Two serials of basic magmas from different mantle sources of Late Cretaceous in east Shandong province, China: A comparative study on basalts from Zhucheng and Jiaozhou

The K-Ar chronological method is utilized to study the ages of basalts from Jiaolai basin in Shandong province. The age data of these basalts from two localities are 76Ma and 72Ma respectively. Although these ages both represent the magmatic events in Late Cretaceous, their geochemistry characteristics are different at two localities. Zhucheng basalt is mainly composed of trachybasalt with enriched LREE and OIB affinity of trace elements, (87Sr/86Sr), (0.7060 ∼ 0.7080), and εNd (t) (-3.0 ∼ -5.1), intervening in values of asthenosphere mantle and lithosphere mantle enriched in Mesozoic, which indicates the magma of asthenosphere origin interlarded the magma of enriched lithosphere origin and thus the result of blending of asthenosphere and lithosphere mantle. Jiaozhou basalt is mainly consisted of alkali basalt which is similar trace elements to Zhucheng without HFSE Nb-, Ta-and Ti-depletion, but with even more enriched in LREE than Zhucheng basalt and fairly different in Sr-Nd isotope compositions of (87Sr/86Sr), (0. 70350 ∼ 0.70355), εNd (t) (5.4 ∼ 5.8) which are similar to that of Cenozoic basalts in Shandong province, indicating the asthenosphere origin of magma. This study shows that the astenosphere beneath Jiaolai basin upwelled unevenly and became gradually the trend of main sources of basalts since Late Cretaceous.