Study on Geochemical Characteristics and Depositional Environment of Pengcuolin Chert, Southern Tibet

Based on the field investigations and analysis on major elements, trace elements and rare earth elements, the Geochemical Characteristics and Depositional Environment of Pengcuolin Chert are studied.The massive chert is green and brown in colour, has high SiO2 content and locally enrich Fe and Mn, Al/ (Al+ Fe+ Mn) ratio is lower, in Fe-Mn-Al triangle diagrams, most samples fall into hydrothermal region, trace elements such as Sr, Zr, Cu, Zn and Ba are higher and ?REE is lower, with Ce negative anomaly and Eu anomaly. Their NASC-normalized REE distribution patterns are slightly left-leaning, which indicate that the chert is hydrothermal origin. In environment discrimination diagram such as 100 × Fe2O3/ SiO2 – 100 × Al2O3/ SiO2, Fe2O3/ (100 - SiO2) - Al2O3 / (100 - SiO2) and Fe2O3/ TiO2 - Al2O3 / (Al2O3 + Fe2O3), most chert samples fall into the areas of mid-ocean ridges or deep-sea. In parameter variation diagrams, samples of PCL-5 and PCL-7 are much closer to the hydrothermal center. It is shown that the Pengcuolin chert, southern Tibet was formed by the hydrothermal systems at convergence and subduction sites of plates.