Abstract For the first time, the eastern flank at Cordon Santa Elena, within the Valle Hermoso district, has been mapped and described in detail. Based on key field observations, petrographic, geochemical and geochronological results, a new Miocene volcanic stratigraphy is proposed for this particular area. The Cordon del Burrero Group (Arroyo del Perdido, Puesto Gutierrez, Bolchiquito and Santa Elena Formations) has been defined for the ~18-13 Ma timespan, whereas the Huincan Formation has been constrained as younger than ~11 Ma. According to La/Yb ratios, Cordon del Burrero volcanics have been emplaced in a relatively thin crust compared to the Huincan dacites, suggesting that the main phase of crust thickening and tectonic deformation took place at ~12-11 Ma. The studies carried out at Cordon Santa Elena revealed a spatial and genetic relationship between the ~13 Ma dioritic subvolcanic pluton and a widespread calcic-sodic hydrothermal alteration. The areal distribution of the hydrothermal alteration shows a core of calcic-sodic alteration accompanied by propylitic alteration, cut by quartz-pyrite veins spatially associated with phyllic alteration and restricted potassic alteration. This hydrothermal system may be considered as the oldest pulse at this latitude.

中文翻译：

---

中新世岩浆弧的早期阶段以及安第斯山脉中南部 VALLE HERMOSO 的相关水热变化（35°07´S, 70°17´W）

摘要 第一次详细绘制和描述了 Valle Hermoso 区内 Cordon Santa Elena 的东翼。根据关键的野外观测、岩相学、地球化学和地质年代学结果，针对该特定地区提出了一种新的中新世火山地层。Cordon del Burrero 组（Arroyo del Perdido、Puesto Gutierrez、Bolchiquito 和 Santa Elena 地层）已被定义为~18-13 Ma 时间跨度，而 Huincan 组被限制为小于~11 Ma。根据 La/Yb 比率，与 Huincan 英安岩相比，Cordon del Burrero 火山岩位于相对较薄的地壳中，表明地壳增厚和构造变形的主要阶段发生在~12-11 Ma。在 Cordon Santa Elena 进行的研究揭示了~13 Ma 闪长岩亚火山岩体与广泛的钙钠热液蚀变之间的空间和成因关系。热液蚀变的区域分布显示钙钠蚀变的核心伴有青岩蚀变，被石英-黄铁矿脉切割，在空间上与叶状蚀变和限制性钾蚀变有关。这个热液系统可以被认为是这个纬度最古老的脉冲。