Tectonic evolution of the Alxa Block and its affinity: Evidence from the U-Pb geochronology and Lu-Hf isotopes of detrital zircons from the Longshoushan Belt
Tectonic evolution of the Alxa Block and its affinity: Evidence from the U-Pb geochronology and Lu-Hf isotopes of detrital zircons from the Longshoushan Belt
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阿拉善地块的构造演化及其亲和性：来自龙首山带碎屑锆石U-Pb年代学和Lu-Hf同位素的证据
DOI：
10.1016/j.precamres.2020.105733
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发表时间：
2020-07
影响因子：
3.8
通讯作者：
Xia Yanfei
中科院分区：
文献类型：
--
作者：
Liu Jingna;Yin Changqing;Zhang Jian;Qian Jiahui;Li Shun;Xu Kaiyuan;Wu Shangjing;Xia Yanfei
北西-南东向的龙首山构造带是阿拉善地块与祁连地块之间的重要过渡带。其基底岩石以绿片岩-角闪岩相变质火山-沉积岩为主，称龙首山杂岩，零星出露于龙首山带中东部。龙首山中段碎屑锆石U-Pb年龄分布在3006-1981 Ma之间，以古元古代为主（>95%），峰值为2.0Ga。这些锆石的176 Hf/177 Hf比值为0.281150-0.281687，对应的铪模式年龄（TDMC）为3.04- 2.15Ga。这些时代特征与阿拉善地块和华北西部地块的时代特征一致。而龙首山东部的原岩年龄范围较宽，为3389 ~ 529 Ma，可明显划分为2.5Ga、1.6Ga、1.0Ga和0.8Ga四个年龄群体。这与近年来河西走廊的时代资料相一致，表明龙首山东部不是龙首山杂岩的一部分，而是与河西走廊有亲缘关系。碎屑锆石结晶年龄和沉积年龄的累积概率曲线表明，龙首山中段可能是在一个汇聚盆地中沉积的，而龙首山东部则是典型的碰撞盆地构造背景（如弧后盆地），前陆盆地）。北祁连洋的闭合在中祁连与阿拉善地块之间形成了北祁连造山带，在河西走廊形成了前陆盆地（即，龙首山东部）。
The NW-SE trending Longshoushan Belt is a significant transitional belt between the Alxa and Qilian blocks. Its basement rocks were predominated by greenschist- to amphibolite-facies metamorphosed volcanic-sedimentary rocks, which were named the Longshoushan Complex and sporadically exposed in the middle and eastern Longshoushan Belt. The U-Pb ages of detrital zircons from the middle Longshoushan are scattered in the period of 3006–1981 Ma, predominated by Paleoproterozoic (>95%) with a single peak of 2.0 Ga. These zircons have the176Hf/177Hf ratios of 0.281150–0.281687, corresponding to hafnium model ages (TDMC) of 3.04–2.15 Ga. These age features are in accordance with those of the Alxa Block and the western North China Craton. In contrast, the protoliths of the eastern Longshoushan reveal a wide age range from 3389 Ma to 529 Ma, which can be apparently divided into four age populations of 2.5 Ga, 1.6 Ga, 1.0 Ga and 0.8 Ga. This is consistent with recent reported age data of the Hexi Corridor, indicating that the eastern Longshoushan is not a part of the Longshoushan Complex, but has affinity with the Hexi Corridor. The cumulative probability curves of measured crystallization ages and depositional ages of detrital zircons imply that the middle Longshoushan could be deposited in a convergent basin (e.g., back-arc basin) in the Paleoproterozoic, but the eastern Longshoushan was typical of tectonic setting of a collisional basin (e.g., a foreland basin) in the Cambrian. The closure of the North Qilian Ocean formed the North Qilian Orogen between the Central Qilian and Alxa blocks, resulting to a foreland basin in the Hexi Corridor (i.e., eastern Longshoushan).
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