东天山觉罗塔格红云滩花岗岩年代学和地球化学及其构造意义
吴昌志1)，顾连兴1)，张遵忠2), 刘四海1)
1）内生金属矿床成矿机制研究国家重点实验室（南京大学），南京大学地球科学系，南京 210093
2）江苏省有色金属华东地质勘查局 深部找矿理论与技术研究院，南京210007；
摘要 东天山觉罗塔格地区广泛发育的晚古生代岩浆岩及相关的矿产资源一直是东天山大地构造研究的焦点。红云滩花岗岩类以黑云母二长花岗岩和花岗闪长岩为主，皆含有不等量角闪石和榍石，与Barbarin (1999)所划分的岛弧富含角闪石钙碱性花岗岩的矿物组合相一致。主量元素研究表明，花岗岩类属典型的钙碱性系，具有与Maniar and Piccoli, 1989划分的CAG（大陆弧花岗岩类）和IAG（岩浆弧花岗岩类）类似的演化特征。微量元素特征进一步证明，该花岗岩类为典型的火山弧花岗岩，是与洋壳俯冲作用有关的下地壳物质部分熔融所产生的岩浆，经历分离结晶和同化混染作用的产物。锆石的LAM-ICP/MS定年结果表明，红云滩花岗闪长岩侵位于中石炭世（328.5±9.3 Ma）。与此岩体毗邻的铁岭岩体、百灵山岩体和骆驼峰岩体可能在深部与红云滩岩体连成一体，并可能与红云滩岩体具有类似的年龄和成因，从而表明觉罗塔格南缘的阿齐山-雅满苏地区中石炭世岩浆活动十分强烈。与此成鲜明对照的是，阿齐克库都克-沙泉子断裂南侧的中天山东段却鲜见此时段的花岗岩。因此，我们推测，觉罗塔格南缘在晚古生代明显受到洋壳俯冲作用的影响，而石炭纪时期寂静的中天山地区应为与洋壳俯冲作用对应的被动大陆边缘。
觉罗塔格构造带石炭纪的火山-沉积建造及其中的矿产分布特征也同样显示由南向北俯冲的极性。研究表明，与钙碱性岩浆活动有关的火山沉积-热液铁矿床主要分布于觉罗塔格南缘靠近中天山一侧，而与花岗岩类有关的斑岩铜钼矿床均分布于其北缘（Qin et al., 2003; Zhang et al., 2004；Xiao et al., 2004）。这种分布规律似与从海沟往大陆方向俯冲带深度的增加相一致。因此，在作者看来，在古觉罗塔格洋向塔里板块俯冲并形成中天山弧之后，至晚古生代时该洋盆并未完全消亡，而是俯极性反转而向北潜没于准-吐-哈地块之下。
从火山-沉积岩的分布来看，泥盆纪的火山-沉积岩主要分布于康古尔-黄山断裂以北地区，而石炭纪火山-沉积岩则广泛分布于整个觉罗塔格地区。因此，泥盆纪觉罗塔格洋与准-吐-哈地块的俯冲向应在大南湖-头苏泉岛弧带南侧康古尔-黄山断裂带附近；至中石炭世，该俯冲带后撤（retreat）至阿奇克库都克-沙泉子断裂附近，并在其北侧觉罗塔格地区形成了广泛发
育的火山岩、近同时代的侵入岩以及相关矿产；至于康古尔-黄山一带的干墩组和梧桐窝子组，周守沄（2005）根据化石组合确定其为晚石炭世沉积物，其时代相当于316.5-305 Ma。因此，这套含放射虫硅质岩和双峰式火山岩的地层（马瑞士等，1997）应是晚石炭世弧后盆地的产物（Gu et al.，1995），代表了当时觉罗塔格洋俯冲带的变陡（steepen）；晚石炭末至早二叠世初，随着觉罗塔格洋的关闭，中天山与觉罗塔格发生碰撞，并造成先前康古尔-黄山弧后拉张薄弱带的脆-韧性剪切变形。在黄山-镜儿泉一带，沿此变形带还有二叠纪（Zhou et al., 2004；Han et al., 2004）镁铁-超镁铁岩及与之有成因联系的壳源花岗岩(260.2 Ma, Gu et al., 1996)侵入。
关键词 花岗岩；年代学，觉罗塔格，东天山，新疆
Chronology, geochemistry and tectonic significances of the Hongyuntan granitoids in the Qoltag area, Eastern Tianshan
WU Changzhi1) GU Lianxing1) ZHANG Zunzhong2) and LIU Sihai1)
1) State Key Laboratory of Mineral Deposit Research (Nanjing University), Department of Earth Sciences, Nanjing University, Nanjing 210093, China
2) Institute of Science and Technology for Deep Ore-Prospecting, Eastern China Geological and Mining Organization for Non-ferrous Metals, Nanjing 210007
Abstract Paleozoic igneous rocks and mineral deposits are keys to revealing the tectonic setting of the Qoltag belt in Eastern Tianshan, Xinjiang Province. Investigation in petrology, mineralogy and geochemistry indicate that the Hongyuntan granitoids at the southern margin of the Qoltag area are typical Calc-Alkaline volcanic arc granitoids, and have genetic relation with melting of the lower crust affected by subduction of the oceanic crust. U-Pb age determinations of Zircon by LAM-ICP/MS show the Hongyuntan granitoids were intruded at 328.5±9.3 Ma of Middle Carboniferous. By contrast, magmatism in the Middle Tianshan, south of the Qoltag area is not important. In the late Paleozoic of the Qoltag area, mineral deposits show zonal distribution with its southern margin being dominate by Fe deposits of the volcanosedimentary and hydrothermal type, and its northern margin being dominated by Cu-Mo deposits of the porphyry type. In combination with distribution of the volcanosedimentary strata and tectonic evolution of the Qoltag and its surrounding areas, it is suggested that a Qoltag ocean occur in the Paleozoic. In early Paleozoic, the Paleo-Qoltag ocean subducted under north the northern margin of the Tarim plate, resulting in the Middle Tianshan island arc. While in late Paleozoic, the Qoltag ocean changed in subduction polarity and decent northward beneath the Junggar-turpan-Hami block. The Hongyuntan granitoids were formed in this volcanic arc above the subducting Qoltag ocean crust of late Paleozoic in association with other Hercynian magmatic rocks, volcanosedimentary strata, and
zonally distributed mineral deposits.
Keywords granitoids, Chronology, Qoltag, Eastern Tianshan, Xinjiang, NW China
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