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首页> 外文期刊>Contributions to Mineralogy and Petrology >Apatite as probe for the halogen composition of metamorphic fluids (Bamble Sector, SE Norway)
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Apatite as probe for the halogen composition of metamorphic fluids (Bamble Sector, SE Norway)

机译：磷灰石作为变质流体卤素成分的探针（挪威东南部Bamble Sector）

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摘要

Halogen composition of replaced apatite formed during a regional metasomatic event (Bamble Sector, SE Norway) reveals information about the composition and evolution of the hydrothermal fluid. Infiltration and pervasive fluid flow of highly saline fluids into gabbroic bodies lead to scapolitization and amphibolitization, where magmatic Cl-rich apatite reacts with the hydrothermal fluid to form OH-and/or F-rich apatite. Apatite from highly altered samples adjacent to the shear zone has highest F (up to 15,000 mu g/g) and lowest Br (4-25 mu g/g) concentrations, whereas apatite from least altered samples has very low F (30-200 mu g/g) and high Br (30-85 mu g/g). In addition, individual replaced apatite grains show a zonation in F with high concentrations along rims and cracks and low F in core regions. Iodine concentrations remain rather constant as low values of 0.18-0.70 mu g/g. We interpret all observed compositional features of replaced apatite to be the result of a continuous evolution of the fluid during fluid-rock interaction. Due to its high compatibility, F from the infiltrating fluid is incorporated early into recrystallized apatite (close to shear zone and rims of individual apatite grains). In contrast, Br as an incompatible halogen becomes enriched in the fluid and is highest in the most evolved fluid. Using experimental partition data between replaced apatite and fluid, we calculated F concentrations of the evolving fluid to decrease from 60 to < 1 mu g/g and Br to increase from similar to 1200 to similar to 5000 mu g/g; I concentrations of the fluid are constant in the order of 370 mu g/g. Although Cl is expected to show a similar behavior as Br, replaced apatite has constant Cl concentrations throughout the alteration sequence (similar to 1 wt.%), which is likely the result of a rather constant Cl activity in the fluid. Chlorine stable isotope values of individual apatite grains are heterogeneous and range from -1.2 to + 3.7 %. High delta Cl-37 values are generally correlated with OH-rich zones of replaced apatite, whereas low delta Cl-37 values are measured in F-rich zones of replaced apatite and in Cl-apatite of probably magmatic origin. Though apatite delta Cl-37 values follow the general bulk trend, the individual delta Cl-37 signature seems to reflect the highly localized composition of interfacial fluid at the reaction front. Our observations suggest that apatite can be used as a fluid probe for F, Br, and I to detect a compositional evolution of the fluid, which can be quantified by using experimentally derived partition coefficients. Partitioning of Cl and Cl stable isotopes between highly saline fluids and apatite is complex and likely controlled by more unknown factors than just the Cl concentration.
机译：在区域变质事件（挪威东南部的Bamble Sector）中形成的置换磷灰石的卤素成分揭示了有关热液流体成分和演化的信息。高盐度流体渗入和普遍渗入辉长岩体会导致崩裂和闪石化，岩浆中富含Cl的磷灰石与热液反应形成富含OH和/或F的磷灰石。来自剪切区附近变化较大的样品的磷灰石具有最高的F（高达15,000μg / g）和最低的Br（4-25μg/ g）浓度，而变化最少的样品的磷灰石具有非常低的F（30-200）克/克）和高溴（30-85克/克）。此外，个别替代的磷灰石晶粒在F上具有带状分布，沿边缘和裂纹的浓度很高，而在核心区域的F较低。碘浓度保持相当恒定，为0.18-0.70μg/ g的低值。我们将所有观察到的替代磷灰石的成分特征解释为在流体-岩石相互作用过程中流体不断演化的结果。由于它的高相容性，来自渗透流体的F会早期掺入到重结晶磷灰石中（靠近剪切区和各个磷灰石晶粒的边缘）。相比之下，作为不相容卤素的Br在流体中富集，在最易挥发的流体中含量最高。使用替换后的磷灰石和流体之间的实验分区数据，我们计算了演化中的流体的F浓度从60降至<1μg/ g，Br从相似的1200增加至相似的5000μg/ g。流体的浓度恒定在370μg/ g的数量级。尽管预计Cl会表现出与Br类似的行为，但被替换的磷灰石在整个蚀变序列中都具有恒定的Cl浓度（约1 wt。％），这很可能是流体中Cl活性相当恒定的结果。单个磷灰石晶粒的氯稳定同位素值不均匀，范围为-1.2至+ 3.7％。高增量的Cl-37值通常与替换磷灰石的OH富集区相关，而较低的增量Cl-37值在替代的磷灰石的F富集区和可能是岩浆成因的Cl-磷灰石中测得。尽管磷灰石δCl-37值遵循总体体积趋势，但单个δCl-37标记似乎反映了反应前沿界面流体的高度局部化组成。我们的观察结果表明，磷灰石可以用作F，Br和I的流体探针，以检测流体的组成演变，可以通过使用实验得出的分配系数对其进行量化。高盐度流体和磷灰石之间的Cl和Cl稳定同位素的分配很复杂，并且可能受不仅仅是Cl浓度的更多未知因素控制。

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