内蒙古狼山地区浩日格山二长花岗岩的地球化学特征、LA-ICP-MS锆石U-Pb定年及Hf同位素组成

Geochemical Characteristic,LA-ICP-MS Zircon U-Pb Dating and Hf Isotopic Compositions of the Haorigeshan Monzogranite in the Langshan Region,Inner Mongolia

内蒙古狼山地区浩日格山岩体位于中亚造山带南缘及华北北缘的结合位置,对其进行系统的岩石地球化学探讨有助于加深对中亚造山带晚古生代—早中生代构造-岩浆演化及地球动力学背景的认识。该岩体主体岩性为二长花岗岩,可进一步划分为二云母二长花岗岩及斑状黑云母二长花岗岩,LA-ICP-MS锆石U-Pb测年分别获得二者的206Pb/238 U加权平均年龄为244.9±1.6Ma及230.2±1.5Ma,指示其形成于三叠纪早—中期。地球化学分析结果表明,浩日格山二长花岗岩SiO2含量介于72.58%～74.42%之间,K2O含量为4.06%～5.82%,Na2O含量为3.08%～3.88%,Al2O3含量为13.39%～14.55%,具有高钾钙碱性和过铝质特征。岩石稀土总量较低,轻稀土相对富集,重稀土相对亏损,具有较明显的负铕异常。岩体富集Rb、U、Hf;亏损Ba、Nb、Ta、Ti和Zr,显示出高分异花岗岩的特点。锆石Hf同位素分析结果显示:εHf(t)值总体为负值,并且与华北北缘三叠纪花岗岩εHf(t)值基本一致,表明源区主要为华北古老地壳。对浩日格山二长花岗岩的研究表明狼山地区在三叠纪早—中期为后碰撞构造环境,可能与古亚洲洋的最终闭合关系密切。

The Haorigeshan pluton in Inner Mongolia is located at the junction between the northern margin of the North China and southern margin of the Central Asian Orogenic Belt.A systematic geochemical study can facilitate understanding the tectonic-magmatic evolution and geodynamics background of the belt from Late Paleozoic to Early Mesozoic.The Haorigeshan pluton consists mainly of monzogranite,which can be further divided into muscovite-biotite monzogranite and porphyritic biotite monzogranite.Zircon U-PbMa and 230.2±1.5 Ma for them respectively,indicating that the Haorigeshan monzogranite formed in the Early-Middle Triassic.Geochemical resultsalkaline and peraluminous.Relatively low total REE,enrichment of LREE relative to HREE,negative Eu anomalies,high contents of Rb,U,Hf and low contents of Ba,Nb,Ta,Ti and Zr,all suggest that the Haorigeshan monzogranite is characteristic of high fractionated granite.Zircon Hf isotopic analysismargin of North China Craton,suggesting that the source region of Haorigeshan monzogranite is more close to the North China Craton.This study shows that the Haorigeshan monzogranite formed in the postcollision tectonic setting,which is closely related to the final closure of paleo-Asian ocean.