Melt inclusions in kimberlitic minerals and diamonds indicate that chlorides are important constituents of mantle carbonatite melts.Besides,alkaline chlorides are important constituents of saline high-density fluids(HDFs)found in diamonds from kimberlites and placers around the world.Continuous composi-tional variations suggest that saline and carbonatitic HDFs could be genetically linked.However,the essence of this link remains unclear owing to the lack of data on phase relations in the chloride-carbonate systems under pressure.Here we studied subsolidus and melting phase relations in the system NaCl-CaCO3-MgCO3 at 6 GPa and 1000-1600℃ using a Kawai-type multianvil press.We found that at 1000℃,subsolidus assemblage consists of halite,magnesite,and aragonite.At higher temperatures,the stabilization of dolomite splits the subsolidus area into two partial ternary fields:halite+magnesite+dolomite and halite+dolomite+aragonite.The minimum on the liquidus surface corresponds to the halite-dolomite-aragonite ternary eutectic,situated at 1100℃.The eutectic melt has Ca#89 and contains 30 wt.％NaCl(26 mol％2NaCl).The system has two ternary peritectics:halite+dolomite=magnesite+liquid located near the ternary eutectic and magnesite+dolomite=Mg-dolomite+liquid situated between 1300 and 1400℃.Although under dry conditions incipient melting yields carbonate-dominated melt,the addition of water facilitates the fusion of NaCl and expands the liquid field to NaCl-rich compositions with up to 70 wt.％NaCl.The obtained results favor the idea that hydrous saline melts/fluids(brines)found as inclusions in diamonds could be a lower temperature derivative of mantle carbonatite melts and disagree with the hypothesis on chloride melt generation owing to the chloride-carbonate liquid immiscibility since no such immiscibility was established.We also studied the interac-tion of the NaCl-CaCO3-MgCO3 system with iron metal and found that carbonate reduction produces C-bearing species(Fe0,Fe-C melt,Fe3C,Fe7C3,C0)and wiistite containing Na2O,CaO,and MgO.Besides,a carbonate chloride compound,Ca2Cl2CO3,was established among the reaction products.The interaction between NaCl-bearing carbonate melt shifts its composition toward Mg-poor and NaCl-rich.Given the above,an alternative hypothesis can be proposed,according to which the interaction of alkaline chloride-bearing carbonate melts formed in the subduction zones with the reduced mantle should be accompanied by diamond crystallization and shift the composition of the melt from carbonatitic to alkali-rich saline.

Anton Shatskiy;Ivan V.Podborodnikov;Anton V.Arefiev;Altyna Bekhtenova;Konstantin D.Litasov

Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Science,Moscow 119991,Russia;Vereshchagin Institute for High Pressure Physics of the Russian Academy of Science,Troitsk,Moscow,108840,Russia

地学前缘（英文版）

[1]Anton Shatskiy;Ivan V.Podborodnikov;Anton V.Arefiev;Altyna Bekhtenova;Konstantin D.Litasov-.Genetic link between saline and carbonatitic mantle fluids:The system NaCl-CaCO3-MgCO3±H2O±Fe0 at 6 GPa)[J].地学前缘（英文版）,2022(06):59-74

carbonatitic,kimberlitic,kimberlites,Kawai,multianvil,halite+magnesite+dolomite,halite+dolomite+aragonite,Ca#89,2NaCl,peritectics,halite+dolomite,magnesite+liquid,magnesite+dolomite,dolomite+liquid,Fe7C3,wiistite,Ca2Cl2CO3

Genetic,between,saline,mantle,fluids,CaCO3,MgCO3,H2O,Fe0,GPa,Melt,inclusions,minerals,diamonds,indicate,that,chlorides,important,constituents,carbonatite,melts,Besides,alkaline,density,HDFs,found,from,placers,around,world,Continuous,tional,variations,suggest,could,genetically,linked,However,essence,this,remains,unclear,owing,lack,data,phase,relations,carbonate,systems,under,pressure,Here,studied,subsolidus,melting,using,type,We,assemblage,consists,At,higher,temperatures,stabilization,splits,area,into,two,partial,ternary,fields,minimum,liquidus,surface,corresponds,eutectic,situated,contains,wt,located,near,Although,dry,conditions,incipient,yields,dominated,addition,water,facilitates,fusion,expands,rich,compositions,up,obtained,results,favor,idea,hydrous,brines,lower,derivative,disagree,hypothesis,generation,immiscibility,since,no,such,was,established,also,iron,metal,reduction,produces,bearing,species,Fe3C,C0,containing,Na2O,CaO,MgO,compound,among,reaction,products,interaction,shifts,toward,poor,Given,above,alternative,can,proposed,according,which,formed,subduction,zones,reduced,should,accompanied,by,crystallization

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