Fluorine and chlorine fractionation during magma ocean crystallization: Constraints on the origin of the non-chondritic F/Cl ratio of the Earth
Fluorine and chlorine fractionation during magma ocean crystallization: Constraints on the origin of the non-chondritic F/Cl ratio of the Earth
复制标题
岩浆海洋结晶过程中的氟和氯分馏：对地球非球粒状 F/Cl 比值起源的限制
DOI：
10.1016/j.epsl.2019.05.041
复制
发表时间：
2019
影响因子：
5.3
通讯作者：
Irifune Tetsuo
中科院分区：
文献类型：
--
作者：
Kuwahara Hideharu;Kagoshima Takanori;Nakada Ryoichi;Ogawa Nobuhiro;Yamaguchi Asuka;Sano Yuji;Irifune Tetsuo
以往的研究表明，硅酸盐地球中挥发性元素的相对丰度是非碳酸盐性的。类地行星中挥发性元素的丰度和分布主要受行星形成过程的控制，包括核幔分离，岩浆海洋结晶和挥发性相关的高温分馏。因此，目前挥发性元素在类地行星硅酸盐组分中的丰度模式是理解类地挥发物吸积历史和类地行星化学分异的关键。虽然类地行星中挥发性元素的非周期性比值的起源以前已经被研究过，但它仍然是一个有争议的问题。在这项研究中，我们专注于超奥氏体F/Cl比的散装硅酸盐地球和实验研究的硅酸盐矿物熔体分配的氟和氯在压力从18 GPa到25 GPa。我们的实验结果表明，氟是适度兼容的地幔矿物，而氯是高度不相容的。这些结果支持了在岩浆洋结晶过程中形成了高F/Cl比的固体地幔和低F/Cl比的残余岩浆洋和蒸汽大气。因此，类地行星残留固体部分的F/Cl比在挥发性元素从行星表面逃逸到外层空间后会变得相对富集。该模型与原始地壳和大气的碰撞侵蚀假说以及目前对陆地氟和氯丰度和分布的观测结果是一致的。
Previous studies have reported that the relative abundances of volatile elements in the silicate Earth are non-chondritic. The abundance and distribution of volatile elements in terrestrial planets would have been predominantly controlled by planetary formation processes, including core-mantle separation, magma ocean crystallization, and volatility-dependent high-temperature fractionation. Thus, the current abundance patterns of volatile elements in the silicate fraction of terrestrial planets are the key to understanding the accretional history of terrestrial volatiles and the chemical differentiation of terrestrial planets. Although the origin of the non-chondritic ratios of volatile elements in terrestrial planets has been previously studied, it is still a matter of debate. In this study, we focused on the super-chondritic F/Cl ratio of the bulk silicate Earth and experimentally investigated the silicate mineral-melt partitioning of fluorine and chlorine at pressures from 18 GPa to 25 GPa. Our experimental results show that fluorine is moderately compatible with mantle minerals, whereas chlorine is highly incompatible. These results support the formation of a solid mantle with high F/Cl ratios, and a residual magma ocean and steam atmosphere with low F/Cl ratios during magma ocean crystallization. Thus, the F/Cl ratio in the residual solid parts of terrestrial planets would have become relatively enriched following escape of volatile elements from the planetary surface into outer space. This model is consistent with the collisional erosion hypothesis of primordial crusts and atmospheres, and current observations on the abundance and distribution of terrestrial fluorine and chlorine.