中天山北缘华力西期造山作用——变质岩锆石U-Pb年代学限定

Variscan orogeny of Central Tianshan Mountains:Constrains from zircon U-Pb chronology of high-grade metamorphic rocks

笔者对中天山微陆块北缘托克逊干沟地区角闪岩相变质岩中的锆石进行了U-Pb年代学研究,结果证明变质沉积岩中的碎屑锆石记录了从太古宙至元古宙(3320～530 Ma)的源区岩浆热事件,变质火成岩中的岩浆锆石记录了新元古代晚期(550 Ma)的岩浆作用,而变质锆石记录了晚泥盆纪(385～360 Ma)的变质作用。这一定年结果表明,中天山微陆块北缘的造山作用很可能发生在华力西期,中天山微陆块形成于新元古代以前,但并没有经历前寒武纪变质作用,具有与塔里木克拉通明显不同的前寒武纪构造演化历史。因此,中天山微陆块很可能是一个独立的块体,并不支持其是从塔里木板块分离出来的观点。

In this paper,the authors have studied zircon U-Pb chronology of the high-grade metamorphic rocks on the northern margin of the Central Tianshan Microplate.The dating results show that the detrital zircons from the meta-sedimentary rocks have recorded the variable magmatic thermal events from Archean to Neoproterozoic（3320 to 530 Ma）,the magmatic zircons of the meta-igneous rocks were crystallized in late Neoproterozoic of 550 Ma,whereas the metamorphic zircons were formed in Devonian of 385-360 Ma.These data demonstrate that the Central Tianshan block was probably formed in Precambrian,and subsequently subjected to Varsican orogeny.Unlike the Tarim Craton with multi-stage Proterozoic tectono-thermal events,the Central Tianshan Microplate which occurred as a single continent did not experience the Precambrian metamorphism.