Discrete element modeling of distal deformation propagation in thrust wedge and implications for early deformation on northern Tibetan and Iranian Plateaus

IF 2.6 2区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY
Chao Zhou , Jiankun He , Hao Su , Weimin Wang , Xinguo Wang , Youjia Zhao , Yong Jiang
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Abstract

Coulomb critical wedge theory predicts that thrust wedges would grow sequentially from the hinterland to the foreland, meaning that distal deformation occurs last. However, in the northern Tibetan and Iranian Plateaus, far away from the southern collision zones, widespread deformation occurs soon after collisions of Arabia and India with Eurasia. Additionally, despite the prevalence of weak lower crust and distal pre-existing faults or weak zones, their relationship to early distal deformation remains poorly understood. For this reason, we run systematic experiments of discrete element models involving basal décollement layer as well as distal pre-existing fault. Our model results reveal that (1) the presence of pre-existing faults is necessary for the occurrence of early distal deformation; (2) the early deformation of distal pre-existing fault is dependent on basal décollement strength and independent of model width; (3) strong basal décollement fails to activate the distal pre-existing faults, instead weak basal décollement can deform them at the early stage; (4) in the presence of weak basal décollement, a slower shortening rate not only facilitates greater shortening absorption by the distal pre-existing fault at the early stage but also results in a more pronounced deviation from sequentially-forward deformation propagation. These findings demonstrate that the preferential reactivation deformations of distal pre-existing faults are mechanically controlled by a weak basal décollement layer. Together with geological and geophysical observations, we suggest that the early deformations of northern Tibetan and Iranian Plateaus may be the result of the reactivation of pre-existing faults due to the existence of weak lower crust soon after collisions.

推力楔块远端变形传播的离散元模型及其对青藏高原北部和伊朗高原早期变形的影响
根据库仑临界楔理论的预测,推力楔会从腹地到前陆依次生长,这意味着远端变形发生在最后。然而,在远离南部碰撞带的青藏高原和伊朗高原北部,阿拉伯和印度与欧亚大陆碰撞后不久就发生了广泛的形变。此外,尽管普遍存在薄弱的下地壳和远端已存在的断层或薄弱带,但人们对它们与早期远端变形的关系仍然知之甚少。为此,我们进行了离散元素模型的系统实验,涉及基底去溶层和远端先存断层。我们的模型结果表明:(1)远端早期变形的发生必须有先存断层的存在;(2)远端先存断层的早期变形取决于基底解理层的强度,而与模型宽度无关;(3)强基底解理层不能激活远端先存断层,而弱基底解理层则能使远端先存断层发生早期变形;(4) 在存在弱基底解理的情况下,较慢的缩短速率不仅有利于远端先存断层在早期阶段吸收更多的缩短量,而且会导致更明显地偏离顺序向前的变形传播。这些发现表明,远端先存断层的优先再活化变形受弱基底去溶层的机械控制。结合地质和地球物理观测结果,我们认为青藏高原北部和伊朗高原的早期变形可能是由于碰撞后不久存在薄弱的下地壳而导致原有断层重新活化的结果。
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来源期刊
Journal of Structural Geology
Journal of Structural Geology 地学-地球科学综合
CiteScore
6.00
自引率
19.40%
发文量
192
审稿时长
15.7 weeks
期刊介绍: The Journal of Structural Geology publishes process-oriented investigations about structural geology using appropriate combinations of analog and digital field data, seismic reflection data, satellite-derived data, geometric analysis, kinematic analysis, laboratory experiments, computer visualizations, and analogue or numerical modelling on all scales. Contributions are encouraged to draw perspectives from rheology, rock mechanics, geophysics,metamorphism, sedimentology, petroleum geology, economic geology, geodynamics, planetary geology, tectonics and neotectonics to provide a more powerful understanding of deformation processes and systems. Given the visual nature of the discipline, supplementary materials that portray the data and analysis in 3-D or quasi 3-D manners, including the use of videos, and/or graphical abstracts can significantly strengthen the impact of contributions.
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