Early Paleozoic tectonic affinity of the Lesser Xing'an–Zhangguangcai Range, NE China: A continental arc along the western margin of the Jiamusi Block

Abstract

The Lesser Xing'an–Zhangguangcai Range (LXZGCR) in NE China was traditionally interpreted to be the eastern part of the Songliao–Xilinhot Accretionary Terrane, separated from the Jiamusi–Khanka Block to the east by the Heilongjiang Complex. However, recent studies have shown that the Heilongjiang Complex formed in the late Paleozoic–early Mesozoic. Therefore, the tectonic affinity of the LXZGCR during the early Paleozoic remains unclear. To constrain this key issue, we present new zircon UPb ages, Hf isotopic compositions, and whole-rock geochemical data for early Paleozoic igneous rocks in the LXZGCR. The new ages, along with previously published data, suggest that the early Paleozoic magmatism in the LXZGCR can be divided into four stages: Middle–Late Cambrian (523–486 Ma), Early Ordovician (485–469 Ma), Late Ordovician (464–443 Ma), and Late Silurian (433–423 Ma). Middle–Late Cambrian igneous rocks are dominated by calc-alkaline I-type granitoids and high-Mg andesite–dacite–rhyolite association. Early Ordovician igneous rocks consist of a suite of calc-alkaline diorites, granodiorites, monzogranites, alkali-feldspar granites, and rhyolites, with I-type affinities. Late Ordovician igneous rocks consist mainly of I-type granitoids with minor A-type granitoids and rhyolites. Late Silurian igneous rocks are composed of calc-alkaline I-type granitoids with minor dacites. The early Paleozoic granitoids and felsic volcanic rocks originated from partial melting of dominantly Paleoproterozoic–Mesoproterozoic lower crust, whereas the Late Cambrian high-Mg andesite–dacite–rhyolite association was probably derived from partial melting of a depleted mantle wedge metasomatized by subduction-related fluids. The rock associations and geochemical characteristics suggest that these early Paleozoic igneous rocks formed in active continental margin and back-arc extension settings. Comparing the early Paleozoic magmatism, zircon Hf isotopic compositions, Nd model ages, and Precambrian basement features of the LXZGCR and the Jiamusi Block suggest that the LXZGCR was part of the same tectonic unit as the Jiamusi Block during the early Paleozoic. We argue that the formation of the early Paleozoic igneous rocks in the LXZGCR was related to the eastward subduction of a branch ocean of the Paleo-Asian Ocean beneath the Jiamusi–Khanka Block.