大兴安岭北端洛古河东花岗岩的地球化学、SHRIMP 锆石 U-Pb 年龄和岩石成因  

Geochemistry, zircon SHRIMP U-Pb age and petrogenesis of the East Luoguhe granites at the northern end of the Great Hinggan Range.

作　　者：武广[1] 陈衍景[1,2] 赵振华[1] 赵太平[1] 李之彤[3] 张哲[3] 

机构地区：[1]中国科学院广州地球化学研究所成矿动力学重点实验室,广州510640 [2]北京大学造山带与地壳演化实验室,北京100871 [3]中国地质调查局沈阳地质矿产研究所,沈阳110032

出　　处：《岩石学报》2009年第2期233-247,共15页Acta Petrologica Sinica

基　　金：国家973计划(2006CB403508);国家自然科学基金项目(40772055);国家科技支撑计划项目(2007BAB25BO3)的资助

摘　　要：大兴安岭北端漠河县洛古河东岩体主要岩石类型为二长花岗斑岩、正长花岗斑岩和石英二长斑岩,内部可见闪长质微粒包体,属高钾钙碱性Ⅰ型花岗岩。花岗岩的元素地球化学和锆石SHRIMP铀-铅年代学研究结果表明,洛古河东岩体形成于早白垩世,其花岗斑岩体的锆石SHRIMP铀-铅年龄为129.8±2.2Ma。花岗岩的SiO_2含量介于68.03%～74-32%之间,Al_2O_3含量介于13.06%～14.55%之间,Na_2O/K_2O介于0.45～0.86之间,铝饱和指数为0.94～1.11,Mg~#指数介于18～42之间且多小于30。稀土元素总量为160.00×10^(-6)～235.15×10^(-6),δEu介于0.31～0.52,(La/Yb)_N介于8.99～17.87.为轻稀土富集型。岩体Sr含量低,介于118×10^(-6)～268×10^(-6)之间,而Y含量高,介于16.9×10^(-6)～26.1×10^(-6)之间,Sr/Y比值低,介于5.62～13.81之间,属低锶高钇型岩石。在原始地幔标准化的微量元素蛛网图中,Rb、Th、U、K、Zr、Hf和轻稀土元素(如La、Ce、Nd和Sm等)富集,Ba、Sr、P和Ti等元素强烈亏损,Nh和Ta具有中等-弱亏损。主量、稀土和微量元素特征表明,岩石具后碰撞花岗岩类的地球化学特征,属后碰撞花岗岩。岩体ε_(Nd)(t)值介于-3.45～-2.64,平均-3.01;亏损地幔Nd模式年龄介于969～1131Ma之间,平均1018Ma;锶初始比值(I_(Sr))介于0.702486～0.707269之间,平均0.705434;钾长石^(206)pb/^(204)Ph、^(207)Pb/^(204)Ph和^(208)Pb/^(204)Pb比值变化范围分别为18.5939～18.6721、15.6019～15.6058和38.4058～38.5249,平均值分别为18.6426、15.6035和38.4613;岩体中的钾长石氧同位素组成很低,δ^(18)O(‰)值介于-8.1～4.1之间,多为负值,表明洛古河东岩体为低^(18)O花岗岩。Nd、Sr、Pb和O同位素组成显示洛古河东岩体形成于含有较多幔源成分的源区物质的部分熔融作用,推测源区主要为Rodinia超大陆会聚过程中(中元古代一新元古代之交)形成的初生地壳。由于古亚洲洋和蒙古-鄂霍茨克洋分别于古生代末期和二叠The East Luoguhe intrusion in Mohe County, Heilongjiang Province, located in the northern end of the Great Hinggan Range, is mainly composed of monzogranite-porphyry, syenogranite-porphyry and quartz monzonite-porphyry, with minor dioritic microgranular enclave. The intrusion belongs to I-type granite, with affinity to high-K calc-alkaline series. The SHRIMP zircon U-Pb age of the granite-porphyry is 129.8 +/- 2.2 Ma, indicating that the intrusion formed in Early Cretaceous. Its SiO(2) and Al(2)O(3) contents range 68.03% similar to 74.32% and 13.06% similar to 14.55%, respectively. The Na(2)O/K(2)O ratios range 0.45 similar to 0.86, ASI values from 0.94 to 1.11 (mostly <1.1 and the Mg(#) index from 18 to 42 (mostly <30). The REE content is between 160.00 x 10(-6) and 235.15 x 10(-6), with delta Eu of 0.31 similar to 0.52 (average 0.41) and (La/Yb)(N) ratios of 8.99 similar to 17.87 (average 13.82). The East Luoguhe intrusion is characterized by low-Sr (118 x 10(-6) similar to 268 x 10(-6)), high-Y (16.9 x 10(-6) similar to 26.1 x 10(-6), generally >18 x 10(-6)), and low Sr/Y ratios (5.62 similar to 13.81). The intrusion is enriched in Rb, Th, U, K, Zr, Hf and LREE (e. g. La, Ce, Nd and Sm), but strongly depleted in Ba, Sr, P and Ti, with notable depiction of Nb and Ta. The geochemical signatures above are similar to those of post-collisional granitoids, Suggesting that the East Luoguhe intrusion call be classified into the group of post-collisional granites. The intrusion has low initial (87)Sr/(86)Sr ratio (0.702486 similar to 0.707269, average 0.705434), clear negative epsilon(Nd) (t) value (-3.45 similar to -2.64, average -3.01), young Nd-model age (969 similar to 1131 Ma, average 1018 Ma), and extremely low delta(18) O ratio (-8.1 parts per thousand to 4.1 parts per thousand for K-feldspar). And the (206)Pb/(204)Pb (18.5939 similar to 18.6721, average 18.6426), (207)Pb/(204)Pb (15.6019 similar to 15.6058, average 15.6035) and (208)Pb/(204)Pb (38.4058 similar to 38.5249, average 38.4613) ratios for K-feldspar

关 键 词：洛古河东早白垩世花岗岩 锆石SHRIMP铀-铅年龄 元素地球化学 同位素地球化学 大兴安岭 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]