Heat flux and topography constraints on thermochemical structure below North China Craton regions and implications for evolution of cratonic lithosphere

Abstract

The eastern North China Craton (NCC) has undergone extensive reactivation during the Mesozoic and Cenozoic, while the western NCC has remained stable throughout its geological history. Geophysical and geochemical observations, including heat flux, surface topography, crustal and lithospheric thicknesses, and volcanism, show significant contrast between the eastern and western NCC. These observations provide constraints on thermochemical structure and reactivation process of the eastern NCC, thus helping understand the dynamic evolution of cratonic lithosphere. In this study, we determined the residual topography for the NCC region by removing crustal contribution to the topography. We found that the residual topography of the eastern NCC region is generally 0.3–0.9 km higher than the western NCC. We computed a large number of two‐dimension thermochemical convection models for gravitational instability of cratonic lithosphere and quantified surface heat flux and topography contrasts between stable and destabilized parts of cratonic lithosphere. These models consider different chemical buoyancy (i.e., buoyancy number B) and viscosity for the cratonic lithosphere. Our models suggest that to explain the difference in heat flux (25–30 mW/m2) and residual topography (0.3–0.9 km) between the eastern and western NCC regions, the buoyancy number B is required to be ~0.3–0.4. This range of B implies that as much as 50% of the original cratonic lithospheric material remains in the present‐day eastern NCC lithosphere and its underlying shallow mantle and that the new lithosphere in the eastern NCC may be a mixture of the relics of old craton materials and the normal mantle.

Moho Depth Variations From Receiver Function Imaging in the Northeastern North China Craton and Its Tectonic Implications

“…Considering the dominant fertile lithospheric mantle that has been well demonstrated in the eastern NCC, refractory compositions constrained by geochemical studies (e.g., Wu et al, ; Xu et al, ; Zheng et al, ) may indicate the existence of local chemical depletion in the thinned lithospheric mantle beneath the eastern NCC. The local chemical depletion in composition may be either recycled cratonic lithospheric materials that accreted to the lithosphere later (e.g., Wang et al, ) or in situ remnants. This effect probably contributes to the buoyancy of the lithospheric mantle in the basin interior to some degree, which is one possibility to explain the correlations in seismic and gravity data in Figure d.…”

The Dynamic Topography of Eastern China Since the Latest Jurassic Period

“…In contrast, few studies have considered the influence of mantle flow on the whole region. To our knowledge, only Y. Wang, Huang, et al () computed some two‐dimensional thermochemical convection models to explain the difference in heat flux and residual topography between the eastern and western NCC regions.…”

Phanerozoic Evolution of Lithospheric Structures of the North China Craton

“…The massive thinning (Figure 4d) occurred in the eastern EB and the northern margin of the study area, as illustrated by the large thinning ratio (Figure 3b). The large ratio of crustal to lithospheric thickness (>0.36) (Figure 3a) shows that the thinning can be attributed to the massive removal of mantle lithosphere, and probably accompanied with large‐scale replacement of juvenile lithospheric mantle (Gao et al., 2002; Zheng et al., 2021) or a mixture of the relics of old craton materials and the normal asthenospheric mantle (Y. M. Wang et al., 2016).…”