Earthquake‐induced Soft‐sediment Deformation Structures in the Dengfeng Area, Henan Province, China: Constraints on Qinling Tectonic Evolution during the Early Cambrian
Soft‐sediment deformation structures are abundant in the Cambrian Zhushadong and Mantou formations of the Dengfeng area, Henan Province, China. Soft‐sediment deformation structures of the Zhushadong Formation consist of fluidized deformation, synsedimentary faults, seismo‐folds and plastic deformation; the Mantou Formation is dominated by small‐scale horst faults, intruded dikes, fluidized veins, and seismo‐cracks. These structures are demonstrated to be earthquake‐related by analysis of trigger mechanisms, and may indicate the activity of the Qinling tectonic belt during the early Cambrian. Furthermore, the assemblages of soft‐sediment deformation structures altered with time: large‐scale, intense deformation in the Zhushadong Formation alters to small‐scale, weak deformation in the Mantou Formation. This striking feature may have been caused by changes in hypocentral depth from deep‐focus to shallow‐focus earthquakes, indicating that the Qinling tectonic belt developed from the subduction of the Shangdan Ocean to the extension of the Erlangping back‐arc basin. This study suggests that soft‐sediment deformation structures can be used to reveal the activity of a tectonic belt, and, more importantly, changes in deformation assemblages can track the evolution of a tectonic belt.
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