摘要
蛇绿岩型金刚石产在蛇绿岩地幔橄榄岩和铬铁矿中,不同于产在大陆克拉通的金伯利岩型金刚石,也不同于产在板块俯冲带中的超高压变质型金刚石和陨石撞击成因的金刚石。蛇绿岩型金刚石的主要特征是粒度普遍较小,多数在200~500μm之间,C同位素显示极低的δ13CVPDB值(-28‰^-18‰),金刚石中包裹体以含富Mn的矿物为特征,金刚石产在蛇绿岩大洋地幔橄榄岩中,其构造背景为板块缝合带。金伯利岩型金刚石粒度可达厘米级,是大颗粒宝石级金刚石的主要来源,其C同位素显示轻微低的δ13CVPDB值(-10‰^-5‰),包裹体矿物多为富Mg的矿物组合,金刚石产在克拉通和大陆岩石圈构造背景。超高压变质带中的金刚石颗粒十分细小,由数微米至<100μm,C同位素为中等低的δ13CVPDB值(-15‰^-7‰),金刚石通常与碳酸岩和地壳成因矿物伴生,含有金刚石的超高压变质岩石形成的构造背景为板块深俯冲边界。形成于陨石撞击的金刚石产出和研究均较少,金刚石通常也是微米级,产出在陨石撞击形成的变质岩中,伴生矿物的成分与与撞击变质的原岩有关。以上四类金刚石无论野外和室内区分显著,由此,可以将蛇绿岩型金刚石归为地球上一种新的金刚石产出类型。
Ophiolitic diamonds can be distinguished from kimberlitic diamonds, ultrahigh pressure （UHP） metamorphic diamonds and meteorite impact diamonds by their character and mode of occurrence. Most ophiolitie diamonds are small （mostly about 200 500tzm across）, contain distinctive inclusions and have extremely light carbon isotope compositions. All occur in oceanic mantle rocks within ophiolites emplaeed in suture zones. Kimberlitie diamonds are famous for their large size （gem quality）, inclusions of mantle minerals and slightly light carbon isotopes. These all occur within continental cratons. In contrast, UHP metamorphic diamonds are very small, a few microns in size, and are accompanied by carbonates and crustal minerals in subduction complexes formed during deep subduetion of continental or oceanic crust. Meteorite impact diamonds are very rare, mostly a few microns in size and accompanied by minerals related to the site of impact. These four categories of diamond are obviously different in their main features and tectonic setting of formation. Thus, the newly confirmed ophiolitic diamonds represent a new occurrence of diamond on Earth.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2014年第8期2113-2124,共12页
Acta Petrologica Sinica
基金
国家行业专项(SinoProbe-05-02)
国家自然科学基金重点项目(40930313)
国家自然科学基金创新群体项目(41221061)
中国地质调查局工作项目(12120114061801)联合资助
