Mélanges characterize Phanerozoic convergent plate boundaries, but have rarely been reported from Archean orogens. In this paper, we document a Neoarchean ophiolitic mélange in the Eastern Hebei Province of the North China Craton. The Zunhua ophiolitic mélange is composed of a structural mixture of metapelites, ortho- and para-gneisses, and magnetite-quartzite mixed with exotic tectonic mafic blocks of metabasalts, metagabbroic rocks, and metadiabases, along with ultramafic blocks of serpentinized peridotites and podiform chromitites. The Zunhua ophiolitic mélange shows typical “block in matrix” structures. All units of the mélange have been intruded by granitic dikes and quartz veins that clearly cross-cut the foliation of blocks and matrix of the mélange. Laser-ablation–inductively coupled plasma–mass spectrometry zircon U-Pb dating of detrital zircons from the meta-sedimentary mélange matrix and intruding granitic dikes constrains the formation time of the Zunhua mélange to be between 2.52 and 2.46 Ga. Metamorphic rims on zircons from meta-sedimentary mélange matrix have ages of 2467 ± 27 Ma, confirming metamorphism of the mélange occurred at ca. 2.47 Ga. High-precision (scale 1:20 and 1:50) litho-structural mapping, along with detailed structural observations along several transects documents the internal fabrics and kinematics of the mélange, revealing a northwest to southeast directed transportation. The asymmetric structures in the mélange with folding and faulting events in the Zunhua mélange record kinematic information and are similar to the tectonic style of an accretionary wedge. Field relationships and geochemical analysis of various mafic blocks show that these blocks formed in an arc-related subduction tectonic environment. We suggest that the Zunhua mélange marks the suture zone of a Neoarchean arc-continent collisional event in the Central Orogenic Belt of the North China Craton. Combined with our previous studies, we demonstrate that a ca. 2.5 Ga tectonic suture exists between an arc/accretionary prism terrane in the Central Orogenic Belt and the Eastern Block of the North China Craton. We correlate this segment of the suture with other similar zones along strike, for >1000 km, including sections of the ca. 2.5 Ga in Dengfeng greenstone belt in the southern margin of the Central Orogenic Belt, and the ca. 2.5 Ga Zanhuang ophiolitic mélange in the center of the orogen. These relationships demonstrate that tectonic processes in the late Archean included subduction/accretion at convergent margins, and the horizontal movement of plates, in a style similar to modern-day accretionary convergent margins.

The exotic Haiyangsuo complex is structurally part of the Sulu belt but its contact relationship with surrounding Sulu gneisses is unexposed and therefore unknown, making its affinity uncertain. It comprises gneisses with in-source leucosomes that host minor metabasite bodies; both are cut by leucogranite dikes. In this study, we determine the timing and petrogenesis of leucosomes and leucogranites and assess the tectonic affinity of the complex based on data from gneisses and metabasites. Most zircon from gneisses and leucosomes has oscillatory-zoned cores with CL-bright overgrowth rims, but some has CL-dark cores or mantles between cores and rims. CL-dark and bright zircon yield weighted mean ages of ca. 1817–1812 Ma. CL-dark zircon has flat heavy rare earth element (HREE) patterns and crystallization temperatures of 829–875 °C, suggesting metamorphic growth, whereas rims have steep HREE patterns but a similar range of crystallization temperatures, suggesting growth from anatectic melt; εHf (t = 1813 Ma) of –18.3 to –10.8 indicates a North China Craton source. Magmatic zircon from metabasites yields ages of ca. 825 Ma, similar to those of scattered metabasite occurrences in the North China Craton. Paleoproterozoic zircon cores were scavenged during magma ascent. By contrast, zircon cores from the leucogranites yield concordant dates of 776–701 Ma, consistent with protolith ages in the Sulu belt, whereas overgrowth mantles and rims yield weighted mean ages of ca. 220 Ma and 162 Ma, respectively. Both mantles and rims host multiphase solid inclusions, representing former melt, suggesting anatexis and crystallization of zircon first during initial decompression and then during orogenic collapse of the Sulu belt; whole-rock Nd and Sr isotope compositions implicate the Sulu belt gneisses as the source of these melts. Our interpretation of these data is that the Haiyangsuo complex has an early geologic history similar to the Jiaobei terrane from the southeastern part of the North China Craton and was incorporated into the Sulu belt during Triassic collision of the Yangtze and North China Cratons. The two stages of melting relate to Upper Triassic early exhumation and Upper Jurassic late-stage orogenic collapse, during which the leucogranite magma was derived from a source similar to one elsewhere in the Sulu belt such as the subducted Yangtze Craton and not the North China Craton. This shows that during continental collisions, crust from the upper plate may be dragged into the subduction channel, deformed, and subsequently exhumed in association with partial melting of the crust.