Petrological and Dynamical Significance of Plagioclase Zoning in Vegetation Island Felsic Rocks (Terra Nova Intrusive Complex, Antarctica)

Vegetation Unit outcrops (Terra Nova Intrusive Complex, Antarctica) are characterised by magma interaction phenomena due to the injection of mafic magmas into felsic magmas. Compositional zoning of plagioclase phenocrysts occurring in the felsic facies are analysed with the aim of tracking the petrological and dynamical history of this magmatic system. Microanalysis across core-rim transects indicates that crystals display two distinct zoning regions. The first region includes a resorbed core and a subsequent increase in An content and is present in all analysed plagioclase crystals. The second region is strongly different from crystal to crystal and is characterised by normal or oscillatory zoning. The resorption and the increase in An content in the first region is interpreted as due to thermal disequilibrium induced by the intrusion of the high-temperature and high-Ca mafic magma. The second region is explained by the onset of chaotic dynamics in the magmatic system, where, the presence of different dynamical regions generated a variable compositional zoning of the crystals depending on the local mixing dynamics.