Fracturing and tectonic stress drive ultrarapid magma flow into dikes.

Many examples of exposed giant dike swarms can be found where lateral magma flow has exceeded hundreds of kilometers. We show that massive magma flow into dikes can be established with only modest overpressure in a magma body if a large enough pathway opens at its boundary and gradual buildup of high tensile stress has occurred along the dike pathway prior to the onset of diking. This explains rapid initial magma flow rates, modeled up to about 7400 cubic meters per second into a dike ~15-kilometers long, which propagated under the town of Grindavík, Southwest Iceland, in November 2023. Such high flow rates provide insight into the formation of major dikes and imply a serious hazard potential for high-flow rate intrusions that propagate to the surface and transition into eruptions.

Liquiñe-Ofqui's fast slipping intra-volcanic arc crustal faulting above the subducted Chile Ridge.

The southernmost portion of the Liquiñe-Ofqui fault zone (LOFZ) lies within the proposed slab window which formed due to oblique subduction of the Chile Ridge in Patagonia. Mapping of paleo-surface ruptures, offsets, and lithological separations along the master fault allowed us to constrain geologic slip rates for the first time with dextral rates of 11.6-24.6 mm/year (Quaternary) and 3.6-18.9 mm/year (Late-Cenozoic) respectively. We had trouble mapping the LOFZ in one local because of a partially collapsed and previously undiscovered volcanic complex, Volcan Mate Grande (VMG: 1,280 m high and thus Vesuvius-sized) that grew in a caldera also offset along the LOFZ and has distinct geochemistry from adjacent stratovolcanoes. Besides the clear seismic and volcanic hazard implications, the structural connection along the main trace of the fast slipping LOFZ and geochemistry of VMG provides evidence for the slab window and insight into interplay between fast-slipping crustal intra-arc crustal faults and volcanoes.

Slip rates along the narrow Magallanes Fault System, Tierra Del Fuego Region, Patagonia.

The up to 1000 km-long Magallanes Fault System (MFS) is the southernmost onshore strike-slip plate boundary and located between the South American and Scotia Plates. Slip-rates, a key factor for understanding neotectonics and seismic hazard are only available there from geodetic models. In this study, we present the first direct geologic evidence of MFS slip rates. Late-Cenozoic slip rates along the main MF is 5.4 ± 3.3 mm/yr based on lithologic geological separations found in regional mapping. Late-Quaternary deformation from offset geomorphologic markers was documented along the MFS in Chile and Argentina based on a combination of satellite mapping, fieldwork, and Structure from Motion (SfM) models developed from drone photography. By combining displacements observed in SfM models with regional Late-Quaternary dating, sinistral slip rates are 10.5 ± 1.5 mm/yr (Chile) and 7.8 ± 1.3 mm/yr (Argentina). By comparing our results with regional models, contemporary plate boundary deformation is narrow, approximately ~20-50 km wide from Tierra Del Fuego (TdF) and east (one of the narrowest on Earth), which widens and becoming more diffuse from Cabo Froward north and west (>100 km wide). In addition to the tectonic implications, these faults should be considered important sources of fault rupture and seismic hazard.