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排序方式: 共有139条查询结果,搜索用时 31 毫秒
61.
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Influence of weather conditions and spatial variability on glacier surface melt in Chilean Patagonia
In order to clarify how differences in weather conditions affect the surface heat balance of a large maritime glacier, meteorological observations were carried out in the ablation area of Glaciar Exploradores in the Chilean Patagonia during the austral summer of 2006/2007. Under cloudy/rainy weather, when the air temperature and wind speed were high due to advection, the average melting heat was 18.8 MJ m?2 day?1 and the turbulent heat fluxes contributed 35% of the total melt. During clear weather, the average melting heat was 16.9 MJ m?2 day?1 and 13% of the total was the turbulent heat fluxes. A decrease in air temperature due to the development of the glacier boundary layer on clear days will lead to an overestimation of the melt using the air temperature at a weather station outside of the glacier. 相似文献
64.
Single crystalline San Carlos olivine (1 mm cube) was transformed to (Mg,Fe)2SiO4β-phase at 13.5–15 GPa, 1030–1330 °C for 0–600 min using a multi-anvil high pressure apparatus. The α-β transformation occurred
by incoherent surface nucleation and interface-controlled growth and recovered partially transformed samples showed sharply
defined reaction rim. The growth rate of the β-phase rim significantly decreased with time and the growth eventually ceased.
TEM observations revealed that many dislocations were created in both the relict olivine just near the α-β interface and the
β-phase in the rim, which show evidence for deformation caused by interfacial stresses associated with the misfit elastic
strain of the transformation. The observed tangled dislocation texture in β-phase suggested that the β-phase rim was hardened
and relaxation of the interfacial stress was retarded. This probably caused a localized pressure drop in the relict olivine
and decreased the growth rate. Time-dependent growth rates of β-phase is possibly controlled by the rheology of β-phase, which
must be considered for the prediction of the olivine metastability in the subducting slabs.
Received: 24 January 1997 / Revised, accepted: 24 July 1998 相似文献
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Hirokazu Maekawa Kazuyoshi Ohtsuka Koshi Yamamoto Nobuo Gouchi Keiko Hattori 《Island Arc》2021,30(1):e12384
Numerous green polished stone axes have been excavated from the Sannai-Maruyama site, one of Japan's largest archeological sites in the Jomon period (5.9–4.2 cal kyr BP). The axes are composed of weakly metamorphosed fine-grained volcaniclastic rock having a peculiar texture that includes numerous acicular actinolites growing in random directions within a quartz and albite matrix. Cobbles of Aotora stone found along the Nukabira River, Biratori town, southern Hokkaido, are the most likely raw material for these stone axes. Aotora stones have alternate bands of a soft dark-green picritic layer and a hard SiO2-rich pale-green layer. The pale-green layer has a texture similar to the stone axes. Basaltic and picritic volcanic rocks of the Sorachi-Yezo Belt occupy the area along the Shidoni River, a tributary of the Nukabira River. Volcaniclastic rocks similar in texture, mineralogy, and bulk rock compositions to the Aotora stone are exposed in the area. These rocks underwent metamorphism under the actinolite-pumpellyite facies conditions. Their protolith is submarine hyaloclastic rocks that are intercalated with laminated picrite detritus. The stone axes, pale-green layers of Aotora stone, and those of the volcaniclastic rocks of the Shidoni River area all have high SiO2 (~ 55 wt%), Cr (~ 840 μg/g), and Ni (~ 370 μg/g). The rare earth element patterns with abundant light rare earth elements and depleted heavy rare earth elements of stone axes were also consistent with the pale-green layers of the outcrop. These pale-green layers, interleaved with dark-green layers of picritic detritus, were the likely source rock of the stone axes. The high SiO2 content in the pale-green layer caused the crystallization of quartz and albite in the matrix, which resulted in high-quality raw material for making stone axes. 相似文献
68.
Ryoichi Nakada Yoshio TakahashiUrumu Tsunogai Guodong ZhengHiroshi Shimizu Keiko H. Hattori 《Applied Geochemistry》2011,26(7):1065-1076
A comprehensive study was performed to characterize, for the first time, the mud, water, and gases released from onshore mud volcanoes located in the southern margin of the Junggar Basin, northwestern China. Chemical compositions of mud, along with the geology of the basin, suggest that a source of the mud is Mesozoic or Cenozoic shale. Oxygen and H isotope compositions of the released water suggest a local meteoric origin. Combined with the positive Eu anomalies of the water, a large 18O shift of the water suggests extensive interaction with rocks. Gases discharged from the mud volcanoes are predominantly thermogenic hydrocarbons, and the high δ13C values (>+20‰ VPDB) for CO2 gases and dissolved carbonate in muddy water suggest secondary methanogenesis with CO2 reduction after oil biodegradation.The enrichments of Eu and 18O in water and the low thermal gradient of the area suggest that the water-rock interactions possibly occur deeper than 3670 ± 200 m. On the other hand, considering the relationship to the petroleum reservoir around the mud volcanoes, the depth of the gases can be derived from about 3600 m, a depth that is greater than that generally estimated for reservoirs whose gas is characterized by 13C-enriched CO2. Oil biodegradation with CO2 reduction likely occurs at a shallower depth along the seepage system of the mud volcano. The results contribute to the worldwide data set of gas genesis in mud volcanoes. Moreover, they further support the concept that most terrestrial mud volcanoes release thermogenic gas produced in very deep sediments and may be early indicators of oil biodegradation, an important problem in the petroleum industry. 相似文献
69.
Equivalent widths and line widths of Ca II infrared triplet emission lines were measured in the high-resolution optical spectra of 39 young stellar objects.We found that the equivalent widths of the emission lines decrease with stellar evolution.It has often been claimed that strong chromospheric activity is generated by a dynamo process caused by fast rotation of the photosphere.However,we found no clear correlation between the strength of the Ca II lines and the stellar rotation velocity.Instead,we found that the objects with high mass accretion rates had stronger Ca II emission lines.This correlation supports the turbulent chromosphere model or the magnetic accretion theory for classical T Tauri stars.We also noticed that the equivalent widths of Ca II lines in transitional disk objects are one-tenth of those in classical T Tauri stars,even if the masses of the circumstellar disks are comparable. 相似文献
70.
Kota Katsuki Yasushi Miyamoto Kazuyoshi Yamada Hiroyuki Takata Keiko Yamaguchi Daisuke Nakayama Hugo Coops Hidenobu Kunii Ritsuo Nomura Boo-Keun Khim 《Journal of Paleolimnology》2008,40(4):1115-1125
Lake Nakaumi, southwest Japan, is an enclosed lagoon characterized by polyhaline and halocline conditions. Since the last
century, its ecological state has been altered by eutrophication. We used a paleolimnological approach and studied multiple
proxies, including chemical compounds, diatoms, foraminifera and molluscs, to infer the eutrophication history of the ecosystem.
Eutrophication in Lake Nakaumi was associated with several factors, including increased nutrient loading, input of herbicides,
and dike building since the 1920s. The ecological condition of this lake was divided into several stages that reflect the
eutrophication process after the 1940s. A catastrophic “regime shift” from a clear state with aquatic vegetation to a turbid
one with phytoplankton occurred in the early 1950s. Environmental degradation in the Honjo area, a part of Lake Nakaumi, was
attributed primarily to physical changes caused by the construction of an enclosing dike. Eutrophication occurred almost simultaneously
with the physical changes to the Honjo area in the 1970s. Until recently, no regime shift was observed in this area, though
the core-top sediments show possible symptoms of incipient change. 相似文献