Collaborative Research: Mid-crustal Strain during Extension: A Field-based Investigation of Rheological Transitions, Doming, and Vertical Coupling

地壳对构造力和重力的反应方式取决于地壳岩石的强度分布。人们普遍认为，在某些情况下，地壳下半部的岩石可能非常脆弱，它们会因地形梯度引起的压力差而横向流动。这种行为对大陆地壳的许多过程都有重要的影响，例如，山地高原的生长，盆地和大陆架的形成，以及大陆内的地震活动。 然而，这些模式需要通过更好的实地调查进行严格检验。爱达荷州的先锋山脉，这些PI将集中他们的研究，暴露的岩石可能代表一个边界区之间的强大的岩石和下面的较弱的流动岩石，如果是这样的话，将提供一个很好的机会来测试模型，涉及流动的弱下地壳岩石。对岩石强度的垂直变化进行更好的野外记录将使我们对大陆变形有一个更全面的认识。许多最近的地壳变形模型都以中地壳和下地壳为特征，这种地壳足够脆弱，以至于它会响应侧向压力梯度而发生膨胀和流动。这种流动对地壳变形的几个方面有着深刻的影响。然而，目前的许多模型弱解耦中下地壳流动，来自间接观测和模型流变层在岩石记录中的代表程度尚不清楚。初步工作表明，在爱达荷州的先锋核心复杂的包含一个地壳中段暴露出一个解耦边界，这提供了一个机会，测试模型的弱和解耦流。在本项目中，将通过基于野外的构造和AMS分析，结合U-Pb地质年代学和Ar/Ar热年代学，通过记录中地壳岩石的应变历史，对具有可变解耦测试模型的PI进行测试。这些数据将使我们能够详细地比较，在不同的结构层次的运动学和应变历史，并调查中地壳流变分层，圆顶和上地壳伸展之间的关系。

The manner in which the Earths crust responds to tectonic and gravitational forces depends on the strength distribution of crustal rocks. It has been widely proposed that in certain settings, rocks in the lower half of the crust may be sufficiently weak that they flow laterally in response to pressure differences induced by topographic gradients. Such behavior has important implications for many processes in the continental crust, for example, the growth of mountain plateaus, formation of basins and continental shelves, and seismicity within the continents. These models, however, need to be rigorously tested through better field-based investigations. The Pioneer Mountains of Idaho, where these PIs will focus their study, expose rocks that may represent a boundary zone between strong rocks and underlying weaker flowing rocks, and if so will provide an excellent opportunity to test models that involve flow of weak lower crustal rocks. Better field documentation of the vertical changes in rocks strength will provide us with a more comprehensive view of continental deformation.Many recent models of crustal deformation feature a middle to lower crust that is sufficiently weak that it decouples and flows in response to lateral pressure gradients. Such flow has profound implications for several aspects of crustal deformation. Many of the current models for weak decoupled middle to lower crustal flow, however, are derived from indirect observation and the extent to which model rheological layers are represented in the rock record is unclear. Preliminary work shows that the Pioneer core complex in Idaho contains a midcrustal section exposing a decoupling boundary, which presents an opportunity to test models of weak and decoupled flow. In this project the PIs with test models of variable decoupling will be tested through documentation of the strain history in the midcrustal rocks through field-based structural and AMS analysis, combined with U-Pb geochronology, and Ar/Ar thermochronology. Together these data will allow us to compare in detail, the kinematic and strain histories at the various structural levels and investigate the relationships between the mid-crustal rheological layering, domes, and upper crustal extension.