9 D12. Mineralogy/Crystallography (Posters)

Friday, 20 March 2020
8:00 AM - 12:00 PM
Grand Ballroom A–D

EBSD AND TRACE ELEMENT ANALYSIS OF REPLACEMENT DOLOMITE IN THE LATEMAR PLATFORM

Paper number: 9-2
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

The Latemar carbonate platform in northern Italy contains bodies of replacement dolomite that have been altered via the infiltration of seawater mixed with hydrothermal fluids. These fluids travelled upwards and horizontally through the platform along fractures and bedding planes, and their flow path is documented by replacement dolomite containing significant amounts of Fe, Mn, and Zn. These zones of replacement dolomite are surrounded by unreacted limestone and the region has remained un-metamorphosed, allowing for detailed analysis of the replacement process. Although replacement dolomitization has long been studied on the regional or outcrop scale, it is still not well understood on the scale of individual crystals. Herein we investigate how trace element content in replacement dolomite is reflected in the zoning and the crystallographic orientation of the individual dolomite crystals. Scanning electron microscopy (SEM) with electron backscatter diffraction (EBSD) and energy dispersive X-ray spectrometry (EDS) was used to identify crystallographic orientation patterns and trace element distribution within replacement dolomite samples across a single outcrop. Analyses reflect a variety of intensities of fluid-rock reactions and are classified as heavy, moderate, minimal, and unreacted. Elevated Fe, Mn, and Zn in replacement dolomite resulted in a less ordered distribution of orientations in a sample, illustrated by weak pole figure patterns. This implies that the dolomite samples from areas with the heaviest fluid-rock reactions have a deformed chemical structure which has affected the replacement dolomitization process, creating an irregular spread of crystal orientations. These results will be compared with stable isotope signatures at the outcrop scale to refine existing heat flow models and time-integrated fluid flux estimates of dolomitization with the Latemar carbonate buildup.

Geological Society of America Abstracts with Programs. Vol. 52, No. 2

doi: 10.1130/abs/2020SE-344130

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