Electrical structure characterization of lithospheric thinning and craton destruction in North China Craton

Abstract:

The North China Craton(NCC) is one of the world’s oldest craton, formed by the amalgamation of the Archean eastern and western blocks along the Trans-North China orogen at ~1.9 Ga. The craton remain tectonically stable before Mesozoic. When large-scale magmatic activities widely occurred in the eastern part of the North China Craton, indicative of lithospheric thinning and craton destruction. It is generally agreed that the subduction of the Pacific plate is the primary trigger of craton destruction. As the subducted oceanic slab rolled back, hot upwelling asthenospheric mantle direct contacted with the base of craton and accelerated gravitational instability of the lower part of the lithospheric mantle. The rollback model is speculated by the distribution of Mesozoic intrusive rocks, lack the geophysical evidence. We present three-dimensional refined electrical structure obtained by inversion of 46 long-period (3-10000s) and 142 broad-band Sinoprobe magnetotelluric sites covering Trans-North China orogen, the eastern and western blocks of NCC. A striking feature of our model is that one conductor rising from mantle connects with three parallel high-conductivity belts in mid-lower crust in Heze country, Henan Province, which tectonically located in the west edge of the eastern NCC. Along with the S and P RF-migrated images, the location of the conductor is consistent with joint area of old craton and the thinning lithosphere. We suggest the conductor traces the position where leading edge of paleo-Pacific plate rolled back at 140Ma.