Quantitative textural analysis reveals magma chamber residence time and magma eruption rate of porphyritic basaltic andesite in the Xiong'er Group
The Xiong'er volcanic rocks,being the first major igneous flare-up following the formation of the North China Craton(NCC),mark the onset of rifting within the craton.As such,understanding their age and tectonic setting is crucial.Although geochronology has provided valuable data,the precise duration of the Xiong'er lavas remains uncertain due to analytical challenges.Additionally,the lavas'geochemical composition is highly debated,obscuring their origin and tectonic setting.A large amount of magma eruption in a short time is one of the characteristics of mantle plume,but it is difficult to prove it only by geochemical methods.Quantitative textural analysis offers a promising approach to decipher magmatic processes.By quantifying crystal distributions and reconstructing crystallization histories,this method can illuminate the condition of magma chambers and estimate the timescale of magmatic events.The Xushan Formation,consisting of porphyritic basaltic andesite,lies at the base of the Xiong'er lava and records early magmatic activity.The phenocrystic plagioclase in that basaltic andesite is suitable for quantitative textural analysis.Our results reveal that the deep magma chamber of the Xushan Formation experienced a low degree of undercooling for a long time,suggesting a long-term thermal stability.Spatial texture parameters further indicate the ongoing replenishment of hot magma within an open system.Characteristics of crystal morphology allow us to estimate the plagioclase growth rate of 10-11～10-10mm/s,which speculating to a residence time of 2400～24,000 years.Based on the thickness of the basaltic andesite layers and the residence time,the eruption rate is estimated to 0.28～13km3/yr.Our findings underscore the rapid and voluminous nature of the early Xiong'er magmatism,implying a genetic link to a mantle plume.The high eruption rate is consistent with models invoking a mantle plume as the driving force behind the NCC's rifting and subsequent volcanism.
万方数据
维普
