深海橄榄岩中的原位锇同位素填补了洋中脊玄武岩与其源区地幔之间的同位素差距。

In situ Os isotopes in abyssal peridotites bridge the isotopic gap between MORBs and their source mantle.

作者信息

Alard Olivier, Luguet Ambre, Pearson Norman J, Griffin William L, Lorand Jean-Pierre, Gannoun Abdelmouhcine, Burton Kevin W, O'Reilly Suzanne Y

机构信息

GEMOC ARC National Key Centre, School of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia.

出版信息

Nature. 2005 Aug 18;436(7053):1005-8. doi: 10.1038/nature03902.

DOI:10.1038/nature03902

PMID:16107845

Abstract

Abyssal peridotites are assumed to represent the mantle residue of mid-ocean-ridge basalts (MORBs). However, the osmium isotopic compositions of abyssal peridotites and MORB do not appear to be in equilibrium, raising questions about the cogenetic relationship between those two reservoirs. However, the cause of this isotopic mismatch is mainly due to a drastic filtering of the data based on the possibility of osmium contamination by sea water. Here we present a detailed study of magmatic sulphides (the main carrier of osmium) in abyssal peridotites and show that the 187Os/188Os ratio of these sulphides is of primary mantle origin and can reach radiogenic values suggesting equilibrium with MORB. Thus, the effect of sea water on the osmium systematics of abyssal peridotites has been overestimated and consequently there is no true osmium isotopic gap between MORBs and abyssal peridotites.

摘要

深海橄榄岩被认为代表了大洋中脊玄武岩（MORB）的地幔残余物。然而，深海橄榄岩和MORB的锇同位素组成似乎并不处于平衡状态，这引发了关于这两个储库共生关系的问题。然而，这种同位素不匹配的原因主要是基于海水锇污染可能性对数据进行了大幅筛选。在此，我们对深海橄榄岩中的岩浆硫化物（锇的主要载体）进行了详细研究，并表明这些硫化物的187Os/188Os比值起源于原始地幔，且能达到放射性值，表明与MORB处于平衡状态。因此，海水对深海橄榄岩锇系统的影响被高估了，所以MORB和深海橄榄岩之间不存在真正的锇同位素差距。