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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Stratigraphy And Significance Of Brown Tuffs On The Aeolian Islands (southern Italy)
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Stratigraphy And Significance Of Brown Tuffs On The Aeolian Islands (southern Italy)

机译：风沙群岛（意大利南部）上的棕色凝灰岩的地层学及其意义

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摘要

Brown Tuffs (BT) are volcanidastic ash deposits prominently represented in the stratigraphic profiles of all the Aeolian Islands (and Capo Milazzo on the northern coast of Sicily). Detailed stratigraphy and tephrochronology together with available radiometric ages suggest that they were emplaced over a long time interval spanning from the end of the last interglacial period (ca. 80 ka BP) up to 4-5 ka BP (age of the overlying Punte Nere pyrodastic products on Vulcano). The most complete BT succession is documented on Lipari where 14 distinct and successive units are subdivided by the interbedding of widespread tephra layers, local volcanic products, paleosols and epidastic deposits and the occurrence of local erosive surfaces. Inter-island occurrence of Ischia-Tephra (a widely known tephra layer in the Aeolian archipelago dated at 56 ka BP) and Monte Guardia pyrodastics from Lipari (dated at 22-20 ka BP) subdivides the BT succession in Upper (UBT), Intermediate (IBT) and Lower BT units (LBT), which can be correlated at regional level: the LBT was emplaced between 80 and 56 ka BP, the IBT between 56 and 22 ka BP and the UBT between 20 and 4-5 ka BP. On the basis of stratigraphy, similarity in lithology and textural features, morphology of glass fragments, composition and consistency of thickness and grain-size variations, UBT units correlate with Piano Grotte dei Rossi tuffs on Vulcano island. They were generated by pulsating hydromagmatic explosive activity giving rise to pyrodastic density currents spreading laterally from a source located inside the La Fossa caldera on Vulcano island. Composition is in agreement with this hypothesis since UBT compositional features match those of Vulcano magmas erupted in that period. The effect of co-ignimbrite ash clouds (or associated fallout processes from sustained eruptive columns) is seen to explain the presence of UBT in areas further away from the suggested source (e.g. Salina and Lipari islands and Capo Milazzo). The origin of UBT exposed on Panarea island is still a matter of debate, due to contrasting compositional data. Due to large uniformity of lithological, textural and componentry characters with respect to the UBT, the lower portions of the BT succession (LBT-IBT) are considered to be the result of recurrent, large scale hydromagmatic eruptions of similar type. Moreover, for the IBT units, the correlation with Monte Molineddo 3 pyrodastics of Vulcano island (on the basis of lithological, compositional and stratigraphic matching) again suggests source(s) related to the Vulcano plumbing system and located within the La Fossa Caldera.
机译：布朗凝灰岩（BT）是火山灰沉积物，在所有的伊奥利亚群岛（以及西西里岛北部海岸的卡波米拉佐）的地层剖面中都有明显的表现。详细的地层学和年代年代学以及可用的放射年龄表明，它们被放置在从最后一个冰期结束（约80 ka BP）到4-5 ka BP（上覆蓬塔尼雷火山岩时代）的很长一段时间内Vulcano上的产品）。在Lipari上记录了最完整的BT演替，其中14个不同的连续单元被广泛的特非拉层，局部火山产物，古土壤和表层沉积物的交叠和局部侵蚀表面的出现所细分。 Ischia-Tephra（在伊奥里亚群岛中一个广为人知的tephra层，日期为56 ka BP）在岛屿间的发生和Lipari的Monte Guardia火山岩（日期为22-20 ka BP）细分了上层（UBT）的BT演替，中级（IBT）和较低的BT单位（LBT），可以在区域级别进行关联：LBT介于80和56 ka BP之间，IBT介于56和22 ka BP之间，UBT介于20和4-5 ka BP之间。根据地层学，岩性和质地特征的相似性，玻璃碎片的形态，厚度和粒度变化的成分和一致性，UBT单位与伏尔卡诺岛上的Piano Grotte dei Rossi凝灰岩相关。它们是由脉动的岩浆爆炸活动产生的，从而产生了从位于Vulcano岛的La Fossa破火山口内部的震源横向扩散的焦岩密度流。组成与该假设一致，因为UBT的组成特征与该时期爆发的Vulcano岩浆的特征相匹配。共燃灰云的影响（或持续喷发柱产生的相关沉降过程）被认为是在距建议来源更远的地区（例如萨利纳和利帕里岛和米开朗基罗）存在UBT的原因。由于成分数据的差异，在Panarea岛上暴露的UBT的起源仍然是一个争论的问题。由于相对于UBT而言，岩性，构造和成分特征的高度统一，因此BT演替的下部（LBT-IBT）被认为是类似类型的周期性大规模水磁爆发的结果。此外，对于IBT单元，与Vulcano岛的Monte Molineddo 3火山岩的相关性（基于岩性，成分和地层匹配）再次表明与Vulcano管道系统有关且位于La Fossa破火山口内的源。

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