Indosinian magmatism and rare metal mineralization in East Tianshan orogenic belt: An example study of Jingerquan Li-Be-Nb-Ta pegmatite deposit
Indosinian magmatism and rare metal mineralization in East Tianshan orogenic belt: An example study of Jingerquan Li-Be-Nb-Ta pegmatite deposit
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DOI：
10.1016/j.oregeorev.2019.103265
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发表时间：
2020-01
影响因子：
3.3
通讯作者：
Siyu Liu;Rui Wang;H. Jeon;Z. Hou;Qing-po Xue;Zhou Limin;Shoubo Chen;Zhonglin Zhang;Binbin Xi
中科院分区：
文献类型：
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作者：
Siyu Liu;Rui Wang;H. Jeon;Z. Hou;Qing-po Xue;Zhou Limin;Shoubo Chen;Zhonglin Zhang;Binbin Xi
东天山造山带与阿拉泰造山带一样，是中亚造山带的一部分，具有很大的稀有金属成矿潜力。镜儿泉Li-Be-Nb-Ta矿床是该区最大的伟晶岩型矿床。东天山造山带东段镜儿泉Li-Be-Nb-Ta伟晶岩矿床发育白云母花岗岩、石英二长岩和辉长岩。根据Li元素的含量和含Li矿物的存在，我们识别出两套侵入岩组合，即I类，包括白云母花岗岩和石英二长岩，富Li，存在锂辉石和/或锂云母；II类，主要是辉长岩，贫Li，不含Li矿物。I类岩石富硅、铝、钠、钾，钙碱性-高钾钙碱性系列，贫钙、磷、铁、镁，A/CNK、≥为1.1，与S型过铝花岗岩相似。I类岩石具有Rb、Ta、Nb、Hf的富集性和明显的钛、钡、锶的亏损特征。球粒陨石归一化稀土元素配分模式显示明显的Eu异常(δEu=0.0 1~0.2 0)、“四分体效应”和相对较低Σ稀土元素的分馏增加。Ⅱ类岩石为钙碱性岩石，富Ca、Al、P，贫Si、K，A/CNK=1，以富Ba、富锶、亏损Th、Nb、Ta为特征。球粒陨石标准化的稀土元素配分模式没有明显的Eu异常(δEu=100.97-1.40)，曲线向右倾斜。I级独居石SIMS U-Th-Pb年龄(246-252.9 Ma)和II级锆石LA-ICP-MS U-Pb年龄(247-250.7 Ma)表明，两类侵入岩均形成于印支期的板内环境。II类岩石的εHf(T)值(12.0~15.2)和亏损地幔模式年龄TDm(2 79~411 Ma)表明，岩浆主要来源于亏损地幔的部分熔融。在板内伸展环境中，以Ⅱ类玄武岩岩浆为代表的地幔岩浆侵入地壳，诱导中上地壳部分熔融，形成I类S型花岗岩浆。之后，花岗岩浆经过不断的差异演化和挥发分富集，最终形成Li-Be-Nb-Ta矿化花岗伟晶岩。对比东天山造山带和阿拉泰造山带的地质背景、成岩成矿年代学和矿物组合，发现两者的稀有金属成矿作用均受印支构造-岩浆事件的控制。
The East Tianshan orogenic belt, a part of the Central Asian Orogenic Belt like Altai orogenic belt, has shown great potential for rare metal mineralization. Jingerquan Li-Be-Nb-Ta deposit is the largest pegmatite deposit in this region. Muscovite granite, quartz monzonite and gabbro have developed in the Jingerquan Li-Be-Nb-Ta pegmatite deposit in the eastern part of East Tianshan orogenic belt. Based on the content of elemental Li and the presence of Li-bearing minerals, we recognize two sets of intrusive assemblages, namely, class I, including muscovite granite and quartz monzonite, which are rich in Li with presence of spodumene and/or lepidolite, and class II mainly gabbro, which are poor in Li and absent of Li-bearing minerals. Class I rocks are rich in Si, Al, Na, K, calc-alkaline to high-K calc-alkaline series, and poor in Ca, P, Fe, and Mg, with A/CNK ≥ 1.1, which are similar to S-type peraluminous granites. Class I rocks are characterized by Rb, Ta, Nb, and Hf enrichments and significant Ti, Ba, and Sr depletions. The chondrite-normalized rare earth element (REE) patterns exhibit significant Eu anomalies (δEu = 0.01–0.20), “tetrad effect,” and increased fractionation of rare earth elements with relatively low ΣREE. Class II rocks are calc-alkaline rocks that are rich in Ca, Al, and P and poor in Si, K, with A/CNK < 1; they are characterized by Ba and Sr enrichments and Th, Nb, and Ta depletions. The chondrite-normalized REE patterns exhibit no significant Eu anomalies (δEu = 0.97–1.40) and a smooth curve that slopes to the right. The monazite SIMS U-Th-Pb ages of class I (246–252.9 Ma) and the zircon LA-ICP-MS U-Pb ages of class II (247–250.7 Ma) indicate that both types of intrusions were formed in intraplate environment in Indosinian period. The εHf(t)values (12.0–15.2) and the depleted mantle model ages TDM(279–411 Ma) of class II rocks indicate that the magmas were mainly derived from partial melting of the depleted mantle. In the intraplate extensional setting, the mantle magmas represented by class II basaltic magmas intraplated into the crust and induced partial melting of the middle and upper crust to produce class I S-type granitic magmas. After that, the granitic magmas underwent continuous differential evolution and volatile enrichment, and finally form Li-Be-Nb-Ta mineralized granitic pegmatite. The geological setting, diagenetic and metallogenic chronology, and mineral assemblages of the East Tianshan orogenic belt and the Altai orogenic belt can be compared, and rare metal mineralization of both belts were controlled by the Indosinian tectonic-magmatic event.