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

大陆造山作用的一个重要组成部分是重力坍缩。这方面的证据是变质核杂岩的发育，它在构造增厚的地壳中发掘出延展性强的中地壳岩石。该项目测试了一个模型，即中地壳岩石的近垂直平流和通过重力塌陷形成的脆性正断层解释了许多岩石学和结构观察结果，这些观察结果是会聚环境中核心复合体的特征。为此，通过综合数值模拟、U-Pb地质年代学、微量元素测温和压力-温度路径相平衡模拟，研究了汇聚环境中变质核杂岩的形成。目前正在研究落基山脉北部地区出土的三个岩心杂岩，这些岩心杂岩在岩心杂岩形成之前具有会聚构造历史的记录：蒙大拿州、爱达荷州和华盛顿州的Bitterroot、Clearwater和Priest River杂岩。目标是限制最大压力和减压压力-温度路径，峰值变质的时间和最大地壳增厚与快速挖掘开始之间的间隔，地壳的热演化及其对地壳随时间流变的影响，以及最后，在崩溃开始时初始减压的挖掘速率。岩石学结果将与数值模拟结果进行比较，包括颗粒路径、时间预测和热条件。变质核杂岩是一种常见的地壳尺度构造，它暴露出下伏的中深部变质基底，上覆较少变质的盖层。高度变形的断裂带通常将基底与盖层分开。岩心杂岩的一个基本特征是深基底岩石的暴露，这通常归因于大规模地壳伸展期间的大量发掘。本研究探索了另一种模型，即在造山活动的衰退期引力坍缩解释了许多变质岩心复合体。了解变质核复合体在大陆缩短过程中的形成地点、时间、原因和方式是很重要的，因为这些特征是岩石变形记录的一部分。此外，变质核杂岩提供了造山晚期中上部地壳关系的最直接观测信息，为研究大陆地壳内部的地壳耦合和物质传递提供了宝贵的机会。该研究使用了对K-12教师的专业发展研讨会的实地活动和基于地点的活动的研究结果，通过与数学和科学伙伴关系项目的合作，重点是改善美国土著学生的科学教学。

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.