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

这项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，而不是高Sr/Y、Na、Al、Sr和低Y)的深成岩和基岩的起源。此外，他们还将研究涉及弧弧和弧陆碰撞的地壳形变事件的意义。在古代和现代造山带中，如新西兰阿巴拉契亚山脉、内华达山脉等地，高、低Sr/Y深成岩占据了很大的面积，但对于它们的产生机制、形成的构造环境以及它们在陆壳随时间的演化中的作用，存在着很大的争议。前人的模型认为，俯冲洋壳或下陆壳的部分熔融可能产生高的锶/Y岩浆。该项目利用构造地质学、年代学、火成岩和变质岩石学对这些已有的模型进行了检验，并提出了岛弧的侧向构造碰撞对高Sr/Y岩浆作用的开始和分布起到重要控制作用的新模型。如果研究成功，将对青山省造山带高、低Sr/Y岩浆的形成机制、时空分布及其与成矿的关系提供新的认识。这项研究对于通过侧向构造碰撞了解青山省中生代地壳结构的变化也具有更广泛的意义。他们的本科生和研究生正在进行一项多学科的研究，以调查成对的高、低锶/Y深成岩和岩浆岩的发育。本研究旨在了解高、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和变质作用的关系。提出了晚侏罗世造山作用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的新模式。这种地壳结构的变化导致了晚侏罗世至早白垩世两条空间上和地球化学上截然不同的同时代带的建立，即147-143 Ma的高、低Sr/Y深成岩带和深成岩带。我们的研究集中在蓝山省，因为它包含了与北美科迪勒拉晚侏罗世收缩变形有关的成对高、低锶/Y岩浆带的最佳暴露实例之一。我们通过完整而详细的地质和构造填图、地球化学和同位素研究(Sr-ND-O)以及U-Pb和Sm-ND放射性测年来检验我们的模型。如果我们对这些岩浆带的解释是正确的，那么这项研究将是研究显生界会聚边缘背景下高、低Sr/Y岩浆生成过程以及碰撞构造、岩浆作用和变质作用相互作用的难得机会。

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.