汉诺坝橄榄岩捕虏体的单斜辉石LAM-ICPMS分析及其岩石圈地幔演化意义

橄榄岩成分及其中矿物(如单斜辉石)微量元素组成可以很好地揭示岩石圈地幔性质．在对汉诺坝新生代玄武岩中橄榄岩捕虏体做详细岩相学和岩石化学研究基础上,重点分析了单斜辉石的激光原位微量元素,并探讨了新生代华北克拉通北缘岩石圈地幔特征及地幔演化．汉诺坝地区岩石圈地幔是相当于原始地幔经过不同程度的部分熔融抽取形成的,除个别样品的部分熔融程度为15％-20％外,多数样品<5％．全岩主元素、单斜辉石成分体现出新生代汉诺坝地区的岩石圈地幔是很不均一的:在主体饱满型中有亏损型地幔的残留．这种共存现象可能是软流圈物质对古老地幔进行侵蚀、混合和改造置换的结果．单斜辉石微量元素组成所体现的碳酸岩岩浆交代作用和硅酸盐熔／流体的交代作用也支持这一认识．

LAM-ICPMS Analysis on Clinopyroxenes of Peridotite Xenoliths from Hannuoba and Its Significance on Lithospheric Mantle Evolution

The compositions of the whole rocks and trace elements of minerals in peridotites can reflect the characters of lithospheric mantle. The nature and evolution of the Cenozoic lithospheric mantle beneath Hannuoba, which is located on the north edge of the intra-North China orogenic belt, are mainly discussed based on the in situ, LAM-ICPMS detected trace element compositions of clinopyroxenes in the Hannuoba peridotitic xenoliths, combined with detailed petrographic and petrochemical studies. The Hannuoba lithospheric mantle was formed by different partial melting of the primitive mantle Most of the samples reflect a partial melting degree of lower than 5% with a few samples of 15% - 20%. Major element compositions of the whole rocks and geochemical compositions of clinopyroxenes reveal the coexistence of both fertile and depleted mantle underneath the Hannuoba region during the Cenozoic. This was probably caused by the asthenospheric mantle that replaced the aged craton mantle through erosion, intermingling and modification. Our conclusion is further supported by the existence of both carbonatitic magmatic material and silicate melt/fluid metasomatism as magnified by the trace element compositions of the clinopyroxenes from the Hannuoba lithospheric mantle.