Geochemical research on C—O and Sr—Nd isotopes of mantle-derived rocks from Shandong Province, China

This paper presents systematic studies on the C—O and Sr—Nd isotopic compositions for Cretaceous Badou carbonatites, Fangcheng basalts, and Jiaodong lamprophyres and Paleozoic Mengyin kimberlites in Shandong Province, China. Paleozoic kimberlites have normal and uniform C—O isotopic compositions with δ 13 C and δ 18 O in the range of -4.8‰— -7.6‰ and +9.9‰—+13.2‰, respectively. However, Cretaceous three different types of mantle-derived rocks have quite different C—O isotopic compositions, indicating that the mantle sources are probably partially contaminated with organic carbon-bearing crustal materials. These Cretaceous rocks show uniform and EMII-like Sr—Nd isotopic compositions and also indicate that the mantle sources were affected by recycled crustal materials. Comparative studies of C—O and Sr—Nd isotopes reveal that the lithospheric mantle beneath the eastern North China Craton had different isotope characteristics in the Paleozoic, the early Cretaceous, and the Tertiary time. This demonstrates that the lithospheric mantle beneath the region underwent at least twice reconstructions since the Paleozoic. Available data imply that the first reconstruction mainly happened during the Triassic −Jurassic time with gradual changes and the second in the Cretaceous with abrupt changes. Results also show that the early Cretaceous (especially at 120—130 Ma) was perhaps the key period leading to the dramatic change of the Mesozoic geodynamics on the eastern North China Craton.