Indosinian tectonics in Vietnam
Indosinian tectonics in Vietnam
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DOI：
10.1016/j.crte.2007.10.005
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发表时间：
2008-02-01
影响因子：
1.4
通讯作者：
Tich Van Vu
中科院分区：
文献类型：
--
作者：
Lepvrier, Claude;Nguyen Van Vuong;Tich Van Vu
在越南，三叠纪的印支碰撞同时影响了长山带和Kontum地块，它们不是独立的构造单元，而是同一个冈瓦纳派生的印度支那大陆块的一部分。这一热构造事件发生在整个越南同步，在下三叠统250-240-Ma的时间间隔，如大量的地质年代学数据，结合Ar-Ar和U-Pb定年方法证明。对印支期变质岩的构造和运动学研究表明，碰撞过程是印支与相邻地块一致的西北走向会聚的结果。这种运动被一对相反的俯冲带所吸收：在北部，华南之下，在西部，印度支那之下，分别沿沿着松马缝合线和蒲柯缝合线。构造标志，钙碱性俯冲有关的火山作用和花岗岩侵入体和高压岩石的产生，最近已经发现支持这种地球动力学背景，至少沿着宝高。沿着西北走向的Song Ma带，俯冲和随后的碰撞过程中的会聚导致在Truong Son带内，在角闪岩相变质作用下，一组近平行的右旋糜棱岩剪切带的发展。中间段仍保持弱变质或几乎没有变质作用。沿着沿着Po Ko，收敛是近正交的，具有左旋走滑分量;正在进行的大陆俯冲导致Kontum麻粒岩基底的改造和印支期高压麻粒岩条件的发展;随后的伸展相关折返大致以相同的西北方向进行。这种印支期的演化，适用于可能受到加里东相关事件影响的大陆地壳，如在中国南方，根据下泥盆统沉积物的一般不整合面、广泛出现的约450 Ma（奥陶纪-志留纪）的岩浆结晶年龄以及孔图姆地块的原始麻粒岩幕的大致相似的年龄来判断。越南中部、北方和中国南部泥盆纪相的相似性意味着陆地的连接，这可能是沿着宋马加里东碰撞的结果，但这并不排除在印支期进一步的海洋开放和闭合。
In Vietnam, the Triassic Indosinian collision affected coevally the Truong Son belt and the Kontum Massif,which were not independent tectonic units, but parts of the same Gondwana-derived Indochina continental block. This thermotectonic event took place synchronously throughout Vietnam, during the Lower Triassic 250-240-Ma time interval, as demonstrated by numerous geochronological data, combining Ar-Ar and U-Pb dating methods. Structural and kinematic investigations, in the Indosinian metamorphic rocks, reveal that the collisional process resulted from a consistent northwest-striking convergence of Indochina with respect to the adjacent blocks. It is suggested that this motion was taken up by a pair of opposite subduction zones: to the north, beneath South China, and to the west, beneath western Indochina, along the Song Ma and Po Ko sutures, respectively. Tectonic markers, calc-alkaline subduction-related volcanism and granitic intrusions and the generation of high-pressure rocks that have been recently discovered support this geodynamic setting, at least along Po Ko. Along the northwest-trending Song Ma zone, the obliquity of the convergence during subduction and subsequent collision resulted in the development, within the Truong Son Belt, of a set of subparallel dextral mylonitic shear zones, under amphibolite-facies metamorphism. The intermediate segments remained weakly metamorphic or even almost devoid of metamorphism. Along Po Ko, the convergence was near-orthogonal, with a left-lateral strike-slip component; the ongoing continental subduction resulted in the reworking of the Kontum granulitic basement and the development of Indosinian HP granulitic conditions; the subsequent extension-related exhumation operated approximately in the same northwestwards direction. This Indosinian evolution, applied on a continental crust that had been probably affected, as in South China, by a Caledonian-related event, as judged by the general unconformity of the Lower Devonian sediments, the widespread occurrence of magmatic crystallisation ages of ca 450 Ma (Ordovician-Silurian), and by the approximately similar age of the primary granulitic episode in the Kontum Massif. The similarities of the Devonian facies over central, northern Vietnam and South China imply a land connection, possibly as a consequence of a Caledonian collision along Song Ma, but this does not preclude a further oceanic opening and a closure during the Indosinian.