39 D1. A Cross-Disciplinary Approach to Investigating Tectonics I - Integrating Field, Laboratory, and Experimental Techniques (Posters)

Monday, 18 March 2019
1:30 PM - 5:30 PM
Casco Bay Hall

MICROSTRUCTURAL EVIDENCE LINKING DAMAGE ZONES AND GRANULITE HYDRATION

Paper number: 39-7
Program: Technical Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

The infiltration of fluid into an anhydrous rock body can produce hydrating reactions which alter the bulk properties of the body. In large enough domains, this process can have macro-scale geodynamic and rheological implications as bulk density and strength change. However, the mechanics behind this process are not yet well documented in literature. In this study, we use optical and electron beam observations to document the links among brittle damage, fluid infiltration, and viscous localization. In the Adirondack Marcy massif, New York, cm-wide shear zones cutting meta-anorthosite show a partial transition from dry, granulite-facies assemblages (pyroxene, garnet, plagioclase feldspar, and alkali feldspar) to hydrated assemblages (scapolite and amphibole + quartz symplectite). Importantly, the modal abundance of hydrous phases increases with proximity to the shear zone cores, correlating damage zones and fluid access. Microstructural evidence along this gradient indicates brittle deformation facilitating fluid infiltration along grain boundaries, allowing for metasomatic replacement reactions. Additionally, this process appears to weaken the rock through grain-size reduction as replacement occurs in junctions between grains and as symplectic rims. This is supported by topological phase relationships and partially truncated reaction rims suggesting that viscous shear zones localized along planar areas weakened by brittle damage, which has further rheological implications regarding the localization of viscous shear strain.

Geological Society of America Abstracts with Programs. Vol. 51, No. 1

doi: 10.1130/abs/2019NE-328022

© Copyright 2019 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.