The Influence of Phase Separation on the Ca isotope Composition and Fluxes in Hydrothermal Systems

相分离对热液系统中Ca同位素组成和通量的影响

• 批准号: 54206897
• 负责人: Professor Dr. Anton Eisenhauer
• 金额: --
• 依托单位: GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2007
• 资助国家: 德国
• 起止时间: 2006-12-31 至 2011-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/54206897?language=en
• 关键词: Influence; Phase; Separation; Ca; isotope

Calcium (Ca) is a key element for the understanding of the chemical history of the ocean and for the global climate on long geological time scales. This is because Ca is interacting with the carbon cycle and is a major constituent of the continental weathering. Beside the continental runoff the mid-ocean ridges are quantitatively important concerning marine Ca concentration and isotope budget Variations of the hydrothermal circulation of seawater through oceanic crust have been recognized to play a significant role for the oceanic Calcium (Ca) mass and isotope (δ44/40Ca) balance. Hydrothermal activity leads to a chemical alteration of the circulating seawater during water-rock interaction, the formation of Ca-bearing minerals, and during phase separation. Within the framework of the subproject 'CARLA' in the 'Special Priority Program SPP1144’ Ca isotope ratios (δ44/40Ca) in hydrothermal fluids sampled from the Logatchev hydrothermal field (15°N/45°W) have been investigated in detail. It could be demonstrated that the Ca isotope composition of the fluid endmember undergoes fractionation effects during the precipitation of anhydrite at high temperatures of up to 300°C. The Logatchev hydrothermal field provides hydrothermal circulation without evidence for phase separation of the circulating seawater. However, with regard to the detected Ca isotope fractionation at high temperatures, the Ca isotopic compositions of phase separated hydrothermal fluids have still to be considered. This is if Ca isotopes become fractionated during phase separation, the global oceanic Ca isotope budget must be reconsidered. Phase separation leads to the formation of a low-salinity vapor and a high-salinity brine phase. The latter is enriched in metal cations that are mostly chloro-complexed. Experimental studies and theoretical models have shown that in aqueous NaCI solutions Ca occurs mainly as stable chloro-complexed species at sub- and supercritical conditions. Latter variation of complexation may influence the complexsensitive Ca isotope composition of the vapor and the brine phase.

钙（Ca）是了解海洋化学历史和长期地质时间尺度上的全球气候的关键元素。这是因为Ca与碳循环相互作用，是大陆风化作用的主要组成部分。除了大陆径流外，洋中脊对海洋钙浓度和同位素收支也具有重要的定量意义。通过海洋地壳的海水热液环流变化对海洋钙（Ca）质量和同位素（δ44/40Ca）平衡起着重要作用。热液活动导致循环海水在水岩相互作用、含钙矿物形成和相分离过程中发生化学蚀变。在“SPP1144特别优先计划”的“CARLA”子项目框架下，对Logatchev热液区（15°N/45°W）热液流体的δ44/40Ca同位素比值进行了详细研究。结果表明，在高达300℃高温下硬石膏的沉淀过程中，流体端元的Ca同位素组成受到了分馏效应的影响。Logatchev热液场提供热液循环，但没有循环海水相分离的证据。然而，对于高温下检测到的Ca同位素分馏，相分离热液的Ca同位素组成仍有待考虑。如果Ca同位素在相分离过程中发生分馏，则必须重新考虑全球海洋Ca同位素收支。相分离导致低盐度蒸汽和高盐度盐水相的形成。后者富含金属阳离子，大多是氯络合的。实验研究和理论模型表明，在nacl水溶液中，在亚临界和超临界条件下，Ca主要以稳定的氯络合物形式存在。后一种络合变化可能影响蒸汽相和盐水相的络合敏感Ca同位素组成。