Carbon cycling in the subduction zones deduced from in-situ Carbon isotope analyses

夏威夷大学开发了使用SIMS的原位碳同位素分析。我分析了4种不同的天然样品：(1)高压变质岩，(2)接触变质岩，(3)翡翠，(4)含石墨的地幔包体。不幸的是，由于这些样品中含碳相中的硅酸盐包裹体的基质效应，我无法从(1)和(2)中获得可靠的日期。翡翠中石墨的碳同位素组成与地幔值相近。这表明在俯冲开始时，具有地幔样碳同位素组成的流体对翡翠的形成负有责任。地幔捕虏体中的石墨具有轻碳同位素组成。这表明样品中的碳是生物成因的。这种石墨将为我们提供地幔中金刚石起源的有用信息。

In-situ carbon isotopic analyses using SIMS was developed at the University of Hawaii. I analyzed 4 different natural samples: (1) high-pressure metamorphic rocks, (2) contact metamorphic rocks, (3) jadeites, and (4) graphite-bearing mantle xenoliths. Unfortunately, I was not able to reliable date from (1) and (2) because of matrix effects of silicate inclusions within carbon-bearing phases in these samples. Graphite in jadeites has similar carbon isotopic compositions to mantle value. This suggests that fluids with mantle-like carbon isotopic compositions are responsible for the formation of jadeite at the beginning of subduction. Graphite in the mantle xenolith has light-carbon isotopic compositions. This suggest the carbon in the sample was of biogenic origin. This graphite will provide us useful information on origin of diamond in the mantle.