Structural control on monogenetic volcanism along the Intipuca Fault, Central America Volcanic Arc, El Salvador

This preliminary study addresses the architecture of the magmatic plumbing system in southeastern El Salvador, where a cluster of recent monogenetic volcanic centers is spatially associated with the Intipuca Fault. This fault is part of the active shear zone located at the volcanic arc accommodating the right lateral motion of the fore-arc sliver with respect to the Caribbean plate in the context of the Cocos plate subduction in the Middle America Trench. The Intipuca fault acts as a link between the El Salvador Fault Zone (ESFZ) and the extensional domain of the Gulf of Fonseca and the Nicaraguan depression.

Four representative lava samples were analysed: three from monogenetic volcanoes emplaced along the fault and one from the underlying Pliocene stratovolcano of the Bálsamo Formation. Detailed petrography, electron microprobe analyses of phenocryst and groundmass minerals in each sample, and Ar/Ar geochronology were performed.

Preliminary results reveal mineralogical and textural differences between lavas from the monogenetic cones and the stratovolcano. The latter are dominated by plagioclase, with abundant small olivine and minor, but large (phenocrystic) pyroxene, and lack hydrated minerals. Some plagioclase macrocrysts display abundant disequilibrium textures, including resorbed plagioclase cores and sieve textures, suggesting prolonged crustal residence and magma recirculation under dry conditions.

Monogenetic lavas are characterized by abundant pyroxene meso- and macrocrysts. Plagioclase shows a range of sizes, some crystals showing disequilibrium features while others are apparently in equilibrium (continuous oscillatory zoning and euhedral shape Olivine is subordinate, commonly with oxidized rims and replacement coronas of pyroxene and plagioclase. Opaque minerals are also common, and minor, subhedral green amphibole occurs locally. The occurrence of hydrated minerals in the monogenetic lavas reflects rapid magma ascent along the Intipuca Fault, which likely acted as a preferential conduit preserving fluids derived from Cocos Plate subduction.

Similar spatial associations between monogenetic volcanism and transtensional faults have been documented in fault systems with comparable orientations near the Gulf of Fonseca. Likewise, monogenetic alignments are identified in association with segments with a dominant E–W strike (between N90°E and N110°E) that characterizes the El Salvador Fault Zone (ESFZ). This supports the idea that strike-slip fault systems play a fundamental role in modulating magma plumbing architectures and controlling the spatial distribution of monogenetic volcanism in subduction-related volcanic arcs.