Cryptic evolved melts beneath monotonous basaltic shield volcanoes in the Galápagos Archipelago

Area of Science:

• Geochemistry
• Volcanology
• Petrology

Background:

• Monotonous volcanic activity is often attributed to chemically homogeneous magmatic systems.
• This homogeneity is believed to result in predictable eruptive behavior over long timescales.
• Previous studies often assume uniformity in sub-volcanic systems based on surface eruption products.

Purpose of the Study:

• To investigate the diversity of melts within the sub-volcanic systems of monotonous shield volcanoes.
• To reconcile the observed uniform surface eruptions with potential deeper magmatic complexity.
• To explore the implications of sub-volcanic heterogeneity for volcanic activity predictability.

Main Methods:

• Petrological analysis of erupted crystals from Wolf and Fernandina volcanoes in the Galápagos.
• Development and application of new thermodynamic models.
• Characterization of melt compositions within the magmatic systems.

Main Results:

• Sub-volcanic systems beneath monotonous shield volcanoes exhibit extreme melt heterogeneity, including rhyolitic compositions.
• Evolved, more silicic melts are present in low abundance.
• Large volumes of basaltic magma from depth frequently flush through the crust, masking the chemical signatures of evolved melts.

Conclusions:

• The observed monotonous surface eruptions mask significant chemical diversity in the underlying magmatic systems.
• The continuous influx of basaltic magma is key to maintaining apparent uniformity and predictable activity.
• A decrease in this basaltic melt flux could lead to a transition towards more silicic volcanic activity.