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

本研究项目的主要目的是了解美国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，而不是高Sr/Y、Na、Al、Sr和低Y）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、低Sr/Y岩体在古、现代造山带，如新西兰的阿巴拉契亚山脉和内华达山脉等地占据了大片区域，但它们的形成机制、形成的构造环境及其在大陆地壳演化中的作用等方面存在着相当大的争议。以往的模式认为，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、年代学、火成岩和变质岩学等方法对已有模型进行了验证，提出了岛弧横向构造碰撞对高Sr/Y岩浆活动的发生和分布起重要控制作用的新模型。如果研究成功，将为蓝山地区高、低Sr/Y岩浆的生成机制、造山带时空分布及其与成矿关系提供新的认识。该研究对认识蓝山省中生代横向构造碰撞的地壳结构变化具有更广泛的意义。该学院的本科生和研究生正在开展多学科研究，研究高、低Sr/Y配对岩体和岩基的岩浆发育。重点研究了高、低Sr/Y岩浆活动的时间、地球化学特征及其与晚侏罗世收缩变形和变质作用的关系。我们提出了一种新的造山模式，认为晚侏罗世造山活动是在相对较短的时间间隔（159-157 Ma）内对碰撞（弧-弧）的响应，并导致贝克地体地壳增厚。这种地壳结构的变化导致在147-143 Ma形成了晚侏罗世至早白垩世两个时间相同但空间和地球化学上截然不同的高、低Sr/Y岩体和岩基带。我们将研究重点放在蓝山省，因为它包含了北美科迪勒拉地区晚侏罗世收缩变形相关的高、低Sr/Y配对岩浆带的最佳暴露例子之一。我们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）以及U-Pb和Sm-Nd放射性测年来测试我们的模型。如果我们对这些岩浆带的解释是正确的，那么这项研究将为研究显生宙辐合边缘背景下的高、低Sr/Y岩浆生成过程以及碰撞构造、岩浆作用和变质作用之间的相互作用提供一个独特的机会。

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.