Geochronology of Intermediate-Acid Intrusive Rocks from Tongling, Anhui

Ar/39Ar isotopic chronologic studies of intrusive rocks from Tongling area, Anhui province have shown that the ages of these rocks are all younger than 140 Ma and belong to Late Yanshanian period, with granodiorite, quartz monzodiorite, pyroxene monzodiorite and gabbro-diabase being 139.8-137 Ma, 137-135.8 Ma, 138.2-136.6 Ma and 133.7 Ma, respectively. Compared with 40Ar/39Ar isotopic chronologic studies of these intrusive rocks, the authors have also dealt with their K-Ar and Rb-Sr isotopic ages, and pointed out that the age error is caused by the late hydrothermal alteration and the mixture of mantle magma and crustal magma. In addition, the mineralization ages are found to be close to the smaller ages of 40Ar/39Ar age spectra, which is in accordance with the regional metallogenic character that mineralization took place later than magmatic activity.