Mardi 1er Décembre à 14h : Julia Hammer (ClerVolc visiting professor 2015)
Title: Snowflakes in volcanic rocks: evidence for diverse mechanisms of crystal growth in basaltic magma reservoirs
Igneous petrologists operate on the assumption that the textures and compositions of magmatic minerals are unique recorders of the temperature, pressure, and composition of magma reservoirs. But how good are the underpinnings of this assumption?
Analysis of the spatial distribution patterns of slow diffusing impurities in olivine crystals from Hualalai volcano reveals that the crystallization record is not a straightforward time progression from crystal core to rim. Clinopyroxene from Haleakala volcano likewise preserves patterns of chemical heterogeneity that are inconsistent with chemical equilibrium. A “dendrite architecture” model links these observations to a diffusion-limited crystal growth mechanism, and challenges the layer-cake paradigm of chemical stratigraphy in the mafic minerals of basaltic rocks.