Geochemistry of tephra from sediment core IZN19-15 from Lake Iznik (NW Turkey)

The occurrence of previously geochemically identified tephra allowed refinement of the age-depth model by comparison with previously established volcanic eruption history (Roeser et al., 2012). Tephra layers were polished on thin sections and the glass shards were geochemically characterized using a JEOL JXA-8230 Electron Probe X-ray Micro Analyzer (EMPA; ISTerre Laboratory, University Grenoble Alpes) equipped with 5 wavelength dispersive spectrometers (WDS) and one energy dispersive spectrometer (EDS) detector. The measurements used the following conditions: 15 kV voltage, 2 nA beam current, and 5 to 7 µm beam size. For standardization, MPI-DING glasses (StHs6/80-G, GOR132-G) (http://georem.mpch-mainz.gwdg.de; Jochum et al., 2000), natural minerals, and synthetic oxides were used. Two glasses, Atho-G (http://georem.mpch-mainz.gwdg.de; Jochum et al., 2000) and KE-12 (Metrich & Rutherford, 1992), were analyzed together with the samples to verify analytical accuracy and to exclude the loss of alkalis. Analyses of glass shards yielding a total oxide sum less than 96% or suggesting mineral impurities were not included in this study. Analytical data were normalized to 100% total oxide values to enable comparison.

此前通过地球化学方法识别出的火山碎屑（tephra）的产出，可通过与已确立的火山喷发历史（Roeser等人，2012年）进行比对，优化年龄-深度模型。研究对火山碎屑层的薄片进行抛光处理，并使用配备5台波长色散光谱仪（WDS）和1台能量色散光谱仪（EDS）探测器的JEOL JXA-8230型电子探针X射线显微分析仪（EMPA；格勒诺布尔阿尔卑斯大学ISTerre实验室）对玻璃碎屑开展地球化学表征。测试采用以下参数：加速电压15 kV，束流2 nA，束斑尺寸5~7 µm。标准化过程采用了MPI-DING玻璃标样（StHs6/80-G、GOR132-G，http://georem.mpch-mainz.gwdg.de；Jochum等人，2000年）、天然矿物及合成氧化物。另有两款玻璃标样Atho-G（http://georem.mpch-mainz.gwdg.de；Jochum等人，2000年）与KE-12（Metrich & Rutherford，1992年），与样品一同开展分析以验证分析精度，并排查碱金属流失情况。总氧化物总量低于96%或存在矿物杂质迹象的玻璃碎屑分析结果，未纳入本研究。为便于比对，所有分析数据均被归一化至总氧化物含量100%。