Neoproterozoic metasedimentary rocks in the eastern Songnen Massif, NE China: Implications for the early evolution and tectonic affinity of microcontinental massifs in the eastern Central Asian Orogenic belt

Abstract

The early tectonic evolution and affinity of microcontinental massifs in the eastern Central Asian Orogenic Belt are uncertain. Here, we present LA–ICP–MS zircon U–Pb and in situ mica Rb–Sr ages, zircon Hf isotopic compositions, and geochemical data for metasedimentary rocks in the eastern Songnen Massif in NE China to constrain their depositional ages and sedimentary provenance, and decipher the early tectonic evolution and affinity of the Songnen Massif. The detrital zircon U–Pb ages yield seven main Neoproterozoic age populations, at ca. 730, ca. 760, ca. 795, ca. 830, ca. 855, ca. 890, and ca. 930 Ma, with six Paleo–Mesoproterozoic and Archean populations at ca. 1020, 1520–1220, 1750–1600, 2050–1950, 2500–2300, and ca. 2800 Ma. Combining this with the ages of later intrusive rocks and overlying sedimentary rocks, we conclude that the Xinxing and Hongguang formations of the Zhangguangcailing Group and the Liangzihe and Honglin formations of the Dongfengshan Group in the study area were deposited during the Neoproterozoic. The in situ mica Rb–Sr ages of the Neoproterozoic metasedimentary rocks suggest that metamorphism occurred during the Middle–Late Jurassic in the eastern Songnen Massif, possibly related to closure of the Mudanjiang Ocean between the Songnen and Jiamusi massifs. Geochemical data for these Neoproterozoic metasedimentary rocks suggest that they were sourced mainly from felsic igneous rocks located close to the sedimentary basin. Furthermore, the consistency between Neoproterozoic detrital zircon age populations and the episodes of magmatism documented in the eastern Songnen Massif suggests that the Neoproterozoic detritus was sourced from the Songnen Massif itself. The occurrence of Paleoproterozoic–Mesoproterozoic detrital zircon grains, together with two-stage Hf model (T_DM2) ages (2.2–1.0 Ga) of zircon grains from Neoproterozoic granitoids, indicates that Paleoproterozoic–Mesoproterozoic crustal material existed in the Songnen Massif. The metasedimentary rocks of the Zhangguangcailing and Dongfengshan groups have similar geochemical compositions and detrital zircon age populations, suggesting that they were formed in a continental arc setting. In addition, the Neoproterozoic–early Paleozoic detrital zircon age peaks, metamorphism, and sedimentary environment of Neoproterozoic strata suggest that the Songnen Massif was part of the North Indo-Australie Orogen and located close to the Tarim Craton during the Neoproterozoic.