Record of Permian–Early Triassic continental arc magmatism in the western margin of the Jiamusi Block, NE China: petrogenesis and implications for Paleo-Pacific subduction

Abstract

In this paper, we report zircon U–Pb ages, Hf isotopes and whole-rock geochemical data for the Permian to Early Triassic granitoids from the western margin of the Jiamusi Block (WJB), NE China. The intermediate to felsic (SiO2 = 59.67–74.04 wt%) granitoids belong to calc-alkaline series and are characterized by enrichments in light rare earth elements and large ion lithophile elements with pronounced negative Nb, Ta and Ti anomalies, revealing typical continental magmatic arc geochemical signatures. The zircon U–Pb determinations on the granodiorite, monzogranite, syenogranite and quartz diorite samples yielded ages between ca. 275–245 Ma, which, together with the published coeval intrusive rocks, indicates that Permian to Early Triassic continental arc magmatism occurred extensively in the WJB. The low and mainly negative zircon e Hf(t) values between −7.6 and +1.6 and the zircon Hf model ages of 1.2–1.8 Ga, which are significantly older than their crystallization ages, suggest that they were mainly derived from reworking of ancient crustal materials with a limited input of juvenile components. The geochemical systematics and petrogenetic considerations indicate that the studied granitoids were generated from a zone of melting, assimilation, storage, and homogenization, i.e., a MASHed zone at the base of Paleo- to Mesoproterozoic continental crust, where large portions of igneous rocks and minor clay-poor sediments involved in the source region. In combination with regional geological data, we argue that the Jiamusi Block was unlikely the rifted segment of the Songliao Block and two possible geodynamical models were proposed to interpret the formation of the ca. 275–245 Ma granitoids in the WJB. In the context of Permian global plate reconstruction, we suggest that Paleo-Pacific plate subduction was initiated in the Permian to Early Triassic beneath the Jiamusi Block, and even whole eastern NE China.