江南造山带东段东源含钨岩体的岩石化学、矿物学特征研究

Petrochemistry and mineralogy of Dongyuan tungsten-bearing pluton in eastern Jiangnan Orogen

东源岩体主要由花岗闪长岩、二长花岗岩、正长花岗岩构成.长石绢云母化、碳酸盐化作用较强, 黑云母发生白云母化和轻微绿泥石化蚀变.锆石LA-ICP-MS U-Pb 定年获得岩体的成岩年龄为晚侏罗世-早白垩世（（146.7±4.1） Ma）; 含有大量新元古代的继承锆石, 加权平均年龄为（770.2±9.7） Ma.岩体中黑云母为镁质黑云母, 显示寄主岩为壳幔混合来源.岩石地球化学特征总体表现为高钾钙碱性系列-橄榄粗玄岩系列, 准铝质-过铝质, 相对高的Sr、Ba 含量, 低Y 和Yb, 弱的Eu 异常（δEu = 0.74~0.83）, 富集轻稀土和大离子亲石元素, 亏损高场强元素.初始87Sr/^86Sr 比值为0.7124, εNd（t）值为–5.53.东源岩体的地球化学特征表现出埃达克质岩的亲缘性, 类似于加厚下地壳部分熔融产生的熔体.锆石εHf（t）值为–13.0- –7.0, 变化较大.结合区域地质和构造演化, 认为在晚侏罗世-早白垩世（约146.7 Ma）, 古太平洋板块向欧亚大陆的俯冲使先前交代的岩石圈地幔发生部分熔融, 幔源岩浆底侵到壳幔过渡带附近, 导致下地壳部分熔融, 可能与少量的幔源岩浆发生岩浆混合作用, 形成了东源岩体.

Dongyuan pluton, geographically located in south Anhui Province, is a part of eastern Jiangnan orogen. It is composed of granodiorite, monzogranite, syenogranite, showing obvious formation of sericite and carbonate in feldspar, and formation of muscovite and chlorite in biotite. Zircon LA-ICP-MS U-Pb dating results show that the pluton was emplaced at 146.7 Ma. In addition, abundant inherited zircons are identified in the granite, showing the average age of the Neoproterozoic zircon is (770.2±9.7) Ma. Biotite in Dongyuan pluton can be classified as high-Mg type, and is plotted in the crust-mantle zone on the material source discrimination diagram. The Dongyuan pluton belongs to the high potassium calc alkaline and shoshonitic series, being metaluminous-peraluminous, showing relatively high Sr and Ba, low Y and Yb, and weak negative Eu anomalies (δEu =0.74~0.83). It is enriched in light rare earth elements (LREE) and light ion lithophile elements (LILE) but is depleted in high field strength elements (HFSE), exhibiting strongly fractionated REE pattern. The pluton exhibits high initial 87Sr/86Sr ratios (0.7124), low εNd(t) (–5.53), and variable zircon εHf(t) (–13.0~ –7.0) values. The elemental and isotopic data suggests that the Dongyuan granite shows some affinities with adakite, so can be postulated to be most likely derived from partial melting of thickened lower crust with little contribution from mantle components.