【摘要】 内蒙古集宁新生代玄武岩产于华北克拉通北缘,属于广义的“汉诺坝玄武岩”。首次在三义堂附近的碱性玄武岩中发现了大量的橄榄岩包体、辉石和长石以及少量的含钛磁铁矿巨晶。包体主要是尖晶石二辉橄榄岩,造岩矿物为橄榄石+斜方辉石+单斜辉石+尖晶石,辉石巨晶主要为透辉石和普通辉石,长石巨晶主要是歪长石和少量斜长石。1.5GPa条件下,尖晶石二辉橄榄岩样品所记录的平衡温度与汉诺坝相近,集中于950℃左右,大体上反映了华北克拉通北缘大陆岩石圈地幔尖晶石相部分的温度状态。单斜辉石巨晶的结晶温压大于幔源包体的平衡温压,表明巨晶的来源深度可能大于包体。包体的结构及矿物成分分析表明,这些包体是玄武质岩浆上升过程中偶然捕获岩石圈地幔的岩石碎块。二辉橄榄岩包体中橄榄石高Mg#值(89.5～91.7)和较高的NiO含量(0.29%～0.55%),暗示集宁玄武岩中的橄榄岩包体来自较高熔融程度的岩石圈地幔。更多还原

【Abstract】 Located in Inner Mongolia, the northern edge of the North China craton, Jining Cenozoic basalts belong to the generalized “Hannuoba Basalts”. A lot of peridotite xenoliths as well as some pyroxene, feldspar and titanomagnetite megacrysts were discovered for the first time in the alkali basalt southeast of Sanyitang. Most of these xenoliths are spinel lherzolites with the assemblage of olivine + orthopyroxene + clinopyroxene + spinel. The pyroxene megacrysts are mostly diopside and augite in composition. Feldspar megacrysts are mainly anorthoclase and minor plagioclase. The equilibrium temperature represented by these spinel lherzolite xenoliths is about 950℃ at 1.5 GPa, which is almost the same as that of the Hannuoba xenoliths and reflects the temperature of spinel phase in the lithospheric mantle beneath the northern edge of the North China craton. The crystallization temperature and pressure of clinopyroxene megacrysts are higher than those of lherzolite xenoliths, implying an origin deeper than that of the peridotite xenoliths. Petrography and mineral chemistry of these xenoliths indicate that they are fragments of the upper mantle captured by basaltic magmas along the ascending way. The high Mg# (89.5～91.7) and high NiO (0.29%～0.55%) contents of olivines demonstrate that Jining peridotite xenoliths are derived from the infusible lithospheric mantle.更多还原