| 扬子北缘大洪山地区早古生代基性岩脉的厘定及其地质意义 |
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| 引用本文： | 陈超,苑金玲,孔令耀,叶竹君,杨青雄,杨成,周峰.扬子北缘大洪山地区早古生代基性岩脉的厘定及其地质意义[J].地球科学,2018,43(7):2370-2388. |
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| 作者姓名： | 陈超 苑金玲 孔令耀 叶竹君 杨青雄 杨成 周峰 |
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| 作者单位： | 1.湖北省地质调查院, 湖北武汉 430034 |
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| 基金项目： | 中国地质调查局项目121201009000160902湖北省地质局科技项目KJ2018-1 |
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| 摘 要： | 扬子北缘大洪山地区广泛出露北西-南东向基性岩脉，脉体主要侵位于区内前南华系基底砂板岩、白云岩中，而南华系及上覆盖层中少见.长期以来，这套基性侵入岩的形成时代和背景都存在疑问.通过对七里冲、姚家咀、姚家冲、刘关4个地区的基性岩脉进行锆石LA-ICP-MS U-Pb测年，获得成岩年龄分别为433.7 Ma、435.6 Ma、433.4 Ma、436.4 Ma，这些年龄值在误差范围内一致，同属于早志留世，为大洪山地区这期基性岩脉提供了精确的同位素年代学依据.地球化学方面，大洪山地区基性岩脉表现为亚碱性系列的特点，较高∑REE含量，轻、重稀土存在分异，富集LILEs而亏损HFSEs，Zr > 100×10-6，TiO2 > 2%，Zr/Y > 3.5，指示其形成于大陆伸展环境.首次在扬子地块北缘识别出一套早古生代晚期代表大陆伸展环境的基性岩脉，为扬子地块北缘大洪山地区存在早古生代近北东向的区域伸展提供强有力的证据.研究表明，早古生代秦岭-大别南缘和扬子地块北缘虽然在沉积上地层存在差异，但可能同属于扬子北缘陆缘裂谷拉张环境.
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| 关 键 词： | 扬子北缘 基性岩脉 早古生代 锆石U-Pb测年 地球化学 |
| 收稿时间： | 2018-03-31 |
Documentation of Early Paleozoic Mafic Dykes in the Dahongshan Region,Northern Yangze Block and Its Geological Significance |
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| Abstract: | NE-SW mafic dykes are widespread in the Dahongshan region, northern Yangtze block. They mainly emplaced the pre-Nanhua basement rock, e.g. dolomite, sandstone and slate, and scarcely found in Nanhuan system and its overlying strata. It has been controversial for their formation age and background of the mafic dykes for a long time. In this paper, LA-ICP-MS zircon dating for 4 mafic dykes from Qilichong, Yaojiaju, Yaojiachong and Liuguan yield U-Pb ages of 433.7 Ma, 435.6 Ma, 433.4 Ma and 436.4 Ma respectively. All the ages belong to the Early Silurian and are consistent within measuring errors, and offer precise isotope chronology to the mafic dykes in the Dahongshan region. The mafic dykes in the Dahongshan region are characterized by subalkalic series, high ∑REE content, medium differentiation between LREE and HREE, enriched LILEs and depleted HFSEs, Zr > 100×10-6, TiO2 > 2%, and Zr/Y > 3.5. Accordingly, it is suggested that they may have formed in a continental extension environment. We have discerned Early Paleozoic mafic dykes swarm indicative of continental extension in the northern Yangtze block for the first time. It provides powerful evidence that the Dahongshan region in the northern Yangtze block shows NE regional extension. Additionally, we tentatively thought that the south Qinling-Dabie mountain and the north Yangtze block belong to same extensional epicontinental rift environment although different sedimentary strata appeared between them in Early Paleozoic. |
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