The trachyte in the Dachangsha basin of the northern Guangdong province was formed in the Early Cretaceous (SHRIMP zircon U-Pb dating shows an age of trachyte as 135.3 ± 1.5 Ma). The Sr-Nd-Pb isotopic composition cnaracteristics of trachyte are as follows: enriched in radiogenic lead,(206Pb/204Pb)I= 18.23-18.39,(207Pb/204b), = 15.78-15.88,(208Pb/204Pb)I=38.83~39.14; moderate initial Nd isotopic ratios, eNll(f)=-3.35-3.21; and higher initial Sr isotopic rations, (87Sr/86Sr)- 0.706871-0.709074. On the Pb-Pb diagrams, the trachyte is plotted above NHRL line and Asr = 99.1-247.0 (140.5 in average), which indicates that the trachyte has obvious Dupal anomaly. The Sr-Nd, Sr-Pb, Nd-Pb and Pb-Pb relationship of the trachyte suggests that the trachyte should be originated from partial melting of the young lower crust, while the lower crust should be influenced by metasomatism of fluids from dehydration of subducted upper crust, and there was no upper crust contamination in the process of magma rising.%广东北部大长沙盆地粗面岩锆石SHRIMP U-Pb年龄为(135.3±1.5) Ma,形成于早白垩世早期,其Sr-Nd-Pb同位素组成为:富放射性成因铅,(206pb/204Pb)i=18.23～18.39,(207pb/204pb )i=15.78～ 15.88,(208Pb/204Pb)i＝38.83～39.14,中等的εNd(t)(=-3.35～-3.21)及较高的(87Sr/86Sr)i(=0.706871～ 0.709074)；在Pb-Pb图解上均位于NHRL上方,△Sr值为99.1～247.0(平均140.5),表明存在典型的Dupal同位素异常.Sr-Nd,Sr-Pb,Nd-Pb和Pb-Pb同位索特征表明,大长沙盆地粗面岩起源于年轻下地壳的部分熔融,但年轻下地壳曾受到深俯冲上地壳析出流体的交代作用,粗面岩岩浆是源区混合的产物,在上升的过程中没有受到上地壳物质的混染.
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