新疆东天山彩中花岗岩体锆石SHRIMP年龄及地球化学特征

Zircon SHRIMP Age and Geochemistry of Caizhong Granite from East Tianshan, Xinjiang,China

对新疆东天山康古尔塔格地区彩霞山一带的彩中岩体黑云母二长花岗岩进行了SHRIMP锆石U-Pb定年、主量和微量元素、Nd-Sr同位素研究。锆石206Pb/238U比值平均加权年龄为316±4(2σ)Ma,表明彩中岩体形成于石炭纪中期,因而修正了前人关于“早二叠世晚期侵入体”的时代划分方案。岩体的主、微量元素研究表明,彩中岩体为铝弱过饱和型钙碱性系列花岗岩,形成于岛弧环境。彩中黑云母二长花岗岩具有高的εNd(t)值(+8.5^+7.4)和低的87Sr/86Sr同位素比值(ISr=0.7034~0.7036),表明其物质来源为亏损的地幔源区。低的Nd模式年龄(TDM=0.38~0.47Ga),暗示其源区物质基本上未受到古老大陆地壳物质的混染。上述特征表明彩中花岗岩与东西准噶尔造山带的花岗岩类有可比性。

SHRIMP U-Pb age for zircons, major and trace elements and Nd-Sr isotopic compositions for biotite monzonitic granite of Caizhong in Kangguertage area in eastern Tianshan of the Xinjiang are studied in this paper. A^206pb/238U weighted mean age of 316 ± 4（2σ） Ma for zircons was gained, presenting the time of emplacement of the Caizhong biotite monzonitic granite. This result indicates that the Caizhong biotite monzonitic granite was formed during early period of Late Carboniferous, which modified uncertainty age that considered Caizhong granite as a intrusion of late of Early Permian. Based on analyms of major and trace elements, Caizhong granite has characteristics of metaluminous and talc-alkaline granite, showing their formation in island arc setting. The Caizhong granite has high values of εNd （ t ） from ＋ 8.5 to ＋ 7.4 and low ^87Sr/^86 Sr ratios （ Isr=0. 7034～0. 7036）, implying its protolith derived from depleted mantle source. Younger Nd model ages of TOM from 0.38 to 0.47 Ga suggest that source of its protolith scarcely was contaminated by older crustal materials. Summarized all results, it is indicated that the Caizhong granite has characteristics as similar as those of granites from the eastern and western Junggar orogen.