碳及碳化物间的碳同位素分馏及其对深部碳循环的指示意义

The carbon isotope fractionation between deep carbonaceous minerals plays a very important role in discussing the carbon isotopic composition of deep carbonaceous minerals, tracing their origin and understanding the carbon movement among reservoirs. However, the lack of nature deep carbonaceous minerals and the difficulty of related high temperature and high pressure experiments limit the knowledge of carbon isotope fractionation between deep carbonaceous minerals, which contains more than 90% carbon in the earth. This project plans to study the carbon isotope fractionation between deep carbonaceous minerals (neutral carbon and carbide) from the Dalihu carbonatitic xenoliths and the Hannuoba carbonatite intrusion, and to trace their origin. The major work to be done include: (1) seeking and identifying the deep carbonaceous minerals using laser Raman spectrometer and environmental scanning electron microscope; (2) analyzing the C isotopic compositions of the deep carbonaceous minerals using Nano-SIMS.

深部各含碳相之间的同位素分馏对正确解释各含碳相同位素组成，示踪其来源，继而理解碳在各储库间的迁移影响重大。但是，受限于深部含碳相天然样品的缺失及相关高温高压实验的难度，我们对占据地球总碳90%的深部含碳相之间的碳同位素分馏还知之甚少，这很大的制约了我们对深部碳迁移的认识。本项目拟通过对达里湖碳酸岩质包体及汉诺坝碳酸岩侵入体中罕见的深部含碳相（碳及碳化物）碳同位素组成及分馏的研究，揭示这些含碳相来源及相互转化关系。主要工作包括（1）利用激光拉曼光谱仪、环境扫描电镜查找碳及碳化物；（2）利用Nano-SIMS测定碳及碳化物的碳同位素组成。

因地球中超过90%的碳都赋存在地球深部，深部碳循环是目前地球科学研究的热点问题。碳在各储库间的迁移是深部碳循环研究的基础问题。我们对内蒙古达里湖碳酸岩质包体和橄榄岩包体进行了详细的岩石学和地球化学研究。利用聚焦离子束铣削技术和透射电子显微镜对原位SiC进行了形态、成分和结构进行了分析，证实了这些为天然碳化硅。利用高温高压实验探讨了俯冲碳酸盐迁移过程中的碳同位素分馏。再循环沉积碳酸盐岩可显著升高地幔氧逸度，并大幅提高PGE等元素的活动性。同时完成了Ge/Si比值在不同矿物相中分配系数测定工作，为示踪深部碳循环，尤其是相关的碱性岩成因提供了新工具。