Improved Characterization of Apatite Fission-track Annealing Kinetics, and Application to Core Complex Exhumation, Southern Basin and Range

磷灰石裂变径迹退火动力学的改进表征及其在南部盆地和山脉核心复杂折返中的应用

• 批准号: 0948636
• 负责人: Richard Ketcham
• 金额: $ 28.81万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-01-15 至 2016-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0948636&HistoricalAwards=false
• 关键词: Improved; Characterization; Apatite; Fission; track

This project is designed to provide a much improved understanding and characterization of the process of fission-track annealing in the mineral apatite. Fission tracks form when uranium decays by spontaneous fission, and the damage caused by the fissioning particles anneals (is repaired) at a rate determined by the ambient temperature. Fission-track analysis has thus proven to be a powerful tool for determining the thermal history of rock bodies, and is widely used for tectonic studies, landscape evolution, and petroleum exploration, among other fields. The advances created by this research will be used to discern the nature of faulting that caused the final stages of uplift of mountain ranges in southern and west-central Arizona. Although apatite fission-track thermochronology is a well-established and robust technique, our understanding of how annealing occurs, and how it is affected by apatite composition, remains extremely vague. Experimental studies have shown that impurities such as chlorine, iron and manganese can increase temperatures required for annealing by several tens of degrees, but the experimental database is currently far too sparse to determine how impurities work individually and/or in concert to bring about these changes. This study will vastly expand the annealing database by utilizing an efficient procedure to determine the relative annealing properties of 30 apatites with widely varying compositions and unit cell dimensions. These data will provide insight not only into compositional effects, but into the annealing mechanism itself. The resulting new model of fission-track annealing will be used to examine the relative roles of high-angle and low-angle normal faulting in the final stages of core-complex exhumation in the Arizona Basin and Range. Recent work has suggested that low-angle faulting may have accelerated to near-plate-tectonic rates. However, the data may also be explained by a transition from low-angle to high-angle faulting. These two scenarios make different predictions about how cooling rates vary in time and space depending on proximity to faults. The improvements in the fission-track method will be used to test these predictions, either confirming a dramatic transition in movement rates possibly caused by the migration of the slab window off of western North America, or illuminating how the nature of unroofing can change during a continuous episode of exhumation.

该项目旨在提供更好的理解和表征矿物磷灰石中裂变径迹退火的过程。 当铀通过自发裂变衰变时，裂变径迹形成，裂变粒子造成的损伤以环境温度决定的速率退火（修复）。 因此，裂变径迹分析已被证明是确定岩体热历史的有力工具，并广泛用于构造研究、景观演化和石油勘探等领域。 这项研究所取得的进展将用于识别导致亚利桑那州南部和中西部山脉隆起最后阶段的断层性质。虽然磷灰石裂变径迹热年代学是一种成熟而强大的技术，但我们对退火如何发生以及它如何受磷灰石成分影响的理解仍然非常模糊。实验研究表明，氯、铁和锰等杂质可以将退火所需的温度提高几十度，但目前的实验数据库太少，无法确定杂质如何单独和/或协同工作来实现这些变化。 这项研究将大大扩大退火数据库，利用一个有效的程序，以确定30个磷灰石的相对退火性能与广泛变化的组合物和晶胞尺寸。 这些数据将提供洞察不仅成分的影响，但到退火机制本身。 由此产生的新模型的裂变轨道退火将被用来检查高角度和低角度的正常断层在最后阶段的核心复杂的折返在亚利桑那州盆地和山脉的相对作用。 最近的研究表明，低角度断层可能已经加速到接近板块构造的速度。 然而，这些数据也可以用从低角度到高角度断层的转变来解释。 这两种情况对冷却速率在时间和空间上的变化做出了不同的预测，这取决于与断层的接近程度。 在裂变轨道方法的改进将被用来测试这些预测，无论是确认一个戏剧性的转变，在运动速率可能造成的迁移北美西部的板窗，或照亮如何去顶的性质可以改变在一个连续的情节挖掘。