2.6–2.7 Ga crustal growth in Yangtze craton, South China
2.6–2.7 Ga crustal growth in Yangtze craton, South China
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DOI：
10.1016/j.precamres.2012.10.017
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发表时间：
2013
影响因子：
3.8
通讯作者：
Kang Chen;Shan Gao;Y. Wu;Jing‐Liang Guo;Zhaochu Hu;Yongsheng Liu;K. Zong;Zhengwei Liang;
中科院分区：
文献类型：
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作者：
Kang Chen;Shan Gao;Y. Wu;Jing‐Liang Guo;Zhaochu Hu;Yongsheng Liu;K. Zong;Zhengwei Liang;
对中国南方扬子克拉通中唯一已知的太古宙微大陆-孔岭地体中的10个英云闪长-奥长花岗闪长质（TTG）和花岗质片麻岩进行了锆石U-Pb、Lu-Hf同位素、全岩常量元素、微量元素和Sr-Nd同位素的联合研究。研究结果表明，除了前人报道的102.9Ga和103.2 -3.3Ga岩浆活动外，还发现了102.6 -2.7Ga的一次重要岩浆事件。2.6-2.7Ga岩石具有相对高的REE（530- 1074 ppm）、明显的负Eu异常（Eu/Eu*=0.22-0.35）、低#Mg（19.51-22.63）和低LaN/YbN（10.3-24.2）。钾长石比例高，（K2 O + Na 2 O）/CaO、TFeO/MgO、Zr、Nb、Ce、Y含量相对较高。它们的10，000 ×Ga/Al比范围在3.00至3.54之间。这些特征表明这些片麻岩的原岩为A型花岗岩。大部分2.6-2.7Ga锆石的Hf（t）值>0（最高可达7.93，接近亏损地幔值）。这清楚地表明，与103.2 -3.3Ga和102.9Ga TTG相比，102.6 -2.7Ga花岗岩类中新地壳成分的比例相当高。我们的研究结果支持了世界范围内对火成岩和碎屑锆石研究的结论，即年龄峰值在2.65-2.76Ga，代表了幼年大陆地壳体积的增加。本次研究也证实了该地区存在两次较老的岩浆活动。2.9Ga TTG的全岩Nd（t）值（−3.74 ~ 1.59）和锆石Hf（t）值（−11.18 ~ 3.55）以及3.2-3.3Ga岩浆锆石的Hf同位素（−7.37 ~ 3.12）均为绿玄质或亚绿玄质，表明它们主要是由较老岩石的改造和少量新地壳的加入而形成的。
A combined study of zircon U–Pb and Lu–Hf isotopes and whole rock major and trace elements and Sr–Nd isotopes has been conducted for 10 tonalitic–trondhjemitic–granodioritic (TTG) and granitic gneisses from the Kongling terrain, the only known Archean microcontinent in the Yangtze craton, South China. The results reveal a significant magmatic event at ∼2.6–2.7Ga, in addition to the previously reported ∼2.9Ga and ∼3.2–3.3Ga magmatism. The ∼2.6–2.7Ga rocks show relatively high REE (530–1074ppm), apparently negative Eu anomaly (Eu/Eu*=0.22–0.35), low #Mg (19.51–22.63) and low LaN/YbN(10.3–24.2). Besides, they have high K-feldspar proportion and relatively evaluated (K2O+Na2O)/CaO, TFeO/MgO, Zr, Nb, Ce and Y contents. Their 10,000×Ga/Al ratios range between 3.00 and 3.54. All these features suggest that the protoliths of these gneisses are A-type granites. Most of the ∼2.6–2.7Ga zircon grains have ɛHf(t) values >0 (up to 7.93, close to the depleted mantle value). This clearly indicates a considerably higher proportion of new crustal components in the ∼2.6–2.7Ga granitoids compared to the ∼3.2–3.3Ga and ∼2.9Ga TTGs. Our results support the conclusion of worldwide studies of igneous and detrital zircons that age peaks at 2.65–2.76Ga represent increases in the volume of juvenile continental crust. The present study also confirms the existence of the two older magmatic events in the Kongling terrain. Both whole rock ɛNd(t) values (−3.74 to 1.59) and the zircon ɛHf(t) values (−11.18 to 3.55) for the ∼2.9Ga TTG and the Hf isotopes of ∼3.2–3.3Ga igneous zircons (−7.37 to 3.12) are chondritic or subchondritic, suggesting that they were mainly generated by reworking of older rocks with a small amount of new crustal additions.