RUI: Exhumation History and Potential Mesozoic Fault Reactivation of the St. Lawrence Rift System, Southern Quebec

魁北克省南部的圣劳伦斯裂谷系是一个目前活跃的地震带，沿西北-西南走向的晚元古代(900 ？5.7亿年前)区域正断层可能在中生代(248 ？6500万年前)。这项研究使用磷灰石裂变径迹分析来确定沿着这些断层以及相关的西北-西南走向的断层的冷却或挖掘历史，这些断层包围着魁北克南部的萨格奈河峡湾。磷灰石裂变径迹定年法可以对岩石进行估算。地球的冷却历史低于100摄氏度，这相当于地壳深度约3-4公里。本次调查的目标是：1)确定这些断层系统最近一次位移和/或重新激活的时间、区域范围和震级；2)将潜在的中生代断裂恢复活动与主要区域断裂的形成联系起来，这些断裂连接了新英格兰的一系列裂谷盆地，这些裂谷盆地是在中生代大西洋打开期间形成的。裂解径迹年龄趋势将更好地描绘出中生代裂陷对北美东北部内部影响的区域范围，这将对北大西洋裂陷的时间和性质具有重要意义。本研究的结果将更好地约束白垩纪北美板块在大流星热点上的通过，同时在纽约州北部和新英格兰地区广泛的区域挖掘，以及目前从纽约东部穿过佛蒙特州进入新罕布什尔州怀特山区的低横波速度地幔上薄岩石圈的存在。该研究将把魁北克的Charlevoix地区（北美东部地震最活跃的地区）当前的活跃地震活动与中生代的区域挖掘和裂谷联系起来，这些裂谷是由北美东北部板块通过大流星热点引起的。该结果也可用于魁北克南部的油气勘探。本科生将实质性地参与项目的各个方面，从现场样本收集到实际年龄确定。参与这项研究工作的学生将大大提高他们对地质研究技术的知识，并将在专业会议上展示他们的成果。

The Saint Lawrence Rift System in southern Quebec is a currently active seismic zone along northwest-southwest-trending Late Proterozoic (between 900 ? 570 million years ago) regional normal faults that may have been reactivated during the Mesozoic (between 248 ? 65 million years ago). This study is using apatite fission-track analysis to determine the cooling or exhumation history along these faults as well as related northwest-southwest-trending faults bounding the Saguenay River fjord in southern Quebec. Apatite fission-track dating allows an estimation of a rock?s cooling history below 100 degrees Centigrade, which corresponds to about 3-4 km depth in the Earth's crust. The goals of this investigation are to: 1) determine the timing, regional extent and magnitude of the most recent displacement and/or reactivation of these fault systems; and 2) relate potential Mesozoic fault reactivation to the formation of major regional faults which bound a series of rift basins in New England that were created in the Mesozoic during the opening of the Atlantic Ocean.The fission-track age trends will better delineate the regional extent of the effects of Mesozoic rifting into the interior of northeastern North America, which will have major implications for the timing and nature of rifting in the North Atlantic. The suggested relationship of the passage of the North American plate over the Great Meteor hotspot in the Cretaceous, widespread regional exhumation across northern New York state and New England during the same time, and the current existence of thin lithosphere over low shear wave velocity mantle from eastern New York across Vermont and into the White Mountain region of New Hampshire will be better constrained by the results of this study. The study will relate the current active seismicity in the Charlevoix, Quebec region, which is the most seismically active zone in eastern North America, to the Mesozoic regional exhumation and rifting attributed to the passage of northeastern North American plate over the Great Meteor hotspot. The results can also be useful in hydrocarbon exploration in southern Quebec. Undergraduate students will be involved in a substantial manner in all aspects of the project from field sample collection to actual age determinations. The students participating in this research effort will greatly enhance their knowledge of geologic research techniques and will present their results at professional conferences.