Geochemistry of eclogite xenoliths in Mesozoic adakitic rocks from Xuzhou-Suzhou area in central China and their tectonic implications

Abstract

Detailed geochemical (major and trace elements, Sr-Nd isotope) and new zircon U-Pb dating data for eclogite and garnet-clinopyroxenite xenoliths within the Mesozoic adakitic rocks from the Xuzhou-Suzhou area in central China provide insight into origin of their protolith and the Mesozoic tectonic evolution of the eastern North China Craton (NCC). The eclogite xenoliths have a basaltic bulk composition with SiO 2 = 44.44–52.30 wt.%, Al 2O 3 = 11.72–20.90 wt.%, FeO total = 7.35–17.28 wt.%, and MgO = 4.35–10.62 wt.%, CaO = 7.80–12.96 wt.%. They are characterized by enrichment in large ionic lithophile elements, depletion in high field strength elements (such as Nb, Ta, Zr, Hf, and Ti) and transitional elements (Ni and Cr), and variable Sr-Nd isotopic compositions (initial 87Sr/ 86Sr ratios and the ε Nd (t) values ranging from 0.7041 to 0.7139 and from 3.03 to – 17.19, respectively), suggesting that their protoliths could have been formed in an island arc setting. The zircon age spectrum suggests that the majority of the eclogite xenoliths have a NCC affinity and that few show characteristics of the Yangtze Craton (YC) basement. The existence of the YC basement beneath the NCC in the Xuzhou-Suzhou area, together with the discovery of the early Mesozoic metamorphic and Neoproterozoic magmatic inherited zircons in the Mesozoic granites from the eastern NCC, implies that the eclogite-facies metamorphism of the eastern NCC basement might be attributed to the early Mesozoic subduction of the YC beneath the NCC along the Tan-Lu fault zone oriented in a north-westward (NW) direction. The subsequent YC clockwise rotation with respect to the NCC, the large-scale lateral extrusion and uplift of the Tongbai-Dabie Mountains in eastern China after the Triassic collision, as well as the early Cretaceous strike-slip in the Tan-Lu fault zone, played the major role in formation of the present tectonic architecture of the Dabie-Sulu belts.