记录地幔中存在氧元素的自然铁-方铁矿组合

笔者在西藏蛇绿岩的铬铁矿石中发现了十分复杂的地幔矿物群,其中包括自然铁-方铁矿的共生组合,它们被认为是外地核和下地幔的物质通过地幔柱作用携带到上地幔的。新发现的自然铁-方铁矿组合表明,外地核液态铁溶解有部分氧,当液态铁由外地核上升时,氧从液态铁中析出并呈不混溶状态存在于液态铁中。随着乳滴状自然铁球粒向上运移,在降压条件下液态铁和氧元素发生化学反应生成方铁矿(包括NI AS结构)。当氧耗尽时,在方铁矿中遗留下氧耗尽的空洞,形成眼球状构造。因此,眼球构造可能是外地核向地幔释放氧,下地幔内存在氧元素的历史记录。

The Native Iron and Wustite Assemblage: Records of Oxygen Element from the Mantle

A very complicated mantle mineral group including the native iron and wustite assemblage was recently discovered in chromitites from the mantle harzburgite of Luobusa ophiolite, Tibet. It is considered that this group was probably derived from the lower mantle and outer core, and then transported to the upper mantle by mantle plume. The assemblage structure shows that the liquid iron from the outer core dissolved some oxygen. When the liquid iron droplets spurted from the outer core into the mantle, they were decomposed into oxygen and iron in the form of immiscibility. Following decompression and ascent of the droplets, wustite (or NiAs structure) was produced by the chemical reaction between the liquid iron and liquid oxygen. When the oxygen was consumed up by the wustite, some holes remained and showed eyeball structures. The eyeball structures might have recorded the history of oxygen activity in the mantle and the Earth's core.