Field observations within the Atg-serpentinite domain of the subducted ultramafic massif from Cerro del Almirez (SE Spain) reveal the existence of two generations of abundant olivine-rich veins formed as open, mixed mode and shear fractures during prograde metamorphism. Type I veins were synchronous with the development of the serpentinite main foliation (S₁) and shearing, whereas Type II veins post-date the S₁ surfaces. These structural relationships indicate that, while the Atg-serpentinites underwent ductile plastic deformation at temperatures of 450°-600 °C and pressures of 0.7–1.7 GPa, they also experienced punctuated brittle behaviour events. The brittle fractures were most likely due to fluid overpressures formed by release of H₂O during the brucite breakdown reaction for the case of Type I veins (2 vol % H₂O) and due to a combination of minor dehydration reactions related to continuous compositional and structural changes in antigorite (0.3 vol % H₂O) for Type II veins. Type II olivine-rich veins were formed by brittle failure in a well-defined paleo-stress field and were not significantly deformed after their formation. Comparison of the principal paleo-stress orientation inferred from Type II veins with those formed at peak metamorphic conditions in the ultramafic rocks at Cerro del Almirez shows a relative switch in the orientation of the maximum and minimum principal paleo-stress axes. These relative changes can be attributed to the cyclic evolution of shear stress, fluid pressure and fault-fracture permeability allowing for stress reversal.

来自 Cerro del Almirez（西班牙东南部）的俯冲超镁铁质地块的 Atg-蛇纹岩域内的现场观测揭示了在前进变质作用过程中以开放、混合模式和剪切裂缝形式形成的两代丰富的富含橄榄石的矿脉的存在。_{I型脉与蛇纹岩主叶理（S 1} ）和剪切的发展同步，而II型脉在S ₁表面之后。这些结构关系表明，虽然 Atg 蛇纹岩在 450°-600°C 的温度和 0.7-1.7 GPa 的压力下经历了韧性塑性变形，但它们也经历了断断续续的脆性行为事件。脆性裂缝很可能是由于释放 H _{2形成的流体超压}水镁石分解反应过程中的 O 对于 I 型矿脉 (2 vol% H ₂ O) 和由于与叶蛇纹石的连续组成和结构变化相关的轻微脱水反应的组合 (0.3 vol% H ₂O) 用于 II 型静脉。II型富含橄榄石的矿脉是在明确的古应力场中脆性破坏形成的，形成后没有明显变形。将 II 型矿脉推断的主古应力方向与 Cerro del Almirez 超镁铁质岩峰值变质条件下形成的主古应力方向进行比较，表明最大和最小主古应力轴方向的相对转换。这些相对变化可归因于剪切应力、流体压力和断层-裂缝渗透率的循环演化，允许应力反转。