Liu Sheng-Ao, Rudnick Roberta L, Liu Wen-Ran, Teng Fang-Zhen, Wu Tian-Hao, Wang Ze-Zhou
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China.
Department of Earth Science and Earth Research Institute, University of California, Santa Barbara, CA 93106, USA.
Sci Adv. 2023 Sep 8;9(36):eadg6995. doi: 10.1126/sciadv.adg6995. Epub 2023 Sep 6.
The continental crust is strongly depleted in copper compared with its building blocks-primary arc magmas-and this depletion is intrinsically associated with continental crust formation. However, the process by which Cu removal occurs remains enigmatic. Here we show, using Cu isotopes, that subduction-zone processes and mantle melting produce limited fractionation of Cu isotopes in arc magmas, and, instead, the heterogeneous Cu isotopic compositions of lower crustal rocks, which negatively correlate with Cu contents, suggest segregation or accumulation of isotopically light sulfides during intracrustal differentiation of arc magmas. This is supported by the extremely light Cu isotopic compositions of lower crustal mafic cumulates and heavy Cu isotopic compositions of differentiated magmas in thick continental arcs. Intracrustal differentiation of mantle-derived magmas and subsequent foundering of sulfide-rich mafic cumulates preferentially removes isotopically light Cu, leaving a Cu-depleted and isotopically heavy continental crust.
与构成大陆地壳的原始物质——原生弧岩浆相比，大陆地壳的铜含量严重亏损，这种亏损与大陆地壳的形成有着内在联系。然而，铜被移除的过程仍然是个谜。在这里，我们利用铜同位素表明，俯冲带过程和地幔熔融在弧岩浆中产生的铜同位素分馏有限，相反，下地壳岩石的铜同位素组成不均一，且与铜含量呈负相关，这表明在弧岩浆的地壳内分异过程中，同位素较轻的硫化物发生了分离或聚集。厚大陆弧中下地壳镁铁质堆积物的铜同位素组成极轻，而分异岩浆的铜同位素组成较重，这支持了上述观点。幔源岩浆的地壳内分异以及随后富含硫化物的镁铁质堆积物的下沉优先移除了同位素较轻的铜，从而留下了贫铜且同位素较重的大陆地壳。
