Crustal architecture at slow-spreading oceanic ridges results from complex interactions between magmatism, hydrothermalism, and tectonics. IODP Hole U1473A was drilled during Expeditions 360 and 362T at the summit of the Atlantis Bank, a gabbroic massif exhumed at the Southwest Indian Ridge. In this study, we identify and quantify plastic deformation processes in gabbroic lithologies and active slip systems in plagioclase from 115 microstructural domains throughout Hole U1473A. We describe deformed zones using petrographic observations and electron backscattered diffraction analyses made all along the core. Ductile deformation is widespread, and in places strongly localized in mylonitic and ultramylonitic zones. Plagioclase represents ∼60% of rock's volume and is the dominant phase accommodating deformation in samples. It shows strong dynamic recrystallization accommodated by subgrain rotation in the dislocation creep regime, forming a fine-grained matrix. Electron backscattered diffraction analyses reveal weak to moderate crystallographic preferred orientations of plagioclase as a result of plastic deformation and strain localization, producing a fabric characterized by (010) parallel to the foliation plane and [100] parallel to the lineation. The fabric strength is first increasing from slightly deformed lithologies to mylonites before decreasing significantly in ultramylonites. This could be explained by orientation scattering after recrystallization, and a change of active slip systems. Subsequent granular flow has likely occurred in some samples. A detailed investigation of intracrystalline misorientations measured at plagioclase subgrain boundaries reveals the activity of four dominant slip systems: [001](010), [100](001), ½[110](001), and ½[](001). These slip systems reflect decreasing temperatures during CPO development and subgrain wall formation.

中文翻译：

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在缓慢扩张的海脊处增生的大洋辉长岩中斜长石的塑性变形（U1473A 孔，亚特兰蒂斯银行，西南印度海脊）

缓慢扩张的洋脊的地壳结构是岩浆作用、热液作用和构造之间复杂相互作用的结果。IODP 孔 U1473A 是在远征 360 和 362T 期间在亚特兰蒂斯银行山顶钻探的，这是在西南印度洋脊挖掘出的辉长岩地块。在这项研究中，我们从整个 U1473A 孔的 115 个微结构域中识别和量化斜长石中辉长岩岩性和活动滑移系统的塑性变形过程。我们使用沿岩心进行的岩相观察和电子背散射衍射分析来描述变形区域。延性变形很普遍，并且在强烈集中在糜棱岩和超糜棱岩带的地方。斜长石约占岩石体积的 60%，是样品中适应变形的主要相。它显示出由位错蠕变状态中的亚晶旋转所容纳的强烈动态再结晶，形成细晶基体。电子背散射衍射分析显示，由于塑性变形和应变局部化，斜长石具有弱到中等的晶体择优取向，产生的织物特征为 (010) 平行于叶面，[100] 平行于线纹。织物强度首先从轻微变形的岩性增加到糜棱岩，然后在超糜棱岩中显着降低。这可以通过再结晶后的取向散射和活性滑移系统的变化来解释。在一些样品中可能发生了随后的颗粒流。](001)。这些滑移系统反映了 CPO 发育和亚晶壁形成过程中温度的降低。