40Ar/39Ar Dating of Feldspars from the KTB Deep Drill Hole: Insight into Post-Orogenic Thermal Relaxation and AR Diffusion Systematics During Closure

长石的40Ar/39Ar定年法在帮助地质学家确定150℃至350℃范围内的定量温度-时间路径方面具有巨大的潜力。在如此低的温度范围内，这样的时间-温度信息对于科学家评估诸如地壳的结构和演化或沉积盆地及其伴随的水和碳氢化合物资源的起源和演化等问题非常重要。然而，到目前为止，这项技术只在短期的实验室加热实验中进行了测试，并且可能是在很有特征的地质环境中进行的。现在已经开发出用于定量热时测定的复杂解释模型，在缓慢冷却的地质环境中评估长石的40Ar/39Ar定年是很重要的。德国的KTB深钻孔提供了一个理想的天然实验室，用于研究长石在缓慢冷却过程中对扩散Ar损失的闭合，因为这个洞的温度已经达到了与长石闭合区间重叠的温度，预计达到~300℃。在这个项目中，将对KTB洞深处的一套样品进行检查，这将使首席研究员能够看到Ar闭合的过程，这将是几乎所有使用长石热时计的应用研究的宝贵基准。同时，对长石中40Ar/39Ar分系统的认识也很好，因此对KTB孔浅层样品的研究将使首席研究员能够详细监测当地地壳的造山后冷却；他将评估热松弛和剥蚀所起的相对作用，并寻找第三纪热事件的证据，即使是非常温和的第三纪热事件，也可能导致KTB洞中出现的高梯度。这些信息将对岩石圈在环期和造山之后的热演化模型有很大的帮助。＊＊＊

9219595 Zeitler The 40Ar/39Ar dating of feldspar has enormous potential for helping geologists determine quantitative temperature-time paths over the range of 150oC to 350oC. Such time-temperature information over such a range of low temperatures is of great importance to scientists evaluating such issues as the architecture and evolution of the crust or the origin and evolution of sedimentary basins and their attendant water and hydrocarbon resources. However, to this point the technique has only been tested in short-term laboratory heating experiments and in presumably well-characterized geological contexts. Now that sophisticated interpretative models have been developed for use in quantitative thermochronometry, it is important that the 40Ar/39Ar dating of feldspar be evaluated in a slow-cooling geological environment. The KTB deep drill hole in Germany offers an ideal natural laboratory with which to examine the closure of feldspar to diffusive Ar loss during slow cooling, as this hole already has reached temperatures which overlap the closure interval for feldspars and is projected to reach ~300oC. In this project, a suite of samples from deep in the KTB hole will be examined which will permit the principal investigator to view the process of Ar closure as it is happening, and would be an invaluable benchmark for virtually all applied studies which use feldspar thermochronometry. At the same time, the understanding of 40Ar/39Ar systematics in feldspar is sufficiently good that study of shallow samples from the KTB hole will permit the principal investigator to monitor in detail the post-orogenic cooling of the local crust; he will assess the relative roles that thermal relaxation and denudation have played, and will look for evidence of even a very mild Tertiary thermal event that might be responsible for the high gradients seen in the KTB hole. Such information will be highly useful for models of thermal evolution of the lithosphere du ring and after mountain building. ***