Collaborative Research: An Exhumed Field Example of Heterogeneous Lower Crustal Flow, Athabasca Granulite terrane, Canada

合作研究：加拿大阿萨巴斯卡粒粒岩地体非均质下地壳流的现场挖掘实例

• 批准号: 0948560
• 负责人: Michael Williams
• 金额: $ 17.09万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-05-15 至 2014-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0948560&HistoricalAwards=false
• 关键词: Collaborative; Research; Exhumed; Field; Example

The role played by Earths lower crust (25-30 km depth) in the dynamic evolution of continents is a fundamental target in Earth sciences. In particular, pervasive ductile flow of the lower crust has been proposed in many tectonically active regions around the world in order to reconcile topography and other surface geologic and climatic processes with lithospheric-scale geodynamic and geophysical data sets. Although commonly modeled homogeneously in two-dimensions, natural observations suggest that this process is fundamentally heterogeneous (e.g., with lateral boundaries and internal gradients in the flow field). In this project, we seek to document the spatial variation and physical characteristics of this heterogeneity in an exposed example of lower crustal flow so that this process may be more easily recognized remotely (i.e., seismically) in the deep crust of active tectonic regions. Two graduate students will base their dissertations on this work, and undergraduate students will participate as field assistants and as researchers in sample analysis and modeling. The Athabasca Granulite Terrane in the western Canadian Shield is arguably the largest exposure of lower continental crust in North America. Within this terrane, a gently dipping and locally pervasive granulite-facies deformation fabric records sub-horizontal ductile flow at 30-40 km paleodepth. The Cora Lake shear zone is a distinct kilometer-scale sub-vertical zone of high-grade strike-slip deformation that is thought to be kinematically compatible and co-eval with the adjacent sub-horizontal flow fabrics. We hypothesize that 1) the early history of the Cora Lake shear zone is an analog for heterogeneity and strain partitioning in some modern lower crustal flow regimes and 2) that the fabric intensity and scale of the shallow and steep fabric domains are sufficient for seismic observation. We will test these hypotheses with three objectives: 1) detailed field mapping with the goal of constructing a map of lower crustal flow and especially flow heterogeneity, 2) Pressure-Temperature-time-Deformation modeling in order to constrain the depth and temporal evolution of heterogeneous flow, and 3) petrophysical analysis and synthetic seismic modeling in order to constrain the rheological evolution of the deep crust and illuminate how similar structures may be recognized and interpreted through seismic anisotropy methods. The ultimate goal is a model for the development of these structures in lower crust and for the evolution of their rheological and seismic properties.

地球较低地壳（25-30 km深度）在大陆动态演变中起的作用是地球科学的基本目标。特别是，在世界各地的许多构造活动区域中都提出了下层地壳的普遍延展性延展性流，以便将地形和其他地面地质和气候过程与岩石圈尺度的地球力学和地球物理数据集进行调和。尽管通常在二维中同质建模，但自然观察表明，该过程从根本上是异质的（例如，在流场中具有横向边界和内部梯度）。在该项目中，我们试图在较低的地壳流动的示例中记录该异质性的空间变化和物理特征，以便在活性构造区域的深层地壳中更容易远程识别此过程。两名研究生将基于这项工作的论文，本科生将作为现场助手和研究人员参与样本分析和建模。加拿大西部盾牌的Athabasca颗粒地层可以说是北美下大陆壳的最大暴露。在这个地形内，在30-40 km古兴趣上，局部倾斜和局部普遍存在的颗粒状变形织物记录了下延性延展性流动。 Cora Lake剪切带是一个独特的公里尺度的高级滑滑变形的次垂直区，被认为在运动学上与相邻的亚侧 - 休闲流面织物相兼容。我们假设1）Cora Lake剪切区的早期历史是在某些现代下层地壳流程中进行异质性和应变分配的类似物，以及2）浅层和陡峭的织物结构域的织物强度和尺度足以使地震观察。 We will test these hypotheses with three objectives: 1) detailed field mapping with the goal of constructing a map of lower crustal flow and especially flow heterogeneity, 2) Pressure-Temperature-time-Deformation modeling in order to constrain the depth and temporal evolution of heterogeneous flow, and 3) petrophysical analysis and synthetic seismic modeling in order to constrain the rheological evolution of the deep crust and illuminate how similar可以通过地震各向异性方法识别和解释结构。最终目标是在下层地壳中开发这些结构的模型以及其流变学和地震特性的发展。