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（Na+K/Al摩尔比> 1的岩石）强烈富集卤素、稀土元素（REE）和高场强元素（HFSE; Zr、Hf、Nb、Ta），代表了未来HFSE和REE供应的一些最有希望的来源。该项目调查的卤素和HFSE/稀土轴承相的纹理和成分分区过碱性深成Monchique复杂（葡萄牙），从辉长岩演变成foid正长岩组合物的行为。将研究方钠石、萤石和各种富F的Na-Ca-HFSE二硅酸盐（FDC）在过碱性岩浆中对卤素的保留的特殊作用，并将区分分离结晶、流体出溶/脱气和流体-围岩相互作用对卤素系统学和HFSE/REE活动性的可变影响。以下三个工作假设将指导预期项目的工作流程：1）Monchique岩石中的卤素丰度和卤素系统学（F/Cl，Cl/Br比值）反映了岩浆阶段分离结晶的影响以及流体出溶和伴随的（自交代）热液蚀变引起的卤素再分布。2)Monchique复杂显示垂直和水平带状相对丰富的方钠岩FDS组合，这可能会或可能不会与HFSE分布在这个板状体。3)Monchique杂岩周围局部发育的长石富Cl贫F，因此不含FDS，但含锆石和钛铁矿，这主要受长石化流体的低F/Cl比控制。为了验证这些假设，我们将结合联合收割机详细的岩相学、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调查（显微测温、LA-ICP-MS）。该项目的预期结果不仅将破译卤素和HFSE行为在这样一个过碱性系统，但肯定会有一般的影响，形成和迁移的含卤素的流体，能够HFSE运输内浅层次的深成复合体。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），并将允许在板状岩浆体的流体出溶/脱气过程的详细视图。