Timing of left-lateral shearing along the Ailao Shan-Red River shear zone: constraints from zircon U–Pb ages from granitic rocks in the shear zone along the Ailao Shan Range, Western Yunnan, China
Timing of left-lateral shearing along the Ailao Shan-Red River shear zone: constraints from zircon U–Pb ages from granitic rocks in the shear zone along the Ailao Shan Range, Western Yunnan, China
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DOI：
10.1007/s00531-012-0831-y
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发表时间：
2013-04
影响因子：
2.3
通讯作者：
Yuan Tang;Junlai Liu;M. Tran;Zhijie Song;Wenbin Wu;Zhaochong Zhang;Zhidan Zhao;Wen Chen
中科院分区：
文献类型：
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作者：
Yuan Tang;Junlai Liu;M. Tran;Zhijie Song;Wenbin Wu;Zhaochong Zhang;Zhidan Zhao;Wen Chen
哀牢山-红河剪切带作为印支地块与华南地块的分界线，沿哀牢山山脉经历了以韧性变形构造为特征的左旋走滑剪切作用。沿着哀牢山山脉。沿着ASRR剪切带左旋剪切的时间问题在约束剪切带的性质和区域意义方面具有头等重要性。因此，它一直是前人研究的重点，但关于剪切带沿着剪切开始和终止的年龄仍存在争议。本文对哀牢山剪切带沿着的5个花岗岩体（脉）进行了测年。4个剪切或部分剪切花岗岩的锆石U-Pb年龄分别为30.9 ± 0.7，36.6 ± 0.1，25.9 ± 1.0和27.2 ± 0.2Ma。未变形的花岗质岩墙侵入糜棱岩面理，结晶年龄为21.8 ± 1 Ma。锆石的Th/U比值可分为0.17-1.01和0.07-0.08两类，反映了锆石的岩浆成因和变质成因。详细的构造和显微构造分析表明，花岗岩侵入体归属于前，同，后剪切岩浆作用。这些花岗岩的锆石U-Pb年龄提供了开始（晚于31 Ma的前剪切花岗岩岩体，但早于27 Ma的同剪切花岗岩脉）和终止（约27 Ma）的时间限制。这与文献中有关点苍山和戴努伊孔沃火山岩的研究结果一致。我们还认为，沿ASRR剪切带沿着的左旋剪切作用是印度-欧亚板块碰撞过程中印支地块向东南方向挤压的结果。此外，左旋剪切作用还伴随着南海洋脊的跃变，其发生时间晚于南海的开启。
As the boundary between the Indochina and the South China blocks, the Ailao Shan-Red River (ASRR) shear zone underwent a sinistral strike-slip shearing which is characterized by ductile deformation structures along the Ailao Shan range. The timing issue of left-lateral shearing along the ASRR shear zone is of first-order importance in constraining the nature and regional significance of the shear zone. It has been, therefore, focused on by many previous studies, but debates still exist on the age of initiation and termination of shearing along the shear zone. In this paper, we dated 5 samples of granitic plutons (dykes) along the Ailao Shan shear zone. Zircon U–Pb ages of four sheared or partly sheared granitic rocks give ages of 30.9 ± 0.7, 36.6 ± 0.1, 25.9 ± 1.0 and 27.2 ± 0.2 Ma, respectively. An undeformed granitic dyke intruding mylonitic foliation gives crystallization age of 21.8 ± 1 Ma. The Th/U ratios of zircon grains from these rocks fall into two populations (0.17–1.01 and 0.07–0.08), reflecting magmatic and metamorphic origins of the zircons. Detailed structural and microstructural analysis reveals that the granitic intrusions are ascribed to pre-, syn- and post-shearing magmatisms. The zircon U–Pb ages of these granites provide constraints on timing of the initiation (later than 31 Ma from pre-shearing granitic plutons, but earlier than 27 Ma from syn-shearing granitic dykes) and termination (ca. 21 Ma from the post-shearing granitic dykes) of strong ductile left-lateral shearing, which is consistent with previous results on the Diancang Shan and Day Nui Con Voi massifs in the literature. We also conclude that the left-lateral shearing along the ASRR shear zone is the result of southeastward extrusion of the Indochina block during the Indian–Eurasian plate collision. Furthermore, the left-lateral shearing was accompanied by the ridge jump, postdating the opening, of the South China Sea.