Boron Isotopic Composition of the Oceanic Crust

海水硼同位素组成（11B/10B）相对于新鲜地幔源岩具有高富集（~40 / mil）特征。最初的工作表明，这种富集主要是与海洋地壳变化有关的大同位素分馏的结果。此外，蚀变地壳的硼同位素组成以海水硼为主，似乎与地幔不同，可能由不同的组成域组成。因此，硼同位素似乎在阐明与海洋地壳变化有关的许多地球化学和地球物理问题方面具有很大的潜力。其中包括俯冲挥发物在岛弧和洋岛火山作用中的作用、热液流体的演化以及海水/地壳交换的长期变化。本次海水/海洋地壳硼同位素交换研究有以下具体目的：1)确定蚀变地壳中硼和硼同位素的分布；2)量化从海水中提取到海洋地壳的硼的净通量和同位素组成；3)为硼同位素的开发提供必要的背景数据，作为热液系统研究的诊断工具。

The isotopic composition of seawater boron (11B/10B) is highly enriched (~40 per mil) relative to fresh mantle derived rocks. Initial work indicates that this enrichment is primarily the result of large isotopic fractionations associated with the alteration of the oceanic crust. In addition, the boron isotopic composition of the altered crust is dominated by seawater boron that appears to be distinct from the mantle and may be composed of compositionally distinct domains. As a result, it appears that boron isotopes have a great potential for elucidating a number of geochemical and geophysical problems associated with the alteration of the oceanic crust. These include the role of subducted volatiles in island-arc and ocean island volcanism, the evolution of hydrothermal fluids and secular changes in seawater/crust exchange. This study of seawater/oceanic crust boron isotope exchange has the following specific goals: 1) to determine the distribution of boron and boron isotopes within the altered crust, 2) to quantify the net flux and isotopic composition of boron extracted from seawater into the oceanic crust and 3) to develop the essential background data that are required for the future exploitation of boron isotopes as a diagnostic tool in the study of hydrothermal systems.