Seismic Evidence for Tectonically Dominated Seafloor Spreading in the Southwest Sub‐basin of the South China Sea
Seismic Evidence for Tectonically Dominated Seafloor Spreading in the Southwest Sub‐basin of the South China Sea
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DOI：
10.1029/2018gc007819
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发表时间：
2018-09
期刊：
影响因子：
3.7
通讯作者：
Junhui Yu;P. Yan;Yanlin Wang;Jinchang Zhang;Y. Qiu;M. Pubellier;M. Delescluse
中科院分区：
文献类型：
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作者：
Junhui Yu;P. Yan;Yanlin Wang;Jinchang Zhang;Y. Qiu;M. Pubellier;M. Delescluse
海底扩张可以用不同的动力学机制来解释，包括岩浆作用或构造作用。西南次盆地位于南海海底扩张的西南端，由于对地壳结构的了解不足且存在争议，其扩张机制仍不清楚。本文对横跨该海盆的两条多道地震测线和一条海底地震测线进行了重新处理和分析，重点是地壳成像。在深海盆地上沉积物通常厚0.5-1.0 km，在少数地堑中沉积物稍厚。最厚（3.3公里）的沉积物被发现在化石传播中心。基底相当粗糙，到处都有地壳断层，断层严重。化石扩张中心的特征是一个深的中央谷，类似于岩浆贫乏的扩张案例。两条多道地震测线都显示，在破碎基底下方1.5至3.6 km处存在少量间歇性和扩散性反射体。这些反射体与海底地震仪速度反演得到的6.8- 7.2km/s的速度有很好的相关性，被解释为莫霍面反射。因此，推断的地壳厚度只有1.5-3.6公里，不包括沉积物，这是比通常薄得多。速度低于8.0 km/s的下伏地幔可能因水沿沿着这些地壳断裂下渗而蛇纹化。因此，提出西南次盆地的扩张是由构造控制的。
Seafloor spreading can be explained by different dynamic mechanisms, magmatically or tectonically dominated. The Southwest Sub‐basin, located at the southwest tip of the propagating seafloor spreading of the South China Sea, remains unclear for its spreading regime owing to poor and debated knowledge of the crustal structures. Here two multichannel seismic lines and one oceanic bottom seismometer line across this subbasin are reprocessed and analyzed with focus on crustal imaging. The sediments are usually 0.5–1.0 km thick over the abyssal basin and slightly thicker in the few grabens. The thickest (3.3 km) sediments are found in the fossil spreading center. The basement is fairly rough and highly faulted by ubiquitous crustal faults. The fossil spreading center is characterized by a deep median valley, similar to that of magma‐poor spreading cases. Both multichannel seismic lines show a few intermittent and diffusive reflectors at 1.5‐ to 3.6‐km depth below the fragmented basement. These reflectors, correlating well with the velocities of 6.8–7.2 km/s obtained from velocity inversion of oceanic bottom seismometer data, are interpreted as Moho reflections. Thus, the inferred crustal thickness is only 1.5–3.6 km excluding the sediments, which is much thinner than usual. The underlying mantle with velocities lower than 8.0 km/s might be serpentinized with water infiltration along these crustal faults. Therefore, it is proposed that the spreading of the Southwest Sub‐basin was tectonically dominated.