Subduction-Induced Sedimentary Metasomatism of Orogenic Lithospheric Mantle:Insights from Potassium Isotope in Lamprophyres of Sanjiang Region
Post-collisional potassic magmas are commonly regarded as evidence for the recycling of subducted sediments in the lithospheric mantle of orogenic belts,with potassium isotope serving as an excellent tracer for these recycled sediments.This study takes the lamprophyres from the Sanjiang region as an example,conducting potassium isotope analysis based on major and trace elements and Sr-Nd-Pb isotopes,to explore the characteristics of the lithospheric mantle source in the Sanjiang region.This study reveals that the lamprophyres from four distinct regions-Jianchuan,Beiya,Yanyuan,and Yao'an-collectively represent the characteristics of the mantle source.These samples exhibit no association with weathering alteration,fractional crystallization,crustal contamination,and dynamic fractionation processes.Overall,compared to the mantle,the samples display slightly lighter potassium isotopic compositions from(-0.61±0.02)％o to(-0.31±0.01)％o,suggesting a correlation with subducted sediment metasomatism rather than with fluids typically enriched in heavier potassium isotopes.Further simulations utilizing the Monte Carlo model for end-member mixing calculations indicate varying degrees of subducted sediment incorporation in the four regions,with the sediment proportion in the Yao'an area potentially reaching up to 10％.This conclusion further substantiates the efficacy of potassium isotope as a sensitive tracer,capable of effectively tracking the recycled subduction sediment components within the mantle.
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