Collaborative Research: Origin of Magnetite and Magnetic Remanence in Submarine Basaltic Glass and Implications for Glass Paleointensities

合作研究：海底玄武岩玻璃中磁铁矿和剩磁的起源以及对玻璃古强度的影响

• 批准号: 0538170
• 负责人: Reid Cooper
• 金额: $ 16.94万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-12-15 至 2009-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0538170&HistoricalAwards=false
• 关键词: Collaborative; Research; Origin; Magnetite; Magnetic

Submarine basaltic glass is increasingly being used in studies of geomagnetic field intensity variation, yet the origin of the magnetic remanence in glass remains poorly understood, leading some to question the validity of paleointensity estimates from glass. To recover valid paleointensity estimates, the magnetic remanence in the glass must be a primary thermoremanence - i.e. magnetization must be locked in at high temperatures when the glass initially cools. If suggestions that the magnetization is instead a low-temperature chemical remanence are true, then paleofield estimates from basaltic glass might be invalid. This study is designed to elucidate the process by which (titano)magnetite forms in basaltic glass, as well as the conditions under which it forms and its fidelity as a recorder of geomagnetic field variations. Glass is synthesized under a range of conditions (oxygen fugacity, cooling rate, composition) and in a known magnetic field. The starting materials are either powdered natural tholeiitic basalt or simplified synthetic compositions prepared by mixing reagent-quality component oxides. Reheating oxidation diffusion experiments, combined with Rutherford backscattering spectrometry and analytical transmission electron microscopy, allow an exploration of the field of conditions under which and the process by which magnetite precipitates and grows in glass. The results have direction implications not only for the origin of magnetite in glass, but also for its stability during reheating paleointensity experiments. The microanalytical techniques also allow characterization of grain size and composition, which are complimented by magnetic characterization using a suite of rock magnetic techniques on both the synthetic glass samples, as well as natural glass samples of varying ages. In this way the resulting magnetic mineralogy and magnetic properties of the synthesized glasses are readily compared to those of natural glasses. Finally, paleointensity experiments provide a direct test of the ability of the synthetic glass samples to accurately record the ambient field intensity.

海底盆底玻璃越来越多地用于地磁场强度变化的研究，但玻璃中磁性雷神的起源仍然很少了解，导致一些人质疑玻璃的古显着性估计值的有效性。为了恢复有效的古显度估计值，玻璃中的磁性恢复必须是主要的热量 - 即，当玻璃最初冷却时，必须在高温下锁定磁化。 如果建议磁化是一种低温化学物质的建议，则玄武岩玻璃的估计值可能是无效的。 这项研究旨在阐明玄武岩玻璃中（Titano）磁铁矿形成的过程，以及其形成的条件及其作为地磁磁场变化的记录器的忠诚度。 玻璃在一系列条件（氧气逸度，冷却速率，成分）和已知磁场中合成。 起始材料是通过混合试剂质量的氧化物制备的天然天然硫质玄武岩或简化的合成组成。再加热氧化扩散实验，结合了卢瑟福的反向散射光谱法和分析透射电子显微镜，可以探索磁铁矿在玻璃中沉淀并生长的条件领域的探索。结果不仅对玻璃中的磁铁矿的起源具有方向影响，而且还对其在重新加热的紫色实验中的稳定性也具有指示。 微分析技术还允许表征晶粒尺寸和成分，通过在合成玻璃样品上使用一套岩石磁技术以及不同年龄的天然玻璃样品，它们通过磁性表征来称赞。通过这种方式，与天然玻璃杯相比，合成眼镜的磁性矿物学和磁性特性很容易。最后，Paleisty实验可直接测试合成玻璃样品准确记录环境场强度的能力。