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Shaocheng Ji Kazuko Saruwatari David Mainprice Richard Wirth Zhiqin Xu Bin Xia 《Tectonophysics》2003,370(1-4):49-76
Ultra high-pressure (UHP) eclogites from Sulu region (China) represent mafic components of the continental crust, which were first subducted to mantle depths greater than 100 km and then exhumed to the earth's surface. Detailed investigation of microstructures, chemical compositions, petrofabrics and seismic properties of the UHP eclogites can provide important information on the operating deformation mechanisms and rheology of subducted continental crust and on the origin of seismic reflections within the upper mantle. We present here results from field, optical and TEM observations, electron back-scattered diffraction (EBSD) measurements and numerical computations of the seismic properties of UHP eclogites collected from fresh surface outcrops at the drill site (Maobei, Donghai County, Jiangsu Province) of the Chinese Continental Scientific Drilling Program (CCSD). Two types of eclogites have been distinguished: Type-1 (coarse-grained) eclogites deformed by recovery-accommodated dislocation creep at the peak metamorphic conditions, and Type-2 (fine-grained) eclogites which are composed of reworked Type-1 materials during recrystallization-accommodated dislocation creep in shear zones which were active during the exhumation of the UHP metamorphic rocks. Both garnet and omphacite in these eclogites deformed plastically and the flow strength contrast between these two constituent minerals is apparently much less than an order of magnitude under the UHP metamorphic conditions. Plasticity of eclogites under UHP conditions can effectively facilitate channeled flow along the interplate shear zone. The preservation of the relict crustal materials within the continental lithosphere may produce regionally extensive, strong, seismic reflections in the upper mantle. This may explain the origin of mantle reflections observed in many areas of the world. 相似文献
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Palaeoenvironment in Java island and its surrounding areas since the last interglacial stage was reconstructed initially using previous studies by various researchers. The karst area in Gunung Sewu on Java island was also examined by the authors in order to reconstruct the palaeoenvironment through the process of karstification. Summarizing the evidence related to palaeoclimate in the various areas made it clear that the palaeoclimatic condition was cooler and drier at the Last Glacial Maximum 18 000 yr BP, than today. Formation of dry valleys in Gunung Sewu was conditioned by lowering of sea-level, and establishment of a cool and extremely dry climate. Subsequent to the initial reconstruction, the results of the estimated palaeoclimate at 18 000 yr BP were plotted at the respective points where the samples were obtained, and maps for northern winter and northern summer were constructed showing the estimated streamlines of monsoon circulations, polar frontal zones and intertropical convergence zones, in order to better explain the distribution of the palaeoclimate conditions of the area. ©1997 John Wiley & Sons, Ltd. 相似文献
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Regional differences in climatic change are of importance in order to establish the counter-measures for the damage by anomalous climate to agricultural production. It is not unusual for some regions to suffer floods while droughts occur in nearby regions at the same time. This paper deals mainly with the regionality of climatic change in E Asia during recent years, using the year-climate method expressed by the Köppen's system of climatic classification. Occurrence frequencies of BW, BS, Cf, Cw, Dwa, Dwb, and Dwc-type showed striking regionalities, which were obtained from the data at the 134 observatories over E Asia during the period from 1951 to 1970. The distribution of climatic types in each year shows various tendencies: Wet and cold as in 1954 and 1957 shows a pattern in which the boundary between C-type and D-type runs south and the Cfa-zone is broad, extending from middle E China to SW Japan. In contrast, in dry and warm years like 1965, the Dwa regions disappear in the N of E China and the BS region is located just north of the Cwa region, which is distributed broadly from China to Japan. Occurrence frequencies of year climate during the last 100 years were calculated for the 4 stations: Hong Kong, Manila, Shanghai and Tokyo. The results were compared with the distribution types of winter temperature and summer precipitation in China. It seems that the precipitation conditions in summer were reversed between the Philippines and China. Summarizing the results obtained, a schema of the regionality of climatic fluctuation in E and SE Asia was given in relation to the upper air streams. The position of the subtropical jet stream in winter shows a close relationship to the N limit of the Aw and Am year climate regions and in summer with the S limit of Dw region in NE China and North Korea. The Cw and Cf year climate regions in E Asia are located roughly in the regions bounded by the axes of subtropical jet streams in winter and in summer. The Dw year climate region in the E of the Tibetan Plateau reflects the altitudinal effect of the Cw climate of SE China. The N of E China has the variable BS year climate, which may related to the summer and winter jet stream conditions. Finally, the interannual change of the agricultural production index was dealt with in relation to the occurrence frequency of year climate types over E Asia during the years 1967–1970. As far as this period is concerned, the drier conditions are more effective than the wetter conditions in reducing agricultural production. 相似文献
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