Altered Spinel as a Petrotectonic Indicator in Abyssal Peridotite from the Easternmost Part of Southwest Indian Ridge-中国期刊网

摘要 TheeasternmostpartofSouthwestIndianRidge(SWIR)hasspecialcrustalstructure,magmaticandtectonicprocesses.AbyssalperidotitefromtheeasternmostpartofSouthwestIndianRidge(63.5oE/28oS)isserpentinizedspinellherzolite.Theaccessoryspinelhaszonedtexture,whichwasstudiedbypetrography,electronprobemicro-analysis(EPMA),andbackscatteredelectron(BSE)imagingtoreconstructthepetrotectonicandhydrothermalmetamorphichistoryofthehostabyssalperidotite.ThefreshcoreismagmaticAl-spinelwithlowCr~#.Theaverageextentofmeltingoftheabyssalperidotiteisabout5.9%.Thecompositionoffreshmagmaticspinelcoreindicatesthestudiedareatobeananomalouslythincrustwithamelt-poorsystem.Hydrothermalreactionmodifiesthechemicalcompositionofmagmaticspinel.Ferritchromitisthefirstproductformingtheinnerrimduringpre-serpentinization.Theabyssalferritchromitcrystalizedasmicro-tonano-sizedparticlewithnotriplegrainboundary,indicatingtheycrystalizedinarapidcoolingprocessduringhydrothermalalteration.Chemicalcompositionsofferritchromitindicateahydrothermalmetamorphisminamphibolitefacies.Magnetiteintheouterrimwasformedbyreplacementofferritchromitduringsyn-orpost-serpentinization.Authigenicchloritescrystallizedintwoevents:(1)afterformationofferritchromitcrystallizedasveininfracture-zonenearthecoreofspineland(2)afterformationofmagnetitecrystallizedatoutermostrim.Theyaredifferentincompositions,indicatingtheirformationtemperaturewasabout289oCanddeclinedto214oC.Theseresultsshowthattheabyssalperidotitehadundergoneamphibolitetolower-greenschistfacieshydrothermaleventsduringpre-tosyn-serpentinizationorpost-serpentinization.

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Altered Spinel as a Petrotectonic Indicator in Abyssal Peridotite from the Easternmost Part of Southwest Indian Ridge

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Altered Spinel as a Petrotectonic Indicator in Abyssal Peridotite from the Easternmost Part of Southwest Indian Ridge

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