Magmatic response to the rifting process of the Caroline Plateau in the West Pacific
The formation,evolution and subsequent rifting of the oceanic plateaus are products of oceanic intra-plate processes,and studies on these plateaus can provide important clues to oceanic intra-plate geodynamics.The Sorol Trough is a product of the initial rifting of the Caroline Oceanic Plateau,but the kinetic mechanism of its rifting process is still controversial.This study performed in-situ major and trace element geochemical analysis of single minerals(plagioclase)hosted in volcanic rocks(basalt,dacite)collected from the basement of the Sorol Trough.The results showed that the plagioclases in the basalts are mainly anorthite and bytownite,with a small amount of labradorite.Plagioclase phenocrysts in basalts are enriched in light rare earth elements(LREEs)and large ionic lithophile elements(LILEs),and depleted in high field strength elements,showing positive Eu anomalies.In contrast,the plagioclases in the dacites are andesine,and the plagioclase phenocrysts in the dacites are more enriched in LREEs and LILEs with stronger positive Eu anomalies compared to those in the basalts.Calculated crystallization temperatures and pressures of the plagioclase are 1110～1171℃(basalts)and 961～966℃(dacites),0.27～0.42GPa(basalts)and 0.16～0.29GPa(dacites),respectively,and there is no significant difference between plagioclase phenocrysts and microlites crystallization temperatures for the same type rocks.In combination with regional geological and geophysical characteristics of the study area and some genetic models for bimodal volcanism in previous studies,we proposed a two-layer magma chamber model to explain the rifting process of Caroline Oceanic Plateau.Firstly,primitive magmas formed through decompressional melting were aggregated in deep magma chambers and crystallized to form basic plagioclase phenocrysts.Then the crystals and most evolving magmas were together ascended and erupted on the surface.Meanwhile,the evolving magmas were partly migrated into the shallow crustal magma chamber and crystallized to form intermediate-acidic plagioclase phenocrysts,both of which were ascended together to the surface from the shallow magma chamber and then erupted to form dacite.
Oceanic plateauInitial riftPlagioclaseMineral chemistryMagmatic process
万方数据
维普
