囊谦盆地新生代高钾岩浆岩的地球化学特征:岩石成因及其构造意义  

GEOCHEMICAL CHARACTERISTICS OF THE CENOZOIC POTASH-RICH VOLCANIC ROCKS IN NANGQIAN BASIN:PETROGENESIS AND TECTONIC IMPLICATIONS

作　　者：程锦[1] 夏斌[1] 张玉泉[1] 

机构地区：[1]中国科学院边缘海地质重点实验室,中国科学院广州地球化学研究所,广东广州510640

出　　处：《大地构造与成矿学》2008年第3期382-391,共10页Geotectonica et Metallogenia

摘　　要：位于青藏高原东缘的囊谦高钾岩浆岩（37．5～38．3Ma）SiO2含量49．9％-66．6％，富集LREE和LILE（K、Rb、Sr、Ba、Th），亏损HREE和HFSE（Nb、Ta、Ti等），在微量元素蛛网图上Nb、Ta、Ti显示负异常。囊谦富钾岩浆岩的Sr—Nd同位素变化范围窄（87Sr／86Sr=0．70425—0．70548，143Nd／144Nd=0．51256～0．51273），显示出EMI富集趋势。通过对囊谦高钾岩石的元素和同位素地球化学的研究，认为其源区同时受到了因俯冲而进入地幔的地壳物质及蚀变洋壳析出流体的改造和交代作用。这套钾质岩石的形成是受到了特提斯洋俯冲消减，进而印度大陆与欧亚大陆碰撞，以及之后发生的岩石圈由挤压转为拉张并由此产生的软流圈上涌等一系列动力体系的控制。The high-K igneous rocks（37.5 -38.3Ma） in the Nangqian area are distributed along the edge of eastern Tibetan Plateau, of which SiO2 contents range from 49.9% to 66.6%. The high-K igneous rocks are characterized by enrichment in LREE and LILE（K, Rb, Sr, Ba, Th） and depletion in HREE and HFSE（Nb, Ta, Ti）. From a primitive normalized spidergram, the trend of distinctly negative anomalies of Nb, Ta, Ti can be seen. Sr-Nd isotope ratios for potassic igneous rocks in the Nangqian area changes in a narrow scope （87Sr/86Sr = 0. 70425 - 0.70548, 143Nd/144Nd =0.51256-0.51273） , showing the trend of EMI enrichment. Depending on the study on the element and isotope for Nangqian high-K igneous rocks, we think that formation of the mantle source for the rock is related to modification and metasomatism by fluids from dehydration of the subducted continental crust and oceanic crust, and the high-K igneous rocks in the Nangqian area were generated through a series of geodynamical processes ： the subduction and consumption of the Tethyan ocean, Indo-Asian continental collision, the transition in stress state of lithosphere from compression to extension since the Tertiary and upwelling of the asthenosphere.

关 键 词：钾质岩浆岩 地球化学特征 岩石成因 构造意义 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]