Formation and tectonic evolution of Southeastern China and Taiwan: Isotopic and geochemical constraints

Abstract The southern part of China consists of the Proterozoic Yangtze Craton and the Phanerozoic South China foldbelts (including the Himalayan foldbelt of Taiwan). Models for continental growth have been many and controversial. Isotopic and geochemical data from Mesozoic and younger granitoids and sediments are used here to place constraints on the tectonic evolution of Southeastern China and to evaluate whether the young Phanerozoic foldbelts are representative of old rejuvenated landmass, whether they characterize crustal accretion through successive subduction processes, hence suggesting a net growth of continental mass, or whether they represent some intermediate situation. Available Sm-Nd isotopic data for Phanerozoic granitoids and metasediments from the South China foldbelts and Taiwan invariably show Proterozoic model ages ( T DM ) ranging from 1 to 2.5 Ga, with a mean of 1.54 ± 0.30 (1σ) Ga. All rocks have negative ϵNd(T) values (−2 to −15), suggesting variable but important contributions of old continental materials to the sources of the Phanerozoic rocks. Obviously they do not represent wholesale growth of continental mass. The granitoids of the South China foldbelts have multiple origins as viewed from their chemical and isotopic characteristics. Secular geochemical variation has been established for inland granitoids of Proterozoic to Mesozoic age. Their high I Sr values (0.710–0.737) suggest that most granitoids are essentially anatectic products of ancient continental crust. This is compatible with remelting via microcontinental collision or terrane accretion. Repeated intracrustal reprocessing by partial fusion and differentiation has undoutedly contributed to important mineralization. Mesozoic granitoids (excluding A -type alkaline granites) in the coastal region and Taiwan show relatively low I Sr (0.705–0.710) and high ϵNd values, implying that greater amounts of mantle components have been added to ancient continental material in the generation of these rocks. This means that Mesozoic magmatism in the coastal region resulted from subduction of a paleo-Pacific plate (Kula) beneath the Asian continent. The overall geochemical evidence seems to be consistent with a model of serial collisions between microcontinental blocks for the bulk of the South China foldbelts. The latest arc-continent collision began about 4 Ma ago in eastern Taiwan.