Abstract:

In the Yanshanian period, large-scale magmatic intrusion occurred in the Laiwu Basin. Certain water source areas, karst and water-rich blocks were developed in carbonate rocks around the intrusions. Marbleization often occurs in the carbonate aquifers near the intrusions. Magmatic-hydrothermal fluids, which are rich in acidic components such as CO₂ and H₂S, can cause significant dissolution of carbonate rocks. The mechanism and characteristics of hydrothermal dissolution in the Laiwu Basin were identified via analyzing the chemical composition of rock samples, hydrogeological surveying and data statistical analysis, together with detail observation on the hydrothermal dissolution spots. Consequently, the hydrothermal dissolution model for the region was constructed. The results show that the high-temperature/-pressure magmatic intrusions likely caused the marble metamorphism of carbonate rocks in the contact zone. Hydrothermal fluids migration along permeable faults, fissures and unconformities could cause acidic hydrothermal dissolution and mixed dissolution in the carbonate formation, and formed dissolution cavities of different scales. The cavities constitute the current sites of groundwater enrichment, and provide a new direction of water reserve exploration for towns and cities.

Key words: carbonate rock, hydrogeology, Majiagou Group, hydrothermal dissolution, central Shandong mountainous area