Tectonic Analysis of the Breakup and Bollision Unconformities in the Nansha Block
Tectonic Analysis of the Breakup and Bollision Unconformities in the Nansha Block
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DOI：
10.1002/cjg2.1685
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发表时间：
2011-11
期刊：
影响因子：
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通讯作者：
Zhen Sun;Zhongxian Zhao;Jiabiao Li;Di Zhou;Zhangwen Wang
中科院分区：
文献类型：
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作者：
Zhen Sun;Zhongxian Zhao;Jiabiao Li;Di Zhou;Zhangwen Wang
南沙块体位于廷加尔断裂（或巴拉姆线）以东，与北方大陆边缘共轭，对南沙块体的研究将有助于对南海演化的认识。地震剖面解释和区域构造分析表明，破碎不整合面和碰撞不整合面是南沙地区两个最重要的边界，它们构成了南沙地区的演化框架。本文通过对南沙块体两大边界地震剖面的分析，结合钻井资料和数学模拟，揭示了南沙块体两大边界的主要构造作用。结果表明，BU是一个历时界线，东部的礼乐盆地为早中新世，西部的北康、南维西盆地为中中新世，约16 Ma，BU与CU同期。南沙地块东部的CU形成于16Ma左右。在南沙地块，CU之后的边界也是同步的，但BU之前的裂谷边界也可能是历时的。通过对深度的分析以及空盆沉降速率（EBSR）模拟，发现南沙地块自Tg以来在中、西部经历了挠曲，并伴随着俯冲和碰撞。在90N09和94N07剖面上，前隆顶部在16Ma左右达到最高。偏转西强东弱，前隆位置迁移不同。我们推测该块体的偏转可能受碰撞时间、岩石圈强度和俯冲原南海海洋宽度等因素的控制。
The Nansha block is located to the east of the Tingjar fault (or the Baram Line) and is conjugate to the Northern continental margin, of which the research will contribute greatly to the understanding of the evolution of the South China Sea. Seismic profile interpretation and regional tectonic analysis suggested that two unconformities, the Breakup Unconformity (BU) and Collision Unconformity (CU), are two most important boundaries, which constitute the evolutionary frame of the Nansha area. This work attempts to reveal the main tectonic processes of the two major boundaries in the Nansha block by analysis of seismic profiles constrained with drilling data and mathematical modeling. The results show that BU is a diachronic boundary and dated as early Miocene in the Liyue basin to the east, while to the west in Beikang and Nanweixi basin it is dated as middle Miocene around 16 Ma, where BU is synchronous with CU. The CU in the east of the Nansha block is of age around 16 Ma. In Nansha block, the boundaries after CU are also synchronous, but the rifting boundaries before BU might also be diachronic. Analyzing the depth as well as the Empty Basin subsiding Rate (EBSR) simulation, we found that the Nansha block experienced deflection since Tg in the middle and west parts accompanied with the subduction and the collision thereafter. On profiles 90N09 and 94N07, the top of the forebulgo increased to the highest around 16 Ma. The deflection is strong in the west and weak in the east, the position of the forebulgo migrates differently. We conjecture that the deflection of the block might be controlled by factors such as collision time, lithospheric strength, and oceanic width of the subducted proto South China Sea.