REE geochemistry of the Liuchapo chert in Anhua, Hunan

Abstract：The Liuchapo chert in Anhua County, Hunan Province, South China, was deposited in a terminal Ediacaran (551-542 Ma) deep-sea basin. It has the following REE geochemical characteristics： it has very low REE concentrations (range 8.6×10－6-18×10－6；average 13.6×10－6) and high Y/Ho ratios (range 33.6-43.9; average 37.4), indicating that the ratio is close to that of modern seawater. They are also characterized by positive La anomalies (LaN/CeN 1.46 on average), moderate negative Ce anomalies (average 0.65), weak positive Eu anomalies (average 1.1), positive Gd anomalies (average 1.07), positive Y anomaly (average 1.22) and depletion of LREE and MREE relative to HREE (LaN/YbN 0.17 on average；GdN/YbN 0.45 on average). These characteristics are similar to those of modern seawater but notably different from those of hydrothermal fluids or jasper related to seafloor hydrothermal sulfide deposits, suggesting the influence of terrigenous detrital input and hydrothermal fluids on is trivial and negligible. The Liuchapo chert formed by chemical deposition of huge amount of dissolved silica that was produced by chemical weathering and brought to the sea. Biological processes promoted precipitation of dissolved silica in seawater.