Mineralogy, Magnetism and Geologic Origin of Fine-Grained Fe-Ti Oxides in Glassy and Devitrified Rhyolitic Rocks

玻璃状流纹岩和非玻璃化流纹岩中1微米或更小的细粒FeTi氧化物的磁性矿物学和这些微晶的地质成因是一个问题，其解决方案对这些岩石的任何古地磁数据的解释都有实质性的影响。这些来自灰流凝灰岩的数据通常被用于构造构造、地层和古极研究。PI将对内华达州尤卡山的火山灰流凝灰岩单元进行详细的磁性、透射电子显微镜(TEM)和穆斯堡尔谱学研究，同时对来自加利福尼亚州北部和俄勒冈州的成分相似的流纹岩黑铁矿和火山碎屑流进行研究，以解决这一问题。TM和穆斯堡尔方法将区分赤铁矿、磁铁矿和磁铁矿。将检验细粒NRM载体的地质成因的初步模型，该模型将原始剩磁归因于淬火玻璃中高温析出的Fe-Ti氧化物和斑晶相。

The magnetic mineralogy of fine-grained FeTi oxides, 1 um in size and smaller, in glassy and devitrified rhyolitic rocks and the geologic origin of these microcrystals are problems whose solution substantively influences any interpretation of paleomagnetic data of these rocks. These data, from ashflow tuffs, are routinely applied to structural-tectonic, strati- graphic, and paleopole studies. The PI will conduct a detailed magnetic, transmission electron microscopy (TEM) and Mossbauer spectroscopic study of ash-flow tuff units from Yucca Mountain, Nevada, in conjunction with a study of compositionally similar rhyolitic obsidian and phroclastic flows from N. California and Oregon, to address this problem. TEM and Mossbauer methods will distinguish amongst hematite, magnetite and maghemite. A tentative model for the geologic origin of fine-grained NRM carriers, which attributes primary remanence to Fe-Ti oxides that precipitated at elevated temperature in quenched glass, and phenocryst phases will be tested.