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&gt；1的岩石)强烈富含卤素、稀土元素(REE)和高场强元素(HFSE；Zr、Hf、Nb、Ta)，是未来HFSE和REE供应的最有希望的来源。该项目研究了从辉长岩演化为FOID正长岩组分的过碱性深成蒙奇克杂岩(葡萄牙)中卤素和HFSe/REE相的行为。研究方钠石、萤石和各种富F的Na-Ca-HFSe二硅酸盐(FDC)对过碱性岩浆中卤素的特殊保留作用，并区分分离结晶、流体出溶/脱气和流体-围岩相互作用对卤素体系和HFSE/REE活动性的不同影响。以下三个工作假设将指导预期项目的工作流程：1)蒙奇克岩石中的卤素丰度和卤素系统学(F/Cl，Cl/Br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(自生)热液蚀变引起的卤素重新分布的影响。2)Monchique杂岩对方钠闪石-FDS组合的相对丰度表现出垂直和水平分带，这可能与板状岩体中HFSE的分布有关，也可能与HFSE的分布无关。3)Monchique杂岩周围局部发育的辉长岩富氯贫氟，不含FDS，只含锆石和钛铁矿，这主要受成岩流体的低F/Cl控制。为了验证这些假设，我们将结合详细的岩石学、全岩分析(XRF、ICPMC、CIC)、矿物化学(EPMA、CIC、LA-ICPMS)、热力学模拟和流体包裹体研究(显微测温法、LA-ICPMS)。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杂岩中传输HFSE的含卤素流体的形成和迁移具有普遍意义。地球化学监测(例如全岩卤素数据、HFSE数据)将与矿物学观察(例如FDS、方钠石、萤石分布)相结合，并将使人们能够详细了解板状岩浆体中的流体出溶/脱气过程。