Salters Vincent J M, Dick Henry J B
National High Magnetic Field Laboratory and Department of Geological Sciences, Florida State University, Tallahassee, Florida 32306, USA.
Nature. 2002 Jul 4;418(6893):68-72. doi: 10.1038/nature00798.
Inferring the melting process at mid-ocean ridges, and the physical conditions under which melting takes place, usually relies on the assumption of compositional similarity between all mid-ocean-ridge basalt sources. Models of mantle melting therefore tend to be restricted to those that consider the presence of only one lithology in the mantle, peridotite. Evidence from xenoliths and peridotite massifs show that after peridotite, pyroxenite and eclogite are the most abundant rock types in the mantle. But at mid-ocean ridges, where most of the melting takes place, and in ophiolites, pyroxenite is rarely found. Here we present neodymium isotopic compositions of abyssal peridotites to investigate whether peridotite can indeed be the sole source for mid-ocean-ridge basalts. By comparing the isotopic compositions of basalts and peridotites at two segments of the southwest Indian ridge, we show that a component other than peridotite is required to explain the low end of the (143)Nd/(144)Nd variations of the basalts. This component is likely to have a lower melting temperature than peridotite, such as pyroxenite or eclogite, which could explain why it is not observed at mid-ocean ridges.
推断大洋中脊的熔融过程以及熔融发生时的物理条件，通常依赖于所有大洋中脊玄武岩源之间成分相似的假设。因此，地幔熔融模型往往局限于那些仅考虑地幔中存在一种岩石类型（橄榄岩）的模型。来自捕虏体和橄榄岩地块的证据表明，在地幔中，除橄榄岩外，辉石岩和榴辉岩是最丰富的岩石类型。但在大部分熔融发生的大洋中脊以及蛇绿岩中，辉石岩却很少被发现。在此，我们展示深海橄榄岩的钕同位素组成，以研究橄榄岩是否真的能成为大洋中脊玄武岩的唯一来源。通过比较西南印度脊两个地段玄武岩和橄榄岩的同位素组成，我们发现需要除橄榄岩之外的一种组分来解释玄武岩（¹⁴³Nd/¹⁴⁴Nd）变化的低端情况。这种组分的熔融温度可能比橄榄岩低，比如辉石岩或榴辉岩，这可以解释为什么在大洋中脊没有观察到它。
