Geochemical Characteristics And Geological Significance Of Elements In The Sediments On The Margin Of The Challenger Deep(Mariana Trench,Western Pacific)

The hadal zone represents one of the last great frontiers in modern marine science,and deciphering the provenance of sediment that is supplied to these trench settings remains a largely unanswered question.Here,this paper examine the mineralogical,U-series isotopic dating,clay minerals,major element,trace element(Cs,Rb,Th,U,Nb,Ta,Hf,Zr,Pb,Sr and Ba),rare earth element(REE)and strontium(Sr)and neodymium(Nd)isotopic composition of a sediment core(core CD-1)that was recovered from the southwestern margin of the Challenger Deep within the Mariana Trench.Based on the two-end-member mixing model of REE data and Sr–Nd isotopic composition,this paper semi-quantitatively and quantitatively calculated the relative contributions of eolian dust and nearby volcanic debris to the study area.Moreover,this paper report the mineralogical and geochemical characteristics of ferromanganese nodules from the bulk sediments.The results show that the sample is a sort of typical pelagic clay,Microscopic smear slide analysis demonstrates that the sediments from core CD-1 comprise deep-sea clays(74%),biological fragments(13%),and detrital minerals(13%).The accumulation rate is very slow,only2.01 mm/ka,which corresponds to an accumulation period of about 82 ka for the study core.The clay mineral assemblage at core CD-1 consists mainly of smectite(averaging?53%)and illite(averaging?35%),with minor chlorite(averaging?9%)and kaolinite(averaging?3%).The illite chemical index varies between 0.17 and 0.33,with an average value of 0.26,indicating that illite is typically rich in Fe-Mg and was formed in an environment dominated by strong physical erosion.The crystallinities of illite and smectite varies between 0.21?0.33°?2?and 1.22?1.44°?2?,with average values of about 0.24°and 1.32°?2?,respectively.Provenance analysis suggests that smectite was derived mainly from the weathering of locally sourced volcanic debris,whereas illite,chlorite and kaolinite were mainly transported as aeolian dust by the East Asian winter monsoon from the Asian continent.The average major element contents of the study cores are similar to those of nearby volcanic materials and aeolian dust,the low average Rb/K ratios of the study cores suggesting a non-negligible input of volcaniclastic debris.The?REE contents ranged from 152 to 223?g/g,with an average value of 189±20?g/g.Major element abundances and rare-earth element patterns from these sediments require inputs from both terrigenous dust and locally sourced volcanic debris.This paper exploit a two-endmember mixing model to demonstrate that locally sourced volcanic material dominates the sediment supply to the Challenger Deep(averaging?72%).The remainder,however,is supplied by aeolian dust(averaging?28%).The average ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios of core CD-1 are 0.70535 and 0.51232,respectively.Sr–Nd isotopic analysis demonstrates that volcanic sediment sources dominated over their aeolian counterparts.This paper propose a two-endmember mixing model(i.e.,the Mariana arc volcaniclastics and Asian aeolian dust)to explain sediment provenances in the Challenger Deep,with most inputs to the southern Mariana Trench from proximal volcanic arcs(?76%)and Asian dust(24%),which is consistent with the conclusion from REE data.Mn/Fe ratios of ferromanganese nodules range from 0.3 to 14.0,with an average value of 6.7,high Mn/Fe ratios reflect birnessite is of diagenetic origin.It shows that the growth of ferromanganese nodules was probably infected by the pore water of deep sea sediments and deep sea bottom water.Recently,only a few studies have been revealed the important role of Asian aeolian dust in the biogeochemical cycling in the southern Mariana Trench sediments,this paper further quantitatively discuss Asian aeolian dust input into the deepest point on the Earth's surface?the Challenger Deep(western Pacific),and provide additional constraints on the importance of the Asian aeolian dust input into the deep sea sediments.