Abstract Lawsonite is an abundant hydrous mineral in subducted oceanic crust and sediments and is an important carrier of water (∼11.5 wt%) and trace elements (REE, U, Th, Sr, Pb) into the mantle. Despite its widespread stability at the high-pressure/low-temperature conditions of subduction, it is rarely preserved in the geologic record, particularly in eclogite. Therefore, scarce fresh lawsonite eclogites in which the composition of lawsonite can be directly determined are important geochemical archives of fluid-mediated processes during subduction. Of particular interest are lawsonite-rich veins and layers that may represent former fluid pathways or metasomatic zones and that therefore may record element mobility related to fluid-rock interaction during subduction and/or incipient exhumation. In the Sivrihisar (Turkey) subduction complex, lawsonite-rich veins and layers comprised of ∼30–50 % lawsonite occur at pod margins where lawsonite eclogite has been partially transformed to lawsonite blueschist. To understand the petrogenesis of these lawsonite-rich assemblages, we conducted a petrographic and geochemical study of a representative lawsonite-rich layer at the margin of a meter-scale lawsonite eclogite pod. Bulk rock and mineral major and trace element analyses were conducted along a transect consisting of the lawsonite-rich layer (Lws + Grt + Ph), its glaucophane-rich margin (Gln + Grt + Lws + Ph + Rt), and the lawsonite eclogite host at varying distances from the layer (∼1–2 cm away and >10 cm away). The bulk-rock composition of the lawsonite eclogite indicates a basaltic protolith that experienced interactions with (meta-)sedimentary rocks before or during the crystallization of high-pressure phases such as garnet and rutile. Integrated major and trace element composition and zoning in high-pressure phases indicate that the lawsonite-rich layer and its associated glaucophane-rich margin likely formed at or near peak eclogite-facies conditions (2.2–2.4 GPa, 520 °C) as a result of fluid-mediated processes that scavenged Al2O3, MnO, Y, Th, HFSE, and REE from the eclogite immediately adjacent to the vein (∼1–2 cm away). Mass balance calculations also suggest the addition of LILE and transition metals (Ni, Cr, Zn) to the lithologic layers at the pod margin; these elements were likely supplied from an external source, such as serpentinites and/or sediments, both of which occur interspersed with mafic rocks in the Sivrihisar complex. Fluid-rock interaction may have also driven changes in fO2, as omphacite, glaucophane, lawsonite, and phengite from the pod margin record core-to-rim increases in Fe3+. These changes in bulk composition preferentially stabilized glaucophane-rich (blueschist) and LREE- and LILE-enriched lawsonite-rich assemblages at the pod margin.

中文翻译：

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作为俯冲地壳中流体和元素流动记录的富含劳森石的层（土耳其锡夫里希萨尔地块）

摘要 硬柱石是俯冲洋壳和沉积物中丰富的含水矿物，是水（~11.5 wt%）和微量元素（REE、U、Th、Sr、Pb）进入地幔的重要载体。尽管它在俯冲的高压/低温条件下具有广泛的稳定性，但它很少被保存在地质记录中，特别是在榴辉岩中。因此，稀有的可直接确定硬柱石成分的新鲜硬柱石榴辉岩是俯冲过程中流体介导过程的重要地球化学档案。特别令人感兴趣的是富含硬柱石的矿脉和地层，它们可能代表以前的流体通道或交代带，因此可以记录与俯冲和/或初期折返过程中流体-岩石相互作用相关的元素流动性。在 Sivrihisar（土耳其）俯冲复合体中，由约 30-50% 硬柱石组成的富含硬柱石的矿脉和层出现在豆荚边缘，其中硬柱石榴辉岩已部分转化为硬柱石蓝片岩。为了了解这些富含硬柱石组合的岩石成因，我们对位于米级硬柱石榴辉岩荚边缘的代表性富含硬柱石层进行了岩相学和地球化学研究。大块岩石和矿物的主要和微量元素分析是沿着由富含硬柱石层 (Lws + Grt + Ph)、富含蓝闪石的边缘 (Gln + Grt + Lws + Ph + Rt) 和硬柱石榴辉岩组成的断面进行的宿主与层的不同距离（约 1-2 厘米远和 > 10 厘米远）。硬柱石榴辉岩的块状岩石成分表明玄武质原岩在高压相（如石榴石和金红石）结晶之前或期间与（变质）沉积岩发生相互作用。高压相中的综合主要和微量元素组成和分带表明，富硬锂辉石层及其相关的富含绿光闪石边缘可能形成于或接近高峰榴辉岩相条件（2.2-2.4 GPa，520 °C）。流体介导的过程，从紧邻静脉（约 1-2 厘米远）的榴辉岩中清除 Al2O3、MnO、Y、Th、HFSE 和 REE。质量平衡计算还表明在豆荚边缘的岩性层中添加了 LILE 和过渡金属（Ni、Cr、Zn）；这些元素很可能是从外部来源提供的，例如蛇纹岩和/或沉积物，它们都散布在 Sivrihisar 复合体中的基性岩中。流体-岩石相互作用也可能推动了 fO2 的变化，因为来自豆荚边缘的绿辉石、蓝闪石、硬柱石和菱镁矿记录了 Fe3+ 的核心到边缘的增加。这些大块组成的变化优先稳定了豆荚边缘富含蓝闪石（蓝片岩）和富含 LREE 和 LILE 的硬柱石组合。