内蒙古达茂旗北部闪长岩锆石SHRIMP U-Pb、角闪石^(40)Ar/^(39)Ar年代学及其地质意义  

Ar-Ar and zircon SHRIMP geochronology of hornblendite and diorite in northern Darhan Muminggan Joint Banner,Inner Mongolia,and its geological significance

作　　者：李建锋[1] 张志诚[1] 韩宝福[1] 

机构地区：[1]北京大学造山带与地壳演化教育部重点实验室,北京大学地球与空间科学学院,北京100871

出　　处：《岩石矿物学杂志》2010年第6期732-740,共9页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金资助项目(40672146);国家重点基础研究发展计划项目(2007CB411305)

摘　　要：内蒙古达茂旗北部的早古生代闪长岩侵入体产于包尔汉图-白乃庙岛弧带的西部,采用SHRIMP锆石U-Pb定年及角闪石40Ar/39Ar测年对其进行了精确的年代学研究。两件闪长岩样品分别获得的SHRIMP锆石U-Pb年龄为453±3Ma和446.8±5.3Ma,角闪石40Ar/39Ar坪年龄为459.2±2.4Ma和442.9±4.2Ma。这为研究该时期弧岩浆作用提供了新的年代学证据,并表明该岩浆侵位后,经历了结晶并快速冷却的过程,可能揭示了本区岛弧带和华北板块碰撞的构造意义。The northern Darhan Muminggan Joint Banner of Inner Mongolia,geotectonically crossing two geological-structural units,is divided into two parts by Bayan Obo-Chifeng deep fault （plate boundary fault）.To the south of the deep fault is the North China block,and to the north is the accretion zone at the northern edge of North China plate.An important magmatic arc belt mainly composed of diorite,quartz diorite,tonalite and granodiorite is developed near Bart-Obao on the north side of Bayan Obo-Chifeng deep fault.In this paper,precise SHRIMP zircon U-Pb dating and hornblende 40Ar/39Ar dating defining the emplacement age of the intrusion and its thermal evolution history were conducted for inclusions of diorite and hornblendite hosted in granodiorite,and the constraints on Early Paleozoic subduction-collision event of the Paleo-Asian Ocean in central Inner Mongolia were provided from isotope geochronology.SHRIMP U-Pb zircon ages of the two diorite samples are 453±3 Ma and 446.8±5.3 Ma,and hornblende 40Ar/39Ar plateau ages are 459.2±2.4 Ma and 442.9±4.2 Ma.SHRIMP zircon U-Pb dating results indicate that the island arc intrusive rocks were formed around 450 Ma,resulting from the Middle-Late Ordovician （or earlier） oceanic subduction event.The results of SHRIMP zircon U-Pb dating are basically in accordance with those of hornblende conventional 40Ar/39Ar dating method,which suggests the crystallization and rapid cooling after the emplacement of the magma and may reveal collision between the Baoerhantu-Bainaimiao island arc zone and the North China plate.The dating results of the diorite imply that tectonic heat events after the emplacement and the cooling of the intrusive body did not affect the hornblende Ar-Ar closed system,and hence strong tectonic heat events did not occur later.

关 键 词：内蒙古达茂旗 SHRIMP锆石U-PB年代学 40Ar/39Ar年代学 奥陶纪 

分 类 号：P588.122[天文地球—岩石学] P597[天文地球—地质学]