Abstract We analyzed high-quality seismic reflection profiles across the ocean-continent transition in the Enderby Basin between the Kerguelen Plateau and the Antarctic margin. There, we observe numerous high-amplitude dipping reflections in the lower oceanic crust which was accreted at a magmatic spreading center as testified by the almost uniform 6.4-7 km thick crust and its unfaulted, flat top basement. The deep reflections are rooting onto the Moho and are dipping both ridgeward and continentward. They occur in dense networks in mature oceanic crust as well as close to the continentward termination of oceanic crust and in the ocean-continent transition zone. The comparison with field observations in the Oman ophiolite suggests that these lower crustal dipping reflectors could correspond to syn-magmatic faults. In Oman, very high temperature (up to syn-magmatic), high temperature (sub-solidus plastic deformation) and low temperature (brittle) deformation coexist along the same fault over distances of a few hundred meters at Moho level. This very high temperature gradient may be explained by the sudden and intense interaction between crystallizing magmas and hydrothermal fluids induced by the episodic nucleation of faults in a context of continuous magmatic spreading. The igneous layering becomes extremely irregular compared to its monotonous sub-horizontal orientation away from the faults which, together with enhanced hydrothermal alteration restricted to the fault zones, might change the physical properties (velocity, density) and increase the reflectivity of syn-magmatic faults. We further speculate that these processes could explain the brightness of the lower crustal dipping reflectors observed in our seismic reflection data. Both the seismic reflection profiles of the Enderby Basin and the Oman ophiolite show evidence for syn-accretion tectonism at depth together with the systematic rotation of originally horizontal lava flows or originally vertical dikes, pre-dating cessation of magmatic activity. This indicates ubiquitous deformation processes within the axial zone of magmatic spreading centers.

中文翻译：

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大洋下地壳的亚轴变形：恩德比盆地地震反射剖面的洞察以及与阿曼蛇绿岩的比较

摘要 我们分析了凯尔盖朗高原和南极边缘之间恩德比盆地海洋-大陆过渡的高质量地震反射剖面。在那里，我们观察到在岩浆扩张中心增生的下洋壳中的大量高振幅倾角反射，这由几乎均匀的 6.4-7 公里厚的地壳及其无断层的平顶基底证明。深深的反射植根于莫霍面，并同时向山脊和大陆倾斜。它们出现在成熟洋壳的密集网络中以及靠近洋壳向大陆的末端和海陆过渡带中。与阿曼蛇绿岩野外观测的比较表明，这些下地壳倾角反射层可能对应于同岩浆断层。在阿曼，沿同一断层在莫霍面数百米的距离内，高温（直至同质岩浆）、高温（亚固相线塑性变形）和低温（脆性）变形共存。这种非常高的温度梯度可以通过在岩浆连续扩张的背景下断层的偶发成核引起的结晶岩浆和热液流体之间突然和强烈的相互作用来解释。与远离断层的单调亚水平方向相比，火成岩层变得极其不规则，再加上仅限于断层带的热液蚀变增强，可能会改变同岩浆断层的物理性质（速度、密度）并增加反射率. 我们进一步推测，这些过程可以解释在我们的地震反射数据中观察到的下地壳倾角反射层的亮度。恩德比盆地和阿曼蛇绿岩的地震反射剖面都显示了深度同吸积构造作用的证据，以及原始水平熔岩流或原始垂直岩脉的系统旋转，早于岩浆活动停止。这表明岩浆扩张中心轴向带内普遍存在变形过程。早于岩浆活动停止。这表明岩浆扩张中心轴向带内普遍存在变形过程。早于岩浆活动停止。这表明岩浆扩张中心轴向带内普遍存在变形过程。