关于成岩成矿深度构造校正测算的理论基础、方法和实例

THEORETICAL BASIS, METHOD AND CALCULATION ON TECTONO-CORRECTED DEPTH OF PETROGENESIS AND METALLOGENESIS

成岩成矿深度的构造校正测算方法 ,是从测算压力中先消除掉构造附加静水压力之后再计算上覆岩石厚度 ,即成岩成矿深度的方法。该方法基于对地壳岩石处于固体应力状态的认识之上 ,采用弹性固体模型代替静止流体模型 ,对“上覆岩石重力在数值上等同于该点所承受的静水压力”这一通常的认识提出了不同见解 ,比沿袭至今单纯用压力 /比重 (或密度 )方法得出深度更符合于实际情况。本文介绍了该方法的理论基础和野外地质研究方法———开展变形岩相形迹填图 ,在室内利用三维变形和古差应力测量 ,根据样品所处构造部位和性质 ,选择不同的参数换算成矿时差应力的众值。以胶东玲珑—焦家式金矿床为例 ,求得成矿深度仅3.5km或更浅 ,进而提出更深部位存在深部金矿富集带的预测意见。胶东几个大型金矿深部第二富集带已揭露的勘探资料证实这一认识比较符合实际情况。用这一方法测算出大别超高压带含柯石英榴辉岩形成深度仅 32km多 ,而不是用压力 /比重方法估算的 1 0 0多公里 。

According to the tectonic correcting method of measurement and calculation of formation depth of rocks and ore deposits, we should subtract additional tectono induced hydrostatic pressure from the total pressure and then measure overlying rock's thickness. This method on basis of the knowledge of the crust rock in solid stress state, taking the elastic pattern rather than the state fluid pattern, was more accorded with the actual situation in the crust than the method weight/special weight. This paper, with the examples of Linglong Jiaojia type gold deposits in the Jiaodong area and the Dabie ultrahigh pressure metamorphic belt in central China, introduced the theoretical basis about this method of measurement with tectonic correction, and field research method-mapping of tectonic deformed petrofacies, the setting up system of strain stress equations to get 3 D principal stresses, the choosing the conversion coefficient of stress value being 0～0.1 in transtension zone, the value 0.1～0.5 in shear zone and the value 0.5～0.75 in transcompression zone, respectively, so as to get the stress values of model. Finally, we could do the calculation and correction method of formation depth of gold deposits with additional tectono induced hydrostatic pressure 〔P S =13(σ 1+σ 2+σ 3)〕,i. e. to subtract P S firstly from measured P and then use P G supposed by Terzaghi and Peck (1948). New data about 2.5～3.5 km of metallogenic depth of gold deposits in the Jiaojia area and over 32 km of formational depth of coesite bearing eclogite in the Dabie ultrahigh pressure metamorphic belt were calculated by the tectono corrected method.