New structural and petrologic data on Mesozoic schists in the Rhodope (Bulgaria): geodynamic implications

Structural analysis of low-grade rocks highlights the allochthonous character of Mesozoic schists in southeastern Rhodope, Bulgaria. The deformation can be related to the Late Jurassic–Early Cretaceous thrusting and Tertiary detachment faulting. Petrologic and geochemical data show a volcanic arc origin of the greenschists and basaltic rocks. These results are interpreted as representing an island arc-accretionary complex related to the southward subduction of the Meliata–Maliac Ocean under the supra-subduction back-arc Vardar ocean/island arc system. This arc-trench system collided with the Rhodope in Late Jurassic times. To cite this article: N.G. Bonev, G.M. Stampfli, C. R. Geoscience 335 (2003).     

印度／亚洲碰撞——南北向和东西向拆离构造与现代喜马拉雅造山机制再讨论

印度/亚洲碰撞形成的喜马拉雅增生地体由特提斯-喜马拉雅(THM)、高喜马拉雅(GHM)、低喜马拉雅(LHM)和次喜马拉雅(SHM)亚地体组成.通过喜马拉雅增生地体中变质基底和盖层的组成、变质演化、变形机制与形成时代的对比,确定高喜马拉雅(GHM)亚地体北缘的藏南拆离断裂(STD)向北延伸于特提斯-喜马拉雅(THM)亚地体之下,与形成在大于650℃温度、具有自南向北剪切滑移性质的康马-拉轨岗日拆离带(KLD)相连,深部地壳局部熔融、物质上涌造成的花岗岩侵位,使康马-拉轨岗日拆离带隆起,形成康马-拉轨岗日穹隆带.在高喜马拉雅(GHM)亚地体北部(普兰-吉隆-聂拉木-亚东一带)的变质基底与盖层之间发现EW向近水平的高喜马拉雅韧性拆离构造(GHD),以发育EW向拉伸线理、缓倾的糜棱面理及具有自西向东水平滑移为特征;而在GHM南部靠近主中央冲断裂(MCT)北侧发育具有挤压转换性质的韧性走滑-逆冲断层.高喜马拉雅亚地体从南到北具有由逆冲→斜向逆冲→EW向伸展→斜向伸展→SN向伸展的连续变形和转换的特征,是在现代喜马拉雅垂向挤出和侧向挤出的耦合造山机制下综合变形的响应.喜马拉雅地体中的东西向和南北向拆离构造的存在为喜马拉雅现代造山机制再讨论提供了基础.     

Geochemistry and geochronology of mafic rocks from Bamenda Mountains (Cameroon): Source composition and crustal contamination along the Cameroon Volcanic Line

Mafic rocks from the Bamenda volcanic province along the Cameroon Volcanic Line have been dated from 17 to 0 Ma. Associated with some trachytes and rhyolites, this volcanism covers a period of more than 25 Ma. The studied rocks are basalts to mugearites. Most of them have been contaminated by continental crust during their transit to the surface. The oldest rocks are the most contaminated. One group of samples shows high Eu, Sr and Ba contents. This characteristic is not due to crustal contamination process, but has a mantle source origin. We argue that these characteristics have been acquired by mixing of melts formed by partial melting of mantle pyroxenites with melts formed in mantle peridotites. Such pyroxenites have been observed as mantle xenoliths in the Adamaoua province, and their chemical and isotopic compositions are consistent with such a model.     

印度/亚洲碰撞——南北向和东西向拆离构造与现代喜马拉雅造山机制再讨论

印度/亚洲碰撞形成的喜马拉雅增生地体由特提斯-喜马拉雅(THM)、高喜马拉雅(GHM)、低喜马拉雅(LHM)和次喜马拉雅(SHM)亚地体组成。通过喜马拉雅增生地体中变质基底和盖层的组成、变质演化、变形机制与形成时代的对比,确定高喜马拉雅(GHM)亚地体北缘的藏南拆离断裂(STD)向北延伸于特提斯-喜马拉雅(THM)亚地体之下,与形成在大于650°C温度、具有自南向北剪切滑移性质的康马-拉轨岗日拆离带(KLD)相连,深部地壳局部熔融、物质上涌造成的花岗岩侵位,使康马-拉轨岗日拆离带隆起,形成康马-拉轨岗日穹隆带。在高喜马拉雅(GHM)亚地体北部(普兰-吉隆-聂拉木-亚东一带)的变质基底与盖层之间发现EW向近水平的高喜马拉雅韧性拆离构造(GHD),以发育EW向拉伸线理、缓倾的糜棱面理及具有自西向东水平滑移为特征;而在GHM南部靠近主中央冲断裂(MCT)北侧发育具有挤压转换性质的韧性走滑-逆冲断层。高喜马拉雅亚地体从南到北具有由逆冲→斜向逆冲→EW向伸展→斜向伸展→SN向伸展的连续变形和转换的特征,是在现代喜马拉雅垂向挤出和侧向挤出的耦合造山机制下综合变形的响应。喜马拉雅地体中的东西向和南北向拆离构造的存在为喜马拉雅现代造山机制再讨论提供了基础。     

砂岩侵入复合体的建筑结构要素及其特征

砂岩侵入复合体是指沉积砂质母岩,在未固结时由于某种机制而积累了异常高压,产生液化、流化、再活动,向上覆细粒沉积物侵入的各种砂体的总和。目前已经在全球50多个深水盆地中(Braccinietal,2008)及所有的年代地层中都发现了从毫米到千米级别的砂岩侵入体。砂岩侵入复合体包含母岩、侵入体系和喷出体系三部分,通过对目前报道的一些砂岩侵入复合体实例分析,对其各建筑要素的外部几何形体和边界特征、内部沉积构造和显微结构进行了总结。不规则的几何形态,突变的边界特征,与液化作用相关的无构造砂岩、碟状构造、管状构造以及独特的泥岩碎屑表现出来的粒序性、条带等沉积构造,形状各异的矿物颗粒以及泥岩碎屑中砂岩裂缝切割等显微结构都可以作为识别砂岩侵入复合体的标准。加强砂岩侵入复合体的研究,为侵入圈闭的勘探和开发提供理论基础。