Structural, metamorphic, and thermal evolution of the Brooks Range (Alaska) metamorphic belts: implications for formation-exhumation of high-pressure rocks and Arctic tectonic evol

阿拉斯加北部布鲁克斯山脉的片岩带长600多公里，是世界上最大的高压变质地体之一，与世界上其他高/超高变质岩具有许多共同的特征。本研究的重点是记录片岩带和邻近的低压变质岩的变形、变质和热历史，以验证与两组问题相关的假设。高压岩石是如何被挖掘到地球表面的？浮力强的大陆岩石圈板块可能是由于俯冲带上附着的致密海洋岩石圈下沉而被拉入俯冲带的，这为大陆岩石深部构造埋藏和伴随的高压变质作用提供了一个简单的解释。然而，人们对这些高压岩石被带回地球表面的过程仍然知之甚少。(2)人们普遍认为，在加拿大盆地（北冰洋）形成期间，布鲁克斯山脉、阿拉斯加北部其余地区和楚科奇半岛逆时针旋转了约66°，远离加拿大北极群岛。布鲁克斯山脉的哪些地质事件（如大陆俯冲和高压变质作用、碰撞、伸展、盆地形成）与旋转盆地张开有动态联系，目前尚不清楚。此外，目前还不清楚这种几何样式的盆地开口是如何沿着从阿拉斯加东北部到楚科奇的约3000公里长的大陆块的走向适应的。该项目将为STEM领域的一名博士生、一名硕士学生和多名本科生提供经济支持和培训，其中可能包括女性和代表性不足的群体。学生将获得实地测绘的经验，以及与两所大学的专家一起在设施中使用各种分析实验室技术。研究生将通过与阿拉斯加地质与地球物理勘探局合作，制作以北极地质学为重点的教材，分发给阿拉斯加的学校。通过对北极地质的进一步了解，本研究将为未来十年北极地区开放勘探提供一个更好的资源经济开发框架。—白垩纪被动边缘与大洋Angayucham地体交汇形成了布鲁克斯山脉造山带（阿拉斯加北部），该造山带包括一条褶皱冲断带和两条变质带：蓝片岩/榴辉岩片岩带和高压绿片岩中央带。然而，这些变质带的构造、变质史和热史的许多关键方面都缺乏，导致高压岩石的发掘和布鲁克斯山脉和大北极地区的构造演化模式不一。在这项研究中，我们将使用现场和分析技术来记录这两个带的结构、变质和热演化，以测试三个相关类别的模型。(1)研究人员将对布鲁克斯山脉南翼正常意义上的构造的时间和地球动力学意义以及两侧盆地的构造背景等备受争议的关系进行模型测试。这项工作将对构造-热事件进行运动学和年龄限制，特别是在阿拉斯加北部和邻近的北极地区发生重要变化的关键时期——阿普提安-阿尔比安时期。(2)研究人员将对高压岩石的形成和挖掘模型进行测试，重点研究浮力驱动的挖掘模型的作用。(3)布鲁克斯山脉和北极阿拉斯加-楚科奇微板块的其余部分被认为逆时针旋转了约66°，远离加拿大北极群岛，导致加拿大盆地的形成。目前尚不清楚布鲁克斯山脉的哪些事件（如大陆俯冲和高p变质作用、碰撞、伸展、盆地形成）与盆地张开有动态联系。此外，关于这个地质上前所未有的几何盆地开口是如何沿着北极阿拉斯加-楚科奇微板块约3000公里长的大陆块的走向被容纳的，还有争论。改进的布鲁克斯山脉构造事件的时间约束将解决这些问题，并测试特定的模型。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With a length of over 600 km, the Schist belt in the Brooks Range of northern Alaska is one of the largest high-pressure metamorphic terranes in the world and shares many characteristics with other high-/ultra-high- metamorphic rocks around the world. This study is focused on documenting the deformational, metamorphic, and thermal histories of the Schist belt and adjacent lower pressure metamorphic rocks to test hypotheses related to two groups of questions. (1) How are high-pressure rocks exhumed to the Earth’s surface? Buoyant continental lithospheric plates may be pulled into subduction zones by sinking of the attached dense oceanic lithosphere at subduction zones, providing a simple explanation for deep tectonic burial and associated high-pressure metamorphism in continental rocks. However, the processes by which these high-pressure rocks are brought back up to the earth’s surface remain poorly understood. (2) The Brooks Range, the rest of the northern Alaska, and Chukotka are widely believed to have rotated about 66° anti-clockwise away from the Canadian Arctic Islands during formation of the Canada Basin (Arctic Ocean). It remains unclear as to what geologic events (e.g., continental subduction and high-pressure metamorphism, collision, extension, basin formation), if any, in the Brooks Range are dynamically linked to rotational basin opening. Furthermore, it is unclear as to how this geometrical style of basin opening is accommodated along the strike of the of the ca. 3000 km long continental land mass from northeastern Alaska to Chukotka. This project will provide financial support and training of a Ph.D. student, a M.Sc. student, and multiple undergraduates in STEM fields, potentially including women and underrepresented groups. The students will gain experience in field mapping, as well as a variety of analytical laboratory techniques in facilities with experts at two universities. Graduate students will be involved in outreach through creation of teaching materials focused on Arctic geology that will be distributed to Alaska schools through collaboration with the Alaska Division of Geological & Geophysical Surveys. Through an increased understanding of Arctic geology, this study will provide an improved framework for economic development of resources as the Arctic region opens for exploration in the coming decade.Jurassic(?)-Cretaceous convergence between a passive margin and the oceanic Angayucham terrane produced the Brooks Range orogen (northern Alaska), which includes a fold-thrust belt and two metamorphic belts: the blueschist/eclogite Schist belt and the high-pressure greenschist Central belt. However, many key aspects of the structural, metamorphic, and thermal histories are lacking for these metamorphic belts, resulting in diverse models for exhumation of the high-pressure rocks, and the tectonic evolution of both the Brooks Range and greater Arctic region. In this study we will use field and analytical techniques to document the structural, metamorphic, and thermal evolution of both belts to test models in three interrelated categories. (1) The researchers will test models for the highly debated relationships regarding the timing and geodynamic significance of normal-sense structures on the south flank of the Brooks Range, and the tectonic setting of flanking basins. The work will place kinematic and age constraints on tectono-thermal events, particularly in during the Aptian-Albian, a key time of important change in north Alaska and the adjacent Arctic realm. (2) The researchers will test models for the formation and exhumation of high-pressure rocks, with a focus on the role of buoyancy-driven exhumation models. (3) The Brooks Range and the rest of the Arctic Alaska – Chukotka microplate is believed to have rotated about 66° anti-clockwise away from the Canadian Arctic Islands, resulting in the formation of the Canada Basin. It remains unclear as to what events (e.g., continental subduction and high-P metamorphism, collision, extension, basin formation), if any, in the Brooks Range are dynamically linked to basin opening. Furthermore, there is debate regarding how this geologically unprecedented geometrical basin opening is accommodated along the strike of the of the ca. 3000-km-long continental land mass of the Arctic Alaska – Chukotka microplate. Improved timing constraints for Brooks Range tectonic events will address these issues and test specific models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.