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南秦岭随州地区正长花岗岩锆石SHRIMPU-Pb年代学与地球化学特征 预览 被引量:1

Zircon SHRIMP U-Pb Age and Geochemical Characteristics of Syenogranite in the Suizhou Area, South Qinling
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摘要 随州北部正长花岗岩体呈岩脉出露,年代学研究表明,正长花岗岩中岩浆锆石SHRIMP U-Pb加权平均年龄为648.8±1.9Ma(MSWD=0.86),属新元古代。岩石地球化学成分显示其属于高钾钙碱性、准铝质系列花岗岩。岩体高硅(SiO2=70.67%-75.75%)、富碱(K2O+Na2O=7.28%-8.53%)、铁镁比(FeOT/MgO=26.37-35.50)较高、钙镁含量较低(CaO=0.60%-1.53%,MgO=0.07%-0.12%);稀土元素配分曲线呈右倾斜型,显示Eu负异常(δEu=0.33-0.56);1000Ga/Al值介于2.60-3.41,Zr+Nb+Ce+Y=552.48×10^-6-648.87×10^-6;微量元素原始地幔标准化蛛网图显示,Rb、K和Th等大离子亲石元素明显富集,相对富集Zr、Hf、Nb、Ta等高场强元素,相对亏损Sr、P和Ti,以上特征表明随州北部正长花岗岩为A1型花岗岩。结合区域构造演化,认为随州北部正长花岗岩形成于板内伸展的构造环境,新元古代晚期,秦岭-桐柏-大别地区构造体制经历了重要的转变,在南秦岭东段由古秦岭洋的俯冲导致的挤压作用转换为弧后拉伸减薄作用。在伸展体制下,岩浆上涌形成本区A1型正长花岗岩。 Located in the north of Suizhou, syenogranite occurs in diabase as vein-like, and strikes NW--SE direction. SHRIMP U-Pb dating yields a weighted mean 206Pb/238U age of 648.8±1.9 Ma (MSWD=0.86) for the zircons from syenogranite, indicating that syenogranite belongs to Neoproterozoic. Lithochemical analysis shows that syenogranite is slightly metaluminous and belongs to the high-K calc-alkaline series. The syenogranite is characterized by high SiO2 (70.67 % - 75.75%), high alkali (K2O+Na2O= 7.28 %- 8.53%), high FeOT/MgO (FeOT/MgO=26.37-35.50), low CaO (0.60%-1.53%) and MgO (0.07% -0.12%) contents. Chondrite-normalized REE patterns of the syenogranite are characterized by weakly HREE depletion with Eu anomalies (δEu=0.33-0.56). The values of 1000Ga/Al and Zr+Nb+Ce+Y range from 2.60 to 3.41 and from 552.48 ×10^-6 to 648.87 × 10^-6 , respectively. The spider diagram of the trace elements shows the enrichment of large-ion lithophile elements (Rb, K, Th, etc), relative enrichment of high field strength elements (Zr, Hf, Nb, Ta), relative depletion of Sr, P and Ti. All these features above suggest that syenogranite belongs to Al-type granite. Combined with the regional tectonic evolution, it can be concluded that syenogranite formed in a regional extensional setting. During the Neoproterozoic, the tectonic regime in the Qinling-Tongbai-Dabie area changed from compression to extension, under which the upwelling magma resulted in the formation of the Al-type syenogranite.
作者 王东升 王宗起 武昱东 王刚 张玉涛 WANG Dongsheng, WANG Zongqi, WU Yudong, WANG Gang, ZHANG Yutao( MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, CAGS, Beijing , 100037)
出处 《地质学报》 CSCD 北大核心 2017年第5期1007-1021,共15页 Acta Geologica Sinica
基金 本文为国家自然科学基金项目(编号41402180)和国土资源部中国地质调查局项目(编号12120113069000)资助成果.
关键词 随州 A1型花岗岩 地球化学 SHRIMP U-PB测年 新元古代 Suizhou Al-type syenogranite geochemistry zircon SHRIMP U-Pb dating Neoproterozoic
作者简介 王东升,男,1988年生。助理研究员,构造地质学专业。Email:wangdsyzy@126.com。
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