Halogen behaviour in subduction zones: Eclogite facies rocks from the Western and Central Alps
Halogen behaviour in subduction zones: Eclogite facies rocks from the Western and Central Alps
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DOI：
10.1016/j.gca.2018.09.024
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发表时间：
2018-12
影响因子：
5
通讯作者：
L. Hughes;R. Burgess;D. Chavrit;A. Pawley;R. Tartèse;G. Droop;C. Ballentine;I. Lyon
中科院分区：
文献类型：
--
作者：
L. Hughes;R. Burgess;D. Chavrit;A. Pawley;R. Tartèse;G. Droop;C. Ballentine;I. Lyon
我们研究了F，Cl，Br和I的浓度和分布在榴辉岩相岩石和矿物从西部和中部阿尔卑斯蛇绿带，以确定卤素行为在俯冲带，并确定潜在的主机相，可能能够运输卤素到更深的地幔。对一系列蛇绿岩岩性-橄榄岩、蛇纹岩、变辉长岩、变玄武岩和变沉积岩-进行了分析，以评估卤素在深俯冲洋壳内的分布情况。单个矿物相中的卤素丰度范围为F的低于检测值（<100 ppm）至<1900 ppm，Cl的<101至<3000 ppm，Br的<101至<11，000 ppb，I的<1至<1300 ppb。散装岩石估计氯，溴和我的丰度是可变的，但一般都比那些在蚀变洋壳（AOC）低一个数量级以上，这表明主要的卤素损失之前或期间榴辉岩相变质。然而，氟，可以富集在变质玄武岩和变质沉积物，相对于重卤素，这表明F可以保留在榴辉岩相条件下的俯冲板片的上层。大块岩石的估计表明，在达到榴辉岩相时，俯冲板片已经损失了90%以上的Cl、Br和I。溴和碘的浓度呈正相关，表明它们在高压下表现出类似的行为。缺乏任何其他相关性表明，F和Cl的行为不同的Br和I在俯冲过程中。升高的F/Cl，Br/Cl和I/Cl的比例，相对于AOC，建议在较浅的深度俯冲的Cl的优先损失。在situanalyses和使用电子探针显微分析和飞行时间的二次离子质谱的化学映射表明，测得的卤素丰度主要托管在矿物结构。总的来说，我们的数据集提供了新的限制卤素的可用库存，可以通过洋壳俯冲转移到更深的地幔。
We examined F, Cl, Br and I concentrations and distributions in eclogite facies rocks and minerals from the Western and Central Alpine ophiolitic zone to determine halogen behaviour in subduction zones, and to identify potential host phases that may be able to transport halogens to the deeper mantle. Analysis was carried out on a range of ophiolitic lithologies — peridotites, serpentinites, metagabbros, metabasalts and metasediments — to assess the distribution of halogens within deeply subducted oceanic crust. Halogen abundances in individual mineral phases range from below detection (∼100 ppm) to ∼1900 ppm for F, ∼1 to ∼3000 ppm for Cl, ∼1 to ∼11,000 ppb for Br and from <1 to ∼1300 ppb for I. Bulk rock estimates of Cl, Br and I abundances are variable, but are generally more than one order of magnitude lower than those in altered oceanic crust (AOC), suggesting major halogen loss prior to or during eclogite facies metamorphism. Fluorine, however, can be enriched within metabasalts and metasediments, relative to the heavy halogens, suggesting F can be retained at eclogite facies conditions within the upper layers of the subducting slab. Bulk rock estimates suggest that upon reaching eclogite facies, the subducting slab has lost over 90% Cl, Br and I. Bromine and iodine concentrations show positive correlation, suggesting that they exhibit similar behaviour at high pressure. A lack of any other correlations suggest that F and Cl behave differently to Br and I during subduction. Elevated F/Cl, Br/Cl and I/Cl ratios, relative to AOC, suggest the preferential loss of Cl during shallower depths of subduction.In situanalyses and chemical mapping using electron probe micro-analysis and time of flight secondary ion mass spectrometry indicate that measured halogen abundances are primarily hosted within the mineral structure. Overall, our dataset provides new constraints on the available inventory of halogens that can be transferred to the deeper mantle via the subduction of oceanic crust.