西秦岭东段秦岭大堡岩体地球化学特征及地质构造意义

Geochemical Character and Tectonic Significance of the Qinling Dabu Granite Body in the Eastern Section of Western Qinling Mountains

通过详细的野外调研,以及岩石学、同位素年龄、地球化学特征研究,将西秦岭东段天水地区原秦岭大堡花岗岩岩基进一步解体为加里东期百花岩体和印支期大堡岩体。百花岩体具I型花岗岩的地球化学特征,形成于岛弧构造环境。大堡岩体岩石化学以高酸度(平均为73.71%)、高碱度(8.50%~9.19%)、低铁镁为特征,次铝-过铝质岩石类型,属钙碱性-偏碱性系列;∑REE=183.27×10^(-6)~267.05×10^(-6),以轻稀土元素富集、明显的Eu负异常(δEu=0.27~0.63)为特征;(^(87)Sr∕^(86)Sr)_0介于0.706 3~0.7077,氧同位素δ^(18) O介于+9.12%^+9.86‰,属壳源花岗岩类,具S型花岗岩的特征,形成于后碰撞构造环境,与大陆抬升作用有关。

After carrying out the detailed study on the petrology, isotope age, geochemistry of the Dabu granite batholithin Southeast Tianshui of Western Qinling Mountains, the original Dabugranite batholith has been further divided into Caledonian Baihua granite body and Indosinia Dabugranite body. The Baihua body has the character of I-type granite, which was formed in island-arc tectonic environment. The Dabu body is characterized by high Al2O3 （with an average of 73.71%）and K2O＋Na2O（8.50%-9.19%）contents,as well as low Fe2O3＋FeO and MgO contents, which belong to peraluminous rocks and calc-alkaline-alkaline series. 2 REE values range from 183. 27× 10^-6 to 267. 05 × 10^-6 , with enriched ∑REE and obvious negative Eu anomaly （δEu=0. 27-0. 53） . The （^87Sr / ^86Sr）0 values vary from 0. 706 3 to 0. 707 7,the δ^18O val- ues range from ＋9. 12% to ＋9. 86‰,showing the features of crust-derived granite and S-type granite, and suggesting that these granites were formed in post-collision tectonic environment and might be the products of continental uplift during the period of post-orogenies.