Geochemical Characteristics And Geological Significance Of The Hadal Trench Sediments In The Mariana Trench

Hadal trenches are the deepest parts of the world ocean,having water depths ranging from 6000-11000 meters.At present,domestic and foreign studies have studied more on their biological characteristics and environmental characteristics,but weak on their mineral composition,geochemical characteristics and provenance.The scientific issues related to the study of hadal trenches play a vital role in the development of the national marine science.The Mariana Trench is one of hadal trenches which currently study the most extensively.Based on the material composition and geochemical analysis of the columnar sediments?SY2?in the Mariana Trench,this paper comprehensively discusses the sedimentary characteristics and sedimentary environment of the Mariana Trench and conducts preliminary research on the provenance of the sample.SEM analysis showed that there were a large number of paleontological fossils in SY2 columnar sediments,including fossil species such as diatoms,radiolaria and sponge needles.SEM also showed that there were a certain amount of clay minerals in the sample,mainly montmorillonite,illite/smectite formation and illite.A very small amount of quartz and feldspar were also found in the sample.The major element analysis of SY2 columnar sediments showed that the main elements were mainly SiO₂,and the average content was 82.86%of the total chemical composition,showing obvious volatility characteristics and the lowest value at 28 cm.Except for the lowest values of SiO₂ and Na₂O at 28 cm,the other major elements exhibited significant high values at 28 cm.The results of trace element analysis showed that the trace elements of the sample showed obvious volatility,and some of them showed extremely high positive anomalies at 28 cm.Moreover,?Ce and?Eu exhibits positive anomaly.On the standardization diagram of chondrite,the LREE is moderately enriched and the HREE is relatively flat.As a result,the material of the sample was comprehensively analyzed by the method of R-type cluster analysis,material source triangulation and DF discriminant.The results show that the provenance of the sample mainly comes from the source of volcanic rock,which is presumed to have a great relationship between the volcanic materials generated by the surrounding and nearby volcanic activities around the Mariana Trench,and biological sources takes second place,and the contribution of terrestrial materials is small.According to the vertical variation of the sample elements,the provenance is complex,and sample may tend to be multi-sources.Moreover,the sediment contains a large amount of diatom fossils,which may explain the characteristics of high silicon and oligotrophy in the ancient marine environment of the Mariana Trench.