Detrital record of Mesozoic shortening in the Yanshan belt, NE China: testing structural interpretations with basin analysis
Detrital record of Mesozoic shortening in the Yanshan belt, NE China: testing structural interpretations with basin analysis
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DOI：
10.1111/j.1365-2117.2007.00321.x
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发表时间：
2007-06-01
期刊：
影响因子：
3.2
通讯作者：
Graham, S. A.
中科院分区：
文献类型：
--
作者：
Cope, Tim D.;Shultz, Michael R.;Graham, S. A.
燕山褶皱冲断带是中国东北部北京以北的一个主要中生代造山系统的出露部分。燕山地区的构造和地层记录了以多次变形事件为特征的复杂的逆冲断裂历史。最初，三叠纪冲断导致冲断带北方厚层元古宙和古生代沉积地层的侵蚀;记录这一事件的三叠纪-下侏罗纪地层沉积在这一侵蚀带以南的薄带中。随后是假定晚侏罗世侵位的一个主要外来体（承德逆冲板块），这被认为是覆盖了与三叠纪事件有关的构造和地层，并被两个年轻的逆冲断层（古北口和承德县逆冲断层）切断。承德外来岩现在被表述为一个主要的东西走向的逆冲构造（承德构造），它被解释为一个20 km宽的褶皱飞来峰，下面是一个单一的北向逆冲断层。燕山带内晚侏罗世-早白垩世发育了两个沉积盆地，它们与承德逆冲断层及其伴生构造密切相关。寿王坟盆地发育于古北口逆冲断层下盘，记录了该断层上盘的同构造去顶。承德盆地部分发育于元古宙地层之上，解释为承德外来岩的上盘，并记录了邻近承德县逆冲断层的去顶。承德县逆冲断层和古北口逆冲断层都比假定的承德外来体的侵位年龄小，并在构造上位于其下，但寿王坟盆地和承德盆地都没有这种上覆构造侵蚀的碎屑记录。此外，被承德逆冲断层切割的上侏罗统地层的岩相、古分散模式和年代学表明，5公里）沿着位移。我们认为，单位形成的承德synform是原地的，和synform是由两个有限的位移断层相对的南北走向，而不是一个单一的大型北向逆冲断层。这一结论意味着燕山带在晚侏罗世经历的缩短程度远低于之前的想象，并且对该地区的中生代演化具有重要影响。具体来说，我们认为，大部分的缩短和隆起燕山带是在三叠纪-早侏罗世的时间，晚侏罗世的结构修改和局部积水沉积物从一个发达的向南排水系统开发的这个老造山带。虽然上侏罗纪地层在燕山带广泛分布，但很明显，这些地层是在几个离散的山间盆地内发育的，这些盆地不能作为一个整体横跨燕山带。因此，燕山没有明显的前陆盆地，并确定该造山带的中生代侵蚀产物的最终位置是围绕华北古地理的一个更有趣的悬而未决的问题。
The Yanshan fold-thrust belt is an exposed portion of a major Mesozoic orogenic system that lies north of Beijing in northeast China. Structures and strata within the Yanshan record a complex history of thrust faulting characterized by multiple deformational events. Initially, Triassic thrusting led to the erosion of a thick sequence of Proterozoic and Palaeozoic sedimentary strata from northern reaches of the thrust belt; Triassic-Lower Jurassic strata that record this episode are deposited in a thin belt south of this zone of erosion. This was followed by postulated Late Jurassic emplacement of a major allochthon (the Chengde thrust plate), which is thought to have overridden structures and strata associated with the Triassic event and is cut by two younger thrusts (the Gubeikou and Chengde County thrusts). The Chengde allochthon is now expressed as a major east-west trending, thrust-bounded synform (the Chengde synform), which has been interpreted as a folded klippe 20 km wide underlain by a single, north-vergent thrust fault. Two sedimentary basins, defined on the basis of provenance, geochronology and palaeodispersal trends, developed within the Yanshan belt during Late Jurassic-Early Cretaceous time and are closely associated with the Chengde thrust and allied structures. Shouwangfen basin developed in the footwall of the Gubeikou thrust and records syntectonic unroofing of the hanging wall of that fault. Chengde basin developed in part atop Proterozoic strata interpreted as the upper plate of the Chengde allochthon and records unroofing of the adjacent Chengde County thrust. Both the Chengde County thrust and the Gubeikou thrust are younger than emplacement of the postulated Chengde allochthon, and structurally underlie it, yet neither Shouwangfen basin nor Chengde basin contain a detrital record of the erosion of this overlying structure. In addition, facies, palaeodispersal patterns and geochronology of Upper Jurassic strata that are cut by the Chengde thrust suggest only limited (ca. 5 km) displacement along this fault. We suggest that the units forming the Chengde synform are autochthonous, and that the synform is bounded by two limited-displacement faults of opposing north and south vergence, rather than a single large north-directed thrust. This conclusion implies that the Yanshan belt experienced far less Late Jurassic shortening than was previously thought, and has major implications for the Mesozoic evolution of the region. Specifically, we argue that the bulk of shortening and uplift in the Yanshan belt was accomplished during Triassic-Early Jurassic time, and that Late Jurassic structures modified and locally ponded sediments from a well-developed southward drainage system developed atop this older orogen. Although Upper Jurassic strata are widespread throughout the Yanshan belt, it is clear that these strata developed within several discrete intermontane basins that are not correlable across the belt as a single entity. Thus, the Yanshan has no obvious associated foreland basin, and determining where the Mesozoic erosional products of this orogen ultimately lie is one of the more intriguing unresolved questions surrounding the palaeogeography of North China.