Collaborative Research: The Cretaceous Sierra Nevada Batholith in the Northwestern Basin and Range: Its Intrusive History and Erosional Exhumation

加州的内华达州山脉下面有大量花岗岩（岩基），这些花岗岩代表了2.5亿至8000万年前中生代期间在北美西缘之下俯冲形成的古火山的根源。 内华达州山脉（作为山脉）在加州北方的苏珊维尔附近结束，但其花岗岩继续向东进入大盆地。这里还没有详细研究它们。 该项目的第一部分将详细说明这些岩石与北方内华达州山脉之间的精确匹配，并将说明岩基的特定部分穿过北方大盆地的位置。该项目还将解决一系列非常有争议的问题，即从白垩纪（8000万年前）到现在的加州和内华达州的景观。有人提出，我们今天所知的内华达州山脉自白垩纪以来就存在了，山脉以东的地区构成了一个巨大的高原，就像安第斯山脉的高原一样。随着盆地和山脉断裂的开始，高原坍塌，导致了大盆地的形成。然而，来自内华达州西北部的数据表明，这部分岩基下面的地壳从来没有厚到足以产生这样一个高原，而且河流似乎已经将古代塞拉山脉侵蚀的碎片带入了北部的海洋（该地区现在被广泛的年轻火山熔岩流所覆盖）。这些不同的观点将用两种方法来检验：1）从盆地和山脉断块中倾斜的火山-花岗岩不整合面之下采集的花岗岩样品阵列的Ar/Ar、裂变径迹和（U-Th）/He热年代学将详细描述侵入后冷却和岩基的侵蚀历史; 2）晚白垩世-早第三纪海相和非海相锆石年龄群加州和俄勒冈州的海洋沉积岩将允许确定大量岩基物质被侵蚀和运输到哪里。该项目填补了我们对白垩纪知识的主要空白，北美科迪勒拉大面积新生代地球动力学演化。Sierra内华达州是大陆弧岩浆作用的一个广泛研究的例子，但岩基的北方，以及最近认识到的延伸到内华达州西北部的部分，却很少受到关注。该地区的构造和岩浆演化是北美西部地质演化中尚未解决的关键问题。该项目将使研究生和本科生参与研究的实地和实验室阶段。一个项目网站，在当地学校和社区中心的演讲，以及报纸文章将继续让当地社区参与研究的进展和成果。

The Sierra Nevada, California, is underlain by a large volume of granite (a batholith) that represents the roots of ancient volcanoes formed by subduction beneath the western margin of North America during the Mesozoic, 250 to 80 million years ago. The Sierra Nevada (as a mountain range) ends near Susanville, northern California, but its granites continue into the Great Basin to the east. Here they have not been studied in detail. The first part of this project will detail the exact match between these rocks and the northern Sierra Nevada and will address where specific parts of the batholith cross the northern Great Basin. This project will also address a very controversial set of questions about the landscape of California and Nevada from the Cretaceous (80 million years ago) to present. It has been proposed that the Sierra Nevada as we know it today existed since the Cretaceous and that the region to the east of the Sierra constituted a vast high plateau like the Altiplano of the Andes. The plateau collapsed with the onset of Basin and Range faulting that led to formation of the Great Basin. Data from northwestern Nevada, however, suggests that the crust beneath this part of the batholith was never thick enough to produce such a plateau and that rivers appear to have carried debris eroded from the ancient Sierra into the ocean to the north (a region now covered by extensive young volcanic lava flows). These different ideas will be tested using two methods: 1) Ar/Ar, fission track, and (U-Th)/He thermochronology for arrays of samples from the granites of the batholith, collected with depth beneath the tilted volcanic-granite unconformity in Basin and Range fault blocks, will detail the post-intrusive cooling and the erosional history of the batholith; and 2) age populations of zircons in Late Cretaceous and early Tertiary marine and non-marine sedimentary rocks in California and Oregon will allow determination of where this large volume of batholithic material was eroded and transported to.This project fills a major gap in our knowledge of Cretaceous to Cenozoic geodynamic evolution large area of North American Cordillera. The Sierra Nevada is a widely studied example of continental arc magmatism yet the northern portion of the batholith, and its recently recognized continuation into northwestern Nevada, has received little attention. The tectonic and magmatic evolution of this area is a key unresolved problem in western North American geologic evolution. The project will engage graduate and undergraduate students in the field and laboratory phases of the research. A project web site, presentations at local schools and community centers, and newspaper articles will continue to engage local communities in the progress and outcomes of the research.