新疆白干湖钨锡矿田东北部花岗岩锆石SIMS U-Pb年龄、地球化学特征及构造意义

SIMS Zircon U-Pb Age,Petrochemistry and Tectonic Implications of Granitoids in Northeastern Baiganhue W-Sn Orefield,Xinjiang

白干湖矿田东北部出露钾长花岗岩和二长花岗岩,具有相近的成岩年龄和相似的地球化学特征,表明为同源演化的复式岩体。利用SIMS方法获得二者锆石U-Pb谐和年龄是422±3Ma和421±3.7Ma,为晚志留世。岩石主量元素地球化学特征二者表现为弱过铝质(A/CNK为0.99～1.02)或准铝质(A/CNK为0.92～0.94)、高钾(K2O/Na2O分别为1.08～1.31和1.03～1.22)、高碱((Na2O+K2O)分别为8.59%～9.38%和9.54%～9.69%)、钙碱性或弱碱性(δ分别为2.39～3.17和4.02～4.22)、Fe#(TFeO/MgO分别为9.58～12.26和8.94～9.96)高。稀土元素总体含量(分别为228×10-6～448×10-6和271×10-6～392×10-6)较高,微量元素亏损Ba、Nb、Sr、Ti、P和富集La、Ce、Zr、Sm,总体显示A型花岗岩的特征。R1-R2图解显示岩体构造背景落入晚造山区域。Sr-Yb图解显示岩体落入低Sr高Yb的区域,暗示拉伸的地壳减薄的环境。Pearce图解显示构造环境为板内为主。综合区域背景资料,认为该岩体形成于加里东造山旋回的后碰撞阶段。

Moyite and adamellite emplaced in northeastern Baiganhue W-Sn orefield have similar rock-forming ages and geochemical characteristics, suggesting a complex rock body of comagmatic evolution. Zircon U-Pb ages obtained by SIMS technique are （422±3） Ma and （421±3.7） Ma respectively, indicating mid-late Silurian. Their petrochemistry is characterized by weakly peraluminous or quasi-aluminous nature （A/NKCI）, high K, （K20/Na20 ratios are 1.08-1.31 and 1.03-1.22）, high alkali（（Na20＋K20）are 8.59%-9.38% and 9.54%~9.69%）, calc-alkaline or weak alkaline （6 values are 2.39-3.17 and 4.02-4.22）, high Fe~ （TFeO/MgO are 9.58-12.26 and 8.94-9.96）, flattened higher total REE （228x106-448x10-6 and 271x10-6-392x10-6 respectively）, depletion of Ba, Nb, Sr, T and P, and enrichment of La, Ce, Zr and Sin, implying that the composite body should be A-type granite. In R1-R2 multi-cation diagram for tectonic environments discrimination, they fall in post-orogenic stage region, and Sr-Yb diagrams give low Sr-high Yb characteristics, indicating a stretching thinning environment of the crust. Pearce discrimination diagrams of tectonic environments show that the granitoids were formed in an intraphate setting. An integrated analysis of the regional background data has led the authors to believe that these two granitoids were formed at the post-orogenic stage of Caledonian orogeny cycle.