Bindeman Ilya N, Ionov Dmitri A, Tollan Peter M E, Golovin Alexander V
Department of Earth Sciences, University of Oregon, Eugene, OR, USA.
Department of Geosciences, Montpellier University, Montpellier, France.
Nat Commun. 2022 Jul 4;13(1):3779. doi: 10.1038/s41467-022-31586-9.
Oxygen isotopic ratios are largely homogenous in the bulk of Earth's mantle but are strongly fractionated near the Earth's surface, thus these are robust indicators of recycling of surface materials to the mantle. Here we document a subtle but significant ~0.2‰ temporal decrease in δO in the shallowest continental lithospheric mantle since the Archean, no change in Δ'O is observed. Younger samples document a decrease and greater heterogeneity of δO due to the development and progression of plate tectonics and subduction. We posit that δO in the oldest Archean samples provides the best δO estimate for the Earth of 5.37‰ for olivine and 5.57‰ for bulk peridotite, values that are comparable to lunar rocks as the moon did not have plate tectonics. Given the large volume of the continental lithospheric mantle, even small decreases in its δO may explain the increasing δO of the continental crust since oxygen is progressively redistributed by fluids between these reservoirs via high-δO sediment accretion and low-δO mantle in subduction zones.
氧同位素比率在地球地幔的大部分区域基本均匀，但在地球表面附近会强烈分馏，因此这些是地表物质再循环到地幔的有力指标。在这里，我们记录了自太古宙以来最浅的大陆岩石圈地幔中δO有一个微妙但显著的约0.2‰的时间下降，而Δ'O未观察到变化。较年轻的样本显示，由于板块构造和俯冲作用的发展和推进，δO有所下降且具有更大的不均一性。我们认为，最古老的太古宙样本中的δO为地球提供了最佳的δO估计值，橄榄石为5.37‰，全岩橄榄岩为5.57‰，这些值与月球岩石相当，因为月球没有板块构造。鉴于大陆岩石圈地幔的体积巨大，即使其δO有微小下降，也可能解释了大陆地壳δO的增加，因为在俯冲带中，氧通过高δO沉积物堆积和低δO地幔在这些储层之间通过流体逐渐重新分布。
