Discovery of granulite‐facies metamorphic rocks in the Yilan area, Heilongjiang Province, China: Geochronology, geochemistry, metamorphic characteristics, and geological implications.

The Mashan Complex of the Jiamusi Massif was traditionally considered as the oldest stratigraphic sequence in eastern NE China. However, the metamorphic degree of the Mashan Complex is different in different areas, which can be divided into Jixi–Mishan–Hulin granulite facies belt and Luobei–Huanan–Mudanjiang amphibolite facies belt. Here, we investigated the Mashan Complex in the Yilan area and present lots of new petrological, mineral chemical, geochemical, and U–Pb geochronological data, in addition to phase equilibria modelling, to constrain the timing of metamorphism, P–T conditions, and the P–T path of the Mashan Complex, and furthermore to deduce the crustal evolution of the Jiamusi Massif. The protoliths of the Mashan Complex in the Yilan area are greywackes and felsic sandstones, whose provenance is dominantly felsic rocks formed from a continental island arc. Petrographic observations, traditional thermobarometry, and quantitative phase equilibria modelling of the studied samples reveal P–T conditions from M2 to M3 of ~7.2 kbar/760–800°C and 4.5–5.0 kbar/585–610°C, respectively, which together define a clockwise P–T path involving decompressional cooling (M3) that followed the peak granulite‐facies metamorphism (M2). It reveals essential information related to the collision orogeny and post‐collision process. Zircon U–Pb dating of two felsic rocks yielded the peak of the granulite‐facies metamorphism in the Yilan area of the Jiamusi Massif that might have occurred at ~500 Ma. The overall deposition of the metamorphic rocks was later than ~760 Ma and that most of the detrital materials came from late Mesoproterozoic and early Neoproterozoic source rocks. [ABSTRACT FROM AUTHOR]