【摘要】 川西北平武地区的碧口地块中出露较多的印支期岩浆侵入岩类,但缺乏精确的年代学资料。笔者运用阴极发光技术,对碧口地块西南缘的南一里花岗闪长岩中的锆石进行了细致的内部结构分析,并在此基础上利用LA-ICP-MS锆石U-Pb原位定年技术进行了同位素年龄测定。结果表明,花岗闪长岩中锆石Th/U比值较高,阴极发光图像显示锆石内部发育振荡环带,具岩浆成因特点;南一里花岗闪长岩的结晶年龄为223.1±2.6Ma(MSWD=1.4),表明其形成时代为晚三叠世早期。南一里花岗闪长岩侵入时代晚于勉略构造带的主碰撞期,侵位于后碰撞环境,或者至少是由同碰撞到后碰撞的转折阶段。更多还原

【Abstract】 Plenty of Indosinian intrusive rocks outcrop in the Bikou massif in the Wuping area, northwestern Sichuan, but accurate chronological data are lacking. The authors analyzed the interior structures of zircons from the Nanyili granodiorite at the southwest margin of the Bikou massif by using the CL technique, and on that basis, they performed the in-situ zircon U-Pb dating using the LA-ICP-MS and obtained reliable age data. The results show that: the zircons from the granodiorite have higher Th/U ratios, and the CL images display oscillatory zoning in the interior of the zircons, suggesting the features of magmatic origin. The crystallization age of the Nanyili granodiorite is 223.1±2.6 Ma (MSWD=1.4), indicating that the granodiorite formed in the early Late Triassic. The Nanyili granodiorite was intruded later than the main collision period of the Mianxian-Lueyang tectonic belt and emplaced in a post-collision setting or at least in a transition stage from syncollision to postcollision.更多还原