Understanding Chromium Redox Systematics Mafic Magmas:  Applications to Magmatic fO2 Calculations and Chromite Solubility

GSTDTAP

项目编号	1848654
	Understanding Chromium Redox Systematics Mafic Magmas: Applications to Magmatic fO2 Calculations and Chromite Solubility
	Aaron Bell
主持机构	University of Colorado at Boulder
项目开始年	2018
	2018-06-04
项目结束日期	2019-06-30
资助机构	US-NSF
项目类别	Continuing grant
项目经费	104494(USD)
国家	美国
语种	英语
英文摘要	Stratiform chromite deposits hosted in layered mafic intrusions are by far the most economically important source of the element Chromium (Cr). Chromium is a key ingredient required for the manufacturing of stainless steel alloys, as well as a myriad of other technologically important 'super alloys'. While it is widely accepted that the chromite deposits found in layered mafic intrusions are a crystallization product of a parental magma body, the fundamental geochemical processes that induce the crystallization of chromite in the magma bodies that host these deposits are still poorly understood and the subject of much scientific debate. One of the main objectives of this study is to quantify how variables such as the chemical composition of a silicate melt and the oxidation state of the Cr dissolved in the silicate melt affect the crystallization behavior of chromite. The results generated from this study can be used to deduce the chemical circumstances under which mafic magmas become saturated with and crystallize chromite. In a broader context, the results of this study can also be applied to quantifying the oxidation state of mafic magmas. Developing new tools to quantify the oxidation state of basaltic magmas is a foundational aspect of understanding the oxidation state of the earth?s mantle and a major step toward understanding the speciation and mobility of volatile elements between the deep earth and surficial reservoirs. This project will support a masters or doctoral student at the University of New Mexico, as well as an undergraduate student thesis. Both of these students will be trained in state-of-the-art analytical and experimental techniques and assist in research conducted at a U.S. synchrotron facility. Understanding chromite stability is a critical aspect of developing models for the formation mechanisms of stratiform chromite ore deposits associated with layered mafic intrusions. Chromite stability in basaltic magmas is influenced by variables such as temperature, pressure, the chemical composition of the melt, and its oxidation state (i.e. fO2). The primary objective of this study is to produce a quantitative portrait of Cr-redox behavior and chromite stability in mafic magmas and how it relates to the aforementioned variables. This study combines high temperature-pressure petrology experiments conducted at the University of New Mexico with X-ray Absorption Near Edge Structure (XANES) measurements of Cr valence ratios in the experimentally grown olivine crystals and quenched melts. The XANES measurements will be conducted at the Advanced Photon Source, Argonne National Laboratory. The phase equilibria and Cr valence data generated by this study will be used to develop a new geochemical model of chromite crystallization in mafic magmas. Furthermore, the Cr valence measurements in olivine crystals will be used to develop a new tool for assessing the fO2 of basaltic magmas. A preliminary investigation has shown that the Cr-valence in olivine records changes in fO2 that may have occurred during pheoncryst growth. In this way, Cr valence measurements in olivine may be developed into a robust, quantitative redox chronometer for magmatic systems.
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/72723
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Aaron Bell.Understanding Chromium Redox Systematics Mafic Magmas: Applications to Magmatic fO2 Calculations and Chromite Solubility.2018.