Applications and Limitations of Elastic Thermobarometry: Insights From Elastic Modeling of Inclusion‐Host Pairs and Example Case Studies

M. Cisneros,K. S. Befus

doi:10.1029/2020gc009231

Abstract

AbstractElastic thermobarometry can be used to constrain the pressure and temperature conditions of mineral crystallization by exploiting the difference in the elastic evolution of a mineral inclusion and its host during cooling and decompression. In this work we examine the pressure‐temperature sensitivity of >5,000 untested inclusion‐host pairs. Hosts such as diamond and zircon are ideal host minerals because their low compressibility makes them rigid containment vessels. Highly compressible inclusions such as albite, graphite, and quartz serve as the most reliable barometers. We provide three case studies of inclusion‐host pairs from different geologic settings to demonstrate the advantages and challenges associated with these mineral pairs. Apatite inclusions in olivine from Yellowstone caldera mostly record negative residual pressures (tension) and suggest magmatic crystallization at ~0.4 GPa. Rutile inclusions in garnet from Verpeneset eclogites record near ambient conditions and do not recover reasonable metamorphic conditions of rutile entrapment. These results suggest that stiff inclusions may have a tensile strain limit, a possible limitation of elastic thermobarometry. Albite inclusions in epidote from a blueschist (Syros, Greece) record geologically reasonable entrapment pressures, but a large range of residual pressures that may be caused by the complex anisotropy of both phases. Our theoretical and applied results indicate that elastic thermobarometry has the potential to be used to understand petrologic processes in diverse geologic environments, including mantle, metamorphic, and magmatic settings but that each elastic thermobarometer requires careful evaluation.

Highlights

Methods that can directly monitor geologic processes that occur in the deep subsurface do not exist
Rutile inclusions in garnet from Verpeneset eclogites record near ambient conditions and do not recover reasonable metamorphic conditions of rutile entrapment. These results suggest that stiff inclusions may have a tensile strain limit, a possible limitation of elastic thermobarometry
We provide a script with a graphical user interface (GUI) that allows for evaluation of our code

Summary

Introduction

Methods that can directly monitor geologic processes that occur in the deep subsurface do not exist. The P‐T conditions of mineral and rock crystallization are central for understanding processes that influence crustal and mantle deformation, crystallization kinetics, molecular diffusion, and melt rheology. Many techniques, such as stable isotope thermometry, cation‐exchange thermobarometry, graphite order‐disorder thermometry, and thermodynamic modeling, have been developed to constrain P‐T conditions of minerals (e.g., Beyssac et al, 2002; Ferry & Spear, 1978; Gualda et al, 2012; Javoy, 1977); these methods often have practical limitations imposed by the requisite mineralogy or equilibrium assumptions

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