Cenozoic tectonic evolution of the Himalayan orogen as constrained by along-strike variation of structural geometry, exhumation history, and foreland sedimentation
Cenozoic tectonic evolution of the Himalayan orogen as constrained by along-strike variation of structural geometry, exhumation history, and foreland sedimentation
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DOI：
10.1016/j.earscirev.2005.05.004
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发表时间：
2006-05
影响因子：
12.1
通讯作者：
A. Yin
中科院分区：
文献类型：
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作者：
A. Yin
尽管喜马拉雅造山带的研究已有150多年的历史，但对其几何学、运动学和动力学演化的认识仍然很少。这主要是由于持续强调喜马拉雅造山构造的二维性，以及从少数研究充分但面积较小的地区到造山带其余部分的地质关系外推。混淆和误解也普遍存在于喜马拉雅文学的地理，地层和结构划分方面。为了澄清这些问题，并提供一个新的平台，为那些谁有兴趣研究这个壮观的山区带的地质发展，我系统地回顾了有关的基本意见沿走向变化的喜马拉雅地质框架及其作用，新生代喜马拉雅折返，变质作用和前陆沉积。我的综合的一个主要重点是阐明侵位历史的高级大喜马拉雅结晶杂岩（GHC），占据了造山带的核心。由于在喜马拉雅山的大部分地区，北倾的主中央冲断层（MCT）和藏南拆离带（STD）限制了GHC，因此在地图和横截面视图中确定它们之间的关系至关重要。喜马拉雅山脉中部的暴露地图模式（即，尼泊尔）指出，MCT具有平坡几何形状。南部的冲断坪在小喜马拉雅层序（LHS）上携带了一个2-15 km厚的GHC板片，并在MCT斜坡带以南>100 km处形成了一个大型上盘断弯褶皱。在喜马拉雅造山带西部，东经177 °，MCT显示出一个主要的横向斜坡（曼迪斜坡）。在该斜坡以西，MCT将低品位特提斯喜马拉雅层序（THS）置于低品位LHS之上，而在斜坡以东，MCT将高品位GHC置于低品位LHS之上。横跨MCT的地层并置和变质程度的这种沿走向变化表明其滑动幅度向西减小，这可能是沿着喜马拉雅造山带的地壳总缩短向西减小的结果。在暴露的各个地方，STD大致遵循THS底部相同的地层层位，显示出一个长（>100 km）的上盘平面。这种关系表明，STD可能是沿着一个预先存在的岩性接触或中地壳近水平的脆-韧性过渡带形成的。虽然STD在喜马拉雅造山带的上盘到处都有THS，但没有发现THS下盘截止。这使得STD的滑动估计变得非常困难。STD的最南端迹线或者与MCT合并（例如，在Zanskar）或位于MCT锋面迹线的1- 2km内（例如，在不丹），这表明MCT可能会加入STD在其向上倾斜的方向向南。这种几何形状，在很大程度上忽略了现有的模型，具有重要意义的变形，折返，和整个喜马拉雅造山带的沉积历史。
Despite a long research history over the past 150 years, the geometry, kinematics, and dynamic evolution of the Himalayan orogen remain poorly understood. This is mainly due to continued emphasis on the two-dimensionality of the Himalayan orogenic architecture and extrapolation of geologic relationships from a few well-studied but small areas to the rest of the orogen. Confusion and misconception are also widespread in the Himalayan literature in terms of the geographic, stratigraphic, and structural divisions. To clarify these issues and to provide a new platform for those who are interested in studying the geologic development of this spectacular mountain belt, I systematically review the essential observations relevant to the along-strike variation of the Himalayan geologic framework and its role in Cenozoic Himalayan exhumation, metamorphism and foreland sedimentation. A main focus of my synthesis is to elucidate the emplacement history of the high-grade Greater Himalayan Crystalline Complex (GHC) that occupies the core of the orogen. Because the north-dipping Main Central Thrust (MCT) above and South Tibet Detachment (STD) below bound the GHC in most parts of the Himalaya, it is critical to determine the relationship between them in map and cross-section views. The exposed map pattern in the central Himalaya (i.e., Nepal) indicates that the MCT has a flat-ramp geometry. The thrust flat in the south carries a 2–15-km-thick slab of the GHC over the Lesser Himalayan Sequence (LHS) and creates a large hanging-wall fault-bend fold continuing >100 km south of the MCT ramp zone. In the western Himalayan orogen at the longitude ∼77°E, the MCT exhibits a major lateral ramp (the Mandi ramp). West of this ramp, the MCT places the low-grade Tethyan Himalayan Sequence (THS) over the low-grade LHS, whereas east of the ramp, the MCT places the high-grade GHC over the low-grade LHS. This along-strike change in stratigraphic juxtaposition and metamorphic grade across the MCT indicates a westward decrease in its slip magnitude, possibly a result of a westward decrease in total crustal shortening along the Himalayan orogen. Everywhere exposed, the STD follows roughly the same stratigraphic horizon at the base of the THS, exhibiting a long (>100 km) hanging-wall flat. This relationship suggests that the STD may have initiated along a preexisting lithologic contact or the subhorizontal brittle–ductile transition zone in the middle crust. Although the STD has the THS in its hanging wall everywhere in the Himalayan orogen, no THS footwall cutoffs have been identified. This has made slip estimates of the STD exceedingly difficult. The southernmost trace of the STD either merges with the MCT (e.g., in Zanskar) or lies within 1–2 km of the MCT frontal trace (e.g., in Bhutan), suggesting that the MCT may join the STD in their up-dip directions to the south. This geometry, largely neglected by the existing models, has important implications for the deformation, exhumation, and sedimentation history of the entire Himalayan orogen.