去白云化作用机理的实验模拟探讨

EXPERIMENTAL APPROACH TO DEDOLOMITIZATION

通过实验模拟,讨论了自然界中广泛存在的去白云化作用机理。在近地表的酸性条件下,尽管有溶解CaSO_4的参与,方解石的溶解速率仍大大超过白云石,因而认为人们长期用来解释去白云化作用的假想化学反应很难从动力学的角度进行合理的解释。在溶解CaSO_4的参与下,白云石中Ca^(2+)的释放受到抑制,Mg^(2+)的释放速率加快,先转变成一种富Ca^(2+)的白云石,最后转变成方解石。该过程可能部分类似于从原白云石到有序白云石过程的逆过程。

Dedolomitization is very common in the geological history . The dedolomitization mecanism is discussed based on the data from solution experiments of different kinds of dolomite. The kinetic conditions for the hypothetical reaction is doubtful,even though its thermodynamic reqirements may be met. The reasons are as follows: a) Calcite is much more readily dissolved than dolomite under the acidic conditions of near-surface,though dissolved CaSO_4 added and , therefore, it is hard to imagine the precipitation of calcite but disolution of dolomite. b)The release tare of Ca^(2+) decreased notably but that of Mg^(2+) increased rapidily when dissolved CaSO_4 was added into the solvent for dolomite disolution.It is suggested that the process of dedolomitization could be an opposite of dolomitization. Protodolomite is the intermediate product of both dolomitization and dedolomitization ,that is ,under the condition of the fluid with high Ca^(2+)/Mg^(2+) ratio ,ordered dolomite transformes into proto-dolomite rich in Ca^(2+) first ,and then into calcite.