Major, trace and rare earth elements were measured in 27 samples of the Middle to Late Permian limestones from the Tieqiao section located on the marginal zone of an isolated platform （Laibin, South China）. Shale-no...Major, trace and rare earth elements were measured in 27 samples of the Middle to Late Permian limestones from the Tieqiao section located on the marginal zone of an isolated platform （Laibin, South China）. Shale-normalized REE＋Y patterns of all samples show notably negative Ce anomalies （0.21-0.66, average 0.33）, slightly positive Gd anomalies （1.08-1.30, average 1.20）, and positive Y anomalies with superchondritic Y/Ho ratios （36-91, average 55）, which are consistent with those of modern shallow seawater. Their relative LREEs enrichment with higher NdsN/YbsN ratios （0.58-1.80） than those of modern shallow seawater （0.21-0.50） suggests complicated sources of REEs for all samples. Compared with geochemical features of sediments influenced by terrigenous particles and hydrothermal fluids, it is concluded that ambient shallow seawater was the primary source of REEs in these limestones. Comparing the indicators of REE＋Y elements （ZREE, NdsN/YbsN, Ce/Ce＊, Gd/Gd＊, Eu/Eu＊ and Y/Ho） in limestones with those in bedded cherts from the Tieqiao section, we consider that limestone and bedded chert have similar sources of REE＋Y elements： ambient shallow seawater with more or less hydrothermal fluids. In addition, there is a completely negative correlation between CaCO3 and SiO2 contents in limestones and bedded cherts. These results imply that precipitation of CaCO3 was inhibited by that of SiO2 which was derived mainly from hydrothermal fluid, es- pecially in bedded cherts from the Tieqiao section.展开更多
基金financially supported by the National S&T Major Project(Grant No.2011ZX05008)National Natural Science Foundation of China(Grant Nos.41273001 and 41103018)
文摘Major, trace and rare earth elements were measured in 27 samples of the Middle to Late Permian limestones from the Tieqiao section located on the marginal zone of an isolated platform （Laibin, South China）. Shale-normalized REE＋Y patterns of all samples show notably negative Ce anomalies （0.21-0.66, average 0.33）, slightly positive Gd anomalies （1.08-1.30, average 1.20）, and positive Y anomalies with superchondritic Y/Ho ratios （36-91, average 55）, which are consistent with those of modern shallow seawater. Their relative LREEs enrichment with higher NdsN/YbsN ratios （0.58-1.80） than those of modern shallow seawater （0.21-0.50） suggests complicated sources of REEs for all samples. Compared with geochemical features of sediments influenced by terrigenous particles and hydrothermal fluids, it is concluded that ambient shallow seawater was the primary source of REEs in these limestones. Comparing the indicators of REE＋Y elements （ZREE, NdsN/YbsN, Ce/Ce＊, Gd/Gd＊, Eu/Eu＊ and Y/Ho） in limestones with those in bedded cherts from the Tieqiao section, we consider that limestone and bedded chert have similar sources of REE＋Y elements： ambient shallow seawater with more or less hydrothermal fluids. In addition, there is a completely negative correlation between CaCO3 and SiO2 contents in limestones and bedded cherts. These results imply that precipitation of CaCO3 was inhibited by that of SiO2 which was derived mainly from hydrothermal fluid, es- pecially in bedded cherts from the Tieqiao section.
