Average chemical compositions of post-Archean sedimentary and volcanic rocks from the Qinling Orogenic Belt and its adjacent North China and Yangtze Cratons

Abstract

The North China and Yangtze (South China) Cratons are the most important tectonic units of China. The two cratons finally coalesced through collision during the Late Paleozoic to Middle Triassic with the formation of the E-W-trending Qinling-Dabie Mountains. We report the average compositions of 13 major, 16 trace and 14 rare-earth elements of post-Archean sedimentary (arenaceous, pelitic and carbonate) and volcanic (mafic with SiO 2 ⩽ 56% and felsic with SiO 2 > 56%) rocks from the Qinling Orogenic Belt (including the North and South Qinling) and the adjacent southern margin of the North China Craton and northern margin of the Yangtze Craton as well as 9 tectonostratigraphic subunits. The results are based on systematic sampling and analyses of > 3,100 individual rock samples taken over an area of 153.200 km 2. The obtained average compositions of sedimentary and volcanic rocks of the study area generally compare well with previously published averages for corresponding rock types. Pb is a notable exception and is 1.5–3 times as high as the earlier estimates for sedimentary and mafic volcanic rocks. Also, the felsic volcanic rock has a bulk composition of quartz keratophyre with Na 2O > K 2O, which is in marked contrast with the rhyolitic composition for both average world-wide Tertiary-Recent orogenic and anorogenic felsic volcanic rocks. Although there are significant intra-unit chemical variations, persistent inter-unit distinctions are also evident, especially in major elements.