新疆阿尔泰山南缘玛因鄂博高温型强过铝花岗岩:年龄、地球化学特征及其地质意义  

Confirmation of hightemperature strongly peraluminous Mayin'ebo granites in the south margin of Altay,Xinjiang:age,geochemistry and tectonic implications.

作　　者：周刚[1] 张招崇[2] 罗世宾 何斌 王祥 应立娟[1] 赵华 李爱红 贺永康 

机构地区：[1]中国地质科学院研究生部,北京100037 [2]中国地质大学地质与矿产资源重点实验室,北京100083 [3]新疆地矿局第四地质大队,阿勒泰市836500

出　　处：《岩石学报》2007年第8期1909-1920,共12页Acta Petrologica Sinica

基　　金：国家305项目(2001BA609A-07-02);新疆维吾尔自治区1:5万区域地质矿产调查项目(XJQD2003-03).

摘　　要：玛因鄂博岩体分布于新疆阿尔泰山南缘玛因鄂博深大断裂北东侧。主体岩石类型包括片麻状英云闪长岩、黑云母花岗闪长岩、二长花岗岩。岩石中含有较高的黑云母,并可见夕线石、堇青石、电气石等富铝特征矿物。锆石的 SHRIMP U—Pb 定年表明该岩体结晶年龄为283Ma。岩石具有低的 SiO_2、CaO、Ba、Sr、Nb、P_2O_5、Al_2O_3/TiO_2比值及高 MgO、FeO^T、Cr、Ni、TiO_2、REE(∑REE=126.8×10^(-6)～218.11×10^(-6))、A/CNK(>1.1)等特征,富集轻稀土((La/Yb)_N=5～11),具有中等的 Eu负异常(δEu=0.52～0.74)。上述特征表明该岩体与典型的高温型强过铝花岗岩相似。岩石的 Nd 同位素分析表明,其 Nd 初始值变化大(-0.3～-3.5),而其中辉长岩体的 Nd 初始值为5.5。基于上述,我们认为花岗岩原始岩浆来源于底侵的玄武岩浆引起的低成熟度碎屑岩部分熔融,并有部分玄武岩浆的加入。结合区域地质资料,推测它形成于后碰撞阶段,属于后碰撞强过铝花岗岩。在阿勒泰地区早二叠纪强过铝花岗岩的界定为阿尔泰乃至中亚造山带的后碰撞花岗岩提供了一种重要的岩石成因类型。Abstract Mayin＇ebo pluton, outcropping at the northeastern side of Mayin＇ ebo Fault, is comprised of gneissic tonalite, granodiorite, and granite. Some Al-riched diagnostic minerals, such sillimanite, cordierite, tourmaline, have been observed in this pluton, which is coherent with their high A/CNK values （〉1.1）. Zircon SHRIMP U-Pb dating indicate it crystallized at ca. 283Ma. It has low SiO2, CaO, Ba, Sr, Nb, P2O5 and relatively high but variable MgO, FeO^T, Cr, Ni, TiO2, REE（∑REE = 126.8 × 10^-6～218.11 × 10^-6）. It is characterized by enrichment of LREE with （La/Yb）N ranging from 5 to 11 and mediate negative Eu anomalies （δEu=0.52～0.74）. Petrography and chemical composition of the Mayin＇ebo granites share characteristics of the typical peraluminous granites. Due to their low Al2O3/TiO2 ratios, it belong high-temperature sub-type of the peraluminous granites. On the other hand, the granites have negative but large-ranged initial Nd values （-0.3～-3.5）. Considering the gabbro with positive initial Nd values （ ＋ 5 ） mingling in the granites, we suggest that the Mayin＇ebo granite was derived from partial melting of the psammitic rocks with low maturity induced by underplating of the mafic magma from a depleted mantle, and to some extent, the mafic magma has been added into the primary magma of the granite. In combination with previous studies, we concluded that the Mayin＇bo granites was formed in an extensional post-orogenic environment. This study provides an important petrogenetic type of post-collision granites in Altay and even in the Center Asian Orogen Belt.

关 键 词：阿尔泰 二叠纪强过铝花岗岩 年龄 地球化学特征 地质意义 

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