Volcanic and sedimentary facies, processes, and tectonics of intra-arc basins: Jurassic continental arc of California and Cretaceous oceanic arc of Baja California

Intra-arc basins are in general poorly defined and poorly understood. The tectonstratigraphic evolution of intra-arc basins in two arc sequences are analyzed: (1) the Jurassic continental arc of SW North America preserved in the Dome Rock sequence, Palen Mountains, California, and (2) the Cretaceous island arc terrane preserved in the Alisitos Formation, Baja California, Mexico. The Dome Rock sequence records the local initiation, development, and cessation of continental arc magmatism. Strata recording volcanic cessation are thinner than correlative rocks recording the same transition in Arizona. This may reflect more rapid arc dissection in California due to more strike-slip faulting relative to rifting.; The Alisitos Formation is part of a fringing island arc terrane. A stratovolcano and flanking fault- and volcano-bounded intra-arc basins preserved in a 50 km arc segment exhibit two evolutionary phases: (1) dominantly silicic- and intermediate pyroclastic rocks, followed by (2) dominantly basaltic effusive and hydroclastic deposits. Abundant associated dikes record an extensional episode. The coeval volcano- and fault-bounded basins have contrasting records resulting from: (1) destruction of pyroclastic flows entering the fault-bounded basin, due to steep, fault-scarp topography. (2) fault-facilitated magma ascent. (3) fault-facilitated voluminous mass wasting. (4) no rudist bioherm development or coarse bioclastic deposits in the fault-bounded volcano flank.; Abundant subaqueous pyroclastic flow deposits in the marine basins comprise four distinct types recognized on the basis of: (1) modification of the grain population, and (2) heat retention. Type I record high emplacement temperature and originate from hot, gas-fluidized pyroclastic flows. Type II are non-sorted, massive, and show record moderate heat retention. Type III record limited heat retention, and significant mixing with water. Type IV record no heat retention, but strong mixing with water. Types II-IV can originate: (1) from subaerial or submarine eruptions or (2) by remobilized hot or cold pyroclastic deposits. Granulometry discriminates nonmodified and modified deposits, supporting the textural classification. Distribution of the deposits reflects eruption dynamics, and mixing with the water column which can be controlled by sea floor roughness.