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.

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Whether modern-style plate tectonics operated on early Earth is debated due to a paucity of definitive records of large-scale plate convergence, subduction, and collision in the Archean geological record. Archean Alpine-style sub-horizontal fold/thrust nappes in the Precambrian basement of China contain a Mariana-type subduction-initiation sequence of mid-ocean ridge basalt blocks in a 1600-kilometer-long mélange belt, overthrusting picritic-boninitic and island-arc tholeiite bearing nappes, in turn emplaced over a passive margin capping an ancient Archean continental fragment. Picrite-boninite and tholeiite units are 2698 ± 30 million years old marking the age of subduction initiation, with nappes emplaced over the passive margin at 2520 million years ago. Here, we show the life cycle of the subduction zone and ocean spanned circa 178 million years; conservative plate velocities of 2 centimeters per year yield a lateral transport distance of subducted oceanic crust of 3560 kilometers, providing direct positive evidence for horizontal plate tectonics in the Archean.

The Beyşehir-Hoyran Nappes, including Mesozoic carbonate platform rocks, deep-sea sediments, and ophiolite-related units, crop out extensively on the western limb of the Isparta Angle in the Central Taurides, Turkey. The ophiolite-related rocks are represented by variably serpentinized harzburgitic mantle tectonites, tectonically underlain by a subophiolitic metamorphic sole and mélange. The harzburgitic mantle tectonites and metamorphic sole are intruded by undeformed isolated dikes. Protoliths of the metamorphic sole are similar to within-plate alkali basalts and associated sediments. The isolated dikes were geochemically derived mainly from tholeiitic magma and, to a lesser extent, from alkaline magma. Five isolated dike samples yielded U-Pb ages ranging from 90.8 ± 1.6 Ma to 87.6 ± 2.1 Ma (zircon) and from 102.3 ± 7.4 Ma to 87.5 ± 7.9 Ma (titanite). Seven amphibolite samples yielded U-Pb age ranges of 91.1 ± 2.1–88.85 ± 1.0 Ma (zircon) and 94.0 ± 4.8–90.0 ± 9.4 Ma (titanite) and a 40Ar-39Ar age range of 93.7 ± 0.3–91.4 ± 0.4 Ma (hornblende). U-Pb and 40Ar-39Ar ages of mineral phases with different closure temperatures (∼900–500 °C) from the isolated dikes and metamorphic sole rocks are almost identical and overlapping within 1σ, suggesting that both the magmatic growth of oceanic crust and formation of metamorphic sole were contemporaneous and cooled very rapidly. Hence, all the data should be interpreted as the crystallization ages of the ophiolite and metamorphic sole pair. Genesis of suprasubduction zone–type oceanic crust, genesis and exhumation of the metamorphic sole, and postmetamorphic dike emplacement within the Inner Tauride Ocean can be best explained by subduction initiation and rollback processes during the Late Cretaceous based on petrological and geochronological data obtained from the ophiolitic rocks of the Beyşehir-Hoyran Nappes.