内蒙古迪彦庙孬来可图侵入岩的年代学、Sr-Nd-Hf同位素特征及其地质意义

Chronology, Sr-Nd-Hf Isotope Geochemistry and Geology Significance of Pluton in the Naolaiketu of Diyanmiao, Inner Mongolia

以内蒙古迪彦庙蛇绿混杂岩带中的孬来可图侵入岩体为研究对象,通过详细的岩石学、年代学以及Sr-Nd-Hf同位素特征分析,探讨岩石成因及构造环境.岩体的锆石U-Pb年龄为322.2±1.3 Ma,表明该岩体属晚石炭世早期岩浆活动的产物.岩石化学成分中SiO2含量较高(62.29%~77.17%);Al2O3含量较低(11.45%~14.11%),属准铝质岩浆系列;富钠贫钾(Na2O=2.91%~3.84%,K2O=0.54%~1.79%),同时富集大离子亲石元素而亏损高场强元素,具有TTG的地球化学特征.岩石稀土元素含量较低,轻、重稀土分异不明显,具中等强度的负Eu异常(δEu=0.64~0.76).岩石的εHf(t)值均为正,介于+8.1^+13.3之间,模式年龄相对年轻,同时(87Sr/86Sr)i较低(0.703457~0.703789),εNd(t)均为正值(+8.4^+9.3),具有MORB源区的特征,推测岩浆起源于古亚洲洋俯冲洋壳.结合西乌旗岩浆弧中不同源区的TTG岩类分析,石炭纪,古亚洲洋在西乌旗地区尚未关闭,而是处于热壳-热幔的壳幔构造背景中,洋壳俯冲消减,岩浆侵位,陆壳增生.

In this study,we carried out zircon LA-ICP-MS U-Pb geochronology,Sr-Nd-Hf isotope geochemistry on the Naolaiketu tonalite to discuss its origin and tectonic setting.The zircon U-Pb age of the rock is 322.2±1.3 Ma,which indicates that the pluton is a product of the Early Carboniferous magmatic event.Geochemically,the tonalite samples are characterized by moderate-high concentrations of SiO2(62.29%-77.17%),low Al2 O3(11.45%-14.11%)and rich in Na2 O and poor in K2 O,and are enriched in LILE and depleted in HFSE,which show the geochemical characteristics of TTG.The fractionation of LREE and HREE are not obvious,and there arenegative Eu anomaly(δEu=0.64-0.76).The(87 Sr/86 Sr)iof the rocks are low(0.703457-0.703789),εNd(t)are all positive(+8.4 to+9.3).The in-situ zircon Hf isotopic analysis show depleted compositions,andεHf(t)range from+8.1 to+13.3,imply that the magma originated from the subducted oceanic crust.Combined with the analysis of regional geological background,the TTG magma event in Naolaiketu indicates that,the palo-Asian Ocean was not closed in the Carboniferous in the Diyanmiao area of West Ujimqin,and the subduction zone was a thermal structure of warm crust-mantle.