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Collaborative Research: Revisiting the water-saturated granite solidus

合作研究：重新审视水饱和花岗岩固相线

基本信息

批准号：
2120598
负责人：
Jay Thomas
金额：
$ 25.36万
依托单位：
Syracuse University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2021
资助国家：
美国
起止时间：
2021-09-01 至 2024-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2120598&HistoricalAwards=false
关键词：
Collaborative Research Revisiting water saturated

项目摘要

Earth’s uppermost continental crust is composed on average of granitic material. Granites are igneous rocks, a subset of rocks that form by the cooling and subsequent crystallization of molten materials. The temperature at which a water-bearing granite melts (or, upon cooling of a magma, the temperature at which the last drop of molten material crystallizes) is known as the granitic water-saturated solidus (G-WSS). The G-WSS is one of the most important phase boundaries in all of geology. Its location in pressure-temperature space controls the formation of our continents, the generation of economically important gem and ore deposits (e.g., sapphire, lithium, gold, and copper), the eruption of devastating and explosive volcanic eruptions, and how rapidly our planet has cooled over eons. The position of the G-WSS changes with depth (pressure; P), temperature (T) and bulk composition. The G-WSS is analogous to the freezing point of aqueous fluids, and the compositional effect on magmatic freezing points is analogous to changes to the freezing point depression of water caused by addition of various salts (e.g., NaCl, KCl, CaCl, etc.). Pioneering work performed over 60 years ago remains the basis for our understanding of the G-WSS. However, numerous observations from natural systems suggests igneous rocks crystallize at temperatures ~75–100 degrees C lower than the widely accept¬¬ed G-WSS. These observations combined with advances in experimental and analytical techniques provide the motivation and opportunity to re-investigate the location of the G-WSS. The PI’s preliminary work surprisingly demonstrated that the G-WSS is 100 degrees C lower than previous findings, which will transform long-standing views on granite formation processes, continental crust formation, thermal structure in terrestrial bodies, plate tectonics, innumerable aspects in hard-rock petrology and affect explorations of economically important ores. The PIs will conduct a series of laboratory-based experiments to systematically re-define the G-WSS, and then apply observations to the natural rocks contained in the National Museum of Natural History collections. Beyond providing research opportunities to PhD students and Washington DC high school students from under-served communities, the PIs will also produce a series of educational outreach experiences to teach National Mall visitors how ancient magmatic systems generated building stone rocks that compose many of the National Mall’s most famous monuments and buildings.Granitic and rhyolitic rocks are the end-product of continental crust differentiation. Most magmatic systems evolve towards granitic bulk compositions during crystallization, and the first melts of many rocks are broadly granitic. The granitic water-saturated solidus (G-WSS) is the lowest temperature phase boundary fundamentally separating metamorphic and igneous realms; thus, understanding its location in -pressure-temperature-composition space is critical for interpreting the rock record. The accepted G-WSS was largely determined 60 years ago using experimental and analytical techniques that leave open the possibility that the G-WSS may be inaccurate. In natural systems, various thermobarometric applications to granitic and rhyolitic composition rocks commonly return temperature estimates ~75–100 degrees C lower than the widely accept¬¬ed G-WSS. The availability of modern experimental and analytical approaches and the low temperature estimates for mineral crystallization in granitic rocks raise two overarching questions that will be resolved by performing work outlined in this proposal: (1) What is the P–T position of the G-WSS?, and (2) What are the compositions of melts and crystals that coexist along the G-WSS? The PIs will perform a systematic experimental and analytical program to determine the P–T position of the G-WSS and related compositional variations over conditions that span the continental crust. Experiments will be conducted in cold-seal pressure vessels (P5 kbar) and piston-cylinder devices (P5 kbar). The PIs will use electron probe microanalysis to measure major element compositions of experimental run products. Fourier transform infrared and Raman spectroscopy will be used to measure water concentrations in the melt. A statistically rigorous experimental approach, called a design of experiments, will be employed to determine compositions along the G-WSS over a range of pressures spanning the continental crust. Geochemical analyses and thermobarometry of natural granitic rocks will reveal the extent to which low temperatures are recorded in the rock record. Preliminary results from experiments performed from 0.5 to 10 kbar on granitic composition rocks demonstrate that the G-WSS is significantly lower than unanimously accepted estimates. A more accurate understanding of the position of the G-WSS will help to reconcile interpretations of granite formation and storage conditions within silicic magmatic systems, provide new opportunities to understand the thermal structure of the crust on Earth and other terrestrial bodies, and will influence myriad aspects of hard-rock petrology, geophysics, and mineral/ore exploration that will benefit from an accurate description of the G-WSS. This program also includes research opportunities for graduate students, DC-local high school students from underserved communities, development/implementation of Next Generation Science Standards for 5-8 grade students across the country, and an outreach program called “Magmas on the Mall” aimed at educating the broad public on magmatism and how it created the building stones used across the National Mall.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.

地球最上层的大陆地壳平均由花岗岩物质组成。花岗岩是火成岩，是熔融物质冷却和随后结晶形成的岩石的一个子集。含水花岗岩熔化的温度(或岩浆冷却时，最后一滴熔融物质结晶的温度)称为花岗岩水饱和固相线(G-WSS)。G-WSS是地质学中最重要的相界之一。它在压力-温度空间中的位置控制着我们大陆的形成，重要经济宝石和矿藏(如蓝宝石、锂、金和铜)的生成，毁灭性和爆炸性火山喷发的喷发，以及我们的星球在亿万年内冷却的速度。G-WSS的位置随深度(压力；P)、温度(T)和块体成分而变化。G-WSS类似于水溶液的凝固点，对岩浆凝固点的成分影响类似于各种盐类(如氯化钠、氯化钾、氯化钙等)对水的凝固点降低的影响。60多年前所做的开创性工作仍然是我们理解G-WSS的基础。然而，来自自然系统的大量观察表明，火成岩在比广泛接受的G-WSS低约75-100摄氏度的温度下结晶。这些观察结果与实验和分析技术的进步相结合，为重新调查G-WSS的位置提供了动力和机会。PI的初步工作令人惊讶地表明，G-WSS比之前的发现低100摄氏度，这将改变长期以来对花岗岩形成过程、大陆地壳形成、陆体热结构、板块构造、硬岩岩石学无数方面的看法，并影响重要经济矿藏的勘探。PIS将进行一系列以实验室为基础的实验，系统地重新定义G-WSS，然后将观察应用于国家自然历史博物馆藏品中的天然岩石。除了为来自服务不足社区的博士生和华盛顿特区高中生提供研究机会外，PIS还将制作一系列教育推广体验，向国家购物中心的游客传授古代岩浆系统是如何产生建筑石块的，这些石块构成了国家购物中心许多最著名的纪念碑和建筑。花岗岩和流纹岩是大陆地壳分化的最终产物。大多数岩浆系统在结晶过程中向花岗岩块体成分演化，许多岩石的第一次熔体是广泛的花岗岩。花岗岩水饱和固相线(G-WSS)是从根本上分隔变质岩和火成岩的最低温度相界，因此，了解其在压力-温度-成分空间中的位置对于解释岩石记录至关重要。被接受的G-WSS在很大程度上是在60年前使用实验和分析技术确定的，这些技术留下了G-WSS可能不准确的可能性。在自然系统中，各种用于花岗岩和流纹岩成分岩石的温压测量通常返回的温度估计比广泛接受的G-WSS低约75-100摄氏度。现代实验和分析方法的可用性以及花岗岩中矿物结晶的低温估计提出了两个突出的问题，将通过执行本提案中概述的工作来解决：(1)G-WSS的P-T位置是什么？(2)沿着G-WSS共存的熔体和晶体的成分是什么？PIS将执行一项系统的实验和分析计划，以确定G-WSS的P-T位置和横跨大陆地壳的条件下的相关成分变化。实验将在冷密封压力容器(P5KBAR)和活塞-气缸装置(P5KBAR)中进行。PI将使用电子探针微量分析来测量实验运行产品的主要元素组成。傅立叶变换红外光谱和拉曼光谱将被用来测量熔体中的水浓度。一种被称为实验设计的统计学上严格的实验方法将被用来确定横跨大陆地壳的压力范围内G-WSS沿线的成分。对天然花岗岩进行的地球化学分析和温压测量将揭示岩石记录中记录的低温程度。在花岗岩成分岩石上进行的0.5-10kbar实验的初步结果表明，G-WSS明显低于一致接受的估计。更准确地了解G-WSS的位置将有助于调和对硅质岩浆系统内花岗岩形成和储存条件的解释，为了解地球和其他陆体的地壳热结构提供新的机会，并将影响将受益于G-WSS的硬岩岩石学、地球物理和矿产/矿产勘探的方方面面。该计划还包括为研究生、华盛顿特区当地贫困社区的高中生提供研究机会，为全国5-8年级学生制定/实施下一代科学标准，以及一项名为“广场上的岩浆”的外展计划，旨在教育广大公众了解岩浆作用及其如何在国家广场使用。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。