Material Transfer and Local Equilibria in a Zoned Kelyphite from a Garnet Pyroxenite, Ronda, Spain

A zoned kelyphite after garnet, from a garnet pyroxenite layer,the Ronda peridotite. Spain, has been studied and the mechanismof kelyphite formation is discussed. The kelyphite is an extremelyfinegrained symplectitic mixture of orthopyroxene, spinel, olivine,plagioclase, and ilmenite. It is concentrically zoned, formingthree mineralogical subzones. They are, from adjacent to a garnetgrain toward a clinopyroxene side, zone I (orthopyroxene+spinel+ plagioclase), zone II (olivine+spinel+plagioclase), and zoneIII (olivine+plagioclase). The analysis of phase equilibriashows that this mineralogical zonation can develop stably asa result of the presence of chemical potential gradients. Onthe basis of microprobe chemical analyses for each zone, materialtransfer across the zone that took place during the kelyphitizationwas quantitatively evaluated, and by locating the initial grainboundary between garnet and clinopyroxene grains and by writingmetasomatic reactions for each zone boundary, a simple dynamicmodel for the kelyphite formation is proposed. The kelyphiteformation probably took place when the host Ronda peridotiteascended from the upper mantle to the crust. It involved a co-operativebreakdown of the garnet and aluminous clinopyroxene, being accompaniedby a material transfer across the zone boundaries. By examiningthe Fe-Mg partitioning between olivine, spinel, and orthopyroxenein the kelyphite and by examining the Al content of the orthopyroxene,an attainment of local equilibrium has been confirmed, and thephysical conditions of the kelyphite formation have been estimatedto be 620–700C and 4–8 kbar.     

Middle to Late Pleistocene vegetation history and climatic changes at Lake Kopais, Southeast Greece

This study presents a detailed vegetation history of Lake Kopais, Southeast Greece based on pollen analysis of a 120 m-long sediment core. The record extends from the Holocene back to Oxygen Isotope Stage 11, and it gives a detailed history of Mediterranean evergreen woodlands during the last 500 ka. Vegetation of glacials consisted of open steppe with Chenopodiaceae and Artemisia associated with Tubuliflorae and other herbs, while that of interglacials was dominated by temperate Quercus forest. The Last Interglacial (Substage 5e) shows a complete vegetation succession starting with Juniperus and Betula, followed by deciduous oak and ending with Pinus and Abies. Wild olive is abundant in Substages 11c and 5e, suggesting very warm climatic conditions in Stage 11. Stages 9 and 7 were significantly cooler than 11 and 5e. The Pterocarya occurrence near the bottom of the core provides a possible equivalent of the Holsteinian Interglacial.     

Observation of Pore Spaces and Microcracks Using a Fluorescent Technique in Some Reservoir Rocks of Oil, Gas and Geothermal Fields in the Green Tuff Region, Japan

Abstract: Pore spaces and microcracks in representative oil, gas and geothermal reservoir rocks from the Green Tuff region, Japan, were examined using a fluorescent technique. This technique was developed to visualize microscopically pore spaces and microcracks filled with synthetic resin mixed with fluorescent paint under ultraviolet light. Various morphology of pore spaces and microcracks was clearly identified. Spaces in studied reservoir rocks are classified into following three types: pore spaces in matrix, pore spaces in particles, and microcracks. It is observed that valuable oil and gas reservoir rocks relatively include many pore spaces, while microcracks are important for geothermal rocks. Correlation between textural characteristics and porosity or permeability was found in the oil reservoir rocks. Effective permeability depends upon pore spaces in matrix more than upon other components such as pore spaces in particles and microcracks. Looseness in matrix caused by larger grain size of particles is strongly correlated with permeability. Pore spaces play an important role as a reservoir in oil and gas fields, but are less important in geothermal field. Instead, microcracks are important for geothermal reservoir system.     

The Ronda Peridotite: Garnet-, Spinel-, and Plagioclase-Lherzolite Facies and the P-T Trajectories of a High-Temprature Mantle Intrusion

The Ronda peridotite is a high-temperature, alpine-type peridotiteemplaced in the internal Zone of the Betic Cordilleras, southernSpain. Using the mineral assemblages of the peridotite and maficlayers, the peridotite mass has been subdivided into 4 zonesof mineral facies: (1) garnet-lherzolite facies, (2) ariégitesubfacies of spinel-lherzolite facies, (3) seiland subfaciesof spinel-lherzolite facies, and (4) plagioclase-lherzolitefacies. It is proposed that this mineralogical zonation developedthrough a syntectic recrystallization of a hot (1100 to 1200°C),solid mantle peridotite during its ascent into the Earth's crust. Coexisting minerals from 12 peridotites covering all the mineralfacies above were analysed with an electron microprobe. Corecompositions of pyroxene porphyroclasts are constant in allmineral facies and indicate that the peridotite was initiallyequilibrated at temperatures of 1100 to 1200 °C and pressuresof 20 to 25 kb. In contrast, the compositions of pyroxene neoblastsand spinel grains (which appear to have grown during later recrystallization)are well correlated with mineral facies. They indicate thatthe recrystallization temperature throughout the mass is moreor less constant, 800 to 900 °C, but that the pressure rangesfrom 5–7 kb in the plagioclase-lherzolite facies to 12–15kb in the garnet-lherzolite facies. Therefore, variation inpressure appears to be primarily responsible for the four mineralfacies types. A pressure range of at least 5 kb appears to be too large tohave been maintained (at the same time) in a mass as small asthe Ronda peridotite. Dynamic cooling may explain the observedvariation in the recrystallization pressure; i.e. during theintrusion of the peridotite body, different parts of the bodyhave followed different P-T paths in response to different localcooling rates. Comparing the inferred P-T paths for the peridotitewith published melting temperature of peridotite and mafic rocks,it is concluded that the peridotite did not go through partialfusion during the ascent. A hypothetical, diapiric uprise thatcaused partial fusion and igneous differentiation of the mantleperidotite is considered to be a separate event prior to theascent that started from about 70 km depth in the upper mantle.Estimates of cooling rates and of Al diffusion rates in pyroxenessuggest that the ascent rate of the peridotite body was greaterthan 1 meter/year. ^* Present address: Dement of Earth Sciences, Toyama University, Gofuku, Toyama 930, Japan.     

Transformation of Spinel Lherzolite to Garnet Lherzolite in Ultramafic Lenses of the Austridic Crystalline Complex, Northern Italy

Numerous lenticular bodies of ultramafic rocks occur withinthe upper amphibolite- to granulitefacies metamorphic terraneof the Austrides between the Non and Ultimo valleys (Nonsbergregion), northern Italy. The ultramafic rocks are divided intotwo textural types: (a) coarse-type; and (b) finetype. The coarse-typerocks have the protogranular texture and are predominantly spinellherzolite. Some coarse-type spinel lherzolites have partlytransformed to garnet lherzolite. The fine-types are consideredto be metamorphic derivatives of the former, and the observedmineral assemblages are: (1) olivine + orthopyroxene + clinopyroxene+ garnet + amphibole ? spinel, (2) olivine + orthopyroxene +garnet + amphibole + spinel; (3) olivine + orthopyroxene + amphibole+ spinel; and (4) olivine+ orthopyroxene + amphibole + chlorite.Based on the microprobe analyses of constituent minerals fromten representative peridotite samples, physical conditions ofthe metamorphism, particularly that of the spinel to garnetlherzolite transformation, are estimated. Applications of pyroxenegeothermometry yield temperature estimates of 1100–1300?Cfor the formation of the primary spinel lherzolite, and 700–800?Cfor that of the fine-type peridotites. A pressure range of 16–28kb is obtained for the garnet lherzolite crystallization dependingon the choice of geobarometers. Two alternative P-T paths, i.e.(1) isobaric cooling or (2) pressure-increase and temperaturedecrease are considered and their geodynamic implications discussed.     

Mass Concentration and Mineralogical Characteristics Aerosol Particles Collected at Dunhuang During ACE-Asia

Measurements were performed in spring 2001 and 2002 to determine the characteristics of soil dust in the Chinese desert region of Dunhuang, one of the ground sites of the Asia-Pacific Regional Aerosol Characterization Experiment (ACE-Asia). The mean mass concentrations of total suspended particle matter during the spring of 2001 and 2002 were 317 μg m-3 and 307 μg m-3, respectively. Eleven dust storm events were observed with a mean aerosol concentration of 1095 μg m-3, while the non-dusty days with calm or weak wind speed had a background aerosol loading of 196 μg m-3 on average in the springtime.The main minerals detected in the aerosol samples by X-ray diffraction were illite, kaolinite, chlorite, quartz,feldspar, calcite and dolomite. Gypsum, halite and amphibole were also detected in a few samples. The mineralogical data also show that Asian dust is characterized by a kaolinite to chlorite (K/C) ratio lower than 1 whereas Saharan dust exhibits a K/C ratio larger than 2. Air mass back-trajectory analysis show that three families of pathways are associated with the aerosol particle transport to Dunhuang, but these have similar K/C ratios, which further demonstrates that the mineralogical characteristics of Asian dust are different from African dust.     

Exploring CO pollution episodes observed at Rishiri Island by chemical weather simulations and AIRS satellite measurements: long-range transport of burning plumes and implications for emissions inventories

The summer of 2003 was an active forest fire season in Siberia. Several events of elevated carbon monoxide (CO) were observed at Rishiri Island in northern Japan during an intensive field campaign in September 2003. A simulation with a global chemistry-transport model is able to reproduce the general features of the baseline levels and variability in the observed CO, and a source attribution for CO in the model suggests that the contribution from North Asia dominated, accounting for approximately 50% on average, with contributions of 7% from North America and 8% from Europe and 30% from oxidation of hydrocarbons. With consideration of recent emission estimates for East Asian fossil fuel and Siberian biomass burning sources, the model captures the timing and magnitude of the CO enhancements in two pollution episodes well (17 and 24 September). However, it significantly underestimates the amplitude during another episode (11–13 September), requiring additional CO emissions for this event. Daily satellite images from AIRS reveal CO plumes transported from western Siberia toward northern Japan. These results suggest that CO emissions from biomass burning in western Siberia in 2003 are likely underestimated in the inventory and further highlight large uncertainties in estimating trace gas emissions from boreal fires.     

Compositional Continuity and Discontinuity in the Horoman Peridotite, Japan, and its Implication for Melt Extraction Processes in Partially Molten Upper Mantle

A hypothetical model is proposed to explain the origin of compositionaldiscontinuities in the layering observed in orogenic lherzolites.The observed collinearity of the whole-rock peridotite compositionsis best explained in terms of partial melting and melt segregation.The presence of chemical discontinuities implies that melt segregationincludes an abrupt and discontinuous process. A key conceptin the model is the topological transformation of melt geometryin partially molten rocks responding to the equality and inequalityof the fluid pressure and solid pressure, which may be realizedin a gravitational field. It is emphasized that the percolationthreshold is a critical boundary, beyond which a rapid microstructuralchange occurs in response to the change of local fluid pressure,thus causing a rapid increase of permeability. The model impliesthat the mode of melting is closer to batch melting than tofractional melting in the upper mantle. KEY WORDS: critical phenomenon; partial melting; percolation threshold; Horoman peridotite; melt segregation