This study aims to decipher the spatio-temporal chronology of tectonic processes leading to ocean widening at a slow-spreading oceanic ridge axis, involving mantle and gabbro exhumation and volcanism. Structural and petrographic studies of deformed lithologies were performed on peridotites, gabbros and basalts from the Chenaillet ophiolite (Alps, France). Inversion of fault-slip data reveals N030° and N060° σ₃ paleostress trends. The dominant N030° extension, is consistent with the NNW-SSE direction of volcano feeder-dykes and ENE dipping low-angle normal faults crosscutting the mantle. The N060° extension accords with the mantle dome structure formation to the east. Low-angle faults intersect roots of volcanoes that thus belong to their hanging walls. Hydrothermalism is contemporaneous with or postdates low-angle faulting. A feeder-dyke major virgation northwards, synchronous with eruptions, suggests a dextral transform fault consistent with a N120° σ₂. Oceanic expansion mechanisms are clarified. At the surface, magma eruption occurs along on-axis active high-angle normal faults, their footwalls enabling mantle exhumation. At depth, off-axis high-angle faults become low-angle faults as they spread at shallow level. With westward drift of the lithosphere, the uppermost levels of the ridge shift westward faster, such that volcanoes move to an off-axis position while their roots are cut by low-angle faults.

本研究旨在破译在缓慢扩张的洋脊轴上导致海洋扩张的构造过程的时空年代学，包括地幔和辉长岩的剥露和火山作用。对来自 Chenaillet 蛇绿岩（法国阿尔卑斯山）的橄榄岩、辉长岩和玄武岩进行了变形岩性的结构和岩相研究。断层滑动数据反演显示 N030°和 N060° σ ₃古压力趋势。占主导地位的 N030°伸展与火山馈给岩脉和 ENE 倾角低角度正断层横切地幔的 NNW-SSE 方向一致。N060°向东延伸符合地幔穹窿构造的形成。低角度断层与火山的根部相交，因此属于它们的上盘。热液作用与低角度断层作用同时发生或发生。与火山喷发同步的向北的馈线-堤坝主要环流表明存在与 N120° σ ₂一致的右旋变换断层. 阐明了海洋扩张机制。在地表，岩浆喷发沿轴上活动的高角度正断层发生，它们的下盘使地幔剥露。在深部，离轴高角度断层在浅层扩展时变成低角度断层。随着岩石圈的西移，山脊最上层向西移动的速度加快，使得火山在其根部被低角度断层切割的情况下移动到离轴位置。