Abstract Fluids released within subduction zones affect many fundamental Earth processes, but very little is understood about processes of fluid transport within subduction zones and the chemistry of the fluids. Centimeter-scale variations in bulk-rock Li isotope compositions in subduction-related metamorphic rocks are observed associated with fluid-related features. The small spatial scales of these variations suggest very short duration fluid infiltration events – on the order of months to centuries. However, bulk-rock measurements record a time-integrated record, while in situ measurements in metamorphic porphyroblasts such as garnet have the potential to record individual events experienced by the rock. In this study, traverses across garnet in Franciscan eclogite and amphibolite were analyzed for Li isotopes in situ using SIMS to determine the potential for inferring the duration of metamorphic fluid flow and for deciphering fluid chemistry. The Li concentrations of these garnet crystals are very low, ∼5 µg/g. The measured range of δ7Li within some Franciscan garnets is 19‰, which falls well outside the uncertainty of the measurement (

中文翻译：

---

方济会榴辉岩和角闪岩石榴石中的锂同位素分带：俯冲相关流体的作用

摘要 俯冲带内释放的流体影响许多基本的地球过程，但对俯冲带内流体输送过程和流体化学知之甚少。观察到俯冲相关变质岩中大块岩石锂同位素组成的厘米级变化与流体相关特征有关。这些变化的小空间尺度表明流体渗透事件持续时间非常短——大约几个月到几个世纪。然而，大块岩石测量记录了时间积分记录，而变质斑岩（如石榴石）的原位测量有可能记录岩石经历的单个事件。在这项研究中，使用 SIMS 分析了穿越方济会榴辉岩和角闪岩中石榴石的原位锂同位素，以确定推断变质流体流动持续时间和破译流体化学的潜力。这些石榴石晶体的锂浓度非常低，约为 5 µg/g。一些方济会石榴石中δ7Li的测量范围为19‰，远远超出了测量的不确定度（