宽甸橄榄岩包体微区地球化学特征及其岩石圈地幔演化  

Micro-geochemistry of peridotite xenoliths from Kuandian: Implications for evolution of lithospheric mantle

作　　者：徐荣[1] 刘勇胜[1] 宗克清[1] 邹东雅[1] 邓黎旭[1] 童喜润[1] 胡兆初[1] 高山[1] 

机构地区：[1]中国地质大学地球科学学院,地质过程与矿产资源国家重点实验室,湖北武汉430074

出　　处：《岩石矿物学杂志》2013年第5期613-636,共24页Acta Petrologica et Mineralogica

基　　金：科技部973项目(2013CB429806);国家自然科学基金资助项目(90914007;41173016);国家自然科学杰出青年基金资助项目(41125013);教育部高等学校学科创新引智111计划(B07039);地质过程与矿产资源国家重点实验室科技部专项经费(MS-FGPMR 201204);中央高校基本科研业务费专项资金(CU G090105)

摘　　要：华北克拉通东部宽甸新生代碱性玄武岩中携带的地幔橄榄岩包体为我们认识该地区岩石圈地幔性质和演化过程提供了约束。根据橄榄石的Mg#可将宽甸橄榄岩包体分成两类：第1类为低Mg#二辉橄榄岩包体（橄榄石Mg#相对较低：89．8～90．3），其单斜辉石具有高rri02（0．38％～0．57％）、A1203（4．41％～6．87％）、Feor（2．46％～3．73％）、MnO（0．08％--0．11％）含量和低＆#（7．42～14．2）的特征，它们所经历的部分熔融程度较低，这些特征类似于中国东部晚白垩世和新生代玄武岩中低Mgt＊橄榄岩，代表了新生饱满的岩石圈地幔；第2类为高Mg#方辉橄榄岩包体（橄榄石Mg#相对较高：91．0～92．3），其单斜辉石具有低n02（0．03％～0．33％）、A1203（2．27％～5．49％）、FeOr（2．04％--2．40％）、MnO（0．07％～0．08％）含量和高Cr#（15．3～25．8）的特征，它们经历了较高程度的部分熔融作用，其难熔的地球化学特征完全不同于低Mg#二辉橄榄岩，却与克拉通内部太古宙和元古宙地幔包体类似，代表了古老难熔岩石圈地幔的残留。两类橄榄岩包体的平衡温度没有显著差异说明宽甸岩石圈地幔不存在明显的分层现象，而是新老岩石圈地幔混杂出现。宽甸橄榄岩包体的微量元素特征表明了它们受到过多期复杂的地幔交代作用，交代介质类型不仅有硅酸盐熔／流体还有碳酸盐熔体，其来源既有太平洋板块俯冲释放的熔／流体，又有因受太平洋板块俯冲扰动而上涌的软流圈熔体，因此太平洋板块俯冲可能对华北克拉通的破坏起到了重要作用。Mantle peridotite xenoliths entrained in the Cenozoic alkaline basalts from Kuandian of eastern North China Craton provide important constraints on the nature and evolution of the lithospheric mantle beneath this area. Two types of xenoliths can be defined based on the Mg# of their olivines： Type 1 low-Mg# lherzolites are characterized by low Mg# in olivines （89.8--90.3）, high TIO2（0.38% N0.57% ）, A1203（4.41% --6.87% ）,FeOT（2.46% -- 3.73%）, MnO （0.08% -- 0.11%） content and low Cr~ （7.42-- 14.2） in the coexisting clinopyroxenes, and have undergone low degrees of partial melting; these characteristics are similar to those of low-Mg~ peridotites in the Late Cretaceous and Cenozoic basahs, thus probably representing newly accreted lithospheric mantle. Type 2 high-Mg# harzburgites are characterized by high Mg# in olivines （91.0-- 92.3）, low TiO2（0.03% --0.33%）, Al2O3（2.27% --5.49%）, FeOT（2.04% --2.40%）, MnO （0.07% --0.08%） content and high Cr# （15.3--25.8） in the coexisting clinopyroxenes and have undergone high degrees of partial melting; these refractory geochemical characteristics are completely different from those of low-Mg# lherzolites, but similar to those of high-Mg# peridotite xenoliths from Arehean and Proterozoic lithospheric mantle in the craton, therefore are considered to be relicts of ancient lithospheric mantle. The nonexistence of obvious differ- ences in equilibrium temperatures of low-Mg# and high-Mg# peridotites suggests that there is no significant stratification within the sub-continental lithospheric mantle beneath Kuandian, but there exists mixture between the newly accreted mantle and the ancient lithospheric mantle. Trace element characteristics of the Kuandian peridotite xenoliths indicate that they have undergone multiple complex mantle metasomatism, and the metaso- matic agents include not only silicate melts/fluids but also carbonate melts; both melts/fluids released by Pacific slab subduction and the heat perturbation and upwelling of ho

关 键 词：华北克拉通 宽甸 岩石圈地幔 橄榄岩包体 LA-ICP—MS 

分 类 号：P588.125[天文地球—岩石学] P594[天文地球—地质学]