Petrogenesis of Jurassic tungsten-bearing granites in the Nanling Range, South China: Evidence from whole-rock geochemistry and zircon U-Pb and Hf-O isotopes
Petrogenesis of Jurassic tungsten-bearing granites in the Nanling Range, South China: Evidence from whole-rock geochemistry and zircon U-Pb and Hf-O isotopes
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华南南岭侏罗纪含钨花岗岩的岩石成因：全岩地球化学及锆石U-Pb、Hf-O同位素证据
DOI：
10.1016/j.lithos.2017.01.018
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发表时间：
2017
期刊：
影响因子：
3.5
通讯作者：
Xiang Yuan Xin
中科院分区：
文献类型：
--
作者：
Zhang Yang;Yang Jin Hui;Chen Jing Yuan;Wang Hao;Xiang Yuan Xin
南岭是中国乃至世界上最大的钨成矿区。钨成矿作用与侏罗纪花岗质岩浆活动有关。然而，这些花岗岩的成因及其与钨矿化的关系仍有争议。本文报道了赣南北陆带含钨花岗质岩体的全岩地球化学、Sr-Nd-Hf同位素、锆石U-Pb年龄和Hf-O同位素等资料，以探讨其岩浆来源和成因。NLR花岗岩包括黑云母花岗岩、二云母花岗岩和石榴白云母花岗岩。锆石和独居石的西姆斯和LA-ICPMS U-Pb定年结果表明，这些岩石的侵位年龄为161-154 Ma。花岗岩是变铝质到强过铝质的，具有高SiO2（> 72.3 wt.%）和高K2 O（> 3.7wt.%）。岩石学和地球化学特征表明它们是高度分馏的I型花岗岩。黑云母花岗岩相对富集轻稀土元素，具弱的Eu负异常，亏损Nb、Ba、P和Ti。相比之下，含二云母和石榴子石的白云母花岗岩具有四元型稀土配分模式，具有强烈的Eu负异常，并且极度亏损Ba、Nb、Sr、P和Ti。岩浆石榴石主要为铁铝榴石和铁铝榴石，具有低锰核和高锰边。（Y + HREE）含量高，一般从岩芯（1.2wt%）开始降低至边缘（平均值= 4955 ppm）。所有这些花岗岩的特征是全岩初始87 Sr/86 Sr（0.7053-0.8000）、εNd（t）（− 12.6-− 9.4）和εHf（t）（− 12.3-− 8.5），以及可变的锆石εHf（t）和δ 18 O，其值分别为− 16.3-− 7.4和7.6 - 10.0‰。它们含有丰富的锆石捕虏晶和云母片岩捕虏体。所有这些特征都与地壳岩浆的结晶分异过程以及沉积岩的强烈同化作用相一致。变质沉积物质的同化作用增加了岩浆中钨、氧化铝和锰的浓度，而高度的晶体分馏作用则使它们在演化的花岗岩中进一步富集。富钨岩浆流体形成含钨石英脉，揭示了北陆壳中钨矿化与含石榴子石二云母或白云母花岗岩侵位的成因联系。
The Nanling Range (NLR) is the largest tungsten metallogenic province in China and perhaps in the world. The tungsten mineralization is believed to be related to Jurassic granitic magmatism. However, the petrogenesis of these granites and their relation to the tungsten mineralization are still debated. Whole-rock geochemical and Sr–Nd–Hf isotopic data and zircon in situ U–Pb ages and Hf–O isotopes are reported for W-bearing granitic intrusions from the southern Jiangxi Province in the NLR, in order to constrain their magmatic sources and petrogenesis. The NLR granites include biotite granites, two-mica granites and garnet muscovite granites. SIMS and LA-ICPMS U–Pb dating of zircons and monazites give emplacement ages of 161–154 Ma for these rocks. The granites are metaluminous to strongly peraluminous with high SiO2(> 72.3 wt.%) and high K2O (> 3.7 wt.%). Petrographic and geochemical features show that they are highly fractionated I-type granites. The biotite granites are enriched in light rare earth elements (LREEs) relative to heavy REEs, have weakly negative Eu anomalies and are depleted in Nb, Ba, P and Ti. In contrast, the two-mica and garnet-bearing muscovite granites have tetrad-type REE patterns with strongly negative Eu anomalies and are extremely depleted in Ba, Nb, Sr, P and Ti. Magmatic garnets are mainly almandine and spessartine, and have low-Mn cores and high-Mn rims. Their (Y + HREE) contents are high and generally decrease from core (1.2 wt.%) to rim (average = 4955 ppm). All of these granites are characterized by variable whole-rock initial87Sr/86Sr (0.7053–0.8000), εNd(t) (− 12.6 to − 9.4) and εHf(t) (− 12.3 to − 8.5), as well as variable zircon εHf(t) and δ18O, with values of − 16.3 to − 7.4 and 7.6 to 10.0‰, respectively. They contain abundant zircon xenocrysts and xenoliths of micaceous schist. All of these features are consistent with a process of crystal fractionation of crustally-derived magmas coupled with strong assimilation of sedimentary rocks. The assimilation of meta-sedimentary materials increased the concentrations of tungsten, alumina and manganese in the magmas, whereas high degrees of crystal fractionation further enriched them in the evolved granitic rocks. The W-enriched magmatic fluids formed the tungsten-bearing quartz veins, revealing the genetic relationship between tungsten mineralization and emplacement of garnet-bearing two-mica or muscovite granites in the NLR.