西准噶尔包古图Ⅰ号岩体的锆石U-Pb年代学和地球化学特征

Geochronology and Geochemistry in Pluton Ⅰ in Baogutu Area,West Junggar

西准噶尔包古图地区发育一些小型的闪长质岩体。前人对这些小岩体开展了岩石学、年代学和地球化学等研究,然而,其成因机制和构造背景仍然存在争议,阻碍了区域构造演化和成矿作用的认识。本文在前人研究的基础上,选择包古图I号岩体为研究对象,有望揭示包古图岩体的岩石成因和构造背景。锆石U-Pb年代学研究显示,包古图I号岩体形成于(313.8±1.1)Ma。包古图I号闪长岩体以富SiO_2(58.0%~59.0%)、Al_2O_3(16.6%~17.4%)和Sr(757×10^(-6)~882×10^(-6)),低的Y(14.6×10^(-6)~15.7×10^(-6))和Yb(1.51×0^(-6)~1.60×0^(-6))质量分数为特征,具有高的Sr/Y(50~59)值和弱的Eu异常,类似于俯冲成因的埃达克岩。另外,这些闪长岩具有较高的Mg(w(MgO)=3.46%~3.77%,Mg#=52.8~53.2),高的Cr(63.8×10^(-6)~74.7×10^(-6))和Ni(45.2×10^(-6)~49.8×10^(-6))质量分数,亏损HFSE(Nb,Ta和Ti)。该闪长质岩体可能由俯冲的板片熔体与上覆地幔相互作用而成。它的形成可能与西准噶尔地区晚石炭世的洋脊俯冲作用有关。

Some small-size dioritic plutons widely occur in the Baotutu area, west Junggar. The petrology, geochronology and geochemistry of thse plutons had been researched, while their petrogenesis and tectonic setting still existed controversy, which restricts the knowledge of the tectonic evolution and mineralization. To reveal the petrogenesis and tectonic setting of Baogutu dioritic plutons during Late Caberniferious, on basis of previous researches, this paper chooses pluton I in the Baogutu area as research subjects. The LA- ICP- MS zircon U- Pb for dioritic pluton I yield 206Pb/238U age of （313.8±1.1）Ma. The dioritic pluton is characterized by relatively high SiO2 （58.0%-59.0%）, Al2O3 （16.6%-17.4%）, Sr （（757-882）×10^-6）, and low Y （（14.6 -15.7））×10^-6） and Yb （（1.51 -1.60）×10^-6） contents, with high Sr/Y （50 -59） ratios and slight Eu anomalies, which are analogous to those of slab-derived adakites. In addition, the dioritic pluton is relatively rich in MgO （MGO=3.46%-3.77% ; Mg#=52.8 - 53.2）, Cr （（63.8 - 74.7 ）×10^-6）, Ni （（45.2 - 49.8）×10^-6）, with negative Nb- Ta - Ti anomalies. The dioritic pluton is generated by partial melting of a subducted oceanic slab and subsequent melt-mantle interaction, The formation of the adakitic pluton in the Baogutu area was probably associated with the ridge subduction during Late Carboniferous period.