Geology of a Large Intact Extensional Oceanic Arc Crustal Section with Superior Exposures

The Rosario segment of the Cretaceous Alisitos arc (Baja California, Mexico) is arguably the best-exposed structurally intact and unmetamorphosed oceanic arc crustal section on Earth. The gently tilted, 50-km-long section exposes the transition from upper-crustal volcanic rocks to mid-crustal plutonic rocks, formed in an extensional environment. This book presents a detailed geologic map, based on an exhaustive data set including geochemistry, geochronology, and annotated outcrop photos and photomicrographs. Subsegments within the Rosario segment include a subaerial edifice, a volcano-bounded basin, and a fault-bounded basin, each underpinned by separate plutons. The entire data set is integrated across these subsegments in a time slice reconstruction of arc evolution and the relationships between plutonism and volcanism. The data set provides constraints on the evolution of silicic calderas and tectonic triggers for caldera collapse, caldera resurgence by emplacement of sill complexes and by incremental growth of plutons, and comparison with velocity profiles in modern arcs.