Binary sources of Chinese loess as revealed by trace and REE element ratios

Chinese loess is generally accepted to be one of the most important archives for establishing the average geochemical compositions of the upper continental crust (UCC), assuming numerous upper crustal recycling processes. However, the effect of such recycling processes on elemental fractionation has still not been systemically and quantitatively assessed. This study investigates the trace and rare earth elements (BEE) of the < 75 mu m and < 5 mu m silicate fractions of ten deserts and sandy lands in northern China, and of Chinese loess, to evaluate the effect of grain size on element ratios. Our results indicated that BEE- and some trace elements (Y, Ta and Nb)-related ratios have the negligible effect of grain size, and can therefore be regarded as size-independent proxies to trace the source of eolian deposits. The principal component analysis (PCA) of these size-independent ratios was conducted for the deserts and loess samples. The PCA results reveal that Chinese loess was ultimately derived from the materials eroded from two tectonic settings, i.e. the northern Tibetan Plateau (NTP) and the Central Asian Orogenic Belt (CAO). We propose that the UCC component of Chinese loess can not only be ascribed to numerous upper crustal recycling processes, but also to the thorough mixing of materials from different tectonic settings.