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.

地球物理动力学手段越来越详细地询问了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拟来揭示。来自深部夹带的捕虏体的输入提高了这两种方法的准确性。然而，榴辉岩作为主要橄榄岩克拉通岩石圈的附属但不可忽视的部分，其物理性质尚未像橄榄岩磅那样得到系统研究。这些岩石已被交代，并且可能被神秘地水合，由于岩石由约 50% 的单斜辉石组成，地幔榴辉岩预计会对岩石圈的水预算做出重大贡献，但对其 H2O 含量及其富集的性质和时间的研究很少。 ，对地球物理可观测值的影响实际上是未知的。因此，本研究的主要目的是：（1）确定单斜辉石中的 H2O 含量及其分布。通过傅里叶变换红外光谱法，结合已发表的橄榄岩成分，可以在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发现石榴石±金红石，从而获得区域的体积密度、地震速度和电导率。 (2) 至通过金云母 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。