Deformation model for the Tongling ore cluster region,east-central China

The Tongling region, an important Cu + Au ore district, consists of a series of S-folds and is defined by an irregular set of boundaries. The regional structural framework was traditionally considered to be the result of coaxial compression, followed by simple shear. By analysing the spatial distribution of fold geometries and fault densities, we propose a new deformation model. Two tectonic stages, that is, early NW-SE compression, and later NE-SW compression, have been newly identified in this region. In the early stage, shortening produced by the collision between the Lower Yangtze block and the North China block mainly acted on the south-eastern and north-western boundaries; NE-SW-trending anticlines adjacent to the regional boundaries are tight to isoclinal and overturned, and the density of NW-SE-trending strike-slip faults is high as revealed by the large box dimensions of the spatial fault distribution. In addition, NW-SE compressions of the two stress boundaries are non-coaxial and asymmetric. With regard to the disposition of the irregular boundaries, non-coaxial and asymmetric compression led to the formation of S-folds and to obvious displacement between the north-eastern and south-western parts of the region. In the later stage, weak NE-SW compression, derived from the south-westward component of subduction of the Izanagi plate beneath the Eurasian plate, acted on the north-eastern boundary and redeformed the local structures to a minor extent. High fault density near the region boundaries promoted the formation of an interconnected fault system, which facilitated magma migration and emplacement, as well as the development of deposits genetically related to the igneous activity.