Geochemical transition shown by Cretaceous granitoids in southeastern China: Implications for continental crustal reworking and growth

• DOI: 10.1016/j.lithos.2014.03.003
• Publication Date: 2014-03-13T17:01:33Z
• Authors: Jing-Yuan Chen; Jin-Hui Yang; Ji-Heng Zhang; Jin-Feng Sun
• Keywords: Underplating; Adakite

Abstract Zircon U–Pb ages and in-situ trace elements and Hf–O isotope compositions, together with whole rock geochemical and Sr–Nd–Hf isotopic data, are presented for Cretaceous granitoids in southeastern (SE) China in order to establish their origin and the evolution of the underlying lithosphere during the Late Mesozoic. Two stages of Cretaceous magmatism, with contrasting geochemical features, have been identified: an earlier adakite-like biotite granite as represented by the Shangying pluton and a later enclave-bearing monzogranite as represented by the Zaoshan pluton. The Shangying biotite granites have a zircon U–Pb age of 99 ± 1 Ma. They have relatively low Y and Yb contents, with high La/Yb and Sr/Y ratios, showing geochemical features of adakite. Their Sr–Nd–Hf isotope compositions are similar to those of Early Cretaceous mafic rocks in the same area, indicating that they were generated by partial melting of juvenile granulitic crust at a depth of about 40 km. The source was formed by underplating of enriched lithosphere mantle-derived magmas. In contrast, the Zaoshan calc-alkaline monzogranites, their enclaves and associated dolerite dykes from the Zaoshan pluton have an emplacement age of ~ 88 ± 1 Ma. The dolerites have high MgO contents, relatively low SiO 2 concentrations and low La/Yb ratios, and depleted Hf isotope compositions. All these geochemical features suggest that they were derived from a depleted spinel Iherzolite mantle source. The enclaves have high SiO 2 contents, indicating that they were derived from a crustal source. They have variable zircon Hf and O isotope compositions, suggesting that two components, i.e., a high e Hf (t) and a low δ 18 O component and a low e Hf (t) and high δ 18 O component, were involved in their origin. The high zircon e Hf (t) values and low δ 18 O values are similar to those of the dolerites, indicating a common source. Thus, we suggest that the enclaves were generated by partial melting of newly underplated depleted mantle-derived materials. The monzogranites have distinctly different zircon Hf and O isotope compositions from the enclaves, indicating that the parental magmas were mainly derived from ancient crust that interacted with underplated depleted mantle-derived magmas. The monzogranites have relatively high HREE contents, suggesting a garnet-free source (