Secular Variation in the Cordilleran Continental Arc: Implications for Arc Geodynamics

在这项研究项目中，研究人员和他的学生将对南加州二叠纪-三叠纪到白垩纪的弧状岩体和大体积的火成岩进行全岩和锆石地球化学分析，以确定岩浆源随时间的变化模式。这些观察到的模式将被用来限制地幔和地壳对岩浆的贡献的区域和时间变化，这些岩浆最终形成弧斑并为大规模火山喷发提供动力。初步数据显示，岩浆源岩的年龄存在很大的区域差异，而且还表明，与邻近的较老的深成岩体相比，较年轻的深成岩体来自不同的地壳来源。因此，岩浆来源的这些区域和时间差异将使我们更好地了解深部发生的过程，特别是热结构的变化、熔体混合或弧后缩短导致的岩石圈增厚，这可能是在这种长期的弧背景下造成大量岩浆活动的原因。火山通常形成于碰撞构造板块之间的边界，这些火山是碰撞过程的表面表现，而碰撞过程是地球S大陆起源的中心。然而，由于产生这种火山活动的过程发生在地球深处看不见的地方，我们仍然有很多需要了解的火山过程及其与板块碰撞的联系。这个项目将研究一系列火山和侵入的火成岩，这些岩石在美国西南部一次非常长的、现已灭绝的板块碰撞中形成了大约1.8亿年。在绝迹的背景下，不仅火山及其下面的岩石暴露在人们面前，研究这一非常长的活动记录的目的是为了对板块碰撞和岩浆生成过程有一个完整的理解。因此，这个项目具有更广泛的意义，因为它旨在统一火成岩岩石学和构造地质学的各个方面，因为这些学科的想法被应用于板块碰撞。该项目还将通过支持有监督的独立实地和实验室经验，支持地球科学本科生和研究生的培训。这些独立的学习通过帮助学生看到他们在课堂上获得的知识的应用和整合，并通过鼓励他们坚持自己的教育来帮助他们。最后，由于大部分实地研究将在加利福尼亚州约书亚树国家公园及其周围进行，因此在研究过程中获得的知识将转化为每年数以千计的公园游客的继续教育。

In this research project, the investigator and his students will undergo whole rock and zircon geochemical analysis of Permo-Triassic to Cretaceous arc plutons and large-volume ignimbrites in southern California to identify patterns of magma source variations over time. These observed patterns will be used to place limits on regional and temporal variations in mantle and crustal contributions to magmas which ultimately form arc plutons and feed large-volume volcanic eruptions. Preliminary data show large regional variations in the age of magma source rocks, and also show that younger plutons were derived from distinct crustal sources compared to adjacent older plutons. These regional and temporal differences in magma sources will therefore allow a better understanding of the processes occurring at depth, especially changes in thermal structure, melt hybridization, or lithospheric thickening by retro-arc shortening, that may have contributed to high volume magmatism in this long-lived arc setting.Volcanoes commonly form at the boundary between colliding tectonic plates, and these volcanoes are the surface expression of a collision process that is central to the origin of Earth''s continents. However, because the processes that generate this volcanic activity occur out of sight deep within the Earth, we still have much to understand about the volcanic process and its link to colliding plates. This project will examine a series of volcanic and intrusive igneous rocks formed over about 180 million years during a very long-lived, yet now extinct plate collision in the southwestern United States. The purpose of examining this very long record of activity in an extinct setting, where not only the volcanoes but their underlying rocks are exposed to view, is to develop an integrated understanding of the plate collision and magma-generating processes. Thus, this project has broader significance in that it is designed to unify aspects of both igneous petrology and structural geology, as the ideas of these disciplines are applied to plate collisions. The project will also support the training of undergraduate and graduate students in the earth sciences, by supporting supervised independent field and laboratory experiences. These independent studies assist students by helping them to see the application and integration of knowledge they have acquired in the classroom and by encouraging them to persist in their education. Finally, because much of the field research will take place in and around Joshua Tree National Park in California, the knowledge gained during the course of this study will be translated into continuing education of thousands of park visitors each year.