Collaborative Research: From Gabbros to Granites - An Investigation of Arc-Scale Differentiation at the Guadalupe Igneous Complex, Sierra Nevada, CA

合作研究：从辉长岩到花岗岩 - 加利福尼亚州内华达山脉瓜达卢佩火成岩杂岩弧尺度分异研究

• 批准号: 1250322
• 负责人: Keith Putirka
• 金额: $ 10.32万
• 依托单位: California State University-Fresno Foundation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-01 至 2016-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1250322&HistoricalAwards=false
• 关键词: Collaborative; Research; Gabbros; Granites; Investigation

Just a few key features allow Earth to be easily recognized from its planetary neighbors: water, continental crust (made of granitic rocks) and plate tectonics. These features are likely interlinked, and appear to be essential for the evolution of a planet that can support human life. This study focuses on the origin and emplacement of granitic rocks, which form the stable continental crust, without which terrestrial life could not have evolved. The origin of granite has been the source of much debate for more than a century, as successive hypotheses survive, are modified, or abandoned in the face of new observations. They weigh in on the debate by examining two currently popular models for the evolution of the Sierra Nevada Batholith in California, which is home not only to the crown jewels of the National Park System (Yosemite, Sequoia and Kings Canyon), but which has long served geologists as a type example of how granitic crust is formed in the plate tectonic setting known as a ?subduction zone?. Subduction zones are regions of Earth's surface where one tectonic plate sinks beneath another, in the process generating both earthquakes and volcanoes. These tectonic regions are also referred to as ?arcs?, for the arcuate patterns of volcanoes that such a setting develops, such as the Japanese, Aleutian or Marianas Islands. It is in these regions that granites are thought to form. When such arcs develop granitic rocks, which are buoyant and difficult to subduct beneath another tectonic plate, these eventually amalgamate to form the continents as seen today.In this project, the team will investigate the two key means by which granitic rocks of the Sierra Nevada Batholith, California are thought to be created: crystallization differentiation, and partial melting of pre-existing lower and upper crust. Recent work has suggested that earlier-formed crust, which consists mostly of basalt and overlying sediments, is heated by the intrusion of more newly-formed basaltic melts, and partially melted to form granitic melts directly. These granitic melts then rise through existing crustal materials to accumulate at shallow depths. An alternative hypothesis is that newly formed basalts are transported to the upper crust directly, and there differentiate to form the granitic materials that now dominate the landscape of the Sierra Nevada. The contrasts between these two hypotheses are significant. In the first case, little new crust is being created during Late Mesozoic time?older crust is simply being recycled and remobilized. The age of the crust then is then older than the age of the youngest granites in this model. In contrast, when newly formed basaltic melts differentiate directly to form granite, then this represents a new addition of granite to the crust. There is no better place to test these models than at the Guadalupe Igneous Complex (GIC) of the western Sierra Nevada. This Jurassic-age pluton (~151 Ma) contains very rare exposures of the newly-formed basaltic melts that intruded the crust at the time that the GIC granites formed: our goal is to test whether such melts primarily caused heating and partial melting of pre-existing crustal materials, or whether they differentiated directly to form granite. Another advantage to our study of the GIC is that the rocks in this region provide an unusual glimpse into the crust into which the newly formed basalts were intruded. Unlike other granitic plutons of the Sierra Nevada, they can test whether pre-existing crustal materials provide an appropriate source material for the formation of granitic rocks within the GIC.

只有几个关键特征使地球可以从其行星邻居中轻松识别：水，大陆壳（由花岗岩岩石制成）和板块构造。这些特征可能是相互联系的，似乎对于可以支持人类生命的行星的发展至关重要。这项研究的重点是构成稳定的大陆壳的花岗岩岩石的起源和化合物，没有陆地生命就无法发展。一个多世纪以来，花岗岩的起源一直是辩论的根源，因为在面对新观察时，连续的假设得以幸存，修改或被抛弃。他们通过检查了两种当前流行的模型来衡量加利福尼亚州内华达州巴斯托里斯山脉的演变，这不仅是国家公园系统的皇冠珠宝（Yosemite，红杉和Kings Canyon）的家园，而且长期以来一直将地质学家作为一个类型的示例，是在板块中形成的类型示例。俯冲带是地球表面的区域，其中一个构造板下沉在另一个地震和火山的过程中。这些构造区域也称为“弧？正是在这些地区，花岗岩被认为是形成的。当这样的弧形发展出花岗岩岩石，这些花岗岩岩石浮动且难以俯冲在另一个构造板下方，这些弧形最终将融化形成了今天的大陆。在这个项目中，该团队将研究两种关键手段，通过将加利福尼亚山脉浴室的花岗岩岩石构成了加利福尼亚州山脉的花岗岩岩石，被认为是创造的：结晶差异化，并呈现出较低的效果。最近的工作表明，早期形成的地壳主要由玄武岩和上覆的沉积物组成，它是通过侵入更新建的玄武岩熔体的侵入而加热的，部分融化以直接形成花岗岩熔体。然后，这些花岗岩熔体通过现有的地壳材料升起，以在浅水深处积聚。另一种假设是，新形成的玄武岩直接运输到上皮，并且有区别形成了现在主导内华达山脉景观的花岗岩材料。这两个假设之间的对比很重要。在第一种情况下，在中生代晚期，几乎没有新的外壳？较老的地壳只是被回收和重新塑造。然后，地壳的年龄比该模型中最年轻的花岗岩年龄大。相反，当新形成的玄武岩熔体直接区分形成花岗岩时，这代表了地壳中的新添加花岗岩。没有比在内华达山脉西部的瓜达卢佩火成岩复合物（GIC）更好的测试这些模型的地方。这种侏罗纪时代的岩石（〜151 mA）包含了新形成的玄武岩融化的非常罕见的暴露，在GIC花岗岩形成时侵入了外壳：我们的目标是测试这种融化的主要是导致加热和部分融化和部分融化的预先存在的硬皮材料，或者它们是否直接形成了Granite。我们对GIC的研究的另一个优点是，该区域的岩石为新形成的玄武岩被侵入的地壳提供了异常的瞥见。与内华达山脉的其他花岗岩岩体不同，他们可以测试现有的地壳材料是否为GIC内的花岗岩形成提供了适当的原始材料。