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

9219595 Zeitler长石的40Ar/39Ar测年具有巨大的潜力，可以帮助地质学家确定150摄氏度到350摄氏度范围内的定量温度-时间路径。这种低温范围内的时间-温度信息对于科学家评估地壳的结构和演化或沉积盆地及其伴生的水和油气资源的起源和演化等问题具有重要意义。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，并可能在具有良好特征的地质环境中进行了测试。现在已经开发了用于定量热计时的复杂的解释模型，因此在缓慢冷却的地质环境中对长石的40Ar/39Ar测年进行评估是很重要的。德国的KTB深孔提供了一个理想的天然实验室，可以用来检查长石在缓慢冷却过程中对扩散Ar损失的闭合情况，因为这个孔的温度已经达到了与长石的闭合间隔重叠的温度，预计将达到~300oC。在这个项目中，将检查一套来自KTB洞深处的样品，这将使首席研究员能够观察到正在发生的Ar闭合过程，并将成为几乎所有使用长石热计时术的应用研究的宝贵基准。与此同时，对长石中40Ar/39Ar系统学的了解已经足够好，对KTB孔浅层样品的研究将使首席调查员能够详细监测当地地壳的造山后冷却；他将评估热弛豫和剥蚀所起的相对作用，并将寻找可能导致KTB孔中看到的高梯度的非常温和的第三纪热事件的证据。这些信息将对都环岩石圈和造山后的热演化模型非常有用。***

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. ***