New ages of Early Cretaceous magmatic rocks in the Yanbian area (NE China): implications for the subduction and slab rollback of the Paleo-Pacific Plate beneath eastern China during Early Cretaceous

Abstract

ABSTRACT The precise age of slab rollback of the Paleo-Pacific Plate during Early Cretaceous has been contentious. In this study, we have conducted LA-ICP-MS zircon U-Pb dating, major and trace elements, and Sr-Nd isotopes analyses on the late Early Cretaceous diabase porphyries, andesitic basalts and basanites in the Yanbian area (NE China). Zircon U-Pb dating of basanites, andesitic basalts, and diabase porphyries yielded weighted average ages of 104 ± 1.9 Ma (MSWD = 0.55, n = 5), 106 ± 1.6 Ma (MSWD = 0.68, n = 6), and 111 ± 2 Ma (MSWD = 16, n = 3), respectively. The whole-rock geochemical results indicate that the late Early Cretaceous rocks predominantly belong to the low-K tholeiitic and medium-K calc-alkaline series. The diabase porphyries and andesitic basalts are characterized by large ion lithophile elements (e.g. Ba, K, and Sr) enrichment and high field strength elements (e.g. Nb and Zr) depletion with weak positive Eu anomalies, low initial 87Sr/86Sr ratios (0.70361–0.70394) and high ε Nd (t) values (5.96–7.87). The tectonic discrimination diagrams show that the diabase porphyries and andesitic basalts formed in the continental Island arc environment related to subduction of the Paleo-Pacific Plate in the late Early Cretaceous. In contrast, the basanites are enriched in Ba, Th, and U and depleted in K, Sr, and Ti, with weak negative Eu anomalies. The basanites display high magnesium values (Mg# = 0.79), which are approaching the primary magma. They have low Ti values (TiO2 = 1.45%) and Al values (A12O3 = 9.98–10.15%) and high Co values (78.1–80.2 ppm) and Ni values (549.5–585.5 ppm). The basanites formed in the intraplate extensional tectonic setting and were the products of lithospheric thinning and mantle upwelling during the late Early Cretaceous. The spatial-temporal relationship of late Early Cretaceous magmatic rocks in NE China suggests a slab rollback from high-angle subduction to low-angle subduction of the Paleo-Pacific Plate at ca. 106 Ma.