Collaborative Research: Collaborative Research: Deciphering the Structure and Evolution of North America?s Cratonic Core

该项目旨在阐明美国中部大陆的形成，组装和随后的演变。来自两所大学的研究人员及其研究生和本科生将研究大陆中部地壳和上地幔的组成。重力和磁力数据与根据地震接收器功能数据估计的地震速度比vP/vS以及根据表面波和体波层析成像的速度结构的新组合将用于确定地壳内多个层的温度变化以及厚度和整体成分。这些努力的新要素包括开发一种新的方法来接收器功能成像使用参数域互相关和叠加，和耦合的地震图像的潜在的场数据通过似然滤波器和速度密度关系。磁性研究还将侧重于了解磁性探测边界的物理性质和构造含义，特别强调划分北美东太平洋核的隐藏的中元古代地球化学和磁性边界，以及田纳西州-伊利诺伊州-肯塔基州线性构造（或TIKL）及其不寻常的带状磁化模式。地球物理模型的结果将结合稀疏采样的基底同位素地球化学和年龄数据来解释岩石圈块体的形成和增生的历史，以及随后的构造岩浆修改。关于地壳的物理性质及其构造作用和火山作用历史的知识是一系列固体地球科学主题的核心。对未来地震可能性的评估和对深层经济矿藏的潜力的评估只是这类知识发挥重要社会作用的应用的两个例子。为了更好地评估这些风险和经济潜力，一个由两所大学的教授、研究生和本科生参与的多学科项目将试图了解形成美国中部大陆地质核心的关键结构、组成和过程。在美国西部的山区，绘制物理性质的变化和推断构造历史相对简单，因为地壳深部和地幔上部的地球物理图像可以通过对岩石暴露和/或通过地质过程带到地表的研究来证实。然而，在美国中部大陆地区，厚厚的沉积岩序列覆盖了岩浆活动阶段产生的古老岩石。到达沉积物覆盖层以下的钻孔很少，而且相隔很远，这使得了解可能控制地震和隐藏矿藏位置的地质过去具有挑战性。因此，该地区的构造和地震危险图更多地依赖于地球物理线性特征：地球物理数据集地图视图中的线性特征，表示地质边界和薄弱地带。这项研究旨在结合联合收割机几种不同类型的地球物理数据集，包括重力和磁力异常，以及图像的EarthScope？的地震仪阵列。从这些数据中得出的大陆中部地壳以前未知的特征将被用来更好地描述地质边界的影响，以全面了解地球的历史和性质？的外层。

This project seeks to illuminate the formation, assembly and subsequent evolution of the US mid-continent. Investigators at two universities and their graduate and undergraduate students will examine composition of the mid-continent crust and upper mantle. A novel combination of gravity and magnetic data with seismic velocity ratios vP/vS estimated from seismic receiver function data and velocity structure from surface wave and body wave tomography will be used to establish variations in temperature as well as thickness and bulk composition of multiple layers within the crust. The novel elements of these efforts include development of a new approach to receiver function imaging using parameter-domain cross-correlation and stacking, and coupling of the seismic images to the potential field data via likelihood filters and velocity-density relationships. Magnetic studies will focus also on understanding the physical properties and tectonic implications of magnetically detected boundaries, with particular emphases on a hidden middle Proterozoic geochemical and magnetic boundary dividing the cratonic core of North America and also on the Tennessee-Illinois-Kentucky lineament (or TIKL) and its unusual banded pattern of magnetization. The geophysical model results will be combined with sparsely sampled basement isotope geochemistry and age data to interpret the history of formation and accretion of lithospheric blocks as well as their subsequent tectonomagmatic modification. Knowledge about physical properties of the crust and its history of tectonism and volcanism is central to a wide array of solid Earth science topics. Assessments of the likelihood of future earthquakes and the potential for economic mineral deposits at depth are just two examples of applications in which such knowledge plays a vital societal role. In order to evaluate better these risks and economic potential, a multi-disciplinary project involving professors and graduate and undergraduate students at two universities will seek to understand key structures, composition and processes that formed the geologic core of the US mid-continent. In mountainous regions of the western US, mapping variations in physical properties and inferring tectonic history are relatively straightforward because geophysical images of the deep crust and uppermost mantle can be corroborated by studies of rocks exposed and/or brought to the surface by geologic processes. In the mid-continent region of the US however, thick sequences of sedimentary rocks cover the ancient rocks produced by episodes of magmatism. Boreholes reaching below the sedimentary cover are few and far between and that has made it challenging to understand the geologic past that may control the locations of earthquakes and hidden mineral deposits. Consequently, tectonic and seismic hazard maps of this region rely more heavily on geophysical lineaments: linear features found in map-views of geophysical data sets signifying geologic boundaries and weak zones. This study seeks to combine several different types of geophysical data sets, including gravity and magnetic anomalies as well as images made possible by EarthScope?s array of seismometers. The previously unknown characteristics of the mid-continent crust derived from these data will be used to better characterize implications of the geologic boundaries for understanding comprehensively the history and properties of the Earth?s outer layers.