沂蒙山区典型断陷盆地岩溶地下水系统特征:以莱芜盆地为例

Characteristics of karst groundwater flow systems of typical faulted basins in Yimeng Mountain area: A case study of Laiwu Basin

2011年以来,中国地质调查局在沂蒙山区组织实施了1∶5万标准图幅水文地质调查4万余km^(2),并在严重缺水村镇开展了大量的找水打井示范工作,获得了较为丰富的地质数据,对断陷盆地地下水流系统取得了新认识。受中新生代构造影响,沂蒙山区发生断裂褶皱、伸展滑脱及岩浆侵入活动,形成一系列"南超覆北断陷"的地堑—半地堑盆地,并最终形成现今典型的"盆—山"岩溶水文地质结构,及以盆地为单元的相对独立的岩溶地下水流系统。为研究沂蒙山区地下水流系统发育特征,选择莱芜盆地为典型研究区,基于野外地质调查,通过综合分析盆地南北两侧地貌单元、含水岩组立体空间分布及地下水水位、水化学及同位素结果等,探讨了沂蒙山区典型"盆—山"结构塑造的多级岩溶地下水流系统特征。结果表明,莱芜盆地岩溶地下水由盆地外围向盆地中心呈"向心式"径流;受人类活动影响、地质构造控制和含水层分布制约,盆地南北两侧地下水流系统特征存在差异:盆地南部发育中间和局部两级地下水流系统;盆地北部则仅发育单一的局部地下水流系统,但占有已勘查论证的近1/2的地下水水源地。此外,研究发现在大汶河最低侵蚀基准面,区域滑脱构造及热液混合作用拆离的空隙,与岩层面、层间裂隙、顺层溶蚀空隙等共同构成立体的岩溶地下水网络,影响着岩溶水循环途径及深度。以此认识为指导,实施的探采结合井成井率达到86%,强化了地下水流系统理论在北方基岩山区水文地质工作中理论与实践的结合。

China Geological Survey has organized and implemented 1∶50 000 standard map hydrogeological survey with an area of more than 40000 square kilometers in Yimeng Mountain area. And it carried out a large amount of water prospecting and well drilling demonstration work in villages and towns with serious water shortage, obtained rich geological data and gained a new understanding of groundwater flow systems. Under the influence of Mesozoic and Cenozoic structures, the faults and folds, extensional detachment and magmatic intrusion occurred in Yimeng Mountain area, formed a series of graben-semi graben basins characterized by overlapping in the south and faulting in the north, and finally formed today’s typical "basin-mountain" karst hydrogeological structure and the relatively independent karst groundwater system, which taking basin as unit. In order to study the development characteristics of groundwater flow system in Yimeng Mountain area, Laiwu Basin was selected as a typical study area. On the basis of the field geological survey, through comprehensively analyze the geomorphic units, the three-dimensional spatial distribution of water bearing rock groups, groundwater level, hydrochemistry, and water isotope results on the north and south sides of the basin, this paper comprehensively discusses the characteristics of multistage karst groundwater flow systems with typical "basin-mountain" structure in Yimeng Mountain area. The results show that, the karst groundwater in Laiwu Basin presents a "centripetal" runoff from the outer periphery to the center of the basin. Affected by human activities, controlled by geological structure and aquifer distribution, the characteristics of groundwater flow systems between the north and south sides of the basin are different. There are mainly intermediate and local groundwater flow systems in the south of the basin, while a single local groundwater flow system is developed in the north of the basin, however, it occupies nearly 1/2 of the groundwater sources that have been explored and demonstrated. In addition, it is found that at the lowest erosion base level of Dawen River, the voids separated by regional detachment structure and hydrothermal mixing, together with rock layer, interlayer fissures and bedding dissolution voids, form a three-dimensional karst groundwater network, which influence the circulation path and depth of karst water. Guided by this understanding, the completion rate of exploration production combined wells has reached 86%, which strengthens the combination of theory and practice of groundwater flow system theory in hydrogeological work in bedrock mountainous areas in North China.