长白山地区新生代火山岩及其幔源包体的矿物化学及矿物包裹体研究

Studies on Mineral Chemistry and Mineral Inclusion of Cenozoic Volcanic Rocks and Their Mantle Enclaves in Changbai Mountains, Northeast China

长白山地区新生代火山岩主要为玄武岩类、粗面岩类和碱性流纹岩类。其中奶头山期碱性玄武岩中含有幔源的尖晶石二辉橄榄岩包体和辉石岩包体。幔源包体及不同期次火山岩的主要矿物是橄榄石、单斜辉石、斜方辉石、尖晶石、斜长石、碱性长石。不同寄主岩石中的矿物组成及其化学成分具有一定的变化，反映了岩浆分异演化的特征；矿物及火山熔岩中的包裹体成分及玻璃熔体结构的激光拉曼光谱分析结果表明，地下深处的岩浆含有较多的挥发分，岩浆上升过程中发生了强烈的出溶作用；岩浆由起源经分异演化上升到地壳浅部直至喷发，幔源的挥发分减少，而浅成或壳源的挥发分增多，特别是在岩浆喷发过程中。

The Cenozoic volcanic rocks in Changbai Mountains consist of basalts, trachytes and alkali rhyolites. A lot of enclaves named spinel lherzolite and pyroxenite derived from the mantle were fount in alkali basalt of Miocene Naitoushan period. The main minerals in mantle enclaves and volcanic rocks of different periods are olivine, clinopyroxene, enstenite, spinel, plagioclase and alkali feldspar. the species and chemical compositions of minerals from different rocks are different, reflecting the trend of magmatic differentiation evolution. The geothermobarometer of minerals indicates that the basaltic magma derived from the mantle at the depth of more than 82 km formed the deep magma chamber in the upper mantle at the depth of 55km to 65km. Laser Raman spectrum analysis of inclusions in minerals from different volcanic rocks show that magma in great depth contained a lot of volatiles, and that strong exsolution occurred during the upward migration of magma. Besides, mantle volatiles decreased and crust volatiles increased in upward direction, and underground water might have played an important role in volcanic eruption.