Extension of a newly identified 500 Ma metamorphic terrane in North East China: further U–Pb SHRIMP dating of the Mashan Complex, Heilongjiang Province, China

Abstract

New single zircon SHRIMP U–Pb dating of paragneiss and garnet-bearing granite from the Mashan Complex in the Jiamusi Massif at Sandaogou and Xi Mashan, Heilongjiang Province, China, indicates that these rocks underwent granulite facies metamorphism ∼500 Ma ago. Sillimanite gneiss from Sandaogou contains a single population of metamorphic zircons which have a 206Pb/ 238U age of 496±8 Ma. Sillimanite gneiss from Xi Mashan, approximately 16 km west of Sandaogou, has a 206Pb/ 238U metamorphic zircon age of ∼500 Ma, but also includes several populations of detrital zircon grains that extend back to ∼1700 Ma. A garnetiferous granite from Xi Mashan has a 206Pb/ 238U igneous zircon age of 507±12 Ma. It contains an enclave of garnet paragneiss and this has a metamorphic zircon age of ∼500 Ma. The enclave also contains zircons that extend back to ∼1900 Ma, with a concordant population at ∼1100 Ma. These data establish that the southern outcrop of the Mashan Complex, extending west from Liu Mao to Xi Mashan, a total distance of 22 km, records the same early Palaeozoic metamorphic event. The older zircon populations in the sillimanite gneiss and garnet gneiss enclave from Xi Mashan indicate derivation from both Palaeo- and Mesoproterozoic sources. These data, together with the ∼500 Ma age for the granulite facies metamorphic event, suggest that the Mashan Complex formed part of a Late Neoproterozoic–Early Palaeozoic orogenic terrane. High-grade metamorphic rocks of slightly younger age (∼480 Ma) are recorded from southern Siberia to the north of the study area, whereas slightly older ages (550–515 Ma) are recorded from various Pan-African terranes formerly associated with Gondwanaland. However, the closest analogue in the literature is with the Delamerian Orogen in southern Australia, where high-grade metamorphism has been dated at 503±7 Ma. Although speculative, it is argued that the Mashan Complex may possibly once have been located in Gondwanaland, drifting northward along with the North China, South China and Tarim blocks to dock with the Siberian Craton sometime between the late Permian and late Jurassic.