Digital.CSIC. Repositorio Institucional del CSIC

oai:digital.csic.es:10261/306608

The analysis of folds within pebbles in conglomerates has been used to infer deformation events before deposition of the conglomerate. However, it is not clear whether folds can develop within pebbles during subsequent conglomerate deformation. We use numerical modelling to investigate folding within internally layered pebbles in a ductile deformation regime and simple shear deformation. We vary the initial orientation and rheology of the layers within pebbles, as well as the relative rheology of the conglomerate matrix, for single isolated pebbles and multiple interacting pebbles. We use a power-law viscous rheology for both the pebbles and their matrix. Folding within pebbles can indeed occur, but only within a narrow range of initial layer orientations, strength or viscosity ratio between the internal layers and that of the matrix relative to the pebble layers. Results are used to interpret the strongly deformed conglomerates from the Proterozoic Hutuo Group in the Wutai Mountains, North China Craton, that contain a small percentage of pebbles with internal folds. Based on field observations and numerical modelling results, we suggest that these formed during deformation of the conglomerate and do not represent inclusion of previously folded lithologies into the unit., Fieldwork by HR in the Wutai Mountains area, China was supported by the China Geological Survey (grant No. 12120114076401). Fieldwork by PDB was kindly supported by the Chinese University of Geosciences (Beijing). We appreciate the help for the fieldwork from Zhongbao Zhao, Changshun Wen, Chao Li and the constructive suggestions from Guoli Yuan and Zhongbao Zhao. HR thanks the financially support by the China Scholarship Council (CSC; No. 201506400014) and the China Geological Survey (grant No. DD20190465). EGR acknowledges funding by the Spanish Ministry of Science, Innovation and Universities (“Ramón y Cajal” fellowship RYC2018-026335-I). M.-G.L acknowledges the support of the Juan de la Cierva programme of the Government of Spain's Ministry for Science, Innovation and Universities (grants FJCI-2015-2417 and IJC2018-036826-I)., Peer reviewed