Growth and fragmentation of the Andean foreland basin during eastward advance of fold-thrust deformation, Puna plateau and Eastern Cordillera, northern Argentina.

The fault-bounded Cianzo basin represents a Cenozoic depocenter between the Puna plateau and Eastern Cordillera of northern Argentina. Analysis of fold-thrust relationships, nonmarine sedimentation, and detrital provenance at 23-24°S helps constrain the origin, interconnectedness, and subsequent uplift and exhumation of the Cianzo basin, a potential analog for intermontane hinterland basins in the Andes. Structural mapping reveals a plunging syncline within the >6000-m-thick, upward coarsening Cenozoic clastic succession in the shared footwall of the N-striking, E-directed Cianzo thrust fault and transverse, NE-striking Hornocal fault. Growth strata within upper Miocene levels indicate syncontractional accumulation adjacent to the Hornocal fault. Measured stratigraphic sections show upsection changes from (1) paleosol-rich, distal-fluvial sandstones (∼400 m Paleocene-Eocene Santa Bárbara Subgroup) to (2) braided fluvial sandstones and mudstones (∼1400 m upper Eocene-Oligocene Casa Grande Formation) to (3) distributary fluvial megafan sandstones and conglomerates (∼3300 m upper Oligocene-Miocene Río Grande Formation) to (4) alluvial fan conglomerates (∼1600 m upper Miocene Pisungo Formation). The ⁴⁰Ar/³⁹Ar geochronological results for interbedded tuffs indicate continuous Río Grande deposition from at least 16.34 ± 0.71 to 9.69 ± 0.05 Ma. Sandstone petrographic results define distinct upsection trends in lithic and feldspar content, potentially distinguishing the Western Cordillera magmatic arc from Puna-Eastern Cordillera thrust-belt sources. In addition to growth stratal relationships and ⁴⁰Ar/³⁹Ar ages, conglomerate clast compositions reflect distinct lithologic differences, constraining activation of the Cianzo thrust and coeval reverse slip on the reactivated (inverted) Hornocal fault. Finally, detrital zircon U-Pb ages, paleocurrents, and facies patterns distinguish local from distal sources, revealing a systematic forelandward (eastward) advance of Eocene through upper Miocene fold-thrust deformation. [ABSTRACT FROM AUTHOR]