Three-dimensional Lithospheric Resistivity Structure and Thermal State of the North China Craton

The North China Craton (NCC) has been affected by the subduction and roll-back of the Paleo-Pacific Plate in the Mesozoic. To study the thinning of the lithosphere and the melting of the NCC, a three-dimensional (3-D) resistivity model of the lithosphere is obtained from a magnetotelluric sounding (MT) deployed in the NCC (Figure 1). In addition, the cause of the low resistivity of the upper mantle of the NCC can be solved by the Nernst-Einstein Equation and the Arrhenius Equation which is used to establish the relationship between the resistivity and temperature. Moreover, the Hashin-Shtrikman (HS) boundary conditions limit the range of electrical conductivity of mixed minerals (Figure 2). Based on the 3D resistivity structure, the temperature and melt fraction model, the lithospheric resistivity of the north of 37.5°N in the Ordos Block (OB), the southern Taihang Uplift (THU) and the Luxi Uplift (LXU) are as low as 1 Ωm which the upper mantle temperature is in the range of 1400 - 1550 °C, and the melt fraction is 1-10% in the high-temperature regions. According to the resistivity model and the thermal state, the westward subduction and roll-back of the Paleo-Pacific Plate provided conditions for upper mantle melting in the LXU and the Bohai Bay Basin (BBB). It also made the Tanlu Fault Zone (TLFZ) and THU channels for the upwelling, and the front of the Paleo-Pacific Plate stagnant slab is blowing the THU. With the remote tectonic stress of the Paleo-Pacific Plate and the Indian Plate, anticlockwise rotation of the OB induced the low resistivity of grabens and rifts around the OB (Figure 3). Moreover, upper mantle volatiles (H₂O and CO₂) and slight carbonatite melts significantly lower the mantle melting temperature.

* This work was supported by National Natural Science Foundation of China (Grants 41974112 and 40434010) and project SINOPROBE on sub-project SINOPROBE-01.

Reference:

Dong, S..T. Li. (2009). SinoProbe: the exploration of the deep interior beneath the Chinese continent. Acta Geologica Sinica, 83(7), 895-909.

Hirschmann, M. M. (2010). Partial melt in the oceanic low velocity zone. Physics of the Earth and Planetary Interiors, 179(1), 60-71.

Zhao, G..M. Zhai. (2013). Lithotectonic elements of Precambrian basement in the North China Craton: Review and tectonic implications. Gondwana Research, 23(4), 1207-1240.

Figure 1 Simplified s tectonic map of the North China Craton (modified from Zhao and Zhai (2013)); Map of MT profiles and sites, in which blue dots represent MT stations in this study, supported by the “SINOPROBE” project (Dong and Li, 2009). TNCO: Trans-North China Orogen 

Figure 2 Schematic diagram of dynamic changes of water and carbon dioxide during heating and melting of upper mantle minerals. NAMs means nominally anhydrous minerals; the “Calculate” in the dashed box is the calculation category of this study; the criterion for determining the interconnection of melts was proposed by Hirschmann (2010).

Figure 3 Schematic diagram of the possible formation mechanisms of the North China Craton inferred from the crustal and upper mantle 3-D resistivity model derived from this research.