蒙阴金刚石的形态形貌特征及其对深部熔流体性质和活动的指示  

Morphology and Surface Features of Diamonds from Mengyin:Geological Implications for the Nature and Activity of Deep-Seated Melts and Fluids

作　　者：丁永康 梁伟章 丘志力 邓小芹 孙媛 马瑛 孙成阳 陆太进 DING Yongkang;LIANG Weizhang;QIU Zhili;DENG Xiaoqin;SUN Yuan;MA Ying;SUN Chengyang;LU Taijin(School of Earth Science and Engineering,Sun Yat-Sen University,Zhuhai Guangdong 519080,China;Guangdong Academy of Sciences,Guangzhou 510070,China;School of Materials Science and Engineering,Guilin University of Technology,Guilin 541004,China;National Gemstone Testing Center Shenzhen Lab Co,Ltd.,Shenzhen Guangdong 518020,China;Gemological Institute,China University of Geosciences(Beijing),Beijing 100083,China;Beijin Research Institude of National Gems&Jewelry Technology Administrative Center,Beijing 100013,China)

机构地区：[1]中山大学地球科学与工程学院,广东珠海519080 [2]广东省科学院,广东广州510070 [3]桂林理工大学材料科学与工程学院,广西桂林541004 [4]国检中心深圳珠宝检验实验室有限公司,广东深圳518020 [5]中国地质大学(北京)珠宝学院,北京100083 [6]自然资源部珠宝玉石首饰管理中心北京研究所,北京100013

出　　处：《地球科学进展》2024年第6期602-615,共14页Advances in Earth Science

基　　金：国家自然科学基金项目(编号:42073008,41473030)资助。

摘　　要：金刚石在金伯利岩浆捕虏前的地幔环境及后续岩浆运移过程中熔流体的共同熔/溶蚀作用下,会产生复杂的晶体形态和表面形貌,这些形态形貌学的表观特征在一定程度上反映了地幔及金伯利岩浆运移过程中熔流体的不同性质。尝试通过对蒙阴金刚石的形态及其形貌学特征进行分析,结合国际大量模拟地幔及金伯利岩温压和化学环境条件下天然金刚石的熔/溶蚀实验的相关成果,对蒙阴金刚石所体现的地幔及金伯利岩熔流体活动的性质和特点进行讨论,得到以下几点认识:①蒙阴金刚石的地幔熔体熔蚀形态及形貌特征以低程度熔蚀的“八面体+三角/锯齿状薄层+联合凹坑/深蚀坑”的组合为主,严重熔蚀的“十二面体+深蚀坑”组合次之,结合统计分析,这在一定程度上暗示了华北克拉通古老岩石圈地幔所经历的小规模、低程度的橄榄岩—熔体反应,熔体性质为相对富CO_(2)贫H_(2)O的含碳酸盐熔体;②蒙阴3个金伯利岩矿带的金刚石溶蚀形态比例指示了其岩浆流体活动性具有一定差异,具有高比例溶蚀形态金刚石的常马庄矿带岩浆流体活动相对坡里和西裕矿带更强;③蒙阴金刚石岩浆流体溶蚀的形态及形貌以“四六面体+浅凹陷+溶蚀凹雕”组合为主,且大多数样品都表现出岩浆流体低程度溶蚀的叠加形貌,另外,所有浅的、独立的三角凹坑均为平底和具有截角的倒三角凹坑,未见特殊类型,以上特征均与浅成金伯利岩释放的富H_(2)O贫CO_(2)流体相关。上述结果表明,即使在比较有限的区域内,金刚石所记录的地幔及金伯利岩浆熔流体活动过程也存在不均一性,其形态及形貌特征可以作为研究地幔熔体及金伯利岩浆流体活动的一个重要参考,也从某些角度揭示出很多金刚石矿区不同岩体、矿带产出的金刚石的品质和品位存在明显差异的内在原因。Diamond undergoes intricate interactions with melts and fluids in the Subcontinental Lithospheric Mantle(SCLM)and kimberlite magma,resulting in a diverse array of crystal morphologies and surface features.These morphological attributes serve as proxies,reflecting the varying distinct properties of melts and fluids during mantle storage and kimberlite magma migration.This study meticulously analyzed the morphology and surface features of diamonds sourced from Mengyin.In addition,we systematically discuss the characteristics of mantle and kimberlite melt and fluids,as inferred from these diamonds,with reference to a comprehensive body of international dissolution experiments on natural diamonds that simulated the mantle and kimberlite temperature,pressure,and chemical conditions.This investigation yields the following key findings:①The morphology and surface features caused by mantle melts predominantly exhibit a combination of low-degree resorption of“octahedron+triangular/serrated laminae+joint pit/deep pit,”with the severe dissolution of“Dodecahedra+deep etch pit”being less common.Statistical analyses suggest that these morphologies indicate the occurrence of small-scale,low-degree peridotite-melt reactions within the ancient lithospheric mantle of the North China Craton(NCC),with melt compositions relatively enriched in CO_(2) and depleted in H_(2)O.②The proportion of dissolution forming among diamonds in the three kimberlite belts in Mengyin indicates discernible differences in the activity of magmatic fluids,with the Changmazhuang belt showing relatively more intense magma fluid activity than Xiyu and Poli belt.③The morphology and surface features of Mengyin diamonds,which result from magma fluid etching,primarily showcase a combination of“Tetrahexahedra(THH)+shallow depression+corrosion sculpture,”with the majority of samples displaying characteristics indicative of an overlay of shallow dissolution by magma fluids.Additionally,all shallow independent trigons were flat-bottomed and truncate

关 键 词：金刚石 金伯利岩 形态及形貌学 金刚石成矿 

分 类 号：P619.241[天文地球—矿床学]