大别山早白垩世基性脉岩SHRIMP锆石U-Pb定年、地球化学特征及成因

研究大别山早白垩世大规模伸展开始时间及地幔属性.采用SHRIMP锆石U-Pb定年法, 测得北淮阳金寨银沙畈辉长脉岩年龄为125.8±2.7 Ma, 西大别大悟东新乡闪斜煌斑脉岩年龄为129.6±2.5 Ma; 大别山不同区块早白垩世基性脉岩的地球化学特征类似: SiO₂介于46.13%~54.42%, Mg#在42~72之间, 大多属碱性系列; LREE富集, HREE亏损, 大离子亲石元素(LILE)富集, 高场强元素(HFSE)Nb、Zr、Ti亏损; I_Sr在0.705 5~0.709 4之间, 低ε_Nd(t)(-12.04~-18.84)值, Nd模式年龄(T_DM)为1.60~2.62 Ga.大别山早白垩世的地壳伸展、大规模岩浆活动开始于130 Ma, 属于整个中国东部晚中生代岩石圈伸展减薄事件的一部分.基性脉岩来源于富集岩石圈地幔, 主要为扬子俯冲陆壳同华北岩石圈地幔混合产物, 有部分软流圈地幔物质的加入. 

SHRIMP Zircon U-Pb Dating,Geochemistry and Genesis of Early Cretaceous Basic Dykes from the Dabie Orogen

This paper aims to constrain the starting time of Early Cretaceous large-scale extensional and mantle properties in Dabie orogen. The SHRIMP zircon U-Pb dating results reveal the Yinshafan gabbro dyke from Jinzhai, North Huaiyang region is 125.8±2.7 Ma, the Dongxinxiang lamprophyre dyke from Dawu, West Dabie is 129.6±2.5 Ma. The Early Cretaceous basic dykes from different regions of the Dabie Orogen show similar geochemical features: These samples have SiO₂ ranging from 46.13% to 54.42%, Mg# between 42 and 72, mainly belonging to alkaline series, enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), evident depletion in high field strength elements (HFSE, e.g., Nb, Zr and Ti), I_Sr=0.705 5-0.709 4 and highly negative ε_Nd (t) values of about -12.04 to -18.84, T_DM=1.60-2.62 Ga. Early Cretaceous crustal extension and large-scale magma eruption in the Dabie orogenic belt began in 130 Ma, and belonged to part of eastern China Late Mesozoic lithospheric thinning extension event. The basic dykes were derived from enriched lithospheric mantle, which originated from North China Craton (NCC) lithospheric mantle contaminated by the deeply subducted Yangtze crust, and maybe have been added in some mantle asthenosphere.