Accretionary complex: Geological records from oceanic subduction to continental deep subduction

Abstract

Accretionary complex was usually formed by offscraping of the subducting crustal material over the trench and thus often referred to as subduction zone melange. The structure, composition and forming process of accretionary wedges can provide important insights into the evolution history of ocean basin, ocean-continent material cycle, continental accretion and thus contribute to understanding of the origin of plates and the growth of continents. Accretionary complex is characterized by a block-in-matrix structure associated with imbricate thrusts and isoclinal folds, diversified metamorphic types and intense water-rock interactions, which are distinct to the traditional stratigraphy. Since the proposal of the concept of accretionary wedge over a hundred years ago, great progress has been made in a variety of research focuses, such as the identification of the distribution of accretionary complexes, their compositions and formation mechanisms, the affinities of the matrix and igneous rocks, the recognition of the Ocean Plate Stratigraphy (OPS), the reconstruction of oceanic basin, the dynamic background of the tectonic evolution, the relationship between subduction zone and orogenic belt and, in particular, the accretionary complexes in continental subduction zones. These studies have significantly improved our understanding of the plate tectonic theory. Challenges remain in the identification of ancient accretionary complexes, the detailed analysis of accretionary complex zones, the accretion characteristics during continental collision, and the geochemical tracing of water-rock interaction during the accretion. China contains representative orogenic belts and accretionary complex zones in the world, and its geological records provide the best opportunity to make new breakthroughs in understanding of the plate tectonics.