Abstract The hinterland Western Domain of the Magallanes Fold-and-Thrust Belt (MFTB) between 52°-54°S is part of a poorly studied region of the southernmost Andean Cordillera. This domain consists of NNW-SSE trending tectonic slices of pre-Jurassic basement units and Late Jurassic-Early Cretaceous ophiolitic complexes and volcano-sedimentary successions of the Rocas Verdes Basin (RVB). New detrital zircon U Pb ages of metatuffs and metapsammopelites constrain episodes of Late Jurassic rift-related volcanism (ca. 160 Ma) followed by Early Cretaceous sedimentation (ca. 125 Ma) during the opening of the RVB. Shear bands developed in the RVB units further record the initial phases of the Andean Orogeny. The 30-km wide thrust stack located on top of the Eastern Tobifera Thrust consists of mylonitic metatuffs, metapelites and metabasalts with a NE-verging brittle-ductile S1* foliation. Phengite-bearing metatuffs commonly record pressure-temperature (P-T) conditions between ~3–6 kbar and ~ 210–460 °C, consistent with underthrusting of the RVB beneath the parautochthonous magmatic arc in the west. Peak metamorphic conditions of ~6 kbar and 460 °C are derived from a metapsammopelitic schist with textures of contact metamorphism overprinting early mylonitic structures (at least S1*). A back-arc quartz-diorite, intruded at ca. 83 Na, is in contact with the metapsammopelites and constrain the minimum age of deformation at deep crustal depths. Campanian-Maastrichtian (ca. 70–73 Ma) 40Ar/39Ar phengite dates from a mylonitic metapelite indicate the timing of thrusting and backthrusting during the initial uplift of the underthrusted crustal stack. These findings reveal a ~ 400 km along-strike connection of mylonite belts in a continent-verging thrust structure that became active at the onset of the Andean orogeny during the closure of the Rocas Verdes back-arc marginal basin.

中文翻译：

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Rocas Verdes 盆地的关闭和麦哲伦褶皱冲断带的早期构造变质演化，巴塔哥尼亚安第斯山脉南部（52-54°S）

摘要 位于 52°-54°S 之间的麦哲伦褶皱冲断带 (MFTB) 的腹地西部区域是安第斯山脉最南端研究不足的地区的一部分。该区域由侏罗纪前基底单元的 NNW-SSE 趋势构造切片和晚侏罗世-早白垩世蛇绿岩杂岩以及 Rocas Verdes 盆地 (RVB) 的火山-沉积层序组成。新的碎屑锆石 U Pb 年龄的变凝岩和变砂岩限制了晚侏罗世裂谷相关的火山活动（约 160 Ma），随后是早白垩世沉积（约 125 Ma）在 RVB 开放期间。在 RVB 单元中形成的剪切带进一步记录了安第斯造山运动的初始阶段。位于东 Tobifera 推力顶部的 30 公里宽的推力堆栈由糜棱岩变质岩组成，变泥质岩和变玄武岩具有接近 NE 的脆性韧性 S1* 叶理。含 Phengite 的变质岩通常记录约 3-6 kbar 和约 210-460 °C 之间的压力-温度 (PT) 条件，这与西部原地岩浆弧下方的 RVB 下冲相一致。~6 kbar 和 460 °C 的峰值变质条件来自具有接触变质纹理的变质片岩，其纹理覆盖早期糜棱岩结构（至少 S1*）。弧后石英闪长岩，侵入于约。83 Na, 与变砂岩接触, 限制了地壳深处变形的最小年龄。Campanian-Maastrichtian (ca. 70–73 Ma) 40Ar/39Ar phengite 来自糜棱质变泥质岩的年代，表明在下冲地壳叠层初始隆起期间冲刺和反冲的时间。