01

We report new whole rock U-Th and in-situ oxygen isotope compositions for partially melted (0–50 vol% melt), low-δ18O Pleistocene granitoid blocks ejected during the ∼7.7 ka caldera-forming eruption of Mt. Mazama (Crater Lake, Oregon). The blocks are interpreted to represent wall rocks of the climactic magma chamber that, prior to eruption, experienced variable amounts of exchange with meteoric hydrothermal fluids and subsequent partial melting. U-Th and oxygen isotope results allow us to examine the timescales of hydrothermal circulation and partial melting, and provide an “outside in” perspective on the buildup to the climactic eruption of Mt. Mazama. Oxygen isotope compositions measured in the cores and rims of individual quartz (n = 126) and plagioclase (n = 91) crystals, and for transects across ten quartz crystals, document zonation in quartz (Δ18OCore-Rim ≤ 0.1–5.5‰), but show homogeneity in plagioclase (Δ18OCore-Rim ≤ ±0.8‰). We propose that oxygen isotope zonation in quartz records hydrothermal exchange followed by high-temperature exchange in response to partial melting caused by injection of basaltic to andesitic recharge magma into the deeper portions of the chamber. Results of modeling of oxygen diffusion in quartz indicates that hydrothermal exchange in quartz occurred over a period of ∼1000–63,000 years. Models also suggest that the onset of melting of the granitoids occurred a minimum of ∼10–200 years prior to the Mazama climactic eruption, an inference which is broadly consistent with results for magnetite homogenization and for Zr diffusion in melt previously reported by others.Uranium-thorium isotope compositions of most granitoid blocks are in 238U excess, and are in agreement with a 238U enriched array previously measured for volcanic rocks at Mt. Mazama. Uranium excess in the granitoids is likely due to enrichment via hydrothermal circulation, given their low δ18O values. The sample with the highest U excess (≥5.8%) also has the most 18O isotope depletion (average δ18Oplag = −4.0‰). The granitoids are a probable assimilant and source of U excess in volcanic rocks from Mt. Mazama. Two granitoids have Th excess and low δ18O values, interpreted to record leaching of U during hydrothermal alteration. A U-Th isochron based on the U excess array of the granitoids and volcanic rocks indicates that hydrothermal circulation initiated ∼40–75 kyrs before the climactic eruption, potentially marking the initiation of a persistent upper-crustal magma chamber. The U-Th ages are consistent with the maximum timescales inferred for hydrothermal alteration based on oxygen isotope zoning in quartz.

Thermal Constraints from Siderophile Trace Elements in Acapulcoite-Lodranite Metals

NASA Technical Reports Server (NTRS)

Herrin, Jason S.; Mittlefehldt, D. W.; Humayun, M.

2006-01-01

A fundamental process in the formation of differentiated bodies is the segregation of metal-sulfide and silicate phases, leading to the formation of a metallic core. The only known direct record of this process is preserved in some primitive achondrites, such as the acapulcoite-lodranites. Meteorites of this clan are the products of thermal metamorphism of a chondritic parent. Most acapulcoites have experienced significant partial melting of the metal-sulfide system but not of silicates, while lodranites have experienced partial melting and melt extraction of both. The clan has experienced a continuum of temperatures relevant to the onset of metal mobility in asteroidal bodies and thus could yield insight into the earliest stages of core formation. Acapulcoite GRA 98028 contains relict chondrules, high modal sulfide/metal, has the lowest 2-pyroxene closure temperature, and represents the least metamorphosed state of the parent body among the samples examined. Comparison of the metal-sulfide component of other clan members to GRA 98028 can give an idea of the effects of metamorphism.

Uppermost mantle (Pn) velocity model for the Afar region, Ethiopia: an insight into rifting processes

NASA Astrophysics Data System (ADS)

Stork, A. L.; Stuart, G. W.; Henderson, C. M.; Keir, D.; Hammond, J. O. S.

2013-04-01

The Afar Depression, Ethiopia, offers unique opportunities to study the transition from continental rifting to oceanic spreading because the process is occurring onland. Using traveltime tomography and data from a temporary seismic deployment, we describe the first regional study of uppermost mantle P-wave velocities (VPn). We find two separate low VPn zones (as low as 7.2 km s-1) beneath regions of localized thinned crust in northern Afar, indicating the existence of high temperatures and, potentially, partial melt. The zones are beneath and off-axis from, contemporary crustal magma intrusions in active magmatic segments, the Dabbahu-Manda-Hararo and Erta'Ale segments. This suggests that these intrusions can be fed by off-axis delivery of melt in the uppermost mantle and that discrete areas of mantle upwelling and partial melting, thought to characterize segmentation of the uppermost mantle at seafloor spreading centres, are initiated during the final stages of break-up.

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 partial melting of chondritic material and generation of Fe-Ni-S-bearing melts are generally consistent with HSE abundances that are within factors of ˜2-10 × CI-chondrite abundances for GRA 06128/9, brachinites and the three brachinite-like achondrites. However, in detail, brachinite-like achondrites NWA 5400, NWA 6077 and Zag (b) are interpreted to have witnessed single-stage S-rich metal segregation, whereas HSE in GRA 06128/9 and brachinites have more complex heritages. The HSE compositions of GRA 06128/9 and brachinites require either: (1) multiple phases in the residue (e.g., metal and sulphide); (2) fractionation after generation of an initial melt, again involving multiple phases; (3) fractional fusion, or; (4) a parent body with non-chondritic relative HSE abundances. Petrological and geochemical observations permit genetic links (i.e., same parent body) between GRA 06128/9 and brachinites and similar formation mechanisms for brachinites and brachinite-like achondrites.

Iron isotope composition of depleted MORB

NASA Astrophysics Data System (ADS)

Labidi, J.; Sio, C. K. I.; Shahar, A.

2015-12-01

In terrestrial basalts, iron isotope ratios are observed to weakly fractionate as a function of olivine and pyroxene crystallization. However, a ~0.1‰ difference between chondrites and MORB had been reported (Dauphas et al. 2009, Teng et al. 2013 and ref. therein). This observation could illustrate an isotope fractionation occurring during partial melting, as a function of the Fe valence in melt versus crystals. Here, we present high-precision Fe isotopic data measured by MC-ICP-MS on well-characterized samples from the Pacific-Antarctic Ridge (PAR, n=9) and from the Garrett Transform Fault (n=8). These samples allow exploring the Fe isotope fractionation between melt and magnetite, and the role of partial melting on Fe isotope fractionation. Our average δ56Fe value is +0.095±0.013‰ (95% confidence, n=17), indistinguishable from a previous estimate of +0.105±0.006‰ (95% confidence, n=43, see ref. 2). Our δ56Fe values correlate weakly with MgO contents, and correlate positively with K/Ti ratios. PAC1 DR10 shows the largest Ti and Fe depletion after titanomagnetite fractionation, with a δ56Fe value of +0.076±0.036‰. This is ~0.05‰ below other samples at a given MgO. This may illustrate a significant Fe isotope fractionation between the melt and titanomagnetite, in agreement with experimental determination (Shahar et al. 2008). GN09-02, the most incompatible-element depleted sample, has a δ56Fe value of 0.037±0.020‰. This is the lowest high-precision δ56Fe value recorded for a MORB worldwide. This basalt displays an incompatible-element depletion consistent with re-melting beneath the transform fault of mantle source that was depleted during a first melting event, beneath the ridge axis (Wendt et al. 1999). The Fe isotope observation could indicate that its mantle source underwent 56Fe depletion after a first melting event. It could alternatively indicate a lower Fe isotope fractionation during re-melting, if the source was depleted of its Fe3+, likely producing a relatively reduced melt. These hypotheses are testable, and will be discussed in detail at the conference.

Origin and evolution of the Nakhla meteorite inferred from the Sm-Nd and U-Pb systematics and REE, Ba, Sr, Rb and K abundances

NASA Technical Reports Server (NTRS)

Nakamura, N.; Unruh, D. M.; Tatsumoto, M.; Hutchison, R.

1982-01-01

Analyses of whole rock and mineral separates from the Nakhla meteorite are carried out by means of Sm-Nd and U-Tn-Pb systematics and by determining their REE, Ba, Sr, Rb, and K concentrations. Results show that the Sm-Nd age of the meteorite is 1.26 + or - 0.7 b.y., while the high initial epsilon(Nd) value of +16 suggests that Nakhla was derived from a light REE-depleted, old planetary mantle source. A three-stage Sm-Nd evolution model is developed and used in combination with LIL element data and estimated partition coefficients in order to test partial melting and fractional crystallization models and to estimate LIL abundances in a possible Nakhla source. The calculations indicate that partial melting of the source followed by extensive fractional crystallization of the partial melt could account for the REE abundances in the Nakhla constituent minerals. It is concluded that the significantly younger age of Nakhla than the youngest lunar rock, the young differentiation age inferred from U-Th-Pb data, and the estimated LIL abundances suggest that this meteorite may have been derived from a relatively large, well-differentiated planetary body such as Mars.

Partial melting under conditions of filter pressing: field and geochemical evidence from the migmatites of NE Minnesota

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheehan, T.J.; Bauer, R.L.; Nabelek, P.I.

1985-01-01

Amphibolite-grade Archean migmatites in the southern Vermilion Granitic Complex with well-defined paleosome-melanosome and melanosome-leucosome boundaries and with exceptionally wide melanosomes (on the order of centimeters) were studied to elucidate granite-forming processes during high-grade metamorphism. Metagreywacke paleosomes containing 50% plag, 28% qtz, 20% biot and minor hbld, and apat, have (Ce/Yb)/sub N/ = 13.5 to 21 with 650-960 ppm Ba, 42-110 ppm Rb, and 982-1159 ppm Sr. Melanosomes containing 45% plag, 35% biot, 20% hbld and minor qtz and apat, have (Ce/Yb)/sub N/ = 6.8 to 9.3 and have 950-1750 ppm Ba, 41-194 ppm Rb, and 1020-1926 ppm Sr. Leucosomes containingmore » 82% plag, 13% qtz, 5% biot and minor hbld and apat, have overall depleted REE patterns with positive Eu anomalies and 460-750 ppm Ba, 41-43 ppm Rb, and 1876-2106 ppm Sr, suggesting cumulate plagioclase. Mass balance calculations preclude formation of the melanosome from mixing the paleosomes and leucosomes. However, major and trace element modeling suggest that the leucosome formed by in situ partial melting followed by fractional crystallization and filter pressing which resulted in the removal of the residual liquid. Model REE patterns for the melt drive off by this process are REE enriched with a negative Eu anomaly. Such patterns which have been found in some low Sr granites are difficult to produce by simple belting models. Partial melting under conditions of tectonic stress may thus provide an explanation for such granites.« less

Oceanization of the lithospheric mantle: the study case of the spinel peridotites from Monte Maggiore (Corsica, France).

NASA Astrophysics Data System (ADS)

Piccardo, G. B.

2009-04-01

The Monte Maggiore peridotite body, cropping out within the Alpine Corsica metamorphic belt, is an ophiolite massif derived from the more internal setting of the Jurassic Ligurian Tethys basin. It is mostly composed by spinel and plagioclase peridotites that are cut by MORB gabbroic dykes. The spinel peridotites, similarly to other ophiolitic peridotites from the Internal Ligurides, have been considered, on the basis of their low abundance of fusible components, low Si and high Mg contents, as refractory residua after MORB-type partial melting related to the formation of the Jurassic basin (e.g. Rampone et al., 1997). Recent studies (e.g. Müntener & Piccardo 2003; Rampone et al. 2008) have evidenced that these depleted spinel peridotites show diffuse melt-rock interaction micro-textures and contrasting bulk vs. mineral chemistry features which cannot be simply reconciled with partial melting. Accordingly, these peridotites have been recognized as reactive peridotites, formed by interaction of pristine peridotites with melts percolating by porous flow. Geochemical data have evidenced the depleted MORB signature of the percolating melts. Recent field studies at Monte Maggiore (Piccardo, 2007; Piccardo & Guarnieri, 2009), have revealed: 1) the presence and local abundance of pyroxenite-bearing, cpx-rich spinel lherzolites and 2) the replacement relationships of the reactive peridotites on the pyroxenite-bearing lherzolite rock-types. The pyroxenite-veined spinel lherzolites record a composite history of subsolidus evolution under lithospheric P-T conditions, thus indicating their provenance from the sub-continental lithospheric mantle. Accordingly, the pristine sub-continental mantle protoliths were infiltrated by MORB melts and transformed by melt-rock interaction to reactive spinel peridotites and refertilized by melt impregnation to plagioclase-enriched peridotites. Available isotopic data on the Mt. Maggiore spinel and plagioclase peridotites and gabbroic rocks (Rampone, 2004; Rampone et al., 2008; 2009) provide reliable geochronological informations (i.e. Sm-Nd cpx-plg-wr isochron ages and Sm-Nd model ages) and evidence that the whole mafic and ultramafic rocks show an overall Sm/Nd isotopic homogeneity. Cpx-plg-wr data from gabbroic dykes define internal isochrones yielding Jurassic ages (162+/-10 Ma and 159+/-15 Ma, respectively). The plg-cpx(-wr) isochrons for impregnated plagioclase peridotites yields age of 155+/-6 Ma. The initial ɛNd values (8.9-9.7) are indicative of a MORB affinity. Calculated DM model ages for both spinel and plagioclase peridotites point to a Late Jurassic age (150 Ma). Isotope ratios of cpx from spinel and plagioclase peridotites conform to the linear array defined by overall gabbroic rocks. The isotopic evidence from the melt-percolated, reactive and impregnated peridotites indicates that the pristine lithospheric mantle protoliths were isotopically homogenized by the melt-rock interaction during percolation/impregnation processes which erased any pre-existing isotopic signature. Moreover, the overall Sm/Nd isotopic homogeneity indicates that the asthenospheric mantle sources of the infiltrating melts were isotopically homogeneous. Accordingly, it is plausible that percolation and intrusion were operated by similar and coeval Late Jurassic MORB-type melts. In conclusion, petrologic and isotopic data allow to recognize that the extending sub-continental lithospheric mantle was infiltrated by Late Jurassic MORB melts, formed by asthenospheric decompression-induced partial melting during continental extension and rifting. Melt-peridotite interaction modified the compositional features of the lithospheric mantle and caused its isotopic resetting. Accordingly, the sub-continental lithospheric mantle underwent an "oceanization" process (i.e. isotope resetting to "oceanic" MORB signatures) during Late Jurassic times operated by asthenospheric MORB melts. Depending on the melt composition, the lithospheric level and the mode of melt-rock interaction, fertile peridotites from the sub-continental lithospheric mantle were transformed, concomitantly, to depleted spinel peridotites and refertilized plagioclase peridotites.

Addition of phosphotungstic acid to ethanol for dehydration improves both the ultrastructure and antigenicity of pituitary tissue embedded in LR White acrylic resin.

PubMed

Sakai, Yuko; Hosaka, Masahiro; Hira, Yoshiki; Watanabe, Tsuyoshi

2005-12-01

Although hydrophilic acrylic resins including LR White have been widely utilized as embedding media for immunocytochemical use, the constituents of tissues are often extracted by the resin monomer during the infiltration process of the embedment, resulting in a discernible impairment of the ultrastructure when the tissue is weakly fixed only with aldehydes. To minimize the extraction by the resin monomer, the embedding procedure with LR White resin was reexamined in the present study. Among the treatments tested, a partial dehydration with 70% ethanol containing 2% phosphotungstic acid (PTA) well preserved the ultrastructure of the pituitary tissue without spoiling the antigenicity of LHbeta and other representative markers for the Golgi apparatus. In addition, treatment with 1% tannic acid (TA) prior to the dehydration described above synergistically improved both the ultrastructure and antigenicity of the tissue so that the orientation of the Golgi apparatus could be determined by double immunogold labeling with commercially available anti-GM130 and anti-TGN38 antibodies. The ultrathin sections from the LR White-embedded tissue treated with TA and dehydrated in 70% ethanol containing 2% PTA also enhanced contrast without conventional heavy-metal staining with uranyl acetate and lead citrate. Our findings further suggest that the precipitation of TA and PTA protected the tissue from being extracted during the embedment, probably because an insoluble complex was transiently formed with the constituents of the tissue. This simple modification of the LR White embedment can extend the application of post-embedding immunocytochemistry as an alternative to pre-embedding immunolabeling with frozen ultrathin sections.

Boron desorption and fractionation in Subduction Zone Fore Arcs: Implications for the sources and transport of deep fluids

NASA Astrophysics Data System (ADS)

Saffer, Demian M.; Kopf, Achim J.

2016-12-01

At many subduction zones, pore water geochemical anomalies at seafloor seeps and in shallow boreholes indicate fluid flow and chemical transport from depths of several kilometers. Identifying the source regions for these fluids is essential toward quantifying flow pathways and volatile fluxes through fore arcs, and in understanding their connection to the loci of excess pore pressure at depth. Here we develop a model to track the coupled effects of boron desorption, smectite dehydration, and progressive consolidation within sediment at the top of the subducting slab, where such deep fluid signals likely originate. Our analysis demonstrates that the relative timing of heating and consolidation is a dominant control on pore water composition. For cold slabs, pore water freshening is maximized because dehydration releases bound water into low porosity sediment, whereas boron concentrations and isotopic signatures are modest because desorption is strongly sensitive to temperature and is only partially complete. For warmer slabs, freshening is smaller, because dehydration occurs earlier and into larger porosities, but the boron signatures are larger. The former scenario is typical of nonaccretionary margins where insulating sediment on the subducting plate is commonly thin. This result provides a quantitative explanation for the global observation that signatures of deeply sourced fluids are generally strongest at nonaccretionary margins. Application of our multitracer approach to the Costa Rica, N. Japan, N. Barbados, and Mediterranean Ridge subduction zones illustrates that desorption and dehydration are viable explanations for observed geochemical signals, and suggest updip fluid migration from these source regions over tens of km.

Manufacture of ceramic tiles from fly ash

DOEpatents

Hnat, James G.; Mathur, Akshay; Simpson, James C.

1999-01-01

The present invention relates to a process for forming glass-ceramic tiles. Fly ash containing organic material, metal contaminants, and glass forming materials is oxidized under conditions effective to combust the organic material and partially oxidize the metallic contaminants and the glass forming materials. The oxidized glass forming materials are vitrified to form a glass melt. This glass melt is then formed into tiles containing metallic contaminants.

Anatomy of a frozen axial melt lens from a fast-spreading paleo-ridge (Wadi Gideah, Oman ophiolite)

NASA Astrophysics Data System (ADS)

Müller, T.; Koepke, J.; Garbe-Schönberg, C.-D.; Dietrich, M.; Bauer, U.; Wolff, P. E.

2017-02-01

At fast-spreading mid-ocean ridges, axial melt lenses (AMLs) sandwiched between the sheeted dyke section and the uppermost gabbros are assumed to be the major magma source of crust formation. Here, we present our results from a field study based on a single outcrop of a frozen AML in the Samail ophiolite in the Sultanate of Oman which presents a whole suite of different lithologies and complex cutting relationships: varitextured gabbro with relics of primitive poikilitic clinopyroxene is intruded by massive quartz diorites and tonalites bearing relics of assimilated sheeted dykes, which in turn are cut by trondhjemite dykes. The whole is cut by basaltic dykes with chilled margins. The geochemical evolutionary trend of the varitextured gabbros, including some of the quartz diorites and tonalites, can be best modelled by fractional crystallisation of an experimental MORB parental melt composition containing 0.4 to 0.8 wt.% H2O. Patchy varitextured gabbros containing domains of primitive poikilitic clinopyroxene and evolved granular networks represent the record of in situ crystallisation. Some quartz diorites, often with xenoliths of sheeted dykes and exceptionally high Al2O3 contents, show a bulk trace element pattern more in accord with melts generated by experimental partial melting of dyke material. Highly evolved, crosscutting trondhjemite dykes show characteristic trace element patterns implying a formation by partial melting of sheeted dykes under lower water activity which is indicated by relatively low Al2O3 contents. The late basaltic dykes with chilled margins crosscutting all other lithologies show a relatively depleted geochemical character with pronounced negative Nb-Ta anomalies implying a genetic relationship to the second phase of magmatic Oman paleo-ridge activity (V2). The field relationships in combination with the petrological/geochemical trends reveal multiple sequences of MORB-type magma cooling (resulting in fractional crystallisation) and re-heating (producing partial melting) during the formation of this special horizon; these are best explained by alternating cycles of vertical AML migration. Since the investigated outcrop shows many characteristic lithological and petrographic features that are well-known from the uppermost gabbros drilled at Site 1256 by the Integrated Ocean Drilling Program (IODP) in the equatorial Eastern Pacific, our results based on 3-D observation in the field help to elucidate the geological observations obtained from the 1-D drill core.

Constraints on the origin of adakites and porphyry Cu-Mo mineralization in Chongjiang, Southern Gangdese, the Tibetan Plateau

NASA Astrophysics Data System (ADS)

Hu, Yong-bin; Liu, Ji-qiang; Ling, Ming-xing; Liu, Yan; Ding, Xing; Liu, Dun-yi; Sun, Wei-dong

2017-11-01

Chongjiang is a low-grade porphyry Cu deposit, located in the Gangdese belt, south Tibet. The petrogenesis and geodynamic settings of the Miocene intrusions associated with the deposit remain controversial. This study presents new results on in situ zircon Hf-O isotopic compositions and U-Pb ages, whole rock major and trace elements, and Sr-Nd isotopes for the adakitic intrusions from Chongjiang deposit. The ore-bearing biotite monzogranite porphyry has adakitic characteristics, with enriched large-ion-lithophile elements (LILE) and light rare earth elements (LREE), and depleted in high-field-strength elements (HFSE), P and Ti. LA-ICP-MS zircon U-Pb dating indicates that the ore-bearing and barren adakites were emplaced at 14.9 ± 0.3 Ma and 12.9 ± 0.3 Ma, respectively. The porphyry is characterized by relatively high initial 87Sr/86Sr ratios (0.7059 to 0.7066), and negative whole-rock εNd(t) values (- 3.8 to - 2.6). Zircon δ18O is slightly higher than mantle values (5.0 to 7.2‰), with varied εHf(t) (- 1.0 to 7.6). Most of the in situ zircon Hf-O isotopic data plot in a binary mixing trend between MORB and lower continental crust-derived melts. These results indicate contributions from mixing of a mantle-like source (e.g., slab melts) with continental crust. Interestingly, most of the samples plot in the field defined by Dabie adakites (representing partial melting of the lower continental crust), with several samples near/in the circum-Pacific adakite field (representing partial melting of subducted oceanic slabs), which seemingly indicates that Chongjiang adakites mostly formed through partial melting of lower continental crust, with a small amount derived from oceanic slab melts. These may be plausibly explained by plagioclase retention in the thickened Tibetan continental crust, which lowers Sr contents in the magmas during crustal assimilation. Such a model is supported by other adakite discrimination diagrams, which all point towards slab melting. Crustal contamination can compellingly explain the low grade of the Chongjiang deposit. Considering the temporal-spatial distribution of porphyry Cu deposits, geochemical characteristics and high oxygen fugacity, we propose that the subducting Ninetyeast Ridge probably played a critical role in controlling the formation of Miocene adakites and porphyry copper deposits in the eastern Gangdese belt.

The stability of hibonite and other aluminous phases in silicate melts: Implications for the origin of hibonite-bearing inclusions

NASA Technical Reports Server (NTRS)

Beckett, J. R.; Stolper, E.

1993-01-01

Phase fields in which hibonite (Hib) and silicate melt coexist with spinel (Sp), CaAl4O7 (CA2), gehlenitic melilite (Mel), anorthite (An), or corundum (Cor) in the system CaO-MgO-Al203-SiO2-TiO2 (CMAST) were determined and activity models developed for Mel and Hib solid solutions. Experimentally determined partition coefficients for Ti between Hib and coexisting melt, D sub t, vary from 0.8 to 2.1 and generally decrease with increasing TiO2 content in the liquid (L). Based on Ti partioning between Hib and melt, bulk inclusion compositions and Hib-saturated liquid use phase diagrams, the Hib in Fluffy Type A inclusions (FTA's) from Allende and at least some of the Hib from Hib-rich inclusions is relict; much of the Hib from Hib-glass spherules probably crystallized from a melt under nonequilibrium conditions. Bulk compositions for all of these Ca-Al-rich inclusions (CAI's) are consistent with an origin as Mel + Hib + Sp + perovskite (Pv) proto-inclusions in which Mel was partially altered. In some cases, the proto-inclusion was partially or completely melted with vaporization occurring over a period of time sufficient to remove any Na introduced by the alteration process but frequently insufficient to dissolve all of the original hibonite. If equilibration temperatures based on Hib-bearing CAI's reflect condensation in a cooling gas of solar composition, then Hib + Cor condensed at approximately 1260 C (referenced to 10 exp -3 atm) and Hib + Sp + Mel at approximately 1215 +/- 10 C. Simple thermochemical models for the substitution of trace elements into the Ca-site of meteoritic Hib suggest that virtually all Eu is divalent in early condensate Hibs but that Eu(2+)/Eu(3+) decreases by a factor of 20 or more during the course of condensation, primarily because the ratio is proportional to the partial pressure of Al, which decreases dramatically as aluminous phases condense. The relative sizes of Eu and Yb anomalies in meteoritic Hibs and CAI's may be influenced by this effect.

Evolved Rocks in Ocean Islands Formed by Melting of Metasomatized Mantle

NASA Astrophysics Data System (ADS)

Ashwal, L. D.; Torsvik, T. H.; Horvath, P.; Harris, C.; Webb, S. J.; Werner, S. C.; Corfu, F.

2015-12-01

Evolved rocks like trachyte occur as minor components of many plume-related basaltic ocean islands (e.g. Hawaii, Gran Canaria, Azores, Réunion), and are typically interpreted as products of extreme fractional crystallization from broadly basaltic magmas. Trachytes from Mauritius (Indian Ocean) suggest otherwise. Here, 6.8 Ma nepheline-bearing trachytes (SiO2 ~63%, Na2O + K2O ~12%) are enriched in all incompatible elements except Ba, Sr and Eu, which show prominent negative anomalies. Initial eNd values cluster at 4.03 ± 0.15 (n = 13), near the lower end of the range for Mauritian basalts (eNd = 3.70 - 5.75), but initial Sr is highly variable (ISr = 0.70408 - 0.71034) suggesting secondary deuteric alteration. Fractional crystallization models starting with a basaltic parent fail, because when plagioclase joins olivine in the crystallizing assemblage, residual liquids become depleted in Al2O3, produce no nepheline, and do not approach trachytic compositions. Mauritian basalts and trachytes do not fall near the ends of known miscibility gaps, eliminating liquid immiscibility processes. Partial melting of extant gabbroic bodies, either from the oceanic crust or from Réunion plume-related magmas should yield quartz-saturated melts different from the critically undersaturated Mauritian trachytes. A remaining possibility is that the trachytes represent direct, small-degree partial melts of fertile, perhaps metasomatized mantle. This is supported by the presence of trachytic glasses in many mantle xenoliths, and experimental results show that low-degree trachytic melts can be produced from mantle peridotites even under anhydrous conditions. If some feldspar is left behind as a residual phase, this would account for the negative Ba, Sr and Eu anomalies observed in Mauritian trachytes. Two trachyte samples that are less depleted in these elements contain xenocrysts of anorthoclase, Al-rich cpx and Cl-rich kaersutite that are out of equilibrium with host trachyte magmas; these may represent fragments of a refertilized mantle source. A model of direct, low-degree partial melting of metasomatized mantle may apply to other worldwide examples of evolved rocks in ocean islands.

TEM Study of Intergranular Fluid Distributions in Rocks at a Nanometer Scale

NASA Astrophysics Data System (ADS)

Hiraga, T.; Anderson, I. M.; Kohlstedt, D. L.

2002-12-01

The distribution of intergranular fluids in rocks plays an essential role in fluid migration and rock rheology. Structural and chemical analyses with sub-nanometer resolution is possible with transmission and scanning-transmission electron microscopy; therefore, it is possible to perform the fine-scale structural analyses required to determine the presence or absence of very thin fluid films along grain boundaries. For aqueous fluids in crustal rocks, Hiraga et al. (2001) observed a fluid morphology controlled by the relative values of the solid-solid and solid-fluid interfacial energies, which resulted in well-defined dihedral angles. Their high-resolution transmission electron microscopy (TEM) observations demonstrate that grain boundaries are tight even at a nanometer scale, consistent with the absence of aqueous fluid films. For partially molten ultra-mafic rocks, two conflicting conclusions have been reached: nanometer-thick melt films wet grain boundaries (Drury and Fitz Gerald 1996; De Kloe et al. 2000) versus essentially all grain boundaries are melt-free (Vaughan et al. 1982; Kohlstedt 1990). To resolve this conflict, Hiraga et al. (2002) examined grain boundaries in quenched partially molten peridotites. Their observations demonstrate the following: (i) Although a small fraction of the grains are separated by relatively thick (~1 μm) layers of melt, lattice fringe images obtained with a high-resolution TEM reveal that most of the remaining boundaries do not contain a thin amorphous phase. (ii) In addition, the composition of olivine-olivine grain boundaries was analyzed with a nano-beam analytical scanning TEM with a probe size of <2 nm. Although the grain boundaries contained no melt film, the concentration of Ca, Al and Ti were enhanced near the boundaries. The segregation of these elements to the grain boundaries formed enriched regions <7 nm wide. A similar pattern of chemical segregation was detected in subsolidus systems. Creep experiments on the partially molten rocks that were analyzed in this study reveal little weakening even at melt contents approaching 4 vol%, consistent with our observations of melt-free grain boundaries.

Experimental constraints on the fate of subducted upper continental crust beyond the "depth of no return"

NASA Astrophysics Data System (ADS)

Zhang, Yanfei; Wu, Yao; Wang, Chao; Zhu, Lüyun; Jin, Zhenmin

2016-08-01

The subducted continental crust material will be gravitationally trapped in the deep mantle after having been transported to depths of greater than ∼250-300 km (the "depth of no return"). However, little is known about the status of this trapped continental material as well as its contribution to the mantle heterogeneity after achieving thermal equilibrium with the surrounding mantle. Here, we conduct an experimental study over pressure and temperature ranges of 9-16 GPa and 1300-1800 °C to constrain the fate of these trapped upper continental crust (UCC). The experimental results show that partial melting will occur in the subducted UCC along normal mantle geotherm to produce K-rich melt. The residual phases composed of coesite/stishovite + clinopyroxene + kyanite in the upper mantle, and stishovite + clinopyroxene + K-hollandite + garnet + CAS-phase in the mantle transition zone (MTZ), respectively. The residual phases achieve densities greater than the surrounding mantle, which provides a driving force for descent across the 410-km seismic discontinuity into the MTZ. However, this density relationship is reversed at the base of the MTZ, leaving the descended residues to be accumulated above the 660-km seismic discontinuity and may contribute to the "second continent". The melt is ∼0.6-0.7 g/cm3 less dense than the surrounding mantle, which provides a buoyancy force for ascent of melt to shallow depths. The ascending melt, which preserves a significant portion of the bulk-rock rare earth elements (REEs), large ion lithophile elements (LILEs), and high-filed strength elements (HFSEs), may react with the surrounding mantle. Re-melting of the metasomatized mantle may contribute to the origin of the "enriched mantle sources" (EM-sources). Therefore, the deep subducted continental crust may create geochemical/geophysical heterogeneity in Earth's interior through subduction, stagnation, partial melting and melt segregation.

Multiple melting stages and refertilization as indicators for ridge to subduction formation: The New Caledonia ophiolite

NASA Astrophysics Data System (ADS)

Ulrich, Marc; Picard, Christian; Guillot, Stéphane; Chauvel, Catherine; Cluzel, Dominique; Meffre, Sébastien

2010-03-01

The origin of the New Caledonia ophiolite (South West Pacific), one of the largest in the world, is controversial. This nappe of ultramafic rocks (300 km long, 50 km wide and 2 km thick) is thrust upon a smaller nappe (Poya terrane) composed of basalts from mid-ocean ridges (MORB), back arc basins (BABB) and ocean islands (OIB). This nappe was tectonically accreted from the subducting plate prior and during the obduction of the ultramafic nappe. The bulk of the ophiolite is composed of highly depleted harzburgites (± dunites) with characteristic U-shaped bulk-rock rare-earth element (REE) patterns that are attributed to their formation in a forearc environment. In contrast, the origin of spoon-shaped REE patterns of lherzolites in the northernmost klippes was unclear. Our new major element and REE data on whole rocks, spinel and clinopyroxene establish the abyssal affinity of these lherzolites. Significant LREE enrichment in the lherzolites is best explained by partial melting in a spreading ridge, followed by near in-situ refertilization from deeper mantle melts. Using equilibrium melting equations, we show that melts extracted from these lherzolites are compositionally similar to the MORB of the Poya terrane. This is used to infer that the ultramafic nappe and the mafic Poya terrane represent oceanic lithosphere of a single marginal basin that formed during the late Cretaceous. In contrast, our spinel data highlights the strong forearc affinities of the most depleted harzburgites whose compositions are best modeled by hydrous melting of a source that had previously experienced depletion in a spreading ridge. The New Caledonian boninites probably formed during this second stage of partial melting. The two melting events in the New Caledonia ophiolite record the rapid transition from oceanic accretion to convergence in the South Loyalty Basin during the Late Paleocene, with initiation of a new subduction zone at or near the ridge axis.

Evidence for stable grain boundary melt films in experimentally deformed olivine-orthopyroxene rocks

NASA Astrophysics Data System (ADS)

de Kloe, R.; Drury, M. R.; van Roermund, H. L. M.

The microstructure of olivine-olivine grain boundaries has been studied in experimentally deformed (1200-1227°C, 300MPa) partially molten olivine and olivine-orthopyroxene rocks. In-situ melting produced 1vol% melt in all samples studied. Grain boundary analyses were carried out using a number of transmission electron microscopy techniques. The grain boundary chemistry in undeformed olivine-orthopyroxene starting material showed evidence for the presence of an intergranular phase along some, but not all, of the olivine-olivine boundaries. In the deformed samples, ultrathin Si-rich, Al- and Ca-bearing amorphous films have been observed along all investigated olivine-olivine grain boundaries. The chemistry of the grain boundaries, which is considered to be indicative for the presence of a thin film, was measured with energy-dispersive X-ray spectroscopy (EDX) and energy-filtering imaging. The amorphous nature of the films was confirmed with diffuse dark field imaging, Fresnel fringe imaging, and high-resolution electron microscopy. The films range in thickness from 0.6 to 3.0nm, and EDX analyses show that the presence of Al and Ca is restricted to this ultrathin film along the grain boundaries. Because thin melt films have been observed in all the samples, they are thought to be stable features of the melt microstructure in deformed partially molten rocks. The transition from the occasional presence of films in the undeformed starting material to the general occurrence of the films in deformed materials suggests that deformation promotes the formation and distribution of the films. Alternatively, hot-pressing may be too short for films to develop along all grain boundaries. A difference in creep strength between the studied samples could not be attributed to grain boundary melt films, as these have been found in all deformed samples. However, a weakening effect of grain boundary melt films on olivine rheology could not be ruled out due to the lack of confirmed melt-film free experiments.

The influence of magma degassing on entrapment pressures recorded in olivine-hosted melt inclusions

NASA Astrophysics Data System (ADS)

Gaetani, G. A.

2013-12-01

The concentrations of H2O and CO2 in olivine-hosted melt inclusions provide estimates for the pressures at which they were entrapped, and represent an important source of information on the depths at which basaltic magmas crystallize [1]. Results from recent dehydration experiments demonstrate that diffusive loss of H2O from melt inclusions, driven by degassing of the external magma, leads to significant decreases to pressure within the inclusion [2, 3]. This, in turn, lowers the solubility of CO2 in the included melt causing a vapor to exsolve and form a bubble. This process has the potential to significantly modify estimates of entrapment pressures derived from volatile concentrations in olivine hosted melt inclusions. I have developed a quantitative model that describes this process, allowing the influence of degassing on entrapment pressures to be rigorously evaluated. Diffusive loss of H2O from the inclusions was determined using the model of [3]. An equation of state (EOS) for the silicate melt was taken from the results of [4] and [5], while the EOS for H2O-CO2 vapor was taken from [6]. The solubilities of H2O and CO2 in the silicate melt were derived from VolatileCalc [7]. Modeling results demonstrate that degassing of H2O-rich magma produces significant pressure drops, so that entrapment pressures never exceed crustal values and always represent a minimum. Conversely, degassing of H2O-poor magma does not significantly perturb the H2O content of olivine-hosted melt inclusions. Therefore, these inclusions preserve reliable records of the pressures at which they were entrapped. These results are consistent with a global compilation of olivine-hosted melt inclusion entrapment pressures presented by [3]. References: [1] Wanless, VD, and Shaw, AM, Nature Geosci, 5, 651-655 (2012); [2] Gaetani, GA, et al., Geology, 40, 915-918 (2012); [3] Bucholz, CE, et al., Earth Planet Sci Lett, 374, 145-155 (2013); [4] Lange, R. A., and Carmichael, ISE, Geochim Cosmochim Acta, 51, 2931-2946, (1987); [5] Kress, VC, and Carmichael, ISE, Contrib Mineral Petrol, 108, 82-92 (1991); [6] Duan, Z, and Zhang, Z, Geochim Cosmochim Acta, 70, 2311-2324 (2006); [7] Newman, S, and Lowenstern, JB, Comput Geosci, 28, 597-604 (2002).

Variations in collagen fibrils network structure and surface dehydration of acid demineralized intertubular dentin: effect of dentin depth and air-exposure time.

PubMed

Fawzy, Amr S

2010-01-01

The aim was to characterize the variations in the structure and surface dehydration of acid demineralized intertubular dentin collagen network with the variations in dentin depth and time of air-exposure (3, 6, 9 and 12 min). In addition, to study the effect of these variations on the tensile bond strength (TBS) to dentin. Phosphoric acid demineralized superficial and deep dentin specimens were prepared. The structure of the dentin collagen network was characterized by AFM. The surface dehydration was characterized by probing the nano-scale adhesion force (F(ad)) between AFM tip and intertubular dentin surface as a new experimental approach. The TBS to dentin was evaluated using an alcohol-based dentin self-priming adhesive. AFM images revealed a demineralized open collagen network structure in both of superficial and deep dentin at 3 and 6 min of air-exposure. However, at 9 min, superficial dentin showed more collapsed network structure compared to deep dentin that partially preserved the open network structure. Total collapsed structure was found at 12 min for both of superficial and deep dentin. The value of the F(ad) is decreased with increasing the time of air-exposure and is increased with dentin depth at the same time of air-exposure. The TBS was higher for superficial dentin at 3 and 6 min, however, no difference was found at 9 and 12 min. The ability of the demineralized dentin collagen network to resist air-dehydration and to preserve the integrity of open network structure with the increase in air-exposure time is increased with dentin depth. Although superficial dentin achieves higher bond strength values, the difference in the bond strength is decreased by increasing the time of air-exposure. The AFM probed F(ad) showed to be sensitive approach to characterize surface dehydration, however, further researches are recommended regarding the validity of such approach.

Melting phase relation of nominally anhydrous, carbonated pelitic-eclogite at 2.5-3.0 GPa and deep cycling of sedimentary carbon

NASA Astrophysics Data System (ADS)

Tsuno, Kyusei; Dasgupta, Rajdeep

2011-05-01

We have experimentally investigated melting phase relation of a nominally anhydrous, carbonated pelitic eclogite (HPLC1) at 2.5 and 3.0 GPa at 900-1,350°C in order to constrain the cycling of sedimentary carbon in subduction zones. The starting composition HPLC1 (with 5 wt% bulk CO2) is a model composition, on a water-free basis, and is aimed to represent a mixture of 10 wt% pelagic carbonate unit and 90 wt% hemipelagic mud unit that enter the Central American trench. Sub-solidus assemblage comprises clinopyroxene + garnet + K-feldspar + quartz/coesite + rutile + calcio-ankerite/ankeritess. Solidus temperature is at 900-950°C at 2.5 GPa and at 900-1,000°C at 3.0 GPa, and the near-solidus melt is K-rich granitic. Crystalline carbonates persist only 50-100°C above the solidus and at temperatures above carbonate breakdown, carbon exists in the form of dissolved CO2 in silica-rich melts and as a vapor phase. The rhyodacitic to dacitic partial melt evolves from a K-rich composition at near-solidus condition to K-poor, and Na- and Ca-rich composition with increasing temperature. The low breakdown temperatures of crystalline carbonate in our study compared to those of recent studies on carbonated basaltic eclogite and peridotite owes to Fe-enrichment of carbonates in pelitic lithologies. However, the conditions of carbonate release in our study still remain higher than the modern depth-temperature trajectories of slab-mantle interface at sub-arc depths, suggesting that the release of sedimentary carbonates is unlikely in modern subduction zones. One possible scenario of carbonate release in modern subduction zones is the detachment and advection of sedimentary piles to hotter mantle wedge and consequent dissolution of carbonate in rhyodacitic partial melt. In the Paleo-NeoProterozoic Earth, on the other hand, the hotter slab-surface temperatures at subduction zones likely caused efficient liberation of carbon from subducting sedimentary carbonates. Deeply subducted carbonated sediments, similar to HPLC1, upon encountering a hotter mantle geotherm in the oceanic province can release carbon-bearing melts with high K2O, K2O/TiO2, and high silica, and can contribute to EM2-type ocean island basalts. Generation of EM2-type mantle end-member may also occur through metasomatism of mantle wedge by carbonated metapelite plume-derived partial melts.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Man, Viet Hoang; Pan, Feng; Sagui, Celeste, E-mail: sagui@ncsu.edu

We explore the use of a fast laser melting simulation approach combined with atomistic molecular dynamics simulations in order to determine the melting and healing responses of B-DNA and Z-DNA dodecamers with the same d(5′-CGCGCGCGCGCG-3′){sub 2} sequence. The frequency of the laser pulse is specifically tuned to disrupt Watson-Crick hydrogen bonds, thus inducing melting of the DNA duplexes. Subsequently, the structures relax and partially refold, depending on the field strength. In addition to the inherent interest of the nonequilibrium melting process, we propose that fast melting by an infrared laser pulse could be used as a technique for a fastmore » comparison of relative stabilities of same-sequence oligonucleotides with different secondary structures with full atomistic detail of the structures and solvent. This could be particularly useful for nonstandard secondary structures involving non-canonical base pairs, mismatches, etc.« less

Dehydration stress extends mRNA 3′ untranslated regions with noncoding RNA functions in Arabidopsis

PubMed Central

Sun, Hai-Xi; Li, Yan; Niu, Qi-Wen; Chua, Nam-Hai

2017-01-01

The 3′ untranslated regions (3′ UTRs) of mRNAs play important roles in the regulation of mRNA localization, translation, and stability. Alternative cleavage and polyadenylation (APA) generates mRNAs with different 3′ UTRs, but the involvement of this process in stress response has not yet been clarified. Here, we report that a subset of stress-related genes exhibits 3′ UTR extensions of their mRNAs during dehydration stress. These extended 3′ UTRs have characteristics of long noncoding RNAs and likely do not interact with miRNAs. Functional studies using T-DNA insertion mutants reveal that they can act as antisense transcripts to repress expression levels of sense genes from the opposite strand or can activate the transcription or lead to read-through transcription of their downstream genes. Further analysis suggests that transcripts with 3′ UTR extensions have weaker poly(A) signals than those without 3′ UTR extensions. Finally, we show that their biogenesis is partially dependent on a trans-acting factor FPA. Taken together, we report that dehydration stress could induce transcript 3′ UTR extensions and elucidate a novel function for these stress-induced 3′ UTR extensions as long noncoding RNAs in the regulation of their neighboring genes. PMID:28522613

Incorporating Graphene Oxide into Alginate Polymer with a Cationic Intermediate To Strengthen Membrane Dehydration Performance.

PubMed

Guan, Kecheng; Liang, Feng; Zhu, Haipeng; Zhao, Jing; Jin, Wanqin

2018-04-25

Two-dimensional graphene oxide (GO) in hybrid membranes provides fast water transfer across its surface due to the abundant oxygenated functional groups to afford water sorption and the hydrophobic basal plane to create fast transporting pathways. To establish more compatible and efficient interactions for GO and sodium alginate (SA) polymer chains, cations sourced from lignin are employed to decorate GO (labeled as cation-functionalized GO (CG)) nanosheets via cation-π and π-π interactions, providing more interactive sites to confer synergetic benefits with polymer matrix. Cations from CG are also functional to partially interlock SA chains and intensify water diffusion. And with the aid of two-dimensional pathways of CG, fast selective water permeation can be realized through hybrid membranes with CG fillers. In dehydrating aqueous ethanol solution, the hybrid membrane exhibits considerable performance compared with bare SA polymer membrane (long-term stable permeation flux larger than 2500 g m -2 h -1 and water content larger than 99.7 wt %, with feed water content of 10 wt % under 70 °C). The effects of CG content in SA membrane were investigated, and the transport mechanism was correspondingly studied through varying operation conditions and membrane materials. In addition, such a membrane possesses long-term stability and almost unchanged high dehydration capability.

The thermal properties of beeswaxes: unexpected findings.

PubMed

Buchwald, Robert; Breed, Michael D; Greenberg, Alan R

2008-01-01

Standard melting point analyses only partially describe the thermal properties of eusocial beeswaxes. Differential scanning calorimetry (DSC) revealed that thermal phase changes in wax are initiated at substantially lower temperatures than visually observed melting points. Instead of a sharp, single endothermic peak at the published melting point of 64 degrees C, DSC analysis of Apis mellifera Linnaeus wax yielded a broad melting curve that showed the initiation of melting at approximately 40 degrees C. Although Apis beeswax retained a solid appearance at these temperatures, heat absorption and initiation of melting could affect the structural characteristics of the wax. Additionally, a more complete characterization of the thermal properties indicated that the onset of melting, melting range and heat of fusion of beeswaxes varied significantly among tribes of social bees (Bombini, Meliponini, Apini). Compared with other waxes examined, the relatively malleable wax of bumblebees (Bombini) had the lowest onset of melting and lowest heat of fusion but an intermediate melting temperature range. Stingless bee (Meliponini) wax was intermediate between bumblebee and honeybee wax (Apini) in heat of fusion, but had the highest onset of melting and the narrowest melting temperature range. The broad melting temperature range and high heat of fusion in the Apini may be associated with the use of wax comb as a free-hanging structural material, while the Bombini and Meliponini support their wax structures with exogenous materials.

Boron isotope fractionation during high-pressure dehydration of antigorite serpentinite

NASA Astrophysics Data System (ADS)

Harvey, J.; Garrido, C.; Agostini, S.; Padron Navarta, J.; López Sánchez-Vizcaíno, V.; Savov, I. P.; Marchesi, C.

2011-12-01

During subduction, antigorite-serpentinite is present in large volumes in both the downgoing slab and the overlying mantle wedge. There is strong evidence to suggest that deserpentinisation reactions are a source for several fluid mobile elements, including boron. The ultramafic rocks of Cerro del Almirez, Betic Cordillera, Spain are the only known outcrops that preserve evidence for the transition between antigorite-serpentinite and chlorite-harzburgite i.e., Almirez antigorite-serpentinite represents an early stage of prograde subduction zone metamorphism overprinting previously hydrated oceanic mantle. The stability of chlorite beyond the antigorite breakdown reaction limits the release of H2O to about 6-7 wt% (in the absence of chlorite up to 12 wt% H2O would be lost), i.e. the reaction at the antigorite-serpentinite / chlorite harzburgite front is a dehydration reaction which may fractionate boron isotopes because of the mineralogical change, because of the loss of fluid over a range of temperatures, or a combination of both. Although the behaviour of boron isotopes under closely controlled experimental conditions with a limited number of variables is reasonably well constrained, the mechanism or combination of mechanisms that fractionate 11B from 10B in natural samples can be complex and difficult to interpret, especially in samples of the sub-arc mantle wedge which is seldom accessible for direct examination. This study investigates the influence of dehydration reactions in the sub-arc region where fluid loss accompanies prograde metamorphism under well constrained pressure and temperature conditions. Initial results suggest that isotopes of boron are strongly fractionated during the dehydration of antigorite-serpentinite with marked differences in δ11B across the antigorite-serpentinite to chlorite-harzburgite isograd. Antigorite-serpentinite has a δ11B of +22.4 (± 0.9) whereas the dehydration reaction product, chlorite-harzburgite, has a δ11B ranging from +2.7 (± 0.4) to -3.5 (± 0.3). A single sample with a transitional antigorite-chlorite serpentinite lithology, taken from as near to the isograd as possible, preserves a δ11B of +3.3 (± 0.3). This suggests that a substantial proportion of fluid loss, and therefore the potential fractionation of boron isotopes, occurs early on in the prograde reaction - the largest changes in δ11B occurring between antigorite-serpentinite and the transitional lithology, while the prograde lithology preserves a narrower, yet still markedly heterogeneous range of δ11B. This suggests that dehydration of serpentinite results in a strong fractionation of boron isotopes and that the results of the dehydration reaction survive high P-T condition (650 °C, 1.7 GPa). Moreover, this may also indicate that a chlorite-hosted, B-rich reservoir with a heterogeneous δ11B can persist in the lithospheric mantle elsewhere and may modify basaltic melts with which it interacts.

High-temperature mass spectrometric study of the vaporization processes and thermodynamic properties of melts in the PbO-B2O3-SiO2 system.

PubMed

Stolyarova, V L; Lopatin, S I; Shilov, A L; Shugurov, S M

2013-07-15

The unique properties of the PbO-B2O3-SiO2 system, especially its extensive range of glass-forming compositions, make it valuable for various practical applications. The thermodynamic properties and vaporization of PbO-B2O3-SiO2 melts are not well established so far and the data obtained on these will be useful for optimization of technology and thermodynamic modeling of glasses. High-temperature Knudsen effusion mass spectrometry was used to study vaporization processes and to determine the partial pressures of components of the PbO-B2O3-SiO2 melts. Measurements were performed with a MS-1301 mass spectrometer. Vaporization was carried out using two quartz effusion cells containing the sample under study and pure PbO (reference substance). Ions were produced by electron ionization at an energy of 25 eV. To facilitate interpretation of the mass spectra, the appearance energies of ions were also measured. Pb, PbO and O2 were found to be the main vapor species over the samples studied at 1100 K. The PbO activities as a function of the composition of the system were derived from the measured PbO partial pressures. The B2O3 and SiO2 activities, the Gibbs energy of formation, the excess Gibbs energy of formation and mass losses in the samples studied were calculated. Partial pressures of the vapor species over PbO-B2O3-SiO2 melts were measured at 1100 K in the wide range of compositions using the Knudsen mass spectrometric method. The data enabled the PbO, B2O3, and SiO2 activities in these melts to be derived and provided evidence of their negative deviations from ideal behavior. Copyright © 2013 John Wiley & Sons, Ltd.

The connection between crustal reworking and petrological diversity in the deep crust: clues from migmatites

NASA Astrophysics Data System (ADS)

Carvalho, Bruna B.; Sawyer, Edward W.; de Assis Janasi, Valdecir

2016-04-01

The deep levels of the continental crust have been extensively reworked as result of crustal differentiation. Migmatites are widespread in these high-grade metamorphic terrains, and provide valuable information on how processes such as partial melting, segregation of the melt from the residue and subsequent chemical exchanges lead to the petrological diversity found in the deep crust. This study investigates processes that transformed a largely uniform, metagranodiorite protolith into a very complex migmatite that contains three varieties of diatexites (grey, schlieren and homogenous diatexites) and several types of leucosomes. The Kinawa Migmatite is part of the Archean TTG crust in the São Francisco Craton (Brazil), which has been reworked in a shear zone environment at upper amphibolite facies conditions (<730°C and 5-6 kbar); thus it may be typical of crustal reworking in the interior of old cratons [1]. Grey diatexites are residual rocks formed by the extraction of a water-fluxed melt created via the reaction Pl + Kfs + Qz + H2O = melt. Diversity within the grey diatexites arises from different degrees of melt segregation (maximum ~40% melt). Schlieren diatexites are very heterogeneous rocks in which residuum-rich domains alternate with leucocratic quartzo-feldspathic domains where melt accumulated. Homogeneous diatexites are coarse-grained leucocratic rocks and represent larger bodies of anatectic melt with minor amounts (<20%) of entrained residuum. Leucosomes display a wide range of compositions from tonalitic to alkali-feldspar granite. Leucosomes, homogeneous diatexites and the quartzo-feldspathic domains in the schlieren diatexites all show a sequence of microstructural stages from plagioclase-dominated to K-feldspar-dominated frameworks many of which show evidence for tectonic compaction. Thus, further segregation of melt from solids occurred during crystallization. Minor amphibolite dykes in the metagranodiorite did not melt. They occur as angular to rounded fragments (schollen or rafts) in the diatexites and show strong evidence for mechanical and chemical interaction with their melt rich hosts. Typically, the diatexites and the leucosomes around the schollen contain higher proportion of amphibole and/or biotite than that farther away; a number of features suggest that this is due to disaggregation that contaminated the melt rich rocks. Our data indicates that in the deep levels of the crust petrological diversity is produced by melt segregation, both during partial melting and crystallization, and by interaction of the anatectic melt with unmelted material in the source. During melting, segregation produced residuum plus anatectic melt and all intermediate stages, whereas during crystallization it resulted in crystal fractionation and generated diverse plagioclase-rich rocks and fractionated melts. Finally, crystals disaggregated from the amphibolites entrained and interact with anatectic melt producing leucosomes and diatexites with the compositional signature of contamination. [1] Carvalho, B.B; Sawyer, E.W.; Janasi, V.A. (2016). Crustal reworking in a shear zone: transformation of metagranite to migmatite. Journal of Metamorphic Geology DOI: 10.1111/jmg.12180

Methods and systems for monitoring a solid-liquid interface

DOEpatents

Stoddard, Nathan G [Gettysburg, PA; Clark, Roger F [Frederick, MD

2011-10-04

Methods and systems are provided for monitoring a solid-liquid interface, including providing a vessel configured to contain an at least partially melted material; detecting radiation reflected from a surface of a liquid portion of the at least partially melted material; providing sound energy to the surface; measuring a disturbance on the surface; calculating at least one frequency associated with the disturbance; and determining a thickness of the liquid portion based on the at least one frequency, wherein the thickness is calculated based on L=(2m-1)v.sub.s/4f, where f is the frequency where the disturbance has an amplitude maximum, v.sub.s is the speed of sound in the material, and m is a positive integer (1, 2, 3, . . . ).

Origin of Archean migmatites from the Gwenoro Dam area, Zimbabwe-Rhodesia

NASA Astrophysics Data System (ADS)

Condie, Kent C.; Allen, Philip

1980-09-01

Archean migmatites in the vicinity of Gwenoro Dam in Zimbabwe-Rhodesia are composed chiefly of trondhjemite gneiss (TR), mafic tonalite (MT), amphibolite (AM), leuco-trondhjemite veins (LTR), and pegmatites. The gneiss is intruded in nearby areas with small tonalite plutons (TN). Geochemical model studies together with field relationships are consistent with the following model for migmatite production: AM is produced by partial melting of a partly depleted ultramafic parent in which neither garnet nor amphibole remain in the residue; TR and TN are produced by partial melting of undepleted to variably depleted amphibolite in which garnet does not remain in the residue; MT is produced by mixing of plagioclase-rich TR with AM; and LTR represents the solid residue after fractional crystallization of TR.

Leucogranites in Lhozag, southern Tibet: Implications for the tectonic evolution of the eastern Himalaya

NASA Astrophysics Data System (ADS)

Huang, Chunmei; Zhao, Zhidan; Li, Guangming; Zhu, Di-Cheng; Liu, Dong; Shi, Qingshang

2017-12-01

Petrogenesis of the Himalayan leucogranite is strongly influenced by conditions which are associated with the tectonic evolution of Himalayan orogen. In this article, we present petrological, geochronological and geochemical results of the Lhozag leucogranites that crop out alongside the South Tibetan Detachment System (STDS) in the east of Himalaya. Zircon U-Pb dating revealed three episodes of leucogranitic magmatism in Lhozag at 17.8 ± 0.1 Ma, 15.1 ± 0.1 Ma, and 12.0 ± 0.1 Ma, respectively. The Lhozag leucogranites show relatively low εNd(t), low zircon εHf(t) and high initial 87Sr/86Sr ratios, which are similar to the High Himalayan Crystalline Series (HHCS), indicating that they were derived from the HHCS. The characteristics of relatively high Na2O and Rb contents, high Rb/Sr ratios and low CaO, MgO, TFe2O3, TiO2, and Sr contents indicate that both the ca. 18 Ma Lhozag tourmaline leucogranites and the ca. 15 Ma Lhozag two-mica granites were derived from fluid-absent muscovite-dehydration melting of metasediments. The opposite geochemistry characteristics of the ca. 12 Ma Khula Kangri two-mica granites imply that these granites are derived from fluid-present melting of metasediments. Four Khula Kangri two-mica granite samples with relatively lower TiO2, TFe2O3, MgO, and CaO contents, higher Rb concentrations and Rb/Sr ratios could be evolved from the Khula Kangri two-mica granites with relatively lower Rb/Sr ratios. The melting behaviors of the Lhozag leucogranites varied from fluid-absent melting to fluid-present melting, implying that there were P-T-XH2O variations in the deep crust. The tectonic evolution would give rise to variation of P-T-XH2O variation, and subsequent transformation of melting behavior. Our new results display the transformation of melting behavior of the Lhozag leucogranites, which implies the tectonic evolution from earlier N-S extension to later E-W extension in the eastern Himalaya at ca. 12 Ma.

Conversion of Nuclear Waste to Molten Glass: Cold-Cap Reactions in Crucible Tests

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Kai; Hrma, Pavel; Rice, Jarrett A.

2016-05-23

The feed-to-glass conversion, which comprises complex chemical reactions and phase transitions, occurs in the cold-cap zone during nuclear waste vitrification. Knowledge of the chemistry and physics of feed-to-glass conversion will help us control the conversion path by changing the melter feed makeup to maximize the glass production rate. To investigate the conversion process, we analyzed heat-treated samples of a simulated high-level waste feed using X-ray diffraction, electron probe microanalysis – wavelength dispersive X-ray spectroscopy, leaching tests, and residual anion analysis. Feed dehydration, gas evolution, and borate phase formation occurred at temperatures below 700 °C before the emerging glass-forming melt wasmore » completely connected. Above 800 °C, intermediate aluminosilicate phases and quartz particles were gradually dissolving in the continuous borosilicate melt, which expanded into transient foam. Knowledge of the chemistry and physics of feed-to-glass conversion will help us control the conversion path by changing the melter feed makeup to maximize the glass production rate.« less