Sedimentary deformation structures in the Nyixoi Chongco rock avalanche: implications on rock avalanche transport mechanisms

Abstract

To learn the transport kinematics of rock avalanches, an outcrop study of the Nyixoi Chongco rock avalanche in the Yadong-Gulu Rift of the south Tibetan Plateau, China, is presented here. Sedimentological analysis associated with the outcrops allows important considerations of rock avalanche transport mechanisms. From the outcrops, a series of plastic-brittle deformations in the substrate, including diapiric structures, convoluted laminations, faults, and basal decollements, were observed, indicating the occurrence of a bulldozing effect between the avalanche mass and substrate. In addition, jigsaw structures, inner shear zones, and aligned clasts were found in the avalanche deposit, indicating the occurrence of a shear-dominated movement with differential internal stresses and limited disturbances. Therefore, this paper proposes that a simple shear process dominated the transport of the Nyixoi Chongco rock avalanche and contributed to the generation of these sedimentary structures. A lack of liquefied sandy structures in the outcrops indicates that liquefaction was not a key factor causing the hypermobility of the rock avalanche.