火星的快速积累和早期分化在SNC石中的142Nd/144Nd表示
C L Harper1, L E Nyquist, B Bansal
1Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138.
概括
纳克拉石中的元素同位素异常揭示了早期的火星地幔分化. 这表明,在太阳系起源的2700万年内,火星避免了巨大的撞击.
科学领域:
- 行星科学 行星科学
- 地质化学 地质化学
- 宇宙化学 宇宙化学
背景情况:
- 行星体中142与144比率的微小变化表明了早期的分化.
- 这些变异是由于已灭绝的放射性核素萨马-146的衰变而产生的.
- 这种同位素异常提供了对行星积累时间尺度的见解.
研究的目的:
- 用新同位素研究早期行星分化.
- 为了限制火星上早期分化和积累的时间.
- 根据同位素证据评估火星的撞击历史.
主要方法:
- 在火星石Nakhla中分析新同位素比率 (新-142到新-144).
- 利用萨马-146的衰变作为太阳系早期事件的计时器.
- 将纳克拉的同位素特征与正常的同位素特征进行比较.
主要成果:
- 纳克拉石显示新-142到新-144.4的含量超过了59 +/- 13 ppm.
- 这种异常表明,火星地幔的分化发生在4539亿年前之前.
- 这些发现暗示,在太阳系形成后的2700万年后,火星并没有经历巨大的撞击.
结论:
- 石中的元素同位素异常是了解早期行星演变的强大工具.
- 火星在其历史上很早就经历了显著的地幔分化.
- 火星的早期历史,特别是它的撞击记录,可以通过对返回样本的同位素分析来破译.
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