De Campos_et_al._Bauxite_Espinhaço

Abstract: Bauxites evolved from unusual parent rocks in quartzite-dominated landscapes have not been previously reported. At the Southern Espinhaço Range, Minas Gerais, Brazil, bauxitic weathering profiles are found in a unique geomorphological-lithological-climatic setting. Resistant quartzites acted as a barrier against erosion and facilitated deep weathering of hematite-phyllite units. The long-term exposure of the hematite-phyllites under alternating wet and dry tropical climates favored widespread bauxitization. Here we investigate the geochemical, mineralogical, geochronological and micromorphological signatures of scaffolded bauxites in order to reconstruct their evolutionary history. Our data suggests that recurrent aluminum and iron mobilization within the profiles were mainly driven by mineral dissolution-reprecipitation mediated by bioturbation and the influx of vegetation-derived organic species. (U–Th)/He geochronology of Al-goethite reveals bauxitization started at least since the Lower Miocene, with important intensification of weathering in the Upper Miocene and Lower Pleistocene. The adjacent resilient quartzites acted as scaffolds for bauxitization and supported the preservation of ancient landscape features. The evolutionary history of Southern Espinhaço Range bauxites suggests a new model of bauxitization in ancient landsurfaces.

Table 2: Geochemistry of profiles
Table 3: Mineral quantification obtained by Rietveld refinement
Table 4: (U-Th)/He geochronology
Supplementary Data 1: Chemical Analysis of hematitic-phyllite
Supplementary Data 2: Electron Microprobe Thin Sections
Supplementary Data 3: Electron Microprobe Goethites

摘要：铝土矿源于石英岩占主导地位的地貌中的异常母岩，此前尚未有相关报道。在巴西米纳斯吉拉斯州的南方埃斯皮纳索山脉，我们发现铝土矿化风化剖面位于独特的地貌-岩性-气候环境中。抵抗侵蚀的石英岩充当了侵蚀的屏障，并促进了赤铁矿-片麻岩单元的深度风化。在交替的湿热带气候条件下，赤铁矿-片麻岩的长期暴露促进了广泛的铝土矿化。本研究旨在通过分析支架型铝土矿的地球化学、矿物学、地质年代学和显微形态特征，以重建其演化历史。我们的数据表明，剖面中铝和铁的周期性迁移主要由生物扰动和植被衍生有机物种的涌入所介导的矿物溶解-再沉淀作用所驱动。（U–Th）/He地质年代学揭示铝针铁矿的铝土矿化至少始于中新世早期，上新世和更新世早期发生了重要的风化强度增强。相邻的耐侵蚀石英岩作为铝土矿化的支架，并支持了古老景观特征的保存。南方埃斯皮纳索山脉铝土矿的演化历史暗示了一种在古老地表上的铝土矿化新模型。

表2：剖面地球化学

表3：通过Rietveld精修获得的矿物定量分析

表4：（U–Th）/He地质年代学

补充数据1：赤铁矿-片麻岩的化学分析

补充数据2：电子探针薄片分析

补充数据3：电子探针针铁矿