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Neoarchean and Paleoproterozoic metamorphism recorded in the Shuangshanzi supracrustal sequence, eastern North China Craton: Constraints from P-T paths and U-Pb geochronology
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DOI：10.1016/j.precamres.2026.108044.png)
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Abstract
En 中文
The Neoarchean supracrustal sequences in the eastern Hebei terrane are overprinted by the Paleoproterozoic metamorphism, which, however, is controversially attributed to different tectonic regimes. Previous studies were mainly focused on granulites as rafts within gneiss domes, whereas the lower grade rocks in the keels which are supposed to preserve more metamorphic information, received little attention. Here, two episodes of metamorphism are reported in three garnet mica-schist samples from the Shuangshanzi supracrustal belt based on systematic data on metamorphic evolution and U-Pb geochronology. Sample A261 contains mineral assemblages of andalusite + cordierite + staurolite + muscovite + biotite + quartz + plagioclase for the early generation and garnet + biotite + plagioclase + quartz for the late generation, interpreted to record two episodes of metamorphism. The first episode is characterized by a peak condition of 3-5 kbar at approximately 540-580 degrees C and a probable retrograde process. The second episode is characterized by a clockwise P-T path involving early heating from similar to 4.4kbar/similar to 550 degrees C to similar to 5.8 kbar/similar to 570 degrees C and a subsequent decompression and cooling process. Samples A223 and A262 preserve mineral assemblages of single generation, recording clockwise P-T paths with peak conditions respectively of 5.4kbar/576 degrees C and 5.7kbar/585 degrees C, similar to the second episode of metamorphism in A261. In situ U-Pb rutile dating yield Paleo-Proterozoic (1827 +/- 13 Ma) ages in sample A262, and Neoarchean (2526 +/- 43 Ma) and Paleo-Proterozoic (similar to 1839 +/- 21 Ma) ages in sample A261 which are suggested to represent timing of the two-episode metamorphism. Zircon U-Pb dating indicates that the supracrustal rock samples have provenance ages of 2637-2574 Ma, and the granitic gneiss samples in the Anziling dome have protolith ages of 2526-2508 Ma with metamorphic ages of 2521-2501 Ma. Associated with the previous studies, we propose that the Neoarchean metamorphism in the supracrustal rocks, with metamorphic ages concurrent with the Anziling dome, correspond to the tectonic regime related to the nuclei formation of NCC. Moreover, the Paleoproterozoic metamorphism may represent an intracontinental response of the orogenic belt along the northern margin of the North China Craton.
Keywords:
Shuangshanzi Group
Paleoproterozoic overprinting
Supracrustal rock
Phase equilibrium modeling
North China Craton
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