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PALAEOMAGNETIC AND STRUCTURAL INVESTIGAtions ON BLOCK ROTAtions AND CRUSTAL SHORTENING IN CENTRAL TIBET

地学前缘 2000年第S1期7卷 168-169页

作者： M. Staiger 1,2 , E. Appel 1, L. Ratschbacher 2, M. Edwards 2 , Bi Siwen 3[WT5,5”BX](1 Universitaet Tuebingen, Institut fuer Geologie und Palaeontologie, Sigwartstr. 10, 72076 Tuebingen, Germany,E\|mail:staiger@geologie.uni\|wuerzburg.de 2 Tec

As a part of INDEPTH 3/GEODEPTH geological surface investigations were carried out during two field campaigns in 1998 and 1999. The working area covers a roughly N\|S (30～36°N) tren ding, 200km wide belt through the Lhasa Terrane and Qiangtang Terrane at a longitude of 88～90°E. Field geology was focused on geological mapping, structural measurements, and extensive sampling for the purpose of fission track geochronology. Additionally a total number of 742 orientated palaeomagnetic samples were drilled at 73 sites. Most of the samples were taken in fine\|grained sediments of Cretaceous, Eocene, and Neogene age. Five sites were drilled in acid to intermediate volcanics.A first sequence of measurements has been applied on a set of specimen. Most of the chosen formations (>80%) have acquired stable remanences which are carried by hematite and magnetite. As an example for the characteristic demagnetising behaviour of fine\|grained probable Cretaceous sandstones see Fig.1a. The unblocking temperature of 650℃ allows to identify hematite as remanence carrier.. Although single sites show well\|defined mean directions (e.g. site 76B: α 95 =3 8; k =185 8) the distribution among several site means of one formation could scatter (Fig.1b). It has to be checked carefully if rotations of single crustal elements are responsible for this effect. There is evidence to assume the detected characteristic remanences to be primary—further analysis including fold tests will be performed after the data set has increased.

关键词： paleomagnetism tectonics crustal shortening block rota tions Central Tibet

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Modified conceptual model for predicting the tendency of alluvial channel adjustment induced by human activities

引用

Chinese Science Bulletin 2001年第S1期46卷 51-57页

作者： XU JiongxinInstitute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China (e-mail: xujxin?***) Institute of Geographical Sciences and Natural Resources Research Chinese Academy of Sciences Beijing China

After a discussion about some limitations of Schumm’s conceptual model for prediction of river metamorphosis, this study introduces the channel boundary material as an independent variable, and thereby establishes a conceptual model that can be used to predict the direction of channel adjustment induced by human activities. This model has been tested by data from natural rivers and a laboratory model river, and can be used to explain the complex behavior of channel adjustment after reservoir construction.

关键词： human influence on channels channel boundary condi- tions feedback in channel system prediction of channel adjustment.

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