, 75:782

Tectonic and magmatic controls on the location of post-subduction monogenetic volcanoes in Baja California, Mexico, revealed through spatial analysis of eruptive vents

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Abstract

Post-subduction (12.5 Ma to less than 1 Ma) monogenetic volcanism on the Baja California peninsula, Mexico, formed one of the densest intra-continental areas of eruptive vents on Earth. It includes about 900 vents within an area ∼700 km long (N–S) and 70 to 150 km wide (W–E). This study shows that post-subduction volcanic activity was distributed along this arc and that modes exist in the volcano distribution, indicating that productivity of the magma source region was not uniform along the length of the arc. Vent clustering, vent alignments, and cone elongations were measured within eight monogenetic volcanic fields located along the peninsula. Results indicate that on a regional scale, vent clustering varies from north to south with denser spatial clustering in the north on the order of 1.9 × 10−1 vents/km2 to less dense clustering in the south on the order of 7.8 × 10−2 vents/km2. San Quintin, San Carlos, Jaraguay, and Santa Clara are spatially distinct volcanic fields with higher eruptive vent densities suggesting the existence of individual melt columns that may have persisted over time. In contrast, the San Borja, Vizcaino, San Ignacio, and La Purisima vent fields show lower degrees of vent clustering and no obvious spatial gaps between fields, thus indicating an area of more distributed volcanism. Insight into the lithospheric stress field can be gained from vent alignments and vent elongation measurements. Within the fields located along the extinct, subduction-related volcanic arc, elongation patterns of cinder cones and fissure-fed spatter cones, vent clusters, and vent alignments trend NW–SE and N–S. Within the Santa Clara field, located more to the west within the forearc, elongation patterns of the same volcanic features trend NE–SW. These patterns suggest that magmatism was more focused in the forearc and in the northern part of Baja California than in its southern region. Within the extinct arc, magma ascent created volcano alignments and elongate cones parallel to NW–SE to N–S oriented tectonic structures. In the forearc, the existence of N–S and NE–SW oriented volcanic features indicates a rotation in the stress field orientation compared to the arc.

Editorial responsibility: S. A. Fagents