Neoarchean tectonic regime of the Eastern Hebei Complex, North China Craton: Constraints from Mafic-Ultramafic rocks in the Zunhua-Shangying ophiolitic Mélange

The Neoarchean era represents a pivotal transition in early Earth evolution, serving as a critical window for investigating continental origins and early geodynamic processes. The tectonic setting of the Neoarchean Eastern Hebei Complex in the North China Craton remains intensely debated, with focus on determining if the tectonic was regime dominated by subduction, sagduction, or other processes. Ultramafic rocks, as petrological probes into deep Earth composition and dynamics, offer key insights into deep crust-mantle evolution, and deep geodynamic processes. We present an integrated study incorporating field investigations, petrology, geochemistry, and zircon U-Pb geochronology on mafic–ultramafic rocks from the Zunhua-Shangying ophiolitic mélange belt, which is mainly exposed in the Songling, Longwan, and Shangying areas. The serpentinized peridotites are metasomatic mantle peridotites formed by melt-rock reaction, characterized by moderately low Mg# (∼85) and relatively flat to slightly depleted rare earth element patterns. The high-Mg# (75.60–80.78) Songling-Longwan pyroxenites represent high-pressure cumulates crystallized from hydrous, subduction-modified basaltic magmas at the base of the lower arc crust, whereas low-Mg# (24.6–41.6), high-Al 2 O 3 (13.7–19.7 wt%) granulites represent their complementary evolved melts. The Shangying garnet pyroxenites, showing typical N-MORB geochemical affinities, are identified as remnants of Archean oceanic crust. Magmatic zircons from the granulites and coexisting metagabbro yield a weighted average age of 2.52 Ga, interpreted as the crystallization age of the mafic–ultramafic suite. Integrated geochronological and geochemical data demonstrate that the Eastern Hebei mafic–ultramafic suite developed in an intra-oceanic arc system and records two distinct stages: formation (2.55–2.52 Ga) and emplacement (2.52–2.47 Ga). During the formation stage, the Songling-Longwan rocks originated at the crust-mantle transition zone beneath the arc root, whereas the Shangying garnet pyroxenites formed at greater depths within the subducted slab. During the emplacement stage, both the N-MORB-type Shangying garnet clinopyroxenites and metagabbros and the arc-related Songling-Longwan mafic–ultramafic blocks were incorporated as coherent, elongated tectonic fragments into the Zunhua-Shangying forearc ophiolitic mélange. Late Neoarchean to early Paleoproterozoic metamorphism coincided with the westward subduction of the Eastern Block beneath the Wutai/Fuping arc terrane and subsequent arc-continent collision. This collisional event led to the stabilization of the Eastern Block and the final accretion of the Zunhua-Shangying ophiolitic mélange belt. Later events include the pan-craton circa 1.8 Ga high-grade (up to granulite grade) overprint, generally interpreted to represent the craton’s incorporation into the Columbia supercontinent.