Behavior of the magnesium formate mineral during aqueous alteration of the Allende meteorite with organic compound-bearing fluid

Abstract

In a protoplanetary disk, the interactions between fluids and meteoritic materials are influenced by their distance from the Sun. This is because of the varying abundance of organic molecules in aqueous fluids. However, a few studies have explored the effects of organic compounds in aqueous alteration fluid. Therefore, we aimed to observe the fractionation behavior of major elements in the early solar system, by focusing on the reaction between organic matter and meteoritic material, particularly on the interaction between organic compound-rich fluids and meteoritic materials and on their role in magnesium/iron (Mg/Fe) fractionation. This experiment is intended to simulate the reactions that are considered to have occurred in dwarf planets. We used two solutions: Fluid A with ∼ 16 wt% formic acid and 10 wt% ethanol, and Fluid B with 30 wt% formic acid and 19 wt% ethanol. The solid phase was the powdered Allende CV chondrite. Experiments were conducted over 10, 40, and 120 days at 150-350 °C. In both solutions, dashkovaite, an Mg formate mineral, formed metastably at 150 °C. During its temporary presence and subsequent extinction, Mg and Fe exchanged between dashkovaite and insoluble Si-Mg-Fe product phases. The extinction of dashkovaite and changes in its Mg/Fe ratio led to an insoluble Si-Mg-Fe phase with an Mg# value as low as 10 in Fluid B. These reactions suggest that organic-rich fluids can influence Mg/Fe fractionation by separating Mg-rich organic minerals.