Geochronology and geochemistry of igneous rocks in the Bailingshan area: Implications for the tectonic setting of late Paleozoic magmatism and iron skarn mineralization in the eastern Tianshan, NW China
Geochronology and geochemistry of igneous rocks in the Bailingshan area: Implications for the tectonic setting of late Paleozoic magmatism and iron skarn mineralization in the eastern Tianshan, NW China
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DOI：
10.1016/j.gr.2015.10.011
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发表时间：
2016-10
影响因子：
6.1
通讯作者：
Weifeng Zhang;Huayong Chen;Jinsheng Han;Liandang Zhao;Jianhan Huang;Juntao Yang;Xuelu Yan
中科院分区：
文献类型：
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作者：
Weifeng Zhang;Huayong Chen;Jinsheng Han;Liandang Zhao;Jianhan Huang;Juntao Yang;Xuelu Yan
晚古生代白岭山岩体和火山岩位于东天山南缘阿奇山—亚曼苏弧带，与一组重要的铁夕卡岩矿床有关。出露的侵入岩主要为花岗闪长岩、二长花岗岩和花岗岩。Tugutublak组凝灰质英长质熔岩的锆石U-Pb测年结果为324 Ma，而白岭山花岗闪长岩、二长花岗岩和花岗岩的锆石U-Pb测年结果分别为317 Ma、313 Ma和307 Ma。结果表明，白陵山花岗岩体是在吐古特布拉克英安岩喷发后不久形成的。这些岩石均表现出钙碱性至高钾钙碱性和成矿亲和关系，A/CNK值为0.83 ~ 1.10。富Rb、K、Pb，贫Nb、Ta、Ti、P， Sr/Y值低（4.16 ~ 23.7），Sr值低（109.0 ~ 347.0 ppm），具有典型的弧形地球化学亲和力。凝灰质英长质熔岩具有低Nb/Ta值（10.3 ~ 14.1）、宽mg#值（6 ~ 64）、正锆石εHf(t)值（3.2 ~ 7.5）、高全岩εNd(t)值（2.03 ~ 4.41）、低isr值（0.70427 ~ 0.70530）等特征，表明源岩浆可能来源于下地壳，地幔输入较小。受Nb/Ta比值、Mg#和同位素特征的限制，白岭山ⅰ型侵入体也表现出混合源信号。花岗闪长岩、二长花岗岩和花岗岩侵入体的锆石εHf(t)（分别为3.3 ~ 7.5、11.8 ~ 13.5和10.2 ~ 14.4）和εNd(t)（分别为3.90、5.78和5.94）高于凝灰质英安质熔岩，表明幔源物质在其成岩演化中发挥了更为突出的作用。综合新的地质、年龄、地球化学和同位素资料，我们认为阿奇山—亚曼苏铁矽卡岩带可能形成于晚古生代依里—中天山地块下康居尔大洋板块向南俯冲所形成的弧内盆地或弧后位置，盆地倒转过程中发生了长质—中质岩浆活动。
The late Paleozoic Bailingshan intrusions and volcanic rocks are located in the Aqishan–Yamansu arc belt in the southern part of the eastern Tianshan and are associated with an important group of iron skarn deposits. The exposed intrusive rocks are mainly granodiorite, monzonitic granite, and granite. Zircon U–Pb dating of the Tugutublak Formation tuffaceous dacitic lava yields an age of 324 Ma, whereas dates of the Bailingshan granodiorite, monzonitic granite, and granite yields ages of 317 Ma, 313 Ma, and 307 Ma, respectively. The results indicate that the Bailingshan granitoids were emplaced soon after the eruption of the Tugutublak dacite. All these rocks studied show calc-alkaline to high-K calc-alkaline and metaluminous affinities, with A/CNK values ranging 0.83–1.10. They are enriched in Rb, K, and Pb, depleted in Nb, Ta, Ti, and P, and contain low Sr/Y (4.16–23.7) and Sr (109.0–347.0 ppm) values, displaying typical arc geochemical affinities. The tuffaceous dacitic lava has low Nb/Ta (10.3–14.1) values, a wide range of Mg#(6–64), positive zircon εHf(t) (3.2–7.5) values, and elevated whole-rock εNd(t) (2.03–4.41), but low ISrvalues (0.70427–0.70530), indicating that the source magma may have been derived from the juvenile lower crust with minor mantle input. The Bailingshan I-type intrusions also exhibit a mixed source signal, as constrained by Nb/Ta ratios, Mg#, and isotopes characteristics. Because the granodiorite, monzonitic granite, and granite intrusions have higher zircon εHf(t) (3.3–7.5, 11.8–13.5, and 10.2–14.4, respectively) and εNd(t) (3.90, 5.78, and 5.94, respectively) values than those of the tuffaceous dacitic lava, it is suggested that mantle-derived materials may have played a more prominent role with their petrogenetic evolution. Integrating our new geological, age, geochemical and isotopic data we propose that the Aqishan–Yamansu iron skarn belt may have formed in a back-arc position or within an intra-arc basin generated by the southward subduction of the Kanggur oceanic plate beneath the Yili–Central Tianshan block during the late Paleozoic, with felsic-intermediate magmatism occurring during the basin inversion.