Cenozoic extension mechanism of the Weihe Graben, central China: constraints from analog modeling

Abstract

The Weihe Graben, a Cenozoic rift system at the Ordos-Qinling tectonic boundary in East Asia, provides critical insights into intracontinental extension mechanisms, with debate continuing among three models: simple shear via detachment faulting, pure shear through distributed crustal thinning, and a hybrid early pure/late simple shear transition. To resolve this, we conducted 11 scaled analog experiments simulating end-member pure shear (basal stretching) and simple shear (detachment-driven) regimes, testing variables such as extension rate, extension direction, basement heterogeneity, and synkinematic sedimentation. Pure shear systems develop basins bounded by pre-existing basement structures (unaffected by listric faults), with homogeneous basements generating domino/conjugate faults and heterogeneous basements forming graben-horst-graben systems. Oblique extension induces en echelon depressions, and a slower extension rate corresponds to reduced subsidence thickness. In contrast, simple shear systems exhibit three kinematic domains: (i) rolling anticlines, (ii) secondary grabens, and (iii) horizontal translation zones, with basin architecture insensitive to basement variations or extension direction. Synkinematic sedimentation and the sand-to-mud ratio moderately enhanced basin evolution. Comparing natural structures indicates that the half-graben structures in the Weihe Graben were controlled by listric faults, and the en echelon distribution of the Xi’an and Gushi depressions resulted from oblique extension under a pure shear mechanism. Controlled by oblique extension, en echelon faults developed along its northern margin, accompanied by two en echelon depressions. Influenced by the relatively cold and rigid basement, these depressions are distributed around the Lishan area, where listric faults are well-developed. A decreased extension rate further enhanced the localization.