The Magmato-tectonic dynamic model for the Indomed-Gallieni segment of the central southwest Indian ridge
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摘要: 利用西南印度洋脊中段Indomed-Gallieni洋段49—51°E区段全覆盖高分辨率多波束水深地形资料，应用构造地貌学分析方法，结合区域地形及其他地球物理等资料，在分段分析49—51°E区段岩浆-构造动力学模式的基础上，进一步探讨了约10 Ma以来Indomed-Gallieni洋段的演化史.28、29洋段目前岩浆供应不足，在轴部不对称深断层的控制之下不对称扩张，属于超慢速扩张洋脊较常见的演化方式.轴部火山建造主要向北翼增生，发育与火山脊相关的火山地貌；南翼构造拉张作用强烈，地貌上可观察到大量断块，拆离断层可能大量存在.而27洋段水深浅、火山密集、轴部缺失裂谷，超慢速扩张下却具有较高的岩浆通量.Indomed-Gallieni洋段地形高地建造于一次岩浆增强事件，但应该不是因为Crozet热点的影响.27洋段为目前仍受该岩浆增强事件影响的唯一区段，但其强度和规模也在逐渐减小；包括28、29洋段在内的Indomed-Gallieni段其他部分，已重新恢复到岩浆供应不足的正常超慢速扩张洋脊演化模式.28、29洋段和27洋段岩浆供应均存在岩浆通量由多至少的周期，周期内岩浆供应较多时期轴部建脊，减少时期轴部火山建造裂离.但27洋段由于仍受岩浆增强事件的影响，与28、29洋段表现形式不同，主要表现为火山建造裂离方式、岩浆供应周期长短以及构造活动强烈程度的不同.Abstract: Based on the analysis of the full-coverage and high-resolution multibeam data of 49—51°E located between the Indomed and Gallieni fault zone of the Southwest Indian Ridge (SWIR), together with regional topography and other geophysical data , we discuss the magmato-tectonic dynamic model of this area segmentedly using the method of morphotectonics, then attempt to deduce the evolution of the entire Indomed-Gallieni segment since about 10 Ma ago further. It is concluded that segments 28 and 29 now follow a typical magma supply model of ultraslow spreading ridges, and have a low magma supply. As a result, they are under an asymmetric spreading by the control of large deep axial asymmetric faults. The volcanic constructions formed at the axis mainly accreted towards the north, and produced volcanic morphology there, while at the south flank hosts numerous large blocks due to the strong extension, and detachment faults may develop commonly there. Segment 27 has a shallow water depth, densely distributed volcanoes, without an axial valley, showing a robust magmatism in spite of an ultraslow spreading rate. The Indomed-Gallieni high terrain is resulted from a magma increase event, but we do not think it is because of the effect of the Crozet hotspot as mentioned in some literature. At present, however, segments 28 and 29 and other part of the Indomed-Gallieni segment have no longer been affected by this magma increase event, and has restored to normal ultraslow spreading evolution evidenced by its topography, while segment 27 is the only area still being affected, whereas its intensity and extent are decreasing. Segments 28, 29 and 27 are all experiencing a similar magma supply variation, during which ridge-shaped volcanic construction formed at the axis while magma supply was high, which was disrupted when magma supply became low. However, as with much larger magma flux, segment 27 behaved quite differently from segments 28 and 29 in the splitting pattern, period length and intensity of tectonic activity.
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Key words:
- SWIR /
- Ultraslow spreading /
- Multibeam /
- Morphotectonics /
- Magma-tectonics
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