皖南竹溪岭花岗闪长岩的岩浆源区:来自矿物学、地球化学证据

Tracer Origin of Zhuxiling Granodiorite in the Southern Anhui, China: Evidence from Mineralogical and Geochemical Characteristics

皖南竹溪岭钨多金属矿床位于江南古陆东缘,与成矿密切相关的岩石主要为花岗闪长岩。针对花岗闪长岩开展岩相学、矿物学和岩石地球化学研究。结果表明:花岗闪长岩SiO_2含量(质量分数,下同)为64.67%～67.33%,Al_2O_3为15.26%～16.26%,MgO为1.09%～1.37%、K_2O/Na_2O值高于1.1,A/CNK值为1.00～1.04,为高钾钙碱性、弱过铝质花岗岩;花岗闪长岩富集Rb、K等元素,亏损Nb、Ta、Zr和Ti等元素,稀土元素总含量为(90.40～166.94)×10^(-6),LREE/HREE值为7.15～15.16,(La/Yb)_N值为11.60～37.32,表现为轻稀土元素富集的右倾配分模式;根据全岩锆石饱和温度计和黑云母的化学成分,测算花岗闪长岩成岩温度为720℃～780℃,成岩压力为73～169 MPa,侵位深度为2.75～6.39 km,成岩时氧逸度为-17.52～-10.09。综上所述,竹溪岭花岗闪长岩属于Ⅰ型花岗岩,形成于中—高温、富水、较高氧逸度的环境下,其形成可能与古太平洋俯冲板片撕裂而形成的近EW向板片窗有关。

The Zhuxiling W-polymetallic deposit in the southern Anhui is located at the eastern margin of Jiangnan paleocontinent, the rock closely associated with the mineralization is the granodiorite. The petrographic, mineralogical and petrogeochemical studies on the granodiorite were carried out. The results show that the granodiorite has moderate contents of SiO2(64.67%-67.33%), Al2O3(15.26%-16.26%) and MgO(1.09%-1.37%), the ratio of K2O/Na2O is higher than 1.1 with the A/CNK ratio of 1.00-1.04, indicating that the granodiorite belongs to high-K cal-alkaline series and weakly peraluminous series;the granodiorite shows enrichment of Rb, K, and depletion of Nb, Ta, Zr and Ti, the total contents of REE are(90.40-166.94)×10-6 with the ratios of LREE/HREE(7.15-15.16) and(La/Yb)N(11.60-37.32), the chondrite-normalized REE pattern displays a characteristic listric-shaped REE profile;the whole-rock zircon saturation thermometer and the chemical composition of biotites in the granodiorite indicate that the diagenetic temperatures range from 720 ℃ to 780 ℃, and the diagenetic pressures range from 73 to 169 MPa with corresponding emplacement depth varying from 2.75 to 6.39 km, and the calculated oxygen fugacity varies from-17.52 to-10.09. Collectively, the granodiorite belongs to I-type granitic rock, which is formed in the moderate-high temperature, water-rich and oxidized environment, and it is likely related to the previously proposed EW-trending slab-window that caused by the rupture of the subduction of paleo-Pacific plate.