南太行山平顺闪长岩体SHRIMP锆石U-Pb年龄、地球化学特征及地质意义

SHRIMP U-Pb Dating,Geochemistry and Tectonic Implications of Pingshun Diorites in Taihang Mountains

南太行山平顺闪长岩锆石SHRIMP测年表明闪长岩体形成于(125.5±2.3)Ma,与太行山其他地区乃至整个华北地区侵入杂岩体具有相近的形成年代,表明在晚中生代(115～135Ma)太行山地区与华北地区经历了相同的构造岩浆事件。平顺闪长岩w(SiO2)=48.57%～63.54%,w(Al2O3)=13.53%～19.15%,w(MgO)=1.20%～9.31%,w(TiO2)=0.34%～1.07%,w(CaO)=3.13%～10.39%,w(K2O+Na2O)=4.78%～7.99%,Mg#=0.37～0.72,LREE富集HREE亏损,略显微弱的正Eu异常,以富集LILE、LREE元素和亏损Nb-Ta等高场强元素为特征。闪长岩(206Pb/204Pb)i=17.775～18.857,(207Pb/204Pb)i=15.522～15.602,(208Pb/204Pb)i=38.044～38.502,εNd(125Ma)=-17.009 56～-9.606 32,ISr=0.705 85～0.707 53,表明起源于EMI富集地幔,并受到地壳物质和EMII型富集地幔混染,可能说明在晚白垩世太行山地区与整个华北克拉通都发生了岩石圈减薄事件。

As the SHRIMP zircon U-Pb dating results show,diagenetic ages of Pingshun diorites in Taihang mountains are（125.5±2.3）Ma,similar to the ages for magmatic activities in other regions of Taihang mountains and whole North China,which indicates that they were the products of the same tectonomagmatic event in Late Mesozoic during 135 Ma to 115 Ma.The major oxides of the Pingshun diorites are SiO2=48.57%-63.54%,Al2O3=13.53%-19.15%,MgO=1.20%-9.31%,TiO2=0.34%-1.07%,CaO=3.13%-10.39%,K2O＋Na2O=4.78%-7.99% and Mg#=0.37-0.72.LREE are enriched and HREE are depleted,coupled with no or a weak positive Eu anomaly.Moreover,diorites are characterized by high abundances of LILE and LREE,and low abundances of HFSE（such as Nb,Ta etc.）.The（206Pb/204Pb）i ratios of diorites range from 17.775 to 18.857,（207Pb/204Pb）i ratios from 15.522 to 15.602,and（208Pb/204Pb）i ratios from 38.044 to 38.502,εNd（125 Ma）=-17.009 56—-9.606 32,ISr=0.705 85~0.707 53.It implies that magma originated from the EMI and was contaminated by crustal composition and the EMII.Its possible manifesting lithospheric thinning event happened in both Taihang mountains area and the whole North China craton during the Late Cretaceous.