Discussion the interaction between hot spots and mid-ocean ridge from the axial morphology and the variation of subsidence rate on both sides of the Southwest Indian Ridge
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摘要: 基于高精度地形数据,将西南印度洋中脊(11.88°E—66.75°E)分为6个区域,按不同区域分析洋脊轴部形态及其两侧基底沉降曲线的变化,从而探讨西南印度洋中脊的岩浆活动及其受热点影响的机制。结果显示:① 对于整个西南印度洋脊,轴部隆起占13.38%,轴部裂谷占82.8%,平坦过渡形占3.82%,其中19°E,36°E,41.2°E,43.7°E,50.4°E和64.5°E等区域为较集中的洋脊轴部隆起;② 埃里克辛普森-英多姆转换断层之间的区域(39.4°E—45.77°E)显示出异常浅的轴部裂谷和异常小且南北不对称的基底沉降速率。这表明埃里克辛普森-英多姆转换断层之间的区域是热点对洋中脊影响较为明显的区域,南侧较北侧异常小的基底沉降速率表明热点与洋中脊的相互作用主要表现为热点岩浆从洋脊南部向上流动到岩石圈底部,然后与岩石圈发生相互作用。
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关键词:
- 西南印度洋中脊 /
- 洋中脊轴部形态 /
- 基底沉降曲线 /
- 热点与洋中脊的相互作用
Abstract: Based on high resolution seafloor bathymetry map, we divided the Southwest Indian Ridg(SWIR) (11.88°E—66.75°E) into six different regions. In each region, we estimate the variation of the morphology of the axis, and the basement subsidence curve over the flanks of the spreading ridge, which can be used to indicate the spreading process of the SWIR and how it was affected by the hot spot. The result shows that: ① For the entire SWIR, axial uplift accounts for 13.38%, axial rift accounts for 82.8%, and flat transitional shape accounts for 3.82%, areas at 19°E, 36°E, 41.2°E, 43.7°E, 50.4°E, 64.5°E have focus magmatic ridge representing axial ridge uplift; ② The area between the Eric Simpson-Indomed transition faults (39.4°E—45.77°E) shows axial valley with anomalous shallow bathymetry and asymmetrical anomalous low basement subsidence rates between north and south. Therefore, we believe that the area between the Eric Simpson-Indomed transition faults has been significantly affected by the hot spots. Compared to the subsidence rate north of the spreading ridge, the anomalous low subsidence rate in the south indicates that the interaction between the hot spots and the ridge is characterized by the hot spots flowing upward from the south of the SWIR to the bottom of the lithosphere, and then interact with the lithosphere. -
图 1 西南印度洋地形图及分区
SWIR:西南印度洋中脊;SEIR:东南印度洋中脊;CIR:中印度洋中脊;BTJ:布维三连点;RTJ:罗得里格斯三连点;SH:沙卡;DT:迪图瓦;AB:安德鲁贝恩;M:马里昂;PE:爱德华王子;ES:埃里克辛普森;DII:发现II号;IN:英多姆;GA:加列尼;AII:亚特兰提斯Ⅱ号;MEL:梅尔。下同
Figure 1. Topographic map of Southwest Indian Ocean
SWIR:Southwest Indian Ridge;SEIR:Southeast Indian Ridge;CIR:Central Indian Ridge;BTJ:Bouvet Triple Junction;RTJ:Rodriguez Triple Junction;SH:Shaka;DT:Du Toit;AB:Andrew Bain;M:Marion;PE:Prince Edward;ES: Eric Simpson;DII:Discovery II;IN:Indomed;GA:Gallieni;AII:Atlantis Ⅱ;MEL:Melville. The same below
图 2 SWIR沿轴水深、地幔布格重力异常MBA和玄武岩Na8含量变化图(修改自Sauter,Cannat,2010)
图中纵向灰色实线为转换断层位置。(a) 沿轴水深;(b) 沿轴MBA变化(Georgen et al,2001);(c) 玄武岩Na8含量变化
Figure 2. Along-axis variation of the depth,MBA,Na8 composition of basalts (modified after Sauter,Cannat,2010)
The vertical gray solid line indicates the location of transform faults (a) Along-axis depth;(b) Variation of the mantle Bouguer anomaly (Georgen et al,2001); (c) Variation of the Na8 composition of basalts glasses dredged along the SWIR axis
图 3 西南印度洋中脊玄武岩同位素比值变化图(修改自孙国洪等,2021)
Figure 3. Variations in isotopic ratios of MORBs along SWIR (modified after Sun et al,2021)
图 4 沿脊水深拟合图
横坐标表示与发现Ⅱ号转换断层的距离;红色实线是最佳的高斯拟合线;灰色条带为转换断层发育位置;红色条带为热点投影到洋中脊的位置;A—F为洋脊研究区域
Figure 4. Fitting diagram of seafloor depth along the spreading ridge
The horizontal axis shows the distance from the DII transform fault;The solid red line is the best Gaussian fitting line; The gray bars indicate the location of transition faults;The red bar is where the plume is projected onto the mid-ocean ridge; A—F are the segmented study areas
图 5 沿洋中脊采样以及扩张方向示意图
(a) 水深地形图;(b) 磁异常分布图,磁异常数据来源于全球2′分辨率磁力网格数据EMAG2 (Maus et al,2009)
Figure 5. Schematic diagram of sampling along the mid-ocean ridge and its spreading direction
(a) Topographic map;(b) The magnetic anomalies map,and the magnetic anomaly data are from EMAG2 (Maus et al,2009)
图 10 SWIR沉降速率图
图(a)中红色实线为各研究区域内沉降速率的拟合线,品红色虚线为SWIR沉降速率平均值,蓝色阴影为全球沉降速率均值范围(Stein,Stein,1992;Crosby,McKenzie,2009);图(b)中蓝色和黑针线分别为洋中脊北侧沉降速率减去南侧所得的正值与负值,灰色及红色条带与图4同。顶部红色区域显示洋脊轴部隆起所占比例(a) 沉降速率沿轴变化图;(b) 洋脊两侧沉降速率差值沿轴变化图
Figure 10. SWIR sedimentation rate diagram
In fig.a,the solid red line is the best fit line of the subsidence rate along the SWIR. The red dotted line shows an average SWIR subsidence rate,while the horizontal blue bar represent the global subsidence rate (Stein, Stein,1992;Crosby,McKenzie,2009);In fig.b,the black and blue lines indicate the values of difference between the northern and southern subsidence rate. The vertical gray bars and red bars indicate the same meaning as in fig.4. The red areas at top represent the percentage of the axial rise for each region(a) Subsidence rate variation along SWIR;(b) Axial variation of the difference between northern and southern subsidence rate
表 1 SWIR各研究区域扩张轴部深度及沉降速率均值表
Table 1. Axial valley depth and subsidence rate of each area in SWIR
各要素均值 轴部裂谷深度/km 沉降速率/(km·${{\rm{M}}{{\rm{a}}^{{\raise0.2ex\hbox{$\scriptstyle 1$}\kern-0.25em/\kern-0.1em\lower0.25ex\hbox{$\scriptstyle 2$}}}}} $) A区 −1.09 0.393 B区 −0.48 0.244 C区 −0.37 0.129 D区 −0.95 0.407 E区 −1.4 0.42 F区 −1.14 0.414 SWIR −1.00 0.368 -
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