Water in mantle eclogite: Origin, distribution and physical consequences

地幔榴辉岩中的水：起源、分布和物理后果

• 批准号: 432249855
• 负责人: Dr. Sonja Aulbach
• 金额: --
• 依托单位: Abteilung Petrologie und Geochemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/432249855?language=en
• 关键词: Water; mantle; eclogite; Origin; distribution

The composition, structure and thermal state of the largely inaccessible deep lithosphere are inter-rogated by geophysical means with increasing detail, and its dynamics revealed by increasingly sophisticated numerical modelling. The accuracy of both approaches is enhanced by input from xenoliths entrained in deep-seated magmas. However, the physical properties of eclogites, as a subordinate but non-negligible part of dominantly peridotitic cratonic lithosphere, have not been systematically investigated. Like their peridotitic counterparts, some of these rocks have been metasomatised and possibly cryptically hydrated. As rocks consisting of ~50% clinopyroxene, mantle eclogites are expected to significantly contribute to the lithospheric water budget, but there are few studies on their H2O contents, and the nature and timing of their enrichment, and effects on geophysical observables are virtually unknown. The main aims of this study are thus: (1) To determine the H2O content in - and distribution between - clinopyroxene, garnet ± rutile in eight exceptionally well-characterised mantle eclogite suites from various cratons and tectonic settings by Fourier-Transformed Infrared Spectroscopy. Combined with published com¬po¬sitions for peridotite, this will allow the bulk densities, seismic velocities and electrical conductivities of regional eclogite-bearing continental lithospheres to be constrained with unprecedented detail and accuracy; (2) To determine the timing of the major hydration event represented by phlogopite-bearing eclogite, possibly linked to H2O introduction into nominally anhydrous minerals, by Ar-Ar dating of phlogopite; (3) evaluate implications for the rheology and stability of cratonic lithosphere.

通过地球物理手段越来越详细地询问基本上难以接近的深层岩石圈的成分、结构和热状态，并通过日益复杂的数值模型揭示其动态。通过来自深层岩浆中夹带的捕虏体的输入，这两种方法的准确性都得到了提高。然而，榴辉岩作为以橄榄岩为主的克拉通岩石圈的从属但不可忽视的部分，其物理性质尚未得到系统研究。与它们的橄榄岩对应物一样，其中一些岩石已经被交代，并且可能神秘地水合。作为由约 50% 单斜辉石组成的岩石，地幔榴辉岩预计将对岩石圈水预算做出重大贡献，但对其 H2O 含量、其富集的性质和时间以及对地球物理可观测值的影响几乎未知。因此，本研究的主要目的是：（1）通过傅里叶变换红外光谱确定来自不同克拉通和构造环境的八个特征非常明确的地幔榴辉岩组中单斜辉石、石榴石±金红石中的 H2O 含量及其分布。结合已发表的橄榄岩成分，这将使含有榴辉岩的区域大陆岩石圈的体积密度、地震速度和电导率受到前所未有的详细和准确度的约束； (2) 通过金云母 Ar-Ar 测年，确定以含金云母榴辉岩为代表的主要水化事件的时间，可能与 H2O 引入名义上无水矿物有关； (3) 评估对克拉通岩石圈流变学和稳定性的影响。