Investigation of Biotite/Sanidine Age Discordance

heizler和McIntoshNew Mexico Institute of Mining and technology .来自火山岩的成因黑云母和银云母通常产生不一致的40Ar/39Ar年龄。典型的年龄差异在0.2 ~ 1.0 Ma之间。这种不一致对于详细、高精度的火山史研究、K/Ar与U/Pb的互定和其他地质年代学方法以及通量监测标准的年龄具有重要意义。本提案将通过对新墨西哥州mogolon - datil火山场两个已被充分研究的中第三纪火山序列进行详细的地质年代学分析，探讨黑云母/sanidine不一致的原因。如果证明黑云母年龄受到个体分析中不明显的不准确性的困扰，那么这项研究的预期结果可能会影响深远。由于黑云母是最常用的定年火山岩和深成岩矿物相，它通常能得出非常精确的表观年龄，因此确定黑云母年龄的准确性对各种构造、火山和地质研究都是至关重要的。

AbstractEAR-0126144Heizler and McIntoshNew Mexico Institute of Mining and TechnologyCogenetic biotite and sanidine from volcanic rocks often yield discordant 40Ar/39Ar ages. The typical age discordance is between 0.2 and 1.0 Ma. The discordance has important implications for detailed, high precision volcanic history studies, for intercalibration of K/Ar with U/Pb and other geochronological methods, and the age of flux monitor standards. This proposal will investigate the causes of the biotite/sanidine discordance through detailed geochronological analyses of two well-studied Mid-Tertiary volcanic sequences from the Mogollon-Datil volcanic field of New Mexico. The expected outcome of this study could be far reaching, if it is shown that biotite ages are plagued by inaccuracy that is not evident in individual analyses. Because biotite is the most commonly dated volcanic and plutonic mineral phase and it often yields highly precise apparent ages, determination of accuracy of biotite ages is essential to a wide variety of tectonic, volcanic, and geological studies.