Concentration variance decay during magma mixing: a volcanic chronometer.

Area of Science:

• Geochemistry
• Volcanology
• Experimental Petrology

Background:

• Magma mixing is a key process in explosive volcanic eruptions.
• Concentration variance decay (CVD) quantifies magma mixing over time.
• Existing methods for dating magmatic processes often struggle with unknown advective histories.

Purpose of the Study:

• To calibrate a new geochronometer based on magma mixing.
• To establish a reliable method for determining magma mingling-to-eruption times.
• To independently assess timescales relevant to volcanic unrest.

Main Methods:

• Performed high-temperature experiments simulating magma mixing.
• Analyzed the exponential decay of compositional variance over time.
• Developed and applied the calibrated concentration variance decay rate (CVD-R) geochronometer.

Main Results:

• Compositional variance decays exponentially with time during magma mixing.
• The CVD-R technique provides a novel geochronometer independent of advective history.
• Mingling-to-eruption times for Campi Flegrei eruptions were determined to be in the tens of minutes.

Conclusions:

• The CVD-R geochronometer offers a new tool for dating volcanic processes.
• The technique yields rapid mingling-to-eruption timescales, implying high ascent velocities (5-8 m/s).
• Routine application of CVD-R can improve volcanic monitoring by targeting relevant timescales.