Birth and evolution of the Rio Grande fluvial system in the past 8Â Ma: Progressive downward integration and the influence of tectonics, volcanism, and climate

Progressive downward integration of Rio Grande rift basins from 8 to 1 Ma was facilitated by a combination of processes: increased river gradients in the upper basin due to construction of volcanic fields and potential epeirogenic uplift; increased discharge due to climate change events; waning rift extension that allowed aggradation to exceed subsidence; dampening of topographic divides between basins by aggradation; probable groundwater connectivity; and lake spillover events. Downward integration events may crudely correlate to climate change “events” at 6 Ma (onset of the southwestern monsoon) and 2.6 Ma (global change toward glacial-interglacial climate). Magmatic influences included the building of the 6-2.5 Ma Taos Plateau volcanic field, construction of the 10 to 0 Ma Jemez Mountains, and 6 Ma to 0 Ma Jemez lineament volcanism that was likely associated with mantle-driven surface uplift in a northeast-trending zone across northern New Mexico. River damming events were driven by volcanism in the northern Rio Grande rift, while basin spillover/groundwater sapping events were punctuated by a combination of pluvial climates and continued headwater uplift in the southern Rocky Mountains. Integration of the Rio Grande system to the Gulf of Mexico by ~ 800 ka was facilitated by headwater uplift as well as the onset of ~ 100 ka high-amplitude glacial-interglacial cycles at ~ 900 ka that provided higher discharge and bedrock incision rates during the Pleistocene. We conclude that magmatic and tectonic forcing dominated over the last ~ 8 Ma, but were amplified by climate change events to determine the fluvial evolution of the Rio Grande system.