地质与资源2026，Vol.35Issue(2)：159-169,209,12.DOI:10.13686/j.cnki.dzyzy.2026.02.004
西秦岭美武黑云母花岗闪长岩及其暗色包裹体成因
Petrogenesis of Miwu biotite granodiorite and its mafic enclaves in West Qinling:Evidence from zircon U-Pb ages and petrogeochemistry
摘要
Abstract
The Miwu pluton,located in the western segment of the West Qinling orogenic belt,constitutes a key magmatic record of the subduction and closure of the A'nyemaqen-Mianlue oceanic basin during the orogenic process.To constrain its petrogenesis,this paper presents an integrated study of petrography,geochronology,and geochemistry on the biotite granodiorite and its associated mafic enclaves.Zircon U-Pb dating yields ages of 240.1±1.3 Ma for the host granodiorite and 247.0±2.1 Ma for the enclaves,indicating an Early-Middle Triassic origin,with the enclaves being distinctly older than the host rock.The mafic enclaves are fine-grained diorite in composition and are characterized by K2O contents of 1.16％-3.25％,K2O/Na2O ratios of 0.33-1.07,A/CNK values of 0.68-1.00,and Rittmann indices(σ)of 1.49-2.95,classified as metaluminous,calc-alkaline to high-K calc-alkaline series rocks.The host biotite granodiorite exhibits K2O contents of 3.87％-4.11％,K2O/Na2O ratios of 1.26-1.40,A/CNK values of 0.96-0.99,and Ritmann indices(σ)of 1.97-2.04,belonging to the metaluminous to weakly peraluminous,high-K calc-alkaline series and being classified as Ⅰ-type granites.Both the host rock and enclaves are enriched in LILEs(Rb)and incompatible elements(U,Th),and relatively depleted in HFSEs(Nb,Ta,Ti,P).They both show relative enrichment in LREEs,with the host granodiorite displaying a weak negative Eu anomaly.The mafic enclaves are interpreted as wall-rock fragments captured during the emplacement of the host granodioritic magma.It is proposed that these enclaves likely represent mixed magmatic rocks formed through MASH(melting,assimilation,storage and homogenization)processes involving hydrous mafic magmas derived from a subduction-related mantle wedge and lower crustal materials.Subsequently,they were disrupted and transported to shallow crustal levels by the later emplaced granodioritic magma.The Miwu Pluton is inferred to have formed in an active continental margin setting associated with subduction.关键词
西秦岭/美武岩体/暗色包裹体/地质年代学/岩石地球化学Key words
West Qinling/Miwu pluton/mafic enclave/geochronology/petrogeochemistry分类
天文与地球科学引用本文复制引用
赵洋,王晓阳,侯红星,刘宁波,孙康,张中跃..西秦岭美武黑云母花岗闪长岩及其暗色包裹体成因[J].地质与资源,2026,35(2):159-169,209,12.基金项目
中国地质调查局项目"西北沿边及特殊地区地质矿产调查"(DD20160079) （DD20160079）
"华北陆块北缘成矿带金矿资源潜力动态评价"(DD20220976). （DD20220976）
