A crustal growth model for the eastern Central Asian Orogenic Belt: Constraints from granitoids in the Songnen Massif and Duobaoshan terrane

Abstract

The crustal growth and reworking processes of accretionary orogen such as the Central Asian Orogenic Belt (CAOB) have been a controversial issue. Here, we present in situ zircon U–Pb and Lu–Hf isotopic data for granitoids from a microcontinent (the Songnen Massif) and an arc terrane (the Duobaoshan arc terrane), which generally represent two main crustal components in the eastern CAOB to establish a crustal growth model for an accretionary orogen and to trace the influence of the assembly and breakup of supercontinents on crustal evolution in an accretionary orogen. Neoproterozoic–Mesozoic granitoids distributed in the Songnen Massif show a step-like crustal growth pattern over time with three major periods of development: Paleoproterozoic crustal growth at 2.2–1.8 Ga, Mesoproterozoic growth at 1.6–1.0 Ga, and a third pulse of growth at 0.85–0.6 Ga, along with two short pauses at 1.8–1.6 Ga and 1.0–0.85 Ga. The assembly and collision phases of supercontinents corresponded to the enhanced and degressive crustal growth rates of the Songnen Massif, respectively, suggesting that the supercontinent cycles are responsible for the episodic crustal growth pattern in the region. Crustal reworking of the Songnen Massif occurred during 1000–180 Ma, with a fluctuation at 800–600 Ma, which provided a major contribution to the isotopic heterogeneity of lower continental crust. Isotopic compositions of granitoids from the Duobaoshan arc terrane located between the Xing'an and Songnen massifs, together with those of granitoids from other microcontinents, suggest that most of the continental crust beneath the microcontinents in the eastern CAOB generated during the Precambrian, whereas a significant amount of lateral crustal accretion occurred in continental arc settings during orogenies and amalgamation of microcontinents during the Phanerozoic.