都庞岭环斑花岗岩的形成时代、成因及其地质意义

发布时间：2018-05-10 18:30

本文选题：环斑花岗岩 + 锆石SHRIMP　；参考：《大地构造与成矿学》2017年03期

【摘要】：以往将位于湘南、桂东北的都庞岭花岗岩基分为西体、中体和东体三部分。野外观察和岩相学研究表明,都庞岭中体和东体主要由黑云母正长花岗岩、黑云母二长花岗岩和二云母二长花岗岩组成,岩石具斑状结构,部分钾长石斑晶呈椭球状至球状,具斜长石环边,构成环斑结构。采用锆石SHRIMP U-Pb法获得都庞岭中体和东体中环斑花岗岩的侵位年龄分别为226.6±6.9 Ma和209.7±3.1 Ma,均属于晚三叠世,相当于印支晚期。都庞岭环斑花岗岩富硅、碱,贫钛、磷、镁和钙,其Rb、Cs、Th、U、REE、Pb、Y含量和Rb/Sr、Rb/Ba比值较高,而Sr、Ba含量和Zr/Hf比值(8.16~25.01)较低,具强烈的Eu负异常(δEu=0.02~0.13),10000×Ga/Al比值(2.64~4.38,平均3.15)高,显示A型花岗岩的地球化学特征。与华南印支早期S型花岗岩相比,都庞岭环斑花岗岩的εNd(t)值(-8.0~-8.3)明显偏高(前者低于-10),而tDM2值(1624~1645 Ma)则明显偏低(前者1800 Ma),表明它们可能直接源于地壳物质的部分熔融,但成岩过程中有地幔物质的参与。都庞岭环斑花岗岩的发现及其时代的确定,揭示了晚三叠世华南东部处于大陆裂解或造山后伸展的构造环境。结合华南东部沉积/岩石大地构造分析,认为华南早中生代构造体制的转换发生在中、晚三叠世,而非前人所认为的发生在中、晚侏罗世;同时,环斑花岗岩的出现,指示了华南中生代大规模成矿作用的来临,晚三叠世是华南中生代大规模成矿的第一个高峰期。
[Abstract]:In the past, the Dupangling granite base, located in the south of Hunan and northeast of Guangxi, was divided into three parts: the west body, the middle body and the east body. Field observations and petrographic studies show that the middle and eastern Dupangling bodies are mainly composed of biotite syenite granite, biotite monzogranite and bigite monzogranite, with porphyry structure, and some potash feldspar porphyry is ellipsoidal to spherical. With plagioclase ring edge to form a ring-spot structure. The emplacement ages of the central and eastern central granitic granites in DuPonling are 226.6 卤6.9 Ma and 209.7 卤3.1 Ma, respectively, obtained by zircon SHRIMP U-Pb method, which belong to the late Triassic and correspond to the late Indosinian period. DuPonling ringlike granites are rich in silicon, alkali, titanium, phosphorus, magnesium and calcium. Their RB ~ (+) C ~ (+) C ~ (1) ~ (+) ~ (10 ~ (10) ~ (10 ~ (10) 脳 Ga/Al) = 2.644.38, with an average of 3.15), and the content of RbC ~ (2 +) and the ratio of RB / Sr ~ (+) ~ (B / Ba) are high, while the ratio of Sr ~ (+) Ba and Zr/Hf is 8.16 ~ 25.01). It has a strong negative EU anomaly (未 -EU _ (0.02N) 0.13 ~ (10 000) ~ (10) 脳 Ga/Al = 2.644.38, average 3.15), which shows the geochemical characteristics of A-type granites. Compared with the early Indosinian S-type granites in South China, the Dupangling ring-macular granite has a significantly higher 蔚 -NdT value (-8.0 ~ 8.3) (the former is lower than -10 ~ (-1), while the tDM2 value of 1624 ~ 1645 Ma) is obviously lower (the former is 1800 Ma ~ (-1), indicating that they may have originated directly from partial melting of crustal material. But the mantle material is involved in the diagenetic process. The discovery and dating of the DuPonling ringed granite reveal the tectonic environment in which the eastern part of South China is located in the continental cleavage or post-orogenic extension in the late Triassic. Based on the analysis of sedimentary / lithotectonics in eastern South China, it is concluded that the transformation of early Mesozoic tectonic systems in South China occurred in the Middle and late Triassic, rather than in the Middle and late Jurassic, and that the occurrence of macular granites occurred in the early Mesozoic in South China. The late Triassic is the first peak of Mesozoic large-scale mineralization in South China.
【作者单位】：武汉地质矿产研究所;中国地质调查局花岗岩成岩成矿地质研究中心;
【基金】：中国地质调查局地质矿产调查评价项目(1212010813061、1212011085405)资助
【分类号】：P588.121

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