青海省都兰县八道班一带晚三叠世侵入岩岩石地球化学特征及构造环境

Geochemical characteristics and tectonic environment of Late Triassic intrusive rocks along Badaoban area, Dulan County, Qinghai Province

青海省都兰县八道班一带侵入岩的岩性为石英闪长岩至正长花岗岩的岩浆演化序列,其空间具有北西-南东向带状分布的特点,为准铝质、高钾、钙碱性镁质花岗岩;稀土总量REE中等,轻重稀土分异和轻稀土分馏强烈;大离子亲石元素（LILE）Rb、K等相对富集,Ba、Sr等相对亏损;高场强元素（HFSE）Th、Hf等相对富集,Nb、Ta、Ti等相对亏损,且由石英闪长岩→花岗闪长岩→二长花岗岩→正长花岗岩演化,相对富集和相对亏损的程度逐渐增强;源岩以壳源为主,亦有幔源物质加入,属壳-幔混合型花岗岩.岩石具“C”型高硅埃达克岩特征.其锆石U-Pb同位素年龄在237～224 Ma之间,侵位时代为晚三叠世;其成因是印支晚期西秦岭构造单元向柴达木东南缘斜向俯冲的产物.本区发现埃达克质岩对于与埃达克岩有关斑岩铜矿成矿规律的研究和找矿意义重大.

The lithology of intrusive rocks along Badaoban area, Dulan County, Qinghai province is magmatic rock evolutionary sequence from quartz-diorite to syenogranite. The intrusive rocks are prospective aluminum, high potassium, calc-alkaline magnesia granites, which space characteristics is Northwest - Southeast banding distri- bution. REE is medium, light and heavy rare earths are different and light rare earth fraction strongly; LILE elements like Rb, K are relatively enriched, Ba, Sr are relatively depleted; HFSEs like Th, Hf are relative enrichment, Nb, Ta, Ti are relatively depleted. The relative degree of enrichment and deficit from quartz-diorite, granodiorite to adamellite, syenogranite is gradually increased. The main source rocks are crust, also have mantle-derived material, which belongs to crust-mantle mixing-type granites. Rocks have ＂C＂ type high silicon adakite fea- tures. Their Zircon U-Pb isotopic ages are between 237 - 224 Ma, emplacement ages are Late Triassic; those rocks are products of west Qinling tectonic unit obliquely dive to the southeastern margin of the Qaidam during late Indosinian. Adakitic rocks found in this area are of great significance to research of porphyry copper mineralization law and prospecting that related to adakites.