Collaborative Research: Investigation of a Late Jurassic Paired Magmatic Belt (Blue Mountains, NE Oregon): Evaluation of Magmatic Growth During Contractional Orogeny

该研究项目的主要目标是了解俄勒冈州东北部蓝山省具有重要化学特征（低Sr/Y、Na、Al、Sr和高Y，与高Sr/Y、Na、Al、Sr和低Y形成对比）的岩体和岩基的起源。 此外，他们将研究涉及弧-弧和弧-陆碰撞的地壳变形事件的意义。高Sr/Y和低Sr/Y的岩体在古代和现代造山带中占据了很大的面积，例如在阿巴拉契亚山脉、新西兰和内华达州的Sierra，然而，关于它们的生成机制、它们形成的构造环境以及它们在大陆地壳演化中的作用存在着相当大的争议。以往的模型认为，俯冲洋壳或下陆壳的部分熔融可能产生高Sr/Y岩浆。本项目利用构造地质学、地质年代学、火成岩和变质岩石学来检验这些已有的模型，并提出了一个新的模型，其中岛弧的侧向构造碰撞在控制高Sr/Y岩浆活动的发生和分布方面发挥了重要作用。如果这项研究成功，将为高和低Sr/Y岩浆的生成机制，它们在造山带中的时空分布，以及它们与蓝山省成矿作用的关系提供新的见解。这项研究也有更广泛的意义，通过横向构造碰撞理解蓝山省中生代地壳结构的变化。他们的本科生和研究生正在进行多学科研究，以调查成对的高和低Sr/Y的岩体和岩基的岩浆发展。本文重点研究了高、低Sr/Y岩浆作用的时间、地球化学特征及其与晚侏罗世收缩变形变质作用的关系。我们提出了一个新的模式，晚侏罗世的造山作用发生在一个相对较短的时间间隔（159-157 Ma）的碰撞（弧-弧），并导致地壳增厚的贝克河。这种地壳结构的变化导致了两个同时代的，但空间和地球化学上不同的带晚侏罗世至早白垩世高和低Sr/Y的岩体和岩基在147-143 Ma的建立。我们把我们的研究重点放在蓝山省，因为它包含了一个最好的暴露的例子配对高，低Sr/Y岩浆带与晚侏罗世收缩变形在北美科迪勒拉。我们测试我们的模型，通过综合和详细的地质和构造测绘，地球化学和同位素研究（Sr-Nd-O），和U-Pb和Sm-Nd放射性测年。如果我们对这些岩浆带的解释是正确的，这项研究将代表一个独特的机会，研究高和低Sr/Y岩浆生成过程和碰撞构造，岩浆作用和变质作用之间的相互作用，在中生代会聚边缘设置。

The main goal of this research project is to understand the origin of plutons and batholiths in the Blue Mountains province of northeastern Oregon with important chemical characteristics (low Sr/Y, Na, Al, Sr, and high Y, in contrast to high Sr/Y, Na, Al, Sr, and low Y). In addition, they will study the significance of crustal deformation events involving arc-arc and arc-continent collision. High and low Sr/Y plutons occupy large areas in ancient and modern orogenic belts, such as in the Appalachian Mountains, New Zealand, and the Sierra Nevada, yet considerable controversy exists regarding mechanisms of their generation, the tectonic settings in which they form, and their role in the evolution of continental crust through time. Previous models have proposed that partial melting of subducting oceanic crust or lower continental crust may generate high Sr/Y magmas. This project uses structural geology, geochronology, and igneous and metamorphic petrology to test these pre-existing models, and proposes a new model in which lateral tectonic collisions of island arcs played an important role in controlling the onset and distribution of high Sr/Y magmatism. This study, if successful, will provide new insights into the mechanisms of high and low Sr/Y magma generation, their spatial and temporal distribution in orogenic belts, and their relationship to mineralization in the Blue Mountains province. This study also has broader implications for understanding changes in the Mesozoic crustal structure of the Blue Mountains province through lateral tectonic collisions.The PIs their undergraduate and graduate students are conducting a multidisciplinary study to investigate the magmatic development of paired high and low Sr/Y plutons and batholiths. This study focuses on understanding the timing and geochemical characteristics of high and low Sr/Y magmatism, and its relationship to Late Jurassic contractional deformation and metamorphism. We propose a new model in which Late Jurassic orogensis occurred in response to collision (arc-arc) during a relatively brief time interval (159-157 Ma), and resulted in crustal thickening in the Baker terrane. This change in crustal structure led to the establishment of two coeval, yet spatially and geochemically distinct belts of Late Jurassic to Early Cretaceous high and low Sr/Y plutons and batholiths at 147-143 Ma. We focus our study on the Blue Mountains province, because it contains one of the best-exposed examples of paired high and low Sr/Y magmatic belts associated with Late Jurassic contractional deformation in the North American Cordillera. We test our model through integrated and detailed geologic and structural mapping, geochemical and isotope studies (Sr-Nd-O), and U-Pb and Sm-Nd radiometric dating. If we are correct in our interpretation of these magmatic belts, this study will represent a unique opportunity to study processes of high and low Sr/Y magma generation and the interplay between collisional tectonics, magmatism and metamorphism in a Phanerozoic convergent margin setting.