库车坳陷克拉苏构造带分层收缩构造变形及其主控因素

库车坳陷中段克拉苏构造带广泛发育盐相关收缩构造变形,总体具有"垂向叠置、分层变形"的整体挤压变形特征。沿东-西向克拉苏构造带不同区段深浅层构造变形样式、断层位移存在明显差异,北部盐下层由1～2条高角度基底卷入逆冲断层为主导,并在断层下盘发育捷径断层。区域结构平衡剖面和先存构造活动趋势分析结果表明,克拉苏构造带北侧变形属于基底卷入变形,早期先存断裂在后期收缩变形中重新活动,形成高角度的逆冲断裂。物理和数值砂箱模拟结果表明,盐岩层先于其上、下地层发生变形,其厚度、分布及边界条件差异是造成垂向分层收缩变形的主要控制因素。     

埃达克岩：关于其成因的一些不同观点

埃达克岩的概念是十多年前提出来的,指由俯冲的年轻洋壳熔融形成的火成岩。自从最初在现代岛弧近十几个地方报道埃达克岩以来,新近又在几个地方发现有埃达克岩（如日本西南部,外墨西哥火山岩带,等等）。但是,过去十 多年的研究也表明,埃达克岩可以由俯冲期间的其它过程产生（例如,沿俯冲板片的撕裂边,留在上地幔中的板片残余等）。另外,埃达克岩似乎与一些岩石呈共生组合,这些岩石包括高镁安山岩、富Nb的弦玄武岩（NEAB）,还可能有玻安岩（几个研究者已在玻安岩中发现有埃达克岩的组分）。高镇安山岩不是来自埃达克与地幔的相互作用（Adak-type),就是来自此相互作用期间地幔的熔融（Piip-type);富Nb的弦玄武岩,据认为是来自一种被埃达我岩广泛交代的地幔的部分熔融。作为一个新的岩套,埃达克岩交代火山岩系列已被建议用来解释各种岩石组合。此外,大量的富Pb弧玄武岩也已被发现包含有超镁铁质的地幔包体,而这些包体有高亏损地幔与埃达克反应的明显证据。关于主要与下地壳熔而不是冲板片有关的埃达克岩的起源已提出几种假说,一个模型认为,下地壳熔融出现在玄武质岩浆底侵下地壳时。但是,有许多理由似乎可以排除这种模式。另一种模型认为,在大陆地壳很厚的区域,下地壳可能变成榴辉岩,从而拆离并下沉到地幔中（拆沉）。这个拆沉过程将导致下地壳下中拆沉的下地壳的上部与相对热的地幔接触,进而可引起下地壳熔融和埃达克岩的形成。这使我们认为,在中国东部发现的与俯冲作用无关的白垩纪埃达克可能是下地壳熔融与拆沉作用的产物。我们 还要强调,如果下地壳熔融与拆沉作用真能形成埃达克岩,那么埃达克岩这一术语不应该仅仅局限于与板片熔融有关的过程,而应包括那些与下地壳熔融有关的过程。太古宙的大陆地壳主要由奥长花岗岩、英云闪长岩和英安岩（TTD）组成。这种大陆地壳是来自板片熔融还是下地壳熔融仍是有争议的。然而,我们认为,太古宙期间地幔的较高温度会导致较多的洋中脊的形成,从而产生比今天“更多”的年轻洋壳的俯冲。据此,我们认为,太古宙TTD大陆地宙主要由板片熔融形成。我们也注意到,太古宙是广泛金矿化的时期。有些研究者还发现,金和铜的矿化与埃达克质交代火山岩系列有关。因此,该火山岩系列可能会寻找金属矿床的一个重要标志。     

Petrogenesis of post-collisional Middle Eocene volcanism in the Eastern Pontides (NE,Turkey): Insights from geochemistry,whole-rock Sr-Nd-Pb isotopes,zircon U-Pb and 40Ar-39Ar geochronology

The debate about whether Eocene magmatism is considered to be post-collisional or subduction-related or not still continues. Here we offer new ⁴⁰Ar-³⁹Ar ad U-Pb zircon geochronology, mineral chemistry, bulk rock and Sr-Nd-Pb isotope geochemistry data obtained from the southern dike (SD) suite, in comparison with the northern dike (ND) suite, from the Eastern Pontides. The geochronological data indicate that the SD suite erupted between 45.89 and 45.10 Ma corresponding to the Lutetian (Middle Eocene). The magmas of the ND suite are characterised by slightly more alkaline affinity compared to the SD suite. The trace and rare earth element (REEs) content of the SD suite is characterised by large ion lithophile element (LILEs; Sr, K₂O, Ba, Rb) enrichment and depletion of Nb, Ta, and TiO₂ elements to different degree with high Th/Yb ratios, which indicate that the magmas forming the SD and ND suites were derived from lithospheric mantle sources enriched by mostly slab-derived fluids in the spinel stability field. The Sr, Nd and Pb radiogenic isotope ratios of the dikes support the view that the magma for the hydrous group (H-SD) was derived from a relatively more enriched mantle source than the other SD and ND suites. The ND suite and the anhydrous group (A-SD) display similar geochemical features characterised by moderate light earth element (LREE)/heavy rare earth element (HREE) ratios, while the H-SD group has respectively lower LREE/HREE ratios indicating higher melting degree. Detailed considerations of the alkalinity, enrichment and partial melting degree for the source of the studied volcanic rocks indicate that the magmas of the northern dike suite are characterised by slightly more alkaline affinity, whereas the magmas throughout the southern dike suite show increments in the enrichment rate and melting degree. In light of the obtained data and comparative interpretations, the geodynamic evolution and differences in petrogenetic character of the Lutetian magmas from both the northern and southern parts of the Eastern Pontides may be explained by different degrees of melting of a net veined mantle source initially metasomatized by mostly subduction fluids during asthenospheric upwelling due to fragmented asymmetric delamination in a post-collisional extensional tectonic environment.     

华北克拉通及邻区晚中生代伸展构造及其动力学背景的讨论

欧亚大陆东部晚中生代伸展构造十分显著,表现为大量发育的变质核杂岩、同构造岩浆岩、韧性拆离断层带等伸展成因的穹隆和地堑-半地堑盆地.通过对这些伸展构造进行系统分析、归纳和总结,将欧亚大陆东部晚中生代伸展构造发育区划分为:泛贝加尔-鄂霍次克带、华北西部带、华北东部带、华北南缘及秦岭-大别带和华南内陆带.这些伸展构造记录了大区域上的NW-SE方向伸展,构成了全球最大的陆壳伸展地区.这些伸展构造使地壳深部的岩石沿拆离断层折返至地表,从而使中下地壳结构发生了强烈的改造.除华北东部带给出了一个较为宽泛的伸展时段外,各个研究区所涉及的伸展穹隆及其相关的拆离断层所表现的伸展峰期时间均十分相近:位于130 ～ 126Ma之间.岩石圈根部的拆沉可能是这个巨型伸展构造带形成的动力学机制.这个模型为探讨华北克拉通破坏和减薄的时限、机制、模式及深部动力学背景提供直接的构造证据.