Data for: Effusive-explosive transitions of water-undersaturated magmas. The case study of Methana Volcano, South Aegean Arc

Data for: Methana Volcano, South Aegean Volcanic Arc

Bulk-rock major and trace elemental compositions: Rock-powders were dehumidified (24h, 110˚C), devolatilized (2h, 850˚C) and fused at 1100˚C after mixing with a Lithium-Metaborate flux. The disks were analyzed for major elements with a PANalytical AXIOS wave-length dispersive X-ray fluorescence spectrometer (WDXRF). The trace element analyses were performed on the same disks using laser-ablation inductively-coupled plasma mass spectrometry (LA-ICPMS). We used a 193 nm ArF-Excimer (Geolas) laser connected to a NexION 2000 ICP mass spectrometer. We ablated 3 points on each sample at a diameter of 100 μm for 40 seconds, with a repetition rate of 10 Hz. The 3 points were averaged for each sample. We used the SILLS data reduction software of Guillong et al. (2008), with NIST610 as a primary standard and the SiO2 content of each sample as internal standard. The basaltic andesite enclave data was acquired with a similar method by V. Dietrich in the 1980s’ and is integrated with the new dataset. For these particular analyses, a Philips PW 1404 sequential XRF spectrometer was used, at the Federal Institute for Material Testing in Dübendorf, Switzerland.

Groundmass glass major elemental compositions: The compositions of the matrix glasses were obtained by using an EDS-calibrated JEOL JSM-6390 LA Scanning Electron Microscope (SEM), equipped with a Thermo Fisher NORAN NSS7 EDS system with LaB6 filament, 30 mm2 silicon-drift detector and Faraday-cup for calibration. The main advantage of using this setup is the possibility of measuring compositions over wide areas (e.g. 50 μm diameter). This allows us to automatically average the microlite and interstitial glass compositions, which is paramount for estimating the pre-eruptive chemistry of the melts in lavas. Hence, we can automatically eliminate the late-stage differentiation effect of post-eruptive microlite crystallization.

Mineral compositions: Amphibole, pyroxenes and plagioclase were analyzed with a JEOL JXA-8200 Electron Probe Microanalyzer (EPMA) equipped with 5 spectrometers, using an energy of 15 kV and a 20 nA focused beam. The calibration was performed on mineral (crystalline) standards. We used a peak-background correction with measurement times varying between 20-40 s per peak. The calibration setup and measurement times were slightly different for plagioclase. For example, we preferred anorthite and albite standards for the calibration of major elements and we increased the measurement times up to 100 s per peak for the key trace elements (Fe, Mg, Ti). We acquired 9% of the plagioclase data with the calibrated SEM described earlier (using a focused beam), during microprobe downtime. The results are perfectly comparable with the EPMA dataset.

All analyses were performed in the laboratories of ETH Zürich, unless otherwise stated.

数据集描述：
Methana火山，南爱琴火山弧数据集

主要和微量元素的岩石成分：岩石粉末经24小时、110˚C的脱湿处理，2小时、850˚C的脱气处理，并与锂硼酸盐熔剂混合后在1100˚C下熔融。所得圆盘经PANalytical AXIOS波长色散X射线荧光光谱仪（WDXRF）分析主要元素。微量元素分析采用激光剥蚀电感耦合等离子体质谱法（LA-ICPMS）在同一圆盘上进行。使用193 nm ArF-Excimer（Geolas）激光器，连接到NexION 2000 ICP质谱仪。在每个样品上进行了3点剥蚀，直径为100 μm，持续40秒，重复频率为10 Hz。每个样品的3点数据被平均。使用了Guillong等人（2008年）的SILLS数据降低软件，以NIST610作为一级标准，并以每个样品的SiO2含量作为内部标准。玄武安山岩侵入体数据采用与V. Dietrich在20世纪80年代类似的方法获取，并与新数据集整合。对于这些特定的分析，使用了位于瑞士杜本多夫联邦材料测试研究所的Philips PW 1404顺序XRF光谱仪。

玻璃基质主要元素成分：通过配备Thermo Fisher NORAN NSS7 EDS系统（配备LaB6灯丝、30 mm2硅漂移检测器和法拉第杯用于校准）的JEOL JSM-6390激光扫描电子显微镜（SEM）获取基质玻璃的成分。使用EDS校准的该系统的主要优势在于能够测量较大区域（例如，直径为50 μm）的成分。这使我们能够自动平均微晶和间隙玻璃的成分，这对于估计熔岩中熔融体的先发破裂化学成分至关重要。因此，我们可以自动消除后发破裂微晶结晶的晚期分异效应。

矿物成分：使用配备5个光谱仪的JEOL JXA-8200电子探针微分析仪（EPMA）分析了角闪石、辉石和斜长石。使用15 kV的能量和20 nA的聚焦束进行校准。校准在矿物（晶体）标准上进行。我们使用峰值-背景校正，测量时间在每次峰值之间变化，介于20-40秒。对于斜长石，校准设置和测量时间略有不同。例如，我们更喜欢使用长石和斜长石标准对主要元素进行校准，并将关键微量元素（如Fe、Mg、Ti）的测量时间增加到每次峰值100秒。在微探针停机期间，使用前面描述的校准SEM（使用聚焦束）获取了斜长石数据的9%。结果与EPMA数据集完全可比。

所有分析均在苏黎世联邦理工学院（ETH Zürich）的实验室进行，除非另有说明。