对湖南中生代邓阜仙岩体进行了LA-ICP-MS锆石U-Pb定年和岩石学、岩石地球化学分析.获得斑状黑云母花岗岩的锆石U-Pb年龄为225.1±1.2Ma,表明其形成于晚三叠世,结合已发表的岩体年龄资料,邓阜仙岩体是侵位于印支期(222.9~225.7Ma)和燕山期(151.1~159Ma)的复式岩体.邓阜仙岩体印支期、燕山期花岗岩均具有高的SiO2含量、高的A/CNK值,含过铝质白云母、堇青石等矿物.富集大离子亲石元素Rb、Th、U,明显亏损Nb、Ba、Sr、Ti,稀土元素配分模式为右倾,轻稀土元素富集,Eu亏损相对明显.邓阜仙岩体具低的εNd(t)值,176Hf/177Hf值小于球粒陨石的值.综上认为,邓阜仙岩体印支期、燕山期为S型花岗岩,源区分别为古元古代地壳贫粘土质岩石、富粘土质岩石部分熔融.研究区印支期、燕山期花岗岩均形成于伸展构造体制下,印支期花岗岩形成于印支运动碰撞后的伸展环境,燕山期花岗岩则在太平洋板块俯冲消减作用下形成.%In this paper, the authors analyzed LA-ICP-MS zircon U-Pb dating, petrology and petro- geochemistry of Mesozoic Dengfuxian pluton in Hu'nan Province. The zircon U-Pb age is 225.1±1.2Ma for granodiorite, which suggests that it was formed in Late Triassic. Combined with the age data available, the authors hold that Defuxian pluton is complex rock which intruded in Indo-sinian(222.9~225.7Ma)and Yanshanian(151.1~159Ma). Granites in Indosinian and Yanshanian Dengfuxian pluton all have high content of SiO2 and high ratios of A/CNK and contain para-aluminous muscovite and cordierite mineral. In terms of trace elements, large ion element Rb, Th, U are rich , whereas Nb , Ba, Sr, Ti are poor obviously. The REE distribution patterns exhibit right devia-tion, with rich light rare earth elements and relatively poor Eu. As for isotopes, Dengfuxian pluton has low values of εNd(t), and the ratios of 176Hf/177Hf are lower than the ratio of chondrite (0.282772). In combination with the above-mentioned characteristics and by means of (87sr/86Sr)i-εNd(t) discrimination, the authors consider that the granites in Indosinian and Yanshanian Dengfuxian pluton are of S-type granites, and the source area was formed by partial melting of crustal argillaceous-poor pluton in the region in Paleo-proterozoic and argillaceous-rich pluton. It is considered that the granites in Indosinian and Yanshanian Dengfuxian pluton were formed under the extended tectonic regime, and the granites in Indosinian intruded in the extension setting after the collision of Indo-sinian movement, whereas the granites in Yanshanian period were formed by the subduction of Pacific plate.
展开▼
