Geochemistry of Mudstones from Mesozoic Jiyuan Basin,West Henan: Implications for Provenance Analysis

The sedimentary development of the Jiyuan basin was controlled by the Qinling orogenic belt during the Early Mesozoic. Therefore, mountain building and uplift of the Qinling orogenic belt can be evidenced by the sediments from the Jiyuan basin. The Mesozoic mudstones geochemistry has been investigated to determine the provenance of the Jiyuan basin. The average values of corrected CIA (chemical weathering index) from the Early-Middle Triassic, Late Triassic and Early-Middle Jurassic samples increase from 68.5 to 76.4, then to 86 successively, but decrease to 73.7 from the late Middle Jurassic samples. The variation of CIA might correspond to the changing paleoclimate during the Mesozoic. However, the much lower values of CIA from the Triassic samples may be restricted to the active tectonic setting. The values of ICV (compositional variation index) reflect that the first cycle sediments are mainly concentrated in the Triassic samples. These sediments may come from the uplifted basement of the North China craton, which should consist of the continental marginal arc and/or arc-continent collision zone. The Early-Middle Jurassic samples showing higher CIA may be related with the recycling clastics of the uplifting orogen, whereas first deposition might occur in the back-arc basin. In the tectonic discrimination diagrams, the sediments from Jiyuan basin mainly formed under the active continental margin and the passive continental margin, but contained much more continental island arc materials. Our data support that sediments from the uplifted basement of the North China craton to the denudation of the orogen is most likely related to the Qinling orogenesis during the Indosinian.