Unlocking and using the potential of Mo stable isotopes as a tracer of crustal recycling

释放和利用钼稳定同位素作为地壳循环示踪剂的潜力

• 批准号: 418227749
• 负责人: Dr. Rachel Bezard, Ph.D.
• 金额: --
• 依托单位: Abteilung Isotopengeologie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/418227749?language=en
• 关键词: Unlocking; using; potential; Mo; stable

The origin of the heterogeneous trace element and radiogenic isotopic compositions of the Earth’s mantle observed through oceanic basalts has been an active question for the last three decades. The return of crust back to the mantle has long been suggested to be responsible for the dominant heterogeneities observed. However, processes such as intra-mantle metasomatism were also proposed to partly or entirely explain the observed variations without crust involvement. Already in the 80s, stable isotope investigations of oceanic basalts were suggested to have the potential to close this debate. This is because the largest stable isotope fractionations occur at low temperature, i.e. at the surface of the Earth. Hence the presence of strongly fractionated signatures in oceanic basalts was expected to be the unambiguous proof of recycled crust back to the mantle. However, the interpretation of stable isotopes revealed more complex than initially predicted, with large isotope fractionation found to occur during high temperature processes such as partial melting, magma differentiation and slab dehydration/melting at subduction zones. For most stable isotopic systems, the lack of a full understanding of the behaviour of stable isotopes during these processes precludes convincing evidence and characterization of recycled crust in the source of oceanic basalts.This proposal aims at unlocking and subsequently using the potential of Mo stable isotopes as a powerful tracer of crustal recycling. The Mo stable isotopic system is a very promising tracer but its full potential is currently hampered by the lack of constraints on Mo stable isotope behaviour during (1) island arc and continental crust differentiation; (2) slab metasediment and metabasite melting at subduction zones and (3) the production and differentiation of low-degree mantle partial melts. The goal is to fill these knowledge gaps on the high temperature behaviour of Mo isotopes and to investigate and characterize recycled crust in the source of oceanic basalts covering the whole compositional spectrum defined by radiogenic isotopes.

在过去的三十年里，通过海洋玄武岩观察到的地幔的异质微量元素和放射性同位素组成的起源一直是一个活跃的问题，长期以来，地壳返回地幔一直被认为是造成观察到的主要异质性的原因。然而，在 80 年代，人们也提出了地幔内交代作用等过程来部分或完全解释所观察到的变化，而无需地壳参与，对海洋玄武岩进行了稳定同位素研究。被认为有可能结束这场争论，因为最大的稳定同位素分馏发生在低温下，即在地球表面，因此海洋玄武岩中强烈分馏特征的存在被认为是明确的证据。然而，稳定同位素的解释比最初预测的更复杂，在部分熔融、岩浆分异和板片等高温过程中发现发生大量同位素分馏。对于大多数稳定同位素系统来说，缺乏对稳定同位素在这些过程中的行为的充分了解，排除了海洋玄武岩来源中再生地壳的证据和特征。该提案旨在解锁并随后使用。钼稳定同位素作为地壳循环的强大示踪剂的潜力 钼稳定同位素系统是一种非常有前途的示踪剂，但目前由于缺乏对钼稳定同位素的限制，其全部潜力受到阻碍。 （1）岛弧和大陆地壳分异期间的同位素行为；（2）俯冲带的板片变沉积物和变碱岩熔融以及（3）低度地幔部分熔融的产生和分异。钼同位素的高温行为，并研究和表征海洋玄武岩来源中的再生地壳，涵盖由放射性同位素定义的整个成分谱。