Ca. 2.9 Ga granitoid magmatism in eastern Shandong, North China Craton: Zircon dating, Hf-in-zircon isotopic analysis and whole-rock geochemistry
Ca. 2.9 Ga granitoid magmatism in eastern Shandong, North China Craton: Zircon dating, Hf-in-zircon isotopic analysis and whole-rock geochemistry
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DOI：
10.1016/j.precamres.2014.09.006
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发表时间：
2014-12
影响因子：
3.8
通讯作者：
S. Xie;H. Xie;Shijin Wang;A. Kröner;Shoujie Liu;Hong-ying Zhou;M. Ma;C. Dong;Dunyi Liu
中科院分区：
文献类型：
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作者：
S. Xie;H. Xie;Shijin Wang;A. Kröner;Shoujie Liu;Hong-ying Zhou;M. Ma;C. Dong;Dunyi Liu
鲁东地区是华北大陆重要的早前寒武纪地区之一，在该区曾发生过广泛的2.5、2.7和2.9Ga岩浆活动，并伴随着强烈的晚新太古代和古元古代构造热事件。对该矿床进行了SHRIMP锆石定年、Hf-锆石同位素分析和全岩地球化学研究。2.9中太古代岩浆岩。这些包括片麻状闪长岩、片麻状石英闪长岩、片麻状英云闪长岩和片麻状高硅奥长花岗岩，并在五个新的地区被发现。所有这些岩石都含有钙。2.5 Ga变质锆石闪长质和英云闪长质岩石富集大离子亲石元素（K、Rb、Ba），亏损Nb、P，稀土元素分异程度中等至高度，与全球太古代TTG岩石化学成分相似。高硅奥长花岗岩以极高的SiO2和极低的FeOt+MgO为特征。这些岩石中岩浆锆石的Hf同位素组成相似，Hf（t）值为+1.3 ~+9.9。结合前人的工作，我们的主要结论是：（1）鲁东地区在约4000年左右经历了一次大的岩浆活动。2.9 Ga;（2）闪长岩和英云闪长岩形成于增厚的下地壳或大洋高原的根部，而高硅奥长花岗岩则来自中长英质岩石的熔融; 2.9（4）2.7 - 2.9Ga岩石经历了强烈的变质作用，形成于2.7 - 2.8Ga。2.5 Ga，可能是岩浆底侵作用的结果。
Eastern Shandong is one of the important early Precambrian areas in the North China Craton, where extensive 2.5, 2.7 and 2.9 Ga magmatic activities have been identified, followed by very strong late Neoarchean and Paleoproterozoic tectono-thermal events. We carried out SHRIMP zircon dating, Hf-in-zircon isotope analysis and a whole-rock geochemical study on ca. 2.9 Ga Mesoarchean magmatic rocks. These include gneissic diorite, gneissic quartz diorite, gneissic tonalite and gneissic high-Si trondhjemite and were identified in five new areas. All these rocks contain ca. 2.5 Ga metamorphic zircons. The dioritic and tonalitic rocks are enriched in large ion lithosphile (LIL) elements (K, Rb, Ba) and depleted in Nb and P with moderate to highly fractionated REE patterns, similar in chemical compositions to Archean TTG rocks worldwide. The high-Si trondhjemites are characterized by very high SiO2and very low FeOt+MgO. The magmatic zircon grains from all these rocks are similar in their Hf isotopic compositions and haveɛHf(t) values ranging from+1.3 to +9.9. Combined with previous work, our main conclusions are: (1) eastern Shandong underwent a major magmatic event at ca. 2.9 Ga; (2) diorites and tonalites formed by melting of thickened lower crust or the root of an oceanic plateau, whereas the high-Si trondhjemites were derived from melting of intermediate to felsic rocks; (3) the Mesoarchean (ca. 2.9 Ga) was a major period of juvenile crustal addition from the depleted mantle, earlier than the major crustal growth period at 2.7–2.8 Ga in the North China Craton; (4) the 2.7–2.9 Ga rocks underwent strong metamorphism at ca. 2.5 Ga, probably as a result of magmatic underplating.