Collaborative Research: What are the Mechanisms and Timescales of Contact Metamorphism in Long-lived Magmatic and Hydrothermal Systems?

犹他谷大学和犹他大学的研究人员将重建一个长期存在的深部系统的热历史，以确定脉冲岩浆活动如何影响地壳中的热量和质量传递。了解地壳中热量和物质的运动直接提高了对其他地壳系统的理解，如地热系统、矿体和与火山活动有关的地质灾害。具有互补优势的多种矿物相作为地球计时器，与多种分析技术一起，将用于为美国犹他州的Alta-Little Cottonwood stock系统产生高保真度的温度(T)时间(T)记录。原位微分析技术将用于将分析结果（矿物年龄，化学）置于结构和空间背景中，以便将这些分析结果与负责该岩浆变质系统演化的地质过程联系起来。研究结果可以重新定义我们对这些系统中岩浆和变质过程的理解，进而影响我们如何最好地利用热资源和矿产资源，并为火山灾害做好准备。这个项目将加强主要是本科院校的研究。此外，一个暑期学校项目将扩大学生对地球科学的参与，并在犹他州科学核心课程的背景下向中学生传播科学内容。该项目将解决以下基本问题：渐增的岩体侵位和演化的渗透率结构如何支配（水）热变质作用的时空模式。初步岩石年代学结果表明，在~10 Myr范围内，阿尔塔组（AS）发生了热液蚀变，也可能发生了接触光圈的生长。该项目将协调AS的小尺寸及其接触光圈（AA）的大面积范围，并确定小棉木（LCS）的侵位是否在邻近AS和光圈中推动了长期的、幕式的热液和接触变质作用。研究人员将利用原位（LASS-ICP-MS）和高精度（CA-TIMS）对钛矿、锆石和石榴石进行U-Pb测年，并结合热建模来构建系统的可靠的T-t历史。他们将测试1)在LCS的安置下，AS是否是一个长期的、偶发的热液流体流动的管道；2) LCS侵位驱动的热液系统仅覆盖AS西部；或者(3)较年轻的侵入造成了这两个种群中持久的热液系统。该项目的研究结果将影响我们对岩浆的转移、储存和结晶、矿体成因的时间尺度、主要矿物相的同位素定年、接触变质反应的时间尺度、造山带的传热传质、岩浆和热液管道的热模拟等方面的认识。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Researchers from Utah Valley University and University of Utah will reconstruct the thermal history of a long-lived plutonic system to determine how pulsed magmatism affects heat and mass transfer in the Earth's crust. Understanding the movement of heat and mass in the Earth's crust directly improves the understanding of other crustal systems such as geothermal systems, ore bodies, and geological hazards associated with volcanism. Multiple mineral phases with complementary strengths as geochronometers, together with multiple analytical techniques, will be used to produce a high-fidelity temperature (T)-time (t) record for the Alta-Little Cottonwood stock system, Utah, USA. In-situ microanalytical techniques will be used to place analytical results (mineral ages, chemistry) in textural and spatial context in order to connect these analytical results to the geologic processes responsible for the evolution of this magmatic-metamorphic system. The research outcomes could redefine our understanding of both the magmatic and metamorphic processes in these systems and in turn affect how we best utilize thermal and mineral resources and prepare for volcanic hazards. This project will strengthen research at a primarily undergraduate institution. In addition, a summer-school program will broaden participation in Earth Science and disseminate scientific content to middle school students in the context of the Utah Science Core curriculum. The project will address fundamental questions of how incremental pluton emplacement and evolving permeability structures govern the temporal and spatial patterns of (hydro-) thermal metamorphism. Preliminary petrochronology results indicate that hydrothermal alteration of the Alta stock (AS), and possibly also growth of the contact aureole, occurred over ~10 Myr. This project will reconcile the small size of the AS with the large areal extent of its contact aureole (AA) and determine whether emplacement of the Little Cottonwood Stock (LCS) instead drove protracted, episodic hydrothermal and contact metamorphism in the adjacent AS and aureole. The researchers will apply in situ (LASS-ICP-MS) and high precision (CA-TIMS) U-Pb dating of titanite, zircon, and garnet in conjunction with thermal modeling to construct a robust T-t history of the system. They will test whether 1) the AS was a conduit for long-lived, episodic hydrothermal fluid-flow driven by emplacement of the LCS; 2) the hydrothermal system driven by emplacement of the LCS merely overprinted the western portion of the AS; or 3) a younger intrusion is responsible for the protracted hydrothermal systems in both stocks. The results of this project will impact our understanding of the transfer, storage, and crystallization of magmas, timescales of ore-body genesis, isotopic dating of major mineral phases, the timescales of contact metamorphic reactions, heat and mass transfer in orogens, and thermal modeling of magma and hydrothermal conduits.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.