Karst water serves as an important water supply source in northern China. Hydrochemical and isotope (¹⁸O, ²H, and ³H) characteristics are invaluable tools to identify water–rock interaction activities in karst water systems. In this study, the investigation of hydrogeological conditions, hydrogeochemistry, and hydrogen and oxygen isotopes of karst water revealed: (1) HCO₃-Ca-type water is widely distributed throughout the study area, while HCO₃-Ca·Mg-type water appears in the direct recharge areas and the discharge areas; karst water of the HCO₃⁻·Cl⁻, Cl⁻·HCO₃⁻, and Cl⁻ types is scattered in low-land areas; (2) karst water has high δ¹⁸O, which may be due to the dissolution and exchange of ¹⁸O from the surrounding carbonate rocks in the western discharge zone; and (3) the ³H concentration of karst water is strongly correlated with the content of major ions (Ca²⁺, Mg²⁺, HCO₃⁻, SO₄²⁻, and Cl⁻) and it increases along the flow path. It was also revealed that the karst water in the discharge areas is mixed with lateral recharge (infiltration recharge from surface water).

The Early Cretaceous intermediate intrusive rocks have important significance in understanding the crust–mantle interaction, iron mineralization, and tectonic evolution in the western Shandong Peninsula. In this study, we present new zircon U–Pb ages, and Hf isotope, whole-rock geochemistry, Sr–Nd isotopes, and the mineral chemistry of the diorite-porphyrite in the southern Xintai area, mid-western Shandong Peninsula. The diorite-porphyrite formed at ca. 125 Ma. They have intermediate SiO₂ (59.57–62.29 wt.%) and MgO (2.78–3.58 wt.%) contents, high Mg# values (53–56), high Sr (589–939 ppm) and low Y (9.2–10.8 ppm) contents, and high Sr/Y ratios (54–94), showing adakitic affinity. The diorite-porphyrite exhibits lower zircon ε_Hf(t) values (−30.1 to 7.5) and whole-rock ε_Nd(t) values (−3.5 to −6.0), with (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.70514–0.70567. We suggest that the diorite-porphyrite was derived from the partial melting of the local delamination of lower continental crust and then by the interaction with the enriched lithospheric mantle. The genesis of diorite-porphyrite may be related to the rollback process of the Paleo-Pacific slab in the Early Cretaceous. This geodynamic process induced the melting of the enriched lithospheric mantle, subducted oceanic crust, and local delamination of lower continental crust, which produced different types of adakitic magmatism in the western Shandong Peninsula.