巴伯顿绿岩带3.3Ga低δ18O科马提岩成因及其与早期深部地幔不均一性的联系

地幔组成的不均一性在主微量元素与多种同位素体系上均有体现，其成因与尺度范围涉及地球早期的圈层分异及之后板块构造的作用，一直受到高度关注。受限于地质记录，对地球早期深部地幔成分特征的认识主要依赖于科马提岩。2017年Gary Byerly教授首次报道了巴伯顿绿岩带~3.27 Ga Weltevreden科马提岩中新鲜的橄榄石具有异常的低δ18O特征(2.9-4.1‰)，表明太古宙时期深部地幔的氧同位素可能存在不均一，但其具体成因仍未确定。本项目拟与Gary Byerly 教授合作，对Weltevreden科马提岩开展进一步研究，采用三氧同位素分析技术以及矿物微区原位δ18O分析，确定地球早期深部地幔的三氧同位素组成特征，揭示低δ18O特征的分布规律，阐明深部地幔氧同位素的分馏机制，并进一步探讨地球早期深部地幔不均一性的成因与尺度范围，及其相关的圈层分异与演化过程的动力学机制。

The heterogeneity of mantle composition is reflected in the major and trace elements and various isotopic systems. The origin and scale of the heterogeneity are related to the stratification of the early Earth strata and the subsequent plate tectonics, which have been highly concerned. Due to the limitation of geological record, the understanding of the composition characteristics of the deep mantle in the early Earth mainly relies on the Komatiite. In 2017, Gary Byerly reported for the first time that the freshest olivines, from the ~3.27 Ga Weltevreden Komatiites in the Barberton greenstone belt, South Africa, has low δ18O (2.9-4.1 ‰) deviating from normal mantle values (5.5±0.5 ‰), suggesting that the oxygen isotopes in the deep mantle during the Archean may be inhomogenous, but the exact origin of the heterogeneity remains undetermined. In this project, a further research on Weltevreden komatiites will be conducted, cooperating with Gary Byerly, using the three oxygen isotopic(δ18O-δ17O)analysis technology, and in situ δ18O analysis, to determine the early earth's deep mantle of three oxygen isotope characteristics, combined with the mineral structure and element geochemical study, further reveal the distribution rule and the characteristic of low δ18O and the link with other mineralogical and geochemical features, to clarify the deep mantle oxygen isotope fractionation mechanism. On this basis, the causes and scale scope of the early Earth's deep mantle heterogeneity, as well as the dynamic mechanism of the related layer differentiation and evolution process are further discussed.