RHEOLOGICAL STRUCTURE AND EFFECTIVE ELASTIC THICKNESS OF CONTINENTAL LITHOSPHERE IN CHINA: IMPLICATIONS FOR CENOZOIC DIFFUSE DEFORMATION

The Cenozoic deformation in China is more diffuse, but the cause is still controversial. Although the control of lithospheric rheology and mechanical strength on deformation is generally accepted, the nature of rheology of continental lithosphere and effective elastic thickness(Te) pattern in China are not investigated well in previous studies. here we presented rheological structure and Te of lithosphere in China with regional scale.

For those areas where the heat flow is really low (<50mW/m²), regardless of crustal thickness, the rheology of lithosphere is of the sandwich model, and the Te under this circumstance is larger than crustal thickness and brittle and ductile transition depth, indicating much contribution from the upper mantle to lithospheric strength. Some Precambrian blocks, including the Tarim, Junggar, Sichuan and Yangtze blocks, are representative of this type. However, the Crème brûlée model is also found in the regions with high heat flow (>65mW/m²) and thin crustal thickness(30~35km), occurring in the eastern margin of China from the northeast to the southeast coastal area, in which the Te is coincident with the crustal brittle and ductile transition depth but much less than crustal thickness. This situation is also observed in some young orogenic belts, such as the Tianshan orogeny in NW China. Of particular interest, the lithosphere in the eastern North China Craton is also with the Crème brûlée model, suggesting the destruction or reactivation of this Precambrian craton, although the timing and mechanism of this destruction are enigmatic. Accordingly, these two end-element rheological modes for continental lithosphere are all available in China, depending on differences in thermal regime, composition and lithospheric configuration.

The deformation style matches well with the pattern of rheology and Te of lithosphere in China. Seismicity and active faults are more diffuse in the areas with low Te and Crème brûlée model in rheology, but only localize at the boundaries of rigid blocks with large Te and sandwich-like rheology, and the Te gradient zones are characterized by intensive deformation. We conclude that rheological heterogeneity and mechanical anisotropy are important factors that control diffuse deformation in China.