| Abstract: | The composition and distribution of elements in terrigenous sedimentary rocks can well reflect the weathering and tectonic conditions in provenance. In pace with the denudation in the provenance and sedimentation in the basin,elements such as La,Ce, Nd,Sr,Cs,Ba,U,Th,Zr, Hf, Sc, Fe,Co, Cr and Ni in the Middle-U pper Triassic Tethys-sediments, show the tendency of enrichment from graywackes to siltstones and slates,smaller canons of alkali and alkaline earth elements (Na,Ca,Sr,etc. )were depleted,and the Chemical Index of Alteration (CLA) of rocks increased . These suggest that the degree of chemical weathering in the provenance increased while the tectonic activity (rate of tectonic uplift) decreased with the elapse of time. The chemical weathering chiefly resulted in the decomposition of Kbearing minerals,the conversion of plagioclase (and glass)to clays,and the depletion of alkali and alkaline earth elements such as Na,Ca and Sr. |
