VolcanicrocksinseamountsoftheSouthChinaSeaconsistmainlyofalkalibasalt,tholeiiticbasalt,trachyandesiticpumice,dacite,etc.Inclusionsinthemineralsofthevolcanicrocksaremain-lyamorphorsmeltinclusions,whichreflectsthatthevolcanicrocksarecharacterizedbysubmarineeruptionandrapidcoolingontheseafloor.Furthermore,fluid-meltinclusionshavebeendiscoveredforthefirsttimeinalkalibasaltsandmantle-derivedxenoliths,indicatingaprocessofdifferentiationbetweenmagmaandfluidinthecourseofmantlepartialmelting.Alkalibasaltsandinclusionsmayhavebeenformedinthisnonhomogeneoussystem.Rock-formingtemperaturesoffourseamounsestimatedasfollows:theZhongnanseamountalkalibasalt1155-1185℃;theXianbeiseamountalkalibasalt960-1200℃;tholeiiticbasalt1040-1230℃;theDaimaoseamounttholeiiticbasalt1245-1280℃;andtheJianfengseamounttrachandesticprmice880-1140℃.EquilibriumpressuresofalkalibasaltsintheZhongnanandXianbeiseamountsare13.57and8.8×10^8Pa,respectively.Pyroxeneequilibriumtem-peraturesofmantlexenolithsfromtheXianbeiseamountwereestimatedat1073-1121℃,andpres-suresar(15.58-22.47)×10^8Pa,suggestingadeep-source(e.g.theasthenosphere)forthealkalibasalts.
