东昆仑祁漫塔格东段晚二叠世-早侏罗世侵入岩岩石组合时空分布、构造环境的讨论

Spatial and temporal distribution of Late Permian-Early Jurassic intrusion assemblages in eastern Qimantag,East Kunlun,and their tectonic settings

祁漫塔格地区是青藏高原北部最重要的多金属矿集区,晚二叠世-早侏罗世岩浆作用与成矿作用关系密切,以祁漫塔格东段为研究区分析讨论了祁漫塔格及临区晚二叠世-早侏罗世花岗岩特点,从晚二叠世-早侏罗世可以识别出4个阶段5个花岗岩组合。（1）晚二叠世弱过铝质高钾钙碱性系列二长花岗岩＋正长花岗岩组合与偏铝质-弱过铝质钙碱性系列英云闪长岩＋花岗闪长岩组合,LA-ICP-MS U-Pb年龄在252.0~258.5Ma,普遍含暗色铁镁质微粒包体;（2）中三叠世闪长岩＋英云闪长岩＋花岗闪长岩＋（二长花岗岩）组合,LA-ICP-MS U-Pb年龄在226.9~238.6Ma,富含暗色铁镁质微粒包体,为偏铝质-弱过铝质钙碱性-高钾钙碱性系列岩石,Sr含量一般在400×1^0-6~537×10^-6,δEu在0.67~0.95;（3）晚三叠世石英闪长岩＋英云闪长岩＋花岗闪长岩＋二长花岗岩组合,LA-ICP-MS U-Pb年龄在211.7~214.1Ma,为偏铝质高钾钙碱性系列岩石,Sr含量一般在341×10^-6~515×10^-6,δEu在0.69~0.95之间;（4）晚三叠世-早侏罗世正长花岗岩组合,LA-ICP-MS U-Pb年龄在199.5~204.4Ma,为偏铝质高钾钙碱性系列岩石,Sr含量在54×10^-6~195×10^-6。晚二叠世花岗岩组合为大陆边缘弧火成岩构造组合,与古特提斯洋俯冲相关;中三叠世花岗岩组合出露面积巨大,构成了印支期北昆仑岩浆弧的主体,形成于俯冲-碰撞转换阶段,与俯冲岩石圈板片的断离相关,这一事件在东昆仑具有普遍意义,是东昆仑造山带最具规模的地幔物质注入与壳幔岩浆混合事件,晚三叠世花岗岩组合形成于后碰撞阶段,是加厚陆壳底部幔源玄武质岩浆底侵作用的结果。

Qimantage area in northern Qinghai-Tibet Plateau is the most important polymetallic ore accumulated area in China.Mineralization is closely related to magmatism and four stages of five granite assemblages have been distinguished during Late Permian to Early Jurassic in the eastern Qimantage and around area：（ 1） Late Permian monzogranite ＋ syenogranite assemblage,belongs to weakly peraluminous K calc-alkaline series and tonalite ＋ granodiorite assemblage belongs to partial aluminum-weakly peraluminous calc-alkaline series with U-Pb ages of 252. 0 ~ 258. 5Ma（ LA-ICP-MS）,generally contains mafic microgranular enclaves（ MME）.（ 2） Middle Triassic diorite ＋ tonalite ＋ granodiorite ＋（ monzogranite） assemblage with U-Pb ages of 226. 9 ~ 238. 6Ma（ LA-ICP-MS）,also rich in dark mafic enclaves,belongs to the partial aluminum-weakly peraluminous calc-alkaline-K calc-alkaline series,with Sr content at 400 × 10^- 6~ 537 × 10^- 6,δEu at 0. 67 ~ 0. 95.（ 3） Late Triassic quartz diorite ＋ tonalite ＋ granodiorite ＋ monzogranite assemblage,with U-Pb ages of 211. 7 ~ 214. 1Ma,belongs to the partial aluminum-high K calc-alkaline series,Sr content is generally at 341 × 10^- 6~ 515 × 10^- 6,δEu rangs in 0. 69 ~ 0. 95.（ 4） Late Triassic-Early Jurassic syenogranite assemblage,the partial aluminum-high K calc-alkaline series,with U-Pb ages of 199. 5 ~ 204. 4Ma,Sr content of 54 × 10^- 6~ 195 × 10^- 6. Late Permian granite assemblage formed in continental margin arc setting,probably due to the Paleo-Tethys subduction. Middle Triassic granites are widely exposed,constitute the main body of Indo magmatic arc in the North Kunlun,formed in subduction-collision conversion stage due to the lithospheric subduction slab break-off. This event has universal significance in the East Kunlun orogenic belt,exhibiting the extensive mantle material injection and crust-mantle magma mixing. The Late Triassic granites formed in the post-collision setting,the production of the mantle-derived basaltic magma underplating from bottom of the thickened continental crust.