Highly fractionated Late Triassic I-type granites and related molybdenum mineralization in the Qinling orogenic belt: Geochemical and U–Pb–Hf and Re–Os isotope constraints
Highly fractionated Late Triassic I-type granites and related molybdenum mineralization in the Qinling orogenic belt: Geochemical and U–Pb–Hf and Re–Os isotope constraints
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DOI：
10.1016/j.oregeorev.2013.07.003
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发表时间：
2014
影响因子：
3.3
通讯作者：
B. Xiao;Qiugen Li;Shuwen Liu;Zong-qi Wang;Pengtao Yang;Junlu Chen;Xueyi Xu
中科院分区：
文献类型：
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作者：
B. Xiao;Qiugen Li;Shuwen Liu;Zong-qi Wang;Pengtao Yang;Junlu Chen;Xueyi Xu
本文报道了中国中部南秦岭亚带中段晚三叠世高分馏I型梨园塘花岗岩的新资料。锆石U-Pb测年结果表明，花岗岩侵位时间为210.1 ± 1.9Ma，单颗粒锆石中含有继承核，其年龄为449.8 ± 7.1Ma。来自花岗岩的岩浆锆石的εHf（t）值为− 4.0至+ 1.5，而继承锆石核的εHf（t）值为− 5.3。计算的地壳形成的Hf模式年龄表明，从1501至1155 Ma的年龄范围内的元古代地壳熔融的实质性贡献。该花岗岩富含Si、Al、Na、K，富Rb、Th、U，Rb/Sr、Ga/Al比值升高，亏损Ti、Fe、Mn、Mg、Ca、P，具明显的Eu负异常（δEu = 0.33-0.50），与其它高度分馏的I型花岗岩相似。这些数据表明，形成梨园塘岩体的岩浆是在部分熔融的元古代石榴子石不石英斜长角闪岩。岩浆在侵位前对磷灰石、长石、含钛相、黑云母和角闪石进行了分馏，测得矿化年龄为200.9 ± 6.2Ma，表明梨园塘钼存款形成于一次未被认识的成矿事件中。结合前人的研究成果，认为南秦岭次带第二次岩浆活动中的高分异I型花岗岩具有很好的找矿前景，重点是三叠纪-早侏罗世花岗岩类。
We present new data on the highly fractionated Late Triassic I-type Liyuantang granite, which is located in the middle segment of the South Qinling Subzone of central China and is associated with molybdenum mineralization. Zircon U–Pb dating indicates that the granite was emplaced at 210.1 ± 1.9 Ma, with a single zircon containing an inherited core that yielded an age of 449.8 ± 7.1 Ma. Magmatic zircons from the granite haveεHf(t) values of − 4.0 to + 1.5, whereas the inherited zircon core has aεHf(t) value of − 5.3. Calculated Hf model ages of crust formation are indicative of substantial contributions from melting of Proterozoic crust that ranges in age from 1501 to 1155 Ma. The granite contains high concentrations of Si, Al, Na, and K, is enriched in Rb, Th, and U, has elevated Rb/Sr and Ga/Al ratios, and is depleted in Ti, Fe, Mn, Mg, Ca, and P, with significantly negative Eu anomalies (δEu = 0.33–0.50), similar to other highly fractionated I-type granites. These data indicate that the magmas that formed the Liyuantang pluton were produced during partial melting of Proterozoic garnet-absent quartz amphibolites. The magmas then fractionated apatite, feldspar, Ti-bearing phases, biotite, and hornblende prior to emplacement.Re–Os isotope analysis of molybdenite from the study area yields a mineralization age of 200.9 ± 6.2 Ma, suggesting that the Liyuantang molybdenum deposit formed during a previously unrecognized mineralization event. The present results, together with previous data, demonstrate that highly fractionated I-type granites associated with the second pulse of magmatism in the South Qinling subzone should be considered highly prospective for mineral exploration, focusing on Triassic–Early Jurassic granitoids.