Abstract
A group of Paleoproterozoic gneiss domes are well preserved in the southern Liaodong segment of the Jiao-Liao-Ji Orogenic Belt (JLJOB), eastern North China Craton. Similar to the domes in many other orogenic belts, they may provide important clues to our understanding of the orogenic processes and related middle-lower crustal mass flow during the tectonic evolution of the orogenic belt. This paper conducted detailed structural analysis of the Hadabei dome, a typical example in the dome group to unravel the Paleoproterozoic structural styles and deformation history of the southern Liaodong orogenic belt. Three stages of deformation (D1-D3) are reconstructed for the structural evolution of the dome. The D1 deformation is characterized by meso- to micro-scale intrafolia folds (F1), penetrative foliations (S1) and mineral lineations (L1) in the metamorphosed volcanic-sedimentary rocks. The D2 deformation intensively transformed S1 foliations to form asymmetrical folds (F2) and crenulation cleavages (S2). The D3 deformation is mainly evidenced by occurrence of open folds (F3) at various scales. U-Pb zircon geochronological dating of syn-tectonic leucogranitic dykes shows that the D2 deformation occurred from >1860 Ma to 1822 Ma. It is also shown that the D2 deformation is the peak stage of deformation that contributed to the formation of the overall tectonic framework of the Hadabei dome, and therefore, the orogenic belt. At this stage, subhorizontal mass flow contributed to the widely developed shear structures. The formation of the Hadabei dome was ascribed to early diapirism (D1), subhorizontal shearing and doming (D2) and fold superposition (D3). The multi-stage structural evolution was resulted from successive E-W oriented rifting, extension and contraction, and subsequent superimposition by N-S shortening in the southern Liaodong Paleoproterozoic orogenic belt. These conclusions provide a better understanding of the mechanisms of doming, regional structural deformation, and tectonic evolution of the JLJOB.
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