非平衡脱气,也是海洋岛屿火山活动中的主要来源
Helge M Gonnermann1, Sujoy Mukhopadhyay
1Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.
Nature
|October 26, 2007
概括
海洋岛基岩 (OIBs) 中的原始 (3He) 并不是来自放射性衰变. 这项研究使用岩脱气模型解释了OIB和中海洋基岩 (MORB) 中的度悖论.
科学领域:
- 地质化学 地质化学
- 同位素地球化学 同位素地球化学
- 世界地幔地力学地力学
背景情况:
- 和的放射性衰变产生-4 (4He),而地球地幔中的-3 (3He) 是原始的,在积累过程中被纳入.
- 海洋岛基岩 (OIBs) 的3He/4He比率高于中洋山脊基岩 (MORBs),传统上归因于未排气的地幔羽毛.
- 在OIBs比MORBs具有较低的度和He/Ne,He/Ar比率的情况下存在差异,称为"度悖论".
研究的目的:
- 解决有关OIB和MORB中贵重气体度的"度悖论".
- 为在MORB和OIB玻璃中观察到的贵气度范围提供一个自我一致的解释.
- 重新评估地幔羽毛及其脱气过程的来源和动态.
主要方法:
- 在MORB和OIB玻璃中分析贵气度 (He,Ne,Ar).
- 模拟不平衡的喷发性岩的开放式系统脱气.
- 在OIB和MORB岩石中具有不同CO2含量的脱气模型的比较.
主要成果:
- 在MORB和OIB玻璃中的"度悖论"和贵气变化是由不平衡的开放系统脱气解释的.
- 与MORB magma相比,OIB magma中的较高CO2含量导致更广泛的脱气.
- 在OIB岩中存在的高贵气体可能源于一个基本上没有气体的原始地幔来源.
结论:
- 特别是受CO2含量影响的岩脱气过程,对于控制基岩石中贵重气体特征至关重要.
- 传统的OIBs模型仅代表未有气体的地幔羽毛,需要改进.
- 这项研究为贵重气体变异提供了统一的解释,通过脱气动力学来协调OIB和MORB数据.
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