内蒙古阿巴嘎旗新生代玄武岩中超镁铁岩包体的特征  

Characteristics of ultramafic xenoliths from Cenozoic basalts in Abagaqi area,Inner Mongolia

作　　者：张臣[1] 刘树文[1] 韩宝福[1] 李德春[1] 

机构地区：[1]北京大学地球与空间科学学院

出　　处：《岩石学报》2006年第11期2801-2807,共7页Acta Petrologica Sinica

基　　金：国家自然科学基金(批准号:40472118;40472096)

摘　　要：内蒙古东部阿巴嘎旗及其以北地区第四纪更新世钠质碱性火山岩中发现的超镁铁岩包体,主要为尖晶石二辉橄榄岩、方辉橄榄岩、纯橄榄岩、橄榄二辉岩、尖晶石单斜辉石岩和单斜辉石巨晶以及辉长岩、花岗闪长岩、石英长石片麻岩等壳源包体。超镁铁岩包体和巨晶的岩相学特征显示它们不是寄主玄武岩岩浆分离结晶堆积体;其主要元素、稀土元素特征与阿尔卑斯型橄榄岩相似,其组成接近于原始地幔岩值;同位素地球化学特征表明它们与寄主岩-玄武岩浆不是同源的;尖晶石二辉橄榄岩包体形成的平衡温度和压力范围分别为1056.9℃～1103.1℃,压力为1.50～1.84GPa,形成相当深度为49.5～60.72km。辉石岩包体形成温度为887.1℃～958.6℃,压力为1.25～1.4GPa,形成相当深度为41.25～46.2km。寄主玄武岩形成温度1390℃～1450℃,压力1.75～2.20GPa,形成相当深度为60～70km。可以认为,研究区在新生代发生了软流圈地幔上涌,导致岩石圈减薄以及地壳的拉张,大量岩浆物质沿构造通道溢出地表。其中超镁铁岩包体与寄主玄武岩浆之间没有熔体与残余物这种成因联系,它们是寄主玄武岩浆在上升过程中捕获的岩石圈地幔碎块。The ultramafic xenoliths in various quantities and scales were found in the. Quaternary alkali basalts at Abagaqi area of Inner Mongolia These ultramafic xenoliths are_composed of spinel lherzolite, saxonite, dunite, olivine websterite, spinel pyroxenite, pyroxene megacrystal, and crust xenoliths which include gabbro, granodiorite, quarfelsic-gueiss. Petrography characteristics of ultramafic xenoliths indicate that they are not accumulation material of fractional crystallization from adventive basalt magma; characteristics of major element and rare earth element of ultramafic xenoliths are akin to Alpine type peridotite, composition of ultramafic xenoliths are similar to primary mantle ; Sm-Nd and Rb-Sr isotopic characteristics indicate that ultramafic xenoliths with adventive basalt magma are not cognate; The equilibration temperature and pressure of the spinel lherzolite xenoliths are estimated to be 1056.9℃ - 1103.1 ℃ and 1.50 - 1.84GPa and this range of depth should be 49.5 - 60.7km ; olivine websterite and spinel pyroxenite are estimated to be 887. 1 ℃ - 958. 6℃ and 1.25 - 1.4GPa and this range of depth should be 41.25 - 46. 2km. The equilibration temperature and pressure of adventive basalt are estimated to be 1390℃ - 1450℃ and 1.75 -2. 2GPa and this range of depth should be 57.7 - 72. 6km.. It is considered that an upper mantle diaper occurred since late Tertiary in study area, giving rise to the thinning of the lithosphere and the formation of extensional environment in this area, the basalts magma direct ejected along structural thoroughfare. The ultramafic xenoliths bear no relation to origin of fused mass and residual body between adventive basalt magma. The uhramafic xenoliths is caught fragment from lithosphere mantle in uplifting process of adventive basalt magma.

关 键 词：新生代 超镁铁岩包体 碱性玄武岩 内蒙古 

分 类 号：P588.145[天文地球—岩石学] P588.125[天文地球—地质学]