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.

在地球海洋下方的密集地壳以称为俯冲的构造过程定期在大陆下方驱动，这导致岩浆的形成。这样的岩浆上升并建立了长长的火山连锁店，例如美国西北部的级联或南美安第斯山脉。随着时间的流逝，俯冲带的岩浆作用帮助建立了地球大陆。这些岩浆过程集中二氧化硅，以产生比周围海洋和海洋壳高的厚且浮动的大陆，这是我们星球的独特特征。这种连续的地壳是人类生存必不可少的资源的重要来源，但是将二氧化硅集中在岩浆中的过程尚未完全理解。这项研究将研究加利福尼亚州内华达山脉山脉的岩浆过程，这是俯冲带火山内部的古老“管道系统”，来自数亿年前，现在暴露在地球表面。这项工作将研究Mafic（富含镁和铁的下二氧化硅）的化学性质，该岩石代表了重要的复合成分，以创建形成大部分持续的高硅岩石。在此地点，在高硅岩石上进行的广泛现有工作将为Mafic End-Mend-Mote构图的新测量提供背景，以了解建立大陆的岩浆过程。这项研究将支持加州理工学院和波莫纳学院之间的合作，包括女性研究生（CALTECH）和多个本科/学士学位的学生（Pomona）的心理，以及对女教师（CALTECH）的早期职业支持。此外，将开发和进行位于研究区域内的欧文斯山谷的大松统一学区（BPUSD）的中学和高中生的地球科学课堂课程和实地考察。 BPUSD为一个约50％的美国原住民和40％的拉丁裔服务的学生人口服务，这是地球科学中两个代表性不足的群体。最终的目标是通过基于地方和文化上适当的教训来增加代理中代表性不足的学生在地球科学中的参与和兴趣，这些课程成功地使土著的认识和科学实践与西方科学模型相结合，形成了高硅弧形浴力石的形成是一个持久的质问题。在俯冲带原始玄武岩的地幔楔的通量融化过程中。上升到地壳中后，需要进一步的这些玄武岩来形成更多的硅衍生物熔体。尽管现场和实验研究强调了原始玄武岩在产生高硅熔体中的下层地壳（0.7 GPA）分数结晶的重要性，但此过程详细无法产生弧浴石的组成。特别的，深层的分数结晶会产生呈细胞的中间体和有机硅熔体，这些中间体和在弧浴中未广泛观察到的成分。为了调和这些观察结果，这项研究将检验以下假设：深层地壳分化会产生高质量，低毫克的玄武岩以及进化的轻度呈细胞的花岗岩。这些熔体代表了可以混合的末端成员，以形成在弧浴中观察到的花岗岩的复合多样性。由于研究重点是健康的终点，测试这种混合模型假设的研究受到限制。尽管与高硫酸花岗岩与花岗岩相比，大小和相对研究的次要和相对研究较少，而花岗岩与浴力石，大型摩克灌木（非主要的gabbros and diorites）相比，在接受的弧形部分的上皮中广泛呈现。通过加州理工学院和波莫纳学院之间的合作，这项研究将调查散装岩石和矿物专业/微量元素化学，地球人工学，氧和氧和斜纹肌同位素组成的巨型体，从经典的连续弧本地跨境，塞拉尼瓦达山脉（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 macrolithic represent suitable mixing endmembers in the production of balancethic granitoids.This award reflects NSF's statutory mission and has been deemed honestly of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.