反向深度剖面LA-ICP-MS方法的研发与其地质应用

锆石地质年代学已经成为主流的方法去研究地球深部动力学、构造演化、地表源-汇系统、以及气候及海平面变化。LA-ICP-MS以其原位、经济、快捷的优势，应用最为广泛。但与此同时，相关问题也暴露了出来。传统LA-ICP-MS方法先打磨，再根据环带确定激光剥蚀位置。其激光斑束直径为20到40微米，当直径小于20微米时，分馏作用和测量误差明显变大。这种问题在喜马拉雅淡色花岗岩定年中尤为突出。喜马拉雅淡色花岗岩的新生锆石，大都以薄增生边的形式存在。另外，结合已发表研究以及申请人的初步研究，部分淡色花岗岩锆石增生边薄至1微米。这更加表明为了获取可靠的定年结果，传统方法亟待改进。.本研究结合传统方法和本人博士期间的深度剖面方法的优点，以研发反向深度剖面方法为基础，以解决喜马拉雅淡色花岗岩定年为指引。拟研发的反向深度剖面方法可以系统性的获取每颗锆石的增生边和继承核年龄，并将测量的纵向空间分辨率提高到1微米。

Zircon geochronology is a fundamental tool to investigate the geodynamics, tectonic evolution, surface source-to-sink systems, and sea-level/climatic changes. In order to obtain large geochronological data set, laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) is most widely used because its in-situ, low-cost, and high-efficiency characteristics. Using traditional LA-ICP-MS method, we polish zircon grains and then determine the position of ablation pits based on the zircon overgrowth (rim). The diameter of the laser ranges from 20 to 40 μm. However, the downhole fractionation effect and analytical errors increase significantly when the laser diameter is less than 20 μm. Thus, the traditional method could not measure the age of rims thinner than 20 μm. This problem is very typical in dating the zircons in Himalaya leucogranite, whose rims are very thin in most of the case. Besides, based on latest publication and my preliminary study, some rims in the zircons of Himalaya leucogranite can be as thin as 1 μm, which even cannot be identified in microscope. These discoveries further support the necessity of revising the traditional LA-ICP-MS method. .This study will combine the advantages of depth-profiling LA-ICP-MS method, which is conducted in my Ph.D study, and the traditional LA-ICP-MS method. The aim of this project is to develop reverse depth-profiling LA-ICP-MS method and apply this method in dating the zircons of Himalaya leucogranite. Proposed reverse depth-profiling LA-ICP-MS method will systematically recover the core and rim ages of each zircon and increase the special resolution of dating to as high as 1μm.