Geochemistry of Cretaceous Argillaceous Rocks in Longquan Mountain, Western Sichuan
As the foreland forebulge,Longquan Mountain records important information about tectonic evolution of the Longmenshan tectonic belt.This paper studies major,trace,and rare earth elements(REE) of the Cretaceous argillaceous rocks in the Longquan Mountain of western Sichuan.Based on these data,we discuss the provenance,tectonic setting,and weathering of source rocks.Ratios of K2O/Al2O3、Al2O3/TiO2,Cr/Zr and Th/Sc show that the detritus were derived mostly from felsic rocks in the source areas.In the REE mantle-normalized pattern,the(La/Yb)n value is 8.99 on average,and δEu value is 0.70 on average,which shows enrichment in light REEs and a moderate negative Eu anomaly.The triangular plots of Th-Co-Zr/10 and Th-ScZr/10 show that the tectonic setting was probably continental island arc,active continental margin and passive continental margin.The average of chemical index of alteration(CIA=71) and index of chemical variation(ICV=1.43)indicate that the provenance area underwent moderate weathering and reveal a hot semiarid to arid climatic environment.