Interaction between the Nazca and South American plates and formation of the Altiplano–Puna plateau: Review of a flexural analysis along the Andean margin (15°–34°S)
Interaction between the Nazca and South American plates and formation of the Altiplano–Puna plateau: Review of a flexural analysis along the Andean margin (15°–34°S)
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DOI：
10.1016/j.tecto.2004.12.014
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发表时间：
2005-04
期刊：
影响因子：
2.9
通讯作者：
A. Tassara
中科院分区：
文献类型：
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作者：
A. Tassara
本文回顾了应用于安第斯边缘的二维弯曲分析结果，该分析是基于地形和布格异常之间的相关性，以描述横跨和沿安第斯山脉前弧弧过渡的刚性变化，并了解前弧弧在高原形成中的作用。弧前刚度在15°~23°S之间达到最大值，向南逐渐减小，向高原方向急剧下降。整个中央安第斯山脉的主造山带(海拔3000米以上)非常弱。根据弯曲刚性与岩石圈的热力控制和成分控制强度之间的关系，对这些趋势进行了半定量的解释，得出以下结论：(1)跨走向刚性变化是由俯冲过程中形成的热结构控制的；(2)弧前是一种强、冷、硬的大地构造单元；(3)弧前向南的减弱与俯冲板块的热年龄下降直接相关；(4)主造山带的刚性很低是由于存在一个厚的、富含石英的地壳，具有低的应变率/热流比：(5)高原岩石圈的强度局限于上地壳，其底部在∼15公里处可以与P-S地震波转换器相关联(袁等，2000)[袁，X.，Sobolv，S.，Kind，R.，Oncken，O.等。2000年。转换地震震相制约的安第斯山脉中央俯冲和碰撞过程。自然，V 408，21/28 Diciembre，p.958-961]；(6)弧前-高原刚性边界对应着一个热条件变化、地壳厚度和地壳中长英质成分向东增加、低应变率变形的区域，这与地表向西的构造系统有关。这些结论表明，坚硬的前弧对弱高原起到了假压痕的作用，并允许从东部前陆向西迁移的韧性地壳物质的积累。这种伪压痕在几何上由一个以TRAC1为根部的地壳尺度的三角形带来表示。这一模型允许整合现有的关于弧前-高原相互作用动力学的相互矛盾的观点，这些观点与上地壳挤压结构和下地壳在弧前下方堆积的相对重要性有关。
The results of a two-dimensional flexural analysis applied to the Andean margin, which is based on the correlation between topography and Bouguer anomaly, are here reviewed in order to characterize rigidity variations across and along the forearc–arc transition of the Central Andes and to understand the role of the forearc in the formation of the Altiplano Plateau. The forearc has maximum rigidities between 15° and 23°S. Forearc rigidity decreases gradually southward and sharply toward the plateau. The main orogen (elevations higher than 3000 m) is very weak along the entire Central Andes. A semi-quantitative interpretation of these trends, based on the relationship between flexural rigidity and the thermo-mechanically- and compositionally-controlled strength of the lithosphere, allows the following conclusions to be made: (1) across-strike rigidity variations are dominated by the thermal structure derived from the subduction process; (2) the forearc constitutes a strong, cold and rigid geotectonic element; (3) southward weakening of the forearc is directly related to the decreasing thermal age of the subducted slab; (4) very low rigidities along the main orogen are caused by the existence of a thick, quartz-rich crust with a low strain rate-to-heat flow ratio; (5) the strength of the plateau lithosphere is localized in an upper-crustal layer whose base at ∼15 km could be correlated with a P-to-S seismic wave converter (TRAC1 of Yuan et al., 2000 [Yuan, X., Sobolev, S., Kind, R., Oncken, O. et al. 2000. Subduction and collision processes in the Central Andes constrained by converted seismic phases. Nature, V 408, 21/28 Diciembre, p. 958–961]); (6) the forearc–plateau rigidity boundary corresponds to a zone of changing thermal conditions, eastward-increasing crustal thickness and felsic component in the crust, and low strain-rate deformation, which correlates with a west-verging structural system at the surface. These conclusions suggest that the rigid forearc acts as a pseudo-indenter against the weak plateau and allows the accumulation of ductile crustal material that moves westward from the eastern foreland. This pseudo-indenter is geometrically represented by a crustal-scale triangular zone rooted at TRAC1. This model allows the integration of existing contradictory ideas on the dynamics of forearc–plateau interaction that are related to the relative importance of upper-crustal compressive structures and lower crustal accumulation below the forearc.