
西北印度洋卡尔斯伯格脊61°24'E—61°48'E段的构造地貌及岩浆-构造活动性
叶盛源, 韩喜球, 李洪林
海洋学研究 ›› 2024, Vol. 42 ›› Issue (4) : 70-82.
西北印度洋卡尔斯伯格脊61°24'E—61°48'E段的构造地貌及岩浆-构造活动性
The tectonic geomorphology and magmatic-tectonic activity in the 61°24'E-61°48'E segment of the Carlsberg Ridge in the Northwest Indian Ocean
洋中脊的地形地貌特征直接受构造运动和岩浆活动控制,对其进行研究可以了解洋中脊的构造演化历史和岩浆作用过程,对于海底矿产资源的勘探具有重要意义。本文利用中国大洋24航次采集的船载多波束声呐数据,用定量分析的方法对西北印度洋卡尔斯伯格脊61°24'E—61°48'E段的地形地貌特征开展研究,计算了岩浆侵入比及断层相关指数,并探讨了研究区的岩浆-构造意义,获得了以下认识:1)研究区可划分为A、B、C、D四个二级洋中脊段,其岩浆-构造活动期间隔分别为0.15、0.50、0.70和0.21 Ma。2)洋中脊A段和B段为不对称扩张段,岩浆贫乏,以构造作用为主,处于构造活动期;洋中脊C段为对称扩张段,岩浆较为充足,以岩浆作用为主,处于轴向火山脊构建期;洋中脊D段为对称扩张段,岩浆贫乏,以构造作用为主,处于构造活动期。3)在洋中脊段两侧断层核密度值高的区域,有可能形成热液活动区,将是未来进一步勘探的目标区域。
The topographic and geomorphologic features of mid-ocean ridges are directly controlled by tectonic movements and magmatic activities, and study of them can help us to understand the tectonic evolution history and magmatic processes of mid-ocean ridges, and is also of great significance to the exploration of deep-sea mineral resources. In this paper, the shipboard multibeam sonar data collected during the China Ocean 24 Cruise were utilize to study the topographic and geomorphologic features of the Carlsberg Ridge in the Northwest Indian Ocean by applying the quantitative analysis method with the 61°24'E-61°48'E segment as the research target, the magma intrusion ratio and the fault correlation index were calculated, and the magma-tectonic significance of the study area was discussed. The study area can be divided into four secondary mid-ocean ridge segments (A, B, C, and D). The active intervals of magma-tectonic periods for segments A, B, C, and D are 0.15, 0.50, 0.70 and 0.21 Ma, respectively. The mid-ocean ridge segments A and B are asymmetric dilatation sections with poor magma and mainly tectonic action, belonging to the period of tectonic activity; the mid-ocean ridge segment C is a symmetric dilatation section with sufficient magma and mainly magmatic action, belonging to the period of axial volcanic ridge construction; the mid-ocean ridge segment D is a symmetric dilatation section with poor magma and mainly tectonic action, belonging to the period of tectonic activity. Faults area with high kernel density on the two flanks of the mid-ocean ridge section has a possibility of forming an area of hydrothermal activity, which is a target area of further exploration.
卡尔斯伯格脊 / 地形地貌 / 岩浆周期 / 定量分析 / 岩浆-构造活动 / 岩浆侵入比 / 不对称扩张 / 核密度
Carlsberg Ridge / topography and geomorphology / magma cycles / quantitative analysis / magmatic-tectonic activity / magma intrusion ratio / asymmetric expansion / kernel density
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Multibeam sonar data can effectively reflect the features of seafloor topography and its substrates. The shipboard multibeam data were used to characterize the topography, geomorphology and the backscatter intensity characteristics of typical tectono-geographic units of the 60°-61°E segment in Carlsberg Ridge, Northwestern Indian Ocean, aiming to describe the strength of the magmatism and tectonism of the studied ridge segments. Basically, the 60°-61°E segment of Carlsberg Ridge showed symmetrical spreading with discontinuous zone. The Segment I was more influenced by tectonism, with more fractures occurred in the rift valley. The segment axis and nearby backscatter intensity reached -29 dB, with the rift wall height difference over 1 200 m. The segment also had deeper valley bottoms, higher rift valley walls, higher flank/width ratio (78.7-126.2) but less off-axial linear structures. In the rift flank, the normal fault plane was wider and the dip angle was smaller. Compared to the center of the segment, the volcanic activities in segment end had lower eruption frequency but larger eruption scale, and erupted volcanic edifices were larger in the aspect of number and volume. In contrast, the Segment II was dominated by magmatism with axial volcanic ridges and numerous symmetrically developed off-axial linear structures. The segment axis and nearby backscatter intensity reached -35 dB. The rift flank/width ratio was 77.6-116.8. The difference of the rift wall height was less than 500 m. The linear structures had relatively high aspect ratio, and were approximately symmetric on the flank of the rift. It is suggested that multibeam backscatter data combining with the topography analysis can provide quantitative evidence for the study of the strengths of the tectonism and magmatism of the mid-ocean ridge.
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The mid-ocean ridge is where the plates spread and the new oceanic crust forms. There are often well-developed central eruptive volcanic cones in addition to fissure eruptive lavas parallel to the ridge axis. These volcanic cones are of great significance for understanding the local and regional magmatism and tectonic activities. These volcanic cones can be identified using manual or machine interpretation methods based on seabed multi-beam bathymetric data. In this study the automatic extraction method of volcanic cones near the mid-ocean ridge was tried by means of unsupervised classification using the DEM data from Carlsberg Ridge obtained from the Chinese DY24 Cruise. The slope, surface roughness, positive and negative topography and other derivative parameters were calculated based on the original DEM data. The morphological characteristics and spatial features of volcanic cones were enhanced by feature transformation. The ISO clustering unsupervised classification method was selected to cluster and analyze the images after feature transformation. Then the method of landscape shape index in landscape ecology was introduced to complete the automatic extraction of volcanic cones. The accuracy of automatic recognition can reach around 0.8 with overlapping rate of ~0.7 comparing with manual extraction. Thus, the automatic extraction of submarine volcanic cones by means of unsupervised classification is robust and efficient, which can be of great help to large-scale data process and interpretation.
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东南印度洋脊(Southeast Indian Ridge, 简称SEIR)是中速扩张洋中脊, 在其中的108°—134°E区域的全扩张速率为72~76 mm·a <sup>-1</sup>。但在接近澳大利亚-南极洲不整合带(Australian-Antarctic Discordance, 简称AAD)区内, 海底地貌沿洋中脊的变化强烈, 其变化范围涵盖了从慢速到快速扩张洋中脊上常见的例子, 且出现了明显的地球物理与地球化学异常, 说明洋中脊在AAD区附近的岩浆供应量极不均匀。文章定量分析了高精度多波束测深数据, 计算了洋中脊不同段的地形坡度、断层比例以及平面与剖面的岩浆参数M值, 结合研究区内剩余地幔布格重力异常以及洋中脊轴部地球化学指标Na<sub>8.0</sub>、Fe<sub>8.0</sub>等资料, 分析与讨论了研究区的断层构造与岩浆活动特征的关系。研究发现, 东南印度洋脊108°—134°E区域的B区(在AAD区内)及C5段(在AAD区外西侧)发育有大量的海洋核杂岩, 而且B区的海洋核杂岩单体规模更大, 其中最大的位于B3区, 沿洋中脊扩张方向延伸约50km。研究结果首次系统性地显示, 相比东南印度洋的其他区域, B和C5异常区具有偏低的平面与剖面M值、偏高的断层比例、偏正的地幔布格重力异常以及偏高的Na<sub>8.0</sub>值与偏低的Fe<sub>8.0</sub>值, 这些异常特征可能反映了B区和C5段的岩浆初始熔融深度较浅以及岩浆熔融程度较低, 因此导致其岩浆供应量异常少, 形成较薄的地壳。研究结果同时表明, 在岩浆供应量极少的洋中脊, 构造伸展作用有利于海洋核杂岩的发育, 导致地壳进一步减薄。
The Southeast Indian Ridge (SEIR) at 108°-134°E has a relatively constant intermediate full spreading rate of 72-76 mm·a -1 but exhibits significant variations in seafloor tectonic faulting and magmatism. This section of the SEIR encompasses the Australian-Antarctic Discordance (AAD), shows a wide range of seafloor morphology similar to the diverse examples from slow- to fast-spreading ridges, and is associated with significant geophysical and geochemical anomalies. We used high- resolution multi-beam bathymetry data to calculate seafloor topographic slopes, ratio of fault scarp areas, map view and profile M factors. Combining residual mantle Bouguer anomaly and geochemical factors of Na8.0 and Fe8.0, we analyzed the fault tectonics and magmatic characteristics in our study area. A large number of Oceanic Core Complexes (OCC) zones are observed in Zone B within the AAD and Segment C5 immediately to the west of the AAD. The OCC features in Zone B are in general larger in size than those of Segment C5. The largest OCC is located in Segment B3, which extends~50 km along the SEIR spreading direction. In comparison to other segments, Zone B and Segment C5 have more negative residual mantle Bouguer anomalies, higher Na8.0 and lower Fe8.0, more fault scarp areas, and lower plane and profile M factors. These anomalies may reflect shallower initial mantle melting and lower degree of partial melting in Zone B and Segment C5, resulting in anomalously low magma supply, thin crust, and the development of OCC features when the magma supply is severely limited. |
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