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The sand-hill section in Hongguang, Pengze County, Jiangxi Province is composed of eolian sand beds interbedded with 12 weakly-pedogenetic
paleosols, and this sedimentary sequence was formed from about 25 to 13 kaBP. A detailed rock-magnetic study demonstrates
that the magnetic minerals in the sequence are dominated by multi-domain magnetite grains in addition to small amounts of
maghemite and hematite. Compared with the eolian sand beds, the paleosols are characterized by smaller magnetic particles,
higher proportion of low-coercivity minerals and markedly increase in the magnetic mineral content. In the section, various
magnetic parameters (K, ARM, SIRM and S ratios) display a roughly gradual increase from eolian sand beds to the overlying
paleosols but an abrupt decrease from paleosols to the overlying eolian sand beds. The content of low-coercivity magnetic
minerals shows the lowest values in the second eolian sand bed from the bottom of the section, and from the bed upwards it
gradually increases on the whole in the eolian sand beds. These magnetic properties reflect regional climatic changes during
the last glacial maximum. 相似文献
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It draws much attention of scientists how early hu- mans occupy and adapt to the rigorous climate and environment at high northern latitudes in East Asia after they stepped out of Africa, passed West Asia and finally arrived in East Asia[1-4]. Reliable age determi- nations of Paleolithic sites from northeastern Asia not only help to find out the earliest occupation of early humans in this region, but also relate to the founda- tion of the overall framework of human origin and migration[1-8]… 相似文献
45.
As an important part of the early Mesozoic granites in the South Qinling tectonic belt (SQTB), the Guangtoushan pluton provides a material basis for research on the composition of magma sources and the effects of peritectic assemblage entrainment (PAE) on the changes in the granite composition. As shown by the results of LA-ICP-MS zircon U-Pb dating, the Guangtoushan pluton was emplaced during the Late Triassic (214–212 Ma) and was formed in the post-collision stage between the SQTB and the Yangtze plate. The collected samples had high SiO2 content and low Cr and Ni contents, indicating that the magmas did not undergo significant crust-mantle mixing during their evolution. The Guangtoushan granitoids were distributed along the trend line of magmatic fractional crystallization in the F–An–Or diagram. This result, combined with the relatively homogeneous Sr-Nd isotopic composition, implies that the Guangtoushan pluton underwent slight assimilation and contamination. As can be inferred from the comparison between the compositions of the Guangtoushan granitoids and various fluid-absent experimental melts, the magma sources of the Guangtoushan granitoids contain a variety of materials, such as graywackes, pyroclastic graywackes, and pelites and are not derived from lower crustal mafic rocks. The correlation between the maficity and the major and trace elements further indicates that the strongly peraluminous granitoids from the Guangtoushan pluton was formed by the partial melting of biotite-bearing crustal rocks and its magmatic evolution was accompanied by the entrainment of clinopyroxenes and accessory minerals. 相似文献
46.
Hanning Wu Rixiang Zhu Vincent Courtillot Lixin Bai Jianxiao Xing Yongxin Zhao Gelian Yang 《中国科学D辑(英文版)》1999,42(2):182-194
The paleomagnetic reconnaissance study of the Paleozoic and Mesozoic sedimentary rocks from the Yangtze Block (YZB) was made
to conduct the Apparent Polar Wander Path (APWP) of the YZB during the Phanerozoic. A total of 825 samples from 84 sites were
collected from a continuous section along the Xiangxi River valley in Xingshan and Zigui counties in Hubei Province, northern
margin of the YZB. Stepwise thermal/alternating demagnetization isolated well defined characteristic magnetization (ChRM)
at a higher temperature in most of the samples, and relatively thermal stability and high coercivity were revealed from these
samples. All the ChRMs can pass the fold and/or reversal tests, suggesting that they are probably primary. Therefore, new
pole positions are presented for the YZB.
Project supported by the National Natural Science Foundation of China (Grant No. 49334050). 相似文献
47.
New Silurian and Devonian palaeomagnetic results from the Hexi Corridor terrane, northwest China, and their tectonic implications 总被引:5,自引:0,他引:5
Baochun Huang Yo-ichiro Otofuji Zhenyu Yang & Rixiang Zhu 《Geophysical Journal International》2000,140(1):132-146
A total of 239 orientated drill-core samples from 23 sites were collected for palaeomagnetic study from Silurian and Devonian red beds, marlaceous sandstone, and limestone rocks in the eastern part of the Hexi Corridor, southwest Ningxia, North China. The characteristic high-temperature component resides in both haematite and magnetite. It clusters around a northwesterly and shallow to moderate downward direction and its antipode after tilt correction. The primary origin of this characteristic remanent magnetization (ChRM) is ascertained by positive fold and reversal tests at the 95 per cent confidence level. The corresponding palaeopoles, at 339.0°E, 60.1°N with A 95 = 11.2° (Silurian) and 336.0°E, 56.0°N with A 95 = 9.2° (Devonian), imply that the North China Block (NCB) had a low palaeolatitude of around 15°N in the Northern Hemisphere during the Silurian–Devonian period. Comparison with the Early–Middle Ordovician palaeopole of the NCB suggests that the NCB moved rapidly northwards by 30.8° ± 10.9° to cross the palaeo-equator during the Early–Middle Ordovician to Silurian. In combination with the palaeobiogeographical data from Ningxia, our palaeomagnetic results suggest that the NCB was located close to Australia during the Late Devonian. 相似文献
48.
Quaternary strata in China mainly comprise continental deposits in a variety of depositional settings. The continental Quaternary in temperate northern China consists mainly of eolian and fluvio-lacustrine deposits; that in subtropical southern China, mainly of vermiculated red soils, cave/fissure deposits, and fluvio-lacustrine deposits; and that in the alpine Tibetan Plateau, mainly of fluvio-lacustrine and piedmont deposits. The marine Quaternary in China consists of detrital deposits and biogenic reef deposits. The integration of biostratigraphy, magnetostratigraphy, climatostratigraphy and an astronomically calibrated chronology has led to the establishment of high-precision climatochronostratigraphic timescales for the detrital marine Quaternary in the South China Sea and the loess-paleosol sequence in the Chinese Loess Plateau. Extremely high-precision230 Th dating has provided a high-precision absolute age model for cave stalagmites over the past 640000 years as well as highresolution oxygen isotope records representing orbital-to suborbital-scale climate changes. By combining magnetic stratigraphy and biostratigraphy, robust chronostratigraphic frameworks for non-eolian continental Quaternary deposits on the scale of Quaternary geomagnetic polarities have been established. The continental Pleistocene Series consists, from oldest to youngest,of the Nihewanian Stage of the Lower Pleistocene, the Zhoukoudianian Stage of the Middle Pleistocene, and the Salawusuan Stage of the Upper Pleistocene. Stages of the continental Holocene Series have not yet been established. This review summarizes recent developments in the Quaternary chronostratigraphy of representative Quaternary strata and associated faunas, and then proposes an integrative chronostratigraphic framework and a stratigraphic correlation scheme for Quaternary continental strata in China. In the near-future, it is hoped to establish not only a Chinese continental Quaternary climatochronostratigraphic chart on the scale of glacial-interglacial cycles but also a Quaternary integrative chronostratigraphic chart including both continental and marine strata in China. 相似文献
49.
ZHANG Rixiang 《中国海洋工程》2000,14(4):503-510
The calculation of the temperature field of an underwater concrete tank system storing crudeoil is relatively complex.Based on experimental data and optimization analysis of relative parameters,unsteady heat-transfer is calculated by use of heat equilibrium theory.It is found that the predicted valueof temperature is in good agreement with experimental data. 相似文献
50.
Luo Rixiang 《海洋学报(英文版)》1998,17(3):357-361
AgglutininactivityinhemolymphofChineseshrimpandinductioneffectofVibrioLuoRixiang(ReceivedMay30,1997;acceptedJuly20,1997)Abstr... 相似文献