Exploring the Effect of Si in Metal on Element Partitioning Behavior

Introduction: Earth's outer core is substantially less dense that pure Fe-Ni, requiring ~3-9% of the core to be composed of a "light" element or elements [1]. Taking into account their cosmochemical availability, the elements H, C, O, Si, and S have been proposed as significant light elements in Earth's core [2]. The iden-tity(ies) of the light element(s) in Earth's core have implications for understanding many fundamental planetary processes, such as: the bulk composition of Earth, the conditions during Earth's differentiation, the thermal evolution of the core and the generation of the geomagnetic dynamo, the present-day interactions at Earth's core-mantle boundary, and the chemical evolution and crystallization of the core. Because of the important implications associated with the composition of the light element in Earth's core, it is of interest to investigate the effects different potential light elements have on the chemical behavior of trace elements. The core's light element composition affected how trace elements partitioned between the silicate mantle and the metallic core during Earth's core formation. The light element composition also affects how trace elements partition between Earth's solid inner core and the liquid outer core as Earth's core continues to crystallize. Previous experimental studies have examined the effects of S and C on the partitioning behavior of numerous trace elements [3, 4]. However, similar studies for the elements of H, O, and Si have not been conducted, due mainly to the different phase relationships of these light elements with Fe, making the simple solid metal-liquid metal studies conducted for S and C not possible for H, O, and Si. In order to explore the effects of Si, we have conducted an experimental study in the Fe-S-Si system. Here we present the methods used in the study and new results for 22 trace elements. This study offers the first look into the effect of Si in metal on trace element partitioning behavior. Methods: To determine the effects of S or C, previous studies conducted solid metal-liquid metal experiments in the Fe-(Ni)-S [3] and Fe-(Ni)-C [4] systems. Similar experiments in the Fe-Si system are not possible because significant amounts of Si are soluble in solid Fe metal, resulting in very little difference in the Si content of coexisting solid metal and liquid metal in the Fe-Si system. Experiments with coexisting metal and silicate could be conducted with varying amounts of Si in the metallic phase. However, varying the Si content …