摘要
南海西北、西南和东部3个次海盆停止扩张之后都存在岩浆活动,扩张中心有多个海山.为了研究海山和扩张中心的地壳结构特征,本文使用穿越南海西北次海盆扩张中心的广角地震剖面(测线OBS 2006-p1),针对海盆区域,通过P波二维地震射线追踪正演,获得了西北次海盆垂直扩张方向的深部速度结构,讨论了西北次海盆及其扩张中心深部地壳结构特征;并结合南海东部次海盆和西南次海盆横穿扩张中心的海底地震仪(ocean bottom seismograph,OBS)剖面,对不同海盆的地壳结构进行了对比研究,获得了扩张后期岩浆活动对洋壳改造的新认识:(1)发现西北次海盆地壳具有明显的洋壳性质,莫霍(Moho)面埋深为11~12 km(从海平面起算),地壳厚度为6~8km,速度为5.7~7.0 km/s.扩张中心轴部双峰海山为西北次海盆扩张之后岩浆活动的产物;(2)西北次海盆、东部次海盆、西南次海盆东北部沿垂直扩张脊方向地壳速度结构均有明显的横向变化,在扩张中心处都表现为洋壳厚度增大约1 km,莫霍面埋深增大,表明后期岩浆活动对地壳结构有较大的改造作用.
This study focuses on the magmatic activities and seamounts in the fossil spreading center of three sub-basins in the South China Sea（SCS）. The northwest sub-basin（NWSB）, southwest sub-basin（SWSB）, and east sub-basin（ESB） are of great importance for understanding the tectonic evolution and post-spreading magmatic activities of the SCS. Deep crustal structures beneath the spreading center of these basins have a significant bearing on the magmatic process. For this study, on the basis of a previous velocity model, we used two-dimensional ray-tracing methods and high-quality ocean-bottom seismometer（OBS） data collected in 2006 to image the NWSB deep P-wave velocity structures. We then performed travel-time analysis and estimated uncertainties of the final model parameters to prove that the velocity model was convincing. Finally, we compared the one-dimensional velocity structures among OBS profiles 2006-p1 in the NWSB, G8G0 in the ESB, and T1 in the SWSB. Our study of crustal structure yielded the following results：（1） the NWSB is confirmed to be oceanic crust compared with typical Atlantic oceanic crust. The crustal velocity is 5.7–7.0 km/s, whereas the crustal thickness is 6–8 km in the basin（90–130 km）. There is no high-velocity layer. The Mohorovi？i？ discontinuity（Moho） is distributed symmetrically along the spreading axis and gradually increases from the basin center to the edge. The depth of the Moho is 11–12 km in the basin（55–70 km） and changes dramatically to 16 km depth under the north margin（170–200 km） and the Zhongsha Islands（0–55 km）. The depth of the Moho in all three sub-basins increases by 1 km in the spreading center. This suggests that crustal structure in the SCS is greatly influenced by magmatic activities. The Shuangfeng seamount, with a 6.5-km-thick crust, located in the center of the spreading ridge, is a post-spreading volcanic seamount. The 6.4-km/s velocity contour beneath the Shuangfeng seamount gradually rises toward the nor
作者
欧阳青
吴振利
卫小冬
牛雄伟
阮爱国
于志腾
OUYANG Qing WU ZhenLi WEI XiaoDong NIU XiongWei RUAN AiGuo YU ZhiTeng(Key Laboratory of Submarine Geosciences, Second Institute of Oceanography （SOA）, Hangzhou 310012, China Key Laboratory of Marine Mineral Resources, Ministry of Land and Resources, Guangzhou 510075, China Department of Earth Sciences, Zhejiang University, Hangzhou 310027, China)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2017年第21期2380-2391,共12页
Chinese Science Bulletin
基金
国土资源部海底矿产资源重点实验室开放基金(KLMMR-2014-B-08
KLMMR-2014-B-07)
国家自然科学基金(41406052
41576037
41176046
41506048
91228205)
全球变化与海气相互作用专项(GASI-GEOGE-01)
科技基础性工作专项(2013FY112900)资助
关键词
海底地震仪(OBS)
西北次海盆
双峰海山
地壳速度结构
扩张后岩浆活动
ocean bottom seismometer
northwest sub-basin
Shuangfeng seamount
crustal velocity structure
post-spreading magmatic activities
