Collaborative Research: Contribution of mafic magmatism to upper crustal batholiths: A case study of the Sierra Nevada batholith

合作研究：镁铁质岩浆作用对上地壳基岩的贡献：内华达山脉基岩的案例研究

• 批准号: 2105371
• 负责人: Claire Bucholz
• 金额: $ 40.51万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2105371&HistoricalAwards=false
• 关键词: Collaborative; Research; Contribution; mafic; magmatism

The dense crust beneath Earth’s oceans is regularly driven beneath the continents in a tectonic process called subduction, which results in the formation of magmas. Such magmas ascend and create long chains of volcanoes like the Cascades of the northwest United States or the Andes in South America. Over time, magmatism at subduction zones has helped build Earth’s continents. These magmatic processes concentrate silica to create thick and buoyant continents that stand higher than surrounding oceans and oceanic crust, which is a unique feature of our planet. This continental crust is an important source for resources essential to human existence, but the processes that concentrate silica in magmas are not fully understood. This research will study magmatic processes in the Sierra Nevada mountain range of California, which is the ancient “plumbing system” from the insides of subduction zone volcanoes from hundreds of millions of years ago, now exposed at earth’s surface. This work will study the chemistry of mafic (more magnesium and iron-rich, lower silica) rocks that represent an important compositional ingredient to create the high-silica rocks that form the bulk of the continents. Extensive existing work on the high-silica rocks at this location will provide context for new measurements of the mafic end-member composition to understand the magmatic processes that build continents. The research will support collaboration between Caltech and Pomona College, including the mentoring of a female graduate student (Caltech) and multiple undergraduate/post-baccalaureate students (Pomona), as well as early career support for a female faculty member (Caltech). In addition, Earth Science classroom lessons and field trips for middle and high school students from the Big Pine Unified School District (BPUSD) in Owens Valley, located within study area will be developed and conducted. BPUSD serves a student population that is ~50% Native American and 40% Latinx, two under-represented groups in geosciences. The ultimate goal is to increase participation and interest of under-represented students in geosciences through place-based and culturally appropriate lessons that successfully aligned Indigenous ways of knowing and scientific practices with Western science modelsThe formation of high-silica arc batholiths is an enduring petrologic problem. During flux-melting of the mantle wedge at subduction zones primitive basalts are produced. Upon ascent into the crust, further differentiation of these basalts is required to form more silicic derivative melts. Although field and experimental studies highlight the importance of lower crustal (0.7 GPa) fractional crystallization of primitive basalts in generating high-silica melts, this process in detail cannot produce the composition of arc batholiths. In particular, deep crustal fractional crystallization generates peraluminous intermediate and silicic melts, compositions that are not widely observed in arc batholiths. To reconcile these observations, this research will test the following hypothesis: Deep crustal differentiation produces high-Al, low-Mg basalts, as well as, evolved mildly peraluminous granitic melts. These melts represent endmembers that can mix to form the compositional diversity of granitoids observed in arc batholith. Testing this mixing-model hypothesis has been limited due to the relative lack of studies focusing on the mafic endmember. Although volumetrically minor and relatively less-studied compared to high-silica granodiorites to granites that dominate batholiths, mafic plutons (non-primitive gabbros and diorites) are widely present in the upper crust of accreted arc sections. Through a collaboration between Caltech and Pomona College this research will investigate the bulk-rock and mineral major/trace element chemistry, geochronology, and oxygen & strontium isotopic compositions mafic plutonic bodies across a transect from a classic continental arc locality, the Sierra Nevada batholith. This data will be placed in the context of both existing and new granitoid data, as well as, quantitative geochemical and rheologic models to understand whether these mafic plutonic bodies represent suitable mixing endmembers in the production of batholithic granitoids.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

地球海洋下面的致密地壳在一个称为俯冲的构造过程中经常被推到大陆下面，这导致岩浆的形成。这样的岩浆上升，形成了长长的火山链，就像美国西北部的喀斯喀特山脉或南美洲的安第斯山脉。随着时间的推移，俯冲带的岩浆活动帮助建造了地球的大陆。这些岩浆过程浓缩了二氧化硅，形成了厚而有浮力的大陆，比周围的海洋和海洋地壳更高，这是我们星球的独特之处。这种大陆地壳是人类生存所必需的资源的重要来源，但在岩浆中浓缩二氧化硅的过程尚未完全了解。这项研究将研究加州的内华达州山脉的岩浆过程，这是数亿年前俯冲带火山内部的古老“管道系统”，现在暴露在地球表面。这项工作将研究镁铁质（更多的镁和铁丰富，低硅）岩石的化学，代表了一个重要的组成成分，以创造高硅岩石，形成大部分的大陆。在这个位置上对高硅岩石的大量现有工作将为镁铁质端元成分的新测量提供背景，以了解建造大陆的岩浆过程。这项研究将支持加州理工学院和波莫纳学院之间的合作，包括指导一名女研究生（加州理工学院）和多名本科生/学士后学生（波莫纳），以及为一名女教师（加州理工学院）提供早期职业支持。此外，地球科学课堂课程和实地考察的初中和高中学生从大松统一学区（BPUSD）在欧文斯谷，位于研究区域内将开发和进行。BPUSD服务于约50%的美洲原住民和40%的拉丁裔学生，这是地球科学中两个代表性不足的群体。最终目标是通过基于地点和文化上适当的课程，成功地将土著人的认知方式和科学实践与西方科学模型相结合，提高代表性不足的学生对地球科学的参与和兴趣。在俯冲带地幔楔的熔融过程中，产生了原始玄武岩。上升到地壳后，这些玄武岩需要进一步分化，以形成更多的玄武岩衍生物熔体。虽然现场和实验研究突出了低地壳（0.7 GPa）的原始玄武岩分离结晶在产生高硅熔体的重要性，这个过程中详细不能产生弧基的组成。特别是，深地壳分离结晶产生过铝质中间和中间熔体，在弧基中没有广泛观察到的组合物。为了调和这些意见，本研究将测试以下假设：深地壳分异产生高铝，低镁玄武岩，以及，发展温和过铝质花岗岩熔体。这些熔体代表的端元，可以混合形成弧基中观察到的花岗岩类的成分多样性。测试这种混合模型的假设一直是有限的，由于相对缺乏研究集中在镁铁质端元。虽然体积小，相对较少的研究相比，高硅花岗闪长岩花岗岩占主导地位的岩基，镁铁质岩体（非原始辉长岩和闪长岩）广泛存在于上地壳的增生弧段。通过加州理工学院和波莫纳学院之间的合作，这项研究将调查大块岩石和矿物的主要/微量元素化学，地质年代学，和氧锶同位素组成的镁铁质深成体的横断面从一个经典的大陆弧的地方，塞拉利昂内华达州岩基。这些数据将被放置在现有的和新的花岗岩类数据的背景下，以及定量地球化学和流变模型，以了解这些镁铁质深成岩体是否代表适当的混合端元在生产岩基花岗岩类。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。