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2 years ago in Earth Sciences , Volcanology By Testing
What would be the possible explanation for vesicles being filled by glassy matter in basalt?
In my Deccan Traps samples, many amygdales contain clear, isotropic glass under the microscope, sometimes with delicate microlites. Typical secondary mineralization is absent. This suggests a primary, magmatic infill. Does this represent trapped residual melt from the final stages of cooling, or could it be a separate injection of melt into already-formed bubbles? I'm trying to reconstruct the eruption's closing stages.
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By Jayalakshmi Answered 1 year ago
Beautiful samples these provide a snapshot of the eruption's last moments. I've seen this in subaqueous or very thin subaerial flows. The process is twofold. First, rapid quenching of the flow margin forms the vesicular basalt and freezes the melt surrounding bubbles to a glassy matrix. Second, the still-molten interior of the flow has a residual, volatile-rich melt. As the interior slowly cools and contracts, this melt is literally sucked back into the already-formed vesicles at the chilled margin via capillary action, where it then freezes to glass. It's a primary injection of the final melt fraction.
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