郯庐断裂带巢湖—庐江段晚中生代火山岩的锆石U-Pb年代学  

Zircon U-Pb geochronology of the Late Mesozoic volcanic rocks from the Chaohu-Lujiang segment of the Tan-Lu fault zone

作　　者：谢成龙[1] 朱光[1] 牛漫兰[1] 王勇生[1] 向必伟[1] 胡召齐[1] 

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009

出　　处：《地质科学》2008年第2期294-308,共15页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金(批准号:40672131;40603010和90714004)资助项目

摘　　要：采用LA-ICP-MS方法对郯庐断裂带巢湖-庐江段的晚中生代火山岩进行了锆石U-Pb年代学研究。由6个样品获得的该处火山喷发时间在距今125-93Ma,为早白垩世晚期至晚白垩世初期,经历了32Ma的喷发历史。与附近的庐枞盆地、北大别造山带及北淮阳地区相比,该地火山喷发具有较晚的结束时间,说明岩石圈减薄具有相对强烈的程度和较长的持续时间。93Ma是已知的华北克拉通残留富集岩石圈地幔最晚的岩浆岩年代学记录。锆石的饱和温度计算、岩浆中较低的MgO含量和Mg^#值均不支持岩浆由拆沉的下地壳部分熔融形成,岩浆活动的可能成因是壳幔相互作用,岩浆源区具有由幔源向壳源再过渡到幔源的时间演化顺序。这暗示断裂带下强烈的软流圈上涌引起岩石圈地幔的熔融（距今125Ma）,随后岩石圈持续的减薄作用导致其内部热流升高,出现了以流纹岩为代表的地热异常背景下地壳源区的部分熔融（距今120Ma）,而最终岩石圈强烈减薄背景下的软流圈物质参与岩浆过程可能是晚期幔源岩浆（距今93Ma）的成因。LA-ICP-MS zircon U-Pb geochronology studies were carried out on the Late Mesozoic volcanic rocks from the Chaohu-Lujiang segment of the Tan-Lu fault zone. The eruption ages acquired by 6 samples ranged from 125 Ma to 93 Ma, namely, from late Early Cretaceous to the earliest Late Cretaceous, and the volcanic eruption elongated for about 32 Ma. The terminal time of the eruption in the area was later compared with neighbouring regions such as the Luzong Basin, the North Dabie orogen and the North Huaiyang belt, which indicated a longer extension along the Tan-Lu fault zone, and a more intensive lithospherie thinning. The age of 93 Ma might be the youngest magmatic record as known on residual enriched mantle of the North China Craton. Zircon saturation thermometry and the low content of MgO, Mg^# didn＇t support the model of lower crust delamination, while crust-mantle interaction might be a reasonable in- terpretation for magma formation. Magma sources varied from mantle to crust and then to mantle again, which hinted that intense asthenosphere upwelling beneath the fault zone caused lithospheric mantle partial melting （125 Ma ago）, then incessant lithospheric thinning conduced heat flow increasing followed by crustal partial melting indicated by occurrence of rhyolite （120 Ma ago）, and the participating of asthenosphere mass in the terminal magma （93 Ma ago） being a reason for its mantle source.

关 键 词：锆石 U-PB年代学 火山岩 岩石圈减薄 巢湖-庐江 郯庐断裂带 

分 类 号：P597.3[天文地球—地球化学]