西秦岭党川地区花岗岩的成因及其构造意义  

Petrogenesis of Granites from Dangchuan Area in West Qinling Orogenic Belt and Its Tectonic Implication

作　　者：王婧[1] 张宏飞[1] 徐旺春[1] 蔡宏明[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室

出　　处：《地球科学（中国地质大学学报）》2008年第4期474-486,共13页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学基金(Nos.40521001,40773019);教育部长江学者和创新团队发展计划(IRT0441)

摘　　要：对西秦岭造山带党川地区的党川花岗岩和石门花岗岩进行了LA-ICP-MS锆石U-Pb定年、元素地球化学和Sr-Nd-Pb同位素组成的研究.结果表明,党川花岗岩和石门花岗岩的岩浆结晶年龄分别为438±3Ma和220±2Ma.在岩石地球化学特征上,党川花岗岩类似于C-型埃达克质岩石,岩浆产生于增厚地壳物质的部分熔融,而石门花岗岩类似于普通的地壳深熔型花岗岩.党川花岗岩的ISr=0.70660～0.70929,εNd(t)=-2.24～-4.48;石门花岗岩的ISr=0.70581～0.70804,εNd(t)=-3.73～-4.72.Sr-Nd同位素组成进一步指示它们的岩浆派生于地壳物质.然而,在Pb同位素组成上,党川花岗岩和石门花岗岩存在着明显的差异.党川花岗岩以相对富放射成因Pb同位素组成为特征,初始Pb同位素比值为:206Pb/204Pb=18.288～18.484,207Pb/204Pb=15.677～15.693,208Pb/204Pb=38.182～38.283;而石门花岗岩以相对低的放射成因Pb同位素组成为特征,初始Pb同位素比值为:206Pb/204Pb=17.989～18.189,207Pb/204Pb=15.560～15.567,208Pb/204Pb=37.982～38.000.这表明党川花岗岩和石门花岗岩的岩浆来自于不同地壳物质的部分熔融.区域分析表明,西秦岭党川地区中古生代和早中生代的岩浆事件、岩石成因机制及岩浆源区均可与东秦岭地区北秦岭构造单元相对比,由此说明西秦岭党川地区是东秦岭地区北秦岭构造单元的西延,并且东秦岭地区早中生代南秦岭块体向北秦岭块体的大陆俯冲作用向西一直延至到西秦岭地区.This paper carries out a study of U-Pb zircon dating using LA-ICP-MS method, geochemical and Sr-Nd-Pb isotopic compositions of the Dangchuan and Shimen granites in Dangchuan area of the West Qinling orogenic belt. The results show that the Dangchuan and Shimen granites have magma crystallization ages of 438± 3 Ma and 220±2 Ma, respectively. Geochemical signatures indicate that the Dangchuan granite is similar to C-type adakitic rock that resulted from partial melting of thickened crustal material and the Shimen granite is similar to common anatexis-type granite. The Dangchuan granite has initial Sr isotopic ratios （ISr） of 0. 706 60-0. 709 29 and εNd（t） values of -2. 24 to -4. 48, and the Shimen granite has ISr of 0. 705 81-0. 708 04 and εNd（t） values of -3.73 to -4. 72. The Sr-Nd isotopic composition of the Dangchuan and Shimen granites provides an additional eveidence that both the granites were derived from crustal source However, Pb isotopic composition of the Dangchuan granite is distinct from that of the Shimen granite. The Dangchuan granite is characterized by more radiogenic Pb isotopic composition with initial Pb isotopic ratios of ^206 Pb/^204 Pb = 18. 288- 18. 484, ^207 Pb/^204 Pb = 15. 677-15. 693 and ^208 Pb/^204 Pb= 38. 182--38. 283, whereas the Shimen granite is characterized by relatively less radiogenic Pb isotopic composition with initial Pb isotopic ratios of ^206 pb/^204 Pb= 17. 989-- 18. 189, ^207 Pb/^204 Pb= 15. 560-- 15. 567 and ^208 Pb/^204 Pb= 37. 982--38. 000. It is strongly suggested that the magmas of the Dangchnan and Shimen granites were derived from different crustal sources. The Early Paleozoic and Early Mesozoic tectono-magma events, their petrogenesis and magma sources of Dangchuan area in the West Qinling orogenic belt can be comparable with those of the North Qinling tectonic unit in the East Qinling orogenic belt, indicating that the North Qinling tectonic unit can be extended to Dangchuan area in the West Qinling orogenic belt. In the East Qinling orogenic bel

关 键 词：西秦岭造山带 花岗岩 U-Pb锆石定年 SR-ND-PB同位素 岩石成因. 

分 类 号：P588.12[天文地球—岩石学]