2024年7月29日出版的《地质学》杂志发表了荷兰阿姆斯特丹自由大学Fraukje M. Brouwer团队的最新研究成果，该研究利用来自锆石-熔体分配实验的新限制，报道了早期地壳岩浆成分和磷有效性的演化。

研究人员通过实验确定了磷(P)丰度对Al (D_Al)、Li (D_Li)和P (D_P)的锆石—熔体分配系数的影响。结果表明，磷含量对D_Al和D_Li有相反的影响，而磷本身和其他微量元素的分配与磷丰度无关。研究人员对其结果进行参数化，得到了冥古代岩浆铝饱和度指数(ASI)和P、Li含量的新评估。岩浆ASI值比以前认为的低约0.5，并在地球演化的前约1Ga期间一直保持在1以下，表明只涉及火成岩原岩。

第一种过铝质(ASI>1)熔体直到ca. 3.6Ga才出现，这支持了一个假设，即在此之前由垂直运动为主的构造样式，向伴有沉积物部分熔融的水平构造样式的转变并未发生。新计算出的年轻锆石岩浆Li浓度与大陆地壳Li丰度吻合得更好。太古代和冥古代岩浆中Li的平均含量偏高(约1000ppm)，表明2 Ga以前形成的锆石中的Li不是原生的。研究计算出的岩浆P丰度在整个地球历史上是一致的(约1900±400ppm)，这表明在整个冥古代期间地壳中有足够的岩浆P来支持生命的起源。

据研究人员介绍，锆石是现存地球近地表过程最古老的见证，冥古代和太古代地壳的条件主要来自于它们的微量元素和同位素组成。然而，锆石与熔体之间元素和同位素分配的定量评估体系仍不完整。

附：英文原文

Title: Evolution of magma compositions and phosphorus availability in early Earth’s crust: New constraints from zircon-melt partitioning experiments

Author: Sheng Shang, Yanhao Lin, Wim van Westrenen, Fraukje M. Brouwer

Issue&Volume: 2024-07-29

Abstract: Zircons are the oldest remaining witnesses of Earth’s near-surface processes, and conditions in the Hadean and Archaean crust are derived predominantly from their trace element and isotopic compositions. However, quantitative assessment of element and isotope partitioning between zircon and melt remains incomplete. We experimentally determined the effect of phosphorus (P) abundance on zircon-melt partition coefficients of Al (D_Al), Li (D_Li) and P (D_P). Results indicate that P content has opposite effects on D_Al and D_Li, whereas the partitioning of P itself and other trace elements is independent of P abundance. Parametrization of our results yields new assessments of the aluminum saturation index (ASI) and P and Li contents of Hadean magmas. Magma ASI values are ～0.5 lower than previously thought and consistently remain below 1 during the first ～1 Ga of Earth evolution, suggesting involvement of only igneous protoliths. First peraluminous (ASI > 1) melts do not appear until ca. 3.6 Ga, supporting the hypothesis that a transition from a tectonic style dominated by vertical motion to horizontal tectonics accompanied by partial melting of sediments did not occur before that time. New calculated magma Li concentrations for young zircons are in much better agreement with the continental crust Li abundance. Average calculated Archaean and Hadean magma Li concentrations are unrealistically large (>1000 ppm), suggesting that Li in zircons formed before 2 Ga is not primary. Calculated magma P abundances are uniform (～1900 ± 400 ppm) throughout Earth history, suggesting sufficient crustal P was available throughout the Hadean to support the origin of life.

DOI: 10.1130/G52304.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G52304.1/645959/Evolution-of-magma-compositions-and-phosphorus