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Numerical modeling of failed rifts in the northern South China Sea margin: implications for continental rifting and breakup
Journal of Asian Earth Sciences ( IF 2.7 ) Pub Date : 2020-09-01 , DOI: 10.1016/j.jseaes.2020.104402
Yaqing Li , Aqeel Abbas , Chun-Feng Li , Tienan Sun , Sergio Zlotnik , Taoran Song , Lulu Zhang , Zewei Yao , Yongjian Yao

Abstract Failed rifts record important information of continental extension and breakup process in the northern South China Sea (SCS) margin. The Tainan Southern Depression and the Baiyun Sag to the east are characterized with lower-crust high-velocity anomalies (LCHVA), and intracrust detachment faults, whereas the Xisha Trough to the west develops on a larger scale with crust-cutting normal faults and absence of LCHVA. These contrasts indicate different rifting processes between the northeastern and northwestern SCS. 2D numerical modeling is performed to understand the formation mechanism of these failed rifts. Two types of mechanisms are proposed: I) syn-rift competitive type and II) rift migration type with a half extension rate of 2 cm/yr and 1.5 cm/yr, respectively. In type I, two rifts develop initially on the shoulders of the weak zone, but they compete with each other during extension. One rift becomes dominant to furnish the final breakup, whereas the other one is abandoned. The crust structure of this type fits the observations in the Baiyun Sag and the Tainan Southern Depression. However, in type II, only one rift develops at the beginning. The initial rifting center will migrate and the final continental breakup will occur at a place far from the initial rifting location. In this type, normal faults cut through whole crust and wide extensional margins will form, such as observed in the Xisha Trough. Our results suggest that the depth-dependent extension of the SCS is strongly heterogeneous, resulting primarily from varying extensional rates.

中文翻译:

南海北部边缘破裂裂谷的数值模拟:对大陆裂谷和破裂的影响

摘要 断裂的裂谷记录了南海北部(SCS)边缘大陆伸展和破裂过程的重要信息。台南南部坳陷和东部白云凹陷以下地壳高速异常(LCHVA)和壳内拆离断层为特​​征,而西部西沙海槽规模较大,具有切壳正断层和缺失LCHVA 的。这些对比表明南海东北部和西北部之间存在不同的裂谷过程。进行二维数值模拟以了解这些失败裂谷的形成机制。提出了两种类型的机制:I) 同步裂谷竞争型和 II) 裂谷迁移型,半延伸率分别为 2 cm/yr 和 1.5 cm/yr。在 I 型中,两个裂谷最初在弱区的肩部发展,但它们在扩展过程中相互竞争。一个裂痕变得占主导地位以提供最终的分手,而另一个则被放弃了。该类型地壳结构符合白云凹陷和台南南部坳陷的观测结果。然而,在 II 型中,一开始只出现一个裂痕。初始裂谷中心将迁移,最终大陆分裂将发生在远离初始裂谷位置的地方。这种类型的正断层会贯穿整个地壳,形成宽阔的伸展边缘,如在西沙海槽中所见。我们的结果表明,SCS 的深度依赖延伸是强烈异质的,主要是由于不同的延伸率。而另一个被遗弃了。该类型地壳结构符合白云凹陷和台南南部坳陷的观测结果。然而,在 II 型中,一开始只出现一个裂痕。初始裂谷中心将迁移,最终大陆分裂将发生在远离初始裂谷位置的地方。这种类型的正断层会贯穿整个地壳,形成宽阔的伸展边缘,如在西沙海槽中所见。我们的结果表明,SCS 的深度依赖延伸是强烈异质的,主要是由于不同的延伸率。而另一个被遗弃了。该类型地壳结构符合白云凹陷和台南南部坳陷的观测结果。然而,在 II 型中,一开始只出现一个裂痕。初始裂谷中心将发生迁移,最终大陆分裂将发生在远离初始裂谷位置的地方。这种类型的正断层会贯穿整个地壳,形成宽阔的伸展边缘,如在西沙海槽中所见。我们的结果表明,SCS 的深度依赖延伸是强烈异质的,主要是由于不同的延伸率。初始裂谷中心将发生迁移,最终大陆分裂将发生在远离初始裂谷位置的地方。这种类型的正断层会贯穿整个地壳,形成宽阔的伸展边缘,如在西沙海槽中所见。我们的结果表明,SCS 的深度依赖延伸是强烈异质的,主要是由于不同的延伸率。初始裂谷中心将迁移,最终大陆分裂将发生在远离初始裂谷位置的地方。这种类型的正断层会贯穿整个地壳,形成宽阔的伸展边缘,如在西沙海槽中所见。我们的结果表明,SCS 的深度依赖延伸是强烈异质的,主要是由于不同的延伸率。
更新日期:2020-09-01
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