Deformation and microfabric of the mafic granulite from the Huai'an area of the North China craton

The rheological behavior of the lower continental crust can provide important clues toward a better understanding of geodynamic processes, such as plateau uplift, lower crust delamination and craton reactivation. We currently know little of such information for the North China craton, which is one of the oldest Archean cratons in the world that experienced dramatic reactivation during the Mesozoic. We present here the deformation microfabric and microstructure in the mafic granulite from the Precambrian terrane in the Huai'an area of the northern margin of the North China craton revealed by the electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) techniques. Unlike the deformation features of granulites from other places of the world that show mainly strong deformation in plagioclase, our results reveal pronounced lattice preferred orientations (LPOs) in orthopyroxene, clinopyroxene and plagioclase. These results are in good agreement with the high density of dislocations found by TEM, indicative of plastic deformation by dislocation creep. The dislocation substructures from the TEM analyses - for example, the free dislocations, dislocation walls and subgrain boundaries, provide important clues for understanding the deformation processes of the minerals in the granulite. Combined with FTIR results, we suggest that the high water contents of the constituent minerals may significantly reduce the flow strengths of pyroxenes to that of plagioclase in the mafic granulite of the north China craton. These results provide direct evidence of a low viscosity Precambrian lower crust for the North China craton that might facilitate thickening and delamination when the cratonic lithosphere is subjected to compressional deformation.