Thallium behavior during high-pressure metamorphism in the Western Alps, Europe
Thallium behavior during high-pressure metamorphism in the Western Alps, Europe
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欧洲西阿尔卑斯高压变质作用过程中的铊行为
DOI：
10.1016/j.chemgeo.2021.120349
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发表时间：
2021-09
期刊：
影响因子：
3.9
通讯作者：
Shelby T. Rader;R. Gaschnig;S. Newby;G. Bebout;Michael J. Mirakian;J. Owens
中科院分区：
文献类型：
--
作者：
Shelby T. Rader;R. Gaschnig;S. Newby;G. Bebout;Michael J. Mirakian;J. Owens
铊（Tl）是一种高度不相容的元素，在矿物脱水和低温热液蚀变等各种岩浆热液事件中，铊会发生再分配。尽管强烈的影响流体-岩石相互作用可以对Tl再分配和俯冲带挥发分循环中的流体的重要性，Tl在高P/T变质作用的地球化学行为尚未被量化。在这里，我们提供了新的Tl同位素组成（ε 205 Tl）和浓度（[Tl]）数据的一套18变岩和变碎屑岩从Lustrés杂岩和附近的Lago di Alpnana暴露在西阿尔卑斯山。这套岩系代表了300-550 °C和1.5-3.0 GPa的峰变质P-T条件范围内的变质作用随着变质程度的增加，[Tl]没有统计变化，而ε 205 Tl在初始阶段保持相当的恒定（按等级递增顺序，Fraiteve（单位A）ε 205 Tlavg = −2.1（± 0.3）; Assietta（单位B）ε 205 Tlavg = −1.6（± 0.6）;阿尔贝格（单位C）ε 205 Tlavg = −1.9（± 0.5）），在高级变质作用期间变为更负的值（Finestre（单位D）ε 205 Tlavg =-2.4（± 0.3）; Cignana（单位E）ε 205 Tlavg =-3.5（± 0.3））。虽然它似乎很可能是在很大程度上保留在这样的岩石接近弧岩浆生成的深度，矿物学主机的Tl的变化过程中，地幔脱挥发分。这可能导致ε 205 Tl的显著变化，这与流体-矿物分配引起的少量损失引起的分馏有关。前变质作用导致矿物和其他次要矿物成分的分解，释放出绿泥质铊，这些铊可能部分并入多硅白云母中，部分流失到流体中。这项研究强调了在研究微量元素如铊的保留或损失时，需要考虑矿物反应史。
Thallium (Tl) is a highly incompatible element which can be redistributed during various igneous and hydrothermal events such as mineral dehydration and low-temperature hydrothermal alteration. Despite the strong influence fluid-rock interactions can have on Tl redistribution and the importance of fluids in subduction-zone volatiles cycling, the geochemical behavior of Tl during high-P/T metamorphism has not yet been quantified. Here we provide new Tl isotope composition (ε205Tl) and concentration ([Tl]) data for a suite of 18 metapelite and metacarbonate rocks from the Schistes Lustrés Complex and the nearby Lago di Cignana exposure in the western Alps. This suite represents metamorphism over a range of peak metamorphicP-Tconditions of 300–550 °C and 1.5–3.0 GPa (similar to the range ofP-Texperienced in most modern subduction zones).With increasing metamorphic grade, [Tl] shows no statistical variation while ε205Tl initially remains fairly constant (in order of increasing grade, Fraiteve (unit A) ε205Tlavg= −2.1 (± 0.3); Assietta (unit B) ε205Tlavg= −1.6 (± 0.6); Albergian (unit C) ε205Tlavg= −1.9 (± 0.5)) before shifting to more negative values during higher grade metamorphism (Finestre (unit D) ε205Tlavg= −2.4 (± 0.3); Cignana (unit E) ε205Tlavg= −3.5 (± 0.3)). Although it appears likely that Tl is largely retained in such rocks to depths approaching those of arc magma generation, the mineralogical hosts for Tl change during prograde devolatilization. This may contribute to a significant shift in ε205Tl related to fractionation induced by only minor amounts of loss due to fluid-mineral partitioning. Prograde metamorphism results in the breakdown of chlorite and other minor mineralogical constituents, releasing chlorite-borne Tl that could be in part incorporated into phengite and in part lost to fluids. This study emphasizes the need for prograde mineral reaction history to be considered in studies of the retention or loss of trace elements such as Tl.