内蒙古东部碧流台地区辉长岩锆石U-Pb测年、地球化学特征及其成因

对内蒙古东部碧流台辉长岩进行了岩石学、地球化学与锆石LA-ICP-MS U-Pb测年分析研究.测年结果显示辉长岩形成时代为早三叠世早期（249±2.9 Ma）.岩石地球化学特征显示该辉长岩为一套钙碱性系列岩石：SiO₂含量为46.43%~50.77%，Al₂O₃ 11.27%~16.32%，TiO₂ 0.20%~0.37%；富钠（Na₂>K₂O，K₂O/Na₂=0.18~0.56）；高Mg^#，含量为75.08~78.93；轻重稀土分异较弱，（La/Yb）_N=2.32~3.99，（Ce/Yb）_N=2.45~3.45；岩石富集大离子亲石元素Rb、Ba、Th、U、K，亏损高场强元素Nb、Ta、P、Ti、Zr，具有俯冲带构造背景特征.结合区域资料，碧流台辉长岩母岩浆应该是古亚洲洋闭合后，西伯利亚古板块和中朝古板块碰撞造山带受流体交代过的岩石圈地幔部分熔融作用的产物.

ZIRCON U-Pb DATING,GEOCHEMISTRY AND GENESIS OF GABBRO IN BILIUTAI AREA OF EASTERN INNER MONGOLIA

Study on the petrology, geochemistry and LA-ICP-MS zircon U-Pb dating of the gabbro from Biliutai area in Eastern Inner Mongolia shows that the gabbro was formed during Early Triassic of(249±2.9) Ma, belonging to calk-alkaline series, with SiO₂ of 46.43%-50.77%, Al₂O₃ of 11.27%-16.32% and TiO₂ of 0.20%-0.37%, high-Na (Na₂>K₂O, K₂O/Na₂=0.18-0.56)and high Mg^#(75.08-78.93). The chondrite-normalized REE patterns and primitive mantle-normalized trace element spiderdiagrams show a slight differentiation between LREEs and HREEs featured by(La/Yb)_N(2.32-3.99) and (Ce/Yb)_N (2.45-3.45). The rocks are enriched in large ion lithophile elements(LILEs, such as Rb, Ba, Th, U and K), whereas depleted in high field strength elements (HFSEs, such as Nb, Ta, P, Ti and Zr), with the characteristics of subduction zone setting. Together with the regional geological information, the parental magma of gabbro might be the product of partial melting of lithospheric mantle, which were metasomatized by the fluid from the collisional orogenic belt between Siberian and Sino-Korean palaeoplates.