内蒙古阿尔山——柴河地区陆下岩石圈地幔性质研究——第四纪碱性玄武岩中橄榄岩捕掳体中单斜辉石微量元素证据

Study on SCLM in Aershan--Chaihe area of Inner Mongolia: evidence from trace elements of clinopyroxene

阿尔山—柴河第四纪碱性玄武岩中地幔捕掳体为尖晶石相的二辉橄榄岩和方辉橄榄岩,方辉橄榄岩数量略多于二辉橄榄岩.采用激光剥蚀等离子体质谱（LA-ICP-MS）对研究区地幔橄榄岩中的单斜辉石和橄榄石等矿物进行了成分分析,结合橄榄岩包体的岩相学、岩石化学的特征,重点探讨了研究区所经历的部分熔融作用和地幔交代作用.结果显示,少数样品的熔融程度＜5％,大多数样品熔融程度范围为10％～20％,研究区陆下岩石圈地慢性质以难熔、亏损为主要特征.同时也经历了复杂的交代作用改造,交代介质为富挥发组分的硅酸盐熔/流体.与华北克拉通东北缘陆下岩石圈地幔比较,推测研究区遭受破坏和改造的程度较小,并保留有相当量的古老地幔残余.

The mantle peridotite xenoliths entrained in the Quaternary alkali basalts in the Aershan-Chaihe area of Inner Mongolia are composed of spinel lherzolite and spinel harzburgite which is slightly higher than the former in quantity.We studied the partial melting process and metasomatism with LA-ICP-MS based on the CPX and Ol analysis in mantle peridotite,combined with the petrographical and geochemical characteristics of peridotite inclusions.The result shows that melting degree of most samples ranges from 10％ to 20％,with a few exceptions less than 5 ％,which implies a depleted mantle source and it was overlapped by silicate melt metasomatic alteration.By comparison with SCLM （sub-continental lithospheric mantle） of the North China Craton,we deduce that it retains appreciable quantity of old mantle residual with little metasomatism in the studied area.