摘要
哈萨克斯坦北部Kokchetav地区的Kumdy Kol金刚石矿床是世界上惟一的变质金刚石矿床。对该金刚石矿床成因以及相关岩石的诸多研究成果不仅深化了对超高压变质岩的研究 ,而且推动了大陆动力学研究的进展。在该金刚石矿床中找到的岩相学证据证明 ,该金刚石矿床的主要含矿岩石大理岩曾经在俯冲带中循环到 >2 4 0km的深部。文章在介绍Kokchetav变质金刚石矿床的地质特征和大地构造背景的基础上 ,讨论了该变质金刚石矿床的形成过程以及变质金刚石的成因。Kokchetav变质金刚石主要表现出蜂窝状或草莓状的特征外形。这种蜂窝状或草莓状金刚石是快速生长条件下结晶的结果。结合最近的研究成果 ,笔者认为Kokchetav金刚石矿床中金刚石的形成与深俯冲大理岩中的白云石分解作用密切相关。白云石分解反应形成文石和菱镁矿组合 ,菱镁矿继续分解形成金刚石 (MgCO3 =金刚石 +MgO +O2 )。基于这个认识 ,Kokchetav金刚石矿床中碳 (金刚石和石墨 )
Kokchetav diamond deposit is the only metamorphic diamond deposit ever reported in the world. The researches on this diamond deposit and related metamorphic rocks greatly improved our understanding of the geodynamics as well as the metamorphic petrology. The petrographic evidences found in the diamond-bearing rocks in this deposit demonstrated that the major diamond-bearing rocks, marble, once recycled into deep mantle greater than 240 km. Based on descriptions of the geology and the tectonic background of this metamorphic diamond deposit, this paper discusses the ore-formation processes and the origin of the metamorphic diamond. Kumdy-Kol metamorphic diamonds generally are honeycomb-like or strawberry-like in shape. Such diamonds were formed at quick crystallization condition. Based on the recent research (Zhu and Ogasawara, 2002, Geology, 30, 947-950), we believe that the Kokchetav metamorphic diamonds were formed during deep subduction, and related with the decomposition reaction of dolomite. Dolomite decomposition produced aragonite and magnesite, magnesite decomposition produced diamond (MgCO_3=diamond+MgO+O_2). The source carbon (diamond and graphite) in Kumdy-Kol diamond deposit thus should be derived from carbonates.
出处
《地学前缘》
EI
CAS
CSCD
2004年第2期333-338,共6页
Earth Science Frontiers
基金
国家自然科学基金资助项目 ( 4 0 3 42 0 18)
