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大学的研究人员将重建一个长期存在的深成体系的热史，以确定脉冲岩浆活动如何影响地壳中的热量和质量传递。了解地壳中的热量和质量运动直接提高了对其他地壳系统的了解，如地热系统、矿体和与火山作用有关的地质灾害。具有互补强度的多种矿物相作为地质计时器，结合多种分析技术，将用于美国犹他州Alta-Little Cottonwood股票系统的高保真温度(T)-时间(T)记录。将使用现场微观分析技术将分析结果(矿物年龄、化学成分)置于结构和空间环境中，以便将这些分析结果与导致这一岩浆-变质系统演化的地质过程联系起来。研究结果可能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，并为应对火山灾害做好准备。该项目将加强以本科生为主的机构的研究。此外，暑期学校计划将扩大对地球科学的参与，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。该项目将解决递增的岩体侵位和不断演变的渗透率结构如何控制(水)热变质作用的时间和空间模式这一基本问题。初步的岩石年代学结果表明，阿尔塔岩体热液蚀变(As)，可能还有接触晕的生长，发生在约10Myr。该项目将调和AS的小面积与其接触光环(AA)的大面积范围，并确定小红木原木(LCS)的侵位是否反而在相邻的AS和光环中驱动了旷日持久的幕式热液和接触变质作用。研究人员将应用钛铁矿、锆石和石榴石的原位(LASS-ICPMS)和高精度(CA-TIMS)U-Pb测年，并结合热模拟来构建该系统的稳健的T-t历史。他们将测试是否1)AS是由LCS侵位驱动的长期、幕式热液流动的管道；2)LCS侵位驱动的热液系统只是叠加了AS的西部；或者3)较年轻的侵入体对这两个生物群中持久的热液系统负有责任。该项目的结果将影响我们对岩浆转移、储存和结晶的理解，矿体成因的时间尺度，主要矿物相的同位素年龄，接触变质反应的时间尺度，造山带中的热和质量转移，以及岩浆和热液管道的热模拟。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。

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.