南海西南次海盆与超慢速扩张西南印度洋中脊地壳结构对比#cod#x0002A;
作者简介:于俊辉(1991#cod#x02014;), 男, 河南省正阳县人, 博士研究生, 现从事海洋地球物理与海洋地质研究。E-mail: jhyu@scsio.ac.cn
收稿日期: 2017-04-13
要求修回日期: 2017-06-02
网络出版日期: 2018-01-18
基金资助
国家自然科学基金(91328205、41376062、91628301、U1606401)
国土资源部海洋地质保障工程项目(GZH20110205)
中国科学院项目(QYZDY-SSW-DQC005、Y4SL021001)
Comparison of crustal structure between the Southwest Sub-basin, South China Sea and the ultraslow-spreading Southwest Indian Ridge
Received date: 2017-04-13
Request revised date: 2017-06-02
Online published: 2018-01-18
Supported by
National Natural Science Foundation of China (91328205, 41376062, 91628301, U1606401)
Security Project of Marine Geology of Ministry of Land and Resources (GZH20110205)
Chinese Academy of Sciences Project (QYZDY-SSW-DQC005, Y4SL021001)
Copyright
近年来对西南印度洋中脊的研究显示, 超慢速扩张(全扩张率: 12~18mm#cod#x000b7;yr-1)的西南印度洋中脊包含岩浆增生型和非岩浆增生型两种截然不同的地壳结构。岩浆增生型中脊段表现为轴向的海底隆起, 通常具有较低的地幔布格重力异常和较强的磁性, 地壳厚度较大; 非岩浆增生型中脊段通常水深较深, 缺乏转换断层, 发育拆离断层和高角度正断层, 具有较高的地幔布格重力异常和微弱的磁性, 大量蛇纹石化的地幔橄榄岩出露海底, 火成岩地壳较薄甚至不存在。南海西南次海盆具有较慢速扩张率(全扩张率: 50~35mm#cod#x000b7;yr-1), 其接近消亡洋中脊中央部分的地壳厚度也较薄, 也有可能存在蛇纹石化地幔, 具有超慢速扩张脊非岩浆增生段的特点。
关键词: 西南印度洋中脊; 岩浆和非岩浆增生型地壳; 蛇纹石化橄榄岩; 西南次海盆; 超慢速扩张
于俊辉 , 阎贫 , 林间 . 南海西南次海盆与超慢速扩张西南印度洋中脊地壳结构对比#cod#x0002A;[J]. 热带海洋学报, 2017 , 36(6) : 51 -61 . DOI: 10.11978/2017044
Recent investigations of the ultraslow-spreading (full spreading rate: 12~18mm#cod#x000b7;yr-1) Southwest Indian Ridge revealed two kinds of crustal structure: Magmatic and amagmatic accretionary crust. Magmatic accretionary segments appear as the axial rise, relatively low mantle Bouguer gravity anomaly, strong magnetization and thick crust. Amagmatic accretionary segments feature detachments and abundant high-angle normal faults, lack of transform faults, deep water, relatively high mantle Bouguer gravity anomaly and weak magnetization. There are also significant amount of serpentinized peridotites exposed on the seafloor, and the igneous crust is thin, even absent. The Southwest Sub-basin of the South China Sea (SWSB) has relatively slow-spreading rates (full spreading rate: 50~35mm#cod#x000b7;yr-1). The central part of SWSB also presents thin crust and there might be some serpentinized peridotites in the basin area, which are similar to the characteristics of the amagmatic accretionary crust in the ultraslow-spreading Southwest Indian Ridge.
Fig. 1 Along-axis bathymetry and MBA map (a) and bathymetry map (b) of the SWIR. The black lines indicate the ridge axis (panel b).The bathymetry chart is mapped by GMT software (Wessel et al, 1998) with the data from National Oceanic and Atmospheric Administration (NOAA). The along-axis bathymetry and MBA data are from Georgen et al, 2001. BTJ: Bouvet Triple Junction; RTJ: Rodrigues Triple Junction; MAR: Mid-Atlantic Ridge; SWIR: Southwest Indian Ridge; CIR: Central Indian Ridge; SEIR: Southeast Indian Ridge; AAR: America-Antarctica Ridge; AB: Andrew Bain Transform Fault; PE: Prince Edward Transform Fault; D#cod#x02161;: Discovery #cod#x02161; Transform Fault; IN: Indomed Transform Fault; GA: Gallieni Transform Fault; A#cod#x02161;: Atlantis #cod#x02161; Transform Fault; ME: Melville Transform Fault 图1 西南印度洋中脊(SWIR) 沿轴水深、地幔布格重力异常(MBA)(a)和水深地形图(b) 黑色线代表中脊轴; 水深图由GMT软件(Wessel et al, 1998)绘制, 数据来源于美国国家海洋大气管理局(NOAA); 沿轴水深和MBA值来源于Georgen et al, 2001。AB: 安德鲁贝恩转换断层; PE: 爱德华王子转换断层; D#cod#x02161;: 探索#cod#x02161;转换断层; IN: 因道姆转换断层; GA: 加里艾尼转换断层; A#cod#x02161;: 亚特兰蒂斯#cod#x02161;转换断层; ME: 梅尔维尔转换断层。BTJ: 布维三联点; RTJ: 罗德里格斯三联点; MAR: 大西洋洋中脊; SWIR: 西南印度洋中脊; CIR: 中印度洋中脊; SEIR: 东南印度洋中脊; AAR: 美洲#cod#x02014;南极洲洋中脊 |
图2 西南印度洋中脊第27和28段轴向速度结构(改自Li et al, 2015)黑色细线代表速度等值线, 数字代表速度值(km#cod#x000b7;s-1) |
Fig. 3 Multibeam bathymetry (a), schematic representation of the axial valley (b) and MBA (c) maps of the SWIR from 54#cod#x000b0;06'E to 57#cod#x000b0;E (modified after Sauter et al, 2001).(a) The white lines indicate the ridge axis. (b) The grey area marks the inner-valley. Vertical black lines mark the location of the central magnetic anomaly. Thick black lines and diamonds show segments and segment centers, respectively. (c) The white lines indicate the ridge axis 图3 54#cod#x000b0;06'E#cod#x02014;57#cod#x000b0;E西南印度洋中脊多波束水深(a)、轴部谷地简图(b)和MBA(c)(改自Sauter et al, 2001) (a)中白线代表中脊轴; (b)中灰色区域代表内谷坡, 黑色竖线对应中心磁异常数据的位置, 黑色横线代表中脊轴, 方块对应中脊段中心; (c)中白线代表中脊轴 |
Fig. 4 Multibeam bathymetry (a), MBA (b) and magnetization (c) maps of the SWIR from 9#cod#x000b0;E to 16#cod#x000b0;E (modified after Dick et al, 2003). (a) Small circles indicate dredge locations. Gravity and magnetic data are derived from the shipboard measurements data. (c) The contour interval is 4 A#cod#x000b7;m-1 in magnetization map图4 9#cod#x000b0;E#cod#x02014;16#cod#x000b0;E 西南印度洋中脊多波束水深(a)、MBA(b)和磁强度(c)(改自Dick et al, 2003) (a)中小圆代表拖网取样点位置; 重、磁数据均来源于船载实测数据; (c)中磁强度等值线以4A#cod#x000b7;m-1为间隔 |
Fig. 5 Seismic velocity models for profile CAM114 (a), CAM116 (b), CAM120 (c) in 66#cod#x000b0;E SWIR (modified after Minshull et al, 2006). The velocity contour interval is 0.4km#cod#x000b7;s-1. The dashed lines just below the 6.4km#cod#x000b7;s-1 contour mark the base of Layer 2. A, B, C, D indicates the spreading segments. VE: Vertical Exaggeration图5 66#cod#x000b0;E 西南印度洋中脊地震测线CAM114 (a)、116(b)、120(c)的最终速度模型(改自Minshull et al, 2006) 速度等值线间隔为0.4km#cod#x000b7;s-1; 6.4 km#cod#x000b7;s-1等值线下方的虚线代表层2的底面; A、B、C、D代表扩张中脊段; VE代表垂向放大比例 |
Fig. 6 Two alternative velocity models for north-south seismic Line CAM101 over Atlantis Bank (modified after Muller et al, 2000 and Dick et al, 2016).Upper panel shows a model of undifferentiated Layer 3; lower panel shows an alternative model of a lower serpentinized mantle Layer 3 and an upper gabbroic Layer 3. These models can both fit the seismic data. Hole 735B is projected from ~1km to the west. Green line: depth of Hole U1473A drilled during IODP Expedition 360, orange and red lines: projected penetration during the remainder of the SloMo project 图6 过亚特兰提斯浅滩南北向地震测线CAM101的两种可选速度模型(改自Muller et al, 2000和Dick et al, 2016) 上图显示了无差别的层3; 下图显示层3包括两部分: 上部的辉长岩层3和下部的蛇纹石化地幔层3。两个模型均能与记录数据很好地吻合。钻孔735B是从该测线西侧约1km处投影而来, 钻孔U1473A为SloMo计划的钻探井位, 绿色代 |
Fig. 7 Three-dimensional view of the axial valley and interpretative cross-section in 64#cod#x000b0;30'E SWIR (modified after Sauter et al, 2013).Models showing that small patches of lavas (#cod#x003b1;) might have been erupted directly onto this earlier detachment fault surface; another patch (#cod#x003b2;) is interpreted to have rafted on the new detachment fault surface 图7 64#cod#x000b0;30'E 西南印度洋中脊轴部谷地东向三维视图及横截面解释图(改自Sauter et al, 2013) #cod#x003b1;表示直接喷发在早期拆离断层表面的小岩浆体; #cod#x003b2;为被搬运至新拆离断层表面的小岩浆体 |
Fig. 8 Location of the Southwest Sub-basin and the NH973-1 seismic survey line.Solid red line indicates the location of profile showed in 图8 西南次海盆区域位置及NH973-1测线分布图 红色实线表示本文展示的剖面位置, 见 |
Fig. 9 The seismic profile (a) and its interpretation (b) of the northwestern segment (see |
Fig. 10 Comparison of morphologic profiles of the Southwest Sub-basin, South China Sea (a), the Southwest Indian Ridge at 15#cod#x000b0;30'E (b)图10 西南次海盆(a)和15#cod#x000b0;30'E西南印度洋中脊(b)地形对比 |
Fig. 11 Seismic crustal thickness versus full spreading rate (modified after Dick et al, 2003).The grey shaded area indicates the range of crustal thickness and full spreading rate in the Southwest Sub-basin, South China Sea 图11 地震地壳厚度与全扩张速率关系(改自Dick et al, 2003) 灰色阴影部分代表南海西南次海盆地壳厚度和全扩张速率范围 |
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