内蒙古二连-东乌旗地区晚石炭世碱性花岗岩时代、成因及地质意义

内蒙古二连-东乌旗地区发育一条晚古生代碱性花岗岩带,代表贺根山洋盆闭合后的伸展背景.本次工作在苏尼特左旗北部红格尔(302±1 Ma)、祖横得楞(～299 Ma)、那仁宝力格(301.7±1.4 Ma)等地区新识别出了晚石炭世碱性花岗岩.野外露头及镜下观察可见其中有钠铁闪石和霓辉石等典型碱性暗色矿物;全岩地球化学分析表...

Geochronology and Petrogenesis of Late Carboniferous Alkaline Granites from Erlian-Dongwuqi Region,and Its Geological Significance

The Late Carboniferous alkaline granite belt in Erlian-Dongquqi area indicates regional extention after the closure of Hegenshan ocean. In this paper, it presents recently discovered Late Carboniferous alkaline granites in these regions: Honger(302±1 Ma), Zuhengdeleng (~299 Ma), and Narenbaolige (301.7±1.4 Ma) plutons. These rocks show characteristics of high silica (73.15%-77.38%), alkali (K₂O=4.28%-5.35%, Na₂O=4.01%-4.79%) contents, low CaO, MgO and relatively enriched FeO_t(FeO_t/MgO ratios are between 8.2-46.1) contents, similar with typical alkaline granite. Trace element analysis display enrichment of Rb, Th, U, K, Zr, Hf, but strong depletion of Sr, Ba, P, Ti. There are "sea gull" REE patterns with strong negative Eu abnormity (δEu ranges from 0.03 to 0.50). Furthermore, these rocks have depleted Nd-Hf isotopic composition, with two stage Hf-Nd model ages of Neoproterozoic-Early Paleozoic, indicating that the sources are juvenile crust derived from mantle in this period. Geochemical and Nd-Hf isotopic signatures argue for derivation from partial melting of juvenile crust by depression and heating of upwelling asthenosphere in post-orogeny extensional setting, demonstrating that the Hegenshan basin had closed before 300 Ma.