The Punta del Cobre district near Copiapó is a center of iron oxide-copper–gold (IOCG) mineralization spatially and temporally associated with regional sodic-calcic hydrothermal alteration, the Atacama fault system (AFS), and two phases of Early Cretaceous magmatism. Here, we investigate the spatiotemporal and geochemical relationships between magmatism, ductile deformation, and hydrothermal alteration along the ~ 200 to 300-m-thick steeply NW-dipping Sierra Chicharra shear zone, interpreted to be the major strand of the AFS. Mylonitic fabrics and oblique sinistral-reverse kinematic indicators together record coaxial flattening in a transpressional regime. Deformation on the AFS took place before, during, and after intrusion of the synkinematic Sierra Chicharra quartz diorite of the Coastal Cordillera arc at ~ 122 Ma and terminated before intrusion of the unstrained ~ 114 Ma Sierra Atacama diorite of the Copiapó batholith. Geochemical data show that the Copiapó batholith was more mafic and more K-rich than the calc-alkaline Coastal Cordillera arc. This time period thus overlaps IOCG mineralization in the Punta del Cobre district (~ 120 to 110 Ma). Multiple phases of sodic-calcic alteration in and around the AFS shear zone are recognized. Textures of altered rock in the shear zone show both synkinematic assemblages and post-kinematic hydrothermal oligoclase. A ~ 775-m-long andradite vein that cuts the shear zone formed broadly at the end of magmatism in the district (~ 95 Ma). Oxygen isotope ratios from the vein indicate that hydrothermal fluids were likely magmatically derived. Together, this work shows the AFS-related shear zone and nearby IOCG mineralization developed in a regional transpressional regime produced by SE-directed oblique convergence across a NE-striking shear zone. IOCG-related magmatic-hydrothermal fluids exploited this transcrustal shear zone to produce multiple episodes of regional sodic-calcic alteration formed from fluids exsolved from magmas or driven by the heat of the Coastal Cordillera arc and Copiapó batholith.

科皮亚波附近的 Punta del Cobre 地区是氧化铁-铜-金 (IOCG) 矿化中心，在空间和时间上与区域性钠钙热液蚀变、阿塔卡马断层系统 (AFS) 和早白垩世岩浆作用的两个阶段相关。在这里，我们研究了约 200 至 300 米厚的西北倾斜 Sierra Chicharra 剪切带（被解释为 AFS 的主线）沿线的岩浆作用、延性变形和热液蚀变之间的时空和地球化学关系。糜棱岩组构和斜左旋反向运动学指标共同记录了压裂状态下的同轴扁平化。 AFS 的变形发生在海岸科迪勒拉弧的同运动 Sierra Chicharra 石英闪长岩侵入之前、期间和之后，时间约为 122 Ma，并在科皮亚波基岩的无应变 ~ 114 Ma Sierra Atacama 闪长岩侵入之前终止。地球化学数据显示，科皮亚波基岩比钙碱性沿海科迪勒拉弧更镁铁质、更富钾。因此，这一时期与 Punta del Cobre 地区的 IOCG 矿化重叠（约 120 至 110 Ma）。认识到 AFS 剪切带内及其周围的钠钙蚀变的多个阶段。剪切带蚀变岩石的结构显示出同运动组合和后运动热液寡长石。一条约 775 米长的钙铁矿脉，切割了该地区岩浆作用末期广泛形成的剪切带（约 95 Ma）。矿脉的氧同位素比率表明热液流体可能源自岩浆。总之，这项工作显示了与 AFS 相关的剪切带和附近的 IOCG 矿化是在区域压扭区域中发育的，该区域压压区域是由横跨 NE 走向剪切带的 SE 定向倾斜会聚产生的。与 IOCG 相关的岩浆热液流体利用这种穿地壳剪切带，产生了多次区域性钠钙蚀变，这些蚀变是由岩浆排出的流体形成的，或者是由沿海科迪勒拉弧和科皮亚波基岩的热量驱动的。