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

来自犹他州山谷大学和犹他州大学的研究人员将重建一个长寿的深成系统的热历史，以确定脉冲岩浆活动如何影响地壳中的热量和质量传递。了解地壳中热量和质量的运动直接提高了对其他地壳系统的理解，如地热系统，矿体和与火山活动相关的地质灾害。将使用多种矿物相作为地质年代计，并结合多种分析技术，为美国犹他州的Alta-Little棉白杨储存系统提供高保真的温度（T）-时间（t）记录。将使用原位微分析技术将分析结果（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导致该岩浆-变质系统演化的地质过程联系起来。研究成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能和矿产资源，并为火山灾害做好准备。该项目将加强一个主要是本科院校的研究。此外，暑期学校计划将扩大地球科学的参与，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。该项目将解决的基本问题，如何增量岩体侵位和不断变化的渗透性结构管理（水）热变质作用的时间和空间模式。初步的岩石年代学结果表明，阿尔塔岩株（AS）的热液蚀变以及接触晕的生长可能发生在约1000万年前。该项目将协调小规模的AS与其接触晕（AA）的大面积范围，并确定小棉白杨股票（LCS）的侵位，而不是驱动长期的，幕式热液和接触变质作用在相邻的AS和晕。研究人员将应用原位（LASS-ICP-MS）和高精度（CA-TIMS）对钛铁矿、锆石和石榴石进行U-Pb测年，并结合热模拟来构建该系统的T-t历史。他们将测试1）AS是否是由LCS的就位驱动的长寿命，间歇性热液流体流动的管道; 2）LCS的就位驱动的热液系统仅仅覆盖了AS的西部;或者3）一个较年轻的侵入体是造成两个股票中长期热液系统的原因。该项目的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、造山带中的热量和质量转移、该奖项反映了NSF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。

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.