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

University Of Florida, Gainesville FL

Investigators

Abstract

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.