The behavior of high field-strength elements (HFSE) in F-rich peralkaline systems

高场强元素 (HFSE) 在富氟过碱性体系中的行为

• 批准号: 526130846
• 负责人: Privatdozent Dr. Michael Marks
• 金额: --
• 依托单位: Arbeitsgruppe Geologie und Geodynamik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/526130846?language=en
• 关键词: behavior; field; strength; elements; HFSE

Peralkaline igneous rocks (rocks with a molar (Na+K)/Al ratio > 1) are strongly enriched in halogens, rare earth elements (REE), and high field strength elements (HFSE; Zr, Hf, Nb, Ta) and represent some of the most promising sources for future HFSE and REE supply. This project investigates the behaviour of halogens and HFSE/REE-bearing phases in the texturally and compositionally zoned peralkaline plutonic Monchique complex (Portugal) that evolved from gabbroic to foid syenitic compositions. The special role of sodalite, fluorite and various F-rich Na-Ca-HFSE disilicates (FDC) for the retention of halogens in peralkaline magmas will be investigated and the variable effects of fractional crystallization, fluid exsolution/degassing and fluid-wall rock interaction on halogen systematics and HFSE/REE mobility will be distinguished from each other. The following three working hypotheses will be guiding the workflow of the anticipated project: 1) Halogen abundances and halogen systematics (F/Cl, Cl/Br ratios) in the Monchique rocks reflect the effects of fractional crystallization during magmatic stages and redistribution of halogens caused by fluid exsolution and accompanied (autometasomatic) hydrothermal alteration. 2) The Monchique complex shows vertical and horizontal zonation with respect to the relative abundance of sodalite-FDS assemblages, which may or may not correlate with the HFSE distribution in this tabular body. 3) Locally developed fenites around the Monchique complex are Cl-rich but F-poor and therefore devoid of FDS but zircon- and titanite-bearing, which is mainly controlled by the low F/Cl ratio of the fenitizing fluids. To test these hypotheses, we will combine detailed petrography, whole-rock analysis (XRF, ICP-MC, CIC), mineral chemistry (EPMA, CIC, LA-ICP-MS), thermodynamic modelling, and fluid inclusion investigations (microthermometry, LA-ICP-MS). The expected results of this project will not only decipher halogen and HFSE behavior in such a peralkaline system, but will certainly have general implications on the formation and migration of halogen-bearing fluids that are capable of HFSE transport within a shallow-level plutonic complex. Geochemical monitors (e.g., whole rock halogen data, HFSE data) will be combined with mineralogical observations (e.g., FDS, sodalite, fluorite distribution) and will allow for a detailed view on fluid exsolution/degassing processes in tabular magma bodies.

过碱性火成岩（摩尔比 (Na+K)/Al 大于 1 的岩石）富含卤素、稀土元素 (REE) 和高场强元素（HFSE；Zr、Hf、Nb、Ta），是未来 HFSE 和 REE 供应的一些最有前途的来源。该项目研究了从辉长岩组合物演化为辉长岩组合物的从结构和成分上分区的过碱性深成蒙奇克杂岩体（葡萄牙）中卤素和含 HFSE/REE 相的行为。将研究方钠石、萤石和各种富氟 Na-Ca-HFSE 二硅酸盐 (FDC) 在过碱性岩浆中保留卤素的特殊作用，并区分分步结晶、流体溶出/脱气和流体-壁岩相互作用对卤素体系和 HFSE/REE 迁移率的不同影响。以下三个工作假设将指导预期项目的工作流程：1）蒙希克岩石中的卤素丰度和卤素系统（F / Cl，Cl / Br比）反映了岩浆阶段分异结晶的影响以及流体溶出和伴随的（自动交代）热液蚀变引起的卤素重新分布。 2) Monchique 杂岩体显示了方钠石-FDS 组合相对丰度的垂直和水平分带，这可能与该板状体中的 HFSE 分布相关，也可能不相关。 3)蒙希克杂岩周围局部发育的辉长岩富Cl但贫氟，因此不含FDS，但含有锆石和钛矿，这主要受控于辉长岩化流体的低F/Cl比。为了检验这些假设，我们将结合详细的岩相学、全岩分析（XRF、ICP-MC、CIC）、矿物化学（EPMA、CIC、LA-ICP-MS）、热力学建模和流体包裹体研究（显微测温、LA-ICP-MS）。该项目的预期结果不仅将破译卤素和 HFSE 在这种过碱性系统中的行为，而且肯定会对能够在浅层深成复合体中进行 HFSE 传输的含卤素流体的形成和迁移产生一般性影响。地球化学监测器（例如，全岩卤素数据、HFSE 数据）将与矿物学观测（例如，FDS、方钠石、萤石分布）相结合，并且可以详细了解板状岩浆体中的流体析出/脱气过程。