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宁晰春 《地球科学与环境学报》1987,(1)
形成旋扭构造的动力可概括为五个方面:地块随着地球自转速率的变化,局部发生的旋扭;漂移在软流圈之上的地块遇到上拱的“热柱”受到局部牵制而旋扭;地幔熔融体物质对流循环产生蠕动式旋扭;岩石圈拖曳牵动引起旋扭;重力控制下密度分异所引起的水平漫流碰接于上升物质而旋转。欧亚大陆上分布着涡轮状、帚状、莲花状、连环状等各种旋扭构造。 相似文献
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利用近年来发表的北半球、北半球各大洲及中国近千年温度序列,分析了年代至百年尺度上北半球和中国温度变化之间的异同性、北半球各大洲百年尺度典型暖期和典型冷期的位相差异,并比较了中世纪典型暖期与20世纪暖期的温暖程度差异.结果表明:1)在150~200年周期段,北半球和中国平均温度变化主要受太阳活动的影响,具有相似的变化特征;2)在50年和100年的尺度上,北半球和中国温度的变化速率具有相似性,近150年来二者都表现出持续的增温趋势;3)北半球洲际尺度上不存在起止时间相近的百年尺度典型暖期和冷期;4)北半球、中国及其他大洲最近30年(1971~2000A.D.)的温度较中世纪(800~1250A.D.)任何30年时段都要高,而最近100年(1901 ~ 2000A.D.)的温度只有北极地区显著高于中世纪最暖100年. 相似文献
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本文收集了1967—2007年全球大陆(不包括中国大陆)29次7.0~7.9级浅源大地震的余震资料。根据震源机制解结果把这29次地震序列分为走滑型和非走滑型, 其中17次是走滑型, 12次是非走滑型, 并分别研究了走滑型和非走滑型地震序列强余震震级分布特征和空间分布特征。研究结果表明, 强余震与主震震级差服从指数分布, 统计得到了走滑型地震序列B值为0.58, 非走滑型地震序列B值为1.07。走滑型地震序列强余震与主震距离的优势分布范围是10~45 km, 而非走滑型地震序列强余震与主震的距离优势分布为20~59 km, 并且强余震与主震震中距服从正态分布。 相似文献
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Lost primordial continents 总被引:7,自引:2,他引:5
We investigate the bulk density variations of some representative compositions for the lower mantle based on the pressure–volume–temperature equation of state of the constituent mineral phases. The density variations of pyrolite, harzburgite, mid-ocean ridge basalt (MORB), tonalite–trondhjemite–granodiorite (TTG), and anorthosite are studied at a temperature of 300 K and at lower mantle pressures. The density of MORB is greater than that of pyrolite throughout the lower mantle, while the density of harzburgite is slightly lower than that of pyrolite. The density of anorthosite is comparable to that of pyrolite in the lower mantle in general, and greater in the lowermost mantle, while the density of TTG is lower than pyrolite throughout the lower mantle. The above results have important implications for the fate of primordial continents, TTG and anorthosite crust. While subducted TTG might be stagnant in the mantle transition zone, dense subducted anorthositic crust could be expected to sink to the core–mantle boundary (CMB) and thus might be a major component of the D" layer immediately above the CMB. Thus, we propose that significant bodies of continental material could be present in the mantle in the transition zone and immediately above the CMB, in addition to the continents on the Earth's surface. 相似文献
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