Metamorphic Core Complexes in Context: Incorporating Gravitational Collapse into the Orogenic Cycle

重力塌陷是大陆造山作用的重要组成部分。这方面的证据是变质核杂岩的发展，它在构造增厚的地壳中挖出了韧性的中地壳岩石。本项目测试的模型，近垂直平流的中地壳岩石和脆性正断层的重力塌陷的启动解释了许多岩石学和结构的观察，是核心复杂的特点，在收敛设置。为此，通过综合数值模拟，U-Pb年代学，微量元素测温，压力-温度路径的相平衡模拟，在收敛设置变质核杂岩的形成进行了研究。目前正在研究北方落基山脉地区的三个核心复合体，它们是蒙大拿州、爱达荷州和华盛顿的比特鲁特、克利尔沃特和普里斯特河复合体。其目标是限制最大压力和减压压力-温度路径、变质作用高峰期的时间和地壳最大增厚与快速剥露开始之间的间隔、地壳的热演化及其随时间对地壳流变学的影响，最后是塌陷开始时初始减压的剥露率。岩石学结果将与数值模拟结果进行比较，包括粒子路径，时间预测和热条件。变质核杂岩是常见的地壳规模的结构，暴露下地壳中至深部变质基底覆盖较少变质盖层岩石。高度变形的断裂带通常将基底与盖层序列分开。核杂岩的一个基本特征，即深部基底岩石的暴露，通常归因于大规模地壳伸展期间的显著折返。这项研究探索了另一种模式，即在造山运动的衰退阶段，重力塌陷解释了许多变质核杂岩。了解变质核杂岩在大陆缩短背景下形成的地点、时间、原因和方式是重要的，因为这些特征是岩石变形记录的一部分。变质核杂岩为造山晚期中、上地壳的相互关系提供了最直接的观测信息，为研究地壳耦合和陆壳内物质传递提供了宝贵的机会。该研究使用的研究结果，通过与数学科学伙伴关系计划的合作，重点是改善美国土著学生的科学教学，与K-12教师进行专业发展研讨会的实地活动和基于场所的活动的发展。

An important component of continental orogenesis is gravitational collapse. Evidence for this is the development of metamorphic core complexes, which exhume ductile, mid-crustal rocks within tectonically-thickened crust. This project test the model that near-vertical advection of mid-crustal rocks and initiation of brittle normal faults through gravitational collapse explains many of the petrological and structural observations that are characteristic of core complexes in convergent settings. To this end, the formation of metamorphic core complexes in convergent settings is investigated through integrated numerical modeling, U-Pb geochronology, trace element thermometry, and phase equilibria modeling of pressure-temperature paths. Three core complexes in the northern Rocky Mountain region that exhumed rocks with a record of the convergent tectonic history prior to core complex initiation are being studied: the Bitterroot, Clearwater, and Priest River complexes in Montana, Idaho, and Washington. The goals are to place constraints on the maximum pressures and decompressional pressure-temperature paths, the timing of peak metamorphism and the interval between maximum crustal thickening and the onset of rapid exhumations, the thermal evolution of the crust and its effect on the rheology of the crust through time, and, finally, exhumation rates for the initial decompression at the onset of collapse. Petrological results will be compared with numerical modeling results, including particle paths, timing predictions, and thermal conditions.Metamorphic core complexes are common crustal-scale structures that expose underlying mid- to deep-crustal metamorphic basement overlain by less metamorphosed cover rocks. Highly deformed fault zones typically separate basement from cover sequences. An essential feature of core complexes, exposure of deep basement rocks, is commonly attributed to significant exhumation during large-scale crustal extension. This research explores an alternate model that gravitational collapse in the waning stages of mountain building explains many metamorphic cores complexes. Understanding where, when, why, and how metamorphic core complexes form in settings of continental shortening is important because these features are part of the rock record of deformation. Moreover, metamorphic core complexes provide the most direct observational information about the relationship between the middle and uppermost crust in the late stages of mountain building, so offer a valuable opportunity to investigate crustal coupling and mass transfer within continental crust. The study uses results from the research in the development of field activities and place-based activities for professional development workshops with K-12 teachers through partnership with a Math & Science Partnership program focused on improving science instruction for Native American students.