不连续生长的金刚石与克拉通地块内部增生过程中的地幔流体作用

DIAMOND WITH MULTISTAGE GROWTH AND ITS SIGNIFICANCE FOR MANTLE FLUID WITHIN ACCRETED CRATON

产于克拉通地块及其边缘褶皱带金伯利岩和钾镁煌斑岩中的原生金刚石 ,其主体上属地幔捕虏晶并具复杂的生长历史。从克拉通岩石圈存在复杂多发的壳幔相互作用和多层次的流体活动事件的角度 ,结合金刚石的精细内部结构所反映的不连续生长及微区原位傅立叶变换红外光谱研究成果 ,认为具复杂生长环带的金刚石是克拉通地块内部增生过程中的地幔流体对已形成金刚石间的相互作用的产物。这一认识有助于增进金刚石微观结构与地块内部改造事件有机联系的研究。地幔交代作用的介质成分主要为SiO2 不饱和的碳酸岩熔体或富含不相容微量元素的CHON流体。多种年龄数据所给出的 1 1～ 1 2Ga结果 ,可能反映华北地块东部的岩石圈深部存在一次明显的地幔增生改造过程。

Diamonds derived from kimberlites within craton and form lamproites within cycle-craton are generally xenocrystals with complex growth history. Based on the consideration of multistage crust-mantle interaction events and multicycle mantle fluid activity within continental lithosphere,and the combination with the discontinuous growth reflected by inter-structure of diamond and the FTIR research results in situ, a conclusion can be drawn that the diamonds with complex growth were the production of the carbonatic melts or the incompatible elements-rich CHON fluid interaction with the pre-existed diamonds in lithospheric mantle during cratonic accretion. The results of 1.1～1.2Ga derived from different methods probably show that a strong accretion and modification took place beneath the lithosphere mantle in the eastern part of the North China Block.