No abstract

The Heilongjiang Complex records the evolution history of the Mudanjiang Ocean, which is of great significance to constrain the amalgamation process of the Jiamusi and Songnen‐Zhangguangcai Range massifs. We carried out petrological, chronological, geochemical, mineral chemical and electron backscatter diffraction (EBSD) fabric analyses on the Heilongjiang Complex in the Yilan area. The latest zircon U–Pb dating results show that the protolith ages of the amphibolite are 261.3 ± 3.0 Ma and 261.8 ± 3.3 Ma, while that of the granodioritic mylonite is 207.8 ± 2.2 Ma. The amphibolites and granodioritic mylonite are enriched in large‐ion lithophile elements (e.g., Rb, Ba, and Sr) and light rare earth elements, with depletion in high‐field‐ strength elements (e.g., Nb, Ta, Zr, and Hf), indicating that the formation of the protoliths of the amphibolites and granodioritic mylonite is related to the subduction of the Mudanjiang oceanic plate under the Songnen‐Zhangguangcai Range Massif. The amphibolites and granodioritic mylonite both experienced two periods of metamorphic and deformation events. The metamorphic degree of the early period of metamorphism is low amphibolite facies, which records a clockwise P–T path from early increased temperature and pressure to a late isothermal depressurization. The P–T path reveals that this period of metamorphism is associated with the collision between two massifs. The later period of metamorphism reaches low greenschist facies, accompanied by deformation, which may be related to the rapid exhumation of the Heilongjiang Complex. This study provides a new perspective for exploring the collision and collage process of the Jiamusi and Songnen‐Zhangguangcai Range massifs.

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 M 2 to M 3 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 (M 3 ) that followed the peak granulite-facies metamorphism (M 2 ). 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.