湿雪的密实化与颗粒粗化过程研究

研究了处于自然状态下的湿雪的密实化和颗粒粗化过程.在野外观测的基础上,通过应用粘滞流体模型,发现与干雪相反,当湿雪的含水率达到一定程度(重量含水率约5%)后,粘滞度随密度增加而降低.通过粒径量测与颗粒大小分布统计发现,与含水饱和的雪相同,在湿雪演变过程中,不同时刻的雪粒粒径积累频率分布曲线形状基本相同,且与含水饱和雪的基本一致,说明含水不饱和的雪与含水饱和的雪在颗粒粗化过程中具有相同的粒径分布及其演进特征.分析还显示,含水不饱和雪的颗粒粗化速率比含水饱和雪的小得多.     

冻结法施工旁通道的冻土压力现场监测方法

冻结法广泛用于盾构隧道的旁通道施工,但设计上对于冻结引起的作用在隧道上的冻胀力还没有明确取值方法,其主要原因之一是缺乏现场测量数据。以上海长江隧道的旁通道施工为背景工程,采用新型土压力计监测。首先介绍了PAD式土压力计的基本特征和安装方法,然后介绍了自动数据采集和测点设置原则,接着通过实例重点说明电缆保护的重要性和保护措施。上述监测工作保证了全部5个土压力计的正常工作,并获得了有效的实测数据。数据显示,冻结工法造成的最大荷载增量远小于预期值,这主要是由于施工上设置了泄压孔,从而减少了作用在管片上的冻胀力     

Tephrostratigraphy of the Pliocene to Middle Pleistocene Series in Honshu and Kyushu Islands,Japan

The Pliocene to Pleistocene Series in each sedimentary basin or area of Japan has been investigated and described; however, their stratigraphic correlation is difficult because of complex geological structures. Regional stratigraphy has therefore been established using many intercalated tephra beds, i.e. by correlating tephra beds between distant areas. A standardized stratigraphic model of the Pliocene to Middle Pleistocene Series in Japan is put forward in this paper on the basis of tephrostratigraphy, magnetostratigraphy, and biostratigraphy. This stratigraphic model is important for studies of environmental changes and explosive volcanism in this period around the Japanese island‐arc.     

Amphiboles of a Metagabbro--Amphibolite Sequence, Hidaka Metamorphic Belt, Hokkaido

The western part of the Hidaka Metamorphic Belt, Hokkaido, consistsof primary pyroxene gabbro and lesser amounts of olivine gabbrothat have been dynamically metamorphosed to metagabbro—gabbroicamphibolite-amphibolite-epidote amphibolite during uplift andshearing about 23 m.y. ago. Textures and the presence of relic and recrystallized amphiboleand plagioclase in the same rock indicate incomplete reactionand non attainment of equilibrium during recrystallization. EPMA and bulk analyses of 165 amphiboles indicate a continuousoverall compositional range from actinolite to dark green hornblende(with 100 mg/(Mg+Fe²⁺+Fe³⁺Mn) ratios varying from 89.5 to 32.0)marked by increasing Al, Fe, Ti, and Na. A compositional gapis usually present between relic and recrystallized amphibolesin any one rock which becomes more prominent with increasingshearing. In addition to host rock chemical control, amphibole compositionis largely dependent on the An content of coexisting plagioclase.Locally epidote and sphene exert a strong influence on bothamphibole and plagioclase compositions. Amphibole Ti and Mncontents decrease with shearing and Fe enrichment of the hostrocks largely as a result of the incoming of rutile, sphene,and Fe-Ti oxides. Analysis of host rock oxidation ratio andamphibole compositions indicates that the rocks essentiallybehaved as closed systems to oxygen during metamorphism. Al^1V-Al^IV, Al^IV-Fe³⁺, and Al^IV-(Na, K)^A are the main substitutionsin the amphiboles. Within any one rock the recrystallized amphibolesare enriched in Al, Fe, Ti, and Na relative to the relice amphiboles.Increasing metamorphism results in a progressive change of amphiboles(recrystallized) to more Fe and Si (rather than Al) rich compositionsreflecting the trend towards greenschist where Fe-actinolite(+Mg chlorite) would be stable. Differentiation of the amphiboles is within the limits of SiAlreplacement and the compositional limits of the early stagereaction rim and replacement amphiboles in the host olivineand pyroxene metagabbros.     

Magnetite/Ilmenite–series Classification and Magnetic Susceptibility of the Mesozoic-Cenozoic Batholiths in Peru

Abstract: Plutonic rocks of the Coastal Batholith of Peru were evaluated in terms of the granitoid-series classification using the bulk ferric/ferrous ratio from the literature and new measurements of magnetic susceptibility. The batholith is largely composed of magnetite-series plutonic rocks; the magnetite series make up 85% by number of chemical analyses (n=130) and 80% by measurement of magnetic susceptibility (n=210). The ilmenite-series rocks are mostly found in the felsic facies of the batholith. Asymmetrical distribution of magnetic susceptibility is not clear as in the Japanese Islands and Peninsular Range Batholith, but the magnetic susceptibility may decreases continentward (i. e., Peninsular Range type).
The Cordillera Blanca Batholith and stocks are also composed of mainly magnetite series plutonic rocks, but ilmenite-series rocks may be more predominant than in the Coastal Batholith, which is also indicated by the presence of Sn and W mineralizations.     

Large amount of fluid migration around shallow seismogenic depth preserved in tectonic mélange: Yokonami mélange,the Cretaceous Shimanto Belt,Kochi, Southwest Japan

Studying subduction zone fluid at shallow seismogenic depths is important to understand the nature of fault rocks at the updip limit of the seismogenic zone because fluid–rock interactions affect heat and mass transfer, and fault strength. In this study, we conducted detailed analyses of distribution of shear veins, and estimation of pressure–temperature conditions for shear vein formation for the Yokonami mélange, Shikoku, Southwest Japan, which is tectonic mélange zone in an on‐land accretionary complex. We found a seismogenic fault at the upper boundary of the Yokonami mélange, indicating that the Yokonami mélange was active at seismogenic depth. The field‐transect distribution of shear veins was examined. The frequency, the total and mean thicknesses of the shear veins were about 3.7 per meter, about 10 mm per meter, and about 3 mm per shear vein, respectively. Quartz within the shear veins shows elongate‐blocky textures, suggesting precipitation from advective flow. The pressure and temperature conditions for shear vein formation were examined by fluid inclusion analysis, ranging 175–225°C and 143–215 MPa, respectively. The temperature is almost consistent with the paleotemperature determined from vitrinite reflectance, suggesting that the shear veins were formed at up to the maximum depth. The depth might be consistent with that where the seismogenic fault was formed. On the basis of the pressure and temperature conditions and the distribution of shear veins, we estimated the minimum volumetric ratio of fluid to host rocks, assuming that the shear veins had precipitated from advective flow. The estimated amount of fluid is about 106 m³ per cubic meter of host rocks. The results suggest that a large amount of fluid migrates through mélange zones at shallow seismogenic depths. This fluid possibly originates from the dehydration of clay minerals from underthrusted sediments and an altered subducting slab.     

A coastal acoustic tomography experiment in the Tokyo Bay

Eight sets of coastal acoustic tomography (CAT) systems were deployed during November 29 to December 10, 2002 at the coasts on both sides of Tokyo Bay to measure tidal current structures at 15-rain interval.Sound transmission across the Tokyo Bay (between Yokohama and Chiba)was successfillly traced,even under severe interference from ship generated wakes and bubbles.Tidal current fields changing from northward to southward flow are well reconstructed by the inverse analysis of travel-time difference data for a period with the best sound transmission condition. It is suggested that the CAT is the most powerful tool to continuously map tidal current fields in the coastal seas with heavy shipping traffic and fisheries activity.     

Characterizing and navigating small bodies with imaging data

Abstract— Recent advances in the characterization of small body surfaces with stereophotoclinometry are discussed. The principal data output is an ensemble of landmark maps (L‐maps), high‐resolution topography/albedo maps of varying resolution that tile the surface of the body. Because they can have a resolution comparable to the best images, and can be located on a global reference frame to high accuracy, L‐maps provide a significant improvement in discriminatory power for studies of small bodies, ranging from regolith processes to interior structure. These techniques are now being used to map larger bodies such as the Moon and Mercury. L‐maps are combined to produce a standard global topography model (GTM) with about 1.57 million vectors and having a wide variety of applications. They can also be combined to produce high‐resolution topography maps that describe local areas with much greater detail than the GTM. When combined with nominal predictions from other data sources and available data from other instruments such as LIDAR or RADAR, solutions for the spacecraft position and camera pointing are the most accurate available. Examples are drawn from studies of Phobos, Eros, and Itokawa, including surface characterization, gravity analysis, spacecraft navigation, and incorporation of LIDAR or RADAR data. This work has important implications for potential future missions such as Deep Interior and the level of navigation and science that can be achieved.