Geochemistry, geochronology, and tectonic setting of Early Cretaceous volcanic rocks in the northern segment of the Tan–Lu Fault region, northeast China

Abstract

We present new geochemical and geochronological data for volcanic and related rocks in the regions of the Jia–Yi and Dun–Mi faults, in order to constrain the late Mesozoic tectonic evolution of the northern segment of the Tan–Lu Fault. Zircon U–Pb dating shows that rhyolite and intermediate–mafic rocks along the southern part of the Jia–Yi Fault formed at 124 and 113Ma, respectively, whereas the volcanic rocks along the northern parts of the Jia–Yi and Dun–Mi faults formed at 100Ma. The rhyolite has an A-type granitoid affinity, with high alkalis, low MgO, Ti, and P contents, high rare earth element (REE) contents and Ga/Al ratios, enrichments in large-ion lithophile (LILEs; e.g., Rb, Th, and U) and high-field-strength element (HFSEs; e.g., Nb, Ta, Zr, and Y), and marked negative Eu anomalies. These features indicate that the rhyolites were derived from partial melting of crustal material in an extensional environment. The basaltic rocks are enriched in light REEs and LILEs (e.g., Rb, K, Th, and U), and depleted in heavy REEs, HFSEs (e.g., Nb, Ta, Ti, and P), and Sr. These geochemical characteristics indicate that these rocks are calc-alkaline basalts that formed in an intraplate extensional tectonic setting. The dacite is a medium- to high-K, calc-alkaline, I-type granite that was derived from a mixed source involving both crustal and mantle components in a magmatic arc. Therefore, the volcanic rocks along the Jia–Yi and Dun–Mi faults were formed in an extensional regime at 124–100Ma (Early Cretaceous), and these faults were extensional strike-slip faults at this time.