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首页> 外文期刊>Precambrian Research >～2.7Ga juvenile crust formation in the North China Craton (Taishan-Xintai area, western Shandong Province): Further evidence of an understated event from U-Pb dating and Hf isotopic composition of zircon
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～2.7Ga juvenile crust formation in the North China Craton (Taishan-Xintai area, western Shandong Province): Further evidence of an understated event from U-Pb dating and Hf isotopic composition of zircon

机译：华北克拉通（山东西部台山-新泰地区）〜2.7Ga幼年地壳形成：进一步证实U-Pb年代和锆石的Hf同位素组成低估了事件

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摘要

The evolution of the North China Craton (NCC) is well known for a marked 2.55-2.50Ga tectonothermal event. However, supracrustal and intrusive rocks of 2.75-2.70Ga are in fact widely distributed in the western Shandong Province, the most important area of Archaean basement in the eastern part of the NCC. This paper reports SHRIMP U-Pb dating and LA-ICPMS Hf isotopic composition of zircons from 2.75-2.70Ga supracrustal and trondhjemite-tonalite-granodiorite (TTG) rocks in that area. Three fine-grained (hornblende) biotite gneiss samples (known locally as leptynite, with meta-volcanic or volcanosedimentary rock protoliths) and five TTG samples have SHRIMP zircon U-Pb ages varying from 2.75 to 2.70Ga and 2.74 to 2.71Ga, respectively. Zircons from most of the samples have high positive e{open}_(Hf)(t) values (+4.7 to +10.0) and t_(DM)(Hf) ages (2.85-2.60Ga) similar to their zircon U-Pb ages. This indicates that the rocks represent largely juvenile crustal additions derived from depleted mantle only a short time before. However, some granitoids show e{open}_(Hf)(t) zircon values of -13.6 to +5.1 and t_(DM)(Hf) of 3.51-2.80Ga. Therefore, the strong 2.75-2.70Ga tectonothermal event in the western Shandong Province involved not only juvenile addition to the continental crust but also intracrustal recycling of older components. Combined with craton-wide data, it is shown that the NCC is similar to many other cratons around the world where tectonothermal events of ～2.7Ga are well developed. However, the main difference is that in the NCC, superimposed ～2.5Ga tectonothermal events were much stronger than in most other cratons.
机译：华北克拉通（NCC）的演化以2.55-2.50Ga显着的地热事件而闻名。然而，2.75-2.70Ga的表壳和侵入岩实际上广泛分布在山东省西部，这是NCC东部最重要的古生界基底区域。本文报道了该地区2.75-2.70Ga上壳和长白云母-tonalite-granodiorite（TTG）岩石的锆石的SHRIMP U-Pb定年和LA-ICPMS Hf同位素组成。 3个细粒（角闪石）黑云母片麻岩样品（当地称为瘦铁矿，具有中火山岩或火山成岩的原生岩体）和5个TTG样品的SHRIMP锆石U-Pb年龄分别为2.75至2.70Ga和2.74至2.71Ga。大部分样品中的锆石具有较高的e {open} _（Hf）（t）正值（+4.7至+10.0）和t_（DM）（Hf）年龄（2.85-2.60Ga），与锆石U-Pb相似年龄。这表明这些岩石代表了不久前从枯竭地幔中衍生出来的大部分幼年地壳。但是，某些花岗岩显示e {open} _（Hf）（t）锆石值为-13.6至+ 5.1，t_（DM）（Hf）为3.51-2.80Ga。因此，在山东省西部发生的2.75-2.70Ga强地热事件不仅涉及陆壳中的幼体，而且还涉及旧组分的壳内回收。结合克拉通范围的数据表明，NCC与世界上许多其他克拉通相似，其中〜2.7Ga的构造热事件发展良好。但是，主要的区别是在NCC中，叠加的〜2.5Ga构造热事件比大多数其他克拉通要强得多。

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