Zircon LA-ICP-MS U-Pb dating and Sr-Nd isotope study of the Guposhan granite complex, Guangxi, China
Zircon LA-ICP-MS U-Pb dating and Sr-Nd isotope study of the Guposhan granite complex, Guangxi, China
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DOI：
10.1007/s11631-007-0290-5
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发表时间：
2007-08
期刊：
影响因子：
--
通讯作者：
S. Gu;Renmin Hua;Huawen Qi
中科院分区：
文献类型：
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作者：
S. Gu;Renmin Hua;Huawen Qi
采用LA-ICP-MS法对姑婆山花岗杂岩体的不同单元进行了锆石U-Pb定年，其中姑婆山东单元为160.8± 1.6Ma，姑婆山西单元为165.0± 1.9Ma，李松单元为163.0± 1.3Ma。这三个单元的时代非常相似，证明了整个姑婆山花岗岩杂岩形成于同一时期。它们是华南燕山中期第一阶段大规模花岗质岩浆作用经地壳重熔的产物。然而，这三个单元在岩石学和地球化学方面都有差异。除主量元素、微量元素和稀土元素存在差异外，Rb-Sr和Sm-Nd同位素组成也存在差异。姑婆山东单元和李沧单元及其包体具有相似的（87 Sr/86 Sr）i值为0.7064，平均Nd（t）=-3.03，说明岩浆演化过程中有较多的地幔物质演化;而姑婆山西单元具有较高的（87 Sr/86 Sr）i值为0.7173，但Nd（t）值较低，为-5.00，具有强烈的Eu负异常和较高的Rb/Sr比值，表明其源区物质由相对古老的地壳组分和新的幔源组分组成。此外，姑婆山东单元（GP-1）的一个继承锆石颗粒获得806.4Ma的206 Pb/238 U年龄，与HZH花岗岩带中的江西北方九林堇青石花岗岩和广西银桥混合花岗岩的年龄相近。这为HZH花岗岩带晚元古代岩浆活动提供了新的证据。
Zircon U-Pb dating by the LA-ICP-MS method was applied to determining the ages of different units of the Guposhan granite complex, among which the East Guposhan unit is 160.8±1.6 Ma, the West Guposhan unit is 165.0±1.9 Ma, and the Lisong unit is 163.0±1.3 Ma in age. Much similarity in ages of the three units has thus proved that the whole Guposhan granite complex was formed in the same period of time. They were the products of large-scale granitic magmatism through crust-remelting in the first stage of the Middle Yanshanian in South China. However, the three units have differences both in petrology and in geochemistry. Besides the differences in major, trace and rare-earth elements, they are distinct in their Rb-Sr and Sm-Nd isotopic compositions. The East Guposhan unit and Lisong unit and its enclaves have a similar (87Sr/86Sr)ivalue of 0.7064 with an average of ɛNd(t)=−3.03, indicating that more mantle material was evolved in the magma derivation; whereas the West Guposhan unit has a higher (87Sr/86Sr)ivalue of 0.7173 but a lower ɛNd(t) value of −5.00, and is characterized by strong negative Eu anomalies and higher Rb/Sr ratios, suggesting that its source materials were composed of relatively old crust components and new mantle-derived components. In addition, an inherited zircon grain in the East Guposhan unit (GP-1) yielded a206Pb/238U age of 806.4 Ma, which is similar to the ages of the Jiulin cordierite granite in northern Jiangxi and of the Yinqiao migmatic granite in Guangxi in the HZH granite zone. All this may provide new evidence for Late Proterozoic magmatism in the HZH granite zone.