Petrogenesis of the Pandao granites in the Wutai Mountains area in the North China Craton: Constraints from geochemistry, zircon U–Pb geochronology, and Hf isotopes

Abstract

The Trans‐North China Orogen (TNCO) is a part of the North China Craton (NCC) and together provides a classic example of lithospheric destruction. The Pandao granites outcropping in the Wutai Mountains area provide a window to investigate the Mesozoic magmatism in the TNCO. Here, this paper presents the new zircon geochronology, whole‐rock geochemistry, and zircon Hf isotope data for the Pandao granites to discuss their petrogenesis and tectonic implications. The Pandao granites are mainly composed of light‐red medium‐ to coarse‐grained biotite granite and light‐grey fine‐ to medium‐grained biotite granite. Zircon U–Pb ages of 110.05 ± 0.67 Ma and 108.35 ± 0.81 Ma suggest that the Pandao granites were crystallized in the Early Cretaceous. The Pandao granites are classified as high‐K calc‐alkaline and weak peraluminous series. The rocks display abundance in large‐ion lithophile elements (LILE) and light rare‐earth elements (LREE) but show depletion in high‐field‐strength elements (HFSE) and heavy rare‐earth elements (HREE), with strong negative Eu anomalies. The classification diagrams indicate that the Pandao granites are A‐type granites and thus belong to the A1 subtype, formed in an intraplate extensional environment. The Pandao granites have homogeneous zircon Hf isotopic compositions. Their zircons have negative εHf(t) values (−19.1 to −17.1) and old Hf isotope crustal model ages (2,250–2,375 Ma), suggesting that the Pandao granites were formed by partial melting of the Paleoproterozoic lower crustal material. Therefore, it is suggested that the Pandao granites were formed under an intraplate extensional tectonic environment of remote effect due to the ancient Pacific Plate subduction and retreat beneath the Eurasian continent. The TNCO was influenced by the subduction and retreat of the ancient Pacific Plate in the late Early Cretaceous.