EAR-PF: Experimental Constraints on Dating Ductile Deformation with Titanite

Moser, Amy Catherine, Goleta CA

Investigators

Abstract

Plate tectonics - the theory that the outermost later of Earth is divided into rigid plates that move - is the fundamental theory that explains nearly all Earth processes. The motion of these tectonic plates causes rocks to break and change shape. This breaking and shape change (also known as deformation) of rocks deep within the Earth builds mountains and produces earthquakes. To better understand how and why mountains are built and earthquakes occur, Earth scientists must be able to pinpoint when and how fast these processes happen. Doing so requires a method or tool that Earth scientists can use to date deformation (i.e., to determine when deformation has occurred in the past). Despite its importance, there is no straightforward way to date deformation. The goal of this project is to develop a tool to date deformation using laboratory experiments on a mineral called titanite. Earth scientists will be able to apply the results of this project to rocks in nature to determine when and how fast deformation has happened in the past, thereby filling a fundamental knowledge gap in Earth science research. In addition, as the Earth sciences are among the least diverse STEM fields, this work also aims to improve the diversity, equity, and inclusion of this scientific subdiscipline through outreach activities with K–12 students and by mentoring undergraduate students from underrepresented groups in research projects. Understanding the fundamentals of tectonic processes, including plate boundary initiation, deformation feedbacks at all crustal levels, and strain partitioning, relies in part on constraining the timing, duration, and rates of crustal deformation. Despite its significance, the ability to directly date ductile deformation remains an outstanding challenge in Earth science research. The mineral titanite (chemical formula CaTiSiO5) is well-suited to date crustal deformation. However, the multitude of processes that recrystallize titanite in shear zones makes it challenging to assess how to tie dates to deformation using natural rocks. The goal of this project is to use high-pressure, high-temperature titanite deformation experiments to develop a new tool to date high-temperature (i.e., >400 °C) deformation. The products of the deformation experiments will be characterized using various electron microscopy techniques, including electron backscatter diffraction (to quantify deformation microstructures and determine the deformation mechanisms that accommodated strain) and X-ray mapping (to determine compositional zoning that developed during experiments). The relationship among these features and U-Pb dates (evaluated using a combination of secondary ion mass spectrometry and atom probe tomography) will reveal how the development of deformation microstructures affects the U-Pb system in titanite. These integrated datasets will inform the best practices for dating crustal deformation with titanite in naturally deformed rocks, thereby providing a transformative advancement in Earth science research. The broader impacts of this work will focus on improving the diversity, equity, and inclusion of the Earth sciences through outreach activities with youth-facing organizations and by mentoring undergraduate students from underrepresented groups in research projects. 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.