Tectonic Controls on Block Rotation and Sheeted Sill Emplacement in the Xigaze Ophiolite (Tibet): The Construction Mode of Slow-Spreading and Ultraslow-Spreading Oceanic Crusts
Tectonic Controls on Block Rotation and Sheeted Sill Emplacement in the Xigaze Ophiolite (Tibet): The Construction Mode of Slow-Spreading and Ultraslow-Spreading Oceanic Crusts
复制标题
西藏日喀则蛇绿岩块体旋转和片状基岩侵位的构造控制：慢扩张和超慢扩张洋壳的构造模式
DOI：
10.1029/2020gc009297
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发表时间：
2021
影响因子：
3.5
通讯作者：
Zhang Zhen
中科院分区：
文献类型：
--
作者：
Liu Tong;Dick Henry J. B.;Liu Chuan-Zhou;Wu Fu-Yuan;Ji Wen-Bin;Zhang Chang;Zhang Wei-Qi;Zhang Zhen-Yu;Lin Yin-Zheng;Zhang Zhen
由于深钻的限制，人们对海洋地壳的内部结构还没有很好地了解。然而，蛇绿岩，即陆地上的古代海洋岩石圈的类似物，可以精确地绘制和测量。在大量野外观测的基础上，我们提供了日喀则蛇绿岩的岩石学和地球化学资料，以解释片状岩杂岩的成因及其对海洋地壳构造的启示。日喀则蛇绿岩中的辉绿岩按取向可分为片状岩、第1组非片状岩和第2组非片状岩。这些辉绿岩切割了其他岩性，因此属于最新阶段的产物。基于岩石学、地球化学和构造数据，我们强调了滑脱断层在片状和非片状断层形成中的重要作用。在洋壳形成过程中，大块体的掘出、多阶段的旋转和沉陷是日喀则片状和非片状脉/岩形成的关键机制，均处于滑脱断裂体系的演化过程中。这些过程在现代缓慢扩张和超低扩张脊的不对称节段中也并不罕见，但在对称节段中却很少见。由于滑脱断层的演化，（超）缓展脊的内部构造比快展脊更为复杂。
The internal structure of oceanic crusts is not well understood due to the limitation of deep drilling. However, that of ophiolites, i.e., on‐land ancient analogs of oceanic lithosphere, could be precisely mapped and measured. The Xigaze ophiolite in Tibet has been regarded as “peculiar”, due to the sheeted sill complex in its upper crust, and non‐sheeted diabase sills/dikes crosscutting its mantle and lower crust, which are geometrically different from the primarily vertical sheeted dike complex. Based on extensive field observations, here we present petrological and geochemical data for the Xigaze ophiolite to decipher the origin of sheeted sill complex and its implications for the construction of oceanic crusts. Diabases in the Xigaze ophiolite could be subdivided into sheeted sills, Group 1 non‐sheeted dikes, and Group 2 non‐sheeted sills, based on their orientations. These diabases cut other lithologies, and hence belong to the latest‐stage products. Based on petrological, geochemical, and structural data, we highlight the important role of detachment fault in the generation of sheeted and non‐sheeted sills. During the formation of oceanic crust, large block exhumation, multi‐stage rotations, and foundering are argued here as key mechanisms for the generation of Xigaze sheeted and non‐sheeted dikes/sills, all of which are in the evolution of detachment fault systems. These processes are also not uncommon for asymmetrical segments at modern slow‐spreading and ultraslow‐spreading ridges, but are rare at symmetrical segments. Due to the evolution of detachment fault, the internal structures of (ultra)slow‐spreading ridges are more complex than those at fast‐spreading ridges.