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前寒武纪古老基底的分布及其构造归属是理解和认识中亚造山带基本构造格架和地壳生长的关键问题.本文报道了中亚南缘北山造山带南部黑云斜长片麻岩和花岗闪长岩的LA-ICPMS锆石U-Pb定年和LA-MC-ICP-MS锆石Hf同位素分析结果.所研究的片麻岩中岩浆结晶锆石给出了1408±4 Ma的原岩形成年龄,揭示了北山造山带南部存在中元古代的古老基底岩石.这些岩浆结晶锆石具有正且高的Hf(t)值(4.1~9.9),其Hf模式年龄(1.50~1.72 Ga)与其结晶年龄接近,反映了片麻岩原岩岩浆可能来自亏损地幔或新生地壳,即北山造山带南部存在中元古代(~1.4Ga)的地壳新生事件.同时,在侵入片麻岩的花岗闪长岩中获得了257±3 Ma的岩浆结晶年龄,并获得了大量~1.4 Ga的继承岩浆锆石.这些继承锆石具有与片麻岩的岩浆锆石一致的结晶年龄和Hf同位素组成,进一步表明北山造山带南部存在中元古代老地壳.通过与敦煌地块和中天山地块前寒武纪基底已有资料的对比,我们认为北山南部古老微陆块可能与相邻的中天山地块具有相同的前寒武纪地壳形成与演化历史,它们并不是来源于塔里木克拉通.这一成果为认识中亚造山带南部的构造演化提供了新的重要信息.
The distribution and tectonic attribution of the ancient Precambrian basement are the key issues for understanding and understanding the basic tectonic framework and crustal growth in the Central Asian orogenic belt.This paper reports the biotite plagioclase gneiss in the southern Beishan orogenic belt in the southern margin of Central Asia LA-ICPMS zircon U-Pb dating and LA-MC-ICP-MS zircon Hf isotopic analysis of granodiorite.The magmatic crystalline zircons in the studied gneisses give an initial value of 1408 ± 4 Ma The age of rock formation reveals the existence of Mesoproterozoic ancient basement rocks in the northern part of the Beishan orogenic belt.These magmatic zircons have positive and high Hf (t) values (4.1-9.9), and their Hf-age (1.50-1.72 Ga ) Is close to its crystallization age, which indicates that the magmatic rocks of the gneiss may come from the depleted mantle or the nascent crust, that is, the Neoproterozoic (~ 1.4Ga) crustal reef in southern Beishan orogenic belt.At the same time, A magmatic age of 257 ± 3 Ma was obtained in the diorite and a large amount of inherited magmatic zircons ~ 1.4 Ga were obtained.These inherited zircons have the same crystal age and Hf isotopic compositions as the magmatic zircons from gneiss, It further shows that there exists the Mesoproterozoic old crust in the southern Beishan orogenic belt In contrast with the Precambrian basement data of Dunhuang and Zhongtian Mountain blocks, we think that the ancient micro-continental blocks in southern Beishan may have the same Precambrian crustal formation and evolution history as the adjacent Zhongtian Mountain block, They are not derived from the Tarim Cratons, and this result provides new and important information for understanding the tectonic evolution in the southern part of the Central Asian orogenic belt.