北京大学学报（自然科学版）2026，Vol.62Issue(2)：327-345,中插4-中插7,23.DOI:10.13209/j.0479-8023.2025.029
广东吴川-四会断裂带北段燕山期超基性岩的发现及其地质意义
Discovery and Geological Significance of Yanshanian Ultrabasic Rocks in the Northern Segment of Wuchuan-Sihui Fault,Guangdong
摘要
Abstract
This paper reports the first documentation of ultramafic rocks exposed in the northern segment of Wuchuan-Sihui fault in Guangdong.These ultramafic rocks,classified as olivine pyroxenite,occur as a dike within early Late Jurassic(≈160 Ma)granites of the Dadongshan pluton.Zircon U-Pb LA-ICPMS analysis of the olivine pyroxenite yields an age of 160±2 Ma,suggesting that zircons were captured from the surrounding granite during dike intrusion.Additionally,the 40Ar/39Ar plateau age of biotite from the olivine pyroxenite is 135±1 Ma,indicating that the dike emplacement occurred at the Early Cretaceous,corresponding to a significant extensional event in South China.Whole-rock major element geochemical analysis reveals enrichment in K and Al,relatively high Ti and P contents,and moderate Mg.SiO2 content(43.78%-44.80%)of the sample is less than 45%.These features classify the rock as an ultramafic rock,predominantly exhibiting characteristics of alkaline basalt.Whole-rock trace and rare earth element(REE)analyses show enrichment of Nb,Ta,Th,U,LILE(large ion lithophile elements),and LREE(light REE),along with pronounced fractionation between light and heavy REE.The rock displays signatures of high-Nb OIB-type mafic rocks(Ocean Island Basalts),suggesting a metasomatized asthenospheric mantle source modified by subduction components,primarily forming in an intraplate extensional tectonic setting.Combining fault activity,geochronological and geochemical characteristics,we propose that during the Early Cretaceous,the tearing and delamination of the subducted Paleo-Pacific Plate beneath South China created metasomatized asthenospheric mantle sources enriched for OIB-type mafic rocks.Subsequently,intracontinental extension caused crustal thinning,while the lithosphere-penetrating Wuchuan-Sihui Fault facilitated rapid ascent of OIB-type mafic magmas along the frac-ture system.These magmas ultimately crystallized to form the Jiangwan olivine pyroxenite,with intraplate geoche-mical affinities.关键词
吴川-四会断裂/超基性岩脉/锆石U-Pb年龄/黑云母40Ar/39Ar年龄Key words
Wuchuan-Sihui fault/ultrabasic dikes/zircon U-Pb age/biotite 40Ar/39Ar age引用本文复制引用
黄建桦,李宏卫,严成文,张献河,李字青,周献清,吴维盛,张波..广东吴川-四会断裂带北段燕山期超基性岩的发现及其地质意义[J].北京大学学报（自然科学版）,2026,62(2):327-345,中插4-中插7,23.基金项目
广东省地质勘查与城市地质专项(No.2024-02)、广东省2021年度自然资源事务管理-生态林业建设专项(2021GJGY001)和中国地质调查局区域地质矿产调查项目(12120114024301,12120113063100)资助 （No.2024-02）
