熔体─上地幔岩石的相互作用及稀土元素模拟计算──以法国中央高原堡雷(Bore)幔源包体为例

MELT-ROCK REACTION IN THE UPPER MANTLE AND ITS REE MODELLING:AN EXAMPLE FROM BOREE, MASSIF CENTRAL, FRANCE

产于法国中央高原堡雷（Boree）的具镶嵌结构方辉橄榄岩包体被认为是大陆活动区碱性玄武岩捕获的、来源最深的尖晶石相上地幔样品。已有的岩浆堆积说和等物理化学环境中重结晶模式难于解释其矿物学、微量元素和Sr－Nd同位素地球化学特征，为此我们提出了热柱来源熔体渗滤岩石圈底部的新成因模式。渗滤熔体和岩石圈地幔之间的反应不仅导致了矿物含量的变化，而且形成了特征的微量元素配分型式和同位素组成。REE模拟计算表明，熔体／岩石比值的大小、熔体性质以及熔体-岩石反应机制的多样性是控制本区幔源包体地球化学及其岩石变形、结晶程度之间相关性的重要因素。

Poikiloblastic harzburgite xenoliths (P-type) within the Quaternary alkali basalts from Boree (Massif Central, France) are believed to be located at the base of the lithospheric mantle and have previously been interpreted either as forming through isochemical recrystallisation from common granular Group I peridotites (G-type) or as metacumulates from tholeiitic magmas. While the major element chemistry of P-type samples is not consistent with the interpretation of partial melting residues, the diversity of REE patterns also precludes a simple cumulative origin for these particular samples. Instead they would more likely represent the products of melt Percolation-reaction with peridotites in which clinopyroxene (spinel) is dissolved and olivine precipitated with decreasing melt mass. Pervasive porous melt flow also enhanced the grain growth and recrystallisation processes. Base on REE modelling using a zero-D approach, it is suggested that the melt / rock ratio, nature of infiltrated melts and melt-rock reaction mechanism are responsible of the striking correlation betWeen texture and REE patterns in --type peridotites.