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141.
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It has been frequently observed that the ferromagnetic minerals in volcanic rocks may undergo some physical/chemical changes when they are heated in a laboratory. For paleointensity determinations, it is therefore desirable to use the Thellier method, in which internal consistency of the data assures that such undesirable changes did not take place in a particular sample. The most serious drawback of this method is that it requires a considerable number of heatings and coolings and measurements of the remanent magnetization. Following a suggestion of Kono, a modified version of Thellier's technique was developed and applied to a historical lava flow of Hawaii and Oligocene rhyolites and welded tuffs of San Juan volcanic field, Colorado, U.S.A. Samples were heated only once to each temperature and cooled under a magnetic field applied perpendicular to the NRM directions. Results were compared to those obtained by the conventional Thelliers' technique. It was found that the modified method gives results as satisfactory as the original method. With the selection of appropriate samples, the modified method will cut down the time required for the experiment to almost half of what is required in the original method, without losing the merits of Thelliers' technique. 相似文献
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A landfill disposal site can be described as “an artificial vessel” and must satisfy the following three demands (1) storage and disposal of waste; (2) protection of the environment; and (3) benefit for nearby residents by taking advantage of consequential effects. The concept of risk was effectively considered to emphasize the importance of monitoring systems in landfill disposal sites, especially to protect the environment. Because a part of the R&D was involved in creating a monitoring system for a landfill disposal site, the present development and future potential of a system which can detect the leakage of watershield sheets, was discussed. 相似文献
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蚌湖洼陷是潜江凹陷潜江组的沉积、沉降中心,其两侧砂体的成因与分布是一个有争议的问题。通过岩心观察、水动力条件及碎屑锆石定年分析,明确了蚌湖洼陷两侧砂体的成因联系;进一步通过连续地层单元内的沉积古地貌恢复,明确了古地貌与砂体分布的关系。研究认为潜江凹陷潜三段沉积时期北部发育荆门地堑与汉水地堑两大物源体系,中部发育蚌湖-王场洼陷,西部发育丫角-新沟低凸起及斜坡带,东部为斜坡带,南部则为缓坡带。潜三段沉积时期,蚌湖洼陷南部的砂体既不是前人认为的“盐湖密度流”越过蚌湖洼陷的沉积产物,也不是牵引流横穿蚌湖洼陷搬运而来,而是牵引流经西部斜坡上的古沟谷搬运沉积下来的。 相似文献
146.
A high-resolution (1/60°), three-dimensional numerical circulation model of the Cariaco Basin (Venezuela) is constructed by
nesting the Regional Ocean Modeling System (ROMS) in the 1/12° global Hybrid Coordinate Ocean Model (HYCOM). A new bathymetry,
computed by merging DBDB2 data and in situ depth measurements using optimal interpolation, is described. This new bathymetry
corrects the depth of the channels that connect the Cariaco Basin with the open ocean and which play a very important role
in the basin circulation. Results from a 2004 ROMS hindcast are presented. Observations (temperature, salinity, and currents)
are used to validate the model results before using the model to describe the annual cycle of the Cariaco Basin and the interactions
between the basin and the open ocean. Two modes of interaction are described, the first being the meanders and eddies that
travel westward with the Caribbean Current, and the second being a subsurface eastward current that flows along the north
coast of South America. The circulation path within the basin is directly related to the intensity of this current. Both mechanisms
described play a role in the ventilation of the basin. The present study is also an example of the feasibility of one of the
objectives of GODAE (Global Ocean Data Assimilation Experiment): downscaling from a large-scale model to a regional model.
In particular, the nesting ratio of 5 used in this work demonstrates that a high-resolution model can be successfully nested
in HYCOM. 相似文献
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Neoproterozoic India within East Gondwana: Constraints from recent geochronologic data from Himalaya 总被引：2，自引：0，他引：2
Recent geochronologic data of detrital zircons and neodymium isotopic signatures of the Himalaya, Arabian–Nubian Shield, and Western Australia–East Antarctica (the Pinjarra Orogen/Circum-East Antarctic Orogen) are assessed to estimate the location of Neoproterozoic basement of the Himalaya.
The protolith of the Higher Himalayan Gneisses is considered to have been derived from the Pinjarra Orogen/Circum-East Antarctic Orogen of Western Australia–East Antarctica, and not from the Indian Craton to the south. This conclusion strongly suggests the juxtaposition of the Indian Craton, which forms the basement of the Himalaya, with the Circum-East Antarctic Orogen during the Neoproterozoic when the protolith of the Higher Himalayan Gneisses deposited. 相似文献