Continental Fragments in the South China Block: Constraints From Crustal Radial Anisotropy

The lithospheric architecture of the South China Block (SCB) is crucial to understanding the formation and evolution of this distinctive and highly reworked continental lithosphere with over 3 billion years of tectonic history. However, due to a lack of high-resolution geophysical datasets, a detailed picture of the SCB lithosphere is absent, and fundamental questions regarding its formation, assembly, and subsequent reworking processes are actively debated. Assuming that unique deformation patterns due to such tectonic processes can be mapped by seismic anisotropy, we present a new crustal radially anisotropic shear-wave velocity model along a 1500-km seismic transect that spans the major tectonic domains of the SCB to characterize the past deformation processes. The new seismic models show significant lateral variations in seismic anisotropy and velocity, suggesting that the SCB consists of several separated (micro)continental blocks or terranes that likely have different origins and have survived the prolonged deformation history since the early formation of these continental fragments. Combining available geophysical datasets, we link individual crustal domains of distinct anisotropy to constrain the multiphase deformation processes of the SCB, including the early formation of the Proto-Yangtze and Cathaysia Blocks, the assembly of the SCB, and the subsequent reactivation of the interior and extensive deformation that have formed the Basin-and-Range style tectonics in the Cathaysia Block. We suggest that relict continental fragments have played critical roles in the formation and reactivation of the SCB lithosphere.