Systematic variations in the eruptive history of the Christiana-Santorini-Kolumbo volcanic field (Greece) - The IODP Expedition 398 tephra time series and its implications

在IODP第398次考察期间，目标是研究希腊岛弧中部的火山记录，记录火山活动/岩浆活动、地壳构造和海平面之间的联系和反馈，并调查海底浅层硅岩浆喷发的过程和产物。重建南部爱琴海的下沉历史，寻找圣托里尼火山口内外的深层生命，是额外的目标。探险队钻探了最初提议的10个地点，加上探险期间要求的另外两个地点。在圣托里尼火山口外，钻探穿透了拥有克里斯蒂亚纳-圣托里尼-科伦坡火山场的地壳裂谷系统的厚盆地填塞，发现了许多浮石和火山灰层，其中一些是陆地上已知的，而另一些则是迄今为止未知的，将该地区火山活动的开始推迟到更新世早期甚至上新世。大量的物质流失进入盆地，伴随着非常高的沉积速率，也被记录下来。这些盆地遗址为盆地的地震地层学奠定了基础，并为解开火山活动与地壳裂谷脉冲之间的关系开辟了道路。盆地边缘的两个浓缩层序站点在主要由生物地层学提供的详细年龄-深度限制范围内对许多火山层进行了采样。圣托里尼火山口的钻探深度达到了120亿立方英尺，获得了Kameni群岛历史的详细记录。Exp. 398的Tephra沉积物与在陆地上发现的tephras相补充，提供了独特的机会来调查和比较位于南欧中心的Christiana-Santorini-Kolumbo火山场的高爆炸性火山活动的历史，包括我们附近最著名和最活跃的火山之一。因此，本项目的重点是在岩心中发现的上新世和第四纪高爆炸性喷发产生的~1200个火山层。将利用地球化学、岩石学和火山学方法对火山泥和沉积物进行表征，定量和定性地解密其物源和喷发演替。此外，由于研究大型火山喷发过程、震级和频率的时空变化需要稳健的年龄模型，因此，绝对年龄定年将改进和确认现有的年龄模型。在此建立的成分数据和喷发时间序列将作为解决复发率和周期性问题的基础，并将其与构造和海平面变化等外部控制机制进行比较。回收的沉积物还将有助于研究爱琴海盆地中与火山碎屑输入有关的沉积物组成的时间和定量特征，并回答如何将其与盆地演化联系起来的问题。

During IODP Expeditions 398 the objectives were to study the volcanic record of the central Hellenic island arc to document the links and feedbacks between volcanism/magmatism, crustal tectonics and sea level, and to investigate the processes and products of shallow submarine eruptions of silicic magma. Reconstructing the subsidence history of the southern Aegean Sea, and searching for deep life inside and outside of Santorini caldera, were additional objectives. The expedition drilled ten sites originally proposed, plus two extra sites that were requested during the expedition. Outside of Santorini caldera, drilling penetrated the thick basin fills of the crustal rift system hosting the Christiana-Santorini-Kolumbo volcanic field, identifying numerous pumice and ash layers, some known from onland and others hitherto unknown, pushing back the onset of volcanism in the area into the early Pleistocene or even Pliocene. Huge events of mass wasting into the basins, accompanied by very high sedimentation rates, were also documented. These basin sites served to groundtruth the seismic stratigraphy of the basins and to open the way to unravelling relationships between volcanic activity and crustal rift pulses. Two sites of condensed sequences on the basin margins served to sample many volcanic layers within the detailed age-depth constraints provided mainly by biostratigraphy. Drilling inside Santorini caldera penetrated to ~120 mbsf and yielded a detailed tephra record of the history of the Kameni islands. Tephra deposits from Exp. 398 complemented by tephras found on land provide the unique opportunity to investigate and compare the history of highly explosive volcanic activity of the Christiana-Santorini-Kolumbo volcanic field in the heart of Southern Europe, including one of the most famous and most active volcanoes in our neighborhood. This project focuses therefore on the ~1200 volcanic horizons derived from highly explosive eruptions during the Pliocene and Quaternary and found in the cores. Geochemical, petrological and volcanological approaches for tephra and sediment characterization will be used to quantitatively and qualitatively decrypt their provenance and the eruption succession. Additionally, absolute age dating will improve and confirm the existing age models since robust age models are needed to study the temporal and spatial changes in eruption processes, magnitudes and frequencies of large volcanic eruptions. The herewith-established compositional data and eruptive time series will serve as base to address questions regarding recurrence rates and cyclicities, and compare them with external controlling mechanism like tectonics and sea level changes. Recovered sediments will also facilitate to investigate the temporal and quantitative characterization of the sediment composition in the basins of the Aegean Sea in relation to the volcaniclastic input and answer the question how this may be connected to the basin evolution.