Advancements in U-Pb dating of deep crustal structures and magmatic/meteoritic events in relation to biotic evolution in earth history

对在形成、再加热或韧性流动事件中结晶的微量(微克)矿物“锆石”进行精确的铀-铅分析，提供了造山期间地壳演化的详细情景。当巨大的大陆板块碰撞时，会产生过厚的地壳岩层，使得逆冲层的下部从下面加热并软化，向更深的内陆滑动。这一定发生在落基山脉下面，因为这些厚厚的沉积物质曾经位于海底，现在位于一块更古老的大陆上方。为了了解在地球表面下10-20公里处我们看不见的界面上发生的过程，我们必须找到一个非常古老的山根，那里的山脉后来被侵蚀掉了。沿安大略省乔治亚湾裸露的格伦维尔省就是这样一个根源。在这里，研究岩石记录的地质学家既观察到了古老的、冰冷的固体下部板块，也观察到了在10亿多年前的一次大板块碰撞中移动到顶部的柔软、高温的上覆岩石。简而言之，我们发现了使落基山脉处于适当位置的过程的本质。在岩石记录中记录的短暂时间间隔内，地球上生命的进化一直受到物种突然急剧丧失的影响。这些大规模灭绝事件可能与陨石撞击和重大火山喷发有关。使用高分辨率的U-Pb测年方法，我们可以准确地确定这些陨石/火山事件的时间，并通过测定发生在灭绝层位附近的火山灰床来建立或驳斥与灭绝事件的同步性。此外，我的研究还涉及在野外选择复杂片麻岩地体中的岩石的新策略，这些岩石提供了与曾经活跃的构造过程直接相关的年龄信息。我还在实验室中开发方法，以更好地解析出现在变质岩中的复杂的、多阶段的锆石群体，并使U-Pb年龄更加准确。

Precise uranium-lead analyses of minute (microgram) quantities of the mineral 'zircon' that crystallize during formation, reheating, or ductile flow events provide detailed scenarios of the evolution of the Earth's crust during periods of mountain building. When enormous continental plates collide, this produces over-thickened stacks of crustal rocks such that the lower part of the thrust stack is heated from below and softened and slides further inland. This must have happened under the Rocky Mountains as this thick pile of sedimentary material, once at the ocean bottom, now sits above an older continent. To understand processes that took place along the interface, 10 - 20 km below the Earth's surface where we cannot see, we must find a very old mountain root where the mountains have since been removed by erosion. The Grenville Province, well exposed along Georgian Bay, Ontario, is such a root. Here, geologists who study the rock record observe both the old, cold solid lower plate and the soft, hot overlying rocks that moved overtop during a great plate collision more than a billion years ago. In short, we discover the nature of the processes that put the Rockies in their place.   The evolution of life on Earth has been subject to sudden drastic losses of species over brief time intervals that are recorded in the rock record. These mass extinction events can be correlated with meteorite impacts and major volcanic eruptions. Using high resolution U-Pb dating methods we can accurately pinpoint the time of these meteoritic/volcanic events and establish or refute synchronicity with the extinction events by dating volcanic ash beds that occur near the extinction horizons.   My research also involves new strategies in the field to select rocks in complex gneiss terranes that give age information directly tied to once active tectonic processes. I am also developing methods in the laboratory to better resolve complex, multi-stage, zircon populations that occur in metamorphic rocks, and to make U-Pb ages more precise.