| 江西相山铀矿田中西部鹅湖岭组与打鼓顶组碎斑流纹岩特征对比及其成因探讨 |
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| 引用本文： | 田明明,李子颖,聂江涛,刘军港,王健,曹建辉.江西相山铀矿田中西部鹅湖岭组与打鼓顶组碎斑流纹岩特征对比及其成因探讨[J].地球科学,2021,46(12):4546-4561. |
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| 作者姓名： | 田明明 李子颖 聂江涛 刘军港 王健 曹建辉 |
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| 作者单位： | 核工业北京地质研究院,北京 100029 |
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| 基金项目： | 相山大型铀矿田科学钻探Ⅱ期铀多金属深部探测研究地HXS1403 |
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| 摘 要： | 以在相山中西部钻孔中揭露到的鹅湖岭组和打鼓顶组碎斑流纹岩为研究对象，从岩石矿物学、岩石地球化学、LA-ICP-MS锆石U-Pb年代学和Hf同位素等方面对比研究了这两套碎斑流纹岩.结果显示其矿物学组成较为接近，且具有相似的岩石地球化学特点，岩石富硅、高K2O低Na2O、低MgO；稀土元素配分曲线形态总体一致，均为富集轻稀土的右倾式，鹅湖岭组碎斑流纹岩Eu负异常更为明显，指示其可能经历了更高程度的斜长石结晶分离作用，或源区残留有更多的斜长石；打鼓顶组碎斑流纹岩轻重稀土分馏更为明显，可能与源区岩浆中的榍石、褐帘石和独居石含量有关；蛛网图上显示K、Ba、Sr等大离子亲石元素和Nb、Ti、P等高场强元素亏损，而Rb、Th、Nd等富集的特点.这些相似的岩石地球化学特征暗示两套碎斑流纹岩之间具有一定的同源性.锆石U-Pb测年结果显示鹅湖岭组与打鼓顶组碎斑流纹岩年龄分别为132.4±0.7 Ma和131.9±0.8 Ma；通过计算测得鹅湖岭组碎斑流纹岩εHf（t）为-9.5~-4.5，两阶段模式年龄tDMC为1 470~1 787 Ma，打鼓顶组碎斑流纹岩εHf（t）为-14.2~-8.1，两阶段模式年龄tDMC为1 704~2 087 Ma.以上岩石矿物学特征、岩石地球化学特征、锆石U-Pb年龄及Hf同位素特征表明鹅湖岭组与打鼓顶组碎斑流纹岩具有一定的相似性，但同时又有差别，结合前人研究资料，认为鹅湖岭组和打鼓顶组碎斑流纹岩的形成可能具有同源性，二者均是在早白垩世弧后拉伸环境背景下，主要由古元古代-中元古带基底变质岩部分熔融而形成，可能伴随有不同程度的地幔物质的加入.
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| 关 键 词： | 碎斑流纹岩 岩石地球化学 锆石U-Pb年龄 锆石Hf同位素 相山铀矿田 |
| 收稿时间： | 2020-02-22 |
A Comparative Study and Its Genesis of Porphyroclastic Rhyolite from Ehuling and Daguding Formations in Midwestern of Xiangshan Uranium Orefield,Jiangxi Province |
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| Abstract: | Porphyroclastic rhyolites of Ehuling and Daguding formations were taken as the research objects in this paper, which was sampled from the boreholes in the midwestern parts of Xiangshan uranium orefield. A comparative study of porphyroclastic rhyolite from these two formations were carried out by means of petromineralogy, lithogeochemistry, U-Pb geochronology and Hf isotopes. The results illustrate that the mineralogical composition and lithogeochemical characteristics of porphyroclastic rhyolite from Ehuling and Daguding formations are relatively semblable, the rock enriching Si and K2O, low Na2O and MgO. Chondrite normalized REE curves are generally consistent, showing right-inclined type with enriched LREE. The samples from the Ehuling Formation demonstrate more intensive Eu negative anormaly, indicating that a high degree of crystallizational fractionation of plagioclase was occured, or more plagioclase residued in source area. While the high fractional degree of LREE and HREE of Daguding porphyroclastic rhyolite is likely related to the high contents of secondary minerals, such as titanite, epidoite and monazite. Primitive mantle-normalized spider diagram shows depletion of lithophile elements (K, Ba, Sr) and high field strength elements (Nb, Ti, P), and enrichment of Rb, Th, Nd. These similar petrogeochemical characteristics suggest a certain homology between Ehuling and Daguding porphyroclastic rhyolite. Zircon U-Pb dating results indicate that the age of porphyroclastic rhyolite from Ehuling Formation and Daguding Formation are 132.4±0.7 Ma and 131.9±0.8 Ma respectively. The εHf(t) of porphyroclastic rhyolite of Ehuling Formation is (-9.5)-(-4.5), and the two-stage Hf model age is 1 470-1 787 Ma; while the εHf(t) of porphyroclastic rhyolite of Daguding Formation is (-14.2)-(-8.1), and the two-stage Hf model age is 1 704-2 087 Ma. The above petromineralogy, lithogeochemistry, zircon U-Pb age and Hf isotope characteristics show that the porphyroclastic rhyolite of Ehuling Formation and the Daguding Formation have certain similarities, but at the same time, some differences exist. Combined with previous research data, a conclusion can be drawn, the formation of two sets of porphyroclastic rhyolite maybe homologous, both of them are derived from the partial melting of Paleoproterozoic-Mesoproterozoic metamorphic rock basement under the background of Early Cretaceous regional extensional environment, and may be accompanied by the merging of mantle material in a certain degree. |
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