跨南海西南次海盆OBS、多道地震与重力联合调查
汪俊(1983—), 男, 浙江省江山市人, 工程师, 硕士, 从事海洋区域地质构造研究, 主要技术手段为联合重、磁、反射及折射地震等地球物理资料进行综合地球物理建模。E-mail: |
Copy editor: 孙淑杰
收稿日期: 2018-10-17
要求修回日期: 2010-01-10
网络出版日期: 2019-07-21
基金资助
中国地质调查局国家海洋专项项目((GZH201100205、DD20160138);)
国家自然科学基金项目((91855101、41876052).)
版权
A joint investigation using OBS, multi-channel seismic and gravity data across the southwestern sub-basin of the South China Sea
*非常感谢3位审稿专家的建设性修改意见及编辑部老师们耐心沟通。
Copy editor: SUN Shu-jie
Received date: 2018-10-17
Request revised date: 2010-01-10
Online published: 2019-07-21
Supported by
China Geological Survey Program((GZH201100205、DD20160138);)
National Natural Science Foundation of China((91855101、41876052).)
Copyright
对跨南海西南次海盆及两侧陆缘的一条1050km长的、包括海底地震(OBS)、长排列多道地震和重磁在内的综合地球物理探测剖面(CFT)进行了构造成像和研究。在多道地震成像基础上建立了CFT剖面初始速度模型, 进而通过初至波层析成像方法反演了CFT剖面的速度结构模型, 在重力异常资料的约束下建立了CFT剖面的综合地壳结构模型。讨论了沿CFT剖面出现的下地壳高速体、龙门海山的低密度物质等地质问题。结果表明, 下地壳高速层在北部陆坡、西南海盆和南部南沙地块均有分布, 厚度在0~4km之间, 可能与陆缘下地壳物质和地幔物质熔融混合, 以及深海盆海底扩张期间构造拉伸导致地幔蛇纹岩化有关。
汪俊 , 邱燕 , 阎贫 , DELESCLUSEM , 王彦林 , PUBELLIERM , 聂鑫 . 跨南海西南次海盆OBS、多道地震与重力联合调查[J]. 热带海洋学报, 2019 , 38(4) : 81 -90 . DOI: 10.11978/2018108
A 1050-km long comprehensive geophysical profile (CFT) was acquired across the conjugate margins of the southwestern sub-basin of the South China Sea, which includes 49 OBSs, 6- or 8-km long streamer, gravimeter, and magnetometer. Various refined processing procedures were applied to the aforementioned geophysical data; and a joint reflection and refraction seismic travel time inversion was performed to derive a 2-D velocity model of the crustal structure and upper mantle. Based on this new tomographic model and shipboard gravity data, a comprehensive crustal structure model was created. Finally, some interesting issues including High Velocity Layer (HVL) in the base of crust, an anomalous low density seamount (long-men seamount) along the CFT profile are discussed in this paper. HVL are widely distributed under the northern slope, southwestern sub-basin and Nansha block along the CFT profile, with the velocity varying from 7.0 to 7.5 km·s -1, and thickness between 0 and 4 km. HVL in the marginal lower crust might be derived from melting and mixing of lower crust material and mantle material, and HVL in the oceanic crust might have originated from serpentinization by tectonically dominated seafloor spreading.
图1 研究区地形及CFT剖面位置红色实心圆圈为CFT剖面布设的OBS站位, 其中蓝色实心圆圈为数据无效台站; 蓝色细线为CFT-MCS2013剖面位置; 灰色细线为南海以往深地壳探测剖面位置; 棕色实心圆圈为IODP349钻孔位置; 黄色五角星为IODP 184钻孔位置 Fig. 1 The bathymetric map of study area and the location of CFT section. Red dots are the OBS stations along the CFT section, blue dots are the OBS stations with invalid data, brown dots are the boreholes of IODP349 cruises, and yellow stars are the boreholes of IODP 184 cruises. Blue line represents CFT-MCS2013 section; gray lines are deep crust detecting sections within the South China Sea |
图2 OBS46、OBS11及OBS18记录的折射波震相识别分析与拾取折合速度为8km·s-1。Psed: 沉积层折射震相; Pg: 地壳折射震相; PmP: Moho反射震相; Pn: 上地幔顶部折射震相; 青色细线为初至折射拾取 Fig. 2 First refraction arrival phase picks of OBS46, OBS11and OBS18 (reduced velocity is 8 km·s-1). Psed: refraction phase from sediment; Pg: refraction phase from crust; PmP: reflection from Moho interface; Pn: refraction phase from upper mantle; cayan lines represent first arrival picks |
表1 初始速度模型速度参数Tab. 1 Parameters of initial velocity model |
层位 | 速度范围/(km·s-1) |
---|---|
水体 | 1.5 |
沉积地层 | 1.7~3.5 |
基底以下壳内 | 4.0~7.5 |
地幔 | 8.0 |
表2 主要反演参数Tab. 2 Major inversion parameters |
参数名称 | 参数值 |
---|---|
横向相关长度/km | 10~30 |
纵向相关长度/km | 0~24 |
速度平滑参数 | 1.7~3.5 |
迭代次数 | 10~20 |
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