Structure and composition of the continental crust in East China

Crustal structures of nine broad tectonic units in China, except the Tarim craton, are derived from 18 seismic refraction profiles including 12 geosci ence transects. Abundances of 63 major, trace and rare earth elements in th e upper crust in East China are estimated. The estimates are based on sampl ing of 11 451 individual rock samples over an area of 950 000 km(2), from w hich 905 large composite samples are prepared and analyzed by 13 methods. T he middle, lower and total crust compositions of East China are also estima ted 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 cru sts. 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 gl obal averages. The hulk lower crust is' suggested to be intermediate with 5 8% SiO2 in East China. The results contrast with generally accepted global models of mafic lower crust. The proposed total crust composition in East China is also more evolved tha n previous estimates and characterized by SiO2 = 64%, a significant negativ e Eu anomaly (Eu/Eu* = 0.80), deficits in Sr and transition metals, a near- arc magma La/Nd ratio (3.0), and a calculated mu (U-238/Pb-204) value of 5. In addition, it has the following ratios of element pairs exhibiting simil ar compatibility, which are identical or close to the primitive mantle valu es: Zr/Hf = 37, Nb/Ta = 17.5, Ba/Th = 87, K/Pb = 0.12 x 10(4), 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/Tl = 177, Er/Ag = 52, Cu/Au = 3.2 x 10(4), Sm/Mo = 7.5, Nd/W = 40, Cl/Li = 10.8, F/Nd = 21.9, and La/B = 1. 8.