Textures and Chemistry of Crystal Cargo of the Pleiades Volcanic Field, Antarctica: Potential Influence of Ice Load in Modulating the Plumbing System

ThePleiadesVolcanicField(PVF)ofnorthernVictoriaLand(Antarctica)ismadeupofadozenscoriaconeswhoseeruptedproductspresentanunusuallycompleteevolutionarytrendfromalkali-basalttotrachyte.WiththeaimofreconstructingtheevolutionofthePVFplumbingsystem,wehaveinvestigatedthepetrographyandchemistryofmainmineralphasesusingscanningelectronmicroscopy(SEM-EDS)coupledwithmajorelementanalysesusinganelectronprobemicroanalyser(EPMA-WDS).Wefurtherfocussedonclinopyroxenephenocrystsobtainingamoredetailedcharacterizationbymeansoftracelaserablation-inductivelycoupledplasma-massspectrometry(LA-ICP-MS)elementanalysescoupledwithmachinelearningthermobarometry.Theresultsindicatethatfractionalcrystallizationandmagmamixingarethemajorprocessesdeterminingthedevelopmentofthecompleteevolutiontrend.Whilefractionalcrystallizationisapersistentlyactiveprocessinallpartsoftheplumbingsystem,mixingamongdifferentlyevolvedmagmabatchespertainingtothesameassociationisresponsiblefortheformationofintermediatecompositionsinthedifferentiationlineageataspecificpressurerange(0.4–0.5GPa).Theseprocessesarecompatiblewithsignificantresidencetimeofmagmasatdepth,resultinginmultipleepisodesofmagmamixing,astestifiedbyresorptionandovergrowthtexturesinphenocrystassemblageoccurringunderisobaricconditions.Theprolongedresidencetimelikelyincreasedtheefficiencyofthemixingprocess,leadingtotheformationofmagmaswithintermediatecomposition.Inturn,thebuild-upofvolatilesduringthemagmadifferentiationatdepthcouldhavefavouredtheeruptionofthese(variablydifferentiated)magmas.ConsideringthatthePVFissituatedinaglacialregion,aprocessforcinglongmagmaresidencetimecanbeenvisagedassociatedwithincreasediceloadingduringglacialstages.Thisstudyspecificallyconsiderstheicefluctuationsinthelast100ka,theorizingthepossibilityofaclimate-controlledvolcanoplumbingsystem.