High-pressure granulite facies and ultrahigh-temperature metamorphism in the Jiaobei Terrane, North China Craton: Implications for tectonic regimes across the Archean-Proterozoic transition

The Archean-Proterozoic transition represents a fundamental turning point in Earth’s tectonic evolution, marked by the emergence of laterally organized orogenic belts and the progressive establishment of plate tectonic processes. High-grade metamorphism developed during this interval provides a unique archive of deep crustal thermal structure, rheology, and tectonic regime. The Jiaobei Terrane, located in the southern segment of the Paleoproterozoic Jiao-Liao-Ji Belt of the North China Craton (NCC), exposes exceptionally well-preserved high-pressure (HP) and ultrahigh-temperature (UHT) granulites, offering a rare opportunity to evaluate metamorphic responses to early plate tectonic processes. Recent studies have increasingly documented Paleoproterozoic UHT metamorphism in the terrane. In contrast to classic sapphirine-bearing UHT rocks, Jiaobei UHT pelitic granulites are commonly graphite-bearing and characterized by relatively low Mg-Al and broader SiO 2 bulk compositions. Nevertheless, the application of ternary feldspar and trace-element thermometry, and diffusion-based approaches has revealed widespread pulsed UHT conditions in this region. Compilation and synthesis of published lithological, geochronological, and pressure–temperature data indicate that a regional HP granulite-facies metamorphic event between ∼ 1.95 and 1.80 Ga (reaching its HP peak at ∼ 1.90–1.86 Ga) affected nearly all pre-existing lithologies in the Jiaobei Terrane. A subset of these rocks subsequently experienced UHT overprinting, with peak temperatures reaching ∼ 900-1100 °C at 1.85 Ga, following the peak burial stage. The transition from HP granulite facies to UHT metamorphism occurred along diverse P-T paths and coincided with episodic magmatism. This chronological succession suggests that crustal radiogenic heat production, coupled with transient mantle thermal input during lithospheric thinning, drove these extreme thermal conditions.. We argue that the coexistence of HP granulite facies and UHT metamorphism in the Jiaobei Terrane reflects a transitional tectonic regime characteristic of early plate tectonics, involving warm subduction, crustal thickening, and post-orogenic extension. Comparison with other Paleoproterozoic mobile belts of the NCC highlights both commonalities and regional variability in metamorphic expression, providing new constraints on the geodynamic architecture of the Archean-Proterozoic transition.