天然富勒烯及其在P-T界线地层的研究进展

Advances in the Study of Natural Fullerenes with Special Discussion on P-T Boundary Fullerenes

富勒烯(Fullerene)为除金刚石和石墨外碳元素的第三种同素异形体,自Kroto等1985年发现以来,对富勒烯的研究一直是世界性的热点话题,并在多个方面取得重要进展。它具有稳定的封闭笼状结构,被认为在星际空间广泛存在。富勒烯的形成条件特殊,普通的地球环境和地质过程不利于富勒烯的生成。1992年天然富勒烯在俄罗斯前寒武纪地层桑加岩(Shungite)中被发现,引起了人们对天然富勒烯研究的兴趣。随着富勒烯在陨石和撞击构造中的发现,人们更加关注事件地层中富勒烯存在的可能性以及它们的可能来源。二叠纪—三叠纪(P-T)之交发生了地质历史上规模最大的生物灭绝事件,因此,学者十分关注P-T界线地层中是否能检测到天然富勒烯的的存在。文章回顾了富勒烯在陨石、撞击构造、K-T界线地层和P-T界线地层的研究进展,并重点对P-T界线富勒烯的存在问题进行讨论,指出从样品采集到样品测试,每一个环节都可能影响富勒烯的检出。P-T界线地层富勒烯可能源于陨石撞击、天然大火等极端地质事件,而包裹在富勒烯碳笼的稀有气体的同位素组成提供了进一步区分的重要证据。事件地层中普遍存在富勒烯,表明天然富勒烯可以作为地层中发生过重大灾变事件的重要的地球化学指标,而具有异常稀有气体同位素组成的富勒烯则是地外撞击事件的最直接证据。

Fullerene, the third carbon allotrope besides graphite and diamond, was discovered by Kroto et al. in 1985. Since then, the studies of fullerenes has become the worldwide hot topic and significant progresses in many fields have been achieved, The stable carbon cage structure of fullerene C60 indicates it should occur abundantly in eireumstellar and interstellar media. For its special conditions of production, fullerene is hardly yielded through the process of the common earth environment and dynamic geology. The first presence of fullerene in Shungite, Russia in 1992 aroused the interest of studying natural fullerene, Since the discover of fullerene in meteorites and meteorite impact structure, the existences of fullerenes in event strata and its origins have come to the front of scientists. The P-T event boundary strata have been long time of the scientists＇interests and puzzles because of the largest mass extinctions in the history of geology during Permian-Triassic boundary. In this paper, advances in the study of fullerenes in meteorites, impact structure, K-T boundary and P-T boundary are reviewed. The occurrence of fullerenes is discussed and it is pointed out that each step may effect the examination of fullerene from sample col- lection to test. Fullerenes have been detected in the different P-T boundary strata by many scientists and the origins of fullerenes were examined in depth. Fullerenes in the P-T boundary strata likely came from meteorite impact or natural fires and the noble gas isotopic composition in fullerene carbon cage can be used to discriminate them. The wide occurrences of fullerenes in the event strata suggest that fullerene can be one of the important geochemical indicators of strata events and fullerene with abnormal noble gas isotopic composition a direct indicator of extraterrestrial impact events.