ALONG-STRIKE TECTONIC EVOLUTION OF THE NEOGENE BERMEJO FORELAND BASIN AND ANDEAN THRUST FRONT, ARGENTINA (30-32°S) (Invited Presentation)

The Bermejo retroarc foreland basin system formed in flexural response to Neogene crustal thickening in the southern Central Andean orogenic system. The along strike evolution of the basin system remains unresolved and contrasting tectonic models have proposed the Bermejo basin evolved synchronously versus asynchronously through time. Our study seeks to constrain the along-strike Neogene tectonics of the Bermejo basin by studying fluvial stratigraphic intervals along the Andean thrust front, integrated with detrital zircon U-Pb geochronology and detrital apatite (U-Th)/He thermochronology datasets. New data from two stratigraphic sections in the southern Bermejo basin constrain deposition between 13-6 Ma. Dominant fluvial-lacustrine mudstones, siltstones, and sandstones transition into fluvial-megafan deposits capped by alluvial fan conglomerate facies, tracking the eastward migration of Precordillera fold-thrust belt deformation. The cessation of sedimentation, and thermal history models of apatite (U-Th-Sm)/He thermochronology ages, indicates basin incorporation into the orogenic wedge by 6 Ma. When we compare our southern datasets with previous constraints from the northern Bermejo basin, we observe, from north to south: (1) a time-transgressive trend in basin initiation, (2) a ~3 km decrease in stratigraphic thickness, and (3) older exhumation along the thrust front. These trends highlight the asynchronous nature of the Bermejo foreland basin system driven by inherited crustal architecture, and along-strike variability of Precordillera thrust-front evolution.