Fundamentals of Surface Exposure Dating: Latitude, Matrix and Geometric Effects

宇宙成因核素提供了一个重要的工具， 岩石暴露在地球上的宇宙射线中的时间 也用于确定地貌的侵蚀速率 表面。 一些重要的应用已经 展示：从暴露年龄测得过去的冰川事件 冰碛石上的岩石，火山爆发的年代，以及流星的年代 撞击坑 虽然这些研究在 产生半定量结果，可靠的解释 需要更好地了解生产的基本原理 宇宙成因核素的机制 表面的三个方面 暴露测年研究得最少的是 宇宙射线通量对纬度的依赖性， 对岩石基质的生产率，以及生产率的依赖性 岩石的几何形状。 现有的有限数据 宇宙射线通量不包括宇宙射线的重要影响。 空中/地面边界 该提案要求提供资金，以衡量 几种同时代岩石中的~（10）Be、~（26）Al和~（36）Cl深度剖面 在同一地点，但不同的岩性， 加速器质谱法 纬度校正将是 研究使用相同年龄的花岗岩，但来自不同的 纬度 所有的岩石都将被独立地测定年代， 冰川抛光以排除侵蚀。 生产率模型将 使用蒙特卡罗粒子输运代码开发， 将测量值与理论值进行比较。 的 开发的生产率模型将可用于其他人 来预测其他不同岩石的地表生产率 岩性、其他几何形状和其他纬度。

Cosmogenic nuclides provide an important tool for determining the time a rock has been exposed to cosmic rays on the Earth's surface and also for determining erosion rates of geomorphic surfaces. Several important applications have already been demonstrated: dating past glacial episodes from exposure ages of rocks on moraines, dating volcanic eruptions, and dating meteor crater impacts. Although these studies have been successful in producing semi-quantitative results, reliable interpretation requires a better understanding of the fundamentals of production mechanisms of cosmogenic nuclides. The three aspects of surface exposure dating that have been studied least are the dependence of the cosmic ray flux on latitude, the dependence of the production rates on the rock matrix, and the dependence of production rates on the geometry of the rock. The limited data available on the cosmic ray flux does not include important effects of the air/ground boundary. This proposal requests funding to measure 10Be, 26Al, and 36Cl depth profiles in several rocks of same age and in the same location but of different lithology using accelerator mass spectrometry. The latitude correction will be investigated using granitic rocks of same age, but from different latitudes. All rocks will be dated independently and will show glacial polish to rule out erosion. A production rate model will be developed using Monte Carlo particle transport codes and measurements will be compared with theoretical values. The production rate model developed will then be available for others to predict surface production rates in other rocks of different lithology, other geometries, and other latitudes.