Crustal and uppermost mantle conductivity distribution beneath the northern portion of Trans North China Orogen and its implication in the scale of destruction of the North China Craton

Abstract:

Formed by the assembly of the Eastern and Western Blocks of North China Craton(NCC) during the Paleoproterozoic, The Trans North China Orogen(TNCO) consists of the Archean to Paleoproterozoic basement overlain by Mesoproterozoic to Cenozoic cover. While the Eastern NCC has experienced significant thinning and modification in mantle since the early Mesozoic, the TNCO exhibits both thick and dramatically thinned lithosphere. In order to investigate the inhomogeneous lithospheric thinning of northern TNCO, the electrical conductivity structure from the crust to uppermost mantle was derived by the 3D magnetotelluric(MT) inversion technique from data of 75 Broadband magneotelluric (BBMT)stations. Our inversion result shows that the relatively stable Yanshan Uplift is characterized by a simply 1-D layer structure about 10000 Ωm in the upper and middle crust and 1000 Ωm in the mantle, which could be illustrated as the intact cold Archean lithosphere with very high resistivity, whereas prominent high-conductivity anomalies of 10 Ωm extensively exist beneath the Datong-Yanggao Basin, the Weixian-Yangyuan Basin and Datong volcanic zone. While petromagnetic studies shows that bi-level magnetic lower crust are preserved beneath northern TNCO, which was the result of the continuous underplating of basaltic magmas from the late Paleozoic to the Cenozoic, We also assume that the conductive middle and lower crust and uppermost mantle beneath the Shanxi rift is related to the addition of juvenile materials form mantle to lower crust, with a mixing of the old crust with melts. Nowadays the heat flow of our study area is 50 mW/m² on average, which is difficult to support the presence of partial melting, but the interconnected iron oxides and iron sulfides were preserved as a signature of the high Cenozoic heat flow as well as lithospheric thinning.