Crustal structure of the French Guiana margin, West Equatorial Atlantic

Geophysical data from the Amazon Cone Experiment are used to determine the structure and evolution of the French Guiana and Northeast Brazil continental margin, and to better understand the origin and development of along-margin segmentation. A 427-km-long combined multichannel reflection and wide-angle refraction seismic profile acquired across the southern French Guiana margin is interpreted, where plate reconstructions suggest a rift-type setting.
The resulting model shows a crustal structure in which 35–37-km-thick pre-rift continental crust is thinned by a factor of 6.4 over a distance of ∼70  km associated with continental break-up and the initiation and establishment of seafloor spreading. The ocean–continent boundary is a transition zone up to 45  km in width, in which the two-layered oceanic-type crustal structure develops. Although relatively thin at 3.5–5.0  km, such thin oceanic crust appears characteristic of the margin as a whole.
There is no evidence of rift-related magmatism, either as seaward-dipping sequences in the reflection data or as a high velocity region in the lower crust in the P -wave velocity model, and as a such the margin is identified as non-volcanic in type. However, there is also no evidence of the rotated fault block and graben structures characteristic of rifted margins. Consequently, the thin oceanic crust, the rapidity of continental crustal thinning and the absence of characteristic rift-related structures leads to the conclusion that the southern French Guiana margin has instead developed in an oblique rift setting, in which transform motion also played a significant role in the evolution of the resulting crustal structure and along-margin segmentation in structural style.     

Comparative characteristics of the Samarka (Sikhote-Alin) and Ultra-Tamba (Japan) terranes as grounds for correlating fragments of the Jurassic accretionary prism in two regions

Comparative data on tectono-stratigraphic complexes of the Ultra-Tamba terrane (Inner Zone of Japan) and upper structural level of the Samarka terrane in the Jurassic accretionary prism of Sikhote Alin are considered. Structural, lithological, petrographic data and age constraints characterizing rock associations of the terranes show that the latter are similar to a great extent, and consequently the Ultra-Tamba terrane can be regarded as an element of the Tamba-Mino-Ashio accretionary prism of the Jurassic but not Permian age, as it was thought earlier. The considered data substantiate confident structural correlation of both fragments of the Jurassic prism and of two regions in general.     

北太平洋环流振荡形成机理的数值研究

利用大洋环流模式,探讨海洋对大气强迫的响应及北太平洋环流振荡模态(NPGO)形成的直接原因。对控制试验模拟的海表温度异常(SSTA)进行经验正交函数(EOF)分解,发现第二模态类似于经典NPGO 模态,说明采用该模式研究海洋对大气强迫的响应是可行的。在控制试验基础上,通过改变大气强迫场设计了一系列敏感试验,发现大气强迫场为NPGO 模态正强年的合成场时,所得SST异常场能较好再现NPGO 空间特征,说明海洋状态强烈依赖于大气强迫,大气强迫是造成NPGO 的直接原因;对大气强迫场中的动力强迫、热力强迫等物理量进行不同配置进行试验,发现风场动力强迫对NPGO 的影响最大,是形成NPGO 的关键强迫,其中又以纬向风应力的影响居首。     

造山橄榄岩及其意义

造山橄榄岩和蛇绿岩的橄榄岩主要由地幔岩组成,造山橄榄岩代表陆壳下的地幔,蛇绿岩的橄榄岩代表洋壳下的地幔。洋壳下的地幔与陆壳下的地幔在物质组成上大体接近,但产出的构造背景明显不同。介绍了造山橄榄岩的组成、与造山橄榄岩有关的高压-超高压变质作用、地幔流体作用、成矿作用、造山橄榄岩侵位的机制等,以及中国几个可能的造山橄榄岩的基本情况,讨论了造山橄榄岩的演变过程及其与蛇绿岩的橄榄岩的区别。造山橄榄岩的形成大体经历了初期的陆壳减薄和裂谷阶段、晚期的挤压造山2个构造演化阶段。有些地区只发育裂谷阶段,构造演化在裂谷后即夭折了,也称为造山橄榄岩。蛇绿岩与造山橄榄岩之间的区别不在物质组成和地球化学方面,而是在构造背景上。如有没有深海沉积、混杂堆积,有,是蛇绿岩;没有,则是造山橄榄岩。有没有超高压变质作用、地幔交代作用或地幔交代作用是否强烈,有且很强,可能是造山橄榄岩;没有,则可能是蛇绿岩。岩体是冷侵位还是热侵位,冷侵位是蛇绿岩,热侵位是造山橄榄岩。蛇绿岩出现在造山带,代表已经消失的洋盆;造山橄榄岩一般也出现在造山带,但代表的是减薄和撕裂的陆壳下的地幔。