Do transcurrent faults guide volcano growth? The case of NW bicol Volcanic Arc, Luzon, Philippines

This paper shows that although volcanoes can be aligned along transcurrent faults, their growth can in reality be controlled by secondary structures that have a different orientation and kinematics. Assessing the relationships between local structures and volcano growth can be very useful for the evaluation of volcanic hazards and for economic purposes such as geothermal and hydrogeological exploration. In the north-western Bicol Volcanic Arc (Luzon, Philippines) the Quaternary Labo and Caayunan volcanoes are aligned with the NW-striking transcurrent Philippine Fault System. They are exceptional examples of composite volcanoes mostly comprising lava domes, where regional tectonic structures and hydraulic radial fracturing have alternated to control volcano growth. Field data and analogue modelling demonstrate that apical depressions affecting the domes reflect the geometry of magma-feeding fractures. These data, together with alignments of domes and hot springs and other structural information, suggest that magma rose at depth along the NW-striking transcurrent faults, but that in the uppermost crust magma rose along NE-striking fractures parallel to the greatest principal stress.