The geology and tectonics of central Bhutan
The geology and tectonics of central Bhutan
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DOI：
10.1144/jgs2015-031
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发表时间：
2015-10
影响因子：
2.7
通讯作者：
L. V. Greenwood;T. Argles;R. Parrish;N. Harris;C. Warren
中科院分区：
文献类型：
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作者：
L. V. Greenwood;T. Argles;R. Parrish;N. Harris;C. Warren
岩石构造测绘、变质观测和 U-Pb 锆石年龄为不丹中部地质学的重大修订奠定了基础，特别是特提斯沉积系列 (TSS) 的露头比之前测绘的更广泛和连续。 TSS 的变质程度向下增加，朝向与底层大喜马拉雅系列 (GHS) 的基底北趋构造接触，被解释为藏南支队 (STD) 的向南延续。中新世（约 17-20 Ma）淡色花岗岩片与该地区的 STD 有关，但似乎向南减少。横切 TSS 结构的两个淡色花岗岩岩脉的年龄分别为 17.8 ± 0.2 和 17.9 ± 0.5 Ma。在以沙粒为主的较低 TSS 内，Pele La 群中的 500 ± 4 Ma（U-Pb 锆石）变质灰床得出了喜马拉雅东部 TSS 的第一个直接同位素年龄，证实了碎屑锆石和化石研究中现有的年龄限制。 GHS 下方的帕罗变沉积单元的延续部分在旺杜波德朗 (Wangdue Phodrang) 附近绘制。我们的观察，特别是迄今为止向南暴露的完全延展性 STD 以及 TSS 中大型推覆状结构的重要性，促使对不丹喜马拉雅山的地质图进行重大修改，并需要重新评估不丹喜马拉雅山的构造解释。补充材料：锆石 U-Pb 年代学数据、样品位置和描述、分析锆石的特征、样品处理方法和详细分析条件可在 http://www.geolsoc.org.uk/SUP18876 上获取。
Lithotectonic mapping, metamorphic observations and U–Pb zircon ages underpin a substantial revision of central Bhutan geology, notably a more extensive and continuous outcrop of the Tethyan Sedimentary Series (TSS) than previously mapped. Metamorphic grade in the TSS increases downward towards a basal north-vergent tectonic contact with the underlying Greater Himalayan Series (GHS), interpreted as a southward continuation of the South Tibetan Detachment (STD). Miocene (c. 17–20 Ma) leucogranite sheets are associated with the STD in this region but appear to diminish southwards. Two leucogranite dykes that cross-cut TSS structures yield ages of 17.8 ± 0.2 and 17.9 ± 0.5 Ma. A 500 ± 4 Ma (U–Pb zircon) metamorphosed ash bed in the Pele La Group within the psammite-dominated lower TSS yields the first direct isotopic age for the TSS in the eastern Himalaya, confirming existing age constraints from detrital zircon and fossil studies. A continuation of the Paro metasedimentary unit underlying the GHS was mapped near Wangdue Phodrang. Our observations, notably the exposure of a wholly ductile STD so far south and the significance of large nappe-like structures in the TSS, prompt a major revision to the geological map of the Bhutan Himalaya and require a reassessment of tectonic interpretations of the Bhutan Himalaya. Supplementary materials: Zircon U–Pb geochronological data, sample locations and descriptions, features of analysed zircons, sample processing method and detailed analytical conditions are available at http://www.geolsoc.org.uk/SUP18876.