伊犁地块达根别里新元古代花岗岩的锆石年代学、地球化学及其地质意义  

Geochronology,Geochemistry of Dagenbieli Neoproterozoic Granites in the Yili Block,and Its Geological Implications

作　　者：李婷[1] 李智佩[1] 白建科[1] 李晓英[1] 

机构地区：[1]中国地质调查局西安地质调查中心,陕西西安710054

出　　处：《西北地质》2015年第3期96-111,共16页Northwestern Geology

基　　金：中国地质调查局项目"西北基础地质综合调查与片区总结"(1212011121137);"天山成矿带基础地质综合研究"(1212010010200);国家自然科学青年基金"西天山伊犁地块早石炭典型沉积序列及对天山古代洋陆转换时限的制约"(41202077)

摘　　要：西天山伊犁地块南缘特克斯县东的达根别里花岗岩具有高硅SiO_2=76.22%~76.86%)、富碱(ALK=7.07~7.93)、贫钙镁(CaO=0.95%~1.21%,MgO=0.10%~0.20%)、弱过铝质(ACNK=1.03~1.08)的特征;稀土元素含量中等,具有强烈的Eu负异常;原始地幔标准化蛛网图上显示其具有较高的Rb、Th、Sm、Ga、Nb和较低的Ba、Ti、Sr含量;锆石饱和温度平均为759℃,固结指数为1.07~2.14,分异指数为89.98~92.11,总体显示弱过铝质高钾钙碱性系列的高分异S型花岗岩的特征。LA-ICP-MS锆石U-Pb测年法获得其形成时代为(942.5±2.6)Ma。岩体中Nb/Ta值接近上地壳,Mg~#值为4.52~7.33,锆石Hf同位素研究显示其ε_(Hf)(t)值为较低的正值或负值(-0.41^+4.34),二阶段模式年龄T_(DM2)=1.41~1.66 Ga,表明该花岗岩岩浆可能是中元古代地壳和新生地壳混合源区部分熔融的产物,同时也暗示了伊犁地块具有形成年龄不小于1.7 Ga的中元古代结晶基底。结合天山地区及塔里木周边地块新元古代岩浆热事件,认为伊犁地块发育与天山造山带各地一样的新元古代花岗岩,这为西天山前寒武纪基底曾经响应过全球Rodinia超大陆汇聚事件,提供了进一步证据。Geochemical studies indicat gin of the Yili Block is a high calc-a SiO2 （76.22%-76.86%）, ALK （7.0 （0.10%- 0. 20%）. This intrusion e that lkaline 7-7.9 the Dagenbieli g and weak peral ranitic intrusion in the northern marumlno 3） and low content of us granite with high CaO（0. 95%-1.21%） content of and MgO has moderate REE concentrations and strong negative Eu anomalies（Eu=0.06 - 0.19）. They are enriched in Rb, Th, Sm, Ga, Nb and depleted in Ba, Ti, Sr. Characterized by average zircon saturation temperature of 759 ℃, consolidation index of 1.07 -2.14, differentiation index of 89.98 - 92.11, the Dagenbieli intrusion is the highly frac- tionated S-type granites. U -Pb zircon analysis suggests that the intrusions were formed at 942.5 ±2.6 Ma. The Nb/Ta ratios were close to ratios of the upper crust, Mg# value is 4.52 -7.33, and the Hf （t） values of zircon range from -0.41 to ＋4.34, which indicates that the source rocks were ancient crustal materials with new crustal materials addition. The zircon of intrusion have two-stage Hf model ages of 1.41 - 1.66 Ga, which means that the Yili Block may be underlain by Middle Proterozoic（）l. 7 Ga） crystalline basement. Combined with Neoproterozoic mag- matic events in the Tianshan and Tarim area, we suggest that the formation of the Dagenbieli in- trusion relate to the Rodinia. This study provides further and important geochemical and age data to support the presence of Precambrian basement in Western Tianshan area and records on the convergence of Rodinia supercontinent.

关 键 词：新元古代花岗岩 锆石U—Pb年龄和Hf同位素 地球化学 西天山 伊犁地块 

分 类 号：P597[天文地球—地球化学]