应用网络理论研究地幔流体的形成机制

北京大学学报（自然科学版）

应用网络理论研究地幔流体的形成机制

朱永峰

北京大学地质学系，北京，100871

收稿日期:1994-09-28 出版日期:1995-07-20 发布日期:1995-07-20

Apply the Net-Work Theory to Study the Mechanism of Mantle Fluid's Formation

ZHU Yongfeng

Department of Geology, Peking University, Beijing, 100871

Received:1994-09-28 Online:1995-07-20 Published:1995-07-20

摘要/Abstract

摘要： 上地幔的不均一性尤其表现在挥发性组分（CO₂，H₂O，H₂，CO，S，Cl，F，CH₄等）和碱金属的含量及分布特征上。地幔中存在过富含碱金属和其它轻元素的独立流体，它是以挥发性组分为主的富含Si的碱质流体。我们应用网络理论通过对地幔熔体结构的分析来讨论地幔流体的形成机制。熔体是由以［SiO₄］为核心的聚合体构成的。挥发性组分填充在聚合体空隙中，或者挥发性组分以及它们的离子、K、Na等元素通过离子键或范德华力与［SiO₄］，Mg，Fe等聚合而形成聚合体。这种聚合体通过主价键形成一种立体网状排列的结构——网络结构。在原始地幔中网络是各向等强的，即结构中的离子或分子团的分布呈随机无序状态，当有剪切力作用时，网络中最弱的键会遭到破坏，从而使网络结构发生调整并在新的环境下寻求新的结构上的平衡状态。地幔熔体网络中最弱的键是范德华键和Na，K与[SiO₄]之间的离子键，这些键首先被破坏。网络结构的调整导致熔体粘度的变化，使网络中杂乱分布的各种离子和挥发性组分重新分配。这个过程是散布于网络中的挥发性组分和K，Na，以及不能进入[SiO₄]或与之形成主价键的不相容元素、成矿元素从网络中分离出来形成独立的流体相。

关键词: 地幔流体, 网络理论, 不均一性

Abstract: The heterogeneous mantle especially was shown by the concentrations of volatiles(CO₂, H₂O, H₂, CH₄, CO)and alkali elements. Some researchers even believed that in mantle presents or had existed alkali-rich and volatile-rich lamination flow. In such fluid the contents of [SiO₄], K, and Na are very high. We studied the forming mechanism of mantle fluid in the light of net-work theory. The primitive mantle was an olivinite traped in melt state, consisted of polymeres, centring around [SiO₄]. Volatiles spread among polymeres, formingionic and/or molecule bonding between K, Na, Fe, Mg and [SiO₄]. The polymeres bound together by ionic and molecule bonding and formed net-workstructure. This is a homogeneous structure, i. e. , in all directions the strengthwas same, volatiles, K, Na, oreforming elements spread in a disorder state. When net-work structure was acted by a shear stress τ₀, the weak bonding in structure would break down, and net-work structure would have a change in order to respond to the new condition. The bonding among K, Na, [SiO₄] and volatiles is weaker than the bonding between [SiO₄], Fe and Mg. So these bondings would be destroied at first. As a result, the volatiles, K and Na would exsolve from the network structure and formed mantle fluid.