英国卡迪夫大学Marc-Alban Millet团队发现了大洋中脊非均匀熔体的地壳与地幔水平聚集。2025年3月4日出版的《地质学》杂志发表了这项成果。

大洋中脊玄武岩（MORB）长期以来一直被用于研究上地幔的组成。MORB的同位素异质性与扩张速率呈负相关，表明在岩浆强劲的快速扩张脊上增强的岩浆混合使地幔异质性的特征消失。然而，目前尚不清楚这种混合是在地幔熔体提取过程中还是在地壳岩浆储层中发生的。

为了区分地幔聚集和地壳岩浆混合，研究组测量了赫斯深渊（赤道太平洋）暴露的快速扩张地壳剖面下地壳辉长岩中的积云斜长石和斜辉石岩芯的Nd同位素组成。数据显示，地幔在熔体提取的尺度上是不均匀的，下地壳的晶体记录显示，¹⁴³Nd/¹⁴⁴Nd的不均匀性大于上覆的MORB。因此，太平洋MORB并不能反映其地幔源的完全异质性，地壳内发生了一些熔体聚集。然而，赫斯深渊下地壳的同位素异质性低于较慢扩散环境，这表明地幔中熔体与地壳聚集的程度受扩散速率的控制。

附：英文原文

Title: Crustal versus mantle-level aggregation of heterogeneous melts at mid-ocean ridges

Author: George F. Cooper, C. Johan Lissenberg, Janne M. Koorneef, Max N. Jansen, Marc-Alban Millet

Issue&Volume: 2025-03-04

Abstract: Mid-ocean ridge basalts (MORBs) have long been used to investigate the composition of the upper mantle. The isotopic heterogeneity of MORB correlates inversely with spreading rate, indicating that enhanced magma mixing at magmatically robust fast-spreading ridges mutes the signature of mantle heterogeneity. It has remained unclear, however, whether this mixing occurs during melt extraction from the mantle or in crustal magma reservoirs. To discriminate between mantle aggregation and crustal magma mixing, we measured the Nd isotopic composition of cumulus plagioclase and clinopyroxene cores within lower crustal gabbros from the fast-spreading crustal section exposed at Hess Deep (equatorial Pacific Ocean). Our data reveal that the mantle is heterogeneous at the scale of melt extraction, and the crystal record from the lower crust shows greater 143Nd/144Nd heterogeneity than the overlying MORB. Hence, Pacific MORBs do not reflect the full heterogeneity of their mantle source, and some aggregation of melts occurs within the crust. However, isotopic heterogeneity in the lower crust at Hess Deep is lower than in slower-spreading settings, suggesting that the extent to which melts aggregate in the mantle versus the crust is controlled by spreading rate.

DOI: 10.1130/G52872.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G52872.1/652552/Crustal-versus-mantle-level-aggregation-of