Recycled crustal melt injection into lithospheric mantle:implication from cumulative composite and pyroxenite xenoliths
会议名称：《中国科学院地质与地球物理研究所第十届(2010年度)学术年会》
会议日期：2011年
学科分类：0709[理学-地质学] 070901[理学-矿物学、岩石学、矿床学] 07[理学]
基 金：support from the Natural Science Foundation of China(Grant 90714008,40534022,40523003,and 40421202) the Chinese Academy of Sciences(Grant KZCX2- YW-103 Beirenjihua)
关 键 词：Composite and pyroxenite xenoliths Cumulates Recycled crustal melt Lithospheric mantle North China Craton
摘 要：A rare composite xenolith and abundant cumulative pyroxenites obtained from the Mesozoic Fan-gcheng basalts on the eastern North China Craton record a complex history of melt percolation and circulation in the subcontinental lithospheric *** composite xenolith has a dunite core and an olivine clinopyroxenite *** dunite is of cumulative origin and has a granular recrys-tallized texture and extremely low Mg#[100 Mg/ (Mg+Fe)=81-82]contents in *** olivine clinopyroxenite contains larger clinopyroxene and/or orthopyroxene with a few fine-grained olivine and tiny phlogopite,feldspar,and/or carbonate minerals interstitial to *** clinopyroxene has low Mg#(83-85). Compositional similarity between dunitic olivine and pyroxenitic one indicates a sequential crystallization of dunite and pyroxenite from a precursor *** xenoliths include olivine websterites and clinopyroxenites, both are of cumulative *** of the melt from major oxides in olivines and REE concentrations in clin-opyroxenes in these composite and pyroxenite xenoliths suggests a derivation from subducted crustal materials, consistent with the highly enriched EMII-like Sr and Nd isotopic ratios observed in the *** of phlogopite,feldspar and carbonate minerals in some xenoliths requires the melt rich in alkalis(K,Na),silica and volatiles(water and CO)at the latest stage as well,similar to highly silicic and potassic ***,the occurrence of these composite and pyroxenite xenoliths provides an evidence for voluminous injection of recycled crustal melts into the lithosphere beneath the southeastern North China Craton at the Late Mesozoic,a reason for the rapid litho-spheric enrichment in both elemental and isotopic compositions.