An experimental study of Ostwald ripening of olivine and plagioclase in silicate melts: implications for the growth and size of crystals in magmas   总被引：4，自引：4，他引：0  

Hugues?Cabane  Didier?LaporteEmail author  Ariel?Provost 《Contributions to Mineralogy and Petrology》2005,150(1):37-53

We carried out an experimental study to characterize the kinetics of Ostwald ripening in the forsterite-basalt system and in the plagioclase (An₆₅)-andesite system. Eight experiments were done in each system to monitor the evolution of mean grain size and crystal size distribution (CSD) with time t; the experiments were performed in a 1-atmosphere quench furnace, at 1,250°C for plagioclase and 1,300°C for olivine. Very contrasted coarsening kinetics were observed in the two series. In the plagioclase series, the mean grain size increased as log(t), from ≈3 μm to only 8.7 μm in 336 h. The kinetic law in log(t) means that Ostwald ripening was rate-limited by surface nucleation at plagioclase-liquid interfaces. In the olivine series, the mean grain size increased as t ^1/3, from ≈3 μm to 23.2 μm in 496 h. A kinetic law in t ^1/3 is expected when Ostwald ripening is rate-limited either by diffusion in the liquid or by grain growth/dissolution controlled by a screw dislocation mechanism. The shape of olivine CSDs, in particular their positive skewness, indicates that grain coarsening in the olivine experiments was controlled by a screw dislocation mechanism, not by diffusion. As the degrees of undercooling ΔT (or supersaturation) involved in Ostwald ripening are essentially <1°C, the mechanisms of crystal growth identified in our experiments are expected to be those prevailing during the slow crystallisation of large magma chambers. We extrapolated our experimental data to geological time scales to estimate the effect of Ostwald ripening on the size of crystals in magmas. In the case of plagioclase, Ostwald ripening is only efficient for mean grain sizes of a few microns to 20 μm, even for a time scale of 10⁵ years. It can, however, result in a significant decrease of the number of small crystals per unit volume, and contribute to the development of convex upwards CSDs. For olivine, the mean grain size increases from 2–3 μm to ≈70 μm in 1 year and 700 μm in 10³ years; a mean grain size of 3 mm is reached in 10⁵ years. Accordingly, the rate of grain size-dependent processes, such as compaction of olivine-rich cumulates or melt extraction from partially molten peridotites, may significantly be enhanced by textural coarsening.  相似文献   

Estimation of nearshore groundwater discharge and its potential effects on a fringing coral reef     

Blanco AC  Watanabe A  Nadaoka K  Motooka S  Herrera EC  Yamamoto T 《Marine pollution bulletin》2011,62(4):770-785

Radon (²²²Rn) measurements were conducted in Shiraho Reef (Okinawa, Japan) to investigate nearshore submarine groundwater discharge (SGD_nearshore) dynamics. Estimated average groundwater flux was 2-3 cm/h (maximum 7-8 cm/h). End-member radon concentration and gas transfer coefficient were identified as major factors influencing flux estimation accuracy. For the 7-km long reef, SGD_nearshore was 0.39-0.58 m³/s, less than 30% of Todoroki River’s baseflow discharge. SGD_nearshore was spatially and temporally variable, reflecting the strong influence of subsurface geology, tidal pumping, groundwater recharge, and hydraulic gradient. SGD_nearshore elevated nearshore nitrate concentrations (0.8-2.2 mg/l) to half of Todoroki River’s baseflow -N (2-4 mg/L). This increased nearshore Chl-a from 0.5-2 μg/l compared to the typically low Chl-a (<0.1-0.4 μg/l) in the moat. Diatoms and cyanobacteria concentrations exhibited an increasing trend. However, the percentage contributions of diatoms and cyanobacteria significantly decreased and increased, respectively. SGD may significantly induce the proliferation of cyanobacteria in nearshore reef areas.  相似文献   

Transcrystalline melt migration in clinopyroxene     

Yann Sonzogni  Ariel Provost  Pierre Schiano 《Contributions to Mineralogy and Petrology》2011,161(3):497-510

Glass inclusions in clinopyroxene phenocrysts from La Sommata (Vulcano Island, Aeolian Arc) were reheated and submitted to a sustained thermal gradient. Each remelted inclusion undergoes a transient textural and chemical reequilibration and concomitantly begins to migrate along a crystallographic direction, at a small angle with the thermal gradient. The completion of morphological evolution requires a characteristic time that is governed by chemical diffusion. Chemical reequilibration results in the formation of a colored halo that delineates the former location and shape of the inclusion after it has migrated away. Transcrystalline migration proceeds by dissolution of the host clinopyroxene ahead and precipitation astern. Its rate is not limited by Fick’s law, but by the crystal-melt interface kinetics. Clinopyroxene dissolution and growth are slower than for olivine in similar conditions but obey the same analytical law, which can be transposed to equally or more sluggish melting or crystallization events in nature. When a gas bubble is initially present, it responds to elastic forces by quickly shifting toward the cold end of the inclusion, where it soon becomes engulfed as an isolated fluid inclusion in the reprecipitated crystal. This study confirms that transcrystalline melt migration, beside its possible implications for small-scale melt segregation and fluid-inclusion generation in the Earth’s mantle, provides an experimental access to interfacial kinetic laws in near-equilibrium conditions.  相似文献   

Formation of syngenetic and early diagenetic iron minerals in the late Archean Mt. McRae Shale, Hamersley Basin, Australia: New insights on the patterns, controls and paleoenvironmental implications of authigenic mineral formation     

Rob Raiswell  Christopher T. Reinhard  Jeremy Owens  Ariel D. Anbar 《Geochimica et cosmochimica acta》2011,75(4):1072-146

A section through the late Archean Mt. McRae Shale comprising, in ascending order, a lower shale interval (LSI), a banded iron formation (BIF), an upper shale (USI) and a carbonate (C1) has been analyzed for total Fe and Al contents and authigenic Fe present as carbonate, oxide, sulfide and silicate phases. The authigenic mineralogy is controlled by the episodic addition of Fe from hydrothermal activity and removal of Fe by sulfide, relative to rates of clastic sedimentation. The LSI and BIF have mean Fe_T/Al values of 2 and 5, respectively, that record iron enrichment from hydrothermal sources. Iron was precipitated primarily as siderite accompanied by Fe-rich chlorite from anoxic bottom waters rich in dissolved Fe. Pyrite formation was probably limited by the availability of sulfate, which was present at low concentrations and became rapidly depleted. The USI has generally lower Fe_T/Al values (0.6-1.3), similar to those found in Paleozoic shales, with the exception of one interval where enrichment may reflect either a weak hydrothermal source or the operation of an iron shuttle. This interval contains authigenic Fe predominantly as pyrite, where high values for DOP (>0.8) indicate the existence of a water column that became rich in dissolved sulfide (euxinic) when sulfate concentrations increased due to a transient or secular increase in ocean/atmosphere oxygenation. High concentrations of dissolved sulfide maintained low concentrations of dissolved Fe, which allowed only minor amounts of Fe to be precipitated as carbonates and silicates. The USI also has elevated concentrations of organic matter that most probably reflect increased productivity and likely limited euxinia to midportions of the water column on the basin margin. The carbonate C1 represents a basinal chemistry where sulfide has been removed and Fe_T/Al values are ∼1 indicating that hydrothermal activity again produced dissolved Fe-rich bottom waters. Detailed iron speciation of the Mt. McRae Shale can be used to recognize spatial and temporal variations in iron and sulfur inputs to the late Archean Hamersley Basin, just prior to the Paleoproterozoic rise in atmospheric oxygenation, and our refined methods have relevance to all Fe-rich deposits.  相似文献   

Salinity and Chlorophyll a as Performance Measures to Rehabilitate a Mangrove-Dominated Deltaic Coastal Region: the Ci��naga Grande de Santa Marta�CPajarales Lagoon Complex, Colombia     

Victor H. Rivera-Monroy  Robert R. Twilley  J. Ernesto Mancera-Pineda  Christopher J. Madden  Ariel Alcantara-Eguren  E. Barry Moser  Bror F. Jonsson  Edward Casta?eda-Moya  Oscar Casas-Monroy  Paola Reyes-Forero  Jorge Restrepo 《Estuaries and Coasts》2011,34(1):1-19

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Downscaling projections of climate change in Sao Tome and Principe Islands,Africa     

Sin Chan Chou  Andr&#; de Arruda Lyra  Jorge Lu&#;s Gomes  Daniel Andr&#;s Rodriguez  Minella Alves Martins  Nicole Costa Resende  Priscila da Silva Tavares  Claudine Pereira Dereczynski  Isabel Lopes Pilotto  Alessandro Marques Martins  Lu&#;s Felipe Alves de Carvalho  Jos&#; Luiz Lima Onofre  Idal&#;cio Major  Manuel Penhor  Ad&#;rito Santana 《Climate Dynamics》2020,54(9):4021-4042

Sao Tome and Principe is a small insular African country extremely vulnerable to rising sea levels and impacts such as inundation, shore line change, and salt water intrusion into underground aquifers. Projections of climate change have considered coarse model resolutions. The objective of this work is to dynamically downscale the global model projections to 4-km resolution and to assess the climate change in the Sao Tome and Principe islands. The global climate projections are provided by the Canadian Earth System Model under two Representative Concentration Pathways greenhouse gas scenarios, RCP4.5 and RCP8.5. The downscaling is produced by the Eta regional climate model. The baseline period is taken between 1971 and 2000, and the future climate period is taken between 2041 and 2070. The 2-m temperature simulations show good agreement with station data. The model simulates temperature more accurately than precipitation. The precipitation simulations systematically show underestimation and delay of the rainy and the dry seasons by about 1 month, a feature inherited from the global climate model. In the middle of the 21st century, projections show the strongest warming in the elevated parts of the Sao Tome Island, especially in February under RCP8.5. Warmer nights and warmer days become more frequent in the islands when compared with those in the present. While under RCP4.5, precipitation increases in the islands; under RCP8.5, it decreases everywhere in both islands. Heavy precipitation rates should increase, especially in the south-southwestern parts of the Sao Tome islands. Detailed spatial variability of the temperature and precipitation changes in the islands can only be revealed at very high spatial model resolution. Implications for the potential energy production from two major river basins are assessed in this work.  相似文献   

A model of an expanding giant that swallowed planets for the eruption of V838 Monocerotis     

Alon Retter  Ariel Marom 《Monthly notices of the Royal Astronomical Society》2003,345(2):L25-L28

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An Adaptive Code for Radial Stellar Model Pulsations     

J. Robert Buchler  Zoltán Kolláth  Ariel Marom 《Astrophysics and Space Science》1997,253(1):139-160

We describe an implicit 1–D adaptive mesh hydrodynamics code that is specially tailored for radial stellar pulsations. In the Lagrangian limit the code reduces to the well tested Fraley scheme. The code has the useful feature that unwanted, long lasting transients can be avoided by smoothly switching on the adaptive mesh features starting from the Lagrangean code. Thus, a limit cycle pulsation that can readily be computed with the relaxation method of Stellingwerf will converge in a few tens of pulsation cycles when put into the adaptive mesh code. The code has been checked with two shock problems, viz. Noh and Sedov, for which analytical solutions are known, and it has been found to be both accurate and stable. Superior results were obtained through the solution of the total energy (gravitational + kinetic + internal) equation rather than that of the internal energy only. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Cosmological parameters from cosmic microwave background measurements and the final 2dF Galaxy Redshift Survey power spectrum   总被引：1，自引：0，他引：1  

Ariel G. Sánchez  C. M. Baugh  W. J. Percival  J. A. Peacock  N. D. Padilla  S. Cole  C. S. Frenk  P. Norberg 《Monthly notices of the Royal Astronomical Society》2006,366(1):189-207

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Eclogite-facies fluid infiltration: constraints from δ18O zoning in garnet     

Ashley K. Russell  Kouki Kitajima  Ariel Strickland  L. Gordon Medaris Jr.  Daniel J. Schulze  John W. Valley 《Contributions to Mineralogy and Petrology》2013,165(1):103-116

In situ analysis reveals that eclogite-facies garnets are zoned in δ¹⁸O with lower values in the core and rims that are ~1.5 to 2.5 ‰ higher. This pattern is present in 9 out of 12 garnets analyzed by SIMS from four orogenic eclogite terranes, and correlates with an increase in the mole fraction of pyrope and Mg/Fe ratio from core to rim, indicating prograde garnet growth. At the maximum temperatures and the time-scales experienced by these garnets, calculated intragranular diffusion distances for oxygen are small (<5 μm), indicating that δ¹⁸O records primary growth zoning and not diffusive exchange. The oxygen isotope gradients are larger than could form due to temperature changes during closed-system mineral growth. Thus, gradients reflect the compositions of fluids infiltrating during prograde metamorphism. Values of δ¹⁸O in garnet cores range from ?1 to 15 ‰, likely preserving the composition of the eclogite protoliths. Two garnet cores from the Almenningen eclogite in the Western Gneiss Region, Norway, have δ¹⁸O ~?1 ‰ and are the first negative δ¹⁸O eclogites identified in the region. In contrast with orogenic eclogites, seven high δ¹⁸O garnets (>5 ‰) from two kimberlites are homogeneous in δ¹⁸O, possibly due to diffusive exchange, which is possible for prolonged periods at higher mantle temperatures. Homogeneity of δ¹⁸O in garnets outside the normal mantle range (5–6 ‰) may be common in kimberlitic samples.  相似文献