Experimental constraints on permeable gas transport in crystalline silicic magmas

The gas and fluid transport in magmas via permeable flow through interconnected bubble networks controls the rate of outgassing from magmas ascending in volcanic conduits and the fluid transport in the mushy boundary layer of magma reservoirs. Hence, clarifying its mechanism and rate is crucial to understanding the explosivity of volcanic eruptions and the evolution and dynamics of a magma reservoir. Recent experimental studies have determined the gas permeabilities in crystal-free rhyolite and basalt. However, no experimental study has investigated the effect of the crystal contents on the permeable gas transport in magmas. In this study, we performed decompression experiments for hydrous rhyolitic melts having crystallinities of 30 and 50 vol% to examine the effect of crystals on the bubble microstructure and gas permeability during magma vesiculation. Size-controlled (100-meshed) corundum crystals were used as an analog of the phenocrysts in silicic magmas. Microstructural analyses using X-ray CT showed that bubbles coalesce and their connectivity increases with a decrease in the final pressure after the decompression, that is, an increase in the vesicularity. As long as the vesicularities of melt part in the crystal-free basis (melt vesicularity) were similar, no clear effect of the crystallinity on the degree of bubble coalescence and connectivity was observed at melt vesicularities <68 vol%. The corundum showed a large contact angle with aqueous fluid as well as plagioclase and alkaline feldspar; this failed to induce the efficient heterogeneous nucleation and coalescence of bubbles on its surface. The gas permeabilities of all the run products were lower than the detection limits of the present analysis (the order of 10⁻¹⁶ m²) at melt vesicularities <68 vol%. These results show that silicic magmas containing 30 and 50 vol% phenocrysts with a large contact angle have low gas permeabilities until the vesicularity becomes large (at least >68 vol%). This result indicates that the permeable fluid transport through a deep volcanic conduit, which has been proposed on the basis of the observations of volcanic gases and natural products, is so slow that other processes, like shear deformation or magma convection, may be needed to explain the observations.     

Compositional variability on the surface of 4 Vesta revealed through GRaND measurements of high‐energy gamma rays

Measurements of the high‐energy gamma‐ray flux emanating from asteroid 4 Vesta by the Dawn Gamma‐Ray and Neutron Detector (GRaND) have revealed variability in the near‐surface elemental composition of the Vestan surface. These observations are consistent with the presence of large (≥8 × 10⁴ km²) regions with distinct, HED‐like elemental compositions. The results agree broadly with other global measurements, such as the macroscopic neutron absorption cross section and spectral reflectance‐derived mineralogic maps. Two distinct regions with eucrite‐like elemental compositions have been identified, the first located primarily within the Lucaria and Marcia quadrangles and the second within Oppia quadrangle. The former region is collocated with some of the oldest, most heavily cratered terrain on Vesta. The interior of the 500 km diameter Rheasilvia impact basin is found to have a composition that is consistent with diogenite‐like material. Taken together, these observations support the hypothesis that Vesta's original crust was composed of basaltic outflows in the form of eucritic‐like material and that the Rheasilvia‐basin‐forming impact exposed lower‐crustal, diogenite‐like material. These measurements also constrain the maximum amount of mesosiderite‐like material to <10% for each 15 × 15° surface element.     

Sea surface ichthyoplankton off southeastern New Zealand,summer 1977–78

Plankton samples from the Chatham Rise, Pukaki Rise, and Campbell Plateau provided information on the young stages of a number of poorly known New Zealand fish species, and on the presence of a large spawning area of barracouta, Thyrsites atun, over the Mernoo Bank, The Chatham Rise was more important as a spawning area than the areas further south.     

Eoarchean–Paleoproterozoic zircon inheritance in Japanese Permo-Triassic granites (Unazuki area,Hida Metamorphic Complex): Unearthing more old crust and identifying source terrranes

U–Pb zircon geochronology of two Permo-Triassic granites (samples OT-52 and OT-272 with ages of 229 ± 8 Ma and 256 ± 2 Ma, respectively) in the Unazuki area, Hida Metamorphic Belt, southwest Japan, revealed the presence of Eoarchean to Paleoproterozoic inheritance. Inheritance is consistent with both samples showing low zircon saturation temperatures for their bulk compositions. In OT-52, dark in CL, low Th/U zircon domains have a mean ²⁰⁷Pb/²⁰⁶Pb age of 1940 ± 17 Ma, which is consistent with an age of 1937 ± 6 Ma for anatexis in the Precambrian Busan gneiss complex in Korea. Eoarchaean inherited zircons with ²⁰⁷Pb/²⁰⁶Pb ages from ca. 3750 to 3550 Ma are common in OT-272 but are few in OT-52, suggesting a source from rocks with affinities to those in the Anshan area in the northeast China part of the North China Craton. On the other hand, a Hida Metamorphic Belt metasedimentary gneiss into which the granites were intruded contains ca. 1840, 1130, 580, 360, 285 and 250 Ma zircons (Sano et al., 2000). These ages suggest that the Unazuki Mesozoic granites did not originate from proximal Hida Metamorphic Complex rocks, but instead from unrelated rocks obscured at depth. The predominance of Eoarchean to Paleoproterozoic age components, and the marked lack of 900–700 Ma components suggest that the source was the (extended?) fringe of the North China Craton, rather than from Yangtze Craton crust. The Mesozoic evolution of Japan and its linkages to northeast Asia are discussed in the context of these results.     

GEOLOGY OF MT. PHULCHOKI AREA, CENTRAL NEPAL

GEOLOGY OF MT. PHULCHOKI AREA, CENTRAL NEPAL     

渤海西岸平原海平面上升危害性评估

本文按照ＩＰＣＣ第三工作组海岸管理小组拟定的国际共同研究大纲与方法，在对渤海西岸平原海平面上升的危害性进行评估时，应用ＴＭ遥感影像与地理信息系统，由土地利用类型、海岸蚀积动态叠加１─６ｍ等高线编制成环境地形图，再与地面形变图等辅助图件对照分析，预测海平面上升对环境和社会经济的危害。     

Profiles of nonylphenol isomers in surface waters from Sri Lanka

Isomer-specific concentrations of nonylphenol (NP) and their predicted estrogenic potency were investigated in Sri Lankan waters for the first time. The total concentration of 13 NP isomers ranged from 90 to 1835 ng/L, while the predicted estrogenic equivalent concentration ranged from 0.072 to 1.38 ng 17β-estradiol (E2)/L. Bire Lake, located in the central area of the commercial capital, Colombo, had the highest contamination among the studied locations. These data show that NP levels in Sri Lankan waters are well within the recently reported concentrations in other regions of the world. The spatial differences in NP concentrations suggest that NP contamination in Sri Lanka may be widespread, and comprehensive study is vital.     

A global survey of perfluorinated acids in oceans

Perfluorinated acids and their salts have emerged as an important class of global environmental contaminants. Biological monitoring surveys conducted using tissues of marine organisms reported the occurrence of perfluorooctanesulfonate (PFOS) and related perfluorinated compounds in biota from various seas and oceans, including the Arctic and the Antarctic Oceans. Occurrence of perfluorinated compounds in remote marine locations is of concern and indicates the need for studies to trace sources and pathways of these compounds to the oceans. Determination of sub-parts-per-trillion (ng/L) or parts-per-quadrillion (pg/L) concentrations of aqueous media has been impeded by relatively high background levels arising from procedural or instrumental blanks. Our research group has developed a reliable and highly sensitive analytical method by which to monitor perfluorinated compounds in oceanic waters. The method developed is capable of detecting PFOS, perfluorohexanesulfonate (PFHS), perfluorobutanesulfonate (PFBS), perfluorooctanoate (PFOA), perfluorononanoate (PFNA), and perfluorooctanesulfonamide (PFOSA) at a few pg/L in oceanic waters. The method was applied to seawater samples collected during several international research cruises undertaken during 2002–2004 in the central to eastern Pacific Ocean (19 locations), South China Sea and Sulu Seas (five), north and mid Atlantic Ocean (12), and the Labrador Sea (20). An additional 50 samples of coastal seawater from several Asian countries (Japan, China, Korea) were analyzed. PFOA was found at levels ranging from several thousands of pg/L in water samples collected from coastal areas in Japan to a few tens of pg/L in the central Pacific Ocean. PFOA was the major contaminant detected in oceanic waters, followed by PFOS. Further studies are being conducted to elucidate the distribution and fate of perfluorinated acids in oceans.     

Magnetic detection of heated soils at paleolithic sites in Japan

We present a methodological approach to detect heated soil on ancient sites, using magnetic measurements. The method is based on changes in magnetic signals of soil by heating. The following three types of soil were used for testing the method: silty soil (SS), weathered volcanic ash (WVA, = loam) and fairly fresh volcanic ash (VA) called Odori tephra. On heating above 250–600°C, the magnetic susceptibility and remanent magnetization intensity increased for the SS and WVA samples, reflecting chemical alteration of magnetic minerals (from goethites to magnetites through hematites). The VA sample showed no susceptibility change suggesting the absence of goethites within it. On heating below 250°C, only the intensities of all the samples increased. This is possibly due to acquisition of thermal remanent magnetization. The largest change of the magnetic signals was identified for the SS sample and the smallest one was seen for the VA sample. Therefore, the in situ susceptibility measurement, which is the nondestructive and indirect method, seems to be effective to detect heated soil for sites of aqueous deposits as the SS. On the other hand, for sites of aeolian deposits as the WVA (loam) and VA, the intensity measurement of collected soils seems to be the most reliable method to detect evidence of heating. The degree of the magnetic stability (coercivity) against progressive alternating-field demagnetization was also an important parameter, indicating whether the investigated soils were heated or unheated. © 1999 John Wiley & Sons, Inc.