Pre-Neoproterozoic continental growth of the Yangtze Block: From continental rifting to subduction–accretion

Abstract

The Yangtze Block exemplifies the gradual formation of cratons since the Archean, and its pre-Neoproterozoic basement constitution needs to be clarified by a study of the combination of spatiotemporal relationship, geochemistry, and radiogenic isotopes of pre-Neoproterozoic rocks within and around the continent. It is suggested that the Yangtze Block could be divided into the north (NYB) and south (SYB) parts before the Neoproterozoic due to distinct rock configuration and tectonic evolution. The NYB consists of extensive Archean lithosphere and witnessed nascent stage (~2.0 Ga) of Columbia (Nuna)-assembly tectonics and was less involved in subsequent supercontinent breakup. It was then surrounded by a series of early Neoproterozoic (1.0–0.93 Ga) intra-oceanic accretionary system, which facilitated the tectonic emplacement of ~1.1–0.95 Ga ophiolite suites and the accretion of allochthonous terranes. The SYB, as well as the south Qinling Orogenic Belt and western Cathaysia Block, in part or in whole, may serve as one of the accretionary terranes around the NYB. These accreted terranes were generally involved in the extensional tectonics in response to the breakup of Columbia supercontinent, with the post-1.5 Ga rift locally evolved to seafloor spreading as evidenced by the occurrences of relic oceanic lithosphere in some areas. We highlight the progressive continental growth from a large-scale, long-term continental rifting during Columbia breakup to subsequent Rodinia-assembly-related tectonics around the NYB. The former stage is characterized by the consuming of ancient continental lithosphere and creation of thick, juvenile volcanic-sedimentary rocks within continents (failed rift) or along passive margins (successful rift). In contrast, the latter stage may have driven the subduction–accretion of allochthonous rift terranes around the NYB and promoted the emplacement of circum-NYB 1.1–0.9 Ga ophiolite suites and island-arc units. We suggest that the significant mantle input in both extension and convergence stages and the successive lateral accretion of terranes may have contributed to the continental growth and reshaping of the Yangtze Block.