Abstract
<jats:title>ABSTRACT</jats:title> <jats:p>This field trip examines the volcano sedimentary and structural evolution of the southern part of La Paz Bay, México, with special emphasis on Miocene rocks (ca. 24−19 m.y. old) traditionally interpreted as part of the Comondú volcanic field. We argue that the source vent(s) of major ignimbrites was located to the east in the Sierra Madre Occidental volcanic province. Day 1 stops explore the coastal exposures at Punta Coyote region and Espíritu Santo and La Partida islands, where participants will observe the contrasting volcanic successions that characterize these areas. Rocks exposed include low- to medium-grade (unwelded to densely welded) felsic ignimbrites; andesitic breccias, interpreted as volcanic debris avalanche (VDA) deposits; epiclastic volcanic deposits; and intra-canyon mafic lava flows. Particular attention is given to the presence of exotic blocks of pre-volcanic eolian sandstones, as well as to lateral variation in facies that record changes in sedimentation and syn-sedimentary deformation caused by slumps and bulldozing effects of a voluminous VDA.</jats:p> <jats:p>Stops on Day 2 focus on the Agua de Yepis structural complex, where Lower Miocene (ca. 23–22 Ma) volcaniclastic and epiclastic volcanic units display evidence of soft-sediment deformation, block transport and rotation, folding, deformation-induced mixing/mingling, and brittle–ductile fabric development. These features are interpreted as produced by emplacement of a voluminous VDA deposit and its interaction with a wet, unlithified substrate. Newly recognized pre-, syn-, and post-kinematic successions, together with field evidence of angular unconformities and exotic blocks, provide key constraints on the timing and mechanisms of deformation.</jats:p> <jats:p>The role of W-dipping Early Miocene major normal faults, the structural role of the La Paz lineament, and the subsequent reorganization of deformation during the localization of Gulf of California rifting are also highlighted and discussed.</jats:p>