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Effect of water on δ18O in zircon
Chemical Geology ( IF 3.6 ) Pub Date : 2021-04-18 , DOI: 10.1016/j.chemgeo.2021.120243
Janne Liebmann , Christopher J. Spencer , Christopher L. Kirkland , Xiao-Ping Xia , Julien Bourdet

The mineral zircon is stable across a wide range of temperature and pressure conditions, and the most widely used geochronometer in felsic rocks. The oxygen isotope ratio recorded by zircon crystals is a sensitive tracer for crustal recycling in magmatic rocks and is a commonly used tool to address zircon petrogenetic questions (e.g. in studies on the evolution of geodynamics and continents). However, secondary processes (i.e. water uptake facilitated by radiation damage) can alter the oxygen isotopic composition of zircon. We present in-situ oxygen isotopic and 16O1H/16O data of natural zircon samples in combination with zircon trace element concentrations, and parameters that quantify crystal damage (i.e. Raman spectral parameters and alpha dose). In agreement with previous studies, our results demonstrate that the uptake of water into the zircon crystal structure strongly influences its recorded oxygen isotope ratio. Two distinct secondary processes are recorded which shift zircon δ18O values towards isotopically heavier and lighter values, respectively. Lower δ18O values associated with broadening of the zircon Raman bands and increasing 16O1H/16O are the result of a local charge-balance process during the interaction of radiation-damaged zircon with meteoric water. In contrast, an equilibrium fractionation process between zircon and percolating water leads to higher δ18O values with increasing 16O1H/16O. The disturbance of the oxygen isotopic system in zircon can be assessed through monitoring zircon 16O1H/16O; a parameter that is highly sensitive to the influx of water into radiation-damaged areas of the zircon grain, providing a powerful tool to access the validity of primary δ18O signatures.



中文翻译:

水对δ影响18在锆石Ø

锆石矿物在各种温度和压力条件下都是稳定的,并且是长英质岩石中使用最广泛的天文钟。锆石晶体记录的氧同位素比是岩浆岩中地壳再循环的灵敏示踪剂,并且是解决锆石岩石成因问题的常用工具(例如,在对地球动力学和大洲演化的研究中)。但是,次级过程(即辐射损伤促进了水分吸收)会改变锆石的氧同位素组成。我们提出了原位氧同位素和16 O 1 H / 16天然锆石样品的数据以及锆石中痕量元素的浓度以及量化晶体破坏的参数(即拉曼光谱参数和α剂量)的数据。与以前的研究一致,我们的结果表明,水吸收到锆石晶体结构中会强烈影响其记录的氧同位素比。两个不同的二次处理被记录其中移锆石δ 18个O值朝同位素较重和较轻的值,分别。低δ 18个与锆石拉曼频带的加宽和增加相关联的O值16 ö 1 H / 16O是辐射受损的锆石与流水相互作用过程中局部电荷平衡过程的结果。与此相反,锆石和水渗滤导致更高δ之间的平衡分馏工艺18个随O值16 ö 1个H / 16 O.在锆石中的氧同位素系统的扰动可以通过监测锆来评估16 ö 1 H / 16 O; 一个参数,其与水的流入锆石晶粒的辐射破坏的地区高度敏感,访问提供一个强有力的工具主δ的有效性18个Ò签名。

更新日期:2021-04-19
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