Superposition of two orthogonal transpressions: An example from the oblique convergent margin adjoining the Tan–Lu Fault Zone, eastern China

Abstract

Deformation in oblique convergent margins, especially non-plane deformation in décollement belts within such a margin, is not fully understood. The northern Zhangbaling tectonic belt represents an oblique convergent margin to the east of the NNE–SSW-striking Tan–Lu Fault Zone that separates the Yangtze Block to the east from the North China Craton to the west, and it provides a good opportunity to understand deformation in the margin. The tectonic belt consists of a fold-and-thrust belt in the east and a low-angle ductile décollement belt in the west. The fold-and-thrust belt in the marginal cover rocks indicates a pure shear-dominated deformation, and the fold axes rotated with the long axis of the horizontal finite strain ellipse. The underlying décollement belt was involved in a non-plane deformation owing to the superposition of wrenching along the Tan–Lu Fault Zone and horizontal décollement shearing. The horizontal décollement shearing dominated in the development of the flat-lying foliation, whereas the wrenching mostly dominated in the development of stretching lineations. Top-to-the-SSW sense of shear dominates in the central to southern parts of the décollement belt, whereas top-to-the-SSE sense of shear is widely present in the northern part of the belt and locally in other parts. Partitioning of the non-plane deformation is shown by kinematic partitioning within the originally flat-lying décollement belt, and it is different from the strain partitioning in a transpressional zone involved in plane deformation. The structural and geochronological data for the oblique convergent margin are consistent with sinistral faulting of the initial Tan–Lu Fault Zone during the Triassic.