Crustal structures of nine broad tectonic units in China, except the Tarim craton, are derived from 18 seismic refraction profiles including 12 geoscience transects. Abundances of 63 major, trace and rare earth elements in the upper crust in East China are estimated. The estimates are based on sampling of 11 451 individual rock samples over an area of 950 000 km2, from which 905 large composite samples are prepared and analyzed by 13 methods. The middle, lower and total crust compositions of East China are also estimated from studies of exposed crustal cross sections and granulite xenoliths and by correlation of seismic data with lithologies. All the tectonic units except the Tarim craton and the Qinling orogen show a four-layered crustal structure, consisting of the upper, middle, upper lower, and lowermost crusts. P-wave velocities of the bulk lower crust and total crust are 6.8–7.0 and 6:4–6.5 km/s, respectively. They are slower by 0.2–0.4 km/s than the global averages. The bulk lower crust is suggested to be intermediate with 58% SiO2 in East China. The results contrast with generally accepted global models of mafic lower crusi. The proposed total crust composition in East China is also more evolved than previous estimates and characterized by SiO2=64%, a significant negative Eu anomaly (Eu/Eu* = 0.80), deficits in Sr and transition metals, a near-arc magma La/Nd ratio (3.0), and a calculatedμ(238U/204Pb) value of 5. In addition, it has the following ratios of element pairs exhibiting similar compatibility, which are identical or close to the primitive mantle values: Zr/Hf=37, Nb/Ta=17.5, Ba/Th=87, K/Pb=0.12x104, Rb/Cs=25, Ba/Rb=8.94, Sn/Sm=0.31, Se/Cd=1.64, La/ As=10.3, Ce/Sb=271, Pb/Bi=57, Rb/TI=177, Er/Ag=52, Cu/Au=3.2×104, Sm/Mo=7.5, Nd/W=40, CI/Li=10.8, F/Nd=21.9, and La/B=1.8.
Geological, geophysical and geochemical evidence for lower crustal delamination in the Qinling-Dabie oro-genic belt is presented and a chemical geodynamic model for lower crustal delamination is developed. The synthetic results suggest that eclogite from the Dabie-Sulu ultrahigh pressure metamorphic belt is the most likely candidate as the de-laminated material, and that a cumulative 37-82 km thick eclogitic lower crust is required to have been delaminated in order to explain the relative deficits in Eu, Sr, Cr, Ni, Co, V and Ti in the present total crust composition of the Qin-ling-Dabie orogenic belt. Delamination of the lower crust can well interpret many geological, geophysical and geochemical characteristics of the belt.
