岩石矿物学杂志2025，Vol.44Issue(3)：501-521,21.DOI:10.20086/j.cnki.yskw.2025.4108
四川盐源小高山晚二叠世玄武岩矿物学、年代学、地球化学特征及源区和成因意义
Mineralogical,geochronological,geochemical characteristics and petrogenesis significances of the Late Permian basalts in Xiaogaoshan,Yanyuan,Sichuan
摘要
Abstract
The source characteristics and origin of high-Ti(HT)and low-Ti(LT)magma types are the first-order geodynamic question for the Large Igneous Provinces(LIPs)and mantle plume,especially the Emeishan LIP(ELIP).In this study,we report LA-ICP-MS zircon U-Pb ages,as well as mineralogical,geochemical,and Sr-Nd isotopic data on the Late Permian basalts in the Xiaogaoshan,Yanyuan,Sichuan.The Xiaogaoshan basalts can be classified as LT/HT transitional type and sodic tholeiitic rock series.Clinopyroxene crystallization temperature and pressure are 1 061 to 1 180℃ and 190 to 352 MPa.The XMt of Fe-Ti oxides(0.24 to 0.38)indicates a relatively low oxygen fugacity environment and the Fenner trend of fractional crystallization(evolving to iron-enriched).The zircon U-Pb data yield age is 260.2±5.0 Ma,i.e.,the peak magmatism of the ELIP.The chondrite-normal-ized rare earth elements(REE)patterns and the primitive mantle-normalized spidergrams show oceanic island ba-salt(OIB)affinity,with a trend to E-MORB(enriched Mid-Ocean Ridge Basalts).The rocks have low age-correc-ted(87Sr/86Sr)i ratios(0.704 650 to 0.705 035)and positive εNd(t)values(+2.91 to+3.02).The geochemical and isotopic features suggest that the lavas have not undergone any significant crustal contamination,and the source is dominated by"plume"components.The Late Permian Xiaogaoshan basalts have a co-genetic relationship with the picritic porphyries in the Pingchuan iron oxide deposit via fractional crystallization.REEBOX PRO modeling of the adiabatic decompression melting for the Emeishan basalts indicate that the mantle sources of the Emeishan ba-salts are characterized by the primitive mantle(PM).Only HT basalts can be generated at elevated mantle potential temperatures(tp=1 550 ℃ to 1 690 ℃)beneath a lithosphere that is 140 km thick.In contrast,expanded melting temperatures(tp=1 400℃ to 1 690℃)and regime spread over LT and HT basalts beneath a considerably thinned lithosphere(50 km).Therefore,the origin of the Emeishan basalts,both LT and HT,is through a continuous melting process of the same source.The modelling suggests that the Xiaogaoshan basalts most likely formed under a thinner lithosphere(50 km),with melting temperature and pressure conditions of 1 403℃/2.38×103 MPa to 1 557℃/3.55×103 MPa.关键词
地球化学/Sr-Nd同位素/REEBOX PRO模拟/峨眉山大火成岩省/地幔柱/四川盐源小高山Key words
geochemistry/Sr-Nd isotope/REEBOX PRO modeling/Emeishan Large Igneous Province/mantle plume/Xiaogaoshan,Yanyuan,Sichuan分类
天文与地球科学引用本文复制引用
李宏博,章西焕,杨小男,彭艳菊,李常权..四川盐源小高山晚二叠世玄武岩矿物学、年代学、地球化学特征及源区和成因意义[J].岩石矿物学杂志,2025,44(3):501-521,21.基金项目
自然资源部部门预算项目(12111300000018001-02) （12111300000018001-02）
国家自然科学基金项目(41772057) Department Budget Project,Ministry of Natural Resources of PRC(12111300000018001-02) （41772057）
National Nature Science Foundation of China(41772057) （41772057）
