Geochronology of shear zones – A review
Geochronology of shear zones – A review
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DOI：
10.1016/j.earscirev.2018.07.007
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发表时间：
2018-10
影响因子：
12.1
通讯作者：
S. Oriolo;K. Wemmer;P. Oyhantçabal;H. Fossen;B. Schulz;S. Siegesmund
中科院分区：
文献类型：
--
作者：
S. Oriolo;K. Wemmer;P. Oyhantçabal;H. Fossen;B. Schulz;S. Siegesmund
剪切带在地壳变形中起着重要的作用，在各种尺度上，作为应变局部化的表现在造山和裂谷，也作为重新激活的结构。它们影响着造山带和裂谷的几何形状和演化、地壳流变学、岩浆上升和侵位以及流体流动。因此，评价剪切带活动的时间是重建岩石圈构造变质演化的关键。然而，剪切带热年代学数据的解释并不简单。首先，闭合温度取决于许多因素（粒度、冷却速率、矿物成分和压力等）。另一方面，变形相关的过程，如动态重结晶，neoconization和流体循环似乎是至关重要的同位素系统，因此，所获得的年龄不能被单独解释为温度的函数在剪切岩石。因此，剪切带的地质年代学数据可能不仅记录了闭合温度条件下的冷却，而且还可能受到新重结晶或重结晶、流体辅助变形和原岩年龄继承的影响。为了可靠地重建长期地壳尺度剪切带的P-T-ε-t轨迹，需要将糜棱岩的构造、显微构造和岩石学数据与不同热年代学系统的年龄相结合。此外，来自相关侵入体和相邻地块的地质年代学数据可以对变形的时间及其区域意义提供进一步的不可替代的约束。未来的调查线应分析的最具挑战性的方面之一是定量评价迄今为止探索不足的同位素扩散方面，特别是与变形过程的耦合，基于自然，理论和实验数据。未来的工作还应调查的应变分区和本地化过程中的作用，以限制变形的时间在不同的部分剪切带或在不同的分支的剪切带网络的闭合。
Shear zones play a major role in the deformation of the crust at a variety of scales, as expressions of strain localization during orogeny and rifting, and also as reactivated structures. They influence the geometry and evolution of orogenic belts and rifts, crustal rheology, magma ascent and emplacement, and fluid flow. Consequently, assessing the timing of shear zone activity is crucial to reconstruct the tectonometamorphic evolution of the lithosphere. The interpretation of thermochronologic data from shear zones is, however, not straightforward. In the first place, closure temperatures depend on a number of factors (grain size, cooling rate, mineral composition and pressure, among others). On the other hand, deformation-related processes such as dynamic recrystallization, neocrystallization and fluid circulation seem to be crucial for isotopic systems and, thus, the obtained ages cannot be solely interpreted as a function of temperature in sheared rocks. For this reason, geochronologic data from shear zones might not only record cooling below closure temperature conditions but may also be affected by neo- or recrystallization, fluid-assisted deformation and inheritance of the protolith age(s). In order to robustly reconstruct P-T-ε-t paths of long-term crustal-scale shear zones, structural, microstructural and petrologic data from mylonites need to be integrated with ages from different thermochronometric systems. In addition, geochronologic data from associated intrusions and adjacent blocks can provide further irreplaceable constraints on the timing of deformation and its regional implications. One of the most challenging aspects that future lines of investigation should analyze is the quantitative evaluation of so far poorly explored aspects of isotopic diffusion, particularly the coupling with deformation processes, based on natural, theoretical and experimental data. Future works should also investigate the role of strain partitioning and localization processes in order to constrain the timing of deformation in different parts of a shear zone or in different branches of anastomosing shear zone networks.