Continental Arc Flare-Ups and Crustal Thickening Events in NE China: Insights from Detrital Zircon U-Pb Dating and Trace Elements from the Heilongjiang Complex

Abstract

Continental arc is characterized by alternant magmatic flare-ups and lulls. From the Permian to the Middle Jurassic period, two flare-ups with a lull developed in NE China, but the tectonic controls that caused the flare-ups remain unclear. Sedimentary rocks of the Heilongjiang Complex were derived from these magmatic rocks; thus, we employed detrital zircon U-Pb dating and trace elements analyses to unravel the regional tectono-magmatic evolution. Eu anomaly, (Dy/Yb)N and Th/U ratios of the detrital zircons and Sr/Y and (La/Yb)N of the regional granitoids together indicate the occurrence of two episodes of crustal thickening during the two flare-ups, accompanied with a westward migration of magmatism. We propose that the Permian flare-up was caused by the shallowing subduction from the east, which thickened the upper plate and enhanced the deep crustal melting. During the Middle Triassic period, the mantle wedge was expelled by the flat slab and thickened crust, leading to the magmatic lull. However, the westward subduction of the back-arc oceanic plate occurred before the lull, gradually producing the Jurassic magmatic flare-up and crustal thickening. Closure of the back-arc ocean caused by the outboard Paleo-Pacific oceanic plate subduction was important in the formation of the episodic magmatic flare-ups and crustal thickening in NE China.