Neoproterozoic high-K granites produced by melting of newly formed mafic crust in the Huangling region, South China
Neoproterozoic high-K granites produced by melting of newly formed mafic crust in the Huangling region, South China
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DOI：
10.1016/j.precamres.2013.04.011
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发表时间：
2013-08
影响因子：
3.8
通讯作者：
J. Zhao;Mei‐Fu Zhou;Jianping Zheng
中科院分区：
文献类型：
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作者：
J. Zhao;Mei‐Fu Zhou;Jianping Zheng
华南扬子地块中部的黄岭火成岩杂岩体由850 Ma英辉长岩和长辉岩组成，被826 ± 13 Ma高K花岗岩侵入。花岗岩由斜长石（30-60%）、碱长石（10-30%）、石英（20-30%）、黑云母（<10%）和角闪石（<5%）组成。角闪石和黑云母都具有高 Ti 和低 Al 含量，表明液相线温度高。花岗岩的 SiO2（63.1–73.3 wt.%）、K2O（2.58–4.79 wt.%）和 Na2O（3.90–5.89 wt.%）含量较高，MgO 含量较低（0.49–1.78 wt.%），成分为镁碱钙。它们的球粒陨石 - 归一化 REE 模式的特点是轻稀土元素富集 (La/YbN= 14.5–32.8) 和大多数负 Eu 异常 (Eu/Eu* = 0.5–1.1)。它们具有较高的 Sr (202–698 ppm) 和较低的 Y (6.13–18.7 ppm)，Sr/Y 比率为 14–64。这些大的元素变化可能是由分级结晶造成的。它们的全岩 Nd 值（-9.75 至 -11.73）和锆石 Hf 值（-7.1 至 -15.8）也为负值，与同一地区新元古代镁铁质岩石的值相似，表明花岗岩可能是由新侵入的镁铁质岩石熔融产生的。黄岭杂岩的英闪长岩和长辉长岩以前被认为分别是富含水的玄武岩岩浆分异和弧形背景下加厚的太古宙大陆地壳熔融的产物。因此，扬子地块的地壳生长和改造很可能完全受俯冲系统控制，从而在新元古代形成了稳定的大陆。
The Huangling igneous complex in the central Yangtze Block, South China, consists of the 850-Ma tonalite and trondhjemite which were intruded by the 826 ± 13 Ma high-K granite. The granites are composed of plagioclase (30–60%), alkali feldspar (10–30%), quartz (20–30%), biotite (<10%) and hornblende (<5%). Both hornblende and biotite have high Ti and low Al contents, indicating high liquidus temperature. The granites have high SiO2(63.1–73.3 wt.%), K2O (2.58–4.79 wt.%) and Na2O (3.90–5.89 wt.%) and low MgO (0.49–1.78 wt.%) and are magnesian alkali-calcic in composition. Their chondrite – normalized REE patterns are characterized by enrichment of LREE (La/YbN= 14.5–32.8) and mostly negative Eu anomalies (Eu/Eu* = 0.5–1.1). They have moderately high Sr (202–698 ppm) and low Y (6.13–18.7 ppm) with Sr/Y ratios of 14–64. These large elemental variations probably resulted from fractional crystallization. They also have negative whole rockɛNd (−9.75 to −11.73) and zirconɛHf values (−7.1 to −15.8) which are similar to those of the Neoproterozoic mafic rocks in the same region, suggesting that the granites may have been produced by melting of newly-emplaced mafic rocks. Tonalites and trondhjemites of the Huangling complex previously were considered as products by differentiation of water-rich basaltic magmas and melting of the thickened Archean continental crust in an arc setting, respectively. Therefore, the crustal growth and reworking of the Yangtze Block were probably wholly controlled by the subduction system which resulted in formation of the stable continent during the Neoproterozoic.