Basch Valentin, Sanfilippo Alessio, Genske Felix, Böhnke Mischa, Zanetti Alberto, Stracke Andreas
University of Pavia, Department of Earth and Environmental Sciences, Via Ferrata 1, Pavia, Italy.
Consiglio Nazionale delle Ricerche, Institute of Geoscience and Earth Resources, Via Ferrata 1, Pavia, Italy.
Sci Adv. 2025 Apr 18;11(16):eadu2044. doi: 10.1126/sciadv.adu2044.
The oceanic crust crystallizes from melts formed within a heterogeneous mantle source, which is mostly composed of variably depleted peridotites and recycled crust. Yet, the compositional variability of this mantle source and the progressive aggregation of heterogeneous melts during extraction are poorly constrained. Here, we show that in situ isotopic analyses in gabbros formed at the East Pacific Rise retain substantially greater Sr-Nd-Hf isotopic heterogeneity than basalts erupted along the fast-spreading ridge. This implies that melt aggregation during migration through the upper mantle and lower crust is inefficient, even at magmatically productive spreading ridges; efficient melt mixing likely occurs in the overlying axial melt lens. Local isotopic heterogeneity of Hess Deep gabbros indicates incomplete mixing of primary melts produced from variably depleted peridotites and oceanic crust recycled at least 1.5 billion years ago. The isotopic heterogeneity recorded in lower gabbros further substantiates that basalt compositions reflect only part of the compositional spectrum of melts passing through the ridge plumbing system.
大洋地壳由源自非均质地幔源区的熔体结晶形成，该源区主要由不同程度亏损的橄榄岩和再循环地壳组成。然而，这种地幔源区的成分变异性以及萃取过程中异质熔体的逐步聚集受到的限制较少。在这里，我们表明，对东太平洋海隆形成的辉长岩进行的原位同位素分析显示，其Sr-Nd-Hf同位素异质性比沿着快速扩张洋中脊喷发的玄武岩要大得多。这意味着，即使在岩浆活动活跃的扩张洋中脊，熔体在上地幔和下地壳迁移过程中的聚集效率也很低；有效的熔体混合可能发生在上覆的轴部熔体透镜体中。赫斯深海辉长岩的局部同位素异质性表明，由不同程度亏损的橄榄岩和至少15亿年前再循环的大洋地壳产生的原始熔体混合不完全。下部辉长岩中记录的同位素异质性进一步证实，玄武岩成分仅反映了通过洋中脊管道系统的熔体成分谱的一部分。
