Progressive accretionary tectonics of the Beishan orogenic collage, southern Altaids: Insights from zircon U–Pb and Hf isotopic data of high-grade complexes
Progressive accretionary tectonics of the Beishan orogenic collage, southern Altaids: Insights from zircon U–Pb and Hf isotopic data of high-grade complexes
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DOI：
10.1016/j.precamres.2012.06.011
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发表时间：
2013-04
影响因子：
3.8
通讯作者：
Dongfang Song;W. Xiao;Chunming Han;Jiliang Li;J. Qu;Q. Guo;Lina Lin;Zhongmei Wang
中科院分区：
文献类型：
--
作者：
Dongfang Song;W. Xiao;Chunming Han;Jiliang Li;J. Qu;Q. Guo;Lina Lin;Zhongmei Wang
中亚阿尔泰造山带南部的高级片麻状岩是解决增生造山作用中基本构造争议的关键因素之一。在阿尔泰山脉南部的北山造山拼贴带中广泛出露高级片麻状岩，被称为北山杂岩或敦煌群，以前被认为是新太古代-古元古代的结晶基底，但缺乏系统的野外、年代学和地球化学资料。本文提供了北山杂岩片麻状岩的野外、地球化学和锆石U-Pb、Hf同位素资料。地球化学数据表明，片麻状岩可能形成于俯冲环境。北山杂岩中锆石的Th/U比值大多在1.0-0.1之间，大部分为岩浆成因，年龄峰值分别为494 Ma、464 Ma和375 Ma，少数为前寒武纪。锆石Hf同位素组成表明，北山杂岩的形成既有古老的物质，也有新生的物质，无论是放射性年龄还是Hf同位素组成都与塔里木盆地基底岩石不同。因此，这些资料并不支持北山地区前寒武纪基底的一致性，而是北山杂岩可能形成于俯冲-增生环境。结合区域地质和地球化学资料，认为北山造山拼贴带在晚前寒武纪-古生代具有渐进式的长寿命增生构造特征，从而澄清了增生造山带结构的争议。
High-grade gneissic rocks of the southern Altaids in Central Asia bear one of the key elements needed to solve a basic architectural controversy in accretionary orogenesis. High-grade gneissic rocks widely crop out across the Beishan orogenic collage, southern Altaids, mapped as the Beishan Complex or Dunhuang Group, which was previously regarded as Neoarchean to Paleoproterozoic crystalline basement, but without systematic field, geochronological and geochemical data. This study provides field, geochemical and zircon U–Pb and Hf isotopic data for gneissic rocks from the Beishan Complex. Geochemical data show that the gneissic rocks were probably formed in a subduction environment. Most zircons from the Beishan Complex are magmatic origins because their Th/U ratios are mostly in the range of 1.0–0.1; they show age peaks at 494Ma, 464Ma, and 375Ma, with a few Precambrian ages. Zircon Hf isotopic compositions indicate that both old and juvenile materials were involved in the formation of the Beishan Complex, which is different from the basement rocks of the Tarim Craton both in radiometric age and Hf isotopic composition. All these data thus do not support a uniform Precambrian basement in the Beishan area as previously proposed, but instead the Beishan Complex probably formed in a subduction–accretion environment. Combined with regional geology and geochemical data, we conclude that the Beishan orogenic collage was characterized by progressive long-lived accretionary tectonics during Late Precambrian to Paleozoic time, therefore shedding light on the controversy regarding the architecture of accretionary orogens.