ALBERT

Description: Coesite is typically found as inclusions in rock-forming or accessory minerals in ultrahigh-pressure (UHP) metamorphic rocks. Thus, the survival of intergranular coesite in UHP eclogite at Yangkou Bay (Sulu belt, eastern China) is surprising and implies locally ‘dry’ conditions throughout exhumation. The dominant structures in the eclogites at Yangkou are a strong D 2 foliation associated with tight-to-isoclinal F 2 folds that are overprinted by close-to-tight F 3 folds. The coesite-bearing eclogites occur as rootless intrafolial isoclinal F 1 fold noses wrapped by a composite S 1 –S 2 foliation in interlayered phengite-bearing quartz-rich schists. To evaluate controls on the survival of intergranular coesite we determined the number density of intergranular coesite grains per cm 2 in thin section in two samples of coesite eclogite (phengite absent) and threee samples of phengite-bearing coesite eclogite (2–3 vol.% phengite), and measured the amount of water in garnet and omphacite in these samples, and also in two samples of phengite-bearing quartz eclogite (6–7 vol.% phengite, coesite absent). As coesite decreases in the mode, the amount of primary structural water stored in the whole rock, based on the nominally anhydrous minerals (NAMs), increases from 107/197 ppm H 2 O in the coesite eclogite to 157–253 ppm H 2 O in the phengite-bearing coesite eclogite to 391/444 ppm H 2 O in the quartz eclogite. In addition, there is molecular water in the NAMs and modal water in phengite. If the primary concentrations reflect differences in water sequestered during the late prograde evolution, the amount of fluid stored in the NAMs at the metamorphic peak was higher outside of the F 1 fold noses. During exhumation from UHP conditions, where NAMs became H 2 O saturated, dehydroxylation would have generated a free fluid phase. Interstitial fluid in a garnet–clinopyroxene matrix at UHP conditions has dihedral angles 〉60°, so at equilibrium fluid will be trapped in isolated pores. However, outside the F 1 fold noses strong D 2 deformation likely promoted interconnection of fluid and migration along the developing S 2 foliation, enabling conversion of some or all of the intergranular coesite into quartz. By contrast, the eclogite forming the F 1 fold noses behaved as independent rigid bodies within the composite S 1 –S 2 foliation of the surrounding phengite-bearing quartz-rich schists. Primary structural water concentrations in the coesite eclogite are so low that H 2 O saturation of the NAMs is unlikely to have occurred. This inherited drier environment in the F 1 fold noses was maintained during exhumation by deformation partitioning and strain localization in the schists, and the fold noses remained immune to grain-scale fluid infiltration from outside allowing coesite to survive. The amount of inherited primary structural water and the effects of strain partitioning are important variables in the survival of coesite during exhumation of deeply subducted continental crust. Evidence of UHP metamorphism may be preserved in similar isolated structural settings in other collisional orogens. This article is protected by copyright. All rights reserved.

Description: Composite granite–quartz veins occur in retrogressed ultrahigh pressure (UHP) eclogite enclosed in gneiss at General's Hill in the central Sulu belt, eastern China. The granite in the veins has a high-pressure (HP) mineral assemblage of dominantly quartz+phengite+ allanite/epidote+garnet that yields pressures of 2.5–2.1 GPa (Si-in-phengite barometry) and temperatures of 850–780 °C (Ti-in-zircon thermometry) at 2.5 GPa (~20 °C lower at 2.1 GPa). Zircon overgrowths on inherited cores and new grains of zircon from both components of the composite veins crystallized at c . 221 Ma. This age overlaps the timing of HP retrograde recrystallization dated at 225–215 Ma from multiple localities in the Sulu belt, consistent with the HP conditions retrieved from the granite. The ε Hf ( t ) values of new zircon from both components of the composite veins and the Sr–Nd isotope compositions of the granite consistently lie between values for gneiss and eclogite, whereas δ 18 O values of new zircon are similar in the veins and the crustal rocks. These data are consistent with zircon growth from a blended fluid generated internally within the gneiss and the eclogite, without any ingress of fluid from an external source. However, at the peak metamorphic pressure, which could have reached 7 GPa, the rocks were likely fluid absent. During initial exhumation under UHP conditions, exsolution of H 2 O from nominally anhydrous minerals generated a grain boundary supercritical fluid in both gneiss and eclogite. As exhumation progressed, the volume of fluid increased allowing it to migrate by diffuse porous flow from grain boundaries into channels and drain from the dominant gneiss through the subordinate eclogite. This produced a blended fluid intermediate in its isotope composition between the two end members, as recorded by the composite veins. During exhumation from UHP (coesite) eclogite to HP (quartz) eclogite facies conditions, the supercritical fluid evolved by dissolution of the silicate mineral matrix, becoming increasingly solute-rich, more ‘granitic’ and more viscous until it became trapped. As crystallization began by diffusive loss of H 2 O to the host eclogite concomitant with ongoing exhumation of the crust, the trapped supercritical fluid intersected the solvus for the granite–H 2 O system, allowing phase separation and formation of the composite granite–quartz veins. Subsequently, during the transition from HP eclogite to amphibolite facies conditions, minor phengite breakdown melting is recorded in both the granite and the gneiss by K-feldspar+plagioclase+biotite aggregates located around phengite and by K-feldspar veinlets along grain boundaries. Phase equilibria modelling of the granite indicates that this late-stage melting records P–T conditions towards the end of the exhumation, with the subsolidus assemblage yielding 0.7–1.1 GPa at 〈670 °C. Thus, the composite granite–quartz veins represent a rare example of a natural system recording how the fluid phase evolved during exhumation of continental crust. The successive availability of different fluid phases attending retrograde metamorphism from UHP (coesite) eclogite to amphibolite facies conditions will affect the transport of trace elements through the continental crust and the role of these fluids as metasomatic agents interacting with the mantle wedge in the subduction channel. This article is protected by copyright. All rights reserved.

Description: Low-frequency, wide field-of-view (FoV) radio telescopes such as the Murchison Widefield Array (MWA) enable the ionosphere to be sampled at high spatial completeness. We present the results of the first power spectrum analysis of ionospheric fluctuations in MWA data, where we examined the position offsets of radio sources appearing in two datasets. The refractive shifts in the positions of celestial sources are proportional to spatial gradients in the electron column density transverse to the lineof sight. These can be used to probe plasma structures and waves in the ionosphere. The regional (10–100 km) scales probed by the MWA, determined by the size of its FoV and the spatial density of radio sources (typically thousands in a single FoV), complement the global (100–1000 km) scales of GPS studies and local (0.01–1 km) scales of radar scattering measurements. Our data exhibit a range of complex structures and waves. Some fluctuations have the characteristics of travelling ionospheric disturbances (TIDs), while others take the form of narrow, slowly-drifting bands aligned along the Earth's magnetic field.

Description: A biomass-based methanol production process was investigated. The process consists of a biomass gasifier, steam reformer, and methanol synthesis reactor as the main units. Reactors were simulated by applying the kinetic models previously developed and the process was analyzed based on the simulation results. The key parameters, the equivalence ratio in biomass gasification, the temperature in steam reforming, and the recycle of hydrogen in methanol synthesis were identified. These parameters affect the methanol production. The process analysis indicates that the optimal combinations of the parameters can greatly enhance the methanol production and the thermodynamic efficiency. Finally, the elemental analysis for carbon and hydrogen along the process was carried out. A green process for methanol production was investigated. The process starts with biomass gasification, followed by steam reforming of the syngas and conversion of the syngas to methanol. Process analysis indicates that optimal combinations of a number of key parameters can greatly enhance the methanol production and the thermodynamic efficiency.

Description: We retrieved column-averaged dry air mole fractions of atmospheric carbon dioxide (XCO2) from backscattered short-wave infrared (SWIR) sunlight measured by the Japanese Greenhouse gases Observing SATellite (GOSAT). Over two years of XCO2 retrieved from GOSAT is compared with XCO2 inferred from collocated SWIR measurements by seven ground-based Total Carbon Column Observing Network (TCCON) stations. The average difference between GOSAT and TCCON XCO2 for individual TCCON sites ranges from −0.87 ppm to 0.77 ppm with a mean value of 0.1 ppm and standard deviation of 0.56 ppm. We find an average bias between all GOSAT and TCCON XCO2 retrievals of −0.20 ppm with a standard deviation of 2.26 ppm and a correlation coefficient of 0.75. One year of XCO2 was retrieved from GOSAT globally, which was compared to global 3-D GEOS-Chem chemistry transport model calculations. We find that the latitudinal gradient, seasonal cycles, and spatial variability of GOSAT and GEOS-Chem agree well in general with a correlation coefficient of 0.61. Regional differences between GEOS-Chem model calculations and GOSAT observations are typically less than 1 ppm except for the Sahara and central Asia where a mean difference between 2 to 3 ppm is observed, indicating regional biases in the GOSAT XCO2 retrievals unobserved by the current TCCON network. Using a bias correction scheme based on linear regression these regional biases are significantly reduced, approaching the required accuracy for surface flux inversions.