辉绿岩斜锆石侵位年龄对华北龙山组中元古界年代属性的限定OA

One of the significant researchadvances in the Meso-Neoproterozoic strata in the Yanliao area of North China is the discovery of the Yanliao Large Igneous Province(YLIP;～1325 Ma).Previous studies have suggested that the YLIP was emplaced only within the Xiamaling Formation and did not intrude into the overlying stratigraphic horizons.However,the authors have recently discovered diabase sills intruding into the Longshan Formation in the Yanliao area.To clarify whether these diabases are genetically related to the YLIP and to constrain the chronostratigraphic attribution of the Longshan Formation,which has lacked reliable age constraints for over half a century,this study conducted U-Pb geochronological analyses on baddeleyite extracted from the diabases intruding the Longshan Formation using secondary ion mass spectrometry(SIMS)and sensitive high-resolution ion microprobe(SHRIMP)methods.The SIMS method yielded a weighted mean 207Pb/208Pb age of 1322±8 Ma,while the SHRIMP method obtained a weighted mean 207Pb/208Pb age of 1304±8 Ma.The results from both dating methods are highly consistent with the peak magmatic activity of the YLIP reported in previous studies.Based on these geochronological results,combined with a comprehensive investigation of spatiotemporal distribution,intrusive contact relationships,and rare earth element(REE)distribution patterns between the diabases intruding the Longshan Formation and the YLIP,this study concludes that the diabases intruding the Longshan Formation are part of the YLIP.Furthermore,these dating results define the stratigraphic age of the Longshan Formation as the Mesoproterozoic,predating 1322～1304 Ma.This research achieves a breakthrough in the study of the chronostratigraphic attribution of the"Meso-Neoproterozoic"Longshan Formation in North China,a long-standing puzzle that has persisted for more than half a century.It also provides new evidence and age constraints for understanding whether the evolution of eukaryotic microorganisms(including algae)during the Proterozoic follows the"Boring Billion"(1.8～0.8 Ga)evolutionary pattern.while simultaneously expanding the spatio-temporal scope of the YLIP.