概括
磁铁中的氧同位素比率显示出显著的谷内异质性,挑战了以前的假设. 相反的交换机制解释了这些变化,影响了氧同位素温度测量应用.
科学领域:
- 地质化学 地质化学
- 同位素地质学的同位素.
- 变态石器学 变态石器学
背景情况:
- 氧同位素比对于理解地质过程至关重要.
- 矿物质中的谷内同位素异质性可以提供对形成后变化的见解.
- 磁铁是变态岩石中常见的辅助矿物.
研究的目的:
- 为了研究磁铁中谷内氧同位素异质性的程度和起源.
- 为了限制后变态氧同位素交换的机制.
- 评估对氧同位素温度测量的影响.
主要方法:
- 在磁铁颗粒中对氧同位素比率 (δ18O) 的离子微探针分析.
- 微观结构分析磁石从颗粒岩面积大理石.
- 从不同尺寸的磁铁颗粒中比较同位素数据.
主要成果:
- 磁铁石颗粒显示出显著的谷内氧同位素变化 (+2到+11‰).
- 异质性观察到在谷物边界附近和更大的谷物内部.
- 小粒的异质性较小,主要在边缘,这表明扩散控制的交换.
- 较大的颗粒显示更的梯度和裂纹辅助扩散的证据.
结论:
- 后变态流体岩石相互作用是负责谷内同位素异质性的.
- 氧同位素交换的机制因颗粒大小和微观结构特征 (例如,愈合的裂) 而异.
- 了解这些变化对于精确应用氧同位素温度计至关重要.
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