Geology of a Neoarchean suture: Evidence from the Zunhua ophiolitic mélange of the Eastern Hebei Province, North China Craton

Abstract

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.

Neoarchean to Palaeoproterozoic tectonic evolution of the Trans‐North China Orogen, North China Craton: Evidence from zircon U–Pb geochronology, Lu–Hf isotopes, and geochemistry of the Zanhuang Complex

“…1,850 Ma orogenic event in the TNCO. Wang et al (2019) demonstrated that a ca. 2.5 Ga tectonic suture existed between an arc/accretionary terrane in the COB (or TNCO) and the Eastern Block, marking a Neoarchean arc‐continent collisional event.…”

“…2.5 Ga Dengfeng greenstone belt, the ca. 2.5 Ga Zanhuang ophiolitic mélange, and the Zunhua mélange formed in an arc‐related subduction tectonic setting (Wang et al, 2019). Trap et al (2009) suggested that the TNCO represented an oceanic basin formed by extension and rifting events identified by opening of the Taihang Ocean during 2,300–2,200 Ma, and underwent continent–continent collision at 1,880–1,850 Ma.…”

Continuity of the Western Qinling and Qaidam‐Qilian blocks: Evidence from Precambrian and Permian–Triassic strata around the Gonghe Basin area, NW China

“…These detritus were likely derived from the adjoining North China Craton, with both samples and inferred source characterized by a prominent age peak at ~2.50 Ga (Wan et al, ; Yu et al, ). In the North China Craton, this strong and widespread superimposed tectonic–thermal event at ~2.50 Ga relates to the stabilization of the cratonic assemblages (Wan et al, ) mainly along the Trans‐North China Orogen (Wang et al, , ). The North China craton also provides a likely source of even older Mesoarchean to Early Neoarchean detritus occur in many parts of the craton (Wan et al, ).…”

Petromagnetic Characteristics of Serpentinization and Magnetite Formation at the Zedang Ophiolite in Southern Tibet

“…The operating conditions are 15 kV accelerating voltage, 20 nA probe current, and a beam diameter of 1–3 μm. A total of 11 major elements were measured for each mineral and standard minerals from SPI (USA) were utilized to determine the compositions (Wang et al, 2019). Dwell times were tens on element peaks and half that on background locations adjacent to peaks.…”