扬子陆核与陆缘新元古代岩浆事件对比及其构造意义——来自黄陵和汉南侵入杂岩ELA-ICPMS锆石U-Pb同位素年代学的约束

Neoproterozoic magmatic events within the Yangtze continental interior and along its northern margin and their tectonic implication:constraint from the ELA-ICPMS U-Pb geochronology of zircons from the Huangling and Hannan complexes.

本文报道分别位于扬子克拉通核部和北缘的黄陵及汉南新元古代侵入杂岩体的惰性气体激光剥蚀-等离子体质谱(ELA-ICPMS)锆石U-Pb年代学研究及其构造意义分析。定年数据显示,黄陵地区的三斗坪、大老岭岩套分别形成于794±7和795±8Ma；晓峰浅成岩岩套形成于744±22Ma,不仅与震旦系莲沱组底部火山岩年龄相同,且同期热事件普遍记录于杂岩体内其它岩套。汉南杂岩体中五堵门岩体形成于789±10Ma,在分析误差范围内与三斗坪、大老岭岩套相同；天平河岩形成于863±10Ma,这是在扬子北缘首次识别出这期岩浆作用。在扬子陆核和北缘侵入杂岩中还分别发现了≈860Ma和945～931Ma的捕获锆石。此外,≈740Ma的后期热事件同样记录于汉南杂岩体,表明扬子陆块内部和北缘共同经历了≈790Ma的峰期中酸性岩浆作用和≈740Ma的后期强烈热改造事件,即事件具有克拉通范围的性质。与天平河岩体岩性相似、年龄相同的侵入岩体已在攀西多处地区发现,说明空间上≈860Ma岩浆作用在扬子北缘和西缘可能具延续性。作者认为,“晋宁期”具造山性质的构造运动开始的时间应以≈830Ma为限,于≈790Ma达到了以壳内物质重熔为主的大规模岩浆侵入事件的峰期,并在≈740Ma以短期内地壳运动由剧烈抬升向快速沉降的构造转换为造山作用结束的标志。本次研究成果为探讨扬子克拉通新元古代大规模岩浆作用与同期全球构造事件的相互关系提供了重要的同位素年代学约束。

U-Pb geochronology of zircons from the Yangtze continental interior, the Huangling complex and its northern margin, the Hannan complex by Excimer laser ablation-ICPMS is presented and its tectonic implication is discussed. In Huangling complex, it is indicated that the Shandouping and Dalaoling suites were formed at 794±7 and 795±8Ma, respectively, whereas the Xiaofeng suite at 744±22Ma, which is synchronous both with the Liantou volcanic rocks from the lowest part of the Sinian stratum, directly covered the Huangling complex, and thermo-disturbed events widely recognized among other Huangling suites. Wudumen intrusive of the Hannan complex gives an age of 789±10Ma, which is coeval, within analysis error, with those of the Shandouping and Dalaoling suites; whereas the Tianpinghe pluton is dated at 863 ± 10Ma, which timing is firstly reported in the northern margin of the Yangtze craton. In addition, inherited zircons of ≈ 860Ma in Huangling area and 945 ≈ 931Ma in Hannan area are documented by this study. It is notable that disturbing thermo-event of ≈740Ma is also recognized among the Hannan intrusives. It is accordingly suggested that the both the interior and northern margin of the Yangtze craton shared a conmen experience of felsic magmatism at ≈790Ma and an evident thermo-tectonic disturbance at ≈ 740Ma, namely these events display a craton-scale character. Intrusives of ≈ 860Ma with similar lithology to the Tianpinghe pluton have been documented along the western margin of the Yangtze craton, i.e. western Sichuan province, suggesting a continuous magmatic zone of ≈860Ma from the northern margin westward to the northwestern margin, although the geodynamic context of the magmatism is yet unclear. Consequently, the so-called Jinningian Movement, in the light of orogeny, is proposed to evolve from ≈830Ma, being peaked at ≈790Ma indicated by extensive felsic magmatism sourced by intro-crust rocks, and ended at ≈ 740Ma characterized by tectonic transition from the regional crust speedy uplifting shortly to rapid subsidence. The documented data and their geochronological patterns presented here give an essential constraint on correlation between the Neoproterozoic magmatism of the Yangtze craton and the coeval globe tectonic events.