Into a new caldera cycle: volcanic and magmatic evolution of Santorini volcano after the Late Bronze Age eruption

从2022年12月到2023年2月，国际海洋发现计划的第398次探险将在希腊爱琴海的克里斯蒂亚纳-圣托里尼-科伦博(CSK)火山田进行钻探活动，这是一个特别危险的地区，因为它的火山过去曾多次爆发。拟议的项目重点是圣托里尼火山，这是CSK火山场最大的火山中心，也是一座标志性火山，因为它在青铜时代晚期众所周知的喷发，也被称为米诺安喷发。这次喷发的威力如此之大，以至于导致了火山的坍塌，形成了被洪水淹没的火山口，周围是塞拉岛、瑟拉岛和阿斯佩罗尼斯岛，而帕莱亚岛和内亚卡美尼岛--卡美尼火山的表面表现--位于中心。我们今天看到，青铜时代晚期的喷发并不是圣托里尼唯一形成火山口的喷发。在过去的36万年中，圣托里尼上总共存在至少四个火山口，这表明了形成火山口的喷发的旋回性。以前的研究使我们在理解岩浆聚集和这些大规模形成火山口的时间尺度方面取得了相当大的进展。相比之下，从火山口形成到火山口后活动的过渡--或在火山口周期开始时重新爆发的活动--在很大程度上仍未得到研究。就目前的破火山口周期而言，这是因为这一活动的火山产物不暴露在陆地上，而是位于圣托里尼火山口内的海底之下，因此需要进行离岸研究。拟议的项目旨在调查圣托里尼火山在青铜时代晚期形成火山口喷发后最新的破火山口周期的开始，利用来自圣托里尼火山口的两个探险398钻探点的样本，这首次提供了从卡梅尼火山的后青铜时代火山活动中恢复以前无法获得的火山产品的机会。特别是，这项研究将描述(1)喷发活动，(2)喷发的方式和频率，(3)岩浆储存条件，(4)在圣托里尼火山当前火山口旋回开始和早期阶段，在火山内部深处发生的岩浆过程及其时间尺度。项目目标将通过宏观和微观钻芯描述，样品的结构分析，通过表征早期(主要是海底)卡米尼火山喷发的岩浆(S)的地球化学成分、矿物含量和其他成分，使用微结构分析技术来实现，应用地球化学和岩石学工具以及元素扩散计时法对火山喷发产物中的主要矿物之一辉石进行了研究，其结果将用于建立从破火山口形成向破火山口后火山活动过渡以及圣托里尼火山新的破火山口周期开始时岩浆作用及其时间尺度的概念框架。

From December 2022 to February 2023, Expedition 398 of the International Ocean Discovery Program will carry out a drilling campaign in the Christiana-Santorini-Kolumbo (CSK) volcanic field in the Aegean Sea of Greece, a particularly hazardous area because its volcanoes have produced many and highly explosive eruptions in the past.The proposed project focuses on Santorini, the largest volcanic centre of the CSK volcanic field and an iconic volcano because of its well-known eruption in the Late Bronze Age, also known as the Minoan eruption. This eruption was so powerful that it led to the collapse of the volcano, forming the flooded caldera, surrounded by the islands of Thera, Therasia and Aspronisi, and with the islands of Palaea and Nea Kameni - the surface expression of the Kameni volcano - in the centre, we see today.The Late Bronze Age eruption was not the only caldera-forming eruption on Santorini. In total, at least four calderas existed on Santorini in the past ~ 360 thousand years, showing the cyclicity of caldera-forming eruptions.Previous research led to considerable progress in our understanding of the assembly of magma and the timescales involved in the lead-up of these large-magnitude, caldera-forming eruptions at Santorini. By contrast, the transition from caldera-forming to post-caldera activity - or the renewed eruptive activity at the beginning of a caldera cycle - has remained largely unstudied. In case of the current caldera cycle, this is because the volcanic products from this activity are not exposed on land but lie beneath the seafloor within Santorini's caldera, therefore requiring research to move offshore.The proposed project aims to investigate the onset of the latest caldera cycle of Santorini following the caldera-forming eruption in the Late Bronze Age, using samples from two Expedition 398 drill sites in the Santorini caldera, which, for the first time, provide the opportunity to recover previously inaccessible volcanic products from post-Late-Bronze-Age volcanic activity of the Kameni volcano. In particular, the research will characterise (1) the eruptive activity, (2) the styles and frequency of eruptions, (3) the magma storage conditions, and (4) the magmatic processes that occur at depth inside the volcano and their timescales, at the onset and during the early stages of the current caldera cycle of Santorini volcano.The project aims will be achieved by macroscopic and microscopic drill core description, textural analysis of samples, and by characterising the geochemical composition, mineral content and other components of the magma(s) that fed the early, mainly submarine eruptions of the Kameni volcano, using a combination micro-textural analytical techniques, geochemical and petrological tools, and elemental diffusion chronometry applied to pyroxene, one of the main minerals in the eruptive products.The results will then be used to develop a conceptual framework for the magmatic processes and their timescales at the transition from caldera-forming to post-caldera volcanic activity and the beginning of a new caldera cycle at Santorini volcano.