Secular mantle oxidation across the Archean-Proterozoic boundary: Evidence from V partitioning in komatiites and picrites
Secular mantle oxidation across the Archean-Proterozoic boundary: Evidence from V partitioning in komatiites and picrites
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DOI：
10.1016/j.gca.2019.01.037
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发表时间：
2019-04-01
影响因子：
5
通讯作者：
Anbar, Ariel D.
中科院分区：
文献类型：
--
作者：
Nicklas, Robert W.;Puchte, Igor S.;Anbar, Ariel D.
氧逸度的9个幔源科马提质和苦橄岩系统的年龄范围从3.55 Ga到现代的一天，使用液相线橄榄石和科马提质/苦橄岩熔体之间的V的氧化还原敏感的分配。来自本研究的七个系统的氧逸度数据和Nicklas等人（2018）研究的六个科马提岩系统的组合数据（所有这些都可能代表地幔的大区域）定义了一个约束良好的趋势，表明熔岩的氧逸度增加，从3.48到1.87 Ga，氧逸度从1.87Ga到现在几乎是恒定的。氧逸度数据为3.55 Ga Schapenburg科马提岩系统，地幔源区，其中以前被认为是孤立的地幔对流内的第一个30马的太阳系的历史，图远高于趋势，并没有被包括在回归。这些科马提岩异常高的氧逸度数据可能反映了早期-在所研究的科马提岩和苦橄岩系统中，观测到的氧逸度增加（近似于1.3 Delta FMQ测井单位）是其地幔源区的一个特征，并被解释为地幔的长期氧化（3.48 - 1.87佐治亚州三种机制被认为是解释所观察到的地幔氧化还原状态的变化：（1）蚀变洋壳的再循环，（2）由于内核结晶，氧从内核中排出，（3）对流驱动的初始氧化还原不均匀的原始地幔的均匀化。结果表明，这三种机制都不能完全解释所观察到的趋势，尽管机制（3）得到了现有地球化学数据的最佳支持。这些新的数据提供了进一步的证据，地幔参与了大气中氧浓度的急剧增加，导致了类似于2.4 Ga的大氧化事件。(C)2019爱思唯尔有限公司版权所有。
The oxygen fugacities of nine mantle-derived komatiitic and picritic systems ranging in age from 3.55 Ga to modern day were determined using the redox-sensitive partitioning of V between liquidus olivine and komatiitic/picritic melt. The combined set of the oxygen fugacity data for seven systems from this study and the six komatiite systems studied by Nicklas et al. (2018), all of which likely represent large regions of the mantle, defines a well-constrained trend indicating an increase in oxygen fugacity of the lavas of similar to 1.3 Delta FMQ log units from 3.48 to 1.87 Ga, and a nearly constant oxygen fugacity from 1.87 Ga to the present. The oxygen fugacity data for the 3.55 Ga Schapenburg komatiite system, the mantle source region of which was previously argued to have been isolated from mantle convection within the first 30 Ma of the Solar System history, plot well above the trend and were not included in the regression. These komatiite's anomalously high oxygen fugacity data likely reflect preservation of early-formed magma ocean redox heterogeneities until at least the Paleoarchean.The observed increase in the oxygen fugacity of the studied komatiite and picrite systems of similar to 1.3 Delta FMQ log units is shown to be a feature of their mantle source regions and is interpreted to indicate secular oxidation of the mantle between 3.48 and 1.87 Ga. Three mechanisms are considered to account for the observed change in the redox state of the mantle: (1) recycling of altered oceanic crust, (2) venting of oxygen from the core due to inner core crystallization, and (3) convection-driven homogenization of an initially redox-heterogeneous primordial mantle. It is demonstrated that none of the three mechanisms alone can fully explain the observed trend, although mechanism (3) is best supported by the available geochemical data. These new data provide further evidence for mantle involvement in the dramatic increase in the oxygen concentration of the atmosphere leading up to the Great Oxidation Event at similar to 2.4 Ga. (C) 2019 Elsevier Ltd. All rights reserved.