Boron Isotopic Composition of the Troodos Ophiolite

大洋中脊的热液作用对海水和洋壳的化学和同位素组成产生了深远的影响，涉及的许多元素的化学通量超过了全球河流排放的化学通量。尽管这些水热过程很重要，但它的基本方面，如在不同温度下的反应程度和流体流动路径，并没有得到很好的限制。此外，蚀变地壳的俯冲导致来自水圈的元素重新注入地幔。这些回收材料的散装化学转移率和化学签名受到的限制很小。最近已经证明，与洋壳的变化有关的是大量的硼同位素分馏(Spivack和Edmond，1987)。这种交换对海水的硼同位素组成施加了初步控制(相对于大陆和海洋火成岩，在11B/10B比率中富含~40/mil)，并赋予地壳一个硼同位素特征，该特征应有助于示踪被俯冲的挥发分，并在评价包括流体反应历史在内的热液过程的性质方面具有诊断作用。反应和流动路径的温度。我们建议对特罗多斯蛇绿岩进行硼同位素研究，其目的有二：1)建立蚀变洋壳的一级硼同位素剖面；2)为未来热液系统研究中开发硼同位素提供背景资料。为此，我们打算在整个岩石和脉体分离中测定矿物学和化学特征良好的(B)和11B。蚀变温度和流体演化将受到氧和锶同位素数据的制约。

Hydrothermal reactions at mid-ocean ridges have a profound influence on the chemical and isotopic composition of seawater and the oceanic crust, involving chemical fluxes of many elements exceeding those from global river discharge. Despite its importance, fundamental aspects of these hydrothermal processes such as the extent of reaction at various temperatures and fluid flow paths are not well constrained. In addition, subduction of the altered crust results in the reinjection of elements derived from the hydrosphere back into the mantle. The bulk chemical transfer rates and the chemical signature of these recycled materials is poorly constrained. Recently it has been demonstrated that there are large boron isotopic fractionations associated with the alteration of the oceanic crust (Spivack and Edmond, 1987). This exchange exerts a primary control on the boron isotopic composition of seawater (~40 per mil enriched in the 11B/10B ratio relative to continental and oceanic igneous rocks|) and imparts a boron isotopic signature to the crust that should be useful as a tracer of subducted volatiles, and diagnostic in evaluating the nature of hydrothermal processes including fluid reaction histories, temperatures of reaction and flow paths. We propose to conduct a boron isotope study of the Troodos ophiolite that is aimed at two goals: 1) establishing a first order boron isotope profile for the altered oceanic crust and 2) developing the background data required for the future exploitation of boron isotopes in the study of hydrothermal systems. To these ends we intend to determine (B) and 11B in whole rocks and vein separates that are mineralogically and chemically well characterized. Alteration temperatures and fluid evolution wii be constrained by oxygen and strontium isotope data.