Cu-Zn isotope compositions of hydrothermal sediments from the southern Mid-Atlantic Ridge:implications to the sediment formation and mineral exploration

Six hydrothermal sediment samples were collected from the Xunmei and Tongguan hydrothermal fields along the southern Mid-Atlantic Ridge during the China Ocean Cruise DY46 in 2017.Sulfides and oxides in the samples were separated,and Cu and Zn isotope compositions were analyzed.Results show that the ranges ofδ^(65)Cu values of the bulk sediments,sulfides,and oxides were 0.36‰-2.46‰,-0.21‰-1.10‰,and 0.68‰-1.52‰,respectively.Theδ^(65)Cu values of sulfides in four samples(46II-14,46II-30,46III-06,and 46II-09)were relatively low(-0.21‰-0.50‰),corresponding to theδ^(65)Cu values of sulfides from inactive old hydrothermal chimneys in northern Mid-Atlantic Ridge(n MAR),suggesting that the sulfides in the sediments were originated from collapsed dead chimney mainly.While theδ^(65)Cu values of the other two samples(46III-02 and 46III-08)were relatively high(1.10‰-0.96‰),corresponding to theδ^(65)Cu values for active hydrothermal chimneys sulfides in n MAR,which indicated that the sulfides in these two samples might mainly come from sulfide particles settled from active hydrothermal plume.Because of the high density of sulfide particles,they tended to settle near the hydrothermal vents first.Therefore,highδ^(65)Cu values of sulfides in 46III-02 and 46III-08 implied that undiscovered active hydrothermal vents near the sampling positions of 46III-02 in the Xunmei hydrothermal field and 46III-08 in the Tongguan hydrothermal field.Theδ^(66)Zn values of hydrothermal sediments and sulfides ranged 0.11‰-0.43‰and 0.29‰-0.67‰,respectively.In the four samples from the Xunmei hydrothermal field,a positive correlation was found between the distance of the sampling position from sulfide mineralized spot and the Zn isotopic ratio,showing that the greater the distance from the mineralized spot,the heavier the Zn isotope composition as seen in two samples(46II-30 and 46II-14)of the Xunmei-3 spot.This result aligned with the findings of Wilkinson et al.(2005)and Baumgartner et al.(2023),suggesting that the lower the Zn isotope composition,the closer it is to the hydrothermal vent.However,in the Xunmei hydrothermal field,the Zn isotope composition in the other two samples(46III-02and 46III-06)showed the opposite trend.This indicated that there might be an active hydrothermal vent near the sampling location of sample 46III-02.This observation aligned with the Cu isotope analysis results.This study showed that Cu-Zn isotopes are good indicators for understanding the formation mechanisms of hydrothermal sediments and for locating active hydrothermal vents.

Powdery mildew disease resistance and markerassisted screening at the Pm60 locus in wild diploid wheat Triticum urartu

Triticum urartu,a diploid wild wheat and progenitor of the A genome of bread wheat,is an important resource for resistance to powdery mildew fungus caused by Blumeria graminis f.sp.tritici(Bgt).In the present study we systematically characterized the interaction between the Bgt fungus and T.urartu at the microscopic level.We also tested 227 T.urartu accessions for reaction to Bgt isolate E09 and discovered previously uncategorized powdery mildew resistance in this collection.Pm60 is a CC-NB-LRR type powdery mildew resistance gene that has at least three functional alleles,Pm60,Pm60a,and Pm60b.A marker-assisted screen targeting the Pm60 locus identified a non-functional allele of Pm60a,designated as Pm60a′.A sequence comparison of Pm60a′and Pm60a revealed that they differed by 58 SNPs and one 3-nucleotide deletion.Based on the sequence variations two molecular markers were developed to differentiate the functional Pm60a allele from the non-functional Pm60a′.Our screen revealed the presence of a previously uncharacterized powdery mildew resistance in T.urartu and provides new insights into the Pm60 locus.We believe that the two molecular markers developed here and new T.urartu resistant accessions will facilitate further identification of novel powdery mildew resistance genes and benefit breeding for powdery mildew resistance.

Clay mineral distribution characteristics of surface sediments in the South Mid-Atlantic Ridge

Clay minerals are usually considered as important indicators to identify sources in both terrigenous and marine sediments.In particular,clay minerals in metalliferous sediments(MS)have long been studied in global oceans except in South Mid-Atlantic Ridge(SMAR)due to limited explorations.Thus,32 MS and 34 non-MS(NMS)samples were analyzed to clarify the distribution characteristics and mineral compositions of clay minerals.All the sediments were collected along the SMAR between 12°S and 27°S.After removal of organic matter and carbonate,clay fractions(<2μm)were investigated by Xray diffraction(XRD)analysis.Results show that clay mineral assemblages of surface MS consist dominantly of smectite,less abundant illite,chlorite,and kaolinite in average weight percentage of 30%,21%,18%,and 16%,respectively.On the other hand,clay mineral assemblages in the NMS consist mainly of illite,less abundant kaolinite,chlorite,and very scarce smectite in average weight percentage of 47%,29%,24%,and 0.2%,respectively.The clay fractions in MS are mainly composed of amorphous or poorly crystallized Fe/Mn oxyhydroxides,clay mineral,quartz,and plagioclase.However,the counterparts in the NMS are mainly composed of well-crystallized clay minerals,quartz,and plagioclase without the presence of Fe/Mn oxyhydroxides.It is suggested that most of the illite,kaolinite,and chlorite in both MS and NMS are likely aeolian dust in origin from South Africa continent.In addition,the abundance of kaolinite dominates the clay mineral assemblage at low latitudes,where the intensive chemical weathering of continental source rocks facilitating the formation of kaolinite.In terms of smectite,it is indicated of authigenic origin in consideration of only smectite is available in several MS and the absence in NMS.Moreover,the MS samples with only smectite available are always accompanied by goethite.Therefore,it is assumed that most of smectite occurred in studied area is the results of interaction between hydrothermal Fe-oxyhydroxide,silica,and seawater.