ABSTRACT
In an area of some 1.4 million km within the North China Platform (NCP), 12,193 various rocks were systematically sampled and combined into 1,207 composite samples which were then analyzed by 15 reliable analytical methods, such as instrumental neutron activation analysis (INAA), X-ray fluorescence analysis (XRF), and atomic absorption spectrophotometry (AAS) etc., with international accepted preliminary national geochemical certified reference materials (CRMs) of identical types for data quality monitoring. The average chemical compositions of igneous rocks, sedimentary rocks and metamorphic rocks as well as high grade granulite facies belts with or without K, Th, U depletion and high grade and medium-low grade amphibolite facies belts in NCP are presented. According to the data of regional geophysics, geology, experimental petrology and geochemistry, a crustal model of 38 km thickness was established and the abundance of 78 elements in the total crust (TC) and exposed crust (EC) were calculated in NCP. The results show that average chemical compositions of both the upper crust (UC) and the middle crust (MC) in NCP are equivalent to granodioritic, that of the lower crust (LC) is equivalent to quartz dioritic, and that of TC is characterized between granodiorite and quartz monzodiorite. The distribution of elements exhibits an obvious vertical zoning: volatile elements like As, Sb, Hg, B, and C are concentrated in the sedimentary cover, U, Th, Rb, Cs, B, and Be decrease remarkably from the sedimentary cover to the lower crust, Nb, Ta, Zr, Hf, W, Sn, and rare earth elements (REE) also tend to decrease gradually, and siderophile elements (SE) and platinum-group elements (PGE) are evidently enriched in LC.
