吉东大栗子铁矿区石英二长斑岩U?Pb年龄、地球化学及Hf同位素组成

Zircon U-Pb Geochronology,Geochemistry and Hf Isotopic Composition of the Quartz Monzonite Porphyry Intrusion from East Jilin Province

吉林东部地区侏罗纪花岗岩的分布较为有限,缺乏区域构造演化环境的判别证据.对侵入到老岭群当中的隐伏岩体石英二长斑岩进行了U-Pb年代学、地球化学和Hf同位素研究.获得石英二长斑岩样品锆石LA-ICP-MS U-Pb定年结果165±1Ma,属中侏罗世;岩石SiO2=61.01%~61.99%,全碱含量(K2O+Na2O)为5.78%~7.98%,属钙碱性系列岩石,贫MgO、CaO、Fe2O3T,A/CNK=1.02~1.39,轻稀土元素富集明显,Eu/Eu*=0.92~1.01,异常不明显,显示Ⅰ型花岗岩特征;岩石εHf(t)值为-15.46^-17.04,二阶段模式年龄TDM2=2189~2290 Ma,富集大离子亲石元素,亏损高场强元素,Mg#=26.90~33.04,贫Yb(0.43×10^-6~0.48×10^-6)和Y(6.63×10^-6~7.12×10^-6),锆石Ti温度均值为744℃,属低温花岗岩.岩浆源区为古元古代下地壳的部分熔融.华北克拉通北缘东段中侏罗世火成岩形成于俯冲背景之下,而非蒙古-鄂霍茨克洋闭合的远程效应,至晚侏罗世-早白垩世早期,中国东北陆缘可能进入走滑的构造属性.

The distribution of Jurassic granite in the eastern Jilin province is relatively limited,with little discriminant evidence for regional tectonic evolution.This paper presents a synthesis study of zircon U-Pb chronology and geochemistry and Hf isotopes of the quartz monzonite porphyry in this area.The rocks yield an average zircon LA-ICP-MS U-Pb age of 165±1 Ma,indicating the Middle Jurassic.They show high SiO2(61.01%-61.99%),ALK(5.78%-7.98%),belonging to calc-alkaline granites.In addition,they also display the characteristics ofⅠ-type granite with obvious enrichment in LREE,unconspicuous europium anomalies(0.92-1.01),low MgO,CaO,Fe2O3T as well as A/CNK(1.02-1.39).The Eu/Eu*values vary from-15.46 to-17.04,and TDM2=2189-2289 Ma.These samples are enriched in LILE and depleted in HFSE,with Mg#=26.90-33.04,low Yb(0.43×10^-6~0.48×10^-6)and Y(6.63×10^-6~7.12×10^-6).Zircon Ti temperature averages 744℃,belonging to low temperature granite.The magma was originated from the partial melting of Paleo-Proterozoic lower crust.The middle Jurassic igneous rocks in the eastpartofnorthern margin of the North China Craton were formed in the subduction rather than the remote effect of MongolsOkhotsk Ocean closure.From late Jurassic to early Cretaceous,the continental margin of northeast China maydisplay the structural features of strike-slip.