李海龙^1,2,,
吴招才^1,,,
纪飞^1,3,
高金耀¹,
杨春国¹,
袁园¹,
许明炬^1,4,
张家岭^1,5
1. 自然资源部海底科学重点实验室, 自然资源部第二海洋研究所, 杭州 310012
2. 自然资源部天然气水合物重点实验室, 青岛海洋地质研究所, 青岛 266071
3. 中国地震局地壳应力研究所, 地壳动力学重点实验室, 北京 100085
4. 浙江大学地球科学学院, 杭州 310027
5. 山东科技大学测绘科学与工程学院, 青岛 266590

基金项目: 国家自然科学基金项目(41676037), 自然资源部第二海洋研究所基本科研业务费专项资金项目(JT1601), "全球变化与海气相互作用"专项(GASI-GEOGE-05、01, GASI02-SCS-DWZP1), 浙江省自然科学基金青年基金(LQ18D040001), 广州海洋地质调查局国土资源部海底矿产资源重点实验室开放基金(KLMMR-2017-B-03), 国家自然科学基金项目(41574004, 40776036)联合资助


详细信息

作者简介: 李海龙, 男, 1993年生, 硕士, 主要从事海洋地球物理和大陆边缘研究.E-mail:lihailong_mg@163.com

通讯作者: 吴招才, 男, 1980年生, 博士, 副研究员, 硕士生导师, 主要从事海洋地球物理和海底构造研究.E-mail:wuzc@sio.org.cn

中图分类号: P738;P312

收稿日期:2019-02-22
修回日期:2019-08-04
上线日期:2020-05-05

Crustal density structure of the northern South China Sea from constrained 3-D gravity inversion

LI HaiLong^1,2,,
WU ZhaoCai^1,,,
JI Fei^1,3,
GAO JinYao¹,
YANG ChunGuo¹,
YUAN Yuan¹,
XU MingJu^1,4,
ZHANG JiaLing^1,5
1. Key Laboratory of Submarine Geosciences, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China
2. Key Laboratory of Gas Hydrate, Ministry of Natural Resources, Qingdao Institute of Marine Geology, Qingdao 266071, China
3. Key Laboratory of Crustal Dynamics, Institute of Crustal Dynamics, China Earthquake Administration, Beijing 100085, China
4. School of Earth Sciences, Zhejiang University, Hangzhou 310027, China
5. College of Geomatics, Shandong University of Science and Technology, Qingdao 266590, China


More Information

Corresponding author: WU ZhaoCai,E-mail:wuzc@sio.org.cn

MSC: P738;P312

--> Received Date: 22 February 2019
Revised Date: 04 August 2019
Available Online: 05 May 2020


摘要
摘要:地壳结构的揭示是研究陆缘伸展机制的基础.尽管在南海北部陆缘已开展了大量地壳尺度的二维地震探测，但目前还存在许多覆盖空白的地区，这些调查所得到的结果无法提供地壳结构的区域视图.为了揭示南海北部的地壳结构，本研究将水深和沉积物厚度信息作为约束条件，对空间重力异常进行区域三维反演，并利用地震研究的结果来衡量反演结果的质量.沿地震测线的密度切片显示，重力反演结果与地震研究结果具有良好的一致性.本研究通过选择两个与地震研究结果最匹配的密度异常等值面分别作为康拉德面和莫霍面，获取了莫霍面深度和上、下地壳的厚度.根据假设的相应初始地壳厚度，本研究进一步计算了全地壳、上地壳和下地壳的拉张因子.通过与已发表的居里面深度比较，发现南海北部大部分地区的居里面深度均位于莫霍面之下，其中西沙海槽的拉张因子β_w大于3.5并且缺乏岩浆活动，是地幔橄榄岩蛇纹石化的潜在区域.南海北部陆缘的地壳拉张因子显示其经历了伸展方向为128°和160°的两组张裂运动，分别对应于神弧运动和珠琼运动一幕及二幕，在张裂过程中应力场发生了顺时针旋转.此外，上、下地壳的拉张因子表明北部陆缘普遍存在正向和反向差异伸展，陆架区域表现为反向差异伸展，洋陆过渡带为正向差异伸展，推测这种正向和反向差异伸展可能是由下地壳流动导致的，由地壳厚度差异引起的横向梯度力、软流圈浮力和沉积物负载共同驱动.
关键词: 地壳结构/
差异伸展/
下地壳流/
大陆张裂/
重力反演/
南海北部

Abstract:The imaging of crustal structure is the basis of studying the extension mechanism of the continental margin. Although a large number of crustal-scale 2-D seismic surveys have been carried out on the northern South China Sea, there are still many areas lacking seismic coverage, and the results obtained from these surveys cannot provide a regional view of crustal structure. To resolve the crustal structure across the northern South China Sea, a 3-D regional inversion of the free air gravity data constrained by bathymetric and sediment thickness information was undertaken, and the results from seismic studies were used to assess the quality of the inverted results. Density anomaly slices along the seismic profiles show an excellent agreement between the inverted results and the seismic Moho. We select two density anomaly isosurfaces that match well with seismic constraints to represent the depth of Moho and Conrad and to provide Moho depth and the upper and lower crustal thickness. Then, the crustal stretching factor as a whole and upper and lower crust are computed by assuming the corresponding initial thickness. Comparing the Moho depth with the published Curie depth, the results show that the Curie depths are larger than Moho depths in most of the northern South China Sea. Among them, the Xisha Trough with crustal stretching factor greater than 3.5 and starving post-rift magmatism is a potential area for serpentinization of the uppermost mantle. The crustal stretching factors (β_w) in the northern margin of the South China Sea show that it has experienced two groups of rifting with extension directions of 128° and 160°, corresponding to Shenhu event and the first and second episode of Zhuqiong event, respectively. The stress field rotates clockwise during rifting. In addition, the stretching factors of the upper and lower crust indicate that the positive and inverse extension discrepancy are widespread in the northern continental margin. The shelf regions exhibit inverse extension discrepancy, and the oceanic-continental transition zones display positive extension discrepancy. It is conjectured that the positive and inverse extension discrepancy may be caused by the lower crustal flow, which is driven by a combination of the lateral gradient press arising from the crustal thickness variations, the asthenospheric buoyancy and the sediment loading.
Key words:Crustal structure/
Extension discrepancy/
Lower crustal flow/
Continental margins: divergent/
Gravity inversion/
The northern South China Sea



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