Evaluating aging and hydration effects on geomagnetic paleointensity in natural glass

GSTDTAP

项目编号	1547483
	Evaluating aging and hydration effects on geomagnetic paleointensity in natural glass
	Julie Bowles
主持机构	University of Wisconsin-Milwaukee
项目开始年	2015
	2015-12-15
项目结束日期	2017-11-30
资助机构	US-NSF
项目类别	Standard Grant
项目经费	147867(USD)
国家	美国
语种	英语
英文摘要	The strength and direction of Earths magnetic field varies in both time and space. These variations are recorded in a variety of geological materials, and by interpreting the records we learn about processes deep in Earth's liquid core (where the field is generated); about how the Earth and our atmosphere have evolved over geologic time; and we can use knowledge of field variations to put age constraints on geologic formations and some archeological artifacts. Although it is relatively easy to recover the direction of Earth's field, it is far more difficult to recover field strength (also known as 'paleointensity'). Typically, laboratory procedures designed to recover paleointensity are only appropriate for very small (less than a few tens of nanometers) magnetic crystals, but these small crystals are rare in nature. Volcanic glass (such as obsidian) is one material in which they are relatively abundant, and previous work has demonstrated that in some cases geologically young volcanic glass accurately records paleointensity. Glass is not a stable material, however, and the glass structure changes over time and with the absorption of water. If the magnetic minerals also change after the initial formation of the glass, they most likely will not provide us with accurate paleointensity information. The proposed work will provide an understanding of how magnetic mineralogy varies with the age and water content of natural glasses and will allow us to evaluate the suitability of natural volcanic glass as a paleointensity recorder over geologic time. In addition to the impact on geoscience disciplines, natural glasses have long been considered an analogue for nuclear waste glasses and other hazardous waste glasses. The proposed work may contribute to our ability to monitor incipient alteration of waste glasses via magnetic properties. Technical description: Although knowledge of the strength of Earth's magnetic field through time ('paleointensity') is critical in our understanding of field generation and evolution, paleointensity data remain sparse throughout Earth's history. This stems partly from the fact that few natural materials have the required fine-grained (single-domain) mineralogy and are also resistant to alteration both in nature and during laboratory reheating. Natural volcanic glasses, because they are quickly cooled, typically contain single-domain titanomagnetite, and the glass serves to at least partially protect the titanomagnetite against alteration. It has been demonstrated that young (<50-100 ka) submarine basaltic glass can reliably record the field, but it is unclear how the magnetic mineralogy and hence magnetization might change with age as the metastable glass structure relaxes and/or the glass becomes hydrated. Limited studies of more silicic glass (such as obsidian) suggest that it may also reliably record the field, but that devitrification and/or hydration will negatively impact paleointensity estimates. While important questions have been raised regarding the suitability of volcanic glass over geologic time, there has been no attempt to systematically address the issues surrounding glass relaxation, devitrification, and hydration. The objective of the proposed work is to assess the reliability of natural volcanic glasses to recover the intensity of Earth's magnetic field throughout geologic time.
来源学科分类	Geosciences - Earth Sciences
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/69015
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Julie Bowles.Evaluating aging and hydration effects on geomagnetic paleointensity in natural glass.2015.