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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。
There are more Indosinian magmatic invaded rocks in Bikou massif in Pingwu area of northwestern Sichuan Province, but accurate geochronological data are not available. Using cathodoluminescence technique, the author has made a detailed internal structure analysis of the zircons in the Nanniyuan granodiorite in the southwestern margin of the Bikou massif. On the basis of this, the authors used LA-ICP-MS zircon U-Pb In-situ dating techniques were used to determine the isotope age. The results show that the ratio of Th / U of zircon in granodiorite is high, and the cathodoluminescence image shows that the zircon ring developed in the interior of the zircon with magmatic genetic characteristics. The crystallization age of granite in the Nan Yili is 223.1 ± 2.6 Ma (MSWD = 1.4), indicating that its formation was Early Late Triassic. The intrusive granodiorites of the Nanyi li are later than the main collision period of the Mianlue tectonic belt, and are invaded in the post-collision environment or at least the transitional phase from collisions to post-collisions.