Abstract The fluid inclusion record of the miarolitic gem beryl-bearing Luumaki pegmatite (SE Finland) has been studied by petrography, microthermometry and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Four types of fluid inclusion assemblages could be distinguished, which record the nature and timing of fluids exsolved in the pegmatite. Type I and type II fluid inclusions are two-phase (LV) aqueous with intermediate salinities of 8.0 ± 2.7 and 8.1 ± 0.9 wt% NaCl, respectively. Type I fluids occur at the transition between the quartz core and euhedral smoky quartz crystals formed in miarolitic cavities. Type II inclusions are present throughout smoky quartz and gem beryl crystals in miarolitic cavities. Type III are three-phase (LLV), low-salinity (1.2 ± 1.1 wt% NaCl), aqueous‑carbonic inclusions, whereas type IV are three-phase (LVS) aqueous inclusions with halite daughter crystals and high salinity (39.6 ± 4.5 wt% NaCl equiv.). Both type III and type IV inclusions occur texturally late in the smoky quartz crystals and are closely related to each other, sometimes coexisting on the same inclusion trail. The chemical data show that type I, type III and type IV inclusions lie on linear trends in many elemental variation diagrams, where type I inclusions plot between the data for type III and type IV inclusions. The saline type IV inclusions are strongly enriched in many elements, such as alkalis, alkaline earths and transition metals, whereas the aqueous‑carbonic type III inclusions are depleted in these metals. The chemical data, in conjunction with petrographic features, demonstrate that type III and type IV inclusions were formed by phase separation of the type I intermediate-salinity fluid. The metal and halogen content of all four fluid types suggests that they are of magmatic-hydrothermal origin and supports the model that the Luumaki pegmatite reached fluid saturation at the transition between core quartz crystallization and formation of miarolitic cavities. Representative fluid inclusion isochores calculated for type II fluids preserved in gem beryl, in conjunction with the P-T slope constructed from the water content in beryl, yield a best P-T estimate for pocket formation of 380 ± 80 °C and 1.2 ± 0.7 kbar. This P-T estimate constrains the range of pressure-depth conditions proposed for the rapakivi granites that host the Luumaki pegmatite, and is consistent with recent estimates suggesting a maximum pressure of emplacement of 1.9 kbar.

中文翻译：

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花岗岩伟晶岩的后期流体出溶和流体相分离过程：来自 Luumäki 宝石绿柱石伟晶岩（芬兰东南部）的流体包裹体研究的见解

摘要 用岩相学、显微测温法和激光烧蚀电感耦合等离子体质谱法 (LA-ICP-MS) 研究了含微晶绿柱石 Luumaki 伟晶岩（芬兰东南部）的流体包裹体记录。可以区分四种类型的流体包裹体组合，它们记录了伟晶岩中流体出溶的性质和时间。I 型和 II 型流体包裹体是两相 (LV) 水相，中间盐度分别为 8.0 ± 2.7 和 8.1 ± 0.9 wt% NaCl。I 型流体出现在石英核和在微晶洞中形成的自形烟晶晶体之间的过渡处。II 型内含物存在于微晶洞中的整个烟晶和宝石绿柱石晶体中。III 型是三相 (LLV)、低盐度 (1.2 ± 1.1 wt% NaCl)、水性碳包裹体、而 IV 型是具有岩盐子晶体和高盐度（39.6 ± 4.5 wt% NaCl 当量）的三相 (LVS) 水性包裹体。III 型和 IV 型包裹体在烟晶晶体中出现结构较晚，并且彼此密切相关，有时共存于同一包裹体轨迹上。化学数据表明，I 型、III 型和 IV 型夹杂物在许多元素变化图中呈线性趋势，其中 I 型夹杂物绘制在 III 型和 IV 型夹杂物的数据之间。咸水Ⅳ型包裹体富含多种元素，如碱金属、碱土金属和过渡金属，而含水碳Ⅲ型包裹体则缺乏这些金属。化学数据，结合岩相特征，证明 III 型和 IV 型包裹体是由 I 型中盐度流体的相分离形成的。所有四种流体类型的金属和卤素含量表明它们是岩浆-热液成因，并支持 Luumaki 伟晶岩在核心石英结晶和形成细粒岩腔之间的过渡处达到流体饱和的模型。为保存在宝石绿柱石中的 II 型流体计算的代表性流体包裹体等浓度，结合由绿柱石中的水含量构建的 PT 斜率，产生了 380 ± 80 °C 和 1.2 ± 0.7 kbar 的口袋形成的最佳 PT 估计值。该 PT 估计限制了为容纳 Luumaki 伟晶岩的 rapakivi 花岗岩提出的压力-深度条件的范围，