摘要
本文对蚌埠隆起晚侏罗世荆山花岗岩和晚期花岗质脉体进行了主要元素、痕量元素、Sr-Nd-Pb 同位素和锆石 Hf 同位素的研究。结果表明,它们之间具有相似的地球化学特征,SiO_2介于72.82%～75.07%之间,K_2O/Na_2O 比值介于0.75～0.98之间,A/CNK 值介于0.96～1.06之间。主体岩石中轻稀土元素(LREE)相对富集(LREE/HREE 比值介于1.33～11.57之间,(La/Yb)_N 介于0.71～10.17之间),具有明显铕的正异常(Eu/Eu~*介于1.23～2.54之间);微量元素富集 Rb、Ba、U、Sr,亏损 Th、Nd、Sm;具高的 I_(Sr)值(0.7082～0.7090)和低的ε_(Nd)(t)值(-15.30～-16.20);Pb 同位素组成相对均一(^(206)Pb/^(204)Pb介于17.030～17.095之间、^(207)Pb/^(204)Pb 介于15.404～15.443之间、^(208)Pb/^(204)Pb 介于37.399～37.535之间);继承锆石和岩浆锆石显示低的ε_(H)(t)值(-0.71～-7.33、-15.05～-18.39)。以上特征表明,荆山花岗岩为弱过铝质系列,具有"Ⅰ"型花岗岩的成因特征。岩浆源区为扬子克拉通下地壳物质。蚌埠隆起区深部地壳中扬子克拉通基底物质的存在暗示扬子克拉通可能沿着郯庐断裂带于北西方向俯冲于华北克拉通之下。
Major, trace element, Sr-Nd-Pb isotopic data, and Hf isotopic data of zircons for Late Jurassic Jingshan granite and late granitic veins in Bengbu uplift show that they have similar geochemical characteristics, i. e. , SiO2 content ranging from 72.82% to 75.07%, K2O/Na2O ratios being between 0.75 and 0.98, A/CNK values ranging from 0.96 - 1.06. The Jingshan granites are relatively rich in light rare earth elements（LREE）and have obviously positive Eu anomalies, i. e. , LREE/HREE ratios ranging from 1.33 -11.57, （La/Yb）N being between 0.71 and 10.17, Eu/Eu^＊ ranging from 1.23 -2.54. In addition, the Jingshan granites are rich in Rb, Ba, U, and Sr, poor in Th, Nd, and Sm, and have higher （ ^87 Sr/^86 Sr） i ratios （0. 7082 ～ 0.7090） and lower εNd （t） values （- 15.30～-16. 20）, and relatively average Pb isotopic compositions （^206 Pb/^204 Pb values ranging from 17. 030 to 17. 095; ^207Pb/^204Pb values being between 15. 404 and 15. 443, and ^208Pb/^204 Pb values ranging from 37. 399 to 37. 535）. The inherited and magmatie zircons from the Jingshan granites show relatively low εHf（t） values （ - 0.71 ～ - 7.33 and - 15.05～ - 18.39, respectively）. It is suggested that the Jingshan granites belong to weak peraluminous series and ＂I＂ type of granite. The primary magma for the Jingshan granite should be derived from the partial melting of the continental lower crust of the Yangtze Craton, which implies that the Yangtze Craton could subducted beneath the North China Craton along the Tan-Lu fault zone in N-W direction in the early Mesozoic.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2006年第12期2923-2932,共10页
Acta Petrologica Sinica
基金
国家自然科学基金项目(40472033)资助。
