Mesozoic intracontinental underthrust in the SE margin of the North China Block: Insights from the Xu-Huai thrust-and-fold belt

• Published in: Journal of Asian earth sciences Vol. 141; pp. 161 - 173
• Main Authors: Shu, Liangshu, Yin, Hongwei, Faure, Michel, Chen, Yan
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15-06-2017; Elsevier
• Subjects: Earth Sciences; Fault-related fold; Intracontinental underthrust; Mesozoic; North China Block; Sciences of the Universe; Tectonics; Thrust; Xu-Huai belt; Mesozoic; Fault-related fold; Xu-Huai belt; North China Block; Thrust; Intracontinental underthrust
• ISSN: 1367-9120; 1878-5786
• DOI: 10.1016/j.jseaes.2016.08.020

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•The fault-related folds and step-type thrust faults are predominant features of the Xu-Huai thrust-and-fold belt.•Two geological cross-sections were used for structural balancing and restoration.•A shortening rate of 43–46% was obtained from the restoration of two balanced cross-sections.•The Xu-Huai belt was derived from the Early Mesozoic crustal underthrusting of the SE margin of NCB beneath the SCB.
The Xu-Huai thrust-and-fold belt, located in the southeastern margin of the North China Block, consists mainly of thrust and folded pre-Mesozoic strata. Its geodynamic evolution and tectonic setting are topics of long debate. This paper provides new evidence from geological mapping, structural analysis, and making balance cross-sections, with restoration of cross-sections. Results suggest that this belt was subjected to two-phase deformation, including an early-phase regional-scale NW-ward thrust and fold, and a late-phase extension followed by the emplacement of dioritic, monzodioritic porphyrites dated at 131–135Ma and locally strike-slip shearing. According to the mapping, field observations and drill-hole data, three structural units were distinguished, namely, (1) the pre-Neoproterozoic crystalline basement in the eastern segment, (2) the nappe unit or the thrust-and-fold zone in the central segment, which is composed of Neoproterozoic to Ordovician carbonate rocks and Carboniferous-Permian coal-bearing rocks, about 2600m thick, and (3) the western frontal zone. A major decollement fault has also been identified in the base of the nappe unit, on which dozen-meter to km-scale thrust-and-fold bodies were commonly developed. All pre-Mesozoic depositional sequences were involved into a widespread thrust and fold event. Six uncompetent-rock layers with biostratigraphic ages (Nanjing University, 1996) have been recognized, and each uncompetent-rock layer occurred mainly in the top of the footwall, playing an important role in the development of the Xu-Huai thrust-and-fold belt. Geometry of the major decollement fault suggests that the nappe unit of this belt was rooted in its eastern side, near the Tan-Lu Fault Zone. Two geological cross-sections were chosen for structural balancing and restoration. From the balanced cross-sections, ramp-flat and imbricated faults as well as fault-related folds were identified. A shortening of 20.6–29.6km was obtained from restoration of balanced sections, corresponding to a shortening rate of 43.6–46.4%. This shortening deformation was likely related to the SE-ward intracontinental underthrust of the North China Block beneath the South China Block during the Mesozoic.