Geochemical implications of rare earth element patterns in hydrothermal fluids from mid-ocean ridges
Geochemical implications of rare earth element patterns in hydrothermal fluids from mid-ocean ridges
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DOI：
10.1016/0016-7037(94)90297-6
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发表时间：
1994-12
影响因子：
5
通讯作者：
G. Klinkhammer;H. Elderfield;J. Edmond;A. Mitra
中科院分区：
文献类型：
--
作者：
G. Klinkhammer;H. Elderfield;J. Edmond;A. Mitra
报告了从八个深海热液区收集的喷口流体的稀土元素数据，包括来自沉积物和裸岩热液系统的样品。从这些不同的设置MORB标准化稀土元素模式是非常相似的，但明显不同于海水或玄武岩，LREE富集，并具有显着的正Eu异常。稀土元素浓度组成这些模式变化很大，但是，无论是在空间和时间的基础上。当绘制离子半径，这些流体的趋势是显着的线性，并表现出相同的分馏模式，斜长石在岩浆分离。这一分析表明，稀土元素之间的分配在MORB的高温热液蚀变过程中的流体和岩石是由结晶化学交换过程中的溶解和重结晶反应在斜长石斑晶暴露的表面。8个配位的REE离子半径比较表明，+3REE和+2Eu的配分分别以Ca+2和Sr+2的化学置换为主。这些考虑因素预测，总的+3稀土元素含量的喷口流体变化的系统的方式在过渡期间，从富An的MORB斜长石，富AB热液斜长石，这些参数可以被用来作为指标的平均范围内的蚀变活跃的热液系统。
Rare earth element data are reported for vent fluids collected from eight deep-sea hydrothermal areas, including samples from sediment-hosted and bare-rock hydrothermal systems. The MORB-normalized REE patterns from these diverse settings are remarkably similar to each other but distinctly different than seawater or basalt, being LREE-enriched and possessing a strikingly positive Eu anomaly. The REE concentrations making up these patterns vary widely, however, both on a spatial and temporal basis. When plotted against ionic radii, these fluid trends are remarkably linear and show the same fractionation patterns exhibited by plagioclase during magma segregation. This analysis suggests that the partitioning of the REE between fluid and rock during high-temperature hydrothermal alteration of MORB is dominated by crystochemical exchange during dissolution and recrystallization reactions at the exposed surfaces of plagioclase phenocrysts. A comparison of REE ionic radii in eight coordination indicate that the partitioning of + 3REE and + 2Eu are dominated by chemical substitution for Ca+2and Sr+2, respectively. These considerations predict that the total +3REE content of vent fluid varies in a systematic way during the transition from An-rich MORB plagioclase to Ab-rich hydrothermal plagioclase and that these parameters can be used as indicators of the average extent of alteration inside active hydrothermal systems.