黔西逆冲滑脱构造及其对铅锌矿床的控制

黔西地区位于上扬子地块西南缘,大地构造处于古特提斯构造域与太平洋构造域共同控制与影响的区域.该区广泛出露中上泥盆统-下三叠统(D2-T1)碳酸盐岩为主的沉积岩,下伏下泥盆统与志留系巨厚页岩和粉砂岩,构成了该区的底部滑脱层.在D2-T1碳酸盐岩为主的强硬岩层中夹有的页岩-粉砂岩、炭质页岩构成了次级滑脱层.在中生代,受上述两大构造域远程复合作用,黔西地区发生了多次构造活动与叠加变形.在挤压收缩过程中,强硬层与软弱层之间的滑脱作用形成了黔西地区复杂的构造格局.不同阶段不同规模的逆冲滑脱作用(顺层滑脱→切层滑脱→小型逆冲→大型逆冲)对铅锌富集起到了不同的控制作用.顺层滑脱形成了与层理一致的铅锌富集;切层滑动(小型逆冲)控制了稍陡于岩层的铅锌矿富集;小型平移或张性断层控制了陡倾铅锌矿的富集;而大型逆冲断层则控制了大型、超大型铅锌矿床的富集.因此,逆冲滑脱作用是控制黔西铅锌矿床富集的最重要因素.

The thrust-decollement structure in western Guizhou and its control of Pb-Zn deposit

The western Guizhou area is located in the southwest margin of the upper Yangtze Block, which is influenced both by the Tethys tectonic process and the Pacific tectonic process. The most widely exposed sedimentary rocks in this area are mainly the Middle and Upper Devonian-Lower Triassic (D₂-T₁) carbonate. The Lower Devonian and Silurian shale and siltstones are overlaid to constitute the bottom detachment layer in this area. Shale, siltstones and carbonaceous shale in D₂-T₁ carbonate hard rock form the secondary detachment layer. In the Mesozoic, due to the remote recombination of the above two tectonic process, many tectonic activities and superimposed deformation occurred in western Guizhou. In the extrusion process, the decollements between the hard and the weak layer formed the complex tectonic pattern. The different scale thrust-decollement in different stage (interlayer decollement-multi detachment-small thrust-large thrust) has different effects for Pb and Zn enrichment. Pb and Zn enrichment was formed by interlayer decollement in accordance with bedding. Furtherly, multi detachment (small thrust) controls Pb-Zn enrichment slightly steeper than the strata. Small parallel displacement or tensile faults control the enrichment of steeply dipping lead-zinc deposits, whereas the large thrust faults control the enrichment of large and very large Pb-Zn deposits. Therefore, the thrust-decollement is the most important factor to control the enrichment of Pb-Zn deposit in western Guizhou.