北京大学学报（自然科学版）2026，Vol.62Issue(4)：794-808,15.DOI:10.13209/j.0479-8023.2026.042
博格达地区晚石炭世和早二叠世火成岩成因分析及构造指示意义
Petrogenesis and Tectonic Implications of Late Carboniferous-Early Permian Igneous Rocks in the Bogda Region
摘要
Abstract
This study focuses on the igneous rocks in the Bogda area along the southern margin of the Junggar Basin.Through geochemical analysis and zircon U-Pb dating,we reveal distinct differences in lithology and distribution of Late Carboniferous and Early Permian volcanic rocks between the northern and southern flanks of the Bogda Mountains.The findings suggest that the Late Carboniferous was characterized by post-collisional extension,while the Early Permian experienced intense extensional activity caused by lithospheric delamination.Late Carboniferous-Early Permian mafic rocks in the Bogda region exhibit significant depletion in high-field-strength elements(HFSE)such as Nb and Ta,slight depletion in Ti,and minor enrichment in Zr.The Nb/Ta and Zr/Hf ratios closely resemble primitive mantle values,reflecting typical mantle-derived magmatic characteristics.This suggests that crustal contamination was limited,while lithospheric contamination played a more dominant role.Late Car-boniferous basalts show greater depletion in large-ion lithophile elements(LILE)and higher Mg#compared with Early Permian basalts.The Zr-TiO₂ tectonic discrimination diagrams indicate that Late Carboniferous basalts exhibit MORB-like affinities,whereas Early Permian basalts are more enriched in large-ion lithophile elements and rare earth elements,showing intraplate basalt characteristics,indicating divergent dynamic mechanisms between the two stages.Following the closure of the North Tianshan Ocean in the Late Carboniferous,due to slab breakoff,post-collisional extension prevailed under a weakly extensional tectonic regime.By the Early Permian,the post-collisional extensional regime changed,and delamination of the subducted slab occurred beneath the Bogda area.With the influx of abundant slab-derived fluids,trace elements were progressively enriched in some mafic rocks,and geochemical indices of certain mafic rocks exhibited intraplate basalt characteristics.The two episodes of extension with contrasting dynamic mechanisms during the Late Carboniferous and Early Permian in the Bogda area impose important constraints on the nature of the southern margin of the Junggar Basin.关键词
博格达地区/晚石炭世/基性岩/后碰撞伸展/拆沉作用Key words
Bogda area/Late Carboniferous/mafic rocks/post-collisional extension/delamination引用本文复制引用
祝贺暄,张元元,杨状..博格达地区晚石炭世和早二叠世火成岩成因分析及构造指示意义[J].北京大学学报（自然科学版）,2026,62(4):794-808,15.基金项目
国家自然科学基金(42090021)资助 （42090021）
