资源环境科技发展态势分析平台

The ca. 2.54-2.51 Ga Dengfeng greenstone belt in the southern section of the Central orogenic belt of the North China craton consists of structurally juxtaposed slices of meta-ultramafic, metamafic, and felsic igneous rocks, metasedimentary rocks, including minor banded iron formation. The complex was metamorphosed to greenschist to amphibolite facies at ca. 2.5 Ga and intruded by ca. 2.50-2.42 Ga mafic and felsic plutons/dikes. Detailed field mapping and structural analyses show that the different lithostructural units, including a metamafic-dominant unit and a metasedimentary-dominant unit, are in tectonic contact, with complex thrust imbrication and multiple brittle and ductile deformation. The metasedimentary-dominant unit consists of coherent schist-metabasalt sequences, metaturbidites, and chaotic melanges that are characterized by typical duplex structures and block-in-matrix fabrics, closely resembling the lithostratigraphy and structural patterns of Phanerozoic accretionary complexes. Together with distinctive and diagnostic geochemical signatures of metabasalts, sanukitoid-like metadiorite, and syntectonic adakitic sills/dikes, we interpret the Dengfeng greenstone belt as Neoarchean forearc and accretionary complexes consisting of dismembered forearc crustal sheets in the west and accreted oceanic plate stratigraphy in the east that were structurally imbricated at a convergent plate margin. The kinematic indicators and the spatial configurations of different tectonic units suggest a near-southwest-dipping intra-oceanic subduction zone beneath the arc in the Central orogenic belt, which later evolved into an arc-continent collision with the Eastern block. The accreted arc and accretionary prism are unconformably overlain by a clastic sedimentary wedge, the lower part of which has a maximum depositional age of ca. 2.45 Ga and is interpreted as a foreland basin sequence related to this collision. Documentation of the Neoarchean Dengfeng forearc and accretionary complexes demonstrates that ca. 2.5 Ga intra-oceanic subduction, oceanic plate stratigraphy accretion, and arc-continent collisional events occurred in the southern section of the Central orogenic belt of the North China craton. The accretion of the 2.54-2.51 Ga arc to the continental margin of the Eastern block marks an early episode of mountain building in the Central orogenic belt, which played an important role in the lateral growth of the North China craton.