Geochemical Characteristics Of River Sediments In Different Regions Of Hainan Island And Their Controlling Factors

The geochemistry of stream sediments were carried out to assess the geochemical characteristics of different drainage area of Hainan Island for the aims of controlling factors investigations.Fourty eight sediment samples were randomly collected at geographically different locations from 20 major rivers and subjected to geochemical analysis using ICP-OES(Iris Intrepid ? XSP,Thermo)and ICP-MS(Perkin-Elmer ELAN DRC ?)for major oxides,trace and rare earth elements determinations.The chemical composition of river sediment samples normalized to(UCC)showed a significant loss for the most soluble elements like CaO,Na2O,and K2O.The depletion of these mobile element was due to their high mobility during chemical weathering.The average values of weathering indices like chemical index of alteration(CIA),weathering index of Parker(WIP),plagioclase index of alteration(PIA),chemical index of weathering(CIW)and also Na/K ratio,and index of composition variability(ICV)indicate that Hainan Island was subjected to a strong chemical weathering with a little regional differences.The total REE abundance(?REE)in Hainan river sediments varied from 112-433 ppm,with an average of 297 ppm.The total abundance of light rare earth elements(?LREE)varied in three different regions in the following order;southwest>northwest>east.But in contrast,the total content of heavy rare earth elements(EHREE)are consistent in the three regions.The chondrite-normalized REEs distribution pattern shows a significant LREE enrichment and a relative loss of HREE with moderate negative Eu anomaly(?Eu=0.55).The ?LREE/?HREE ratio in the northwestern,southwestern,and eastern parts were found close with an average value of 11.01,10.2,and 10.72,indicating that LREE and HREE were clearly differentiated.The comparable average values of LREE/HREE in the three different regions show similar enrichment and loss which may be influenced by strong weathering in the source region.The standard normalization curves of the UCC and the world shale indicate that the Eu anomalies in the western region were more prominent than the eastern region.This is because the Eu anomaly of bedrock and parent rock in western Hainan is more obvious than eastern Hainan.The contents of REEs in studied river sediments were higher than those of large rivers in China such as the Yellow,Yangtze and Pearl river,and Taiwan Island rivers.This may be due to the high temperature and heavy rainfall of Hainan Island.By comparing the enrichment factor(EF)values,heavy metals e.g.,As,Ni,Pb,and Cu in the river sediments were relatively enriched may be due to human activities.