铁锰结核结壳生长过程的一种理论假设

GROWTH OF FERROMANGANESE NODULES AND CRUSTS: A THEORETICAL HYPOTHESIS

铁锰结核成矿物质的直接来源是大洋底层水和沉积物孔隙水，结壳只有底层水，因此，底层水和孔隙水的物理化学特征就成为理解铁锰结核（壳）成矿作用特征与过程的关键。铁锰结核（壳）内部构造的两个明显特征是：①韵律性的环状纹层构造，和②树枝状构造，这两种构造是典型的远离平衡的非线性地质作用的产物。正常情况下，海底水—沉积物界面系统的底层水、孔隙水中Ｍｎ、Ｆｅ是不饱和的。因此，铁锰结核（壳）不可能在平衡状态下连续生长。本文提出铁锰结核（壳）生长的自反馈“振荡式”模型。

The direct source of ore- forming elements of deep sea ferromanganese nodules andcrusts is deep sea bottom water and pore water of deep sea sediments. Therefore,thephysical-chemical features of the bottom water and pore water are the key to under-stand the characteristics and process of the mineralization of nodules and crusts. The main features of the inner structure of nodules and crusts are irregular growthof minerals,particular lamination and element zonation. All these are the results of non-linear geological process at nonequilibrium state. Ferromanganese nodules and crusts aredominantly composed of Fe and Mn oxides and hydroxide which δ-MnO_2 and FeOOH canstand for. Generally,Mn and Fe are not saturated in the bottom water and pore water,therefore,nodules and crusts can not continuously grow in equilibrium condition. Presently,we suggest a nonlinear auto-feedback model for the growth of ferromanganesenodules and crusts.This rnodel can be summarised as follows:Due to the influence of an accidental geological factor,such as Antarctic BottomCurrent,Fe-Mn-unsaturated bottom and pore water near the oceanic bottom can reach atemporary and local saturation,which induces the ferromanganese oxide to begin its ini-tial growth at the sea bottom. As sea bottom water-sediment(rock)surface system lies in the whole open oceanicsystem,it inevitably has a continuous material and energy exchanges with its neigbours. Because the factor inducing the initial growth of ferromanganese oxides is temporary andlocal and there is inertia of chemical reactions and geological process(as in other physicalmovements),there must be a lowering tendency of Fe and Mn concentrations in sea wa-ter near the precipitated ferromanganese oxides,and at the same time,the precipitationrates of the oxides also become lower and lower,and the Fe and Mn concentration in seawater near the precipitated ferromanganese oxides becomes lower than those in the pri-marv sea water,which causes ions of Mn and Fe from farther-awav sea water to diffusetowards the precipitated ferromanganese oxides,and again because of the inertia,the ele-ment concentrations in the narrow sea water area near the oxides increase andferroman-ganese oxides grow。Repeated like this,ferromanganese oxides grow to form nodules andcrusts in an intermittent way. Each inducement-growth-stop cycle produces a basic con-tinuously-growing microlamination in the internal fabric of a ferromanganese nodule andcrust.Of course,geological process is very cornplicated,and violent geological changessueh as volcanic explosion can destroy this nonlinear auto- feedback process to cause agreat hiatus of nodule and crust growth.Then another inducement begins to re-establishanother similar growth process in a new physical- chemical environment.Every induce-ment-growth-stop- growth- stop……destruction-inducemetit cycle can produce a basicstructural group for the ferromanganese nodules and Crusts,Repeated cycles can make asuperimposition of multiple structural groups.