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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. [ABSTRACT FROM AUTHOR]

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]

Blueschists in the Yilan area, Heilongjiang Province, are known as important parts of the Heilongjiang Complex. However, their metamorphic evolution history is still unclear. Petrographical, and mineral chemical investigations on the blueschists from the Yilan area are carried out in this study. P‐T pseudosections are calculated in the system Na2O‐CaO‐K2O‐MnO‐FeO‐MgO‐Al2O3‐SiO2‐H2O‐TiO2‐O (Fe2O3) (NCKMnFMASHTO) with the PERPLE_X software for three blueschist samples. Peak metamorphic conditions are estimated to be 500‐525°C, 1.14‐1.2 GPa for garnet‐barroisite schist (g‐brs‐wnc‐act‐phn‐chl‐ep‐ab‐stlp); 480°C, 1.4 GPa for chlorite‐epidote glaucophane schist (gl‐brs‐wnc‐act‐chl‐ep‐stlp) and 450‐500°C, 0.95‐1.2 GPa for phengite‐glaucophane schist (gl‐wnc‐phn‐ab‐ep‐chl‐sph), which indicate that they all underwent peak metamorphism in the limit epidote‐blueschist facies conditions. Combined with the previously reported geochemical and geochronological data, the clockwise P‐T paths of the blueschists are constructed. The formation of blueschists in the study area marks the young oceanic crust subduction, and represents the final closure of the Paleo‐Asian Ocean and the beginning of the Paleo‐Pacific tectonic system. The P‐T pseudosection recorded the P‐T increasing process before the metamorphic peak and that the maximum temperature was coincident with the maximum pressure in the process, which indicates that the epidote‐blueschist facies conditions implemented in the process of subduction, rather than exhumation. The retrograde trajectory nearly coincidently retraced the prograde trajectory, which represents the similar geothermal gradient (11‐14°C/km) in the subduction and the relatively slow exhumation process. [ABSTRACT FROM AUTHOR]

• Four metamorphic generation assemblages were recognized in high-grade granulite facies rocks of the Mashan Complex. • A clockwise P-T path with nearly isothermal decompression segments was established. • The peak of the granulite facies metamorphism might have occurred at ca. 530 Ma, and its final cooling stage could take place at ca. 490 Ma. The nature and age of the Mashan Complex (or Mashan Group) in northeast China is key for determining the Precambrian geological evolution and origins of the Jiamusi Massif. Here we present a detailed investigation of high-grade granulite-facies rocks of the Mashan Complex from the Liumao area, Heilongjiang Province, China. This includes zircon U–Pb dating, petrological and geochemical analysis, geothermobarometry, phase equilibria modelling, and a P–T path. The metamorphic rocks consist mainly of two groups: pelitic and felsic granulites; amphibolite-facies Sil–Grt–Bi, Sil–Grt, and Grt–Bi gneisses. The protoliths of the metamorphic rocks were clay rocks and sandstones, which were derived dominantly from silicic rocks in a continental island arc setting. In the pelitic granulites, four metamorphic assemblages (M 1 –M 4) were recognised. Three metamorphic assemblages (M 2 –M 4) were identified in the felsic granulites. Geothermobarometric data and phase equilibria modelling indicate that the M 2 , M 3 , and M 4 assemblages in the pelitic granulite were metamorphosed at 9.2 kbar/845–865 °C, 4.7–5.1 kbar/820–865 °C, and 4.0–4.8 kbar/660–720 °C, respectively. These features imply a collisional orogenic process with a clockwise P–T path with nearly isothermal decompression segments. Similar results were obtained for the felsic granulite, with the metamorphic P–T conditions of the peak assemblage (M 2) evaluated as 9.0–9.2 kbar/845–870 °C. The similar P–T paths indicate that the rocks underwent an evolutionary process that started with crustal thickening (M 2), followed by rapid crustal uplift (M 3), and then final cooling (M 4). Based on our new zircon U – Pb age data, the peak of granulite-facies metamorphism in the Liumao area of the Jiamusi Massif occurred at ca. 530 Ma and final cooling occurred at ca. 490 Ma. [ABSTRACT FROM AUTHOR]