Investigation of Biotite/Sanidine Age Discordance

EAR-0126144 Heizler和McInto新墨西哥州采矿与技术研究所来自火山岩的同源黑云母和玄武岩经常产生不一致的40Ar/39Ar年龄。典型的年龄不一致性介于0.2~1.0 Ma之间。这种不一致性对于详细、高精度的火山史研究、K/Ar与U/Pb和其他地质年代学方法的相互标定以及通量监测标准的年龄都具有重要的意义。这项建议将通过对新墨西哥州莫高隆-达蒂尔火山田两个研究较好的中第三纪火山岩序列进行详细的年代学分析，来研究黑云母/珊瑚岩不整合的原因。这项研究的预期结果可能是深远的，如果它表明黑云母年龄被个别分析中不明显的不准确所困扰。由于黑云母是最常见的火山岩和深成矿物相，其表观年龄往往非常精确，因此黑云母年龄的准确测定对各种构造、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.