Zircon U‐Pb Dating and Hf Isotope of the Metavolcanics, Gabbro and Plagiogranite in the Mianxian‐Lueyang Areas of Mianlue Belt

Abstract

AbstractThe Mianlue Belt is located in the central China and regarded as a tectonic mélange belt, representative of suture zone formed in the early Mesozoic between North and South China Blocks. However, its forming age has been controversial for a long time. This study provides the reliable LA‐ICPMS U‐Pb zircon dating and in‐situ Hf isotopes from the meta‐volcanics, gabbro and plagiogranite in this belt. Of which, two meta‐andesites yielded the ages of 934 Ma and 933 Ma, two meta‐dacites give the ages of 999 Ma and 873 Ma, and another plagiogranite define an age of 923 Ma, respectively, evidently older than those previously thoughted. Their Hf isotopes are quite coincident. The andesites have the εHf(t)= ‐0.03 ∼ +11.76 with the TDMC of 1032‐1629 Ma, εHf(t) = +9.81∼ +16.06 and the TDMC = 867‐1185 Ma for dacite and εHf(t) = +8.65 ∼ +16.66 and the TDMC = 805∼1123 Ma for plagiogranite, suggesting an important crustal growth in the early Neoproterozoic. In addition, the gabbro yielded younger ages of 224‐213 Ma and variable ages from 1225 Ma to 280 Ma in some inherited zircons, consistent with early Mesozoic mafic dykes in South Qinling belt. Their TDMC range from 1.2 to 2.7 Ga, indicating early‐middle Proterozoic crustal residence involved minor Neo‐Archean crustal materials. All new results lead us to propose that most of components in the Mianlue Belt were generated in the early Neoproterozoic and related to the subduction process in the northern margin of the Yangtze block, representative of an important juvenile crust growth in South Qinling during the Neoproterozoic.