石榴石的-分离:证据表明海洋玄武岩的深源和快速上升
概括
中洋山脊玄武岩和海洋岛屿玄武岩显示-230过剩,表明地幔深处开始部分融化,特别是在石榴石稳定场. 这一发现需要在海洋山脊下进行动态的融化过程.
科学领域:
- 地质化学 地质化学
- 石化学 石化学是一门学科.
- 同位素地球化学 同位素地球化学
背景情况:
- 中洋山脊玄武岩 (MORBs) 和海洋岛屿玄武岩 (OIBs) 起源于上层地幔的部分融化.
- 这些玄武岩表现出与其母体,-238 (238U) 相比,-230 (230Th) 活动的特征过剩.
研究的目的:
- 调查负责海洋玄武岩中观察到的230Th-238U不平衡的地幔融过程.
- 为了确定地球上层地幔最初部分融化的深度和条件.
主要方法:
- 实验测量 (Th) 和 (U) 在主要地幔阶段和融化阶段之间的分离.
- 对地幔融过程的热力学建模.
主要成果:
- 石榴石被确定为唯一能够保留超过的主要上层地幔阶段,这是与克林诺普洛克森相反的分离.
- 这种石榴-保留解释了在年轻的海洋玄武岩中观察到的230Th过量.
- 计算表明,MORBs中的230Th-238U不平衡是从约80公里深度开始动态部分化的结果,孔度≥0.2%.
结论:
- 无论是MORB还是OIB,都会在石榴石稳定场 (70公里以下) 内启动部分化.
- 海洋山脊下面的融化发生在一个广的区域,岩以每年至少0.9米的速度上升.
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