摘要
高精度LA-ICP-MS锆石U-Pb测年结果表明,黄羊山岩浆混合花岗岩加权平均^(206)Pb/^(238)U年龄为311±12Ma,首次获得闪长质微细粒包体加权平均^(206)Pb/^(238)U年龄为300±6Ma,在误差范围内完全一致,均属于晚石炭世,前者代表黄羊山岩浆混合花岗岩成岩年龄,后者代表暗色闪长质微粒包体的形成年龄,表明两者是同时代形成的,属于300Ma前后准噶尔周边地区后碰撞岩浆活动的产物。岩石地球化学研究表明,寄主岩石具有高硅、低铝、贫钙镁、富碱和高分异的特征,寄主岩石、包体和辉绿岩脉成分均落在了混合趋势线上,寄主岩富集Rb和Th等大离子亲石元素及Zr、Hf等高场强元素,亏损Ba、Sr、Ta和Ti等元素,δEu值(为0.01)极低,具有低的^(87)Sr/^(86)Sr初始比值和高正的ε_(Nd)(t)值。黄羊山碱性花岗岩是在后碰撞拉张的构造背景下,幔源岩浆发生底垫作用,由于幔源岩浆底垫作用,下地壳温度升高而熔融形成酸性壳源岩浆,部分幔源岩浆沿着地壳中的深断裂带上涌,发生不同程度壳幔混合形成的,其中闪长质微细粒包体就是基性的幔源岩浆和酸性的壳源岩浆不同程度的混合的记录者,研究区的辉绿岩脉是幔源岩浆直接分异演化的产物。
High-precision LA-ICP-MS zircon U-Pb dating has revealed that the Huangyangshan pluton in eastern Junggar, northern Xinjiang, was formed at 311 +/- 12Ma, which represents the age of lithogenesis of the Huangyangshan magma mixing pluton, and that microgranular enclaves in the alkaline granite were formed at 300 +/- 6Ma. It' s the first time obtain the microgranular enclaves age in Huangyangshan pluton, which represents the age of the enclaves formed,both ages are very consistent within errors,the time belongs to Late Carboniferous,implying the host rock and its enclaves were formed at the same time,that is the product of post-collisional magma activity around the Junggar area in 300Ma approximately. Petrochemistry and geochemistry researching suggested host rock characteristics of high silicon and enrich alkali,low magnesium,calcium and aluminous,and high differentiation, ingredient of the host rock, microgranular enclaves and diabase dykes project on line of the magma mixing. Host rock enrichment of LILE (such as Rb and Th) and HESE (such as Zr and Hf), depleted of Ba,Sr,Ta and Ti, have lowest delta Eu (0.01), low initial (87)Sr/(86)Sr ratios and high positive epsilon(Nd) (t) values. Huangyangshan magma mixing pluton formed in expansion tectonics setting of post-collisional stage, mantal magma take place underplating, because the underplating of the mantal magma,low crust melt by the high temperature forming the acid crust-magma,part of the mantal magma up to crust along the deep fault belt, the basic magma from mantle and acid one from crust mixing,formed the Huangyangshan magma mixing pluton. The diorite microgranular enclaves are the recorder of the crust and mantal magma mixing process,the diabase dykes in research area is the product from direct differentiation and evolution of the mantal magma.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2009年第12期3197-3207,共11页
Acta Petrologica Sinica
基金
新疆青河、奇台县红柳沟-苏吉泉一带1:5万区域地质矿产调查项目(QD200508)资助
