Abstract The Brown Tuffs (BT) are widespread reddish-brown to grey, ash-rich pyroclastic deposits recognized in the stratigraphic sequences of the Aeolian Islands and Capo Millazzo peninsula (Sicily) that span the last 80 ky. They have very homogeneous lithological, textural and sedimentological features which make it difficult to reliably correlate units on the islands to proximal units in the source areas. Here we carefully re-interpret the stratigraphic profiles of the BT on Vulcano and Lipari where the deposits are thickest and present the most complete succession. The investigation is based on a large dataset of major and minor element geochemistry of juvenile glass components for the majority of the recognized BT depositional units, whilst also providing new radiocarbon ages. The distinctive chemical groupings observed within the glass analyses, both temporally and spatially, allow us to fingerprint the three main stratigraphically defined macro-units in which the BT succession can be sub-divided using prominent tephra marker beds, the Ischia Tephra (Monte Epomeo Green Tuff; 56 ky) and Monte Guardia pyroclastics from Lipari (herein radiocarbon dated to 27–26 ky). The Lower (80–56 ky; LBT), Intermediate (56–27 ky; IBT) and Upper BT (here dated at 24–6 ky; UBT) macro-units display K-series volcanic glasses ranging from basaltic trachy-andesites, through trachy-andesites, to more evolved trachytes, all consistent with an origin on Vulcano. The UBT are clearly distinguished from the lower macro units by their higher-SiO2 trachy-andesite to trachytic glasses, which extend to noticeably lower TiO2, CaO and MgO contents. These features make it possible to re-define the geochemical-evolutionary boundary between IBT and UBT as corresponding to the 24 ky Spiaggia Lunga scoria bed on Vulcano, which is stratigraphically higher (and younger) than the previous boundary marker (Monte Guardia). The glass compositions of the LBT, IBT and UBT are used to: (1) assess links to known proximal eruption units outcropping on Vulcano; (2) validate medial-distal BT occurrences across the Aeolian archipelago (Salina, Filicudi and Panarea) and on Capo Millazzo; (3) confirm that the BT are responsible for distal volcanic ash layers preserved in Central Mediterranean marine sedimentary archives. Interestingly, the glass compositions of the UBT are very similar to those of the Punte Nere unit, the earliest pyroclastic products erupted from the currently active La Fossa cone on Vulcano, indicating the corresponding magmatic system has likely erupted similar melts and products over the last 24 ky and thus extending its life cycle. Such information is crucial for evaluating the long-term eruption scenarios underpinning hazard assessment of the La Fossa caldera magmatic system.

中文翻译：

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Vulcano（意大利）的频繁活动跨越过去 80 ky：来自棕色凝灰岩化学地层学的新见解

摘要 棕色凝灰岩 (BT) 是广泛分布的红棕色至灰色、富含灰烬的火山碎屑沉积物，在伊奥利亚群岛和 Capo Millazzo 半岛（西西里岛）的地层序列中发现，跨越了过去 80 公里。它们具有非常均匀的岩性、构造和沉积学特征，因此很难将岛上的单元与源区的邻近单元可靠地关联起来。在这里，我们仔细地重新解释了 Vulcano 和 Lipari 上 BT 的地层剖面，那里的沉积物最厚，序列最完整。该调查基于大多数公认的 BT 沉积单元的幼年玻璃成分的主要和次要元素地球化学的大型数据集，同时还提供了新的放射性碳年龄。在玻璃分析中观察到的独特的化学分组，在时间和空间上，使我们能够对三个主要地层定义的宏观单元进行指纹识别，其中 BT 序列可以使用突出的 tephra 标记床细分，Ischia Tephra (Monte Epomeo Green凝灰岩；56 ky）和来自利帕里的 Monte Guardia 火山碎屑（此处放射性碳的年代为 27-26 ky）。下层（80–56 ky；LBT）、中层（56–27 ky；IBT）和上层 BT（此处日期为 24–6 ky；UBT）宏观单元显示 K 系列火山玻璃，范围从玄武质粗安山岩、通过粗面安山岩，到更进化的粗面岩，所有这些都与火山岩的起源一致。UBT 与较低的宏观单元的明显区别在于它们的高 SiO2 粗面安山岩到粗面玻璃，其延伸到显着较低的 TiO2、CaO 和 MgO 含量。这些特征使得重新定义 IBT 和 UBT 之间的地球化学演化边界成为可能，以对应于 Vulcano 上的 24 ky Spiaggia Lunga 火山渣层，该层在地层上高于（且更年轻）于之前的边界标记（Monte Guardia）。LBT、IBT 和 UBT 的玻璃成分用于：(1) 评估与在 Vulcano 上露头的已知近端喷发单元的联系；(2) 验证伊奥利亚群岛（Salina、Filicudi 和 Panarea）和 Capo Millazzo 上的中远 BT 事件；(3) 确认 BT 负责保存在地中海中部海洋沉积档案中的远端火山灰层。有趣的是，UBT 的玻璃成分与 Punte Nere 单元的玻璃成分非常相似，这是从目前活跃的 Vulcano 上活跃的 La Fossa 锥体喷发的最早的火山碎屑产物，表明相应的岩浆系统可能在过去 24 ky 内喷发了类似的熔体和产物，从而延长了其生命周期。这些信息对于评估支撑拉福萨火山口岩浆系统危险评估的长期喷发情景至关重要。