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.

在过去的三十年中，通过海洋玄武岩观察到的地球地幔的异质痕量元件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，长期认为，地壳返回地幔的归还是造成观察到的主要异质性的原因。然而，还提出了诸如大通内交叉学之类的过程，以部分或完全解释观察到的变化而无需地壳参与。在80年代，建议对海洋玄武岩进行稳定的同位素研究，有可能结束这一辩论。这是因为最大的稳定同位素分馏发生在低温下，即地球表面。因此，在海洋玄武岩中存在强烈分馏的特征，预计将是回收壳的明确证明。然而，稳定同位素的解释比最初的预测更复杂，在高温过程中发现大型同位素分馏发生在俯冲区域的高温过程中，例如部分熔化，岩浆分化和平板脱水/熔化。对于最稳定的同位素系统，在这些过程中缺乏对稳定同位素的行为的完全理解，这是令人信服的证据和在海洋玄武岩来源中的再生地壳的表征。该提案旨在解锁并随后将Mo Stable同位素的潜力作为强大的同位素作为强大的磨碎的胶状胶囊。 MO稳定的同位素系统是一个非常有希望的示踪剂，但目前由于对MO稳定的同位素行为缺乏约束（1）岛弧和连续的地壳分化而受到阻碍。 （2）俯冲带时的平板定源和元地板熔化，以及（3）低度地幔部分熔体的产生和分化。目的是填补有关MO同位素高温行为的这些知识差距，并研究和表征涵盖放射性同位素定义的整个组成谱的海洋玄武岩来源的再生地壳。